Macro-meso fatigue failure characteristics of a bimsoil under multistage cyclic triaxial loads with different frequencies

Abstract

The dynamic mechanical response of block-in-matrix-soils (bimsoils) is crucial to the long-term stability predication of constructions and building structures made of bimsoils. Although the dynamic failure behaviors of bimsoil under cyclic loads have been widely understood, the influence of loading frequencies on the macro-meso structural deterioration governing localized band propagation have not been well understood. Herein, multistage cyclic triaixal tests and post-test X-ray computed tomography (CT) scanning have been performed on bimsoil with various loading frequencies (f = 0.1 Hz, 0.2 Hz, 1.0 Hz, and 2.0 Hz). The cyclic triaxial tests simulated the behavior of bimsoil material under varied velocities of passing vehicle herein. The macro-meso fatigue failure characteristics were analyzed in terms of stress-strain responses, stiffness degradation, and meso-structural changes. Testing results show that the applied loading frequency alters the coupling degree of soil matrix and rock blocks, and damage develops fully within bimsoil under relatively low loading frequency. In addition, the failure mode of bimsoil changes from bulging failure to shear failure with the increases of loading frequency, and the volumetric deformation is the largest for a bimsoil sample subjected to low loading frequency. Moreover, post-test CT scanning reveals the meso-structural degradation within bimsoil, the multiple interface damage and cracking contribute a lot to the strength, volumetric deformation and failure modes. It is suggested the contact, interlocking, occlusion, and separation among the rock blocks promote the volume dilatancy when subjecting to low loading frequency.