A New Strain-Softening Model for Interpreting Undisturbed and Remolded Shear Strength of Clayey Soils

Abstract The strength properties, especially the strain-softening behavior, of marine sediments are critically important for the design of subsea structures. This study conducted laboratory tests on undisturbed marine samples collected from the East China Sea, primarily aiming to investigate the evolution of undrained shear strength and strain-softening behavior using the full-flow ball penetrometer. The test results indicate that the strength degradation curve can be divided into two stages: the initial drastic reduction caused by the damage of soil structure (e.g., bonding and cementation) and the secondary gentle reduction resulting from the reorganization of soil particles. Moreover, the natural structured soil does not reach a fully remolded state even after experiencing 50 penetration–extraction cycles. Therefore, a new strain-softening model adopting a power-law expression is proposed to characterize the strain-softening behavior of marine soils. The exponent in the expression is determined by fitting the cyclic test data from a limited number of cycles and can be extrapolated to evaluate the progressive strength degradation under a high number of cycles. The initial drastic reduction of the soil is also characterized using a power-law expression, enabling the determination of the undisturbed strength prior to any softening. The derived undisturbed strength and soil sensitivity are validated against experimental data from vane shear tests.