Influence of Ground Water Table Fluctuation on Lateral Load Behavior of Rigid Drilled Shafts in Stiff Clay

A series of static one-way lateral load tests was performed on prototype-scale drilled shafts installed in a stiff surficial clay crust to investigate the effect of ground water on lateral load behavior. Tests were conducted under different ground water conditions at the National Geotechnical Experimentation Site at the University of Massachusetts, Amherst. The load-displacement results of the tests are presented herein. The results of the tests show that the load-displacement behavior was significantly influenced by the ground water regime at the time of testing. The ultimate lateral load capacity, defined as the load at a displacement of 10% of the shaft diameter, and the initial stiffness increased as the water table dropped. A drop in the ground water table from 0.4 m to 2.3 m below ground surface increased the ultimate lateral load from 30 kN to 95 kN. The paper presents a summary of the testing and illustrates the influence that ground water can have on field tests.