Full-Scale Field Test Study of Skin Friction Development in Sand for ACIP Piles under Compressive and Tensile Loading Conditions for Bridge Support

In this study, the performance of a non-displacement auger cast-in-place (ACIP) piles in sand under compressive and tensile loading was investigated by performing a field load test. In this full-scale load test study, ACIP piles were installed in layered sand, with loose sand [minimum Texas cone penetrometer (TCP) blow count of 7] in the top 4 m with very dense sand (maximum TCP blow count of 95) in the bottom layer 7 m below ground. The load test was performed on a 760 mm (30 in.) diameter fully instrumented ACIP pile with eight 450 mm (18 in.) diameter reaction piles. The test pile utilized a load cell and multiple pile top dial gages to measure applied load and settlement during the load test. Also, vibrating-wire sister bar strain gauges with thermocouples were attached along the length of the test pile and selected reaction piles. The design load for the test pile was 816 kN (92 t) and the test pile was loaded to 2,840 kN (320 t) before unloading. Using the Vipulanandan ACIP pile model, the ultimate capacity was predicted to be 4,545 kN (512 t), more than five times the design capacity. Skin friction-displacement relationships for the test pile in compression and reaction piles in tension were developed with depth representing the loose to very dense sand. The maximum skin friction measured in the very dense sand was 210 kPa (2.2 tsf) in compression and 57.3 kPa (0.6 tsf) in tension. The measured skin friction in the ACIP test pile in compression was more than 50% higher than the TxDOT design standard for drilled shafts in high blow count dense sands.