Fracturing and Energy Evolution of Rock Around Prefabricated Rectangular and Circular Tunnels Under Shearing Load: A Comparative Analysis

• Published in: Rock mechanics and rock engineering 2023-12, Vol.56 (12), p.9057-9084
• Main Authors: Xin, Jie, Jiang, Quan, Li, Shaojun, Chen, Pengfei, Zhao, Herui
• Format: Article
• Language: English
• Subjects: Acoustic emission; Bearing capacity; Civil Engineering; Coalescence; Comparative analysis; Compression; Confining; Crack initiation; Crack propagation; Cracking (corrosion); Cracking (fracturing); Cracks; Deformation; Dissipation; Distribution; Earth and Environmental Science; Earth Sciences; Elastic deformation; Energy; Energy conservation law; Energy conversion; Evaluation; Evolution; Fracturing; Geophysics/Geodesy; Geotechnical engineering; High speed cameras; Impact damage; Load; Mathematical models; Mechanical properties; Microcracks; Model testing; Numerical models; Original Paper; Peak load; Plastic deformation; Pollution monitoring; Prefabrication; Rock; Rocks; Shear strength; Shear tests; Shearing; Strain; Stress distribution; Tunnels
• ISSN: 0723-2632; 1434-453X
• DOI: 10.1007/s00603-023-03532-8

Mechanical behavior and energy evolution of rock around the tunnel are critical for evaluating the instability of geotechnical engineering. To reveal the influence of tunnel section shape on deformation, stress distribution, and fracturing mechanism of rock around the tunnel, a series of physical model shear tests for rock around prefabricated rectangular and circular tunnels were carried out, and corresponding fracturing and energy evolution analysis were also presented. In the shear test, the cracking evolution of rock around tunnel specimens was monitored and recorded by a high-speed camera and acoustic emission monitor to reveal the macro- and meso-fracture features. In addition, to examine the continuous-discontinuous shear process, four typical numerical models of rock around the tunnel were exploited to explore meso-mechanical behavior and fracturing mechanism. In light of the first law of thermodynamics, energy conversion process, damage characteristics and rockburst tendency of rock around tunnel specimens were investigated. The test results manifested that fracturing evolution, energy characteristic conversion, and micro-cracks evolution of rock around tunnel specimens generally were classified as four unified stages. In terms of fracturing evolution, rock around tunnel specimens experienced shearing compression stage (stage I), elastic stage (stage II) dominated by crack initiation, shearing fracture stage (stage III) dominated by crack propagation, coalescence and shear-induced rockburst, and shearing friction stage (stage IV). In the aspect of energy characteristic conversion, rock around tunnel specimens were mainly elastic deformation before peak shearing load, and the plastic deformation was relatively small. Partial dissipated strain energy acted on closing hole and crack initiation, and the rest was stored as elastic strain energy. After peak shearing load, the shear strength dropped rapidly, and a large amount of strain energy was converted into dissipated strain energy for crack propagation, coalescence and shear-induced rockburst. In the evolution of micro-cracks, the specimens underwent crack quiet period (stage I), crack initial increase stage (stage II), crack rapid increase stage (stage III), and crack stable stage (stage IV). Interestingly, the damage stress and rockburst tendency of rock around prefabricated rectangular tunnels were superior to those of rock around prefabricated circular tunnels, indicating that the bearing capac