Research On Deformation Behavior And Integrated Construction Technology For The Shallow-buried Sandy Stratum Tunnel

The deformation behavior and construction technology of the shallow-buried sandy stratum tunnel have been the research focus in the Geotechnical engineering field due to its difficulty to construct, large deformation and poor stability. There have been shallow-buried sandy stratum of 450 metres long in the Xining entry segment of Guanjiao Tunnel. Because of the poor mechanical behavior of rockmass and the unsymmetrical pressure condition, there has been high danger to construct. So it has realistic engineering value to carry out research on the stability and construction technology of the shallow-buried sandy stratum tunnel. The detailed contents are as fellows:1. Firstly, the study actuality of internal and overseas were introduced about the construction and deformation behavior of shallow-buried sandy Stratum tunnel. The relative mature, advanced construction practice and theory achievements were also summarized. Then the Geotechnical and hydrological geology were three introduced, alternative construction methods - cut-and-cover method, shield method and mining method were presented .2. Based on the engineering charaters of the shallow-buried sandy stratum in the entry segment of Guanjiao tunnel, Fuzzy Judgment theory was adopted to evalue the three optional construction methods. By comprehensive evaluement of the three methods form aspects of safety, construction process, economic benefit and environmental influence, the optimal method was choosed. Mining method was recommended to the entry segment of Guanjiao Tunnel.3. Numerical simulation method was adopted to analyse the deformation and plastic area changing rule of surrounding rock under different stress release rate of Guanjiao Tunnel. Based on above results and catastrophic theory, limit state and limit displacement were defined . When the stress release rate reach to 80%, the state of surrounding rock was defined as limit state, and the corresponding displacement(i.e. settlement of vault is 90mm, interior horizontal convergence is 160mm ) was defined as limit displacement. 4. Based on 3D finite element numerical model, the modified construction method was simulated and the displacement of surrounding rock and stress distribution of support structure were analysed. The maximal settlement and horizontal converge of surrounding rock were respectively 35mm and 64mm . And the maximal tension and compression stress of primary support were respectively 1.89MPa and -13.8MPa. It was concluded that new construction technology could control deformation of tunnel, improve the stability and assure the safety of support structure of tunnel.5.At last, the key construction technologies of shallow-buried sandy stratum tunnel were formed by practical engineering practice and exploration, i.e.â‘ setting long and large advanced horizontal roof pipes and full-face advanced ductule;â‘¡mini four-steps excavation;â‘¢setting temporary horizontal steel brace to control deformation of surrounding rock.6.From monitoring measurement of ground settlement and interior deformation, it was concluded that the deformation of tunnel markedly minished and stability improved compared with the former design scheme.