Experimental Study on Undrained Instability of Saturated Silty Sand under Disturbance of Underground Construction

Density reduction of saturated silty sand layers caused by construction disturbance of underground engineering in soft soil, can lead to pore-pressure accumulation under undrained loading and triggering instability. To investigate the mechanical behavior of saturated silty sand under different levels of construction disturbance, a quantitative index is developed to characterize the degree of construction disturbance, based on which reconstituted specimens are prepared and tested using consolidated drained and consolidated undrained triaxial shear tests. The stress-strain curve analysis shows that, under low confining pressure, loose and medium-dense saturated silty sand exhibits static liquefaction accompanied by strain softening, and the extent of softening decreases with increasing confining pressure. Loose and medium-dense silty sand shows a higher susceptibility to static liquefaction under low confining pressure; low-density silty sand demonstrates a stronger liquefaction potential and a higher undrained brittleness index under low confining pressure. With increasing initial relative density, the region between the failure line and the instability line in stress space shrinks, implying a reduced likelihood of staticliquefaction instability.