Effect of lateral confinement method on excess pore pressure generation under strain-controlled cyclic direct simple shear test

Abstract

This article compares two lateral confinement methods, wire reinforced membrane (WRM) and stacked rigid rings (SRR), used in the ASTM D6528 and D8296 standards for conducting the direct simple shear and the cyclic direct simple shear tests on soil samples in the laboratory. A series of undrained strain-controlled cyclic direct simple shear tests on Jumunjin sand with medium density was conducted using the WRM and SRR confining methods at various strain levels of 0.1%, 0.2%, and 0.5% to compare the excess pore pressure (EPP) generated after each cycle during the testing process. The study found that the effect of the confinement method on EPP generation is negligible at low shear strain levels of 0.1%, but as the shear strain level increases, the difference between the two methods becomes more pronounced. The EPP generated using the WRM method is slightly smaller than that produced by the SRR method at a shear strain level of 0.2%, and significantly smaller at a shear strain level of 0.5%. However, the difference between the two methods gradually decreases as the number of cycles increases. The study concludes that the sample confined with the WRM method had a higher liquefaction resistance than the SRR method. The difference between the two methods gradually decreased with an increase in cycles, and the magnitude of the shear strain level was a crucial factor affecting the difference between the two methods, with larger shear strain levels resulting in greater differences.