Analysis Of The Small Spacing Tunnel's Support Structure Based On The Stability Of Surround Rocks

Due to complicated topographical and geological conditions as well as large numbers of mountainous areas, constructions of high-grade highway unavoidably meet with lots of tunnel works. As a result of special geological and topographical limitations, space of tunnels cannot satisfy with general terminal codes. Therefore, such special structure shape as small spacing tunnel, twin-bore tunnels should be applied.Small spacing tunnel are highly accepted in recent years by civil engineers for certain advantages comparing with twin-bore tunnel. A lot of problems come up, such as the optimal parameters of major parts, the assessment and control standard of explosion effect, proper construction methods, suitable monitor system and benchmarks, long safety evaluation and so on. To ensure the stability of surrounding rocks is the uppermost which should be paid great importance. Therefore, it is necessary to improve the theory to instruct the practical project at present, and so the meaning of the work this paper has done is profound.This paper has done some research on the stability of surrounding rocks and the security of supporting system of JIULING tunnel at the following aspects, of which the finite element method is adopted.(1) This paper gives introduction about factors affecting the stability of surrounding rocks, which includes gravity stress and tectonic stress(2) This paper analyzes the elastic and plastic stress distribution and displacement distribution of surrounding rocks after the excavation and timbering intheory.(3) The finite element method of ANSYS is adopted to simulate the tunnel surrounded by different levels of surrounding rocks(III,IV,V surrounding rocks) after excavation and different support(different shotCrete thickness, set Convert or not and so on), so to obtain the stress distribution and arch displacement and to do comparative analysis to ensure the validity between simulated data and actual measurement. (4) The stress distribution of surrounding rocks and the force situation of second lining have been analyzed at the case that different load ratios are undertaken by first and second lining.Above all, the research gives out the optimal supporting parameters of small spacing tunnel in various surrounding rocks, and turns out that convert can enhance the structure's bearer about 10 percents, improve the forces of surrounding rocks by reducing the tensile stress, Manish the arch displacement about 40 percents, and decrease the plastic area of surrounding rocks and so on.Also, it describes the load distribution ratio problems rooting that the loading release needs time, not come out in a flash. Taking V rocks as an example, loading release problems are studied, and it turns out that it is better to set up second lining early so to control the deformation of first lining.