| With the rapid development of China’s economy,a large number of infrastructure,especially the construction of railway tunnels,are growing in blowouts.In the process of building so many tunnels,a variety of weak surrounding rock areas will inevitably be encountered.In the process of excavation,the instability of the face is very easy to occur,which brings great trouble to the construction..Fully weathered red sandstone is a kind of geotechnical material with complex composition,changeable structure and special mechanical properties.It has the characteristics of softening and easy disintegration in contact with water,and its stability is poor.Red sandstone is prone to quicksand and instability after meeting water during tunnel construction.However,at present,there is almost no research on the stability of tunnel face in fully weathered red sandstone stratum tunnels.The key technology for construction in fully weathered red sandstone tunnels is not mature enough,and some reliable construction countermeasures are lacking.Therefore,relying on the Yangcheng tunnel of the Haoji Railway,this paper adopts a variety of research methods such as field investigation,literature investigation,indoor experiment,mathematical model and numerical simulation to study the stability and control technology of the tunnel face of the fully weathered red sandstone tunnel.The main research work is as follows:(1)Carry out indoor physical and mechanical tests of fully weathered red sandstone.The physical parameters such as moisture content,natural density,particle density and optimal moisture content of the undisturbed soil were measured through basic physical experiments in the laboratory,and the relevant physical characteristics of the undisturbed soil of the fully weathered red sandstone were obtained.The original soil is remolded into remolded soil with different moisture content.Through consolidation compression test and direct shear test,the compression modulus,cohesion and internal friction angle of remolded soil under different moisture content are obtained.(2)Based on the results of laboratory tests,a tunnel excavation model in completely weathered red sandstone is established by numerical simulation.The deformation characteristics of tunnel face in fully weathered red sandstone stratum with different buried depth and water content are compared and analyzed from five aspects: extrusion displacement of tunnel face,deformation in front of tunnel face,vault settlement,stress in front of tunnel face and plastic zone in front of tunnel face.(3)Based on the catastrophe theory,using the characteristic point displacement of the tunnel face as the criterion of instability,the stability of the tunnel face under different water contents is analyzed.Through the strength reduction method,the relation curve between the displacement of the characteristic point of the tunnel face and the reduction coefficient is constructed,and then the catastrophe point is found out according to the cusp catastrophe model in the catastrophe theory,and the corresponding reduction factor can be regarded as the safety factor of the tunnel face.(4)Research on the stability control technology of the tunnel face,analyze the stability control principle of the tunnel face,and briefly introduce different control measures.Finally,according to the implementation of the actual control measures in Yangcheng Tunnel,the deformation and stability of the face after adopting the control measures are compared and analyzed by numerical means. |
