Experimental insights and evaluation method for thixotropic strength recovery in marine clays applied to offshore engineering

The thixotropic behavior of marine soils provides an inherent cost-optimization mechanism for the design of foundation systems for marine clean renewable energy infrastructure. his study investigates the thixotropic strength recovery characteristics of marine soft clay from the Yangtze River Estuary through unconfined compression, triaxial compression, and cyclic triaxial tests under varying curing periods. The results indicate that the clay exhibits significant thixotropic strength recovery, the extent of which is considerably influenced by water content ( w ) and the plasticity index ( I P ). Under identical conditions, the thixotropic unconfined compressive strength ratio A q , the thixotropic static shear strength ratio A s , and the thixotropic cyclic strength ratio A d all increase with I P and decrease with w , following the order A d < A s < A q . Over a 60-day curing period, the maximum values of A q , A s , and A d reached 1.502, 1.475, and 1.375, respectively. By introducing a normalized water content ( w / w L , where w L is the liquid limit), a critical state response law has been identified: A q , A s , and A d peaked at w / w L = 0.76, exhibiting a non-monotonic trend characterized by an initial increase followed by a decrease. Consequently, a time-dependent thixotropic strength prediction model, based on the theory of bonded granular geotechnical materials, is developed for application to marine clays. This model is validated using data from literature. Furthermore, a unified evaluation method for cyclic strength was proposed using unconfined compressive strength and shear strength as normalization indexes, providing quantitative basis and design guidance for long-term performance assessment of marine foundation engineering.