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| Study on fracture characteristics and rockburst process of hard sandstone with high ground stress |
| ZHANG Zhiqiang1，2，ZHANG Kangjian1，2，XU Jialei1，2，LUO Chun1，2 |
| (1. Key Laboratory of Transportation Tunnel Engineering of Ministry of Education，Southwest Jiaotong University，Chengdu，Sichuan 610031，China；2. School of Civil Engineering，Southwest Jiaotong University，Chengdu，Sichuan 610031，China) |
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Abstract To study the hard sandstone rockburst failure characteristics under high ground stress and simulate the "damage" failure characteristics of the rock mass in that state，a Mode I/II mixed cohesive zone model based on Park-Paulino-Roesler(PPR) potential energy function was established. Through disk-shaped compact tension test and punch-through shear test，the Mode I and Mode II fracture characteristics of hard sandstone were studied，and model parameters were obtained. Then，a numerical model is established to simulate the rockburst of hard sandstone tunnel under high ground stress. The stress and energy of the elements in the process of rockburst are tracked to analyze the process and failure characteristics of rockburst in hard sandstone tunnel. The research results indicate that：(1) The shear strength and Mode II fracture energy of hard sandstone increase with the increase of confining pressure. When the confining pressure exceeds 30MPa，the Mode II fracture performance tends to stabilize. (2) When the vertical stress is much greater than the horizontal stress，the hard sandstone tunnel mainly experiences tensile-toppling rockburst in the form of layered spalling or wedge-shaped burst；On the contrary，shear-bursting rockburst characterized by penetrating shear failure in rock mass will occur. When the horizontal stress and vertical stress are both large，the unloading failure mode of rock mass mostly shows the characteristics of tensile-shear composite failure，and the tensile-stripping rockburst mainly occurs.
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