Research on Rock Bolt Support Parameters of Tunnels in Gently Dipping Sandshale Stratum
The interbedding of sandstone and shale is usually discovered as a gently dipping soft-hard rock stratum with significant anisotropy in strength and deformation,and the stress mechanism of tunnel support structure is complex.Taking a deep-buried section of Wujiayuan Tunnel on Xi'an-Yan'an HSR as the study object,based on on-site geological survey,this paper establishes a generalized numerical model of horizontal sandshale interbedded tunnel by rock fracture software RFPA2D,analyzes the influence law of rock bolt length and arrangement mode on surrounding rock fracture characteristics,puts forward reasonable rock bolt support parameters,and verifies the rationality of support parameters through on-site monitoring.The study results show that:(1)The anisotropy of gently dipping sandshale stratum is significant,and shear and tension cracks are generated in soft rock stratum after tunnel excavation.After the shotcrete bolt lining is applied,the shear slips and tension cracks between soft and hard rock strata at the tunnel arch crown can be effectively suppressed.(2)With the increase of rock bolt length,the stress status of surrounding rock is improved,and the shape of fracture zone is changed from X-shape to crescent shape around the tunnel.The fracture range is gradually decreased,the acoustic emission number is decreased,and the stability of surrounding rock is improved.(3)With the distribution range of rock bolts changing from local arch crown to full circumference,the range of surrounding rock fracture zone is decreased,the maximum principal stress value is decreased,and the acoustic emission number is decreased.(4)In order to give full play to the reinforcement effect of composite beam of rock bolt,it shall be arranged at a large angle with the rock stratum.The length of rock bolt shall be greater than the thickness of soft rock stratum and penetrate into hard rock stratum.
Xi'an-Yan'an HSRgently dipping sandshale stratumrock bolt supportsurrounding rock fracturenumerical simulationRFPA
NETL
NSTL
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