Bidirectional and Conventional Static Load Test on Bored Piles in Soil: A Field Comparison

Abstract

For the past three decades, a novel technique for bored pile static capacity evaluation using the bidirectional static load test (BDSLT or O-cell method) has been proven beneficial to the traditional axial load testing method in various aspects. Nevertheless, as the BDSLT method uses a loading mechanism within the pile, completely different from the top-down pile loading testing method, many researchers and designers have been concerned that the BDSLT method would give an inaccurate result. This paper focuses on the comparison of both testing procedures using load test data to give confidence in the piled foundations of soil. In order to assess the validity of both testing methods in soil conditions, pile load tests were performed on two 1500 mm diameter cast-in-place concrete piles of 26.0 m long to a test load of 20,900 kN under the same geotechnical conditions in Kuwait. Geokon model 4200 strain gauges were installed on the piles at six designated locations with four numbers at each level. Based on the analysis, it is confirmed that both methods are accurate to assess the pile settlement at the design and ultimate test loads. Hence, it is identified that BDSLT is an innovative, feasible replacement of the conventional static load test to determine the static behavior of bored piles to ensure a safe foundation system in the construction industry.