Analysis of field data

The data used for this study are collected from five numbers of instrumented bored piles. Three of these piles were constructed using dry method of construction and the other two using wet method of construction. Each pile was statically and dynamically tested. Typically, the static load test was conducted prior to the PDA test on each pile.

The data was obtained from construction site at three different sites. Based on the Geological Map of Selangor (Scale 1:63,360) and the borehole logs, the Site 1 is located in Kenny Hill Formation. A relationship is tabulated in Table 4.1 between the SPT (Standard Penetration Test), N value obtained from bore hole and the weathering grade of the rocks. Site 2 and Site 3 are located in Old Alluvium based on the Geological Map of Johor Bahru (Scale 1:63,360).

Kenny Hill Formation consists of monotonous sequence of interbedded clastic sedimentary rocks such as sandstones, siltstones, shale/mudstone. Frequently this formation is also referred to as meta-sedimentary with interbedded meta-arenite and meta-argillite, taking into account that the sedimentary rocks have been partly metamorphosed into quartzite and phyllite.

Old Alluvium is consider to be of the pliestocene age that comprises of continental deposits of consolidated sand, clay and boulder beds of fluviate and shallow-marine origin. Holocene marine clays are nearly absent. Studies of these types of sediments, mainly from exposures were done by Kumar (1972) in Johor and Tai (1972) in Singapore. Their measurements of paleo-current directions show a south to eastward trending sediment transport. From this it was concluded that Straits of Johor did not exist at the time of deposition of the Older Alluvium (Bosch, 1988). In the drill holes data of the Public Works Department of Singapore, the base of the formation was found between 100m and 145m below sea-level, while the highest deposits were found at 45m above sea level.

Table 4.1: Relationship between SPT, N Value and Weathering Grade Weathering Grade Ting (1979) – SPT Komoo (1986) - SPT

VI 0-20 V <50 20-50 IV >50 50-200 III *CRR<70%

*CRR-Core Recovery Rate

Table 4.2 shows the subsoil classification based on the weathering grade. Based on the geological condition, Kenny Hill formation at Site 1 predominantly Grade IV material with SPT – N value greater than 50. The subsoil exists at shallow depth, thus the pile length ranges from 7m to 12m. These piles can be categorized as short piles.

Old Alluvium formation at Site 2 and Site 3 are generally overlain by comparatively weak alluvium called young alluvium to depths of between 10 to 30m. The SPT, N values are generally less than 15. The old alluvium underlies the young alluvium extends to depths beyond the toe of all piles. The SPT, N values in this type of formation are generally varies between 20 and 100. All the pile length in this formation ranges between 40m to 50m. These piles can be categorized as long piles.

The location of the site and the reference number; date of casting as well as the length and diameter of the piles are tabulated in Table 4.3. The piles from Site 1 are cylindrical with diameter of 750mm. The length of the piles ranges between 7m to 12m. All these piles were cast in July of 2003. The pile from Site 2 pile is 1000mm in diameter and was cast on the end of 2002. The length of the pile is about 48m. The pile from Site 3 is also cylindrical with diameter 1200mm and length of 42m. The pile was cast at the end of September 2004.

Static load test was conducted on the piles at some time after the installation. The PDA test was carried out after a certain interval of time. The date of testing and the interval durations for the static and PDA tests are tabulated in Table 4.4.

The waiting period would allow for the curing of concrete and set-up of the soil. The time interval between the tests will govern the capacity of the piles because it related to the development of shaft friction along the pile. The longer the time interval, it is expected that the shaft contribution would be larger towards the capacity.

Table 4.2: Subsoil Classification (Komoo and Morgana, 1988) Weathering Classification Grade Description

Residual Soils VI All rock material is converted to soil. The mass structures and material fabric are destroyed. The material has not been significantly transported. Completely Weathered V All rock material is decomposed

and/or disintegrated to soil. The original mass structure is still largely intact.

Highly Weathered IV More than 50% of the rock material is decomposed and/or disintegrated to soil. Fresh or discolored rock is present either as a discontinuous framework or corestones.

Moderately Weathered III Less than 50% of the rock material is decomposed and/or disintegrated to soil. Fresh or discolored rock is present either as a discontinuous framework or corestones.

Slightly Weathered II Discoloration indicates weathering of rock material and discontinuity surfaces. All the material may be discolored by weathered and maybe somewhat weaker than in its fresh condition.

Fresh Rock I No visible sign of rock material weathering, some discoloration on major discontinuity surfaces.

Table 4.3: Pile Details

Location Pile Reference Pile Diameter (mm) Pile Length (m) Date of Casting Pile 1 750 7 04/07/2003 Pile 2 750 9 11/07/2003 Site 1 Pile 3 750 12 17/07/2003 Site 2 Pile 4 1000 48.2 28/12/2002 Site 3 Pile 5 1200 41.5 24/09/2004

Static load test was conducted on piles at Site 1 within one month of casting. The piles at Site 1 are consists of short piles, therefore there is no need for long wait period to allow for soil-setup since large contribution is expected from the base of the piles. Pile 4 and Pile 5 was tested three weeks to two months from the casting date.

PDA tests were conducted on the piles that were earlier tested statically. Piles at Site 1 and Site 3 were tested after about seven to eleven weeks after casting the piles. Pile 4 at Site 2 was tested about 9 months after conducting static load test. A large shaft friction is expected for Pile 4 from the PDA test results due to the wait period.

The piles at Site 1 were tested 3.3 times the working load or to failure and piles at Site 2 and Site 3 were tested 2.5 of working load or to failure. Table 4.5 show the maximum load applied to the pile during static load test.

Table 4.4: Date and time interval between tests Pile Reference S.L.T. Date Time Between Casting and S.L.T. (days) PDA Test Date Time Between S.L.T. and PDA Test (days) Pile 1 18/07/2003 14 11/09/2003 55 Pile 2 30/07/2003 19 03/09/2003 35 Pile 3 12/08/2003 26 03/09/2003 22 Pile 4 18/01/2003 21 07/10/2003 262 Pile 5 13/11/2004 50 08/12/2004 25

Note: S.L.T. = Static Load Test

The working load and test load and the pile settlements for the given working load and test load from both static load and pile driving analyzer are tabulated in Table 4.6. All the tested piles have achieved the required test load of two times the working load. It can be seen from Table 4.6 that the short piles exhibit small settlements for both static and dynamic test. Large settlements were noted for the long piles founded in old alluvium soil. Overview of the settlement results shows that the settlements predicted from the PDA tests is lower compared to that of static load test. The settlement at working load for PDA tests is observed to be plus or minus 2mm of that obtained from static load tests.

Table 4.5: Maximum Load Implied During Static Load Test Pile Reference _{Maximum Load – Static Load Test (kN)}

Pile 1 10,064 (3.3xWL)

Pile 2 10,000 (Failure)

Pile 3 10,027 (3.3xWL)

Pile 4 14,974 (2.5xWL)

Pile 5 16,573 (2.0xWL)

Table 4.6: Pile Settlement

Settlement (mm) Static Load Test PDA Test Pile Reference Working Load,WL (kN) Test Load,TL (2xWL) (kN) WL TL WL TL Pile 1 3,000 6,000 2.3 4.5 2.3 4.8 Pile 2 2,250 4,500 2 4.9 2.3 6.3 Pile 3 3,000 6,000 3.5 9.8 2.4 5.1 Pile 4 5,800 11,600 6.5 15 5.3 10.7 Pile 5 8,400 16,800 7 52 5.3 12