Surrounding Rock Control Mechanism Of Confined Concrete Arch Initial Support For Large-span Tunnel

With the need of economic development in our country, the infrastructure construction such as traffic tunnel become an important engine of economic development, the tunnel construction is into a big development period which is unprecedented. With the rapid development of tunnel construction, more and more tunnel have to build in the area, which under high in-situ stress, the complex geological conditions, and is fault fracture zone. At the same time, large-span tunne such as eight traffic lanes become more and more. And there is no design norms and construction norms for large-span tunnel, then safety problems of the tunnel construction in complicated condition is very important. Constraint concrete technology is widely used in the ground structure, and it was successful applicated in the complex conditions roadways of mine. In this paper, Control mechanism of confined concrete arch initial support for large-span tunnel is researched by model experiment, indoor test and numerical test.(1)Model test research on high strength support of large-span tunnel two side-wall pilot tunnel method construction processTaking GangGou tunnel for engineering background, a model test study on high strength support of large-span tunnel two side-wall pilot tunnel method construction process were conducted. The surrounding rock displacement, the stress evolution law and force characteristics of support component are analyzed with or withoutofhigh strength support. Deformation failure mechanism of surrounding rock and the control mechanism of surrounding rock in the construction process of super section tunnel are revealed.The rock mass displacement without the support is greater than the high strength support. Near point displacement of left and right vault with high strength support is reduced by 69%and 75% separately compared the non-support condition, far point displacement is reduced by 77.8%and 88.6% separately, small spacing is reduced by 47.1% and 52.4% separately, surrounding rock displacement of strength support is overall lower than that condition of non-support, surrounding rock control effect is obvious. In 300 m to 800 m depth, high strength support tunnel vault displacement than supporting conditions was reduced by 78.1%,78.9%,70.8%.78.1%.72.3%,74.1%, in a certain depth range, high strength bolting can effectively control the deformation of the surrounding rock.(2) Large scale indoor experimental on mechanical properties of confined concrete archA large scale mechanics test is carried out by transforming large mechanical test system of confined concrete arch applied to underground engineering. Combined with numerical contrast experiment, deformation failure mode, internal force and stress distribution characteristics, critical damage location, ultimate bearing capacity are researched deeply.Arch become flat under uniform loading, displacement and strain of the biggest parts appear in the vault and the two position; Laboratory test yield capacity and ultimate bearing capacity were 1980.7 kN and 2370.6 kN, numerical experiment arch yield bearing capacity is 1890.9 kN, ultimate bearing capacity is 2196.6 kN. Laboratory test and numerical experiment are in good consistency; Arch subjected to axial compression and bending, bending moments even more significant.(3)Primary support characteristics of confined concrete archThe numerical comparison tests of constraint concrete arch, H-beam arch in view of the actual size are carried, and the influence law of arch cross section steel pipe length, wall thickness, concrete strength, load model on arch mechanical properties is studied. The bearing mechanism of confined concrete arch is cleared.Under uniformly distributed load, SQCC180 x 10 arch thanH200x200,H200x200-Carch capacity increased by 81.4% and 58.4%. Under the load model of vertical pressure/level= 1.5, SQCC 180x10 arch than H200×200, H200x200-C arch capacity increased by 128% and 72.3%. The bearing capacity of square steel confined concrete arch has increased significantly than the section steel arch made by the same content of steel. The influence laws of steel tube wall thickness, side length, the strength of core concrete, load model on the mechanical properties of the arch are studied, and the relation equation of each factors and bearing capacity is obtained by fitting.(4)Control mechanism of confined concrete arch initial support for large-span tunnelThe different supporting method numerical experiment of large-span tunnel excavated by the double sidewall drift method was carried out. The change laws of tunnel surrounding rock deformation and plastic zone development are contrasted and analyzed under four types of supporting schemes, which include excavation without support, bolt-shotcrete support, H-beam arch+bolt-shotcrete support, SQCC arch+bolt-shotcrete support. The high strength control mechanism of large-span tunnel is researched.Under the condition of a broken surrounding rock, confined concrete arch compared with the H steel arch control effect is most obvious, especially the fifth part, vault displacement only 29.5% for h-beam support of. For Large-span tunnel in the condition of complex, confined concrete arch support largely improve the control effect than h-beam, especially under the condition of the soft and broken surrounding rock, the supporting advantages more apparent.