The Study Of Strata Deformation And Support Behavior Of Tunnel With Shallow Burid Depth And Unsymmetrical Pressure

In the recent years, the construction of railway draws the attention of the government again. Tunnel, as the indispensable part of railway construction, can make up more than50%of the whole line. However, the entrance segment of tunnel is usually an intractable issue, especially in the northern part of our country. The entrance segment of tunnel are shallow buried and covered by entirely and strongly weathered rocks in most cases. Therefore, the overlying strata is quite sensitive to the disturbance caused by excavation of tunnel and the ground arch cannot form in it. In general, the construction of tunnel entrance can’t avoid the geological disaster such as landslide, collapse, unsymmetrical pressure, debris flow and avalanche on. The mechanism of deformation, rock pressure and the safety evaluation of preliminary support are the core problems of shallow buried tunnel. Based on the Hejie Tunnel in Guiyang-Guangzhou high speed railway line, the paper conducted a comprehensive in-situ monitoring experiment and obtained a serious of useful conclusions. The main work and conclusions are listed below.(1)The paper deducted the distribution character of the initial ground stress and made a comparison with the symmetrical tunnel. Utilizing the Mathmatica math software, the paper elaborated the choosing rule of the slope angle to calculate rock pressure based on the current railway tunnel code. The code is verified the feasibility to predict the rock pressure of tunnel roof, but not suitable to the lateral pressure. With Flac3D, the thesis analysis the soil deformation characters numerically.(2) The paper analyzed the deformation character of different buried depth, and summarized the general rule that soil layer obeys. Base on the rule, the paper put forward to a new method to predict the stability of soil near the arch roof. Compared with the traditional indicators, the indicator in this method is much timely and exact, which provides the time needed to take measures of remediation.(3)By the fitting software of Origin, the paper analyzed the character of settlement trough from different excavation method. It concluded that the settlement of ground surface in the deeply buried side is higher than that of the shallow buried side, and the width of the settlement trough in the deeply buried side is much wider than the shallow buried side. The ground loss rate is also presented.(4)The paper analyzed the distribution character of the pressure between rock and preliminary support and studied the influence of each excavation step on the pressure. The paper presented the final rock-preliminary support as well. It concluded that the pressure on the roof and inverted arch is comparely stable, free from the influence of excavation method and surrounding rock quality and the lateral pressure shows the feature of uncertainty.(5)Using the stability of steel as the criterion to judge the safety of preliminary support, the paper analyzed the evolution character of axial force and moment. It concluded that the minimum safety factor is1.86, and the maximum safety value is38.9, which indicate that the current steel structure fulfill the need of supporting and reserves sufficient emergency capacity.