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

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