Experimental study on influence of excess pore water pressure and unloading ratio on unloading mechanical properties of marine sedimentary soft soils

Abstract The paper discussed the effects of pore water pressure and unloading ratio on the mechanical properties of soft soils. The Shenzhen marine sedimentary soft soils were selected in this study. The results revealed that the excess pore water pressures had significant weakening effects on the unloading strength of soft soils. Comparing with the unloading strength without excess pore water pressure, the reduction rate of unloading strengths at excess pore water pressure ranging from 20 to 60 kPa were found to be 3.4%–21.4% and 1.3%–19.2% for unloading ratio 0.0 and 0.5 respectively. Meanwhile, the excess pore water pressures had greater impact to cohesion than to internal friction angle. The unloading failure modes of soft soils are sudden and concealed, and the lower confining pressures and higher excess pore water pressures can make the unloading failure more destructive. Moreover, the initial unloading modulus is linearly proportional to the confining pressure but linearly inversely proportional to the excess pore water pressure.