Mechanical behaviors of bimsoils during triaxial deformation revealed using real-time ultrasonic detection and post-test
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ORIGINAL PAPER
Mechanical behaviors of bimsoils during triaxial deformation revealed using real-time ultrasonic detection and post-test CT image analysis Y. Wang 1 & C. H. Li 1 & Z. Q. Hou 1 Received: 15 May 2018 / Accepted: 14 December 2018 / Published online: 28 December 2018 # Saudi Society for Geosciences 2018
Abstract 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 prepeak 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. Keywords Bimsoils . Mechanical behaviors . Ultrasonic testing . Triaxial compression . CT images
Introduction The term bimrock (block-in-matrix rock) introduced by Medley (1994) is used to describe geological formations composed of a mixture of stiff rock blocks within a bonded matrix of finer texture. Due to the structural difference of the individual components, large elastic contrast exists among the rock blocks and weak matrix.
* Y. Wang [email protected] C. H. Li [email protected] Z. Q. Hou [email protected] 1
Beijing Key Laboratory of Urban Underground Space Engineering, Department of Civil Engineering, School of Civil & Resource Engineering, University of Science and Technology Beijing, Beijing 100083, China
The rock block proportion and its size distribution, orientation, and spatial distributions affect the geomechanical behaviors of the mixtures at all scales of engineering interest. If the weak matrix is soil, this kind of geomaterial is often called bimsoil (block-inmatrix soil) (Medley 1994; Kalender et al. 2014; Wang et al. 2017a,b). The bimsoils are characterized by heterogeneity, environmental sensitivity, and poor blockmatrix cementation. Typical bimsoils include op
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