Interpretation on pile capacity from instrumented sacrifical pile load test for deep foundation system

Abstract

A deep foundation system often offers a lot of uncertainty even though it is the only option for the demanded highly loaded structure to be able to construct. Hence, to increase the level of confidence in the design, a lot of method and procedure have been established to evaluate the certainty of the pile design. This paper will discuss the prediction of geotechnical capacity of the pile from the instrumented pile load test conducted at very deep strata of more than 30m below ground level in a residual soil originated from the youngest metasedimentary rocks; Kenny Hill formation in Kuala Lumpur area. A sacrificial instrumented pile load test using both traditional static load method which is top-down maintained load test via anchor reaction system and alternative test using bi-directional load test with an axially compressive load are assessed to find and compare the behaviour of the geotechnical pile capacity. The comparison of pile capacity was attempted by using various method of interpretation such as Van der Veen, Chin, Decourt’s extrapolation, Fuller and Hoy, Butler and Hoy, De Beer, and the Davisson method. From the study, the method of interpretation has been grouped accordingly namely as mathematical method group by Van der Veen, Chin and Decourt’s extrapolation; settlement limitation group by Fuller & Hoy, Butler & Hoy and De Beer; and lastly the graphical construction group by the Davisson method. This grouping method is suggested by Hirany & Kulhawy, 1988.From the study, it can be concluded that the settlement limitation method is the most suitable to be adopted since the result are found consistent in producing the lower bound between three interpretation group. The skin friction evaluation also has been access using the said method and resulted in a good agreement with the pile capacity trend, hence it can be assured that the method of interpretation can be applied to find both total geotechnical capacity and skin friction of the geotechnical parameter in foundation design. In addition, the study has also helped to eliminate the variability of independent factor by having a similar type of sacrificial replacement pile namely barrette pile cast-in situ, cases are using static pile load test with similar axially compressive load and located in the identical region of ground profile. From this, it is found out that both type of pile load test is able to produce identical result irrespective the chosen traditional by head down top load method or even bidirectional method, irrespective the deep strata of soil condition and also irrespective the higher load applied at relatively more than 40MN.The comparison of these interpretation method could help the designers to interpret the most suitable prediction analysis for deep foundation analysis for a more robust and confidence design.