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Home , Bearing capacity, Soil texture

Japanese Geotechnical Society Special Publication The 15th Asian Regional Conference on Mechanics and

Excess and its impact

Akira Wada

Asia Georesearch Agency Corporation Pte Ltd (AGA)

ABSTRACT

This paper presents about the high level of excess pore water pressure. The high excess pore water pressure was monitored during pile driving work at saturated stiff to hard soil layer of Pleistocene. This high pressure zone under the pile toe is considered to destroy the soil texture and generate liquefaction soil. From this case study, liquefaction phenomenon is understood to be developed in any type of soil, if the level of excess pore water pressure is big enough to destroy the soil texture.

Keywords: pile driving, excess pore water pressure, liquefaction

1 INTRODUCTION (N > 35), by more than 0.5 depth socket in. The specifications of pile and termination criteria of driving This paper is prepared based on the monitoring were as follows. data during the pile driving work at hill area where it Pile type : RC pile 450x450mm consists of Pleistocene deposit material. In these monitoring data, the excess pore water = 10m (w ≑ 5 t/pile) showed remarkable high level, such as 3 nos. of Working load : 130 ton/pile being damaged and lost its function. Penetration depth : 9.5m (from RL+12.05m) Refer to the study of these data, the excess pore Layout of Pile : Square layout water pressure was considered to destroy the original Space 1.2x1.2m grid soil texture. There were not many report of such a high Pile driving method excess pore water pressure being developed, and this is Hydraulic hammer : 7.0 ton considered due to very few case studies about Falling height : 1.28m monitoring the excess pore water pressure at in-situ Criteria on termination depth: Confirm 20mm/10 blow condition. The distribution area and the pressure level of excess pore water are affected by the scale factor, During the piling work, pre-driven pile was observed to and if excess pore water pressure is monitored by heave up by driving neighbour pile. Static load test was laboratory equipment or small scale model in the test proposed to confirm the bearing capacity of heave up tub, it is considered to be difficult to produce the high pile. The selected test pile was monitored as 74mm pressure. heave up and was re-driving before static load test One of the conclusions from this case study is to (criteria of driving - 20mm/10 blow) for enough socket carry out the monitoring of excess pore water pressure into bearing layer. The static load test result was as at in-situ for to study the interaction behaviour with follows: soil. Test load (200%) 260 ton/pile Test result 2 THE PROBLEM PHENOMENON DURING Yielding load & settlement : 162 ton/pile DRIVING PILE WORK S = 4.6mm The project site was mild sloped hill area with the Max load & settlement : 260 ton/pile elevation level being RL+12m ~ +20m. The ground S = 94.4mm material consists of saturated over consolidated silty Residual settlement after Unloading : S = 89.1mm and dense silty which are classified as Pleistocene. The stratigraphic properties and soil The test result shows the allowable bearing capacity parameters of this project site is shown in Table 1. was lower than 50% of design load and monitored The proposed design was RC pile and it settlement was more than 5 times of predicted required to drive into over consolidated hard silty clay settlement which was evaluated from the soil parameters. http://doi.org/10.3208/jgssp.SEA-16 335 TTaabblele 1 1.. SSooiill Parrametterrs aatt PPrroojject Site l

e Unconf. Comp. Triaxial Comp. v SPT (N Value) Grain Size Distribution Consistence of Test Remark e s ) L ) s

h Test (CU) Test m t e m ) n - n + p ( o k i m

L Diagram Soil Name N Values e Content Ratio of Each Atterberg Limit LL (% ) t ( L c i a D G

R Range / Average of h ( t qu e c' F' eo Pc Mv Pile v ( g

T (Blows/30cm) e Grain (% ) PL (% ) l

E Average Content 3 2 2 o 2 2 10 20 30 40 50 10 20 30 40 50 60 70 80 90 # 20 40 60 80 100 PI (% ) (kN/m ) (kN/m ) (%) (kN/m ) ( ) (kN/m ) (m /kN)

32 46 73 Light 72.16 LL = 73% gt = 15.5~18.8 82.0 3.2 17.0 27 26 Brownish 4 5 G=0.1% 71 PL = 29% gt = 17.15 72.0 3.8 31.0 34 1.51 220.0 0.019 Gray / N = 3~7 S=8.3% PI = 44% G = 2.64 Soft-Firm N = 4.33 Si=45.8% Silty Clay 4 5 7 C=45.9% w = 46.00 ~ 72.16% w = 57.38% 8.45 3.60 3.60 3 4 GL-3.75m Light Brown G=9.7% 38 LL = 45% gt = 16.6~16.7

10 19 23 Medium Dense N = 10~25 S=54.9% 45 PL = 38% gt = 16.65 - - - - 0.84 950.0 0.032 Silty Sand N = 19.8 Si=27.3% PI = 7% G = 2.59 C=8.2% w = 29.76 ~ 44.61% 6.55 5.50 1.90 8 22 25 w = 32.57%

42 12 17 19 G=0.0% 81.6 LL = 81.6% - Light Brown N = 8~19 S=4.0% PL = 42% - Very Stiff 12 16 19 N = 14.9 Si=46.4% w = 51.70 ~ 70.11% PI = 39.4% G = 2.66 - - - - 1.60 - - Silty Clay C=49.5% w = 63.76% Pre Augering GL-8.00m 14 15 17 3.35 8.70 3.20 Dark Gray G=2.8% - - Hard 41 43 50 N = 30~50 S=15.6% GL-9.50m Silty Clay N = 38.7 Si=43.3% w = 53.87 ~ 60.61% ------1.43 - - with Fine Sand C=38.3% w = 57.05% G=2.59 1.60 10.45 1.65 30 32 36 Lamination

PL w Legend: Clay Sand LL

Line 5 Line 4 Line 3 Line 2 Line 1 Piezometer 1 Piezometer 2 Piezometer 3 1200 1200 1200 1200 450 750 450 750 450 375 375 375 375 500 450 750 450 750 450 750 450 750 450 GL - (m) GL - (m) 3 3 8

1 . .

. o 0.0 o 0.0

Pile Pile Pile Pile Pile o N N

450 N

3 e

Row 3 e l

15 14 13 12 11 l e i i l i P P P 375 1.0 1.0 1200 750 Piezometer 1 375 m m Soft-Firm Pile Pile Pile Pile Pile m 0 0 2.0 0 2.0

450 5 5 5 . Row 2 . 10 9 8 7 6 2 . 9 9 9

Brownish Gray = = =

l l l

375

, , , Silty Clay 0 0 1200 750 Piezometer 2 0 5 3.0 5 3.0 5 4 4 4

375 x x x

0 0 0 5 5 5 4 Pile Pile Pile Pile Pile 4 4

e

450 e e l 1 l Row 1 l i

i 5 4 3 2 1 4.0 i 4.0 P P P

n n

n Medium Dense e e e v v

Load Test v i i i

r r 500 r

D Light Brown D D Piezometer 3 5.0 5.0 Silty Sand

Fig. 1. Test Driving Layout and Driving Sequence 6.0 6.0 Fig. 1. Test Driving Layout and Driving Sequence Very Stiff 7.0 7.0 Light Brown P3-1 Silty Clay This discrepancy is considered to be generated by the 8.0 P1-1 P2-1 GL-7.70m 8.0 GL-7.80m GL-7.80m change of soil properties at below the pile toe which P2-2 Hard 9.0 GL-8.70m 9.0 was influenced by the driving work. So, for to study Dark Gray P1-2 P3-2 Silty Clay the soil properties change at pile toe, test driving work 10.0 GL-9.70m 10.0 GL-9.80m w ith was carried out at this project site. Fine Sand 11.0 11.0 Lamintation 12.0 12.0

3 RESULT OF TEST DRIVING WORK Fig. 2. Section Along Line 3 Fig. 2. Section Along Line 3 The test driving work was carried out using same pile layout as original design and as shown in Fig. 1, and monitored the heave up height of pre-driven pile Type of piezometer : Vibration wire strain gauge and the excess pore water pressure at near the pile toe Measuring range : 0 ~ 2000 KN/m2 depth. The locations of 6 nos. of piezometer were Accuracy ±0.5% of FS (10 KN/m2) shown in Fig. 2. The specifications of piezometer were Qty. of Piezometer : 6 nos. as follows: 3 locations x 2 depth

336 Table 2. Monitored Excess Pore Water Pressure

Piezometer at Upper Delluvium Silty Clay Piezometer at Lower Delluvium and Silty Clay with Fine Sand P1-1 (RL+4.25m) P2-1 (RL+4.25m) P3-1 (RL+4 .35m) P1-2 (RL+2.25m) P2-2 (RL+3.35m) P3-2 (RL+2.35m) Ex cess Ex cess Excess Ex cess Excess Ex cess Measured Measured Measured Measured Measured Measured Pore Pore Pore Pore Pore Pore Date Pressure, Distance Pressure, Distance Pressure, Distance Pressure, Distance Pressure, Distance Pressure, Distance Pile Time Water Water Water Water Water Water No (DD/Month) (hr:min) U (m) U (m) U (m) U (m) U (m) U (m) Pressure, Pressure, Pressure , Pressure, Pressure, Pressure, (KPa) (KPa) (KPa) (KPa) (KPa) (KPa) Ue (KPa) Ue (KPa) Ue (KPa ) Ue (KPa) Ue (KPa) Ue (KPa) 1 29-Dec 11:58 48.9 11.4 3.0 59.2 21.7 2.5 47.4 10.9 2.5 118.7 61.2 3.0 116.1 69.6 2.5 114.1 57.6 2.5 12:15 2 29-Dec 13:55 66.0 28.5 2.2 237.8 200.3 1.3 88.0 51.5 1.3 168.8 111.3 2.2 258.0 211.5 1.3 87.4 (30.9) 1.3 14:04 3 29-Dec 15:03 62.3 24.8 1.8 484.1 446.6 0.6 533.3 496.8 0.5 231.1 173.6 1.8 269.5 (223.0)* 0.6 - - * 15:11 4 29-Dec 16:04 72.0 34.5 2.2 2223.1 2185.6 1.3 221.1 184.6 1.3 203.0 145.5 2.2 16:11 5 29-Dec 16:59 66.7 29.2 3.0 - - 47.0 10.5 2.5 252.8 195.3 3.0

6 29-Dec 17:20 59.6 22.1 2.5 441.4 403.9 2.5 149.3 112.8 2.9 195.6 138.1 2.5

7 29-Dec 17:50 372.2 334.7 1.3 635.3 597.8 1.3 326.2 289.7 2.1 522.5 465.0 1.3 8 30-Dec 8:05 500.9 463.4 0.6 - - - - - 376.6 319.1 0.6 8:14 9 30-Dec 8:55 497.5 460.0 1.3 - - 46.8 10.3 2.1 271.3 213.8 1.3 10 30-Dec 9:19 466.8 429.3 2.5 - - - - - 163.4 105.9 2.5 11 30-Dec 10:08 246.6 209.1 2.5 45.4 8.9 3.8 222.5 165.0 2.5 12 30-Dec 10:45 1169.1 1131.6 1.3 51.4 14.9 3.1 295.5 238.0 1.3 13 30-Dec 11:26 - - * 139.2 102.7 2.9 667.4 609.9 0.6 30-Dec 13:40 14 55.8 19.3 3.1 275.1 217.6 1.3 15 30-Dec 14:15 52.0 15.5 3.8 155.4 97.9 2.5

* At Pile 13, Piezometer * At Pile 3, Piezometer * At Pile 3, Piezometer damaged by excess pore Cable off by piling rig damaged by excess pore damaged by excess pore pressure pressure pressure

FiFgi.g 3.. 3R.e Rlaetiloantisohnips hbieptw beeetwn Deeisnt aDnciset a/ nEcxec e/ sEs xPcoerses P Preosres uPrere /s s ure / Fig. 4. Estimation of the Excess Pore Pressure L i ftL Uipft oUf pP roef-D Prrivee-nD Priivlee n Pile vs. Lift Up of Pre-Driven Pile

The sequence of driving started from Row 1 to Row 2, The monitoring result during pile driving work was then Row 3, as shown the direction by arrow in Fig. 1. summarized into the following points

The monitored excess pore water pressure is (1) 3 nos. of piezometer were damaged and lost its summarized in Table 2. In this table, piezometer P2-1, function by more than 2000 KN/m2 excess pore P2-2 and P3-2 were damaged by the high water water pressure which was generated by driving pressure (>2000 KN/m2). The monitored heave up work at 0.375 ~ 0.500m distance. The height and the excess pore water pressure with distance monitored maximum excess pore water pressure from driving point was shown in Fig. 3. The was 2185 KN/m2. relationship between heave up height and the excess (2) The excess pore water pressure increased sharply pore water pressure was shown in Fig. 4. (more than 200 KN/m2) at the distance less than1.3m from the driving point.

337 (3) The maintained time period of excess pore water Driven Pile pressure was 3 ~ 7 min for P > 200 KN/m2 and 1 min for P > 1000 KN/m2. After this maintained time period, the pore water pressure dissipated sharply to less than 100 KN/m2. (4) The heave up height of pre-driven pile showed the Water Flow relationship with the distance from pile driving Water Flow point and it was also the parameter of the excess

pore water pressure. High Excess Pore Water Water Flow Water Flow Pressure Zone 4 EXCESS PORE WATER PRESSURE UNDER DRIVING PILE

Large void zone is produced at high The excess pore water pressure under driving pile pored water pressure zone was analysed from the data of test driving.

(1) High level of excess pore water pressure (> 2000 Fine grain soil flows out by high pore water pressure zone KN/m2) generated at near the toe of drilling pile 2 and the excess pore water pressure (> 200 KN/m ) Low permeable zone by clogging of

developed at the area of 1.0m ~ 1.3m radius from fine Grain soil

the pile toe. Fig. 5. Illustrated Figure of Large Void Zone under Driven

(2) At the outside of high excess pore water pressure Pile Toe

zone (>200 KN/m2), the decreasing ratio of excess

pore pressure with distance was small. So a low

permeable barrier layer was considered to be High

formed at the boundary of high excess pore water

pressure zone. This barrier was formed by fine

grained soil which was suspended in the high

pressure zone and flowed towards outside of high

e c

water pressure zone. This fine grained soil were r

o F

clogging / stacking at certain distance point where

d e

original soil texture were preserved and thus form i l

p

barrier layer. Fig. 5 shows the illustrated figure p

A of this high excess water pressure zone.

- The high excess pore water pressure zone

showed resistance against pile penetration during

driving work. Low

- The flow out of fine grained soil caused the

increment of at under the pile toe.

Then pile was sinking down under the static load

after the dissipation of excess pore water pressure. Strength of Ground Material

(3) The sharp dissipation of high excess pore water Fig. 6. Relationship Pressure Level of Pore Water pressure after certain time period was considered and Material Strength / Applied Force to be caused by the fissures developed at the

barrier layer. Then flow out high pressure water The relationship of these 2 parameters and level of from below the pile toe. excess pore pressure are shown in Fig. 6. As shown in

this figure, if the strength of soil material being low, the 5 FIELD OF HIGH EXCESS PORE WATER low level excess pore water pressure will destroy the PRESSURE soil texture and then produce liquefaction. Under The monitored excess pore water pressure was liquefaction circumstances, the excess pore water more than 20 times of over burden pressure and also pressure is not so much increase, so the level of excess over the of soil material. This high pore water pressure is considered to be related with soil level of excess pore water pressure generated under the strength. If the strength of soil material is high and following two parameters conditions. high magnitude of force being applied, the excess pore water pressure will increase upto the destruction of soil o Applied high magnitude of force on soil material. texture. During this process, if the presence of o Preserve the high strength in soil material which has fissures / drainage layer is developed, it will control the resistance against developed pore pressure. pressure level. So the destruction of is

338 not so often to develop in natural environment. But Through this study, the level of excess pore water review of several natural disasters and large/big scale pressure is considered to be produced under the civil engineering work, high magnitude of force is following parameters conditions. applied to certain soil material. If the soil is saturated, o The magnitude level of applied force the applied force generates high level of excess pore o The strength level of soil material water pressure. If these two parameters are being high level, the excess The effect of excess pore water pressure on the pore water pressure is considered to increase up to the destruction of soil texture is considered to be progress destruction of soil texture, and then produce the by the following 3 stages. liquefaction phenomenon. (1) The excess pore water applied the pressure on the As a result of this study, liquefaction is considered surface of the soil grain and disconnects / not special phenomenon in special soil. The separates each soil grain from the original texture. liquefaction phenomenon can be developed in any type (2) The external force boosted the pressure level of of soil if high excess pore water pressure generates. excess pore water and then the soil grain is

suspended in pressured water. REFERENCES (3) The gradient of pore water pressure generated the flow and the flow of pore water transports the soil 1) Tom. P. Airhart, T.J. Hirsch and Harry M. Coyle grain towards the lower pressure area. (1967): “Pile-Soil System Response in Clay as a The liquefaction is one type of soil failure and this function of Excess Pore Water Pressure and Other phenomenon is different with shear failure of soil Soil Properties”, Research Report No. 33-8, Texas mechanics theory by the following points: Transportation Institute. o The medium of stress transmission 2) Motonobu Yoshinori (1969): Bearing Capacity of o Direction of motion Pile Foundation, Annual Report of Building o The damping factor during stress transmission Research Institute. o Type of failure 3) American Society for Testing and Materials ASTM D1143-81, “Standard Method of Testing Piles under Refer to the review on the failure case studies of soil Static Axial Compressive Load,” Vol. 04.08, material, most of the failures are classified as composite Philadelphia (1989). failure type of shear failure and hydraulic failure 4) Randolph, M.F., Carter, J.P. and Wroth, C.P. (1979) (liquefaction). Driven piles in clay – the effects of installation and From this review and for to discuss the risk of subsequent consolidation. Geotechnique, 29, 4, ground stability, the potential of the liquefaction 361-393. phenomenon is recommended to study considering the interaction between excess pore water pressure and soil material. For to confirm the liquefaction study, the excess pore water pressure is requested to monitor at in-situ condition for to grasp the level of pressure and distribution area because pore water pressure is very sensitive to scale factor.

6 CONCLUSION The excess pore water pressure was monitored to be generated under pile toe during driving work and it has influenced on the pile foundation by the followings: (1) High pressure zone of excess pore water was forming under the pile toe. This high pressure zone acted as resistance against pile driving and pile was difficult to penetrate deeper. (2) Generated excess pore water pressure diffused from pile toe to surrounding area and this pressure applied towards pile toe of pre-driven pile. Due to this pressure, pre-driven pile was heave up. (3) Inside the high pressure zone, fine grained soil flow out and then produced high void ratio area. After the dissipation of excess pore water pressure, pile showed some settlement under static load and also decreasing the bearing capacity.

339