Mukaichi - Large and deep cast-in-place reinforced concrete piles using shaft grout.pdf

8/14/2019 Mukaichi - Large and deep cast-in-place reinforced concrete piles using shaft grout.pdf

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1 INTRODUCTION

This is the final report on the pile loading tests for the piles for piers at MP2 through MP7 of the Main Bridge

on the river prepared based on the previous preliminary and interim reports on the pile loading tests. This re-port consists of studies on the causes of this unusual phenomenon of piles, review of factors to determinebearing capacity of piles and the load test results including analysis of the reads of the strain gauges, and de-termination of countermeasures to increase bearing capacity of the piles for piers with estimation of bearingcapacity after the grouting.

Figure 1. Location Map

Figure 2. General View of Rupsa Bridge

IABSE-JSCE Joint Conference on Advances in Bridge Engineering-II, August 8-10, 2010, Dhaka, Bangladesh. ISBN: 978-984-33-1893-0

Amin, Okui, Bhuiyan (eds.) www.iabse-bd.org

Large and deep cast-in-place reinforced concrete piles using of shaftgrout

Hiroaki MukaichiOriental Consultants C., Ltd., Hanoi 1000, Vietnam

ABSTRACT:The Main Bridge of Rupsa Bridge has 5 spans with the length of 100.00 m in the middle and2 spans with the length of 70.00 m on both ends. Foundations for the mid-piers on the river (MP2 throughMP7) are cast-in-situ reinforced concrete piles with the diameter of 2,500 mm and those for the end piers onland (MP1 and MP8) are the same with the diameter of 900 mm. The Contract requires static pile loadingtests and detailed soil investigations for review of the design length of piles shown on the ContractDrawings. Accordingly a pile loading test for the piles of piers of the Main Bridge on the river wasconducted in May 2002. However large settlement of the test pile was observed during the first PileLoading Test (PLT No.1). Therefore the second Pile Loading Test (PLT No.2) was decided to carry out onJuly 2002. However the same results were realized in the first stage of the PLT No.2 and the PLT No.2 wassuspended temporarily. Since the results of the PLT No.1 and the first stage of the PLT No.2 were notsatisfactory, the second stage of the PLT No.2 and the third Pile Loading Test (PLT No.3) were conductedafter execution of grouting for the test piles on 22 through 25 November 2002 and 12 through 15 January2003, and the both tests completed with satisfactory results.


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2 PILE LOADING TESTS

2.1 Features of Test Pile

Features of the test piles are as shown below.1) Type of Piles : Cast-in-situ reinforced concrete piles2) Diameter : 2.50 m3) Length : 74.0 m (No.1), 79.0 m (No.2), 90.5 m (No.3)4) Ultimate Bearing Capacity : 55,200 kN5) Allowable Bearing Capacity : 22,100 kN (Factor of safety : 2.5)

6) Bearing Layer : Silty fine sand (N = 50 or more)7) Sub-surface Layer : Silt - Silty fine sand (N = 15 - 50)8) Construction Site : River (Riverbed depth : 10 m, Scouring depth : 25 m)9) Drilling Method : Reverse Circulation Method

Figure 3. Geological Condition

2.2Results of Pile Loading Tests

(1) Pile Loading Test No.1

Results of the PLT No.1 are shown in Table 2 on the next page. When the test load reached 10,800 kN, largesettlement of the test pile started occurring and settlement of the pile was 26 cm, more than 10 % of the pilediameter at the test load of 21,600 kN, which is the working load on the piles for piers of the Main Bridgeon the river. Then the final settlement reached 63 cm at the maximum test load of 32,400 kN. The pile tiplayer is silty fine sand, which has high mica content, which is compressive soil. When the test loadincreased, skin friction reached ultimate and all the test loads reached the tip. Then it is considered that the

pile tip layer failed progressively and large settlement occurred.

Table 1. Results of Pile Loading Test No.1

Settlement (mm)Description

Load : 21,600 kN Load : 33,300 kNAfter loading 253 619Gross

After holding 268 630Residual After releasing 257 618

Rebound 11 12

For details, refer to a figure of Load - Settlement Curve of the PLT No.1 and a table of settlement at variousloading stage.

(2) First Stage of Pile Loading Test No.2

Results of the first stage of the PLT No.2 are shown in Table 2 below.


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When the test load reached 7,800 kN, large settlement of the test pile started occurring and settlement of thepile was 33 cm, when the test load reached 21,600 kN. Thus the PLT No.2 was suspended to find cause andstudy on countermeasures.

For details, refer to a figure of Load - Settlement Curve of the first stage of the PLT No.2 and a table ofsettlement at various loading stage.

Table 2. Results of Fist Stage of Pile Loading Test No.2

Settlement (mm)Description

Load : 21,600 kNAfter loading 250Gross

After holding 328Residual After releasing 319Rebound 9

(3) Second Stage of Pile Loading Test No.2

Results of the second stage of the PLT No.2 are shown in Table 3 below.The settlement of the test pile was 8 mm at the design load of 21,600 kN and 14 mm at the maximum testload of 32,400 kN. The settlement after grouting was remarkably small compare to that before grouting.Residual settlement was only 2 mm. Soil around the test pile was still elastic zone at the maximum test loadsof 32,400 kN. Therefore ultimate bearing capacity of the pile is expected to be much larger than the 32,400kN.

Table 3. Results of Second Stage of Pile Loading Test No.2

Settlement (mm)

Description Cycle 1Load : 21,600 kN

Cycle 2Load : 32,400 kN

Gross 8.3 14.0

Residual 1.0 2.3Rebound 7.3 11.7

For details, refer to a figure of Load - Settlement Curve of the second stage of the PLT No.2 and a table ofsettlement at various loading stage.

0

50

100

150

200

250

300

350

400

450

500

550

600

650

0 550 1100 1650 2200 2750 3300 3850

Load (ton)

Settlement(mm)

Figure 4. Load-Settlement Curve

-80

-75

-70

-65

-60

-55

-50

-45

-40

-35

-30

-25

-20

-15

-3,500 -3,000 -2,500 -2,000 -1,500 -1,000 -500 0

Load (ton)

Elevation(m)

Figure 5. Axis Force of Test Piles

PLT

PLT No.2 before

PLT No.2 after

32,400

26 500 kN

Axis Force of Test

Test

Depth


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In accordance with the results of the second stage of the PLT No.2 after grouting, skin friction and endbearing of the Test Pile No.2 are evaluated as shown in Table 4 below.

Table 4. Skin Friction and End Bearing of Test Pile No.2 after Grouting

Ultimate Bearing Capacity

Skin Friction End BearingSoilType

Depthof

Strata Unit Total Bearing Capacity

(Unit) (m) (kPa) (kN) (kN) (kN)Silt 1 22.0 44 7,650 - 7,650

Silt 2-1 12.0 39 3,700 3,700Silt 2-1 16.0 78 9.900 - 9.900

Sand 19.0 74 10,950 2,450 13,400Weight - - - -2,350 -2,350

Total - - 33,200 100 33,300

In accordance with the reads of strain gages, skin friction was still under development with increase of testload. Therefore the ultimate skin friction is expected to be larger than the above figure.


The PLT No.3 was conducted using Osterberg Cell Method. Osterberg Cell Method is a test method loadingby Osterberg Cell embedded in a pile. Own weight of the pile above a cell, and skin friction of the pilesabove and below the cell act reaction each other. Therefore reaction piles are not required for this pileloading test method. Results of the PLT No.3 are shown in Table 5 below.

Table 5. Results of Pile Loading Test No.3

Settlement (mm)Description Stage 1

Load : 22,600 kNStage 2

Load : 33,300 kN

Gross 51 41Residual 39 26

Rebound 12 15

The load by the upper cell was 22,600 kN and the load by the lower cell was 33,300 kN 2 = 66,600 kN.The effective maximum test loads of PLT No.3 were about 89,200 kN after adjustment of own weight of the

pile. Since surrounding soil of the pile did not reach ultimate stage at the effective maximum test load of81,400 kN, it is expected that the ultimate bearing capacity of the Test Pile is greater than 81,400 kN.

In accordance with the results of the PLT No.3 after grouting, skin friction and end bearing of the TestPile No.3 is evaluated as shown in Table 6 below.

Table 6. Skin Friction and End Bearing of Test Pile No.3 after GroutingUltimate Bearing Capacity

Skin Friction End BearingSoil TypeDepth

ofStrata Unit Total Bearing Capacity

(Unit) (m) (kPa) (kN)) (kN) (kN)Sand / Silt 1 29.5 20 4,800 - 4,800

Silt 2 11.0 52 4,500 - 4,500Clay 6.0 102 4,800 - 4,800

Silt 3 6.0 230 10,900 - 10,900Sand 27.5 219 47,300 11,950 59,250

Weight - - - -2,450 -2,450

Total 80.0 - 72,300 9.500 81,800

Since the surrounding soil did not reach ultimate stage, skin friction of the Test Pile No.3 is estimated to be

greater than that shown in the table above.(5) Summary of Piles Loading Test ResultsResults of each pile loading test are shown in Table 7 below.

Table 7. Summary of Piles Loading Test Results

PLT No.1 PLT No.2 PLT No.3Description Unit

- Stage 1 Stage 2 Stage 1 Stage 2

Date - 8 May 2002 27 July 2002 22 Nov. 2002 13 Jan. 2003 15 Jan. 2003Test Load kN 33,300 21,600 32,400 22,600 33,300

Settlement mm 630 325 14 51 41Rebound mm 10 10 12 12 15

Notes :1. The PLT No.1 and the PLT No.2 were conducted by Reaction Pile Method. The test load was charged on the pile heads.2. In the PLT No.2, the first stage was conducted before grouting and the second stage was conducted after grouting.


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3. In the PLT No.3, test load was charged by the lower cell in the first stage and test load was charged by the upper cell with freemode of the lower cell in the second sage.4. Analysis of Pile Loading Test Results

3 EFFECTS OF GROUTING

3.1Results of Bearing Capacity

Increase of beating capacity of test piles by grouts is shown in this section.

(1) Second Stage of Pile Loading Test No.2As the results of the first and second stages of the PLT No.2, the increase of bearing capacity by thegrouting is 21,600 kN as shown in Table 8 below.

Table 8. Comparison of Bearing Capacities of Test Pile No.2 and after Grouting

Description PLT No. Unit Value Method Remarks

Bearing Capacity after Grouting PLT No.2 Second Stage kN 32,400 Evaluation Note 1

Bearing Capacity before Grouting PLT No.2 First Stage kN 10,800 Evaluation Note 2

Bearing Capacity with Grouting - kN 21,600 Calculation

Notes :1. 32,400 kN is the maximum test load of the second stage of the PLT No.2, and the Test Pile No.2 has not reached the ultimatestage. Therefore it is recognized that the ultimate bearing capacity of the Test Pile No.2 is 32,400 kN or more. Based on the load -settlement curve of the second stage of the PLT No.2 shown in Table 3 and those of the previous tests, however, it is estimatedthat actual ultimate bearing capacity of the Test Pile No.2 is 49,000 kN or more.

The settlement of the Test Pile No.2 was only14.0 mm at the maximum test load of 32,400 kN. Meanwhile the load - settlementcurve of the second stage of the PLT No.2 is still almost a straight line up to the maximum test load and the residual settlementwas 2.3 mm only. These facts indicate that the surrounding soil of the Test Pile No.2 still has elastic behavior. Therefore it isexpected that larger load is required that the Test Pile No.2 reaches the ultimate stage.Since the piles for piers of the Main Bridge on the river are supported by sandy soil at the pile tips, settlement of the piles is larger

but the transitional range from elastic zone to ultimate stage is wider compare to those when piles are supported by bedrock. Fromthis point of view, it is determined that the ultimate bearing capacity of the Test Pile No.2 after grouting is 1.5 times of themaximum test load or more (32,400 kN 1.5 = 48,500 kN, approximately 49,000 kN) referring to the load - settlement curves ofthe other pile loading tests in this project.2. 10,800 kN is the ultimate bearing capacity of the Test Pile No.2 before grouting determined based the load - settlementobtained by the results of the first stage of the PLT No.2.Ultimate stage is a situation that settlement of a pile progresses without increase of load and a load - settlement is almost parallelto the vertical axis. According to the load - settlement curve of the first stage of the PLT No.2, therefore, it has been decided thatultimate bearing capacity of the Test Pile No.2 is 10,800 kN.The soil at the pile tip is silty fine sand, which has very special characteristic due to high mica content. This is compressive soil

and causes progressive failure of soil at the pile tip with large settlement of the pile. At test load of 10,800 kN, creep phenomenonthat settlement continues increasing at the same load, occurred and the surrounding soil already showed plastic behavior.Meanwhile it is realized that when the test load increased more, very large settlement is observed, but end bearing was still underdevelopment. From a point of shear strength of surrounding soil, it is recognized that surrounding soil has not reached theultimate stage and ultimate bearing capacity is larger. However this large settlement is not acceptable from the point of function ofa bridge. Therefore, it has been concluded that 10,800 kN, which is the test load when surrounding soil reached a plastic zone,shall be the ultimate bearing capacity of the Test Pile No.2 before grouting.


As the results of the PLT No.1 and the PLT No.3, the increase of bearing capacity by the grouting is 65,600kN as shown in Table 9 blow. Since the PLT was conducted 1 month after construction of the Test Pile

No.3, it is recognized that only the effect of grouting has increased bearing capacity of the pile without anyeffect of recovery of surrounding soil due to its remolding.

Table 9 : Comparison of Bearing Capacities of Test Pile No.3 before and after Grouting

Description PLT No. Unit Value Method Remarks

Bearing Capacity after Grouting PLT No.3 kN 8,340 Evaluation Note 3

Bearing Capacity before GroutingPLT No.1PLT No.2

kN 1,375Evaluation(Reference)

Note 4

Bearing Capacity with Grouting kN 6,965 Calculation

Notes :3. 81,800 kN is the ultimate bearing capacity of the Test Pile No.3 determined by the results of the PLT No.3 and the Test Pile

No.3 has not reached the ultimate stage by the effective maximum test load of 83,200 kN. Therefore it is recognized that ultimatebearing capacity of the Test Pile No.3 is 81,800 kN or more.The PLT No.3 was conducted using Osterberg Cell Method and load cells (O-Cells) were embedded in the Test Pile No.3. In thePLT No.3, the actual maximum test load by the lower load cell was 22,800 kN and that of the upper load cell was 33,300 kN.Taking consideration of balance of resistance to the load i.e. skin friction, end bearing and pile weight, of each side of the loadcells, the test load by the lower cell worked effectively to the downward direction of the load cell only, but that by the upper cell


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worked to both upward and downward directions from the load cell.Accordingly, the effective maximum test load was 81,200 kN after deduction of the pile weight of 6,300 kN from the actualmaximum test load. As the results of analysis of the special company conducted this loading test, the effective maximum test loadwas 81,350 kN with consideration of load loss and load transfer to the other cell.The ultimate bearing capacity of 81,800kN was estimated according to the net unit skin friction of each pert of the pile and theend bearing evaluated based on the results of analysis on the data of the PLT No.3 by the special company.4. Since a pile loading test was not conducted on the Test Pile No.3 before grouting, average of the bearing capacities of the TestPile No.1 and the Test Pile No.2 before grouting was applied as that of the Test Pile No.3 before grouting for this estimation.With the same consideration as the first stage of the PLT No.2, the ultimate bearing capacity of the PLT No.1 has beendetermined to be 16,200 kN.

As shown in results of the PLT No.1 and the first stage of the PLT No.2, large settlement of the test pilesoccurred before grouting. It is evaluated that the ultimate bearing capacities of those piles are 10,800 kN forthe Test Pile No.1 and 16,200 kN for the Test Pile No.2. These figures are less than working load of the

piles.A comparison between the results of the PLT No.1 and the first stage of the PLT No.2 conducted before

grouting, and the results of the second stage of the PLT No.2 and the PLT no.3conducted after groutingshow, settlement of the test piles decreased remarkably the after grouting. As the results, it is estimated thatincreased bearing capacities by grouting are 40,000 kN or greater for the Test Pile No.2 and 70,000 kN to80,000 kN for the Test Pile No.3.

3.2 Estimation of Bearing Capacity

In accordance with the results of the second stage of the PLT No.2 and the PLT No.3, the bearing capacities

of the test piles are estimated as shown below.(1) Test Pile No.2The maximum test load of the second stage of the PLT No.2 was 32,400 kN. But the soil surrounding theTest Pile No.2 did not reach ultimate stage. Therefore it is expected that the ultimate bearing capacity of theTest Pile No.2 is more than 49,000 kN as mentioned above.

(2) Test Pile No.3The maximum test load of the PLT No.3 was 81,800 kN. But the soil surrounding the Test Pile No.3 did notreach ultimate stage at this load. Therefore it is expected that the ultimate bearing capacity of the Test Pile

No.3 is 83,300 kN or greater.

4. COUNTERMEASURES

4.1Alternatives of Countermeasures

After completion of the first stage of the PLT No.2, studies on countermeasures against the large settlementto increase bearing capacity or decrease loads acting on the piles.The following possible alternatives were studied.1) Increase of bearing capacity by grouting (End bearing and skin friction)2) Increase of bearing capacity by extension of pile length3) Decease of load by increase of number of piles

4.2Results of Studies on Countermeasures

Outline and results of studies on countermeasures are shown below.

(1) Increase of Bearing Capacity by GroutingThis method has past record to be applied in cities where bearing strata is situated in deep such as HongKong and Bangkok. This method is expected to increase bearing capacity of a pile remarkably andeconomical compare to extension of pile length to bearing strata.

(2) Increase of Bearing Capacity by Extension of Pile LengthSince skin friction in silty fine sand layer is estimated almost 0 Pa, extension of pile length within this layeris expected to has no effect. Meanwhile it has realized that there is a clay layer at the depth of 100 m.However this layer cannot consider as sufficient bearing layer due to its high moisture content. According tothe result of trial calculation, therefore it has been concluded that the pile tip shall be penetrated till EL-140m. In case that pile length exceeds 85 m, it is necessary to reinforce the present machines and equipment, ormobilize new machines and equipment.


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(3) Decease of Load by Increase of Number of PilesAccording to requirements of river control and size of the pile caps, 9 piles in 3 rows are maximum numbersof pile per pile cap. It is impossible to obtain sufficient bearing capacity by increase of 3 numbers of pileswithout other countermeasures such as grouting.Therefore this option cannot be applied as a countermeasure independently and shall be used as subsidiarymeasures with the above 2 options if necessary.

4.3 Selection of Countermeasures

As the results of the above study, it was decided that the grouting should be applied as a countermeasure toincrease bearing capacity of the piles. The following types of grouting were applied for the piles for piers ofthe Main Bridge on the river.1) Constructed Piles : Toe Grout, Skin Grout (Execution of grouting around the piles)2) Constructing Piles : Base Grout, Shaft Grout(Execution of grouting from inside of the piles)Refer to schematic drawing for further information of groutingSince the bearing capacity of the Test Pile No.3 was much greater than it had been expected and there was asmall different in sin frictions between silt layer and silty fine sand layer, it was decided to maintain theoriginal pile length of 75 m. However for consideration of further safety of the bridge, shaft grout length has

been decided to extend by 5 m to 35 m from 30 m applied for the Test Pile No.3.Estimate values of skin friction, end bearing and ultimate bearing capacity of the piles in case of pile lengthof 75 m and shaft grout length of 35 m. As shown in Table 10 below, the pile is expected to be with factor ofsafety of 2.5 or more against the estimated working load.

Table 10. Skin Friction and End Bearing of Piles for Piers

Ultimate Bearing Capacity

Skin Friction End BearingSoil TypeDepth

ofStrata Unit Total Bearing Capacity

(Unit) (m) (kPa) (kN) (kN) (kN)Sand / Silt 1 15.0 2.0 2,450 - 2,450

Silt 2 11.0 115 9,900 - 9,900Clay 6.0 230 4,800 - 4,800

Silt 3 6.0 230 10,900 - 10,900Sand 12.0 230 20,600 11,950 32,550

Weight - - - -2,450 -2,450

Total 50.0 - 48,650 9,500 58,150

5. CONSIDERATIONS

5.1Increase of Bearing Capacity by Remolding of Surrounding Soil

During the study on increase of bearing capacity of the piles, effect on recovery of strength of surroundingsoil due to its remolding after casting concrete of a pile has been considered. The results of study aresummarized as shown below.

(1) Relationship between Construction, Loading and Results of Pile Loading TestsThe relationship between casting concrete of the test piles and loading with the test results is summarized asshown in Table 11 below.

Table 11. Relationship between Construction, Loading and Result

DescriptionDate of

Concreting

Date of

Loading

Period of

Remolding

Grout Result

PLT No.1 7 March 02 7 May 02 62 days Without NG

First Stage of PLT No.2 14 June 02 27 July 02 44 days Without NGSecond Stage of PLT No.2 14 June 02 22 Nov. 02 162 days With Good

PLT No.3 12 Dec. 02 13 Jan. 03 33 days With Good

(2) Increase of Bering Capacity by Remolding of Surrounding SoilAs the results of the PLT No.1 and the first stage of the PLT No.2, it is recognized almost no recovery ofstrength of surrounding soil by its remolding in two months after casing concrete of the test piles.Meanwhile from this point and the results of the PLT No.3, it is considered that the required bearingcapacity of the Test Pile No.3 is mostly obtained by effect of grouting.It is a fact that combined effects of remolding and grouting increased the bearing capacity of the Test Pile

No.2. As results of analysis of all pile loading tests and consideration of characteristic of silty fine sand it is


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concluded that major effect to increase bearing capacity is grouting and effect of remolding is considered tobe small.

5.2 Sequence of Development of Resistance Forces on Piles

(1) Development of Skin Friction and End BearingConsidering the mechanism of development of bearing of a pile, procedure of development of skin frictionand end bearing of a pile, is summarized as described below.When load acts on the top of a pile, at first, the settlement (displacement) of the pile is likely to occur and

skin friction of the pile is developed to resist this movement. Since the entire pile is settled together in onebody, skin friction of entire parts of a pile is developed simultaneously. In the next, when the load increases,settlement of the pile is increased and displacement of soil at pile tip is occurred. As the result end bearing isdeveloped in proportion of the soil displacement. And then when load increases more, skin friction of the

pile is increased and surrounding weak soil in the upper part of pile reaches its ultimate. Accordingly loadborn in this part transfers to the lower part of pile and consequently skin friction in the lower part of the pileand end bearing are developed more to support more load. Finally when load increase further more, this

phenomenon extends to the lower part of pile and the surrounding soil reaches its ultimate in the entire partof pile and soil around the pile is failed. At this stage, the entire load is transfer to the pile tip. If the end

bearing of the pile cannot support the load, the pile will fail.A figure of distribution of axis compressive force measured by strain gauges in the second stage of the PLT

No.2 is shown in Figure 5. According to this figure, skin friction of the lower part of the Test Pile No.2 wasdeveloped since early stages of loading. Reaction of ground (end bearing) was developed at the test load of

21,800 kN.The load - settlement curves of the PLT No.1 and the first stage of PLT No.2 indicate the above-mentioned

process of failure of a pile.

(2) Skin Friction of Silty Fine Sand LayerAs a result of analysis of bearing capacity of the test piles based on the results of the PLT No.1 and the firststage of the PLT No.2, the skin friction of silty fine sand layer has not been developed and is considered to

be almost 0 Pa.According to the relationship between test load and settlement or pulling up of the Test Pile No.1 and thereaction piles in PLT No.1, it was recognized that total of the end bearing and skin friction of silty fine sandlayer is 6,650 kN. Based on the fact that the soil at the pile tip supported the weight of fresh concrete and theanalysis of the Load - Settlement Curve of PLT No.1, it was concluded that the end bearing is 6,650 kN andthe skin friction of silty fine sand layer is almost 0 Pa.

This is unusual phenomenon of sandy soil and this is the cause of the problem of unusual large settlement ofthe piles.Although some hypotheses of causes of this phenomenon such as stress release or disturbance of silty finesand, which is very sensitive and is not able to remold once disturbed, by excavation have been studied, theactual mechanism of this phenomenon has not been found yet. Further investigation and studies arenecessary to find out the mechanism.

6. SUMMARY AND CONCLUSIONS

As the results of the second stage of the PLT No.2 and PLT No.3, it has been proved that grouting was themost effective and economical countermeasure to increase bearing capacity of the piles in order to obtain itsrequired value. Therefore it has been concluded that the grouting was the only solution for the problem of

insufficient bearing capacity of the piles for piers of the Main Bridge on the river.Piling work was resumed using grouting to obtain sufficient bearing capacity of the piles at the beginningFebruary 2003. All the piles for the Main Bridge including grouting were completed at the beginning ofAugust 2003.

In order to increase bearing capacity of the piles for certain, supervision methods of grouting to achievehigh quality of grouting and measurement method to confirm effect of grouting were established. Thegrouting methods used for the test piles were applied for grouting of the working piles for piers of the MainBridge on the river.

The effects of grouting are proving by survey of elevations of the top of pile caps and measurement ofaxis stress of the piles by strain gauges. Comparison in axis stress between the test pile and the working

piles are been conducting to confirm increase skin friction by the effects of grouting. Both results of


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measurements of top level of the pile caps and axis stress of the working piles are satisfactory and it isconcluded that grouting is exhibiting its effects so far.

Since grout consists of cement and water, grout itself considered being perpetual. If end bearing of a pileis increased by a pressure bulb constructed using grout, there is a possibility that the end bearing will bedecreased due to pressure release of the bulb. However the purpose of the grout applied for this project isdifferent and increase in bearing capacity is not depended on the pressure bulb. Therefore it is concludedthat the grout applied for the working piles has sufficient durability within the life span of the bridge.It has been recognized that applying grouting as the countermeasure was the right decision, since grouting isconsidered to be the most effective and economical solution to cope with the problem insufficient bearing

capacity of the piles. However, grouting in the test piles was executed through trial and error, since thismethod was applied to increase bearing capacity of a pile for the first time. Thus some trail executions ofgrouting were made and it took time to finalize details of grouting methods. As the results, proper groutingmethods were established and it has been realized that the grouting methods applied for the working pilesfor piers were reasonable.

It has been also recognized during the studies of countermeasures that investigations and preliminarystudies for design of the large pile were not enough. By some reasons, the design of the piles was conductedin Phase 2 of the Feasibility Study for this project and the detailed design has not been carried out. The pileswere constructed in the area, which has the deepest alluvial soil layer in the world and the pile tip was notembedded in sufficient bearing strata. Therefore it has been considered that further investigations andstudies should have executed for design of the very large and deep cast-in-suit reinforced concrete piles,which do not have enough past records to construct.

In case that pile tips are not penetrated into sufficient bearing strata such base rock, it is recommendable

to shorten pile length using grout around the piles for economical design of piles. However, it is recognizedthat it is very difficult to estimate of the effects of grout and establish quantitative design method of pileswith grout, since the effects of grout are various depend on soil.

Through studies and execution of countermeasures to cope with the problem of insufficient bearingcapacity of the piles, various knowledge and valuable data were obtained. These knowledge and data shall

be shared by all structure engineers and applied for future design of piles and supervision of piling works.

REFERENCE

1) The Study on Construction of the Bridge over the River Rupsa in Khulna, Phase 1, JICA, March 1999 and Phase 2, JICA,March 2000

2) Rupa Bridge Construction Project. Tender Documents: Volume A, B, C, JICA, March 2000

3) Plumbridge, G.D., Littlechild, B.D., Hill, S.J. and Pratt, M.: Full Scale Shaft Grouted Piles and Barrettes in Hong Kong,Foundations, The 19thAnnual Seminar, Geotechnical Design, 2000.5

4) Bruce, D.A., Enhancing the Performance of Large Diameter Piles by Grouting, Ground Engineering, Vol.19 (4), pp.9-14,1986.5

5) Plumbridge, G.D and Hill, S.J.: Performance of Shaft Grouted Piles and Barrettes, 14thSouth East Asia Geotechnical

Conference, Geotechnical Engineering, pp.10-14, 2001.126) Plumbridge, G.D and Hill, S.J.: Performance of Shaft Grouted Piles and Barrettes, Geotechnical Engineering Meeting of

Societys Needs, Vol.1, Geotechnical Engineering, pp.407-413, 2001.127) Osterberg, J.O.: The Osterberg Load Test Method for Bored and Driven Piles - The First Ten Years, The 7

thInternational

Conference of Piling and Deep Foundations, Deep Foundation Institute, 19988) Osterberg, J.O.: What Has Been Learned about Drilled Shafts form the Osterberg Load Test, 2000.5, The Annual Meeting,

Deep Foundation Institute, 1990.10