Strain softening characteristics and stress–strain relationship of Guiyang carbonate laterite

The strain softening characteristics of carbonate red clay materials will have a significant impact on the safety and economy of engineering construction. To study such stress‒strain characteristics and influencing factors, this paper takes the native carbonate red clay in Guiyang as the research object and conducts triaxial consolidated undrained tests and scanning electron microscopy under different moisture content and confining pressure conditions. The test results show that the stress‒strain curve of the native red clay in Guiyang exhibits a peak-shaped variation and that the strain softening characteristics are jointly influenced by moisture content and confining pressure. With increasing confining pressure, the consolidation time of the specimen becomes longer, and the drainage volume increases. The volume change of the specimen during shearing follows the pattern of shearing contraction and then shearing expansion. After the shear test, the pore diameter of the specimen decreases, and numerous crack-like pores appear. A double-logarithmic strain softening model is established based on the characteristic stress‒strain curves (DL model). This model includes three parameters that can be determined based on the test curve. And it is used to simulate the stress‒strain curve of the native red clay in Guiyang; the results show that the DL is a new nonlinear model that can be applied to strain-softening soils.