Experimental study on undrained thixotropic cyclic resistance characteristics of marine soft clay

A series of unconsolidated undrained cyclic triaxial tests are carried out on the marine soft clay in the estuary of Yangtze River. The effects of age T, water content w and plasticity index I_P on the thixotropic cyclic resistance of the remolded marine soft clay are investigated. The test results show that the cyclic resistance CRR₁₅ for 15 cycles of the remodeled marine soft clay increases with T when the failure criterion is defined as the double-amplitude axial strain ε_ad = 5%, and the fastest growth rate of CRR₁₅ is observed when T = 14 d, and the CRR₁₅ increases slightly ortends to be stable when T > 28 d. The thixotropy of soft clay is weakened by early disturbance or cyclic loading, and the thixotropy cyclic resistance ratio A_d is obviously smaller than the static shear strength ratio A_s. A_d first increases and then decreases with the increasing I_P, but increases with the increase of w. A_d first increases and then decreases with the increase of the normalized water content w/w_L, an increase in the normalized water content w/w_L causes A_d to first increase and then decrease, and it reaches the maximum value when w/w_L = 0.76. The unconfined compressive strength tests under parallel test conditions are carried out, and the cyclic stress level is characterized by the ratio of the cyclic axial stress amplitude σ_d to 2 times the unconfined compressive strength q_u, σ_d/2q_u, and it is found that σ_d/2q_u is uniquely related to the failure cycle N_f required for the specimen to reach ε_ad = 5%, and σ_d/2q_u decreases as a power function with the increase of N_f.