Comparison of axial load capacity of piles from theoretical methods and static load tests

Abstract

This study has been carried out to compare some selected empirical and theoretical equations used globally. The comparisons have been made among the various equations concerning the static load test result, which is widely believed to be providing a reliable pile capacity. The study has been based on the data obtained from the sub-soil investigation reports and corresponding pile load test results collected from twenty-two projects all over the country. Among these projects, fewer than twelve projects fifteen precast piles have been tested and under another ten projects fifteen cast-in-situ piles have been tested. The tests have been performed between1997 to 2018 and funded by Public Works Department (PWD), RAJUK, Roads &Highways Department, and Dhaka Mass Transit Company (MRT). Almost 70% pile load tests are carried out under the direct supervision of the Department of Civil Engineering, BUET, and the rest of the pile load test are carried out by Icon Engineering Services, Dhaka. In this study, five calculation methods, namely Meyerhof(1976),NAVFAC DM 7.2(1984),AASHTO(1986), O’Neill& Reese(1988) and Decourt (1995) methods for cast-in-situ/ bored pilesand Drilledshaft,and another five calculation methods, namely Meyerhof(1976),API RP 2A(1993),Tomlinson(1994),Norwegian Pile Guideline(2005),and Indian Standard(2010) methods for precast piles have been used. The static load test has been performed and analyzed by Davisson method, BNBC code (1993), and Indian Standard (2010).

It has been observed that the Tomlinson (1994), API (1993) and Meyerhof (1976) methods provide the most reliable and justified correlation between predicted and measured capacity for precast/ driven piles. On the other hand, for the cast in situ/ bored piles, AASHTO (1986) and O’Neill& Reese(1988) and NAVFAC DM 7.2(1984)methods provide the most reliable and justified correlation between predicted and measured capacity.

It has also been observed that the methods for predicting the ultimate capacity of precast/ driven piles give relatively more reliable and justified result with minimum error compared with the cast in situ/ bored piles.In all the cases a considerable correlation between the static analysis of pile capacity and capacity of the pile from the static load test are found. This study has supported the idea to put a higher degree of confidence to use the statics formulae to find out the ultimate capacity of the piles. For precast piles, the correlation coefficients vary from 0.919 to 0.972 and for cast-in-situ bored piles the correlation coefficients vary from 0.518 to 0.794.No such reliable correlation can be established for cast-in-situ drilled shafts.