Experimental and Numerical Investigation on Shear Failure Behavior of Rock-like Samples Containing Multiple Non-Persiste
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ORIGINAL PAPER
Experimental and Numerical Investigation on Shear Failure Behavior of Rock‑like Samples Containing Multiple Non‑Persistent Joints Yuanchao Zhang1 · Yujing Jiang1 · Daisuke Asahina2 · Changsheng Wang1 Received: 27 February 2020 / Accepted: 24 June 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract The instability of rock slopes and underground engineering structures is usually caused by shear sliding along discontinuities, such as joints or faults, which are usually non-persistent. It is important to study the shear failure behavior of non-persistent joints to better understand the instability mechanism of jointed rock masses. In this research, rock-like samples containing multiple non-persistent joints were prepared and used for direct shear tests under constant normal load. The test results showed that the shear failure of multiple non-persistent joints usually involves multiple coalescence modes of rock bridges, which are affected by joint configurations and normal stress. Under the same normal stress, the shear strength, and dilation behavior are mostly dominated by joint persistency, which essentially determines the roughness of the macroshear fracture surface. Furthermore, the acoustic emission characteristics of non-persistent joints were evaluated by the hit rate, energy rate, and b value. A lower b value, indicating a more intense shear failure, is usually related to a smaller joint persistency and medium joint spacing. Finally, the cracking process, force evolution, and micro-cracking mechanism of multiple nonpersistent joints were revealed using particle flow code. Keywords Non-persistent joint · Shear strength · Acoustic emission · Particle flow code Abbreviations JRC Joint roughness coefficient AE Acoustic emission DEM Discrete element method PFC Particle flow code BPM Bonded particle model PB(M) Parallel bond (model) UCS/Ts Ratio of unconfined compressive strength to tensile strength CNL Constant normal load DT Direct tensile crack RT Relative tensile crack ST Shearing tensile crack DS Direct shear crack RS Relative shear crack CS Compressive shear crack
* Yujing Jiang jiang@nagasaki‑u.ac.jp 1
Graduate School of Engineering, Nagasaki University, 1‑14 Bunkyo‑machi, Nagasaki 852‑8521, Japan
National Institute of Advanced Industrial Science and Technology, Ibaraki 305‑8567, Japan
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List of Symbols D Joint spacing β Rock bridge angle Lj Joint length Lr Rock bridge length k Joint persistency factor d Joint spacing factor e Joint overlapping factor Jm,n Joint in row m and column n δh Shear displacement δv Normal displacement τ Shear stress τp Peak strength τp-sub Sub-peak strength τr Residual strength τini Crack initiation stress δvp Peak dilation δvt Terminal dilation σn Normal stress Nr Number of non-persistent joint rows N Event number M Earthquake magnitude AdB Peak amplitude of the AE events a,b Coefficient of Eqs. (1) and (2) α Coalescence angle
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Vol.:(0123456789)
Rmin Minimum radius of particle ρ Densi
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