Accumulative Deformation Characteristics and Microstructure of Saturated Soft Clay under Cross-River Subway Loading

Abstract

The cross-river subway in the Hangzhou Bay area often passes through deep, thick, soft soil at the bottom of the river. At the same time, overlying erosion, siltation, and changes in water levels adversely affect the deformation of the subway, thereby causing hidden dangers to its safe operation. Using two-way dynamic triaxial testing, the effects of cyclic loading of the cross-river subway on the soft clay foundation were investigated for the first time, using simulation methodology as the prime objective of the present study. A strain development curve for the soft clay was obtained as a result. Considering the effects of effective confining pressure (p′) and radial cyclic stress ratio (τr), an explicit model of accumulative strain on soft clay under cyclic loading of the cross-river subway was established. The results showed that the accumulative axial strain (εd) was closely related to p′ and τr. Under certain conditions, as p′ and τr increased, the εd produced by the soil tended to decrease. Furthermore, through non-destructive testing based on nuclear magnetic resonance (NMR), pore distribution and pore size changes in soft clay during cyclic loading were analyzed. It was observed that under the action of the cross-river loading, the large internal soft clay pores were transformed into small pores, which manifested as a significant decrease in the number of large pores and an increase in the proportion of small pores. Lastly, the macroscopic dynamic soil characteristics observed during triaxial testing closely correlated with the microscopic pore size of the soil obtained in the NMR test, which indicated that using pore distribution and pore size changes to describe microscopic changes was a valid method.

Effects of compaction coefficients on microscopic pore structures and fractal properties of soft clay and freeze- thawed soft clay

“…They were then placed on the triaxial instrument with a back-pressure set to 200 kPa for saturation. The saturation operation was complete when the B (Saturation index) value had been verified to exceed 0.95 [28][29]. After saturation, each sample was placed in the sample tube of the NMR scanning device for scanning, and then removed from the sample tube and transferred to the freeze-thaw machine to undergo a freeze-thaw cycle.…”

“…Among these, the former two affect both horizontal and vertical relaxation, while the latter only affects horizontal relaxation. The transverse relaxation time of pore fluid can be expressed as [29,30]:…”

Accumulative Strain of Sand-Containing Soft Soil Reinforced by Cement and Sodium Silicate under Traffic Loading

“…Furthermore, in order to study the impact of repeated cyclic stress amplitude on the accumulative strain in more detail, the repeated cyclic stress amplitudes used in this paper were 0.124 kN, 0.15 kN, 0.17 kN, 0.19 kN, 0.22 kN, and 0.25 kN. Based on previous studies [38,41,43], a general conclusion that the confining pressures of 50 kPa, 100 kPa, and 150 kPa can represent the actual confining pressures of traffic loading has been accepted. Furthermore, in order to study the impact of confining pressure on the accumulative strain in more detail, the confining pressures used in this paper were 50 kPa, 100 kPa, 150 kPa, 200 kPa, 250 kPa, and 300 kPa.…”

Laboratory measurements of dispersed soils as construction materials for railway embankments

“…Laboratory stability tests provide the most complete information about the behavior of cohesive, rocky or artificially fixed soils under load [9,10]. However, no methodology for pre-compaction of dispersed soil samples prior to testing has been developed for stabilisation tests [11][12][13], with the exception of tests on frozen dispersed soils [14].…”