The Research Of Dynamics Property And Longtime Subsidence About Corrosion Weathered Red Layer Under Base Of Subway Tunnel

The stability and deformation of foundation has been one of the main research topics of geotechnics. With the rapid development of urban rail transit construction, the substrate deformation and stability has become a hot research topic at present to assure a safe operation of subway system.Red layer is a widely distributed rock in Changsha. The weathered conglomerate layer is red layer formed by weathering and dissolution combined affection. The characteristic of weathered conglomerate layer is complex, which possesses a loose structure and low formation strength. In this paper, subway tunnels encountered weathered conglomerate layer. The dissertation is granted from the National Natural Science Foundation of China.Laboratory experiments, theoretical analysis and numerical method are used comprehensively to study the basic dynamic characteristics of the subway tunnel surrounding rock under train vibration loads. The settlement of tunnel base under long-term of railway loads with weathered conglomerate layer are solved, and the main contents and results are as follows:(1) The characteristics of weathered conglomerate layer:combined with litho logy composition, tectonic environment, and site conditions, and other factors, the engineering properties of weathered conglomerate layer are studied, which provide a basis for the dynamic analysis.(2)The cycle loading tests of weathered conglomerate layer: using dynamic trail test instrument, a series of tests conceding different dynamic stress, static deviator stress, confining pressure, consolidation ratio and load frequency are carried out to study the law of dynamic deformation of weathered conglomerate, and are compared by the impaction of different factors.The test results show that:the axial cumulative deformation of weathered conglomerate under cycle vibration loads were significantly affected by the dynamic stress and static deviator stress factors. Under the dynamic stress and static deviator stress, the axial cumulative deformation increased as well. The loading frequency, confining pressure, consolidation stress ratio factors have subtle effect on the cumulative deformation. The dynamic elastic modulus of weathered conglomerate reduced significantly when the strain increased.(3) Boundary surface constitutive model:based on the elastic-plastic theory and the theory of boundary surface, the constitutive equation of weathered conglomerate rock is established. The constitutive integration algorithm and iterative format were derived. Using the finite difference software, the calculation model were completely developed and the validity of the model are verified by the experimental results.(4) the long-term settlement deformation of tunnel base with weathered conglomerate rock prediction:With the finite difference numerical computing software, long-term settlement deformation of tunnel base with weathered conglomerate rock were predicted respectively under different driving speeds, different structure thickness, different thickness of distribution. It is concluded that the significant affection depth of subway tunnel under train vibration was about4m below the base.(5) The long-term subsidence deformation of shield tunnel substrate dissolution weathered rock was analyzed in accordance with the proposed settlement prediction model system. Around this question, it is concluded that:the cumulative deformation of tunnel foundation increases with the increase of train speed. The thickness of shield tunnel segment has less affected on accumulation deformation.After reinforcement treatment dissolution weathered layer under tunnel bottom, it effectively reduces the amplitude of the dynamic stress of the basement rock. So it effectively controls the subsidence cumulative deformation of basement. The results suggest that the thickness of pre-reinforcement treatment of weathered conglomerate rock should be not less than2m.