Experimental investigation on strength characteristics of marine soft clay under monotonic and cyclic loading

Sea areas with an average water depth of 5-15 m in the East China Sea are mostly muddy soft-foundation seabed. The wind power infrastructure built on them must fully consider the mechanical properties of marine soft clay during design process. In this study, monotonic and cyclic tests were conducted to study the strength characteristics of soft clay at various strain rates, cyclic stresses and initial effective vertical stresses using a simple shear apparatus. The test results showed that, as the strain rate increased, the peak shear stress of the samples under different confining pressures increased. However, the failure lines of the effective stress path of samples under different strain rates and vertical stresses are uniform. Compared to the traditional cyclic failure criteria, the failure criterion based on the inflection point of double amplitude strain can reflect the deformation characteristics of the specimen more accurately. The peak shear strength obtained from the monotonic tests was used to normalize the cyclic stress. Subsequently, the relationship between the number of failure cycles and normalized cyclic stress level of the soft clay specimens was established.