Soft ClaysTHE CORRELATIONS AND SOIL PROPERTIES ANALYSIS OF MARAN, PAHANG

SOFT CLAYS & PROBLEMATIC SOILS

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THE CORRELATIONS AND SOIL PROPERTIES ANALYSIS OF MARAN, PAHANG

Muzamir bin Hasan Faculty of Civil Engineering and Earth Resources, Universiti Malaysia Pahang, Lebuhraya Tun Razak, 26300 Gambang, Kuantan, Pahang, Malaysia. [email protected]

Aminaton binti Marto Professor of Geotechnical Engineering, Faculty of Civil Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia [email protected]

Noor Nazihah binti Ma’amor Quantity Surveyor, Department of Contract & Quantity Surveying, 12th Floor, Jabatan Kerja Raya Pahang, Kompleks Tun Razak, Bandar Indera Mahkota, 25582 Kuantan, Pahang [email protected]

ABSTRACT: The characteristics of soft soil are different compared to other soils due to their low strength and high compressibility. It is very difficult to obtain undisturbed samples for this type of soil especially for the laboratory testing. Hence, the correlations between engineering characteristics and basic properties or between engineering characteristics itself will be useful for civil engineers, especially for preliminary design purposes. This paper presents correlations of engineering characteristic of soft soil in Maran, Pahang. Generally, the correlations show that the liquid limit and plasticity index increase with the moisture content. The plasticity index also tends to increase with liquid limit. An attempt was also made to get correlation between the liquid limit with the clay/silt content. It is found that the liquid limit increases with the increase of clay/silt content, probably due to the clay particles tend to pull or absorb water to the surface of soil particle, making the liquid limit to be much higher. The results give an alternative for engineers to use the basic soil properties to predict the nature of soil. This will allows a quick and economic design for construction in Maran, Pahang.

Keywords: soft soil, correlations, engineering characteristics.

1. INTRODUCTION

The booming development in construction industry has minimized the good site with geotechnical quality for construction although these sites are known to have little technical problem and thus reduce the cost associated with their construction. By that, socio-economic and political considerations have forced the use of marginal sites that mainly covered by compressible soils. By this, it becomes a challenge for civil engineers all over the world to do construction on these problematic soils.

Soils with low strength characteristics and compressibility exist all over the world. One of the most significant problem arises by these type of soils is it difficulties in supporting loads on such foundation. This is because soft soil possesses low strength and because of that, it leads to difficulties in guaranteeing the stability of the embankment. Furthermore, this type of soil also associated with high compressibility which leads to large settlements and deformations of the structure.

The construction on soft soil is increasing lately because there are not too many suitable sites for construction of infrastructures and other development. The problems that related to this type of soil are stability and settlement. Because of that, the understanding and knowledge of engineering characteristics of soft soil are critical and should be concentrated by people that related in this field. The selection of construction method on this formation is restricted by costs, duration of completion, and many more.

The rapid growth in South East Asia generally has acknowledged the importance of studies in soft soil. But past studies only concentrated on major cities, such as Bangkok, Kuala Lumpur, Jakarta, Singapore, and many more. Because of that, Pahang state is chosen for this study to develop correlations that hopefully will be use by the engineers for preliminary design purposes as well as increasing the database on engineering characteristics of soil properties for this particular area. Generally, all districts in Pahang state are involved in this research; Bentong, Bera, Kuala Lipis, Maran, Kuantan, Raub, Rompin, Jerantut, Temerloh, Pekan and also Kuala Lipis’ high population residential area known as Cameron Highlands. Data are taken with some helps from Public Work Department (JKR) Malaysia.

The aims of this study are:-

i) To determine the engineering properties and design parameters for soil in Pahang State.

ii) To produce correlations between engineering characteristics and basic properties of soil for design purposes.

iii) To produce correlations between engineering characteristics and basic properties with depth of soil for design purposes.

iv) To contribute to Pahang soil analysis development.

This study was conducted generally in Pahang. The data were taken based on the site investigation report obtained from several construction project sites in every district in Pahang state. The results presented in this paper are focused on Maran district.

To overcome the problem encountered in soft soil, knowledge and deep understanding about the engineering characteristics of the soft soil are very important. The data that had been obtained are analyzed and hopefully will become a part of soft soil

database in Malaysia. This is because there are lack of studies in soft soil properties and engineering characteristics in Malaysia. The result from this study can be referred by engineers as useful guidance for them to apply in construction on soft soil. Whereby, the correlation that been produced can be used as preliminary design for structure on soft soil.

2. LITERATURE REVIEW There are only limited correlations on soil characteristics available to date, in particular for soft soil. The generated correlations in the studies are correlation between plasticity index with liquid limit, liquid limit with clay/silt content, natural moisture content with clay/silt content, natural moisture content with liquid limit and natural moisture content with plasticity index.

2.1. Correlation between Plasticity Index and Liquid Limit

Hussein (1995) has generated the correlation between plasticity index and liquid limit with the equation as follows:

Ip = 0.7(wL - 6) (1)

Abdullah & Chandra (1987) also generated a correlation between plasticity index and liquid limit. The equation of the correlation is:

Ip = 0.64(wL - 8.8) (2)

Saiful Azhar (2004) has generated another correlation between plasticity index and liquid limit with the equation as follows:

Ip = 0.77(wL - 10) (3)

Muzamir, Amizatulhani & Faruq (2009) has generated a correlation between plasticity index and liquid limit with the equation as follows:

Ip = 0.4384(wL) + 1.5301 (4)

where,

Ip = plasticity index

wL = liquid limit

Liquid limit and plasticity index obtained by Saiful Azhar (2004) is 31% to 142% and 17% to 101% respectively. While the liquid limit and plastic limit obtained by Hussein [1] is 40% to 125% and 10% to 40% respectively and Hasan, Abdullah & Saadon [5] reported that liquid limit is from 20.3% to 71% and plastic limit for this site is from 24% to 37%.

2.2. Correlation between Natural Moisture Content and Clay/Silt Content

Saiful Azhar (2004) has generated the upper and lower limit between natural moisture content and clay content with the equations as follows:

Upper limit: w = 1.93 (%clay) + 53 (5)

Lower limit: w = 0.43 (%clay) + 11 (6)

While Muzamir, Amizatulhani & Faruq (2009) have generated the correlations as follow:

Upper limit: w = w = - 0.07(% clay/silt) + 40 (7)

Lower limit: w = w = 0.04(% clay/silt) + 5.5 (8)

where,

w = natural moisture content

Natural moisture content obtained by Saiful Azhar (2004) and Ting & Ooi (1977) is 18% to 139% and 20% to 140% respectively. While Muzamir, Amizatulhani & Faruq (2009) reported that natural moisture content is 13% to 25%.

2.3 Correlation between Liquid Limit Moisture Content and Clay Content

Saiful Azhar (2004)] has generated the upper and lower limit between liquid limit and clay content with the equations as follows:

Upper limit: wL = 1.92 (%clay) + 56 (9)

Lower limit: wL = 0.39 (%clay) + 24 (10)

Muzamir, Amizatulhani & Faruq (2009) has also generated the upper and lower limit between liquid limit and clay content with the equations as follows:

Upper limit: wL = 0.23(% clay/silt) + 105 (11)

Lower limit: wL = 0.44(% clay/silt) + 3 (12)

where,

wL = liquid limit

3. RESULTS AND DISCUSSIONS

From the results, some correlations were generated. The correlations are liquid limit and plasticity index with natural moisture content, plasticity index with liquid limit, natural moisture content with clay/silt content and liquid limit with clay/silt. Table 1 shows the generated correlations. While Fig. 1 and Fig. 2 show some correlations between natural moisture content with clay/silt content and generated between plasticity index with liquid limit respectively.

Table 1. Simplified Correlations Produced.

Fig. 1. Correlations generated between natural moisture content and clay/silt content.

Fig. 2. Correlations generated between plasticity index and liquid limit.

3.1 Moisture Content

Percentage of moisture content in this area is inconsistent from 1.5m to 35m depth. The percentage of moisture content in this area is in 12% to 35% range.

3.2 Plasticity

Percentage for liquid limit in this area is inconsistent but the percentage looks higher from 2m to 12m depth before the percentage inconsistently decreases from 12m to 35m depth. The percentage of in this area is in 37% to 83% range.

Percentages of the plastic limit of this area look more consistent in the sense that the percentage are tend to be within at the same range. The percentage of this area is in 17% to 35% range.

Meanwhile, percentage for plasticity index for this area is more decreasing from 2m to 35m depth. The samples are non plastic. The percentage ranges of the plastic index are within 7.67% and 51%.

The plasticity is controlled by fine particles (clay and silt) and in particular, the plasticity of the soil is strongly influenced by clay content. Natural moisture contents are increases with clay content. Plasticity index are also increases with the increases of natural moisture content and liquid limit. Liquid limit and natural moisture content are also increase to one

No. Correlations Equations R2

1 Liquid limit (%) & natural moisture content (%)

wL=1.1905(w)+20.706 0.4124

2 Plasticity index (%) & natural moisture content (%)

Ip=1.1351(w)-11.557 0.5605

3 Plasticity index (%) % liquid limit (%)

Ip=0.7772(wL)-17.88 0.9262

4 Liquid limit (%) & clay/silt content (%)

wL=0.5579(%clay/silt)+25.267

0.4139

5 Natural moisture content (%) & clay/silt content (%)

w=0.2854(%clay/silt)+14.301

0.5761

other. For liquid limit and clay content, the value had showed some linearity.

4. CONCLUSIONS Several conclusions can be drawn from the study as follows:

i) The correlation developed shows that the clay content influences the liquid limit.

ii) The liquid limit plasticity index with moisture content show that all the parameters increase with the increase of moisture content.

iii) The correlation developed show that plasticity index are proportional with liquid limit.

iv) The correlation also produced a proportional line in liquid limit versus clay/silt content correlations.

v) Natural moisture content with clay/silt content had produced a proportional increases in this area.

vi) The plasticity index is also increases with natural moisture content.

vii) The correlation had showed that soil content for every district area are largely dominated by clay follow by sand and lastly gravel.

viii) Percentage of moisture content in this area is inconsistent from 16% at 1.5m to 17% at 35m depth. The percentage of moisture content in this area is in 12% to 35% range.

ix) Percentage for liquid limit in this area is inconsistent but the percentage looks higher from 82.63% at 2m to 73% at 12m depth before the percentage inconsistently decreases from 73% at 12m to 37% at 35m depth. The percentage of in this area is in 37% to 83% range.

x) Percentages of the plastic limit of this area look more consistent in the sense that the percentage are tend to be within at the same range. The percentage of this area is in 17% to 35% range.

xi) Meanwhile, percentage for plasticity index for this area is more decreasing from 45.33% at 2m to 20% at 35m depth. The samples are non plastic. The percentage ranges of the plastic index are within 7.67% and 51%.

ACKNOWLEDGEMENTS

The authors would like to thank UMP for funding this research under UMP Short Research Grant RDU070351.

REFERENCES

Abdullah, A. I. M. B. and Chandra, P. (1987). Engineering Properties for Coastal Subsoils in Peninsula Malaysia. Proceeding of the 9th Southeast Asia Geotechnical Conference. Vol. 1. Bangkok: Thailand. 127-138.

Hussein, A.N. (1995). The Formation, Properties and Behaviour of Coastal Soft Soil Deposits at Perlis and Other Sites in Peninsula Malaysia. University of Stratchlyde, PhD Thesis, Vols I and II.

Muzamir bin Hasan, Amizatulhani binti Abdullah, and Faruq bin Saadon (2009). The Correlations and Soil Properties Analysis of Temerloh, Pahang. Proceedings of MUCEET 2009, Kuantan,Pahang, Malaysia.

Saiful Azhar (2004). Ciri-ciri Kejuruteraan, Mineralogi, and Mikrostruktur Tanah Liat Lembut di Semenanjung Malaysia. Universiti Teknologi Malaysia, Master Thesis.

Ting, W.H. and Ooi, T.A. (1977). Some Properties of the Coastal Alluvia of Peninsula Malaysia. Proceeding of International Symposium on Soft Clay. Bangkok, 89 – 101.

Geotropika Conference 2010, Malaysia

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REVIEW OF CONSTRUCTION CHALLENGES ON SIBU PEAT: CASE STUDY AND LESSONS LEARNED Associate Professor Dr. Mohd Idrus Hj. Mohd Masirin

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1 – Associate Professor in Civil Engineering, Universiti Tun Hussein Onn Malaysia [email protected]; [email protected]

Rufaizal Bin Che Mamat2

2 – Lecturer, Department of Civil Engineering, Politeknik Merlimau Melaka Malaysia [email protected]

Adnan Zainorabidin3

3 – Researcher University of East London, UK [email protected]

Prof. Dr D.C. Wijeyesekera4

4– Professor in Civil Engineering, University of East London, UK [email protected]

Rasimah Mohd Zain5, Anati Hanum Ahamadi Hazali

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5 – Researcher Universiti Tun Hussein Onn Malaysia

ABSTRACT Failures after constructions is common especially for projects on difficult ground conditions. Different types of soils will result in different types of failure severity. Engineers and researchers are continuously challenged to study and overcome problems on soft clays and peat soils but, till now, no perfect solutions are obtained for cost effective and suitable to ensure the community will have a peace of mind when inhibiting their residences or offices. This situation has motivated many to suggest ideas on how to construct houses and roads on peat soil. In this paper, the researchers have attempted to study the behaviours and properties of different types of failures focusing on Sibu peat soils. This type of peat is located in East of Malaysia and in the state of Sarawak. The authors have also attempted to discuss and present some experiences and facts on peat soils including Sibu peat. As settlement are common problems on soft soils, some information on settlements are included in this paper. Some research findings conducted in Sibu Sarawak are also presented and shared to study the types of failures especially on Sibu peat. Techniques used by local authorities in Sibu were also presented with innovations suggested for continuous enhancement when construction on peat is concerned. It is hoped that these information which are overview of Sibu peat, some construction works and problems which has been completed 20 years ago will eventually give us some perspective and motivations to continuously find solutions and reduce failures when constructing structures on difficult ground conditions especially on peat. Keywords: Sibu, Peat, Construction failures, Physical, Properties, Engineering Properties. 1.0 INTRODUCTION

Geotechnics has been the most important

component when construction is concerned. The geotechnical conditions of soft soils will determine many parameters such as design requirements of structures, cost of projects, time or completion duration of projects and quality of the construction works. These factors are also related to short term and long term effects on structures. Thus, it creates many challenges to engineers and researchers to ensure the quality of life in the community is maintained or improved. This will also includes fears if structures fail and accidents might happen unexpectedly. In Malaysia, difficult ground conditions will include soft clays and peat.

Malaysian peat is a tropical peat (Jarret, 1997). This peat has unique characteristics, which makes it significantly different from other peat. In its

natural state, this soil is normally dark reddish brown to black in colour and consists of partly decomposed leaves, branches, twigs and tree trunks with a low mineral content. These are formed through accumulation of disintegrated plant remains, which have been preserved under conditions of incomplete aeration and high water content. Hobbs (1986) as quoted by Zainorabidin et al (2007) stated that it was important to include and recognize the peat by not only its morphology but also by its basic engineering properties. The “special” characteristics for this soil are a high water content (>200%), high compressibility, high organic content (>75%), low shear strength (5-20kPa) and low bearing capacity (<8 kN/m2). These geotechnical characteristics make any form of construction on this soil very challenging in Malaysia (Zainorabidin and Bakar, 2003). Masirin et al (2009)


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have conducted a field study at Sibu to investigate the causes of roads and building structural failures. These findings have lead to the possibility of soil nature whereby they are mostly constructed on Sibu peat soil. 2.0 BACKGROUND

Sarawak has the largest peat area in Malaysia with 16,500 km2 that makes up 13% of the state, of which about 90% is more than 1m in depth. Sibu is the centre for Sibu Division, Sarawak, and it is an inland town in the Island of Borneo (Robert et al, 2004). Located on deep peat swamp Sibu experiences lots of constraints in development which include the sinking problems due to excessive soil settlement. The term peat is described as a naturally occurring highly organic substance derived primarily from plant materials (Tai et al, 2004). It is formed when organic (usually plant) matter accumulates more quickly than it humidifies (decays). Peats are therefore superficial deposit or soils with high organic matter content. However, the cut-off value of the percentage of organic matter necessary to classify a superficial deposits or soil as peat varies throughout the world, usually depending on the purpose of classification. This cut-off value also serves to differentiate peat from superficial deposits or soils with lesser amounts of organic matter content.

Peat in strict definition usually refers to the accumulation of a purely one hundred percent organic material and the distinction between soil and vegetation accumulation is not clear (Mei et al, 2003). On the other hand, organic soil is an analogous term for superficial deposits or soil that contains organic matter. Soils with organic matter in it have undergone a change in perception accompanied by a change in terminology in Sarawak during the past 50 years particularly in the discipline of soil sciences itself. Peats and organic soils, both terms used for describing soils with an organic content, were used in soil sciences at separate times and today these terms have also come into engineering literature. Peat soil exhibits very low bearing capacity and its soil is not suitable for constructing embankment, highway, building or other load bearing engineering structure. Peat in its natural state consists of water and decomposing plant fragments with virtually no measurable bearing strength (Mutalib et al, 1991). Peat is considered as soft soil because this soil has high settlement value and even under moderately applied load. Thus peat by virtue of its heterogeneity is a problematic soil. The high natural water contents coupled with the extraordinary compressibility of the organic material cause undesirable and unpredictable settlement. The performance of peat is dominated by the macro and

micro structure which is continuously changing with the material digenesis. Research leading to a better understanding of the performance of peat is urgently required for better geotechnical design.

Figure 1: Distribution of peat in Sarawak (JKR, 1995)

Correlations of peat behaviour with these parameters will help engineers to appreciate the complex behaviour of peat soil. The geotechnical properties of Malaysian peat soil shows in Table 1 below. Table 1: Geotechnical properties some of Malaysian soils

Soil Deposit Carey Island Marine Clay

West Malaysia Peat and Organic Soil

East Malaysia Peat and Organic Soil

Johore Hemic Peat

Natural water content, W (%)

28-93 200-700 200-2207 230-500

Liquid limit, LL (%)

33-104 190-360 210-550 220-250

Plastic Limit, PL (%)

24-41 100-200 125-297 -

Plasticity Index, PI (%)

21-63 90-160 85-297 -

Specific gravity (Gs )

2.55-2.68

1.38-1.70 1.07-1.63 1.48-1.8

Organic content (%)

- 65-97 50-95 80-96

Unit weight (kN/m3)

13-16.9 8.3-11.5 8.0-12.0 7.5-10.2

Undrained Shear strength (kPa)

- 8-17 8-10 7-11

Compression Index,Cc

0.5-1.25

1.0-2.6 0.5-2.5 0.9-1.5

Refs. Shanul et al (2004)

Bujang (2004)

Bujang (2004)

Zainorabidin and Ismail (2003)


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Thus peat by virtue of its heterogeneity is a problematic soil. The high natural water contents coupled with the extraordinary compressibility of the organic material cause undesirable and unpredictable settlement. The performance of peat is dominated by the macro and micro structure which is continuously changing with the material digenesis. Research leading to a better understanding of the performance of peat is urgently required for better geotechnical design. The Malaysian case histories related to construction projects on peat area is as shown in Table 2. Table 2: The Malaysian case histories related to construction projects on peat soil area.

Perspective on Peat and Organic Soils The commonly found peat soil in Sibu occurs as extremely soft, wet unconsolidated superficial deposits which normally form as an integral part of wetland systems. They may also occur as strata beneath other superficial deposits. As commonly known, the term peat is described as naturally occurring highly organic substance derived primarily from plant materials. It is

formed when organic (usually plant) matter accumulates more quickly than it humidifies (decays). This usually occurs when the organic matter is preserved below a high water table like wetlands (3). Peats are therefore superficial deposit or soils with high organic matter content. However, the cut-off value of the percentage of organic matter necessary to classify a superficial deposits or soil as peat varies throughout the world, usually depending on the purpose of classification. This cut-off value also serves to differentiate peat from superficial deposits or soils with lesser amounts of organic matter content (Harwant, 2003). On the other hand, organic soil is an analogous term for superficial deposits or soil that contains organic matter. Soils with organic matter in it have undergone a change in perception accompanied by a change in terminology in Sarawak during the past 50 years particularly in the discipline of soil sciences itself. Peats and organic soils, both terms used for describing soils with an organic content, were used in soil sciences at separate times and today these terms have also come into engineering literature (Wong, 2003). 3 .0 FIELD RESEARCH & BASE DATA As mentioned in 1.0, a field study was conducted by the authors regarding the challenges faced by locals in Sibu city in Sarawak in 2009. A complete investigation was conducted on a housing area which was constructed more than 25 years ago and 2 road-bridge interface sections where differential settlements were pertinent. More than 4 houses were investigated and measurements were taken which include the size of structural cracks, the differential settlement depths and the types of failures on walls and main structures. As for the road-bridge study, a survey field work was conducted along longitudinally and at cross-sections to determine the intensity of differential settlements between the road and bridge surface along two roads identified as experiencing differential settlements. From these results, the authors then arrive to a summary of their findings, focusing on the intensity and seriousness of the conditions and recommended some countermeasures to ensure that the situation does not lead to unnecessary lost of lives and unexpected complications to the community. Currently, further research is still conducted for more conclusive data and outcomes. Table 3 demonstrated some of the conditions previously studied locations encountered by engineers and researchers in studying the Sarawak peat.

Region Location Topography Total Area

Characteristics

Peni

nsul

ar West

Johore, Kuantan, Pekan, Selangor, Perak

Peat land is flat

Approximately 80,000km2 with 89% of it having deep peat (>1m)

Normally found in the coastal areas of the east and west coasts

Sara

wak

Kuching SamarahanSri Aman Sibu Sarikei Bintulu Miri Limbang

The basin peat swamps are dome-shaped

16500 km2 with 89% of it having deep peat (>1m)

Peat occurs mainly between the lower stretches of the main river courses (basin peats) and in poorly drained interior valleys (valley peats).

Saba

h

Kota Belud Sugut Labuk Kinabatangan

Peat land is flat

86 km2. There was no estimates on the depths

Peat soils are found on the coastal areas


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Table 3: Historical Research facts on Sarawak Peat Soil

Types of building settlements (See Figure 2) Typical problems and concerns might occur toward structures on peat soil are: settlement, foundation failure, suspended slab failure, buckling or damage column, hostile environment and balcony damage. Main focus is on settlement behavior, the condition may affect the entire building and the internal structures. But the affect could have no implication or could be a major problem; hence, some judgment will be calls. In this research the types of building settlements are classified as follows (Masirin et al, 2009): 1. Implications of Tipping Settlement

The building may continue to settle. The floors may not be level, affecting building use.

Substantial costs may be associated with stabilizing the building.

2. Implication of Uniform Settlement.

The building may continue to settle. Services to the building may be affected.

3. Implications of Differential Settlement.

The building may continue to settle. The floors may not be level, affecting building use. Substantial costs may ne associated with stabilizing then building.

Figure 2: Types of possible settlement situations to

houses 4.0 SITE OBSERVATIONS AND CASE STUDIES As mentioned in section 3.0, two types of case studies were conducted. The first was on building condition and the second was on roads. However, in this paper, only case studies on buildings are being presented in detail whereas the road case study is briefly presented due to on-going analysis work by the researchers. From the observations, the followings are some analyses conducted by the authors: 4.1 Case Study 1: Structural Settlements at Hua

Khiew Housing Estate in Sibu City, Sarawak

The old residential areas bound by Jalan Pedada/Brooke Drive/Kampong Nyabor/Oya Road and Hua Khiew Road is located in the heart of Sibu City (See Figure 3). The area measures about 300 acres with about 3000 houses. Many houses were built about 40 – 50 years ago and most of the owners have moved out of the areas leaving their houses for rent. Most of the roads and drains here need relaying every two to three years. Otherwise, they will be subjected to frequent flooding during high tide or after torrential downpour. In fact, a

Rep

ort

Location Project Soil Types Problems

Won

g (2

003)

Sri Aman (Sarawak)

Earth filling project for 6 acre site for building site and football field.

Underlain with 5.6m to 7.0m thick very soft dark brown peat and woods.

Settlements continued after reaching the platform level for earth filling.

Bintulu (Sarawak)

Earth filling 4.5 acre site for housing development

8m to 13m thick very soft dark brown peaty clay with decomposed wood.

The settlement for first year exceeds 300mm and the differential settlements were found to be more 1:150 in many block houses.

Tai e

t al (

2004

)

Sibu City (Sarawak)

Part of Sibu Town

Substantial peat formations over than 10 m depth

Ground subsidence caused by uncontrolled land filling and lowering ground water


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number of houses have sunken beyond repair (Robert, 2003).

4.1.1 Resettlement Schemes – Kampung Usahajaya at Jalan Sentosa and Kampung Bahagia at Jalan Teku. (See Figure 4) These schemes comprise of local people who were resettled from squatters. These are about 2000 households staying in these schemes. The schemes are located in low-lying areas subjected to frequent floods.

4.1.2 Summary From the site investigations conducted, the followings are concluded:

(a) Cracks on the walls (See Figure 5) were seen in the four houses investigated with cracks of average between 5mm to 10mm formed vertically and diagonally. This shows that the walls were failing unevenly due to uneven settlements to its foundations.

(b) Floor settlements and failures seem to cause extensive heaving effects and substantial damages. From the coring, it was found that the imported soils under the floors reacted differently when the building settled vertically downwards.

(c) Some houses experienced structural failures especially to its columns and beams. Cracks between 5 to 15mm were seen and some columns collapsed as a result of excessive settlements.

4.2 Case Study 2: Road-Bridge Construction 4.2.1 Road-bridge interface investigation at

Jalan Nang Sang Teku and Jalan Maaw, Sibu, Sarawak

From the site works and surveys conducted on two selected road-bridge sites, the authors have found the followings: (a) There were surface cracks on the road-bridge

interface sections at both Jalan Nang Sang Teku and Sungai Maaw, Sibu City sites of 10mm to 15mm during the investigation between December 2009 and January 2010.

(b) Roadside erosions were noticed on both wing walls which might be due to rainfalls and water overflowing the river during monsoon seasons.

(c) The difference in levels between the roads and bridges were quite significant whereby for Jalan Nang Sang Teku, the level difference were between 200mm to 350mm whereas for Jalan Sungai Maaw were recorded between 1400mm to 1500mm.

Figure 3: Location of the site investigation

Figure 4: The flooded housing area

Figure 5: Failures on site


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4.2.2 Summary The outcomes of the survey works conducted indicated that within one month, the differential settlements of both road-bridge interfaces experienced extensive loadings and settlements. This might be due to the existence of big trucks carrying logs and construction materials. Furthermore, the low bearing capacity of peat soils hasten the settlement process thus pertinent differences in levels were seen significantly.

5.0 CONCLUSION & RECOMMENDATIONS As a conclusion, Sibu peat soil is a challenging soil type and construction in Sibu City itself is a great challenge to civil engineers. The authors have always consider Sibu City as a huge open laboratory for geotechnical engineering and challenges are in store to engineers in finding ways and alternatives to improve quality of construction on Sibu paet soil. Furthermore, it may be a great contribution to Sibu community if engineers are able to find creative and innovative ways to construct sustainable housing and infrastructure systems on Sibu peat soils. 6.0 ACKNOWLEDGEMENT First of all, I would like to thank Mr Adnan Zainorabidin and Prof Dr DC Wijeyesekera for their support in preparing this paper. I would also like to thank Ms Rasimah Md Zain and Ms Anati Hanum for their continuous determination in assisting the author to gather research materials for this research work. Lastly, I would like to thank my family members for the support and for doing some of the field observations as part of our family outing program. 7.0 REFERENCES B.L.H.Mei, E.Padmanabhan, Mohamed.M,W.B.Siong,

(2003). The Peat Soils of Sarawak. Proceedings of 2nd International Conference on Advances in Soft Soil Engineering and Technolo., Universiti Malaysia Sarawak, Malaysia.

Mutalib, A.A.,Lim, J.S., Wong, M.H. and Koonvai, L. (1991). Characterisation,Distribution and Utilization of Peat in Malaysia, Tropical Peat, in Proceeding of theInternational symposium on Tropical Peatland, Kuching, Sarawak, Malaysia, 7-16.

Jabatan Kerja Raya (Sibu) Malaysia and Jarret, P.M. (1995). Geoguide 6: Site Investigation for Organic

Soils and Peats, JKR Document 20709-0341-95, Institut Kerja Raya Malaysia.

Jarret P.M (1997). Recent development in design and construction on peat and organic soils. In Proceedings of Recent Advances in Soft Soil Engineering,ed. Huat and Bahia, pp.1-30.Sarawak.

Harwant, S. and Bujang, B.K.H. (2003). Perspective on Peat, It’s Occurrence in Sarawak and some Geotechnical Properties., in Proceedings of Conference on Recent Advances in soil Engineering, eds. Huat, B.B.K and Bahia, H.M., 5-7 March, 1997. Kuching, Sarawak. Pp. 135 –

Masirin, MIM; Anati Hanum (2009). Construction challenge on peat soil: Sibu long term effect on housing construction. Presented to UTHM RMC office after site investigation works on December 2009 (Report)

Masirin, MIM; Rasimah Md Zain, Md Fizal Abu Bakar and Daud Mohamad (2009). Site investigation on Road-Bridge Interface problems due to differential settlements at Jalan Nansang Teku and Jalan Sungai Maaw, Sibu Sarawak. Presented to UTHM RMC office after site investigation works on December 2009 (Report)

Robert L. H.C, Hee, H. C. (2003).Urban Environmental Management Initiatives in Sibu, Sarawak, Malaysia Borneo, Sibu Municipal Council. 6 – 7.

Tai L.Y, Lee K.W and Ting W.H.2004. Some aspect of peat formation in Sibu Town and related engineering problem. In Proceedings of The Malaysian Geotechnical Conference 2004 ed. Chan. P. Kuala Lumpur.

Wong, K.M., (2003). Earth-Filling– Experiences on peat soils at Sri Aman, Sibu & Bintulu, In Proceedings of 2nd International Conference.

Zainorabidin, A. and Bakar, I. (2003). Engineering properties of in-situ and modified hemic peat soil in Western Johor. In Proceedings of 2nd International Conference on Advances in Soft Soil Engineering and Technology, ed. Huat et al, p.173-182.Putra Jaya, Malaysia.

Zainorabidin, A. and Wijeyesekera, DC. (2007). Geotechnical Challenges With Malaysian Peat. In Proceedings of Advance in Computing and Technology Conference. no pp. University of East London, UK.


DEVELOPMENT OF IRB TEST-BED AT RESEARCH CENTRE FOR SOFT SOIL MALAYSIA (RECESS MALAYSIA): FROM CONCEPT TO TESTING

Associate Professor Dr. Mohd Idrus Hj. Mohd Masirin

1

1 – Lecturer in Civil Engineering, Universiti Tun Hussein Onn Malaysia [email protected]; [email protected]

Professor Dato’ Dr. Ismail Hj Bakar1

1 – Lecturer in Civil Engineering, Universiti Tun Hussein Onn Malaysia

Norazah Abdul Rahman2

2 – Lecturer, Politeknik Johor Baru Malaysia

Mohd Firdaus Ab Aziz 3

3 – Engineer, Lembaga Lebuhraya Malaysia

Rasimah Mohd Zain3, Anati Hanum Ahamad Hazali

4

4 – Researcher Universiti Tun Hussein Onn Malaysia

ABSTRACT

Road has been constructed by many engineers to enhance the communication efficiency between regions and places. In Malaysia, roads are constructed in many situations, whether they are located in highlands, swampy areas, soft clays, peaty soils or coastal condition. Local and federal authorities in Malaysia responsible with road construction are always faced with undulating effects when roads meet bridges and those which are constructed on soft soils such as peaty and soft clays. Thus, it is of utmost important for us to study the effect of bridge designs and choice of structures for a particular condition. In this project, the authors have acquired a research grant to study the methods commonly used in road projects especially when roads and bridges interfaced. Initial studies were conducted via site investigations, simulation and small scale modelling. However, in order to get better conclusive observations and results, the authors have attempted to develop a test bed on soft soil named IRB Test-Bed or Road-Bridge Test Bed. A description of the test bed which is being constructed is presented in this paper and some types of test are also proposed. It is hoped that as a new facility being developed at RECESS Malaysia for full scale tests on Batu Pahat soft clay IRB Test-Bed can contribute to better road bridge designs and attract more researchers to conduct their research at RECESS Malaysia located in Batu Pahat, Johor. Keywords: Batu Pahat Soft Clay, Road, Bridge, Undulating, Small Scale Modeling, IRB Test Bed. 1.0 INTRODUCTION

Settlement has been an issue when construction on soft soils is concerned. Many types of soils are classified as soft soils such as peat soils, soft clays and organic soils. On the field, these types of soils may also create a situation classified as difficult ground condition. Thus, construction may cause many uncertainties and problems. In this research, differential settlement between bridges and pavements was studied to understand the behaviour of soils and bridge structures. The introductions of approach slabs by many engineers have reduced some of the problems at the interface sections but only for a short period of time. This research includes, simulation using PLAXIS computer software and field geotechnical forensic studies which later lead to the development of a proposed new interface road bridge test-bed at RECESS Malaysia, UTHM by the researcher acronymed IRB Test Bed. 2.0 BACKGROUND OF STUDY

Construction of structures on soft soils

experienced many difficulties especially when long term effect is concerned. Engineers and scientists likewise have been putting efforts into enhancing the bearing capacity of structures constructed on soft soils by stabilizing them using various methods. With the diverse types of soils in Malaysian geological environment especially on soft soils, construction of many structures such as buildings and roads are experiencing continuous settlement. This includes construction of roads and bridges. If settlement problems of buildings are due to their foundations and continuous consolidation of soils which may be an element that might lead to complication in the housing industry, similarly, settlements may also happen in road-bridge constructions. Differential settlements between roads and bridges have been continuous problems faced by engineers. These problems have not only created geotechnical problems but also safety


hazards to road users. Some accidents can be avoided if drivers are careful or slowed down their vehicles when passing over a bridge which has steep gradient when compared to the approach roads. However, in many cases, accidents happened because drivers could not control their vehicles after passing the differential settlement section between the road and bridge, thus knocking into approaching vehicles or plunging into the road side ditches. Introducing lime stabilizing agent, geotextiles and piling to name a few have successfully reduced the differential effects to the structures. In general, the research outcomes of this project can contribute towards identifying the causes of differential settlements caused at the road-bridge approach slab interface whether they are constructed on peat or soft clays. 3 .0 RESEARCH METHODOLOGY This research was initiated by the main author through his fundamental research grant awarded by the Ministry of Higher Education in 2007. Initially, this research was conducted by analyzing the possible cases of different road-bridge interface failures and using computer software, PLAXIS, the settlement and numbers of years that can be correlated. Secondly, a field investigation or geotechnical forensic studies were conducted at selected locations. In this research, four sites were selected that is, Parit Karjo and Parit Haji Ali in Batu Pahat Johor (on Batu Pahat Soft Clay - BPSC) and Jalan Maaw and Jalan Nang Sang-Teku in Sibu Sarawak (on Sibu Peat Soils - SPS). With addition to this, a special investigation was also conducted at Hua Khiew road in Sibu, Sarawak to look at the disastrous conditions of many houses constructed more than 20 years ago on peat soils. With these field information, the researcher has also conducted some laboratory tests to understand the soil properties and model testing on the selected approach slab concepts thus, confirming the settlement effects with time after loading were imposed. However, in this paper the authors would only elaborate more on the proposed development of IRB as a test bed for any road and bridge tests on full scale size at RECESS Malaysia, UTHM. 3.1 The computer simulations As mentioned earlier, before a full scale test is conducted on the IRB test bed, researchers are needed to determine the viability and feasibility of a certain project using computer simulation software. In this case, PLAXIS was used to determine the effect of a certain model during short or long term. A typical data analysis is then obtained and concluded. Figure 1 and

Figure 2 showed a typical output from PLAXIS software. 3.2 The site investigations Site investigations will include the soil properties determination, types of failures as reference and case study. In developing this test bed, the authors have actually conducted a few site investigations to understand the types of road-bridge interfaces and connections that exist in the actual construction. Using this knowledge, it can be used for testing on the IRB test bed developed in RECESS Malaysia. Figure 1: Typical output from PLAXIS Simulation

process Figure 2: Simulation of Deformation Profiles for

Different Approach Slab Models. 3.3 The laboratory investigations The author has, prior to the development of the proposed IRB test bed, conducted a small scale laboratory model test. The equipment used to simulate the dynamic loading was Wheel Tracking System available at UTHM’s Highway and Transportation Engineering Laboratory. The results obtained were


than compared with the results which were supposed to be obtained from IRB test bed. 4.0 IRB TEST BED MODEL IRB test bed model is proposed to conduct any full scale testing related to bridge and road materials or systems. It consists of two supporting walls, fixed on a railing for adjustability depending on the length of the bridge. Two fixed embankment walls are constructed as to simulate the strong wing-walls of bridges. These walls are constructed on a very strong foundation and concrete floor, designed to carry a weight of more than 5 tons including the weight of concrete structures and standard vehicles for testing. Since the bridge, the approach slab and the road will be applied with dynamic loading, the IRB test bed will be equipped with a circular road pavement for the standard vehicle. Some sensitive monitoring equipments such as transducers for load and settlement monitoring will be fixed at certain positions and connected to a data logger for record purposes. Figure 3: Author’s illustration of the proposed IRB test

bed 5.0 CONCLUSIONS & RECOMMENDATIONS • From the research, it was found that differential

settlements have been common phenomena when road and bridge meet or interface concerned. The difference in rigidity played an important element, as differently structural rigidity of different materials will react differently when imposed a certain loading. The tests and investigations conducted has shown that different types of approach slabs will also react differently when imposed with various types of loading especially dynamic loads.

• Analysis using repeated loads of moving traffic should be considered for future research work. With this research project, further research on the

selected approach slab can be carried-out by conducting a full-scale or real-field testing project at a controlled site such as Research Centre for Soft Soil (RECESS Malaysia) located at UTHM.

• The proposed IBR Test –Bed is a viable alternative and future project to better understand acquires solutions to reducing bumps and undulating effect at Road –Bridge interface sections.

• With IRB test bed, better understanding to solve the problems that occurred at the road-bridge interface can be documented and implemented to prolong road and bridge design life.

6.0 ACKNOWLEDGEMENT I hereby would like to thank my co-authors and researchers especially Bibi Sarah, Norazah and Hor Peay San for their support in preparing this paper. I would also like to thank Ms Rasimah Md Zain and Ms Anati Hanum for their continuous determination in assisting the author to gather research materials for this research work. Last but not least I would like to thank my family members for the support and understanding while conducting this research work. 7.0 REFERENCES Cai, C. S., Shi, X. M., Voyiadjis, G. Z., and Zhang, Z.

J. (2005). “Structural Performance of Bridge Approach Slabs under Given Embankment Settlement.” Journal of Bridge Engineering, July 2005, Vol. 10, No. 4, pp 48-489

Gue, S. S., Tan, Y. C., and Liew, S. S. (2002). “Cost Effective Geotechnical Solutions for Roads and Factories Over Soft Ground.” 20th Conference of the ASEAN Federation of Engineering Organization, 2002.

Huang, Y. H. (2000). “Pavement Analysis and Design 2nd Edition.” New York: John Wiley & Sons.

Jestin Jelani. (2006). “Forensic Study on Rural Road Pavement Failure along Parit Sumarto.” UTHM : Postgraduate Project Report.

Masirin, M.M.I., Wijeyesekara, D.C., Bakar, I., Aziz, A.A., Rahim, A.K.A.A., Zainorabidin, A. (2003). “A New Research and Development Facility on Malaysia Soft Soil.” AIT, Thailand.

Masirin, M. M. I., Adnan, Z., Ahmad, K. A. A. R and Azman, H. (2005). “Defect of Rural Road Constructed On Soft Soils In Batu Pahat District Johor Malaysia.” 2nd International Seminar on Geotechnical Transportation Engineering, Diponegoro University, Indonesia.

Piles

Roller railingRoller

Adjustable Walls

Fixed Embankment / wall

Bridge Slab for testingApproach Slab

Piles

Roller railingRoller

Adjustable Walls

Fixed Embankment / wall

Bridge Slab for testingApproach Slab


Masirin, MIM; Anati Hanum (2009). Construction challenge on peat soil: Sibu long term effect on housing construction. Presented to UTHM RMC office after site investigation works on December 2009 (Report)

Masirin, MIM; Rasimah Md Zain, Md Fizal Abu Bakar

and Daud Mohamad (2009). Site investigation on Road-Bridge Interface problems due to differential settlements at Jalan Nansang Teku and Jalan Sungai Maaw, Sibu Sarawak. Presented to UTHM RMC office after site investigation works on December 2009 (Report)

Nazrin, M. D. (2007). “Simulation of Pavement Deformations for Different Approach Slab Concept Constructed on Batu Pahat Soft Clay (BPSC).” UTHM : Postgraduate Project Report.

PLAXIS, Haag, D. D. (2002). “Reference Manual Plaxis Version 8.” Delf University of Technology & Plaxis, Netherland: A. A Balkelma Publisher.

Wong, H. K. W., Small, J. C., and Member, ASCE. (1994). “Effect of Orientation of Approach Slab on Pavement Deformation.” Journal of Transport Engineering, July 1994, Vol. 120, No. 4, pp 590- 602.

Zainorabidin, A. and Wijeyesekera, DC. 2007. Geotechnical Challenges With Malaysian Peat. In Proceedings of Advance in Computing and Technology Conference. no pp. University of East London, UK.

1

FIELD TESTS ON NATURAL CLAY DEPOSIT REINFORCED WITH GRANULAR FILL LAYERS Ahmet DEMIR Civil Engineering Department, Cukurova University, Balcali, Adana, Turkey [email protected] Murat ORNEK

Civil Engineering Department, Mustafa Kemal University, Iskenderun, Hatay, Turkey

[email protected] Mustafa LAMAN Civil Engineering Department, Korkut Ata University, Osmaniye, Turkey

[email protected]

Abdulazim YILDIZ Civil Engineering Department, Cukurova University, Balcali, Adana, Turkey [email protected]

ABSTRACT: In this study, field tests were carried out to determine the improvement of bearing capacity and settlement characteris-tics of circular shallow footings supported by a compacted granular fill over natural clay soil. For this purpose, a series of field tests were performed using circular footings which have diameters of 12 and 60cm. Granular fill layer thicknesses were changed as 0.33D, 0.67D and 1.00D according to the footing diameter. The parameters, Bearing Capacity Ratio (BCR) and Percentage Reduction in Set-tlement (PRS) were defined to evaluate improvement performance of granular fill-natural clay deposit system. It was found based on the test results that the BCR and PRS values of reinforced natural clay deposit increase with an increase in granular fill thickness. The results of the experimental studies indicate that the thickness of the granular fill has considerable effects on the bearing capacity and settlement characteristics of the circular footings, rested on natural clay deposits reinforced with granular fill layers.

Keywords: Field tests; Circular footing; Bearing capacity; Settlement

1. INTRODUCTION

Soil deposits exhibit low strength and high deformability can be found in most of the residential areas around the world. Shallow footings, when built on these problematic soils, have low load-bearing capacity and undergo large settlements. In many civil engineering applications, the need of soil reinforcement has been enormously raised in recent decades, due to economical and social development of the popula-tions. Depending on these developments, the necessity has been oc-curred in using soils with problematic geotechnical characteristics as footings of multiple engineering works. Problematic soils cause diffi-culties in geotechnical applications. Reinforcement of these proble-matic soils with granular fill layer is soil improvement technique that widely used. Problematic soil behavior can be improved by totally or partially replacing inadequate soils with granular fill compacted in layers. Several experimental and numerical studies have been described about the reinforcement of a weak soft soil (Ochiai et al. 1996, Adams and Collin 1997, Yin 1997, Otani et al. 1998, Alawaji 2001, Dash et al. 2003, Thome et al. 2005, Chen 2007, Deb et al. 2007). Ochiai et al. (1996) summarized the theory and practice of geosynthetic reinforce-ment of fills over extremely soft ground in Japan. Adams and Collin (1997) conducted 34 large model load tests to evaluate the potential benefits of geosynthetic-reinforced spread foundations. It was con-cluded that the soil–geosynthetic system formed a composite material that inhibited development of the soil-failure wedge beneath shallow spread foundations. Otani et al. (1998) studied the behaviour of strip

foundation constructed on reinforced clay. Settlement was found to be reduced with the increase in reinforcement size, stiffness and number of layers. The load carrying capacity of a foundation has been found to increase more on soil in which reinforcements are provided at clos-er spacing. Alawaji (2001) discussed the effects of reinforcing sand pad over collapsible soil and reported that successive reduction in col-lapse settlement up to 75% was obtained. Dash et al. (2003) per-formed model tests in the laboratory to study the response of reinforc-ing granular fill overlying soft clay beds and showed that substantial improvements in the load carrying capacity and reduction in surface heaving of the foundation bed were obtained. In this study, field tests were carried out to determine the improve-ment of bearing capacity and settlement characteristics of circular shallow footings supported by a compacted granular fill over natural clay soil. For this purpose, a series of field tests were performed using circular footings which have diameters of 12 and 60cm. Granular fill layer thicknesses were changed as 0.33D, 0.67D and 1.00D according to the footing diameter. The parameters, Bearing Capacity Ratio (BCR) and Percentage Reduction in Settlement (PRS) were defined to evaluate improvement performance of granular fill-natural clay depo-sit system. It was found based on the test results that the BCR and PRS values of reinforced natural clay deposit increase with an in-crease in granular fill thickness. The results of the experimental stu-dies indicate that the thickness of the granular fills has considerable effects on the bearing capacity and settlement characteristics of the circular footings, rested on natural clay deposits reinforced with gra-nular fill layers.

2

2. FIELD TESTS

Before conducting the tests, a comprehensive soil investigation was performed to determine the soil properties. The site investigation cov-ers an area of about 350m2 which the sizes of 30m and 11.6m for length and width, respectively and situated in the west part of Adana, Turkey. First layer of 0.80m depth observed as topsoil and the second layer between the depths of 0.80m and 2.60m observed as silty clay from the test pits. Then, boreholes were drilled with depths of 13m. Water table level was determined as 2.40m from borehole drillings. Standard Penetration Test (SPT) was carried out during drilling each borehole the values refer that the soil tested classified as medium stiff clay. Conventional laboratory tests were performed in Geotechnical Laboratory of Civil Engineering Department at Cukurova University, Adana, Turkey. Detailed information of the testing procedure can be found in Laman et al. (2009) and Ornek (2009).

2.1 Model Footings

The model footings with the diameters of 60cm and 12cm used in the tests were made of mild steel. The thickness for the model footings diameter of 60cm was 3cm and that of 2cm for 12cm footing diame-ter. The footings were loaded with a hydraulic jack against a reaction steel frame. Two different hydraulic jacks were used. Big one which has 60tons of capacity was used for 60cm diameter footing and small one which has 10tons of capacity was used for 12cm diameter footing. Calibrations were performed for 60tons and 10tons capacity hydraulic jacks.

2.2. Test Material

2.2.1. Clay Soil Laboratory tests were conducted on representative soil samples for gradation, specific gravity, maximum and minimum densities and strength parameters. These properties are summarised in Table 1. As seen that mean water content value of soil is measured at 23% and that of mean unit weight 2.07kN/m3. Table 1 shows that the soil is normally consolidated (P0<1).

Table 1. Soil profile in test area Depth (m)

Soil Type

ωmean (%)

γs (kN/m3)

IP (%)

cu (kPa)

P0 (kPa)

0.8-2.2 CH 20-21 2.57-2.60 30-39 30-45 63-81 2.2-3.5 CL 22-24 2.60-2.69 12-33 15-27 44-67 3.5-5.0 CL 22-24 2.57-2.66 17-19 15-27 40-70

ωmean= mean value of water content; γs = soil unit weight IP= plasticity index; cu=undrained cohesion; P0= preconsolidation pressure

2.2.2. Granular Fill The granular fill material used in the model test was obtained from the Kabasakal region situated northwest of Adana, Turkey. Some conven-tional tests were conducted on this material. Granular soil was pre-pared at optimum moisture content of 7% and maximum dry unit weight of 2.17gr/cm3 obtained from the standard proctor test. The val-ues of internal friction angle and the cohesion of clay soil were ob-tained as 42° and 1.5kg/cm2, respectively from direct shear tests. Spe-cific gravity of the granular soil was obtained 2.64gr/cm3. From the sieve analysis, granular soil was classified as well graded gravel-silty gravel, GW-GM according to the unified soil classification system.

3. EXPERIMENTAL PROCEDURE

The experimental set-up has been used extensively for the bearing ca-pacity of shallow footings on reinforced clay soils. The schematic view of the test is shown in Figure 1, where, D is the footing diameter and H is the granular fill thickness.

In the tests, steel loading beam (I240) with a length of 3.5m was as-sembled on drilled shafts. The loads were applied against this reaction steel frame. Then model footing, transducer, hydraulic jack and two LVDTs were placed. Hydraulic jack and LVDTs were connected to a data logger unit and data logger unit was connected to a computer. Load-settlement curve was drawn with loading simultaneously during tests. Loading was performed until the vertical deformation, i.e. set-tlement recorded until 10% of footing diameter. In the tests, granular fill layer with different thicknesses was located under the footing. A total of 8 tests were performed in the experimental studies and the de-tails of the tests are given in Table 2. The tests were carried out for a short term until the initial settlements were measured under undrained conditions. So long term settlement (consolidation) of clay was not measured in the testing program. Fig. 1. Schematic view of the test (unscaled)

Table 2. Details of the tests Test No D (cm) H Description

1 60 - unreinforced 2 12 - 3 60 0.33D

granular fill effect

4 60 0.67D 5 60 1.00D 6 12 0.33D 7 12 0.67D 8 12 1.00D

D= footing diameter; H=thickness of granular fill layer

3.1. Interpretation of Test Results

In field tests, the relation of bearing capacity to settlement (q-s or q-s/D) for the following various arrangements of granular fill rein-forcement is obtained and discussed. In the tests, the plot of q against s/D takes almost a linear shape and a peak value (ultimate bearing ca-pacity) is not obtained clearly. So, the ultimate bearing capacity was defined at a specific settlement ratio, s/D=3%. Similarly, settlement reductions due to granular fill are evaluated at a specific loading pres-sure of 300kPa. Although this technique is arbitrary, it: (1) is conve-nient and easy to remember; (2) may actually be close to the average soil strain at failure; and (3) forces a fixed value at qult (Cerato and Lu-tenegger, 2006). The contributions from granular fill on bearing capacity and settle-ment characteristics are presented by the terms of Bearing Capacity Ratio (BCR) and Percentage Reduction in Settlement (PRS). The term “bearing capacity ratio” (BCR) is commonly used to express and compare the test data of the reinforced and unreinforced soils. The following well-established definition (Binquet and Lee, 1975a) is used for BCR: BCR= qR / q0 (1)

Reaction pile Clay soil

Loading beam

Foundation Hydraulicjack

Granular fill layer H D

3

where qR and q0 are the bearing capacity for the reinforced and unrein-forced soils, respectively. The parameters investigated, including the settlement of rigid plate, s, are normalized by the diameter of the rigid plate, D (Laman and Yildiz 2003). For comparison of test results, Settlement Ratio (SR) and Percentage Reduction in Settlement (PRS) were used as previously described by Mandal and Sah (1992) and others; SR = SR / S0 PRS = (S0 – SR) / S0 = 1 – (SR / S0) (2) where S0 and SR are the settlements for the unreinforced and rein-forced soils, respectively. The general type of bearing capacity-settlement curves obtained in the tests and evaluation of the terms BCR and SR are shown in Figure 2. The bearing capacity obtained at s/D=5% is used to calculate the cor-responding BCR’s and PRS’s obtained at loading pressure of 400kPa are presented. The settlement ratio (s/D) is defined as the ratio of rigid plate settlement (s) to rigid plate diameter (D). qu (ultimate bearing capacity), BCR (bearing capacity ratio), s (settlement) and PRS (per-centage reduction in settlement) values were obtained from load-settlement curves of the tests.

Fig. 2. Definition of BCR and SR

3.2 Test Series I: Tests on Natural Clay

These tests were conducted using two different footing diameters of 12cm and 60cm. The aims of carrying out these tests are to investigate the bearing capacity of clay soils with different footing sizes and to create a reference for the oncoming tests with granular fills.

3.3 Test Series II: Tests with Granular Fill

The effect of granular fill layer thickness on bearing capacity and set-tlement behavior was investigated in test series. The relations of the loading pressure to rigid plate settlement for various values of H/D obtained from field tests are presented together with the result of Test Series I. Typical plots for bearing capacity-settlement behaviour ob-tained from the experimental test for diameters of 12cm and 60cm footings are shown in Figure 3 and Figure 4, respectively. In the tests, granular fill thickness was changed depending on the rigid plate di-ameter as 0.33, 0.67 and 1.00D. The width of the granular fill layer was kept about 3.1D for all the reinforced soil conditions.

Fig. 3. The effect of H/D (D=12cm)

Fig. 4. The effect of H/D (D=60cm) As seen from Figure 3 and Figure 4 that the bearing capacity keeps increasing with an increase in granular fill thickness. At settlement of s/D=5%, Figure 3 shows that the bearing capacity increases from 400kPa (natural clay deposit) to 680kPa (H=1.00D). For the diameter of 60cm (s/D=5%) bearing capacity increases 390kPa to 550kPa (Fig-ure 4). It is also noted that the ultimate bearing capacity is a function of H/D (Madhav and Vitkar 1978; Hamed et al. 1986). Figure 5 and Figure 6 show the relation of BCR to H/D and PRS to H/D ratios obtained from the tests, respectively. BCR values were cal-culated using the bearing capacities correspond to s/D=5%. H/D is a ratio defined as the ratio of granular fill thickness (H) to rigid plate di-ameter (D). It is shown from Figure 5 that BCR increases with an in-crease in the granular fill thickness. BCR values obtained are 1.16, 1.45 and 1.67 (for D=12cm) and 1.16, 1.30 and 1.35 (for D=60cm) for H=0.33D; H=0.67D and H=1.00D, respectively. It is seen that BCR increases with an increase in the granular fill thickness. The increment in granular fill layer increases the stability of rigid plate and provides a confinement effect against lateral shear stress. Reduction of shear stress transmitted from the fill layer to soft clay increases the bearing capacity of the soft clay. The construction of wide granular fill layer also leads to “surcharge effect” and can prevent soil from moving up-

Applied Pressure

Foot

ing

Settl

emen

t

Reinforced Soil

Unreinforced Soil

q0 qR

sR

s0

BCR = qR/q0 SR = sR/s0

0

2

4

6

8

10

12

14

0 200 400 600 800 1000

q (kPa)

s/D

(%)

0.0

2.4

4.8

7.2

9.6

12.0

14.4

16.8

s (m

m)

Clay

H=0.33D

H=0.67D

H=1.00D

0

1

2

3

4

5

6

7

8

9

10

0 200 400 600 800

q (kPa)

s/D

(%)

0

6

12

18

24

30

36

42

48

54

60

s (m

m)

Clay

H=0.33D

H=0.67D

H=1.00D

4

ward at locations far away from the rigid plate, and thus improve the bearing capacity of natural clay deposit. PRS values were obtained using the settlements correspond to 400kPa. PRS values obtained are 30%, 65% and 70% (for D=12cm) and 25%, 50% and 55% (for D=60cm) for H=0.33D; H=0.67D and H=1.00D, respectively. It is seen that settlement decreases with an in-crease in granular fill thickness. Increase in the thickness of the granu-lar fill layer results an increase in stiffness of the fill material, which reduces vertical strains within the fill layer. The improvement of flex-ural stiffness of the fill layer, which distributes the footing loads, re-duces the maximum vertical stress on the soft clay deposits. The com-pacted granular fill layer placed below the circular rigid plate creates a rigid body for improving the performance of natural clay-granular fill layer soil system. Such a compacted granular fill layer works like a plate and also results in redistribution of the applied load to a wider area and thus minimizing stress concentration and achieving improved distribution of induced stress. The redistribution of applied load to a wider area below the granular fill layer leads to an increase in bearing capacity and a decrease in settlement of the footings compared to the natural soil.

Fig. 5. BCR relations in the tests Fig. 6. PRS relations in the tests

4. CONCLUSIONS

In this study, field tests were carried out to determine the improve-ment of bearing capacity and settlement behaviour of circular shallow footings supported by a compacted granular fill layer over natural clay soil. Based on the results from this investigation, the following main conclusions can be drawn: • The results of the study show that the soft soils having low load

bearing capacity and exhibiting large settlement can be improved by replacing with an inadequate soft soil with granular base ma-terial being compacted in layers. Natural clay deposit replaced partially by a granular fill increases the bearing capacity and re-duces the settlement.

• Ultimate bearing capacity is a function of H/D. • Bearing capacity increase is about 45% and 30% at H=0.67D for

12cm and 60cm footing diameter, when s/D=5%. • Reduction in settlement of the rigid footing is obtained about 65%

and 50% at H=0.67D for 12cm and 60cm footing diameter, when q=400kPa.

• The compacted granular fill layer placed below the circular rigid plate creates a rigid body for improving the performance of natu-ral clay-granular fill layer soil system. Such a compacted granular fill layer works like a plate and also results in redistribution of the applied load to a wider area and thus minimizing stress concentra-tion and achieving improved distribution of induced stress.

• This investigation is considered to have provided a useful basis for further research leading to an increased understanding of the ap-plication of soil reinforcement to bearing capacity and settlement problems.

ACKNOWLEDGEMENTS

The work presented in this paper was carried out with funding from TUBITAK (The Scientific and Technological Research Council of Turkey) grant number 106M496. REFERENCES Adams, M.T. and Collin, J.G. (1997). Large model spread

footing load tests on geosynthetic reinforced soil founda-tion. ASCE Journal of Geotechnical and Geoenvironmental Engineering, 123 (1), 66–72.

Alawaji, H.A. (2001). Settlement and bearing capacity of geo-grid-reinforced sand over collapsible soil. Geotextiles and Geomembranes, 19, 75-88.

Binquet, J. and Lee, K.L. (1975a). Bearing capacity tests on reinforced earth slabs. Journal of Geotechnical Engineer-ing Division, ASCE, 101 (GT12), 1241-1255.

Bowles, J.E. (1988). Foundation analysis and design. McGraw-Hill International Editions, 4th Edition.

Cerato A.B. and Lutenegger A.J. (2006). Bearing capacity of square and circular footings on a finite layer of granular soil underlain by a rigid base, Technical Note, Journal of Geotechnical and Geoenvironmental Engineering, 132 (11), 1496-1501.

Chen, Q. (2007). An experimental study on characteristics and behavior of reinforced soil foundation. PhD thesis, Louisi-ana State University, Baton Rouge, USA.

Dash, S.K., Sireesh, S. and Sitharam, T.G. (2003). Model stu-dies on circular footing supported on geocell reinforced sand underlain by soft clay. Geotextiles and Geomem-branes, 21, 197-219.

Deb, K., Sivakugan, N., Chandra, S. and Basudhar, P.K. (2007). Numerical analysis of multi layer geosynthetic-reinforced granular bed over soft fill. Geotechnical and Geological Engineering, 25, 639-646.

Hamed J.T., Das B.M. and Echelberger W.F. (1986). Bearing capacity of a strip foundation on granular trench in soft

0

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PRS

D=12cm

D=60cm

0.0

0.4

0.8

1.2

1.6

2.0

0.00 0.33 0.67 1.00 1.33

H/D

BC

R

D=12cm

D=60cm

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clay. Civil Engineering for Practising and Design Engi-neers, Paragon Press, 5 (5), 359.

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Madhav, M.R. and Vitkar P.P. (1978). Strip footing on weak clay stabilized with a granular trench or pile” Canadian Geotechnical Journal, 15 (4), 605.

Mandal, J.N. and Sah, H.S. (1992). Bearing capacity tests on geogrid-reinforced clay. Geotextiles and Geomembranes, 11 (3), 327-333.

Ochiai, H., Watari, Y. and Tsukamoto, Y. (1996). Soil rein-forcement practice for fills over soft ground in Japan. Geo-synthetics International, 3 (1), 31-48.

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Yin, J.H. (1997). Modeling geosynthetic-reinforced granular fills over soft soil. Geosynthetics International, 4(2), 165-185.

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1. INTRODUCTION

Peats are formed naturally through the decomposition of plant and animal matter under anaerobic conditions that take place over long periods of time. Peat can be found worldwide and occurs in many different climatic zones from arctic to tropical in both northern and southern hemispheres. The physical and chemical properties of peat and the vegetation which supports vary with geographical location, climate, topography, hydrology and hydrochemistry. Peat in northern temperate regions of the world is formed normally from the remains of grasses, sedges and bog mosses. However, tropical peats found in Malaysia, it consists mainly of sediments from woody remains such as roots, branches and tree trunks. While the estimated and reported extent of Malaysian peat was approximately 2.6 million hectares respectively, there is an estimated 1.6 million hectares (minimum) of peat land

available in British. Hobbs (1986) gave excellent summaries of the development and properties of British peat. There are two types that are fen and bog peat. The morphological differences between fen and bog are attributable to the types of plant remains which occur in the peat and their mode of origin. Bog receives water solely from rain and/or snow falling on its surface meanwhile fen receives water and nutrients from the soil, rock and groundwater as well as rain and/or snow. He found that the differences involve degree of humification, structure, fabric and proportion of mineral material contained in the peat, and this in turn affects their engineering behaviour. While in Malaysia, the colour of peat soils in Malaysia is generally dark reddish brown to black. It consists of loose partly decomposed leaves, branches, twigs and tree trunks with a low mineral content. The ground water table in these areas is always high and occurs at or near the surface.

GEOTECHNICAL CHARACTERISTICS OF PEAT SOILS THROUGH THE FABRIC AND MICRO-STRUCTURE PERSPECTIVES Adnan Zainorabidin Researcher University of East London and Research Fellow Research Centre for Soft Soil (RECESS), Universiti Tun Hussein Onn Malaysia [email protected] Chitral Wijeyesekera Professor in Civil Engineering, University of East London, London , United Kingdom [email protected] Ismail Bakar Professor, Head of Centre, Research Centre for Soft Soil (RECESS), Universiti Tun Hussein Onn Malaysia [email protected] Mohd Idrus Mohd Masirin Associate Professor, Research Fellow, Research Centre for Soft Soil (RECESS), Universiti Tun Hussein Onn Malaysia [email protected]

ABSTRACT : Peat deposits that occur in many countries have been exploited as an agricultural and / or fossil fuel product. For the purpose of such peat extraction, the established geological peat classifications did suffice. However, the rapid advancement of urban infrastructure, diminishing land resources for such development and the abundance of peat soil deposits in the marginal areas demands an urgent need for a thorough geotechnical characterisation of peat soils. The heterogeneity of the peat soil deposits by virtue of its genesis and the increasing recognition of such as problematic soils exacerbate the need for focussed geotechnical research on peat soils. Furthermore, despite the strict geological classification of peat as a soft “soil”, it contradicts some of the main assumptions in classical soil mechanics theory, viz; soil particles are incompressible, homogeneity and isotropy. Therefore these accentuate the necessity for a more appropriate engineering geology classification for peat (and organic) soils. This paper presents case studies that support this emerging viewpoint. It also presents some of the results for geotechnical characteristics of a variety of peat soils collected from United Kingdom and Malaysia. Results of fabric studies carried out using innovative methods at macro and micro levels are presented. Consequently some thought provoking concepts of fabric and micro structural studies of the tested peat soils are discussed with a view to initiating a peat classification that will prove useful in ground investigation and subsequent geotechnical design. Authors found that for classification of peat, need to include image analysis for fabric and not based on the laboratory tests only. However the preparation of sample for image analysis need to be done carefully as explained in this paper in order to minimize the disturbance to the sample particle. Keywords; Peat, fabric, classification, geotechnical characteristics, imaging technique

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The consequent rapid development within the country, coupled with a strong economic performance has resulted in vast infrastructure development. These developments are hindered by a dearth of suitable land for development and as a consequence, an area with adverse ground conditions such as peat soil is being considered for infrastructure construction such as roads, housing, drainage and others. One of the issues still facing peat engineering is the lack of satisfactory and internationally accepted definitions and classification. Most common definition of peat is based on ash (or organic) content. Peat is geotechnically is described as soils with more than 75% organic content. It is mainly governed by the quantity and the quality of organics it contain, as well as its physical properties. However the definition and descriptions of peat between soil scientists and engineers are diverse. This forms a fundamental difference between the views of a soil scientist from that of a geotechnical engineer. The concepts of soil description and the approach to soil micro-morphology have changed over the years with the new techniques developed to describe them. The term, ‘Soil Fabric’ is usually defined as the geometrical aspects of a particle and the associated inter particle forces between adjacent particles (Raymond et al., 1975). The fabric of peat is totally different to that of inorganic soil (clay, sand and gravel) by virtue of the abundance of fibrous material. Macroscopically, peats can be divided into three basic groups such as fibrous, hemic, or sapric. Fibrous peats are the least decomposed and comprise of intact fibre. Hemic peats are somewhat decomposed, while sapric are the most decomposed.

2. GEOTECHNICAL CHARACTERISTICS OF THE TESTED PEAT

The physical characteristics of peats soil are often very variable in its properties, both from one deposit to another and from point to point although it is in the same deposit (Zainorabidin and Wijeyesekera, 2008). This makes it a non uniform and inhomogeneous soil. Table 1 compares the physical properties of the four different types of peat. Samples were collected from three different location were Holme Fen Post, Cambridgeshire; Solway Post, Carlisle and Western Johore, Malaysia. These samples can be categorized into two groups; fibrous and hemic. These classifications are based on the percentage of fibre content in the sample. Holme Fen 1 (HFP1) and Holme Fen 2 (HFP2) peat are categorized as fibrous peat as they have fibre content more than 70%. Meanwhile for Malaysian (MHP) and Solway (SHP) peat are categorized as hemic peat with fibre content between 43-63%. Moisture content for HF2 is the highest with 775% compared to the other samples. This is due to the depth of sampling, which was at a depth of more than 1.5m. In order

to investigate the more details the fibre of peat, authors included analysis based of the ratio of the length/width of fibre. Authors determined that for fibrous peat (HFP1 and HFP2), the aspect ratio for the fibre ratio was in the ranges of 2 to 11, meanwhile for hemic peat (MHP and SHP) the range between 1 to 4.5respectively. Results show that the liquid limit for fibrous peat is more than 180% compared to hemic which is in the range 140%-150%. Due to the presence of fibres in the sample, authors found from the experiments that it was impossible to determine the plastic limit for peat. Figure 1 shows the comparison of the moisture content versus fibre content with the previous research. It shows that sample HFP2 had the higher moisture content with the fibre content >75%. Table 1 Comparison of basic physical properties for the samples tested

Geotech. Charac.

Samples Designated/ Parameters

Holme Fen 1

(HFP1)

Holme Fen 2

(HFP2)

Malaysia Peat

(MHP)

Solway Peat

(SHP)

Cla

ssifi

catio

n

Type of Samples

Fibrous Fibrous Hemic Hemic

Degree of Humification

H3 H3 H6 H5

Bas

ic p

rope

rtie

s

Moisture Content (%) 670 775 472 554

Organic Content (%) 88 92 92 96

Liquid Limit (%) 180 240 140 150

Specific Gravity 1.46 1.30 1.14 1.40

Fibr

e an

alys

is Fibre

Content (%) 73 75 43 63

Aspect ratio (L/W) 2-11 1.5-6 1-4 1-4.5

Peat soils have a high water content that can be >100%. This is because the fibre of the peat has cell tissues that are microscopically thin and can hold the water inside it. The water content in the peat was held in three phases; (i) free water in large cavities of the peat (ii) capillary water in the narrower cavities and (iii) water bound physically, chemically, colloidally and osmotically. To be more specific, authors categorized these as known as intracellular free water (ICW) held within the internal cells, interparticles water (IPW) held by capillary forces in any part of peat and adsorbed water (AW) retained under suction. Water in peat consists of intracellular and interparticle water. To investigate the pattern of moisture loss in peat, 14 different drying temperatures were chosen from 150C up to 1050C. Undisturbed samples were used in this study. Authors pointed out and proves that the three different stages in the loss of moisture for peat.

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Fig.1. Moisture content versus fibre content

Figure 2 shows the comparison of this moisture retention for peat, sand and clay samples tested in a similar way. All peat samples show consistent curves for moisture retention. It shows that the release of moisture in the peat samples occur slowly at different temperature until it is constant for temperatures exceeding 600 C. In the case of clay and sand samples, the patterns of water retention curves are uniform but they are different from that of peat. Sand samples release the water totally at a lower temperature of 300C whilst in clay; the moisture is released at 400C. Authors observed that at lower drying temperatures between 200C to 350C the IPW was released rapidly. Meanwhile for drying temperatures between 350C to 400C the AW and ICW are released. To understand further more, the effects of the fibre in hold the water need to be investigated using image analysis.

Fig. 2. Comparison of moisture content loss for different samples

3. FABRIC ANALYSIS

Image analysis is one of the methods adopted by previous researchers to analyse the morphology of the fibres (Aydemir et al., 2004). Anand et al. (2004) explained the use of digital imaging methods as providing numerous opportunities for direct or indirect fabric analysis. This

method that can be used to measure and quantify more accurately the size and shape distribution of all the particles. This enables researchers to obtain a better understanding of the soil structure and behaviour. Comprehensive literature reviews on fabric analysis on peat have been made by Landva and Pheeney (1980), Kruse (1998) and O’Loughlin and Lehane (2003). However, these studies concentrated more on the use of Optical Microscopy and Scanning Electron Microscopy (SEM) The sample preparation for these two methods is very costly and laborious. The representability of such a high magnification photomicrograph is still questionable. Authors have obtained the images with a digital camera and the image was subsequently analyzed using two different software, viz; PICASA 3 and analySIS®. One of the challenges of preparing the samples for image analysis is to minimise the sample disturbance. Authors avoided cutting the surface of the samples using scissors or a sharp knife as it will disturb the particle arrangement in the sample. A new technique was adopted by authors to prepare the sample. Undisturbed samples were obtained directly from the U100 samples by extrusion and trimming. A minimum 300mm height of sample is necessary to minimise sample disturbance. To prepare an undisturbed surface, both ends of the sample were glued using a very strong adhesive and attached to a glass plate. The sample was then left dry to make sure the sample and glass plates would bond together. Air dry method was chosen by authors to minimise the otherwise rapid shrinkage of the samples. After the glass plates were bonded together, the sample was split into two parts by carefully pulling apart the glass plates. This technique was adopted to ensure that the surface of the sample was not touched or disturbed by hand. This step was very crucial and important. The samples were imaged using a digital camera Canon S5IS lens with a close up 500D attached to a frame grabber. The height of the frame grabber to hold the camera was adjustable. To ensure an enhanced quality of the image, the process of photographing was done in a dark room. To analyse the images, authors used PICASA 3 and analySIS® software. This suitable software showed the conjunction of interfaces that ensured the appropriate observations for different fields. PICASA 3 software has an advantage of enhancing and differentiating the image to a better perspective. Figure 3 shows the fibrous sample (HF1) image enhanced after using PICASA software. It shows the fibre arrangement more clearly. It helped authors in the initial differentiation of the fibrous and hemic peats. Typical image analysed using analySIS® software is illustrated in Figure 4. Image clearly shows the presence and the

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orientation of the fibres. This can be used to investigate detailed particle arrangements. Further it can also be used to demonstrate the presence of void and cracks in the sample. The authors also can set the Region of Interest (ROI) as defined as the percentage area of fibre to the total area selected. It helps authors to assess or describe the fabric of the peat in a more statistically reliable way in order to better ascertain its fabric.

Fig. 3. Image Analysis using PICASA 3 software (Fibrous Peat)

Fig. 4. Defining the Region of Interest (ROI) using analySIS®

(Fibrous Peat)

The main advantage of this technique is that authors could analyse the whole sample surface without any disturbance to the fibres in the sample. Therefore, the result is more representative and accurate. The composition of peat consists of high fibre content. The texture is not homogenous and that will affect the shrinkage behaviour of the soil. This is an important property of the image processing technique for an engineer to understand clearly the shrinkage behaviour of the sample. It also shows the

size of the fibres. From this point, engineer could observe more clearly and classify the type of the sample. Also he may be able to do the comparison with the index properties of the soil. The fabrics have also been made with a thin section study. The image (see Figure 5) was taken using a petrographic microscope. This figure shows the detailed orientation of the fibre at x100 magnification. This image can be used to determine types of vegetation of the peat. To understand more about the cell structure, an image from the Scanning Electron Microscopy (SEM) (see Figures 6 and 7) were used to verify the composition of fibrous structure in each type of peat. The main purpose of this step was to classify the fibre structure based on whether it is shrub rootlets, plant root hairs, rhizods or rootlike.

Fig. 5. Image from optical microscopy for sample (HFP1)

At magnification of X500, the size of the individual particles can be measured. As we can see for sample HFP1 (Figure 6), it shows that there are large pore spaces between the compositions. It also appears that the particles are elongated and more comparable. Contrarily for SHP (Figure 7) where can see the consistency of the particle sizes. Sample SHP (hemic peat) is appeared denser compare to HFP1 (fibrous peat). This due to the percentage of the fibre are between 33% to 66% compare to HFP1 (>66%), respectively. Comparing the techniques, the image analyses of a digital image was more representative as the analysis was carried out on the whole sample. Therefore, it is necessary for the engineers to appreciate the various techniques available in image processing to investigate the particle arrangement

ROI

5

Fig.6. Fibrous peat sample (HF1sample)

Fig. 7. Hemic peat sample (SP sample)

4. CONCLUSIONS & RECOMMENDATIONS

In this study, authors classify the fibrous and hemic samples not only based on the laboratory tests and also by making fabric observations using image analysis. For fibrous peat, the sizes of the particle in term of aspect ratio shows that the ratio is higher (>5) compare to hemic peat (<5). In order to get clearly better understanding to the fibre sizes, image analysis need to be done whereas it also can contribute to the classification of peat. As shown in Figure 3, we can observe and analyse the fibre of peat using software. This will help geotechnical engineer to do early observation to differentiate the peat classes. This technique can be also extended to investigate the effect of sample disturbance in tube sampling due to the expansion of soil when extruding the sample out. The representability is an important factor to describe the fibre of the peat samples. Research leading to a better understanding of the performance of peat is urgently required for better geotechnical design.

5. ACKNOWLEDGEMENTS

Firstly I would like to thank Prof. Dr. Wijeyesekera for his full support when author did this research at University of East London and also preparing this paper. I also would like to thank Prof. Dr. Ismail Bakar and Associate Prof. Dr. Mohd Idrus Mohd Masirin for their idea and continuous helps to assisting the author.

6. REFERENCES

Anand J. P., Balakrishna K. and Laureano R.H (2004). Volumetric shrinkage strain measurements in expansive soils using digital imaging technology, Geotechnical Testing Journal, 27(6), pp. 547-556. Aydemir S., Keskin, S. and Dress, L.R. (2004). Quantification of soil features using digital image processing (DIP) Techniques, Geoderma Elsevier 119, pp. 1-8.

Hobbs, N.B. (1986). Mire morphology and the properties and behaviour of some British and foreign peats, Quart. J. of Eng. Geol., (19), 7-80.

Kruse, H.M.G. (1998). Quantitative micro-morphological analysis of one dimensional peat. 8th International IAEG Congress, Balkema, Rotterdam, pp. 449-453.

Landva, O.A and Pheeney, P.E (1980) Peat Fabric and Structure. Canada Geotechnical Journal , 17, pp. 416-435.

Manual of software package analySIS®. Soft Imaging System.www.soft-imaging.de

Manual of Picasa Software3 (picasa.google.com)

O’Loughlin, C.D. and Lehane, B.M. (2003). A study of the link between composition and compressibility of peat and organic soils. Proceedings of 2nd International Conference on Advances in Soft Soil Engineering and Technology, Putra Jaya, Malaysia ed. Huat et al., pp. 135-152.

Raymond J. K., Tuncer B. E. and Kutay O.I. (1975). Preparation and Identification of Clays Samples with Controlled Fabric. Engineering Geology, Elsevier 9, pp.13-38.

Zainorabidin, A. and Wijeyesekera, D.C. (2008). Geotechnical Characteristics of Peat. In Proceedings of 4th Advances Computing and Technology Conference, 2008, ed. Stephen et al., London, United Kingdom, pp. 71-78.

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PERFORMANCE OF VARIOUS PIEZOMETERS IN SOFT MARINE CLAY IN KANDANG, MELAKA Edayu binti Saleh @ Aman Road Engineering & Geotechnical Division, Public Works Department, Kuala Lumpur, Malaysia [email protected] Ramle bin Othman Road Engineering & Geotechnical Division, Public Works Department, Kuala Lumpur, Malaysia [email protected] Mohd Raihan Taha & Khairul Anuar Mohd Nayan Department of Civil and Structural Engineering, Universiti Kebangsaan Malaysia, Bangi, Malaysia [email protected] / [email protected] ABSTRACT: The main problem in construction of embankments on soft clay other than stability is settlement. Usually the more important parameters that govern the consolidation process is pore water pressure. The objective of this study is to evaluate the performance of various types of piezometer under loading which changes with time. A 2.7 m high trial embankment constructed on top of soft clay was installed with 24 piezometers from four different types; standpipe, pneumatic, vibrating wire and fiber optic. The instruments were installed at 2.0 and 5.0 m depths. A site in Kandang, Melaka was chosen as a research area under a JKR project entitled “Menaik Taraf Jalan Simpang Ampat - Alor Gajah – Muar - Melaka”. The performances of the piezometers were observed for one year to monitor excess pore water pressure patterns. The study was also conducted to observe the performance of the piezometers under different type of installation methods: conventional and grout-in method. In the conventional method, sand was used as intake zone whereby in the grout-in method, water, cement and bentonite mix was used to grout the whole borehole. Eight (8) different mixes were prepared in the laboratory and only 2 mixes which have similar strength and permeability characteristics with the surrounding ground were chosen for use at the site. The results of the study indicated that the standpipe piezometer gave higher excess pore water pressure readings compared to the other types of piezometer. The piezometer readings for the two methods of installation yield the same results. This shows that with suitable mixes, installation of piezometer using grout-in method can be practically used in Malaysia. Keywords: piezometer, soft clay; pore water pressure 1. INTRODUCTION Apart from embankment stability, settlement is another major problem that has always been associated with road construction over soft soil that requires designers’ in-depth consideration. Pore water pressure measurement is one of the important parameters that has to be acquired in order to assess the rate of embankment settlement. Piezometers of various types were installed on site to measure pore water pressure. Nevertheless as a means to measure pore water pressure each and every type of piezometer owns advantages and disadvantages (Dunnicliff, 1993). In conventional installation, piezometers tip is placed in sand at intake zone and topped by bentonite tablet. However due to simplicity, rapid installation, accuracy and economics, grout-in method is most preferred (Mc Kenna, 1995). Figure 1 demonstrates the difference between conventional and grout-in method of installation. 2. STUDY OBJECTIVES a. To compare the performance of various types of piezometer subjected to loading over finite period of time.

b. To compare the performance of various types of conventional piezometer and grout–in piezometer subjected to loading over finite period of time.

Fig. 1: Conventional and Grout-In Piezometer

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3. STUDY LOCATION The study was conducted in Kandang, Melaka of west Peninsular Malaysia which is shown in Figure 2.

Fig. 2. Study Location 3.1 Soil Investigation Amongst the test that had been conducted on site were two numbers of boreholes and one penetration vane. Borehole results revealed that the soil comprises of 20 meters soft layer of varied undrained strength from 15.5 kPa to 38 kPa that increases with soil depth. Summary of soil properties of the study location is shown in Table 1.

Table 1: Summary of Soil Properties of the Study Location

3.2 Trial Embankment Trial embankment of 2.7 meters high was quickly constructed one layer per day. Nevertheless a gap of 10 days between the first and second layer occurred largely due to inevitable site constraint. Filling works was controlled as such every fill layer did not exceed 300 mm thick to ensure that the filling process is in compliance with JKR Standard Specification for Road Works: 1988. In planning stage, trial embankment was planned to be constructed symmetrically. However due to inevitable site constraint during construction, all piezometers

location were concentrated in only one side as shown in Figure 3. The outermost piezometers were installed at minimum distance at 2 meters from embankment edge. 3.3 Instrument Installation Works Four types of piezometers in 24 numbers which comprises of standpipe, pneumatic, vibrating wire and fibre optic were installed on site to a depth of 2 meters and 5 meters respectively. Their performances were monitored for about one year to investigate pore water pressure dissipation trend. However, fibre optic piezometer was inevitably excluded from this study due to its malfunction subsequent to embankment completion. Piezometers were installed at six locations namely location A,B and C which comprise of 2 meter depth piezometers and on the other hand location D,E and F comprise of 5 meter depth piezometers. By installation method, at location A and D they were conventional and in contrast to location B and E they were grout-in of M1 mix (13% cement: 5% bentonite: 82% water) and at location C and F, they were also grout-in of M2 mix(10.5% cement: 7.5% bentonite:82% water). All the standpipe piezometers at all locations were installed by conventional method. Observation well was also constructed away from the embankment to measure ground water level for the purpose of this study and monitored continuously for one year. Piezometers layout plan is shown in Figure 3. Magnetic extensometers were installed at 2meters and 5 meters depth at location C, D and F to measure the settlement rate at piezometers tip level for the purpose of adjustment of piezometer reading.

Fig. 3. Piezometer Layout Plan on Site 4. GROUT MIX DESIGN Eight numbers of grout mix of different cement:bentonite:water ratio were designed and tested in laboratory to investigate their rheology, strength and permeability in order to obtain two grout mixes that satisfying predetermined criteria where by the two mixes will be subsequently applied in grout-in piezometer installation on site.

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The grout mix predetermined criteria are as follow:

1. Grout permeability coefficient is less than or equal to actual soil permeability coefficient.

2. Grout strength is almost equal to soil strength.

From the test, M1 and M2 mix were chosen and applied on site. Summary of the gout mix test result is shown in Table 2.

Table 2. Summary of Test Result of Grout Mix

5. PIEZOMETERS PERFORMANCE UNDER LOADING Within the first four month after the embankment construction completion, generally, pore water pressure shows a fast dissipation trend. However beyond that period the dissipation trend is fluctuating. Typical pore pressure measurement at Location A is shown in Figure 3. Piezometer performance is investigated in two phases, namely undrained phase whereby filling works is in progress and drained phase whereby filling works completed.

Fig. 3. Excess Pore Water Pressure at Location A

(Conventional Piezometer at 2m Depth)

5.1 Performance of various types of piezometers in undrained soil condition Soil condition in which the filling works is in progress is known as undrained condition owing to the fact that no excess pore water pressure dissipation takes place (Lambe & Whiteman 1973, Parry &Worth 1981, Tavenas & Leroueil 1980). During loading stages (filling works), excess pore pressure behavior at the depth of 2 meters and 5 meters for all piezometers irrespective of installation method shows an increasing trend corresponding to increasing filling (embankmet) height as shown in Figure

3. Excess pore water increases as a result of load increase shows a linear relationship between them. Figure 4 shows increment of excess pore water pressure as a result of embankment load increment at Location A.

Fig. 4. Excess Pore Water Pressure Increment against Vertical Stress Increment at Location A

∆µ/∆σ ratio as shown in Table 3 is derived from gradient of straight line plot in Figure 4. At the depth of 2 meters, conventional piezometer (by installation method) and grout-in piezometer of M1 and M2 mix show ∆µ/∆σ ratio in the range of 0.13 to 0.21. On the other hand, at the depth of 5 meters the piezometers show ∆µ/∆σ ratio in the range of 0.17 to 0.28. In a trial embankment of 1:2.5 slope profile, Tavenas et al (1974) reported that the soft founding clay behaves elastically until the embankment attained 2.4 m high and at piezometer tip of 2.6 meters in soft clay, the corresponding ∆µ/∆σ ratio is 0.32. According to Tavenas et al (1974), founding soil will be behaving elastically until the embankment attained its critical height which is equivalent to 50% of total height. However, in this trial, critical height could not be determined due to the fact that 2.7 meters high is still well below critical height. Table 3. Δu/Δσ Ratio and Maximum Excess Pore Water

Pressure

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Maximum excess pore water pressure obtained from piezometer at 2 meters depth of conventional, grout -in M1 or grout-in M2 is in the range of 1.3m H2O to 1.99 m H2O as compared to at depth of 5 meters whereby the maximum excess pore water pressure is in the range of 1.48m H2O to 2.59 m H2O. Based on data obtained from the study, the maximum excess pore water pressure obtained from various types of piezometers reveals wide range of variation whereby the highest reading is shown by stand pipe piezometer. 5.2 Performance of various types of piezometers during pore pressure dissipation As filling works progress, excessive pore water pressure increases and as the embankment is completed the pore pressure keep on increasing for a few days before it starts to dissipate. The same pore pressure behavior was observed in trial embankment conducted in Kuala Perlis (Hussein 1995). According to Hoeg et al. (1969), rapid increase in excessive pore water pressure can be attributed to the time consumed before dissipation started. Similar possibilities could had happened in this investigation as the filling works was carried out at fast rate of 0.3m per day which had resulted in rapid increase of excessive pore water pressure. Dissipation percentage of excessive pore water pressure is shown in Table 4. Generally, within the first four month after the embankment construction completion, pore water pressure shows a fast dissipation trend. Beyond that period the dissipation trend is fluctuating. Stand pipe piezometer shows relatively slow rate of dissipation of excessive pore water pressure as compared to other types of piezometer. Disregard stand pipe piezometer, other piezometers show dissipation percentage of excess pore water pressure for the first four months is in the range of 42% to 79%.Similar result was reported by Adachi and Todo (1979) for west coast of Malaysia Peninsula with some variation in figures which could be attributed to different location and different rate of filling.

Table 4: Dissipation Percentage of Excess Pore Water Pressure

These dissipation trends probably could be attributed to reduction in soil permeability properties and rearrangement of soil grain structure resulting from filling

works. Table 5 shows dissipation percentage of excess pore water pressure on study site and result from previous study in west coast of Malaysia Peninsula for comparison purposes. Table 5. Comparison of Dissipation of Excess Pore Water

Pressure in Present Study and From Previous Study in west coast of Malaysia Peninsular

Generally, the trend of pore pressure dissipation revealed by the grout-in M1 and grout-in M2 piezometers almost similar as compared to conventional (by installation method) piezometers both at 2 meters depth and at 5 meters depth. This indicates that both grout mix are applicable for grout-in piezometer installation. 6. CONCLUSION During filling works, excess pore water pressure increases and as the embankment is completed the pore pressure keep on increasing for a few days before it starts to dissipate. Soft clay remains in elastic condition until filling works completed. Within the first four month after the embankment construction completion, pore water pressure shows a fast dissipation trend between 42% and 79%. Beyond that period the dissipation trend is fluctuating. These dissipation trends probably could be attributed to reduction in soil permeability coefficient and rearrangement of soil grain structure resulting from filling load. Standpipe piezometer shows relatively slow rate of dissipation of excess pore water pressure due to the its relatively slower respond as compared to pneumatic and vibrating wire piezometer. Therefore its application in clay (low permeability) is not so suitable. Piezometer that has been installed conventionally and by grout-in method show similar reading indicates that grout mix is suitable and applicable in clay on study site. Owing to the fact that the soft clay parameters on the site within the range that shown by the clay in the west coast of peninsular Malaysia, probably the grout mix is also applicable in most part of west coast of peninsular Malaysia. Due to its simplicity and lower installation cost as compared to conventional method, grout-in method is suggested in piezometer installation in the future. However grout mix quality must be given due attention for the mix is highly affected by bentonite quality, mixing method, mixing duration, temperature and water pH value.

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ACKNOWLEDGEMENT This study was conducted in “Projek Menaik Taraf Jalan Simpang Ampat-Muar-Alor Gajah-Melaka” and funded by the Government of Malaysia. The authors wish to express their gratitude to all those involved and have contributed to this study. REFERENCES Adachi, K. & Todo, H. 1979. A case study on settlement

of soft clay in Penang. Proc. 6th Asian Regional Conference on Soil Mechanics and Foundation Engineering 1: 117-120.

Dunnicliff, J. 1993. Geotechnical instrumentation for

monitoring field performance. New York : John Wiley & Sons.

Hoeg, K., Andersland, O. B. & Rolfsen, E. N. 1969.

Undrained behavior of quick clay under load tests at Asrum. Geotechnique 19 (1): 101-115.

Hussein, A. N. 1995. The formation, properties and

behavior of coastal soft soil deposits at Perlis and other sites in Peninsular Malaysia. Tesis Ph.D. University of Strathclyde, Glasgow.

Lambe, T.W. & Whitman, R.V. 1979. Soil mechanics. SI

version. New York : John Wiley & Sons. McKenna, G.T. 1995.Grout-in installation of piezometers

in boreholes, Canadian Geotechnical Journal 32: 355-363.

Parry, R.H.G. & Wroth, C. P. 1981. Shear stress strain

properties of soft clay. Dlm. Brand, E. W. & Brenner, R. P. (pnyt.). Soft clay engineering, hlm. 311-364. Amsterdam: Elsevier/North-Holland Inc.

Tavenas, F., Chapeau, C., Rochelle, P. L. & Roy, M.

1974. Immediate settlement of three test embankment on Champlain clay. Canadian Geotechnical Journal 11: 109 – 140.

Tavenas, F. & Leroueil, S. 1980. The behaviour of

embankments on clay foundations. Canadian Geotechnical Journal 17: 236-260.

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INNOVATIVE HIGH VACUUM DENSIFICATION METHOD (HVDM) FOR SOFT COHESIVE SOIL IMPROVEMENT Robert Y. Liang Distinguished Professor, Department of Civil Engineering, University of Akron, Akron, Ohio 44325-3905, Tel: (330) 972-7190 e-mail: [email protected] Shi-Long Xu Chairman, Shanghai Geoharbor Group e-mail: [email protected] ABSTRACT: An innovative technique termed HVDM (high vacuum densification method) for improving large areas of soft, cohesive soils with relatively inexpensive cost and fast speed has been successfully applied in China and other countries over the last 8 to 10 years. The working principles, technology breakthrough, and analyses of improvement effects in undrained strength and density, as a result of the HVDM application are presented in this paper. Keywords: clay; improvement; vacuum; densification

1. INTRODUCTION In the past, the application of vacuum to facilitate consolidation in saturated cohesive soils has been used either alone or in combination with static surcharge loading (Holtz, 1975). The effectiveness of vacuum consolidation with or without surcharge loading is highly dependent upon soil permeability and the specific vacuum application techniques, as well as the desired degree of improvement and the allowable time duration for completing improvements. The dynamic compaction technique, although was mentioned by Menard (1975) as a feasible technique for use in saturated cohesive soils, has not been widely accepted by the U.S. Federal Highway Practice Manual for use in cohesive soils. Recently, a new soft clay improvement method was advanced in China by integrating the two known ground improvement technologies in an intelligent and controlled manner. The innovative soft clay improvement method is referred to as “High Vacuum Densification Method (HVDM)” to reflect its combined uses of vacuum and dynamic compaction techniques. Over the past four years, this innovative soft cohesive soil improvement technique has been widely and successfully used in China for numerous large - scale soft clay improvement projects. In this paper, the working principles of the HVDM will be described, followed by elucidations of the breakthrough of the HVDM. Furthermore, analyses of increased undrained shear strength and density (or reduced void ratio) of the improved soils will be briefly illustrated. A short description is given of the Shanghai Pudong Airport Runway No.2 project where the HVDM was used to treat the subgrade down to about 5 to 6 meters depth. The economic benefits of HVDM, in terms of reduced construction cost and shortened duration, have been documented in vast project experiences in China and Vietnam. This paper contributes to the state of practice in soft cohesive soil improvement by introducing a new and

viable soft clay improvement technique for a large area project, with the expected benefits of savings in construction cost and construction time. 2. WORKING PRINCIPLES OF HVDM IN COHESIVE SOILS The general construction method of HVDM is illustrated as a flow diagram in Fig. 1. First, as shown in Fig. 2, it involves installation of perforated steel pipes into the ground as vacuum pipes. Next, specially designed and air tight elbow connectors are used to connect vertical vacuum pipes with the horizontal PVC pipes, which in turn are connected to vacuum pumps for vacuum dewatering of the soils. Fig. 3 provides a photo of the horizontal PVC pipe network at a project site. Once vacuum dewatering has successfully reduced water content of clays to the extent that the degree of saturation is in the range of 85 to 90%, then dynamic compaction (see Fig. 4) is commenced to not only densify the soil but also to generate positive pore water pressure in the soil zone influenced by DC. The combination of negative pore pressure generated by vacuum and positive pore pressure generated by dynamic compaction can create a very high pore pressure gradient which in turn expedites dissipation of pore water pressure and further reducing water content and void ratio of the soils in the affected zone. Since pore pressure gradient is greater than that can be generated by vacuum only, the rate of pore pressure dissipation with HVDM principles can be very fast. It should be pointed out that the HVDM is a repeated process of vacuum and dynamic compaction, with each successive cycle involving the use of higher tamper impact energy to achieve the desired density and depth of treatment. To ensure the success of the HVDM, experience and calculation based methods have been developed to assist engineers to determine the appropriate tamper energy at each round of DC and the optimum vacuum duration in

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between each round of DC. Furthermore, on-site monitoring and observation on the variation of pore water pressure, water content, groundwater elevation, and CPT cone resistance is conducted not only for QA/QC purposes but also for real-time feed to allow engineers to adjust the HVDM operation parameters.

Fig. 1. Work flow of HVDM

Fig. 2. Vacuum pipe installation

Fig. 3. Array of PVC pipes

Fig. 4. Dynamic compaction at a job site 3. TECHNOLOGY BREAKTHROUGH HVDM method embodies at least four technology breakthrough that is worthy of mentioning. First, the HVDM method successfully utilizes an intelligent combination of cycles of well designed vacuum dewatering and dynamic compaction to create not only very high pore water pressure gradient to expedite pore pressure dissipation, but also to provide active drainage conduits through the air tight innovative vacuum pipe system. With this generation of high pore pressure gradient and the ability to shorten the pore water drainage path, the HVDM technology essentially extends the applicable range of vacuum well drainage method into highly impermeable soils with permeability in the order of 1 × 10-7 cm/sec. The second distinctive breakthrough of the HVDM is its breaking the barrier of limiting the use of dynamic compaction in soft, saturated cohesive soils. The main reason that dynamic compaction can be applied to advantage in saturated soft clay is due to its combined use with vacuum well dewatering. The vacuum well dewatering is effective in reducing water content in cohesive soils to the point that the degree of saturation is about 75 % to 85 %. Therefore, dynamic compaction can be executed in such a way to avoid rubber soil phenomenon. As shown in Fig. 5, a finite element simulation of equivalent static loading on cohesive soil deposits with 100 % and 75 % degree of saturation indicated that there is significant difference in the volume of the plastic zone. With the reduction of degree of

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saturation in the cohesive soils down to 85 %, HVDM effectively captures the advantages of dynamic compaction while avoiding its limitations.

Fig. 5. Finite element simulation results of stress contours under simulated load for (a) S= 100 % and (b) S=75 %

Fig. 6. Effective stress distribution due to hard, over consolidated top clay layer The third distinctive feature of the HVDM is the actual densification achieved due to dynamic compaction, which in turn creates a very hard and over-consolidated top layer with thickness to the order of 3 to 4 meters. As illustrated in Fig. 6, the presence of this hard, over-consolidated clay layer serves as an effective stress diffuser to spread the surface load with a wider angle of alpha. Therefore, the

stresses transmitted to the underlying soil layer are reduced, which would place less stringent requirement on the soil improvement for this underlying soil layer. The fourth breakthrough is hinged on the ability of being able to retrieve the vacuum pipes during and after the ground improvement at the site. With the production of hard, over-consolidated clay, which is essentially impervious, in conjunction with the retrieval of vacuum pipes (contrast to leaving PVD in place); the post treatment water drainage path is restricted to horizontal direction. As a result, even with additional pore pressure generation due to surface structure loads, the rate of pore pressure dissipation under this restrictive drainage condition would be very slow. Thus, the HVDM can improve a soft clay site with a product illustrated in Fig. 7 that clearly minimizes the post treatment total and differential settlements.

Fig. 7. Comparison of drainage path: (a) PVD left in place and (b) vacuum pipes with drawn 3.1. Undrained Strength Gain The action of HVDM in the e-log p’ plot is illustrated in Fig. 8 to show the benefits of cycles of vacuum and dynamic compaction in densifying the cohesive soils and in increasing undrained strength of cohesive soils underneath the bottom of the crater. Assuming the cohesive soils is normally consolidated and the state prior

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to HVDM treatment is at point A. With dynamic compaction, positive excess pore pressure is generated, moving the soil state from A to B1 (ignoring the apparent reduction of void ratio due to dynamic compaction). Subsequent to dynamic compaction, high vacuum is used to dissipate excess pore pressure rapidly to bring the soil state from point B1 to point D1. The reduction of the void ratio is due to dissipation of excess pore pressure during accelerated consolidation process. With repeated cycles of vacuum and dynamic compaction, both density and undrained strength of the cohesive soils can be significantly improved. The enhanced undrained shear strength of the improved cohesive soils can be estimated by relating the undrained shear strength to the apparent over-consolidation ratio (OCR) as follows.

'

'Ei

Ai

pOCRp

= (1)

( )( )

u OCR

u NC

SOCR

SΛ= (2)

where Λ = empirical constant. e

B1 ANCL

p0' pDi

' pDj' pi

' pAi' pAj

' pEj' logp'

B2B3

D1

D2

Dj

A1

A2

Aj

Ej

Fig. 8. e-log p’ plot under many times impact 3.2. Void Ratio Reduction (Densification Effect) As a first order estimate, the change (reduction) in void ratio of the cohesive soils beneath the bottom of the crater could be estimated through the measured ground subsidence during HVDM process. The ground subsidence is generally related to void ratio change as shown in Equation (3).

1i

ioi

eS He

Δ=

+∑ (3)

where S = total ground settlement; ieΔ = change in void ratio

in layer i; oie = initial void ratio of layer i; iH = layer thickness of layer i.

Shanghai Pudong Airport Runway No. 2 Subgrade Improvement Project The Runway No. 2 soil improvement was carried out to further improve the subgrade soils with shallow depth to ensure adequate bearing capacity, minimize post-treatment settlement, and produce more uniform improved properties throughout the area. The performance requirements include the following stipulations: (a) resilient modulus to be at least 40 Mpa, (b) cone penetration resistance greater than 3 Mpa in the upper 6 meter depth, and (c) SPT N values greater than 9 in the upper 6 meters. The construction sequence involves two cycles of dynamic compaction and two cycles of high vacuum dewatering. The vacuum pipes were generally spaced at 7 to 10 D, where D is the diameter of tamper. The energy used in dynamic compaction was 2500 kN-m, with grid spacing of 5 meter and 8 to 10 drops per spot. The performance of Runway No. 2 has been very good since commencing its service about 9 years ago. 4. CONCLUSIONS The development of theory, construction equipment, and construction techniques of the HVDM for soft clay improvement has led to four major breakthroughs in four distinctive areas: (a) “accelerated consolidation” due to combined uses of vacuum and dynamic compaction, (b) enabling effective uses of dynamic compaction in initially saturated cohesive soils, (c) producing a layer of over-consolidated clay down to about 5 to 6 meter below the ground surface, and (e) eliminating drainage path after treatment to minimize post-treatment settlement. The HVDM method is a “green” soil improvement technology by using purely mechanical process without the use of any chemical additives. Finally, the savings in construction time and construction cost have been documented in numerous real projects. The HVDM provides an attractive soft soil treatment technology for treating large areas, such as land reclamations and roadway subgrade improvements. REFERENCES Holtz, R. D. (1975) Preloading by Vacuum: Current

Prospects. Transportation Research Record, No. 548, pp. 26-29.

Menard, L. (1975) Theoretical and Practical Aspect of Dynamic Consolidation. Geotechniques, 25(1): 3-17.

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