Research On Construction Method And Stability Control Of Shallow Buried Tunnel Group With Small Spacing In Parallel

With the increasing demand for infrastructure construction such as high-speed rail,highways and sea-crossing bridges in China,it has greatly promoted the development of bridges and tunnels,China presents many tunnel projects under complex environmental conditions.Such as tunnel group,deep buried tunnel,shallow buried soft rock tunnel,three high condition tunnel,These projects put forward higher standards for tunnel construction safety,so it is necessary to further improve the theory of tunnel engineering and strengthen the research and innovation of technology and equipment.This paper takes’Tencent Guiyang Qixing Data Center’as the engineering background.The data center is orthogonally composed of five parallel super-large cross-section tunnels and a contact tunnel in the mountain,which are named as B1～B5 tunnels and A1 contaction tunnels from left to right.At the same time,11 vertical air shafts are set in the five tunnels and contact tunnels,which jointly form the tunnel project of the data center.The span and height of the tunnel in the data center are 16.47 m and 11.7 m,respectively.The net cross-section area is 183.4 m~2.The average length of the five tunnels is 267 m,and the maximum buried depth is 63 m.It belongs to the tunnel group with large cross-section and small spacing.It is the first parallel small spacing shallow tunnel group at home and abroad.Due to the poor engineering geological conditions,the construction is difficult,and there are problems such as the interaction between adjacent tunnel construction,stress superposition,and the stability of slope rock and soil mass.Based on the above situation,this paper uses theoretical calculation to obtain the basic mechanical parameters of tunnel surrounding rock and the vertical pressure and horizontal pressure of tunnel under different buried depths.Through numerical simulation,the change of surrounding rock pressure,surrounding rock settlement and stability of supporting structure before and after tunnel excavation are analyzed.The tunnel vault settlement,the convergence of two sides and the surface settlement are obtained by field monitoring.At the same time,new methods are studied,such as five-line parallel tunnel rapid construction method,intersection rapid construction method.The main conclusions are as follows:(1)The construction method of five-line parallel small-space shallow-buried tunnel group is optimized,and the rapid construction technology of the combination of the middle partition method(CD method)and the bench method of shallow-buried large-section tunnel is invented,which accelerates the construction progress and reduces the hidden danger in the construction process.(2)Based on the rheological theory of tunnel surrounding rock,the prediction criterion of creep fracture instability zone of rock mass,the settlement of tunnel vault and the horizontal displacement,the deformation law of ground settlement is summarized,and the ground settlement is predicted in advance,which ensures the safety of tunnel construction.(3)According to Rankine’s earth pressure formula,the calculation model of surrounding rock pressure of five-line parallel tunnel group is established.The numerical simulation software is used to simulate the pressure superposition and deformation law of surrounding rock during tunnel construction.The results are basically consistent with the field monitoring data,which verifies the rationality of theoretical analysis.The research results in this paper enrich the engineering theory and technical system of shallow-buried large-section soft rock tunnel,which have important research significance and can be applied in similar projects.