Potential Liquefaction of Locations Along the Pasig city Segment of the Valley Fault System

Comparative Study of Potential Liquefaction of Three Selected Locations Along the Pasig City Segment of the Valley Fault System

A Research Presented to Faculty of Civil Engineering

College of Engineering, Computer Studies and Architecture

Lyceum of the Philippines University - Cavite

General Trias City

Submitted by:

Engr. Anjerick J. Topacio

Engr. Joanna Carla A. Pacamparra

Engr. Alyssa Erika P. Ramos

Engr. Jayson E. Villaester

1

Abstract

A seismic – induced liquefaction is a complex ground failure phenomenon

observed when saturated loose sand deposits loss its shear strength. It may be

quantified as to the damage that it causes to the built infrastructures within the vicinity.

This study was conducted to determine the potential liquefaction of three specific

locations along the Pasig City segment of the Valley Fault System in Barangay

Kapitolyo, Manggahan and Ugong and correlate it with their respective soil suitability.

The study employed secondary data from geotechnical firms, DOST –

PHIVOLCS and the local government unit of Pasig City.

The results were assessed through the use of an excel program devised by the

researchers based on a simplified procedure by Seed and Idriss (1997), and Das

(1995). The factor of safety due to liquefaction (FS) at specific soil conditions was

computed using this program and proved that the chosen location in barangay Ugong is

the most susceptible to liquefaction among the three chosen locations. The mitigation

measures for the soil and/or the type of foundations to be applied was considered and

pile foundations are recommended in the locations in baranggay Manggahan and

Ugong. Shallow foundations are, on the other hand, safe in barangay Kapitolyo.

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Chapter 1

The Problem and its Background

1.1 Introduction

A seismic – induced liquefaction is a complex ground failure phenomenon

observed when saturated loose sand deposits loss its shear strength. During seismic

activity, the continuous cyclic loading increases the pore water pressure that causes the

soil to behave like liquid. The potential soil liquefaction is primarily influenced by factors

such as void ratio and relative density of soil, depth of water table, effective confining

stress, coefficient of lateral earth pressure, seismic and geologic history of the site and

the recorded intensity and duration of the locale (Raychowdhury & Basudhar, 2011).

The effects of liquefaction may be quantified as to the damage that it causes to

the built infrastructures within the vicinity. The loss of the effective stress of the soil

affects the structure’s foundation through settlement. Surface rapture and structure

failure are some of the detrimental effects produced by the instability of subsoil

conditions. Major earthquakes that have occurred in the past years such as 1964

Alaska, 1964 Niigata, 1989 Loma- Prieta and 1995 Hyogoken- Nambu have

demonstrated the damaging effects of soil liquefaction (Liyanapathirana & Poulos,

2003).

In the Philippine setting, the Valley Fault System is one of the country’s active

fault lines that are found in Central Luzon. It is a group of strike- slip fault extending from

San Mateo to Marikina and running through the cities of Marikina, Makati, Pasig,

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Parañaque and Taguig. The fault is divided into two segments namely East Valley Fault

and West Valley Fault. Valley Fault System or the formerly known as Marikina Valley

Fault System is classified under a Seismic Source Type “A”. As defined in the National

Structural Code of the Philippines, it is described to be an active fault capable of

producing large magnitude events with a high rate of seismic activity. The projected

magnitude under Source Type “A” is greater than or equal to seven (7) which has an

intensity range of “Destructive” to “Completely Devastating (DOST- PHIVOLCS, 2011).

Aside from the seismic source type, Near Source Factor is also used for

designing the earthquake loading for a structure. The proximity of the location to the

nearest active fault varies the factor of safety required by an infrastructure. The nearer

the location to the epicenter, the greater the damage that may be expected, and it

includes the higher possibility of liquefaction occurrence (Sumer et al., 2007).

The cities along the Valley Fault System are classified to be the most highly

urbanized locations within Metro Manila. Large infrastructures and skyscrapers may be

found to the vicinities where traces of fault are visible or approximated to lay. These are

where the country’s prime business districts like the Ortigas Center, which lies in the

west of Pasig City, the Tiendesitas along the C-5 road, large billboards in Ugong Pasig

City and other establishments are situated, thus a large portion of the economy is

derived from it. Natural geological hazards like earthquake and its sub consequences

may be imminent, but proper pre-assessment of the risk may eliminate its worse effects.

The main objective of the study is to determine the potential liquefaction of three

barangays along the Pasig City segment of the Valley Fault System which is developing

in to the city’s economic resources namely Barangay Kapitolyo, Barangay Manggahan

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and Barangay Ugong and correlate it with the land use of the specific location gathered

in these barangays.

1.2 Statement of the Problem

Pasig City has been widely developed into one of the country’s prime business

districts despite its proximity to the Valley Fault System which is an active fault line. The

seismic activity of a source can never be determined; thus, parameters such as unit

weight of soil, depth of water table, effective stress and seismic history of the site should

be evaluated. Specifically, the study attempts to answer the following:

1. Can the potential liquefaction of the three selected locations along the Pasig City

segment of the Valley Fault System namely the chosen location in Kapitolyo,

Manggahan, and Ugong be determined in terms of factor of safety due to

liquefaction?

2. Which of the three selected areas has the greatest potential liquefaction?

3. What are the possible mitigation measures for the soil and/or the type of

foundation that can be applied to the selected areas considering their potential

liquefaction?

1.3 Objectives of the Study

The main objective of this study is to determine the potential liquefaction of three

locations along the Pasig City segment of the Valley Fault System namely Kapitolyo,

Manggahan, and Ugong by evaluating the parameters such as unit weight of soil, depth

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of water table, effective stress and seismic history of the site obtained from secondary

data. This study seeks to achieve the following objectives:

1. To determine the potential liquefaction of the three selected areas in Pasig City in

terms of factor of safety due to liquefaction.

2. To determine which of the areas has the greatest potential liquefaction.

3. To determine the mitigation measures for the soil and/or the type of foundation

that can be applied to the selected areas considering their potential liquefaction.

1.4 Significance of the Study

The goal of this study is to determine the potential liquefaction of three locations

along the Pasig City segment of the Valley Fault System namely Kapitolyo, Manggahan,

and Ugong and to identify which of the areas has the greatest susceptibility. The local

soil’s unit weight, depth of water table, effective stress and seismic history of the site

were used to evaluate its vulnerability to liquefaction. Through this, the study was able

to determine the possible mitigation measures for the soil and/or the type of foundation

that can be applied to the selected locations taking into consideration the sites’ potential

liquefaction.

In the Philippine setting, natural hazards like typhoons and earthquakes are

common scenarios. However, the simultaneous occurrence of two natural hazards may

further amplify the damage that each may cause. This study could help engineers and

planners in considering the probable effects of these hazards to their design. Through

this, the possible damages could be mitigated.

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For civil engineering students, this study would help them to derive further

studies on the branch of seismic and geotechnical engineering. This study will promote

long term planning and designing of infrastructures in the micro and macro setting

taking into consideration the potential liquefaction of the selected areas.

1.5 Scope and Limitations

The study focuses on the investigation of the potential liquefaction of three

specific locations along the Pasig City segment of the Valley Fault System specifically

on a site in barangay Kapitolyo, Manggahan, and Ugong through evaluating the

parameters such as unit weight of soil, depth of water table, effective confining stress,

and seismic and geologic history. The data that were used in evaluating the potential

liquefaction of the vicinities were obtained from soil tests reports from geotechnical

firms, secondary data from the local government unit of Pasig City and records from

Department of Science and Technology- Philippine Institute of Volcanology and

Seismology (DOST- PHIVOLCS). The specific locations that were evaluated are only

those which are within five kilometers (5km) range of distance from the Valley Fault

System to determine the maximum possible effect of a seismic activity.

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1.6 Study Framework

The study employed the process as shown in the diagram below.

Figure 1.1 Study Framework of the Study

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Data Gathering

Secondary Data

Assessment of Liquefaction Parameters by Seed and

Idriss Simplified Procedure

Soil Suitability Evaluation

Summary of Results

Conclusions and Recommendations

1.7 Definition of Terms

Liquefaction. the process by which saturated, unconsolidated soil is converted into

a suspension

Cyclic stress ratio (CSR). the loading induced at different depths in a soil profile

during seismic activity

Cyclic resistance ratio (CRR). the amount of seismic/ cyclic load that a soil profile

may resist

Factor of safety (FS). the ratio of CRR and CSR; a constant value that defines the

required strength amplification to resist liquefaction

Standard Penetration Test (SPT). an in situ test conducted to measure soil density

through the resistance of soil to penetration by quantifying the blow count needed in

able to get through the soil layer

Soil Suitability. adequacy of the soil to support infrastructures during a large seismic

event

Total Vertical Stress. overburden pressure of soil

Pore Water Pressure. the pressure of groundwater held within a soil or rock, in

gaps between particles (pores)

Effective Vertical Stress. pore water pressure subtracted to total overburden of soil

9

Energy Correction. using different kinds of hammers, with different energy delivery

systems which also have varying degrees of efficiency. The main reason for this

variation is due to the use of different methods for raising and dropping the hammer

Acceleration in g. maximum horizontal acceleration of the ground surface in units of

g from earthquake records of magnitude M

Deformability Reduction. to reduce the ability to change the original state or size of

a rock mass, especially by folding or faulting

Magnitude. the magnitude is a number that characterizes the relative size of an

earthquake

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Chapter 2

Review of Related Literature

2.1 Earthquake

Earthquake is a natural phenomenon caused by sudden movement of faults and

trenches (tectonic) or by movement of magma beneath volcanoes (volcanic). This

geologic hazard poses detrimental effects to lives and properties which are manifested

either directly or indirectly. Seismic activities may cause threat to lifelines and utilities

that people basically need (i.e. water supply, communication and transportation

facilities, and electrical networks). The stability and the integrity of an infrastructure may

also be at risk if the local soil reaches failure. The condition where the soil behaves like

liquid after exposure to a devastating shaking is called liquefaction (DOST- PHIVOLCS,

2011).

In the Philippines, the seismic activities are quantified to be twenty (20) recorded

earthquakes per day, two hundred (200) felt earthquakes per year and ninety (90)

destructive earthquakes for the past four hundred (400) years. The seismicity of the

country is directly associated with the two earthquake zone classification of the country

(Zone 2 and Zone 4) and that it belongs to the “Pacific Ring of Fire” (DOST-

PHIVOLCS, 2011).

One of the seismic generators in Central Luzon is the Valley Fault System and

one of the cities that it traverses is Pasig City. The Pasig City segment of the Valley

Fault is shown in Figure 2.1.

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(Planning Department of Pasig City Hall, 2011)

Figure 2.1 Pasig City Segment of the Valley Fault System

(Planning Department of Pasig City Hall, 2011)

Figure 2.2 Location of the Considered Sites(left, Brgy. Kapitolyo; right, Brgy. Manggahan and Brgy. Ugong)

12

The Valley Fault System’s major historical activities are presented in Table 2.1.

Table 2.1 Major Historical Earthquakes Generated by Valley Fault System that have Affected Manila and Vicinity

Event Intensity Impact1599 Jun VIII Violent earthquake; damaged many buildings in

Manila including the Sto. Domingo Church located on bedrock (adobe); other effects include fissuring of the stone vault of the society of Jesus and other principal edifices in the city.

1601 Jan VIII Violent earthquake; completed destruction wrought by 1599 June earthquake; damage to the city was immense, destroying many stone houses, churches and injuring/ killing an unspecified number of people.

1658 Aug IX Most buildings in Manila, mainly made of wood and timber, were wiped out; several persons killed/ injured.

1885 Nov VII Strong but no serious damage; strong sub- terranean noise observed in Marikina and suburbs of Manila.

(PHIVOLCS Professional Paper 01, 1997)

2.2 Liquefaction

One of the major effects of a moderate to large earthquake is the seismic

induced liquefaction which is technically the generation of excess water pressure, loss

of shear strength and excessive volume contraction of saturated loose soil

(Raychowdhury & Basudhar, 2011). It is the transformation of the granular material from

a solid to a liquefied state after the induction of cyclic loading made by a seismic

excitation (Sumer et al., 2007). Liquefaction is one of the major causes of destruction

whenever an earthquake occurs and it should be one of the considerations in hazard

investigations for buildings, pipelines, railway, highway bridges and land use planning.

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Primary method used in the United States and many other countries in analyzing

liquefaction hazard is the simplified procedure developed by Seed and Idriss (1971).

Potential liquefaction depends on the nature of ground shaking and the site’s

geological condition (Sumer et al., 2007). The factors that significantly affect liquefaction

are the void ratio and relative density of soil, depth of water table, effective confining

stress and coefficient of lateral earth pressure (Raychowdhury & Basudhar, 2011). The

term liquefaction, however, varies with respect to soil classification. For loose sand,

liquefaction occurs after the complete loss of strength due to the 100% build up of pore

water pressure, accompanied by a softening and large deformation. For medium dense

to dense sand, it is characterized by the 100% build up of pore water pressure

accompanied by about 5% double amplitude axial strain but of limited deformation. The

plasticity of fines to silty sands or sandy silts defines its liquefiability. Silty soils with non

plastic fines make it easily liquefiable while cohesive fines increase its cyclic resistance

(Sumer et al., 2007).

Such condition is catastrophic to infrastructures especially when the effective

stress of the soil reaches the level that it can no longer support the building’s

foundation. Settlement on footings and piles may occur as the shear strength of the soil

depletes. Structures built underground are also directly affected by liquefaction.

Example of which are buried pipelines and storage tanks. The extent of damage may be

further magnified when structures are located near the epicenter of the earthquake.

In understanding the potential liquefaction of an identified location, the locale’s

geologic and seismic history must be considered. This would include the recorded

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intensity, duration and the characteristics of the ground shaking of the specific vicinity.

The study and analyses of the potential liquefaction of vicinity are strongly

recommended especially when infrastructures of special purpose are to be built within

the site. Locations for high risk infrastructures such as dams and nuclear power plants

must be evaluated (Raychowdhury & Basudhar, 2011).

Liquefaction in Dagupan City, 1990

Liquefaction is a major secondary effect of the July 16, 1990 Luzon earthquake

with a magnitude of 7.8 in a large elongated zone of the Central Plain. Cohesionless

saturated fine sandy and silty sediments near the ground surface are liable to liquefy

under the effect of intense cyclic ground shaking.

Dagupan City is located on a flat terrain where extensive deposits of loose sand

and gravels are present. There are numerous abandoned stream meanders and

wetlands, which are prone to liquefaction (Torres et al., 2001).

The mid-Luzon tectonic depression, known as the Central Plain (about 30,000

sq. km), was filled with clastic sediments during the Tertiary and Quaternary. The

uppermost part of the sequence, consisting of loose to very loose fine sand, reacted to

the ground-shaking with liquefaction on a regional scale (Orense, 2011).

The earthquake was said to have been accompanied by a terrifying noise with felt

aftershocks lasting until the following year (Punongbayan, 2011).

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a. Effects of 1990 earthquake

Close to around 500 buildings and residential houses underwent severe

settlements as well as varying amounts of tilting as a result of the loss in strength of the

underlying soil in Dagupan City. Except for one, no building in the affected area was

supported by piles and, therefore, no resistance was possible against subsidence after

liquefaction. Earthquake shaking did not destroy buildings in the area nor cause any

structural damage (Orense, 2011). Also lateral spreading occurred along the banks of

Pantal River of about 3 to 5 meters. The 5-storey Asia Career Building subsided by

more than 1m, with minor structural damage; however, the 1-storey section adjacent to

it was severely distorted. Magsaysay Bridge collapsed as a result of the lateral

movement of the opposing banks of Pantal River where the bridge abutted. As a result

of liquefaction of the river bank, the bridge piers sank and tilted towards the center of

the river. Roads became virtually impassable because of cracks in road pavements.

Several buried structures, such as gasoline tanks, septic tanks and buried pipes, were

uplifted due to the buoyant force exerted by the liquefied soil. A buried water pipe along

Rizal Street buckled and was thrust upward. Immediately after the earthquake, much of

the town was coated in dark-grey mud and water ejected from fissures in the ground

(Orense, 2011).

2.3 Liquefaction Ingredients

Current sediments or fills of saturated, cohesionless soils located at shallow

depths will be heavily prone to liquefaction during large earthquakes. Geologic history,

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confining pressure, density, and characteristics of the soil grain affect the liquefaction

susceptibility of a specific deposit (Rauch, 2001).

The ground at the site must be “loose” – uncompacted or unconsolidated sand

and silt without much clay or stuck together. The sand and silt must be “soggy” (water

saturated) due to a high water table. Lastly, the site must be shaken long and hard

enough by the earthquake to “trigger” liquefaction (Perkins, 2001).

Table 2.2 shows the liquefaction hazard based on combinations of Modified

Mercalli Intensity (MMI) and liquefaction susceptibility (Perkins, 2001).

Table 2.2 Liquefaction Susceptibility based on Combinations of Modified Mercalli

Intensity (MMI)

MMI Value

Description of MMI Shaking Severity

Liquefaction Susceptibility CategoryVery low Low Moderate High Very High

I - - - - - -II - - - - - -III - - - - - -IV - - - - - -V Light - - - - -VI Moderate - - - - -

VII Strong - -Moderately

Low Hazard

Moderately Low Hazard

Moderate Hazard

VIII Very Strong - - Moderate Hazard

Moderate Hazard

Moderate Hazard

IX Violent - - High Hazard High Hazard High

Hazard

X Very Violent - - High Hazard High Hazard High

Hazard

(The Risk Plates Supplemental. Retrieved August 2011, http://www.abag.ca.gov/bayarea/eqmaps/mitigation/TheRisk-Plates-Supplemental.pdf)

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2.4 Liquefaction Measurement

If sand boils, ground cracking, lateral ground movement, settlement or transition

of structures, bearing capacity failures, or uplifting of buried pipes and tanks are

observed, liquefaction occurs. It is assumed that there’s no liquefaction if there is no

surface evidence observed. Still, deeper soils could have liquefied without producing

surface indication (Rauch, 2001).

2.5 Liquefaction Resistance Assessment

Assessing the liquefaction resistance of soil is one of the most significant

measures in the engineering design of new structures and in the retrofitting of existing

ones especially those earthquake prone areas. Simplified Procedure which was first

introduced by Seed and Idriss is the method used in the United States and most of the

countries in the world. Simplified Procedure uses the blow counts from the Standard

Penetration Test (SPT) which is correlated with a parameter representing the seismic

loading on the soil, called Cyclic Stress Ratio. Small-strain shear wave velocity Vs,

measurements can be an alternative way to the penetration-based approach. Void ratio,

state of stress, stress history and geologic stress influence both Vs and liquefaction

resistance, and for that reason the use of Vs as index of liquefaction is completely

supported. (Andrus & Stokoe, 2001)

Mathematically, the potential liquefaction of a location may be quantified through

tests. There are two general approaches used in determining the susceptibility of the

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local soil to such ground condition. First is the use of laboratory testing of undisturbed

samples and second is the use of empirical relationships obtained from in situ “index”

test. The laboratory testing of soil samples requires a good preparation of the specimen

because it strongly affects its resistance to cyclic loading. Remolded and reconstituted

samples have less in situ stress history which leads to the underestimation of

liquefaction. Undisturbed soil sampling techniques have been developed through the

years. Examples of which are the in situ freezing and frozen shelby tube samples.

Investigations were conducted and it was determined that the sampling method have

lower liquefaction resistance compared with the undisturbed samples. Due to this,

empirical approaches were used as a viable tool for testing. Four Empirical Liquefaction

Models (ELMs) are used in assessing the potential liquefaction of a location. First is the

standard penetration test (SPT), second is the cone penetration test (CPT), third is the

measurement of shear wave velocity (Vs) and last is the Becker penetration test. SPT is

executed to determine the stiffness of the local soil and it is done inside a borehole. The

CPT, on the other hand, measures the stress, sleeve friction and the pore water

pressure. The Vs measures the shear wave velocity profile of the soil. The assessment

methods used in determining the susceptibility of the soil is aided with the values

expressed in terms of cyclic stress ratio (CSR) and the cyclic resistance ratio (CRR).

The evaluated variables dictate the factor of safety at a given depth (Sumer et al.,

2007).

The simplified methods in potential liquefaction assessment are very useful in

creating preliminary designs. The loading parameters that are often used in testing are

represented by either the generated cyclic shear stress due to earthquake or by the

19

amount of energy released (Liyanapathirana & Poulos, 2003). The relationship between

the values of CSR and CRR derives the factor of safety for liquefaction that may be

used in structural analysis.

The most comprehensive liquefaction data catalogues are based on Standard

penetration Test (SPT) blowcounts (NSPT). Starting in 1970’s, H. B. Seed and his

colleagues worked to develop a reliable method for assessing liquefaction potential

based on SPT data. Their framework for SPT-based assessment of liquefaction

potentials was developed in a series of papers that includes Seed and Idriss (1971),

Seed et al (1977), Seed (1979), Seed and Idriss (1981; 1982), and Seed et al (1983)

(Rauch A. F., 2001).

The simplified procedure formulated by Seed and Idriss in evaluating potential

liquefaction is dicussed below.

Induced Shear Stress, τi can be computed using the Seed-Idriss Simplified

Liquefaction Evaluation Procedure. The maximum shear stress induced at depth z is

given by:

¿¿ Equation 2-1

where:

σv is the total vertical stress

amax is the peak horizontal acceleration at the ground surface

rd is the stress reduction coefficient at depth z.

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For the period of ground shaking, at least a maximum shear stress is induced.

Seed and Idriss (1967) used a 0.65 coefficient to be multiplied to (τ i)max to characterize

an “equivalent uniform shear stress”.

¿¿ Equation 2-2

The values of the magnitude scaling factor (MSF) consider that MSF=1 for

Mw=7.5.The value of the MSF can be computed using the equation:

MSF=6.9exp (−M4 )−0.06 Equation 2-3

The anticipated value of MSF is restricted up to MSF=1.82 for Mw < 5.2. The

controlled value is because of the fact that the equivalent uniform induced stress is

measured to be equivalent to 0.65 of the maximum induced stress. The maximum

stress must be at least more than half to one cycle. It can be practical to consider that

the peak shear stress would work at about ¾ cycle.

MSF value cannot be more that of the ratio of the CSR at ¾ cycles divided by

CSR for 15 cycles multiplied by 0.65 and can be written as:

MSF < CSR for 3

4Cycles

CSR for 15Cycles∗065=2.8

1∗0.65=1.82 Equation 2-4

The equivalent uniform induced stress at a certain depth z with regards to ground

motions produced by an earthquake with a magnitude Mw can be written as:

¿ Equation 2-5

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The stress reduction coefficient, rd was originally formulated by Seed and Idriss

(1971) and was given in chart form with an average value ranging from 1 at the ground

surface to about 0.85 at depth of 40 ft (-12.2m), while the complete range of the

parameter r d was from a range of magnitudes of earthquakes. Recent studies of

Golesorkhi (1989) under the supervision of the late H.B. Seed show the variations of rd

with earthquake magnitude.

The induced shear stress at depth z is proportional to the ratio (rd/MSF). If rd has

no connection with magnitude, then it is essential to adjust MSF to reflect the potential

reduction rd with decreasing value of magnitude.

The effect of magnitude on rd at shallow depths is not as important as it is at

greater depths. Consequently, it is necessary that the two parameters be determined

separately and properly include in assessing the liquefaction potential at a site (Idriss,

1999).

The liquefaction potential index may be introduced to the analysis to determine

the severity of the possible liquefaction at a given depth of soil sample. LPI exhibits the

probability of surface manifestation of liquefaction. It may be assumed that the severity

of liquefaction is proportional to the thickness of the liquefied layer, proximity of the

affected layer to surface and to the factor of safety amounting to less than 1 (Toprak &

Holzer, 2003).

2.6 Liquefaction Modeling

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Through the continuous search for the quantification of the liquefaction

vulnerability of soil, numerous modeling were derived in order to get the most precise

values that may be used in the engineering practice. The common means of

measurement in the field are the penetration tests (standard penetration test (SPT) and

cone penetration test (CPT)) that are used in determining the soil density and stress of

soil. These in situ tests are said to produce volumetric stresses in soil; thus, pore water

pressure induced by the shear is not directly measured. In order to mitigate the

discrepancies produced by the method and to better understand the basic mechanisms,

liquefaction modeling like torsional shear test, centrifuge model, and constitutive model

were then developed.

Torsional shear test may be done through laboratory experiments or field tests.

Laboratory set up intends to identify the distinct pattern between the torsional moment

and the rotation angle of cylinder for dilative behavior of sample. The field test, however,

is executed by slightly modifying the standard penetration test (Dehghani et al., 2001).

Centrifuge earthquake modeling is intended to produce an artificial gravitational field

higher than that of the earth’s gravitational field. The prototype simulates the soil

structure system and the response of the system to dynamic loading (Dobry & Liu,

2002). Lastly, the constitutive model is focused on the deviatoric stress- strain response

mechanism of soil. Cyclic laboratory tests are included in this model to produce salient

relations of deformations to the cycle of applied load (Elgamal et al., 2002).

2.7 Effects of Liquefaction: Ground Failure and Settlement

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When ground liquefies and “fails,” it may cause damage to built environment.

These failures take the form of flows, lateral spreads, ground oscillations (or movement

of the surface layer of ground separately from the underlying liquefied layers), loss of

bearing strength (to hold up buildings or hold tanks and pipes underground); and

settlement and differential settlement (Perkins, 2001).

Typically, “flows” failure occurs on slopes of more than 3 degrees, while

“spreads” failure are on less steep slopes (EERI, 1994). A lateral spread failure is a

failure where a layer of ground at the surface is carried on an underlying layer of

liquefied material over a nearly flat surface toward a river channel or other bank

(Perkins, 2001). Also, when soil liquefies, it becomes “weaker.” It may lose its capacity

to support buildings, particularly large buildings with poorly designed foundations. In

addition, underground tanks and pipelines can “float” upwards, sometimes all the way to

the surface. Another common problem is settlement as soil compacts and consolidates

after the ground stops shaking.

Settlement can range from 1% - 5% of the liquefiable layer. In very loose sands,

it can be as large as 10% of the thickness of the saturated loose materials that liquefy

(Tokimatsu & Seed, 1984). Although small uniform changes are typically not damaging,

the soil can settle unevenly. This problem, called differential settlement, occurs when

the layers that liquefy are not of a uniform thickness, a common problem when the

liquefaction occurs in artificial fills, particularly fills that have been placed during

different times and using different techniques. Thus, using the 10% settlement

estimate for loose materials, if the liquefying layers are 10 feet different in thickness,

differential settlement of a foot can be achieved (Perkins, 2001).

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2.8 Soil Improvement: Soil Grouting

Grouting is a widely used method for strengthening and sealing rock, soil and

concrete. The possibilities for sealing structures are of great importance from both an

economic and environmental point of view. The primary purpose of any grouting project

is to alter, to a desired degree, the properties of an existing medium by the most

economical means. Different grouting types that can be used include:

Portland-cement grout is a mixture of portland cement, water, and, frequently,

chemical and mineral additives (Guyer, 2009).

Soils used as the primary grout ingredient can be divided into two classifications.

One includes the natural soils found at or near the project with little or no modification

required. The second includes commercially processed clay such as bentonite (Guyer,

2009).

In 1957 there had been some 87 patents issued for processes related to

chemical grouting. Since then, there undoubtedly have been more. These processes

cover the use of many different chemicals and injection processes. The primary

advantages of chemical grouts are their low viscosity and good control of setting time.

Disadvantages are the possible toxic nature of some chemicals and the relatively high

cost (Guyer, 2009).

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Chapter 3

Methodology

The study employed secondary data from geotechnical firms, Department of

Science and Technology- Philippine Institute of Volcanology and Seismology (DOST-

PHIVOLCS) and the local government unit of Pasig City in determining the potential

liquefaction of selected locations in three different barangays namely Barangay

Kapitolyo, Barangay Manggahan and Barangay Ugong along the Pasig City segment of

the Valley Fault System. The process, as shown in figure 2, was followed.

3.1 Data Gathering

The data used in this study such as surface geology maps were obtained from

Department of Science and Technology- Philippine Institute of Volcanology and

Seismology (DOST-PHIVOLCS). The quantities were utilized as a secondary data in

assessing the liquefaction susceptibility of a selected location in three different

barangays namely Barangay Kapitolyo, Barangay Manggahan and Barangay Ugong

along the Pasig City segment of the Valley Fault System. The researchers also

coordinated with geotechnical engineering professionals in determining the soil

properties of the selected locations through soil test results.

Also, the researchers secured the local fault line map of the selected locations

from the local government of Pasig City.

26

The figure below shows the flow of the study. The inputs and the corresponding

outputs are stated. Different methods were used to yield these results.

Figure 3.1 Methodological Framework

27

Input Process Output

Secondary Data (Metro Manila Earthquake Impact Reduction Study Report and Maps) from Philippine Institute of Volcanology and Seismology (PHIVOLCS)

Secondary Data (Soil Tests Results) from Geotechnical Firms

Secondary Data (Comprehensive Land Use Plan and Maps) from Local Government Unit of Pasig City

Assessment of Parameters through Excel Program

Calculation of the Local Soil’s Effective Stress

Calculation of the Factor of Safety due to Liquefaction

Quantification of the Sites’ Factor of Safety Due to Liquefaction

Identification of the Location with the Greatest Potential Liquefaction

Identification of Possible Mitigation Measures for the Soil and/or the Foundation

3.2 Data Analysis

The specific test locations were derived from the Active Fault Map, Geological

Surface Map, and Valley Fault System Map that were obtained from the Department of

Science and Technology- Philippine Institute of Volcanology and Seismology (DOST-

PHIVOLCS); and from the Pasig City segment of the Valley Fault System Map that was

obtained from the local government unit of Pasig City.

The gathered quantified subsurface parameters (void ratio, ground water level,

relative density of soil, and effective confining stress) of the selected locations were

assessed through the use of an excel program based on a simplified procedure by Seed

and Idriss (1997), and Das (1995) for SPT correction. The input values were obtained

from the geotechnical tests results. The assessment aimed to determine the factor of

safety due to liquefaction (FS) at specific soil conditions. The FS values were derived

from the Cyclic Stress Ratio (CSR) and Cyclic Resistance Ratio (CRR) by following the

simplified procedure formulated by Seed and Idriss (1997). The corresponding results

from the test locations were compared to identify which has the greatest liquefaction

susceptibility. The equations used to determine the Factor of Safety (FS) are

mathematically written as:

a. Total Vertical Stress, σTZ

σ TZ=(MDZ−MDZ−1 )ƔSOILZ+σ TZ−1 Equation 3-1

28

where:

MDz – middepth at depth z (m)

MDZ=DEPTH Z−DEPTH Z−1

2+DEPTH Z−1

Ɣsoil – dry unit weight of soil (kN/m3)

b. Pore Water Pressure, Uz

U Z=IF (U 1Z<0,0 ,U 1Z)

U 1Z=DEPTH Z−DEPTH Z−1

2DEPTH ZƔW−(GWT·ƔW ) Equation 3-2

where:

Ɣw – unit weight of water (9.81 kN/m3)

GWT – Ground Water Table (m)

c. Effective Stress, σEZ

σ EZ=σTZ−|UZ| Equation 3-3

where:

σTZ= total stress (kN/m2)

UZ= pore water pressure (kN/m2)

d. SPT Correction (Das, 1995), NCORZ

NCORZ=9.78√σ EZ

Equation 3-4

NCORZ=IF ¿)

29

e. Energy Correction, CERZ

CERZ=IF (DEPTH Z<3 ,0.75,1 .0) Equation 3-5

f. Corrected Blow Count, NCZ

NCZ=NVALUE ·N CORZ ·CERZ Equation 3-6

where:

NVALUE= field blow count

NCORZ= SPT correction

CERZ= energy correction

g. Fines Content Correction of SPT-N (Seed and Idris, 1997), NCFZ

NCFZ=αZ+ βZ · NCZ Equation 3-7

where:

NCZ= corrected blow count

α Z=IF (FINESCONTENT Z<5 , α 1Z , IF (FINESCONTENT Z<35 , α 2Z , α 3Z ))

βZ=IF (FINESCONTENT Z<5 , β 1Z , IF (FINESCONTENT Z<35 , β 2Z , β 3Z ))

α 1Z=0 β1Z=1.0

α 2Z=e1.76− 190

(FINESCONTENTZ)2 β2Z=0.99+

(FINESCONTENT ¿¿Z )1.5

1000¿

α 3Z=5.0 β3Z=1.2

h. Earthquake-Induced Stress

Acceleration in g, a

30

where:

a=0.4

Deformability Reduction, rdZ

rdZ=IF (DEPTH Z<9.15 ,rd 1Z , IF (DEPTH Z<23 , rd 2Z , IF (DEPTH Z<30 ,rd 3Z , rd4Z )))

rd1Z=1−0.00765 · DEPTH Z

rd2Z=1.174−0.0267 ·DEPTH Z

rd3Z=0.744−0.008 · DEPTH Z

rd 4Z=0.5

Shear-Stress Average, τAVEZ

τ AVEZ=0.65 · a· σTZ ·rdZ Equation 3-8

where:

a= peak ground acceleration

σTZ= total stress (kN/m2)

rdZ= deformability reduction factor

Cyclic Stress Ratio, CSRZ

31

CSRZ=τ AVEZσ EZ

Equation 3-9

where:

τAVEZ= shear- stress average

σE= effective stress (kN/m2)

i. Liquefaction Strength

Magnitude Scaling Factor, MSF

MSF=102.24

m2.56 Equation 3-10

where:

m= magnitude of earthquake

Cyclic Resistance Ratio, CRRZ

CRRZ=0.007 ·(N CFZ)1.155 Equation 3-11

where:

NCFZ= fines content correction of SPT-N

Factor of Safety, FS

FSZ=CRRZ

CSRZ· MSF Equation 3-12

32

where:

CRRZ= cyclic resistance ratio

CSRZ= cyclic stress ratio

MSF= magnitude scaling factor

Figure 3.2 shows the sample user interface of the Excel based program devised

by the researchers in calculating the selected locations’ potential liquefaction. The

program includes input cells that can be filled up using the Standard Penetration Test

results specifically the depth of soil layer, blow count value, soil class, magnitude, and

depth of ground of water table. The output includes the parameters defined in the Seed

and Idriss Simplified Liquefaction Evaluation Procedure. Through the program, the

factor of safety due to liquefaction is determined.

33

Figure 3.2 Sample User Interface of the Potential Liquefaction Program

34

Figure 3.3 Sample User Interface of the Liquefiable Zone Diagram

Figure 3.3 shows the sample user interface of the liquefiable zone diagram

included in the Excel based program devised by the researchers. The diagram presents

the soil classification and the probability of liquefaction occurrence of the soil layer at a

given depth. The plots that the figure exhibits are based from the input values entered at

the user interface of the potential liquefaction program.

Chapter 4

Presentation, Analysis and Interpretation of Data

The data obtained from soil test results were processed through the use of an

excel program devised by the researchers. The program followed the simplified method

of analysis formulated by Seed and Idriss (1997) and Das (1995) for the SPT correction.

The peak ground acceleration value that was used in determining the earthquake

induced stress is equal to 0.4g, the value assigned to Pasig City by Philippine Institute

of Volcanology and Seismology (PHIVOLCS) based on its proximity to a seismic

generator.

4.1 Assessment of Parameters

35

4.1.1 Barangay Kapitolyo

Borehole 1

ground water table = 1.1m

Table 4.1 In-situ Soil Index Properties for Barangay Kapitolyo- Borehole 1

Depth (m)

N- Value Soil Class Dry Unit Weight, γsoil

(kN/m3)

Fines Content (%)

Effective Stress, σ’

(kN/m2)0 0 - - 0 0

1.50 10 CL 15.25 66.78 11.193.00 67 SP 15.72 4.19 23.74

(Terms Concrete Testing, 2011)

Table 4.1shows the subsurface properties in Borehole 1 of Barangay Kapitolyo,

Pasig City. The parameters such as depth, blow count value, soil class, unit weight of

soil, and fines content are the quantities obtained from the soil test reports. The table

shows that parameters vary with depth. The soil’s effective stress depends mainly on

the type of soil and the depth of the water table. The saturation of soil to water

decreases its effective stress due to the accumulation of pore water pressure.

0.97 0.98 0.99 1.00

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

DEFORMABILITY REDUCTION FACTOR

DEPT

H (m

)

Figure 4.1 Deformability Reduction versus Depth of Barangay Kapitolyo-Borehole 1

36

Figure 4.1 shows the relationship of the deformability reduction value (rd) with

respect to depth. The rd decreases as soil exploration extends deeper. The shallower

the depth, the greater deformability reduction factor it receives.

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

EFFECTIVETOTAL

OVERBURDEN PRESSURE (kPa)

DEPT

H (m

)

Figure 4.2 Overburden Pressure versus Depth of Barangay Kapitolyo - Borehole 1

As presented in figure 4.2, the total overburden pressure increases with depth. It

may be monitored that the value of the effective overburden pressure is equal to or less

than the value of the total overburden pressure. The discrepancies between the two

overburden pressure values were derived from the effect of the ground water table

where pore water pressure value was obtained. It may be observed that the changes

between the two plots start at depth 1.5m, and it may be synthesized that it is due to the

water table encounter at depth 1.1m.

37

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00 160.00

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

N-FIELDN-CORRECTED

BLOW COUNT (N-VALUE)

DEPT

H (m

)

Figure 4.3 Blow Count Value versus Depth of Barangay Kapitolyo- Borehole 1

The plotted field blow count values were obtained from bore logs presented in

the soil test results. The corrected blow count values were obtained from field blow

count values multiplied with SPT correction and energy correction as computed per

layer of soil. Correction values were introduced to provide adjustments on possible

errors that the in situ conditions may have incurred. The discrepancies between plots

were amplified starting at depth 1.5m due to the correction values that increased with

depth.

Borehole 2

ground water table= 2.9m

Table 4.2 In-situ Soil Index Properties for Barangay Kapitolyo- Borehole 2

Depth (m)


(kN/m3)

Fines Content (%)


(kN/m2)0 0 - - 0 0

1.50 10 CL 15.25 59.5 11.443.00 59 SP 15.72 4.48 35.02


38

The preceding table 4.2 exhibits the soil conditions obtained from Borehole 2 of

Barangay Kapitolyo. Similarities with the bore logs presented in Table 4.1 and 4.2 may

be observed and it is due to the proximity of the hole locations with each other thus

posting resemblance to soil properties. However, the depth of the encountered ground

water table has a negligible effect to the effective overburden stress of soil.

0.97 0.98 0.99 1.00

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0DEFORMABILITY REDUCTION FACTOR

DEPT

H (m

)

Figure 4.4 Deformability Reduction versus Depth of Barangay Kapitolyo-Borehole 2

It may be observed that in figure 4.4, the deformability reduction value decreases

with the increase in soil depth.

39

0 5 10 15 20 25 30 35 40

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

EFFECTIVETOTAL


DEPT

H (m

)

Figure 4.5 Overburden Pressure versus Depth of Barangay Kapitolyo - Borehole 2

The values of the total and effective overburden pressure plotted in figure 4.5

possess equal quantities. It may be synthesized that ground water level was not

encountered, or had a very negligible effect to soil, thus inducing pore water pressure

equal to 0. The value of the pore water pressure made the total overburden pressure

equal to the effective stress.

0.0010.00

20.0030.00

40.0050.00

60.0070.00

80.0090.00

100.00

-3.5

-3

-2.5

-2

-1.5

-1

-0.5

0

N-FIELDN-CORRECTED


DEPT

H (m

)

Figure 4.6 Blow Count Value versus Depth of Barangay Kapitolyo-Borehole 2

40

As shown in figure 4.6, the field and corrected blow count values are almost

similar up to 1.5 meters of depth. The difference between the two blow count values

beyond the 1.5 meter depth was greatly affected by the required energy correction for it

also increased with depth.

4.1.2 Barangay Manggahan

The table 4.3, as shown below, presents the bore logs of Borehole 1 of Barangay

Manggahan. The soil exploration extended up to 15 layers equivalent to 21 meters of

depth. Similar to the previous logs, Borehole 1 exhibited discrepancies in the soil index

properties per layer.

Borehole 1


Table 4.3 In-situ Soil Index Properties for Barangay Manggahan- Borehole 1

Depth (m)


(kN/m3)

Fines Content (%)


(kN/m2)0 0 - - 0 0

1.50 4 ML 16.50 93.65 12.383.00 5 ML 16.50 81.19 29.774.50 9 ML 16.50 82.31 43.486.00 33 SC 15.72 37.16 56.037.50 11 CL 15.25 96.65 67.869.00 7 CL 15.25 92.37 79.7010.50 9 CL 15.25 90.89 91.5412.00 12 CL 15.25 92.12 103.3813.50 14 CL 15.25 93.71 115.2215.00 20 SC 15.72 36.28 127.7616.50 22 CL 15.25 96.36 139.6018.00 27 CL 15.25 63.18 151.4419.50 43 CL 15.25 80.25 163.2821.00 51 CL 15.25 65.46 175.12


41

0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

-25

-20

-15

-10

-5

0


DEPT

H (m

)

Figure 4.7 Deformability Reduction versus Depth of Barangay Manggahan-Borehole 1

It may be observed that in figure 4.7, the deformability reduction value decreases

as the soil depth increases. The greatest depth reached by SPT which is 21 meters was

calculated to have a depth reduction factor equal to 0.6133.

0.00 50.00 100.00 150.00 200.00 250.00 300.00 350.00

-25

-20

-15

-10

-5

0

EFFECTIVETOTAL


DEPT

H (m

)

Figure 4.8 Overburden Pressure versus Depth of Barangay Manggahan - Borehole 1

As presented in figure 4.8, the total overburden pressure and the depth of the soil

are directly proportionate. It can also be monitored that the value of the effective

42

overburden pressure can be equal to or less than the value of the total overburden

pressure. The discrepancies between the two overburden pressure values were derived

from the effect of the ground water table to the soil where pore water pressure value

was obtained.

0.00 10.00 20.00 30.00 40.00 50.00 60.00

-25

-20

-15

-10

-5

0

N-FIELDN-CORRECTED


DEPT

H (m

)

Figure 4.9 Blow Count Value versus Depth of Barangay Manggahan - Borehole 1

The plotted field blow count values were obtained from bore logs presented in

the soil test results. The corrected blow count values, however, were obtained from field

blow count values multiplied with the two considered corrections, SPT correction and

energy correction, as computed per layer of soil. Correction values were introduced to

provide adjustments on possible errors that the in situ conditions may have incurred.

The behavior of graph shown above represents the different soil characteristics at each

layer. For example, depth 6m required great number of blow count to penetrate through

it, an implication that the layer is tough.

43

Borehole 2


Table 4.4 In-situ Soil Index Properties for Barangay Manggahan- Borehole 2

Depth (m)


(kN/m3)

Fines Content (%)


(kN/m2)0 0 - - 0 0

1.50 4 ML 16.50 93.15 12.383.00 6 ML 16.50 82.79 29.774.50 11 ML 16.50 84.81 43.486.00 35 SC 15.72 32.1 56.037.50 10 CL 15.25 95.58 67.869.00 8 CL 15.25 91.86 79.7010.50 11 CL 15.25 91.35 91.5412.00 13 CL 15.25 90.15 103.3813.50 16 CL 15.25 94.61 115.2215.00 17 SC 15.72 24.69 127.7616.50 22 CL 15.25 96.32 139.6018.00 28 CL 15.25 56.96 151.4419.50 47 CL 15.25 71.68 163.2821.00 54 CL 15.25 61.27 175.12


The table above shows the soil properties that Borehole 2 has. Most of the soil

layers encountered in the soil exploration were classified as inorganic clays with low to

medium plasticity (CL) equivalent to a value of dry unit weight of 15.25kN/m3.Similar to

the previously presented logs, it may be observed that the effective stress increases

with depth.

44

0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

-25.00

-20.00

-15.00

-10.00

-5.00

0.00


DEPT

H (m

)

Figure 4.10 Deformability Reduction versus Depth of Barangay Manggahan–Borehole 2

The deformability reduction values as presented in Figure 4.10 vary with depth.

The values needed to determine the stress induced by a seismic activity to the given

soil is adjusted by the deformability reduction value; thus, it may be synthesized that

reduction increases with depth.

0.00 50.00 100.00 150.00 200.00 250.00 300.00 350.00

-25

-20

-15

-10

-5

0

EFFECTIVETOTAL


DEPT

H (m

)

Figure 4.11 Overburden Pressure versus Depth of Barangay Manggahan –

Borehole 2

45

The difference between the effective stress and the total stress present in the soil

is an implication of ground water table encounter. Soil exploration reached the level

where water induced pore water pressure to soil particles, reducing the amount of

stress needed in order to displace the soil.

0.00 10.00 20.00 30.00 40.00 50.00 60.00

-25

-20

-15

-10

-5

0

N-FIELDN-CORRECTED


DEPT

H (m

)

Figure 4.12 Blow Count Value versus Depth of Barangay Manggahan - Borehole 2

Figure 4.12 shows that most of the blow count value is less than 20. It implies

that the soil sample needed less blows to reach the stable part of the borehole. It may

also be observed that the toughest layer is found at depth 21m because it exceeds 50

blows where standard penetration test is stopped.

46

4.1.3 Barangay Ugong

Borehole 1


Table 4.5 In-situ Soil Index Properties for Barangay Ugong- Borehole 1

Depth (m)


(kN/m3)

Fines Content (%)


(kN/m2)0 0 0 0 0 0

1.00 14 CL 15.25 98 7.633.00 18 CL 15.25 96 15.796.00 20 SM 19.75 45 6.309.00 12 CH 15.00 97 7.1612.00 13 CH 15.00 98 8.0115.00 17 CH 15.00 96 8.8718.00 19 CL 15.25 99 10.47

(DPWH, 2002)

The table above shows the distinctive characteristics of the borehole situated in

Barangay Ugong. It may be monitored that among the effective stresses encountered in

the soil exploration, Borehole 1 of Ugong possesses lowest values. The values

presented in Table 4.5 are implication that the soil in the site has the greatest potential

to be displaced from its current position.

47

0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0


DPET

H (m

)

Figure 4.13 Deformability Reduction versus Depth of Barangay Ugong - Borehole 1

The deformability reduction values posted by figure 4.13 shows that as the soil

exploration extends deeper, the required reduction value is lesser. These values are

used in order to introduce larger adjustments at greater depths in order to determine the

shear- stress induced by a seismic activity.

0.00 50.00 100.00 150.00 200.00 250.00 300.00

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

EFFECTIVETOTAL


DEPT

H (m

)

Figure 4.14 Overburden Pressure versus Depth of Barangay Ugong - Borehole 1

48

It may be observed in the figure above that the values of the effective stress and

the total stress have a large difference. The effective stress of the soil sample is

relatively low; thus, it may be synthesized that it has a great probability of displacement.

The great discrepancy between plots is yielded from the ground water table effect to

soil.

0.00 5.00 10.00 15.00 20.00 25.00 30.00 35.00 40.00 45.00

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

0

N-FIELDN-CORRECTED


DEPT

H (m

)

Figure 4.15 Blow Count Value versus Depth of Barangay Ugong - Borehole 1

The figure shown above presents the differences incurred by the correction

factors introduced to the blow count value obtained in the field. The plots show that

there is a great difference between the in situ values to the required quantity to be used

in determining the liquefaction vulnerability.

49

Borehole 2


Table 4.6 In-situ Soil Index Properties for Barangay Ugong- Borehole 2

Depth (m)


(kN/m3)

Fines Content (%)


(kN/m2)0 0 0 0 0 0

1.00 2 SW 15.29 7 7.653.00 1 SM 19.75 24 22.566.00 3 CH 15.00 80 1.209.00 20 CH 15.00 97 2.0512.00 16 CH 15.00 98 2.9115.00 19 CH 15.00 80 3.7615.90 50 SM 19.75 34 192.8117.95 50 SM 19.75 28 111.6419.95 50 SM 19.75 41 136.41

(DPWH, 2002)

The table above is the bore log for Barangay Ugong- Borehole 2. It may be

observed that the upper layer of the sample is soft soils while the lower layer consists of

hard material. The blow count value and the effective stress, as presented, define the

condition quantitatively. The greater the blow count value, the tougher the soil layer is.

The figure below shows the graph of the reduction factor required for each depth

of the soil sample. Greater adjustments are required as the sample extends deeper.

The reduction factor decreases from 0 meters from the ground up to greater depths.

50

0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

-25

-20

-15

-10

-5

0


DEPT

H (m

)

Figure 4.16 Deformability Reduction versus Depth of Barangay Ugong - Borehole 2

The deformability reduction values posted by figure 4.16 shows that as the soil

exploration extends deeper, the required reduction value is lesser. These values are

used in order to introduce larger adjustments at greater depths in order to determine the

shear- stress induced by a seismic activity.

0.00 50.00 100.00 150.00 200.00 250.00 300.00 350.00

-25

-20

-15

-10

-5

0

EFFECTIVETOTAL


DEPT

H (m

)

Figure 4.17 Overburden Pressure versus Depth of Barangay Ugong - Borehole 2

51

The effective and total overburden plots show great discrepancy; however, the

behavior of the soil property exhibits the large effect of the ground water table. The

presence of water and the soil classification could alter the overburden pressure of soil.

0.00 10.00 20.00 30.00 40.00 50.00 60.00

-25

-20

-15

-10

-5

0

N-FIELDN-CORRECTED

BLOW COUNT (N-VALUE)DE

PTH

(m)

Figure 4.18 Blow Count Value versus Depth of Barangay Ugong - Borehole 2

The blow count values of Borehole 2 show that as the test extends at greater

depths, the greater number of blows it requires. It may be synthesized that the soil gets

harder with depth. Thus, more blow count is needed to penetrate through the layer.

52

4.2 Liquefaction Analysis

4.2.1 Barangay Kapitolyo

Borehole 1

Table 4.7 Elements of Factor of Safety Due to Liquefaction in Barangay Kapitolyo-

Borehole 1

Depth(m)

CSR CRR Magnitude MSF FS

0 0 0

5.0 2.82 -5.5 2.21 -6.0 1.77 -6.5 1.44 -7.0 1.19 -7.5 1.00 -8.0 0.85 -8.5 0.73 -9.0 0.63 -

1.50 0.2570 0.2618

5.0 2.82 2.815.5 2.21 2.206.0 1.77 1.766.5 1.44 1.447.0 1.19 1.197.5 1.00 1.008.0 0.85 0.858.5 0.73 0.729.0 0.63 0.63

3.00 0.2540 1.3882

5.0 2.82 15.095.5 2.21 11.836.0 1.77 9.466.5 1.44 7.717.0 1.19 6.387.5 1.00 5.358.0 0.85 4.538.5 0.73 3.889.0 0.63 3.35

53

0.00 0.50 1.00 1.50 2.00 2.50 3.000.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

M=5M=5.5M=6M=6.5M=7M=7.5M=8M=8.5M=9

DEPTH (m)

FACT

OR O

F SAF

ETY

DUE T

O LIQ

UEFA

CTIO

N

Figure 4.19 Factor of Safety Due to Liquefaction versus Depth of Barangay Kapitolyo- Borehole 1

Table 4.7 and Figure 4.19 show that the shallow layers of the soil in Borehole 1

of Barangay Kapitolyo post greater potential liquefaction since the factor of safety

values is close to or less than 1. The probability of liquefaction occurrence diminishes

with depth. However, the magnitude of the seismic activity greatly affects potential

liquefaction. Non liquefiable zones could be liquefiable at a certain magnitude. For

example, at depth 1.5, it is a non liquefiable up to magnitude 7.0 but the increase in

magnitude makes it susceptible to liquefaction.

54

Borehole 2

Table 4.8 Elements of Factor of Safety Due to Liquefaction in Barangay Kapitolyo-

Borehole 2

Depth(m)

CSR CRR Magnitude MF FS

0 0 0

5.0 2.82 -5.5 2.21 -6.0 1.77 -6.5 1.44 -7.0 1.19 -7.5 1.00 -8.0 0.85 -8.5 0.73 -9.0 0.63 -

1.50 0.2626 0.2618

5.0 2.82 2.885.5 2.21 2.256.0 1.77 1.806.5 1.44 1.477.0 1.19 1.227.5 1.00 1.028.0 0.85 0.868.5 0.73 0.749.0 0.63 0.64

3.00 0.3748 2.0040

5.0 2.82 15.425.5 2.21 12.096.0 1.77 9.676.5 1.44 7.887.0 1.19 6.527.5 1.00 5.468.0 0.85 4.638.5 0.73 3.979.0 0.63 3.425

55

0.00 0.50 1.00 1.50 2.00 2.50 3.000.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

M=5M=5.5M=6M=6.5M=7M=7.5M=8M=8.5M=9

DEPTH (m)

FACT

OR O

F SAF

ETY

DUE T

O LIQ

UEFA

CTIO

N

Figure 4.20 Factor of Safety Due to Liquefaction versus Depth of Barangay Kapitolyo- Borehole 2

Table 4.8 and Figure 4.20 post a similar soil behavior with Borehole 1. It may be

observed that up to magnitude 7.5, no liquefaction occurrence may be expected.

However at magnitude 8.0, depth 1.5m posts liquefaction susceptibility. Quantitatively,

liquefaction occurrence is expressed as a factor of safety less than 1.

56

4.2.2 Barangay Manggahan

Borehole1

Table 4.9 Elements of Factor of Safety Due to Liquefaction in Barangay Manggahan-

Borehole 1

Depth(m)


0 0 0

5.0 2.82 -5.5 2.21 -6.0 1.77 -6.5 1.44 -7.0 1.19 -7.5 1.00 -8.0 0.85 -8.5 0.73 -9.0 0.63 -

1.50 0.26 0.13

5.0 2.82 1.385.5 2.21 1.086.0 1.77 0.876.5 1.44 0.717.0 1.19 0.587.5 1.00 0.498.0 0.85 0.428.5 0.73 0.369.0 0.63 0.31

3.00 0.32 0.17

5.0 2.82 1.515.5 2.21 1.186.0 1.77 0.956.5 1.44 0.777.0 1.19 0.647.5 1.00 0.538.0 0.85 0.458.5 0.73 0.399.0 0.63 0.34

4.50 0.36 0.24 5.0 2.82 1.865.5 2.21 1.466.0 1.77 1.176.5 1.44 0.95

57

7.0 1.19 0.797.5 1.00 0.668.0 0.85 0.568.5 0.73 0.489.0 0.63 0.41

6.00 0.38 0.74

5.0 2.82 5.545.5 2.21 4.346.0 1.77 3.476.5 1.44 2.837.0 1.19 2.347.5 1.00 1.968.0 0.85 1.668.5 0.73 1.429.0 0.63 1.23

7.50 0.39 0.23

5.0 2.82 1.675.5 2.21 1.316.0 1.77 3.986.5 1.44 0.857.0 1.19 0.717.5 1.00 0.598.0 0.85 0.508.5 0.73 0.439.0 0.63 0.37

9.00 0.40 0.15

5.0 2.82 1.065.5 2.21 0.836.0 1.77 1.056.5 1.44 0.547.0 1.19 0.457.5 1.00 0.388.0 0.85 0.328.5 0.73 0.279.0 0.63 0.24

10.50 0.39 0.17

5.0 2.82 1.255.5 2.21 0.986.0 1.77 0.676.5 1.44 0.647.0 1.19 0.537.5 1.00 0.448.0 0.85 0.378.5 0.73 0.329.0 0.63 0.285.0 2.82 1.55

58

12.00 0.38 0.21

5.5 2.21 1.216.0 1.77 0.786.5 1.44 0.797.0 1.19 0.657.5 1.00 0.558.0 0.85 0.468.5 0.73 0.409.0 0.63 0.34

13.50 0.37 0.23

5.0 2.82 1.745.5 2.21 1.376.0 1.77 0.976.5 1.44 0.897.0 1.19 0.747.5 1.00 0.628.0 0.85 0.528.5 0.73 0.459.0 0.63 0.39

15.00 0.35 0.30

5.0 2.82 2.405.5 2.21 1.886.0 1.77 1.096.5 1.44 1.227.0 1.19 1.017.5 1.00 0.858.0 0.85 0.728.5 0.73 0.629.0 0.63 0.53

16.50 0.34 0.31

5.0 2.82 2.635.5 2.21 2.066.0 1.77 1.506.5 1.44 1.347.0 1.19 1.117.5 1.00 0.938.0 0.85 0.798.5 0.73 0.689.0 0.63 0.58

18.00 0.32 0.37 5.0 2.82 3.225.5 2.21 2.536.0 1.77 1.656.5 1.44 1.657.0 1.19 1.367.5 1.00 1.148.0 0.85 0.97

59

8.5 0.73 0.839.0 0.63 0.72

19.50 0.30 0.56

5.0 2.82 5.215.5 2.21 4.086.0 1.77 2.026.5 1.44 2.667.0 1.19 2.207.5 1.00 1.858.0 0.85 1.568.5 0.73 1.349.0 0.63 1.16

21.00 0.29 0.65

5.0 2.82 6.355.5 2.21 4.986.0 1.77 3.276.5 1.44 3.257.0 1.19 2.687.5 1.00 2.258.0 0.85 1.918.5 0.73 1.639.0 0.63 1.41

60

0.00 5.00 10.00 15.00 20.00 25.000.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

Series2Series4Series6Series8Series10Series12Series14Series16Series18

DEPTH (m)

FACT

OR O

F SAF

ETY

DUE T

O LIQ

UEFA

CTIO

N

Figure 4.21 Factor of Safety Due to Liquefaction versus Depth of Barangay Manggahan- Borehole 1

Table 4.9 and Figure 4.21 are the representation of the soil behavior of Borehole

1 of Barangay Manggahan. It may be observed that soil properties vary with depth.

Each layer has a different response to the probable loading during a seismic event.

However, it could be synthesized that the liquefaction vulnerability of a layer could be

greatly affected by the magnitude of the earthquake. The graph shows that the factor of

safety decreases with the increase in magnitude, thus shifting layers to a value closer to

1 which is critical for liquefaction.

61

Borehole2

Table 4.10 Elements of Factor of Safety Due to Liquefaction in Barangay Manggahan-

Borehole 2

Depth(m)


0 0 0

5.0 2.82 -5.5 2.21 -6.0 1.77 -6.5 1.44 -7.0 1.19 -7.5 1.00 -8.0 0.85 -8.5 0.73 -9.0 0.63 -

1.50 0.2570 0.1258

5.0 2.82 1.385.5 2.21 1.086.0 1.77 0.876.5 1.44 0.717.0 1.19 0.587.5 1.00 0.498.0 0.85 0.428.5 0.73 0.369.0 0.63 0.31

3.00 0.3168 0.1960

5.0 2.82 1.755.5 2.21 1.376.0 1.77 1.106.5 1.44 0.897.0 1.19 0.747.5 1.00 0.628.0 0.85 0.528.5 0.73 0.459.0 0.63 0.39

4.50 0.3573 0.2826 5.0 2.82 2.235.5 2.21 1.756.0 1.77 1.406.5 1.44 1.147.0 1.19 0.947.5 1.00 0.798.0 0.85 0.67

62

8.5 0.73 0.579.0 0.63 0.50

6.00 0.3784 0.7683

5.0 2.82 5.735.5 2.21 4.496.0 1.77 3.596.5 1.44 2.937.0 1.19 2.427.5 1.00 2.038.0 0.85 1.728.5 0.73 1.479.0 0.63 1.27

7.50 0.3912 0.2131

5.0 2.82 1.545.5 2.21 1.206.0 1.77 0.966.5 1.44 0.797.0 1.19 0.657.5 1.00 0.548.0 0.85 0.468.5 0.73 0.409.0 0.63 0.34

9.00 0.3985 0.1661

5.0 2.82 1.185.5 2.21 0.926.0 1.77 0.746.5 1.44 0.607.0 1.19 0.507.5 1.00 0.428.0 0.85 0.358.5 0.73 0.309.0 0.63 0.26

10.50 0.3911 0.2035

5.0 2.82 1.475.5 2.21 1.156.0 1.77 0.926.5 1.44 0.757.0 1.19 0.627.5 1.00 0.528.0 0.85 0.448.5 0.73 0.389.0 0.63 0.33

12.00 0.3799 0.2228 5.0 2.82 1.665.5 2.21 1.306.0 1.77 1.04

63

6.5 1.44 0.857.0 1.19 0.707.5 1.00 0.598.0 0.85 0.508.5 0.73 0.439.0 0.63 0.37

13.50 0.3669 0.2551

5.0 2.82 1.965.5 2.21 1.546.0 1.77 1.236.5 1.44 1.007.0 1.19 0.837.5 1.00 0.708.0 0.85 0.608.5 0.73 0.519.0 0.63 0.44

15.00 0.3517 0.2308

5.0 2.82 1.855.5 2.21 1.456.0 1.77 1.166.5 1.44 0.957.0 1.19 0.787.5 1.00 0.668.0 0.85 0.568.5 0.73 0.489.0 0.63 0.41

16.50 0.3364 0.3130

5.0 2.82 2.635.5 2.21 2.066.0 1.77 1.656.5 1.44 1.347.0 1.19 1.117.5 1.00 0.938.0 0.85 0.798.5 0.73 0.689.0 0.63 0.58

18.00 0.3204 0.3792

5.0 2.82 3.345.5 2.21 2.626.0 1.77 2.096.5 1.44 1.717.0 1.19 1.417.5 1.00 1.188.0 0.85 1.008.5 0.73 0.86

64

9.0 0.63 0.74

19.50 0.3038 0.6147

5.0 2.82 5.715.5 2.21 4.476.0 1.77 3.586.5 1.44 2.927.0 1.19 2.417.5 1.00 2.028.0 0.85 1.728.5 0.73 1.479.0 0.63 1.27

21.00 0.2867 0.6849

5.0 2.82 6.745.5 2.21 5.286.0 1.77 4.236.5 1.44 3.447.0 1.19 2.857.5 1.00 2.398.0 0.85 2.028.5 0.73 1.739.0 0.63 1.50

0.00 5.00 10.00 15.00 20.00 25.000.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

M=5M=5.5M=6M=6.5M=7M=7.5M=8M=8.5M=9

DEPTH (m)

FACT

OR O

F SAF

ETY

DUE T

O LIQ

UEFA

CTIO

N

Figure 4.22 Factor of Safety Due to Liquefaction versus Depth of Barangay Manggahan- Borehole 2

65

Table 4.10 and Figure 4.22 are similar to the soil characteristics of Borehole 1 of

Manggahan. The behavior of soil differs with depth. However, magnitude amplifies the

possibility of liquefaction occurrence. For example depth 18m shows no potential

liquefaction at magnitude 5, and from the value of 3.340 it drops to 0.742 at Magnitude

9, thus posting a high rate of vulnerability to liquefaction.

4.2.3 Barangay Ugong

Borehole 1

Table 4.11 Elements of Factor of Safety Due to Liquefaction in Barangay Ugong-

Borehole 1

Depth(m)


0 0 0

5.0 2.82 -5.5 2.21 -6.0 1.77 -6.5 1.44 -7.0 1.19 -7.5 1.00 -8.0 0.85 -8.5 0.73 -9.0 0.63 -

1.00 0.2580 0.3585

5.0 2.82 3.925.5 2.21 3.076.0 1.77 2.466.5 1.44 2.007.0 1.19 1.667.5 1.00 1.398.0 0.85 1.188.5 0.73 1.019.0 0.63 0.87

3.00 0.4908 0.6152 5.0 2.82 3.545.5 2.21 2.776.0 1.77 2.226.5 1.44 1.817.0 1.19 1.50

66

7.5 1.00 1.258.0 0.85 1.068.5 0.73 0.919.0 0.63 0.79

6.00 3.1451 0.6865

5.0 2.82 0.625.5 2.21 0.486.0 1.77 0.396.5 1.44 0.327.0 1.19 0.267.5 1.00 0.228.0 0.85 0.198.5 0.73 0.169.0 0.63 0.14

9.00 4.2253 0.4083

5.0 2.82 0.275.5 2.21 0.216.0 1.77 0.176.5 1.44 0.147.0 1.19 0.127.5 1.00 0.108.0 0.85 0.088.5 0.73 0.079.0 0.63 0.06

12.004.7068 0.4420

5.0 2.82 0.275.5 2.21 0.216.0 1.77 0.176.5 1.44 0.147.0 1.19 0.117.5 1.00 0.098.0 0.85 0.088.5 0.73 0.079.0 0.63 0.06

15.00 4.8746 0.5800

5.0 2.82 0.345.5 2.21 0.266.0 1.77 0.216.5 1.44 0.177.0 1.19 0.147.5 1.00 0.128.0 0.85 0.108.5 0.73 0.099.0 0.63 0.08

0.6507 5.0 2.82 0.41

67

18.00 4.4877

5.5 2.21 0.326.0 1.77 0.266.5 1.44 0.217.0 1.19 0.177.5 1.00 0.158.0 0.85 0.128.5 0.73 0.119.0 0.63 0.09

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.000.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

M=5M=5.5M=6M=6.5M=7M=7.5M=8M=8.5M=9

DEPTH (m)

FACT

OR O

F SAF

ETY

DUE T

O LIQ

UEFA

CTIO

N

Figure 4.23 Factor of Safety Due to Liquefaction versus Depth of Barangay Ugong- Borehole 1

Table 4.11 and Figure 4.23 show that subsurface conditions at depths 1m-3m

are more stable compared to other layers. However, it may be observed that the other

lower layers post potential liquefaction even at a magnitude of 5.0; thus, greater

vulnerability could be expected as the magnitude increases. At magnitude 9.0, it is

predicted that the entire sample are already liquefiable.

68

Borehole 2

Table 4.12 Elements of Factor of Safety Due to Liquefaction in Barangay Ugong-

Borehole 2

Depth(m)


0 0 0

5.0 2.82 -5.5 2.21 -6.0 1.77 -6.5 1.44 -7.0 1.19 -7.5 1.00 -8.0 0.85 -8.5 0.73 -9.0 0.63 -

1.00 0.2580 0.0263

5.0 2.82 0.295.5 2.21 0.236.0 1.77 0.186.5 1.44 0.157.0 1.19 0.127.5 1.00 0.108.0 0.85 0.098.5 0.73 0.079.0 0.63 0.06

3.00 0.4198 0.0597

5.0 2.82 0.405.5 2.21 0.316.0 1.77 0.256.5 1.44 0.217.0 1.19 0.177.5 1.00 0.148.0 0.85 0.128.5 0.73 0.109.0 0.63 0.09

6.00 15.5213 0.1258 5.0 2.82 0.025.5 2.21 0.026.0 1.77 0.016.5 1.44 0.017.0 1.19 0.017.5 1.00 0.018.0 0.85 0.01

69

8.5 0.73 0.019.0 0.63 0.01

9.00 14.1445 0.6865

5.0 2.82 0.1375.5 2.21 0.1076.0 1.77 0.096.5 1.44 0.077.0 1.19 0.067.5 1.00 0.058.0 0.85 0.048.5 0.73 0.049.0 0.63 0.03

12.00 12.5881 0.5450

5.0 2.82 0.125.5 2.21 0.106.0 1.77 0.086.5 1.44 0.067.0 1.19 0.057.5 1.00 0.048.0 0.85 0.048.5 0.73 0.039.0 0.63 0.03

15.0011.2199

0.6507

5.0 2.82 0.165.5 2.21 0.136.0 1.77 0.106.5 1.44 0.087.0 1.19 0.077.5 1.00 0.068.0 0.85 0.058.5 0.73 0.049.0 0.63 0.04

15.900.2509

0.5943

5.0 2.82 6.695.5 2.21 5.246.0 1.77 4.196.5 1.44 3.427.0 1.19 2.837.5 1.00 2.378.0 0.85 2.018.5 0.73 1.729.0 0.63 1.49

17.95 0.4489 0.7503 5.0 2.82 4.725.5 2.21 3.706.0 1.77 2.96

70

6.5 1.44 2.417.0 1.19 1.997.5 1.00 1.678.0 0.85 1.428.5 0.73 1.219.0 0.63 1.05

19.95 0.3880 0.7201

5.0 2.82 5.245.5 2.21 4.116.0 1.77 3.296.5 1.44 2.687.0 1.19 2.217.5 1.00 1.868.0 0.85 1.578.5 0.73 1.359.0 0.63 1.16

0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00 16.00 18.00 20.000.00

1.00

2.00

3.00

4.00

5.00

6.00

7.00

8.00

M=5M=5.5M=6M=6.5M=7M=7.5M=8M=8.5M=9

DEPTH (m)

FACT

OR O

F SAF

ETY

DUE T

O LIQ

UEFA

CTIO

N

Figure 4.24 Factor of Safety Due to Liquefaction versus Depth of Barangay Ugong- Borehole 2

Table 4.12 and Figure 4.24 show the behavior of soil layers with respect to the

increase in magnitude of the seismic activity. It may be observed that liquefaction

susceptibility from depth 0m to depth 15m is present even under a low magnitude of 5.

71

Hence, under a seismic activity, the lateral load induced by earthquake overpowers the

reaction force of the soil.

4.3 Mitigation Measures for the Soil and/or the Foundation

Table 4.13 Mitigation Measures for Barangay Kapitolyo Borehole 1

Magnitude Depth of Liquefiable Zone (m) Mitigation Measures

5.0 - Shallow foundations5.5 - Shallow foundations6.0 - Shallow foundations6.5 - Shallow foundations7.0 - Shallow foundations7.5 - Shallow foundations8.0 - Shallow foundations8.5 - Shallow foundations9.0 1.50 Soil improvement

The table above shows the recommended mitigation measures for the soil of the

selected vicinity in Barangay Kapitolyo for Borehole 1. The action to be applied is

determined by the depth of the liquefiable zone.

A practical limit for unbraced or open excavations for shallow foundations is eight

feet (2.48 meters) (French, 1930). If the depth of the affected soil is within this range,

soil improvement in the affected soil depths may be applied to strengthen the soil. If the

depth of the liquefiable zone exceeds the maximum depth for shallow foundations, two

choices may be enforced. Either there will be a soil improvement in the affected soil

depths or pile foundation will be used.

72

Table 4.14 Mitigation Measures for Barangay Kapitolyo Borehole 2

Magnitude Depth of Liquefiable Zone(m) Mitigation Measures

5.0 - Shallow foundations5.5 - Shallow foundations6.0 - Shallow foundations6.5 - Shallow foundations7.0 - Shallow foundations7.5 - Shallow foundations8.0 - Shallow foundations8.5 - Shallow foundations9.0 1.50 Soil improvement

The table above shows the recommended mitigation measures for the soil of the

selected vicinity in Barangay Kapitolyo for Borehole 2. The action to be applied is








73

Table 4.15 Mitigation Measures for Barangay Manggahan Borehole 1


5.0 - Shallow Foundation5.5 3.00 Soil Improvement6.0 7.50 Pile Foundation6.5 12.00 Pile Foundation7.0 12.00 Pile Foundation7.5 15.00 Pile Foundation8.0 16.50 Pile Foundation8.5 16.50 Pile Foundation9.0 16.50 Pile Foundation

The table above shows the recommended mitigation measures for the soil and

the foundation of the selected vicinity in Barangay Manggahan for Borehole 1. The

action to be applied is determined by the depth of the liquefiable zone.







74

Table 4.16 Mitigation Measures for Barangay Manggahan Borehole 2


5.0 - Shallow Foundation5.5 - Shallow Foundation6.0 6.00 Pile Foundation6.5 7.50 Pile Foundation7.0 13.50 Pile Foundation7.5 15.00 Pile Foundation8.0 15.00 Pile Foundation8.5 16.50 Pile Foundation9.0 16.50 Pile Foundation

The table above shows the recommended mitigation measures for the soil and

the foundation of the selected vicinity in Barangay Manggahan for Borehole 2. The

action to be applied is determined by the depth of the liquefiable zone.







75

Table 4.17 Mitigation Measures for Barangay Ugong Borehole 1


5.0 7.50 Pile Foundation5.5 7.50 Pile Foundation6.0 7.50 Pile Foundation6.5 7.50 Pile Foundation7.0 7.50 Pile Foundation7.5 7.50 Pile Foundation8.0 7.50 Pile Foundation8.5 9.00 Pile Foundation9.0 10.50 Pile Foundation

The table above shows the recommended mitigation measures for the foundation

of the selected vicinity in Barangay Ugong for Borehole 1. The action to be applied is








76

Table 4.18 Mitigation Measures for Barangay Ugong Borehole 2


5.0 9.00 Pile Foundation5.5 9.00 Pile Foundation6.0 9.00 Pile Foundation6.5 9.00 Pile Foundation7.0 9.00 Pile Foundation7.5 9.00 Pile Foundation8.0 9.00 Pile Foundation8.5 9.00 Pile Foundation9.0 9.00 Pile Foundation

The table above shows the recommended mitigation measures for the foundation

of the selected vicinity in Barangay Ugong for Borehole 2. The action to be applied is








77

Chapter 5

Summary of Findings, Conclusion and Recommendation

5.1 Summary of Findings

The factor of safety due to liquefaction calculated through the simplified

procedure formulated by Seed and Idriss shows that the behavior of soil varies with

classification, depth of water table and magnitude. It may be monitored from the

presented tables of the preceding chapter that the blow count values and undrained

shear strength may project the factor of safety due to liquefaction.

Table 5.1 Summary of Liquefaction Susceptibility of the Selected Locations

Magnitude Ugong Manggahan Kapitolyo5.00 0.12 1.06 2.815.50 0.10 0.83 2.206.00 0.08 0.67 1.766.50 0.06 0.54 1.447.00 0.05 0.45 1.197.50 0.04 0.38 1.008.00 0.04 0.32 0.848.50 0.03 0.27 0.729.00 0.03 0.24 0.62

Table 5.1 shows the susceptibility of the locations to liquefaction. It may be

observed that Barangay Ugong and Manggahan exhibit vulnerability since the yielded

factor of safety is less than 1at any given magnitude. However, Barangay Kapitolyo

shows partial susceptibility. Liquefaction occurrence starts at magnitude 7.5 while the

factor of safety exceeds the critical value of 1 at lower magnitudes.

78

By comparing the selected sites’ potential liquefaction, it was identified that

Borehole 2 in Barangay Ugong at depth 6m has the greatest vulnerability. It was

determined through its value of factor of safety due to liquefaction that the induced

lateral force of a seismic event overcomes most layer of the soil’s lateral force, thus

posting an FS value less than 1. Results show that magnitudes 5, 5.5, 6, 6.5, 7, 7.5, 8,

8.5, and 9 yielded factor of safety values of 0.12, 0.10, 0.08, 0.06, 0.05, 0.004, 0.004,

0.003 and 0.003 respectively.

The probable foundation or mitigation used for the safety of the future

establishments that may be developed on the specific locations was considered in the

study. For the specific location in barangay Manggahan and Ugong, liquefaction will

occur at a magnitude 7.5 earthquake, in which the Valley Fault System is capable of

producing; thus, settlement will occur and pile foundations are recommended in these

locations. The data for the specific location in barangay Kapitolyo show that shallow

foundations can be safe from liquefaction up until a magnitude 9 earthquake; thus, only

soil improvement is recommended.

5.2 Conclusions

The figure below shows the vulnerability of the three selected locations along the

Pasig city segment of the Valley Fault System. This presents the most vulnerable area

among the three locations which is the site in Barangay Ugong. This is followed by

barangay Manggahan. And among the three locations, Barangay Kapitolyo shows

greatest resistance against liquefaction occurrence.

79

0.00 0.50 1.00 1.50 2.00 2.50 3.004.00

5.00

6.00

7.00

8.00

9.00

10.00

SAFEUGONGMANGGAHANKAPITOLYO

FACTOR OF SAFETY DUE TO LIQUEFACTION

MAG

NITU

DE

Figure 5.1 Summary of Liquefaction Susceptibility of the Selected Locations

Based on the blow count values (N-Field) and undrained shear strength of each

layer of soil considered in this study, the factor of safety due to liquefaction values was

grouped into their respective soil profile type. The individual values of factor of safety

classified for each soil type were used to provide the range of the probable factor of

safety for each profile.

80

Table 5.2 Augmented Table of Soil Profile Types

Soil Profile Type

Soil Profile Name/

Generic Description

Average Soil Properties for Top 30m of Soil ProfileShear Wave

Velocity, Vs (m/s)

SPT, N (blows/300mm)

Undrained Shear

Strength, SU (kPa)

Factor of Safety Due to

Liquefaction, FS (at Magnitude 7.5)

SA Hard Rock >1500 -SB Rock 760 to

1500-

SC Very Dense Soil and

Soft Rock

360 to 760

>50 >100 >2

SD Stiff Soil Profile

180 to 360

15 to 50 50 to 100 >1 but <2

SE1 Soft Soil

Profile<180 <15 <50 <1

SF Soil Requiring Site-specific Evaluation

(National Structural Code of the Philippines, 2010)

Table 5.2 shows the average properties of soil for top 30m of soil profile. The

original table obtained from the National Structural Code of the Philippines 2010 was

augmented based from the results yielded by the researchers. In determining the range

of factor of safety due to liquefaction for each soil type, blow count values and

undrained shear strength were considered. It may be synthesized from the results that

Soft Soil Profile (SE) is vulnerable to liquefaction since the expected factor of safety due

to liquefaction is less than or equal to the critical value of FS which is 1. On the other

hand, Stiff Soil Profile (SD) has an FS range of greater than 1 but less than or equal to 2

and Very Dense Soil, and Soft Rock (SC) has an FS value of greater than 2 which can

be considered as non liquefiable stratum.

Potential liquefaction in the selected locations is considered in determining the

probable mitigation measures for the soil and/ or the type of foundation that can be

81

applied to the selected areas. The summation of the liquefiable depths is referred as the

possible settlement of the soil. At a given magnitude, the soil may liquefy and the

affected soil will act as liquid; thus, the tough layers in between the liquefiable zones will

settle up to the depth of the deepest liquefiable stratum. This data can then be

considered for soil improvement or pile foundation.

5.3 Recommendations

Through the yielded values of factor of safety due to liquefaction, the extent of

mitigation can now be determined. The measures that will be applied will depend on the

severity of the site’s vulnerability to liquefaction. In the case of the site in Barangay

Ugong, where most of its layers are comprised of soft soils and the factor of safety is

below the critical value of 1, soil improvement must be considered on the soils where

light structures like residential houses are to be built. On the other hand, pile

foundations must be considered if heavy structures like high rise building are to be built

in the selected site.

The augmented soil profile type table may provide the probable values of factor

of safety at specific soil classification. The table will enable the people concerned to

determine the probable mitigation measures that the location requires, given the extent

of the site’s susceptibility to liquefaction.

Further studies may be conducted in determining the potential liquefaction of

other locations within the selected baranggays. The quantification of their susceptibility

to such condition will enable future researchers to create a model that could generalize

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the susceptibility of each baranggay to liquefaction. It can also provide precision to the

range of values of factor of safety due to liquefaction in the augmented soil profile type

table.

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Chapter 6

Bibliography

Arab, A., Shahrour, I., & Lancelot, L. (2010). A Laboratory Study of Liquefaction of

Partially Saturated Sand. Journal of Iberian Geology, 37(1), 29-36. Retrieved July

2011, doi: 10.5209/rev_JIGE.2011.v37.n1.2

Gordon A. Fenton, G.M. Paice, & D. V. Griffiths (1978). Probabilistic Analysis of

Foundation Settlement

Guyer, J. P.,P.E., R.A., Fellow ASCE, Fellow AEI. (2009), An Introduction to Soil

Grouting

Ozcep, F. & Zarif H. (2009). Variations Of Soil Liquefaction Safety Factors Depending

On Several Design Earthquakes In The City Of Yalova. Scientific Research and

Essay, 4(6), 594-604.

Perkins (2001). The REAL Dirt on Liquefaction. Earthquake Program Manager,

Association of Bay Area Governments

Poulos (2000). Foundation Settlement Analysis – Practice versus Research (The Eighth

Spencer J. Buchanan Lecture). TX 77840: College Station Hilton 810 University

Drive East College Station.

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Raychowdhury, P. & Basudharz P.K. (2011). Liquefaction Characteristics Evaluation

Through Different Stress- Based Models. A Comparative Study. Journal of

Engineering Research and Studies. 2(2), 131-142.

Sumer, B., Ansal A., & Cetin, K. (2007). Earthquake Induced Liquefaction around

Marine Structures. Journal of Waterway, Port, Coastal, and Ocean Engineering.

Retrieved July 2011, doi: 10.1061/_ASCE_0733-950X_2007_133:1_55_

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Documents

Potential Liquefaction of Locations Along the Pasig city Segment of the Valley Fault System