Experimental Study on Strain Burst Characteristics of Sandstone Under True Triaxial Loading and Double Faces Unloading i
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ORIGINAL PAPER
Experimental Study on Strain Burst Characteristics of Sandstone Under True Triaxial Loading and Double Faces Unloading in One Direction Manchao He1 · Fuqiang Ren2 · Dongqiao Liu1 · Shudong Zhang1 Received: 9 January 2019 / Accepted: 5 October 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract In this study, a new strain burst test system was used to conduct two types of strain burst experiments by rapidly unloading single and double faces (in one direction), to simulate the strain burst occurring in surrounding rock of tunnel or double tunnel faces during the opposite tunneling. A high-speed image recording system and an acoustic emission system were used to monitor the failure process of strain burst of red sandstone. The commonalities of these two types of strain burst are as follows: failure stress and percentage of dissipation energy due to crack propagation were approximately equal; the evolution of mean velocity of free face was similar, which suddenly increased first and then decreased, then the gradient increased to the extremum value, and finally decreased to zero. Subregions of the fracture were consistent, and both showed shear, buckling, splitting, and ejection zones. However, the strain burst intensity for unloading double faces was larger than that for unloading single face, as demonstrated by a larger initial ejection velocity, larger volume of burst pit, and lower peak frequency. Furthermore, when double faces were unloaded, the flaky and massive features of fragments obtained due to strain burst were more obvious than the fragments obtained from the unloading of single face. Moreover, from yield to burst, when double faces were unloaded, the sandstone strain burst contained more shear microcracks, whereas the strain burst when unloading single face contained more tensile microcracks. Keywords Strain burst · Unloading double faces · Ejection velocity field · Fracture subregions · Peak frequency List of Symbols σ10, σ20, σ30 Initial maximum, intermediate, minimal principal stress, respectively σH, σh, σv Two horizontal and a vertical in situ stresses σX1, σX2 Minimal principal stress in negative and positive X-directions, respectively U Total strain energy Ue Elastic strain energy Uk Kinetic energy Ud Dissipation energy Uer Releasable elastic strain energy Udp Dissipation energy due to plastic deformation before yield Ud1 Dissipation energy due to crack propagation from yield to burst * Fuqiang Ren [email protected] 1
State Key Laboratory for Geomechanics and Deep Underground Engineering, Beijing 100083, China
School of Civil Engineering, University of Science and Technology LiaoNing, Anshan 114051, China
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Ud2 Dissipation energy due to crack propagation during burst process v Ejection velocity vy, vz Horizontal and vertical ejection velocity vmax Maximum initial ejection velocity m Total mass of ejection fragments d, d1, d2 Maximum distance between buckling cracks and free face l, w, h Length, width and thickness of fragments
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