Characterizing the shearing strength of compacted Qiantang River silty clay from a state-dependent perspective

Compacted clay is widely used in geotechnical projects involving road embankment, subgrades, backfillings, etc. The shearing strength of saturated compacted clay is an important parameter in the analysis of the stability of these structures, and it is affected by states of soil, fabric, stress history, etc., making the characterization of the shearing strength remain difficult. This study investigated the shearing behaviors and shearing strength of a saturated and compacted Qiantang River silty clay using undrained triaxial compression tests. The specimens were compacted to different void ratios and saturated, followed by consolidation to different effective confining pressures for triaxial compression. The shearing behaviors are found to be state-dependent, namely, dependent on the void ratio and effective confining pressure before shearing. Several characteristic states, such as the undrained instability state, quasi-steady state, phase transformations state, and critical state, have been identified for each specimen. The deviatoric stresses at these states were characterized in the framework of critical state soil mechanics. The state parameter can be used to characterize the state-dependent shearing strength, while a modified state pressure index was proposed and found to be a better state variable for characterizing the state-dependent shearing strength of the compacted clay.