Appraisal of reliable skin friction variation in a bored pile

Abstract

The design of bored piles in Malaysia is usually based on the results of the standard penetration test. It is important to predict the geotechnical capacity of a designed bored pile through the multilayer soil strata. The back-analysis of a test pile is a reliable means of obtaining the range for the ultimate skin factor (Ksu) and the ultimate end-bearing factor (Kbu). In this research, two case histories of maintained load tests on single bored piles (PTP-1 and 2) under full-scale static load (up to twice designed load) are examined. Measurements are taken using various embedded transducers, including both conventional instrumentation and a state-of-the-art global strain extensometer. The results show the rates of the pile base and pile head load mobilisation with settlement, the variation of the skin friction factors and stresses along the pile, and their proportion in relation to the total pile capacity. The Ksu and Kbu factors for both tested piles are obtained and compared using a conventional vibrating-wire global strain gauge and a global strain extensometer. It is also observed that for the stiff soil layers the skin friction is significant. However, the increase in the applied load increases the proportion carried by the end-bearing.