Novel pore pressure measurements along a shear surface in liquefied soil

Physical modeling is an efficient method to simulate practical geotechnical problems and to provide insights into soil behavior. This study used geotechnical centrifuge models equipped with motorized pulling systems to pull coupons (thin metal plates) at constant speeds horizontally through clean, saturated sand models that were liquefied by cyclic loading. The model setup was aimed to mimic shearing mechanisms, large shear strains, and large strain rates observed in field-scale flow slides. In-flight cone penetration testing and bender element-based shear wave velocity measurements helped in characterizing soil state at coupon levels before liquefaction. In addition, a miniature pressure transducer was embedded in the coupon along its top horizontal surface to directly measure pore pressure response on the shear surface within the liquefied soil. In total, 11 coupon pulls were completed, with 6 of the 11 tests providing shear-induced pore pressure measurements at the coupon surface. Measured coupon pulling forces and pore pressure responses at shear-surface and free-field were interpreted to identify key behaviors. These key behaviors illustrated that relatively low coupon velocities were required to maintain liquefied conditions at the coupon surface. In addition, pulling force recovery during pore pressure dissipation appeared to be related to coupon velocity (i.e. strain rate).