LAUSR

Real-time ultrasonic experiments were conducted to investigate the mechanical responses of block-in-matrix soil (bimsoil) samples under triaxial deformation. Although the mechanical behaviors of bimrocks and bimsoils have been widely studied, the rock-soil (block-matrix) interface cracking, rock-soil interaction, block occlusion, and interlocking effects during triaxial deformation are still incompletely understood. This paper aims to investigate the effect of confining pressure and block proportion on ultrasonic and mechanical properties of bimsoils using ultrasonic pulse velocity (UPV). Conventional compaction soil testing was adapted to produce cylindrical bimsoil samples of different rock block percentages (RBP) with various hammer counts, to ensure roughly the same compactness of soil matrix. The experimental results show that UPV reflects the complex mechanical behavior of bimosils during deformation. UPV measurements became more variable as samples deformed at the pre-peak and post-peak stages. It is suggested that the UPV is affected not only by stress level but also the meso-structures that develop during failure in bimsoils. Observation of macroscopic fracture morphology combined with image analysis of mesoscopic computed tomography (CT) scans reveals that multiple localized tortuous bands form during deformation due to the presence of rock blocks in bimsoils. The changes of UPV are mainly attributed to the interactions of soil matrix and rock block. The post-test CT images further confirm this result.