Mechanical Performance Of Long-span Underground Structure With NTR Construction Method

The New Tubular Roof (NTR) method is a new type of tunneling construction technology introduced from foreign countries to construct underground structures. The NTR technology is used to build the air channel and the main structure in Xinle Ruin Station, Shenyang2nd Metro Line for the first time in China and the remarkable economic and social benefits have been achieved. The application of the NTR method shows that it has great application prospects not only to solve the construction of the underground structure in the kinds of complex conditions and the high environmental requirements but also to deal with the construction of underground structures with the large span, ultra-shallow-buried level, or small adjacent distance.Based on the NTR engineering project of the Xinle Ruin Station of Shenyang2nd Metro Line, the mechanical behaviors of the proposed NTR structure and the force characteristics of the ribbed beam structure were researched in the dissertation by using comprehensive method of theoretical analysis, numerical simulation, experimental research as well as the results of the in-situ monitoring. The main contents are discribed as follows:(1) The mechanical behaviours of the closely distributed steel pipes with lardge diameters during construction were firsly developed. The closely distributed steel pipes needed to be forced into soil by the hydraulic jacks at the same time to make the new tubular foof structure which is the basic of the NTR mothod. Based on the numerical simulation and the measured data in situ for the construction process of the Xinle Ruin Station of Shenyang2nd Metro Line, the deformation of the ground surface and variation regular as well as the force characteristics of the great diameter steel pipes were researched, and influences of material parameters, construction sequence and other factors on the pipes jacking were discussed during the process of the pipes jacking in this dissertation.(2) The static experiment for the joints of the NTR structure was performed. The ribbed beam structure is the new kind of underground structure system with large-section constructed by the NTR method. Due to the specificity of the NTR structure, the longitudinal beams and the ribbed ring beams are connected by a large number of nodes. Therefore, whether the node design is reasonable or not has a direct effect on the reliability of the structure. The failure characteristics and the ultimate bearing capacity of the node of the ribbed beam structure were discussed by experiment method, especially analyzed on the failure modes and failure mechanism of the nodes. On the basis of above-mentioned analysis, the effects of the deviation rate of the cross-section and other factors on characteristics of the node were given. According to the different failure characteristics of nodes, a simplified calculating formula was proposed.(3) The flexural static performance test for a local mode of the NTR structure was performed. According to the results of the experiment, the failure characteristics and ultimate bearing capacity were analyzed for the different members. At the same time, a simplified calculating formula for the bending bearing capacity was presented, and the corresponding construction measures in details for the different situations were put forward as a reference for practical engineering.(4) The whole construction process of the main structure was numerecally simulated by using numerical simulate method combined with the field test data. The results of the three-dimension elastic-plastic numerical simulation were obtained. The mechanical states and variation regular of the internal force, the characteristics of the structure deformation and ground surface deformation in the process of construction were discussed for the diferent time of the construction. Through the analysis, some regularity results of the force and deformation were induced and summarized. The effective factors of the internal force and the ground deformation were numerically developed to provide the reference for the engineering design and further improvement on the application and generalization of the NTR method.