ANALYSIS OF LOAD-SETTLEMENT CURVES OF PILE LOAD TESTS CONDUCTED IN VARIOUS N.W.F.P. LOCALITIES

Abstract

Pile load tests cost generally about Rs.200,000/- and are included in almost all major bridge Projects in NWFP. Since in Pakistan very little work is done to understand the pile soil behavior keeping in view the local data base available, the confidence level of the designers is very low and as a result a lot of money goes on over-designing of pile or unnecessarily providing pile foundation. This work is directed towards understanding the pile soil interaction keeping in view the load settlement data available from pile load tests of various NWFP localities and their corresponding soil profiles. A good understanding of this behavior means a rise in the confidence level of the designer and much economy and safety. In this paper a simple numerical technique based on load transfer approach presented in the sister Paper' is used to capture the response of the soil to movement of pile relative to surrounding soil (t-z curve), as experimental technique of instrumenting the pile along the length of pile for the same purpose would have been very costly. This technique uses the available load settlement data from pile load test not instrumented along pile length during load testing and establishes an average t-z curve. This technique is applied to load settlement data of four pile load tests conducted in various localities of NWFP. Once the t-z curve is established for a particular pile-soil system, ilie curve can be used for the same site to carry out the parametric study i.e. to predict the effect of different length and/or diameter for the pile on the load settlement curve of pile. In addition, the settlement curve for other sites can be generated if the soil profile does not vary remarkably from that soil profile from which the t-z curve is developed. This investigation reveals that due to little effort devoted to the understanding of the Pile-Soil interaction on indigenous pile load tests data and soil profiles in Pakistan in general and in NWFP in particular, a very over conservative approach is followed in Pile designing.