Deformation characteristics and damage mechanism of Guiyang red clay under axial cyclic loading and unloading

Abstract

[Objective] In order to study the effect of axial loading and unloading on the deformation properties of Guiyang red clay, [Methods] the loading and unloading tests of soil samples under different axial stress ratios and cyclic numbers were designed, supplemented by low-field nuclear magnetic resonance technology and SEM electron microscope scanning. The evolution laws of macro-deformation and inner pore structure of soil samples during the whole cycle loading-unloading process were discussed to reveal the damage mechanism of soil samples. [Results] The result show that the internal structure of Guiyang red clay underwent a process from compaction to deterioration due to cyclic loading and unloading. With the increase of cycle number and stress ratio, the stress-strain curve of Guiyang red clay gradually changed from strain hardening type to strain softening type. The T₂ spectrum curve of pore distribution was developing from “mountain peak type” to “hilly type”, and the pore size range and peak spectrum of the sample were gradually decreasing. The number of large-medium pores gradually decreased, while the number of small-micro pores gradually increased. The clay particles around the pores were mostly in the form of closely cemented mineral particles, and the surface contact between the particles was changed into the form of line and point contact. The damage coefficient was defined by the change of unloading modulus and plastic deformation, indicating that the more the number of cycles and stress ratio, the more serious the damage of the soil sample, which was consistent with the law of pore change. [Conclusion] The result can provide theoretical guidance for the compaction and stability evaluation of red clay subgrade during construction period.

Keywords

Guiyang red clay / axial loading and unloading / nuclear magnetic resonance technology / damage / pore structure / deformation