Experimental Studies on Cyclic Shear Behavior of Steel-Clay Interface Under Constant Normal Load

The degradation of the shear stress between pile-clay interface caused by undrained cyclic jacking affects the jacking force. A series of large displacement monotonic shear, cyclic shear and post-cyclic monotonic steel plate-clay interface shear tests were performed under the constant normal load (CNL) condition to investigate the effects of normal stress, cyclic amplitude, and number of cycles on a steel plate-clay interface using the GDS multi-function interface shear tester. Based on the experimental results, in monotonic shear tests, change of shear stress took place in the specimen, the shear stress rapidly reached the peak value at shear displacement of 1 mm, and then abruptly decreased to the residual value. In cyclic shear tests, accumulated displacement was a better parameter to describe the soil degradation characteristics, and the degradation degree of shear stress became greater with the increasing of normal stress and accumulated displacement. Shear stress in post-cyclic monotonic shear tests did not generate a peak value and was lower than that in monotonic shear tests under the same normal stress. The soil was completely disturbed and reached the residual strength when the cumulative displacement approached 6 m. An empirical equation to evaluate shear stress degradation mechanism was formulated and the procedure of parameter identification was presented.