The Study On Large Deformation Evolution Characteristics And Supporting Technology Of Swelling Loess Tunnels

Since engineering construction starts in loess areas, the mechanical properties and protection of loess have been the scientific questions which have troubled scientists. Because of the awareness of the loess expansion and large deformation at the early stage of the construction, normal design cannot control the tunnel safety. So the study on the large deformation evolution characteristics and effective supporting technology of swelling loess tunnels is a core technical problem which needs to be solved immediately. Based on the ministry of railway research project "Research on the Large Deformation Evolution Characteristics and Key Construction Technology of Swelling Loess Tunnels", this paper takes a swelling loess tunnel as the engineering background, applying field observation, numerical simulation and monitoring test to study the large deformation evolution characteristics and supporting technology of swelling loess tunnels.Firstly, the relationship between tunnel collapse and landslide was analyzed with the slice method. Then the expansion force which is the main factor of swelling loess tunnel collapse was revealed. Based on the convergence-confinement method, considering the expansion force, the failure model of swelling loess tunnels was summarized:the infiltration caused by the rainfall arouse the expansion of the surrounding rock. Then the expansion force caused the tunnel large deformation, which induced the tunnel large volume collapse.Secondly, the thermal expansion and the humid expansion were similar, so this paper applied the thermal expansion to simulate the loess expansion with the ABAQUS software. Based on the strength reduction method, the tunnel large deformation evolution was simulated. Then the tunnel safety coefficient was also solved. After a comprehensive analysis of the numerical simulation, the construction recommendations are proposed.Thirdly, on the basics of the theory in the above, the "steel+lattice grid" supporting technology was proposed. Then the ABAQUS was used to analyze the properties of the supporting technology. Summarizing the performance of four different kinds of the support, the supporting mechanism was proposed. Finally, the "one steel+one lattice grid" was applied in the swelling loess tunnel in TAIXING railway. The supporting effect was evaluated by the arch stress monitoring and deformation monitoring. The result showed that this supporting technology was effectively used to control the deformation of swelling loess tunnels.