Based On Orthogonal Experimental Design Bias Of The Shallow Tunnel Finite Element Analysis

According to various terrain and geological circumstances, physical and mechanical characteristics of the surrounding rock, different structure forms, constructing methods and corresponding assistant engineering measures have always been chosen for low-buried and unsymmetrical pressure tunnels. The influencing otherness of mentioned factors and coupling relations of each factor, impose too much difficulty on design and construction of low-buried and unsymmetrical pressure tunnels. So, it is very necessary to analysis influence grade of each factor for low-buried and unsymmetrical pressure tunnels. In this thesis, including project designing by orthogonal experimentation, numerical simulating by ANSYS, analyzing various factors on low-buried and pressure-unbalanced tunnels like depth, gradient, elasticity modulus, etc, a lot of instructional conclusions on design and construction of low-buried and unsymmetrical pressure tunnels have been drawn.After meticulous analysis, main conclusions are as follow:1) Through orthogonal experimentation, the simulation times and computing quantities of numerical simulation project design have been consumedly reduced.2) Asymmetry of rock pressures on tunnels gradually increases along with the decreases of depth and the increases of gradient, but when the depth is up to 30 meters, the influence of gradient on unsymmetrical pressure tunnel will remarkably decrease, which is consistent with that of low-buried tunnel with V- class surrounding rock at critical.3) During the process of distortion, surrounding rock not only has displacement to the critical surface and sinking trend of coping earth, but also has outboard extrusion moving trend. This trend is gradually reduced along with the increases of the depth and decreases of gradient, and may be ignored when the depth is up to 15m and gradient is less than 1:1.5. When the depth exceeds 30m, this trend will not exist at all, and the extrusion of the outboard earth on lining will take the place.4) Anchor bars at small depth side are always in press condition and timbering effect is limited from excavation and timbering of the tunnel to a steady displacement field and stress field.5) v and conglutination aggregation force have a close relation with vault vertical displacement, and elasticity modulus and v have a close relation with circumjacent constringency.6) The influences on stress of tunnel with decreasing trend: elasticity modulus, v , conglutination aggregation force and friction angle, on displacement of tunnel, the same with those on stress of tunnel, on plastic region of surrounding rock: conglutination aggregation force, friction angle, v and elasticity modulus.7) The influence of unsymmetrical pressure at horizontal direction on carrying capacity of tunnel is tremendous. The influence of unsymmetrical pressure at vertical direction on carrying capacity of tunnel is much less.