An Experimental Study on Excess Pore-Water Pressure Generation of a Poorly Graded Sand Using Combined RCTS Device

The combined dynamic torsional resonant column and cyclic torsional shear (RCTS) device is employed to study the generation of excess pore-water pressure, especially the threshold shear strain of excess pore-water pressure, gamma degrees degrees t, in an uncemented poorly graded granular soil. Reconstituted specimens of uncemented sand were constructed under water and then tested in the RCTS device using a newly designed base pedestal, with which pore-water pressure is measured at four points systematically located at 0.75 times the radius of the base pedestal. Specimens were tested under different mean effective confining pressures, and all specimens had B-values above 0.95 at the start of testing. During testing, the excess pore-water pressure was measured continuously during 30 cycles of loading at multiple increasing loading levels. The three major factors influencing gamma degrees degrees t that were investigated are as follows: (1) mean effective confining pressure, (2) relative density, and (3) loading frequency. The results are presented in terms of the following: (1) excess pore-water pressure ratio versus shear strain, and (2) threshold shear strain versus number of loading cycles. Other related behaviors such as softening during cycling and post-cyclic moduli changes are also discussed.