Study On Bearing Characteristics And Reasonable Support Of Rock Pillar In Small Clearance Deeply Buried Tunnel

The small clearance tunnel is a tunnel with a small clearance and mutual influence between the two holes in the parallel double-hole tunnel,and the main bearing feature of the small clearance tunnel is the rock pillar of the tunnel exerts its self-supporting capacity and maintains the stability of the tunnel.Relying on the self-supporting capacity of the rock pillar,the mechanical conversion of the small clearance tunnel is more complicated,the pressure arch effect is more significant,and the tunnel is under the state of high crustal stress,so it is a major difficulty in the actual construction process of the small clearance tunnel.Based on the literature research,this paper uses theoretical analysis and numerical simulation to study the rock-entrapment area in the deeply buried small clearance tunnel,and the main work and conclusions are as follows:(1)Based on the principle of Platts pressure arch,the extended Platts pressure arch load model of small clearance tunnel is proposed,and the calculation method of surrounding rock pressure is derived.(2)Combined with the theory of rock pillar partitioning,the shear strength of the rock wall is studied,and the shear strength is composed of fracture surface,slip resistance and sliding force,so as to analyze the bearing capacity of rock pillar and explore the weak area of rock pillar.Taking the displacement and plastic zone of both sides of the rock pillar as the criterion,the weak zone of the rock pillar was discussed from three perspectives: the morphology,shear strength and plastic zone of the rock pillar: the form of the rock pillar affected the stress concentration state of the rock pillar.The ultimate slip resistance on the fractured surface of the rock wall in the limit state is the basis for the shear strength.The plastic zone is the weak area affected by plastic strain on both sides of the rock pillar or the central axis.(3)Clear distance,burial depth,surrounding rock grade and the physical and mechanical parameters of rock pillar area were selected as the influencing factors,and the orthogonal test method was used to classify the influencing factors horizontally,and the mechanical characteristics and the laws of strain under multiple influencing factors were analyzed by numerical simulation of the small clearance tunnel under different working conditions.There are different reasonable clearance distances under different burial depths;The level of the surrounding rock of the tunnel with low clearance affects the strain rate and the diffusion of loose stress.The change of physical and mechanical parameters of the rock pillar area is a fundamental change in the bearing capacity of the rock pillar,which affects the stress-strain state of the rock pillar.(4)Taking the two reinforcement methods of grouting reinforcement and prestress on the tension bolt as the research object,analyzing its mechanism of action and construction mechanical response,combined with the zoning theory of rock pillar,the effective support of rock pillar is discussed.