Strain accumulation and microstructure characteristics of soft clay under cross-river subway loading

The cross-river subway often passed through deep soft clay layers at the bottom of the river, and these soil layers were prone to excessive deformation and settlement, which will adversely affect the safety of subway operations. Through the indoor bidirectional dynamic triaxial test, the effect of the cross-river subway cyclic loading on the soft clay foundation was simulated, the curves of the soft clay strain development law were obtained, and the cumulative strain model of the soft clay under the cyclic load of the cross-river subway was established. Combined with the NMR scanning test, the soil microscopic pore structure before and after cyclic loading was analyzed. The effects of effective confining pressure and radial cyclic stress ratio on pore distribution under the load of the cross-river subway were analyzed, and the correlation between pore structure and macroscopic dynamic characteristics was studied from a microscopic point of view. Based on the experimental data, an explicit relationship of strain accumulation of soft clay under the load of the cross-river subway was proposed, and the effects of effective confining pressure and radial cyclic stress ratio were comprehensively considered. The results show that under certain circumstances, the accumulative strain generated by the soil body is inversely proportional to the confining pressure and radial cyclic stress ratio. The cyclic loading process will destroy the connection between the soil units, resulting in a significant change in the pore size distribution. Under the load of the cross-river subway, the pore structure of the soil has a tendency to vibrate, the degree of soil particle fragmentation increases, the large pores of the soil decrease, and the small pores increase. There is a negative correlation between the average pore diameter and the axial cumulative strain under cyclic loading of cross-river subway. © 2021, Central South University Press. All right reserved.