Study And Prediction The Surface Settlement In The Loess Strata During Shield Construction

The strata displacement、ground subsidence、building crack and damages and other issues caused bytunnel construction have become the most concerned problems of environmental and engineering by thetunnel builders, designers and builders. In recent years, domestic and foreign scholars have made a lot ofstudy on the surface subsidence induced by shield construction， also did a lot of research, and achievedcertain results. which attained a lot of achievements. But in the present surface subsidence predictionresearch, most of the studies did not consider the effect of the elastic-plastic deformation and movementmode of excavation tunnel’s surrounding soil on the shape and size of shield tail annular convergencespace.Therefore, this paper on the basis of the random medium theory prediction model, using relevantknowledge of elastic-plastic theory and the analysis of soil movement mode, analysised and calculated theconvergence space and shield tail ring formation main influencing Angle. Has achieved the followingresults.Explaining the formation mechanism of deformation when the shield forward theoretically, andsummarized the main factor causing formation damage. Based on this, using elastic-plastic theoryknowledge analyzed the state of stress and strain on single-hole circular tunnel after shield excavation.Analysis the influence of the random medium theory formation Angle of main on the result ofprediction, And through analyzing the influence of casing body moving patterns of tunneling after shieldthrough on surface subsidence, and Combining the theory of soil mass mobile focus, Got the determinemethod of main influencing Angle in the cohesive soil, which can be used in prediction the surfacesubsidence cause by shield construction.Using the Matlb software, and write the Matlab calculation program of the random medium surfacesubsidence prediction formula,achieved prediction the surface subsidence by subway shieldconstruction.And analyzed the influence of the buried depth of the tunnel, tunnel radius, main influencing Angle, the size of section convergence, the elastic-plastic deformation in shield tail, overbreak volume ofeccentric and the additional pressure in excavation face on surface subsidence.According to the calculation of the section convergence after shield through and the calculation ofmain influencing Angle in this paper,and Combined with the existing calculation model of the non-uniformconvergence of tunnel surrounding soils, divided The random medium model into two parts, Obtained thenon-uniform convergence calculation model,which can not only consider the effect of elastic-plasticdeformation, but also can consider the affect of soil movement mode.Using The method which described in this article to predict the ground settlement induced by shieldconstruction for xi ’an metro line1, line2, line3, and made a compare with the measured results. Analysisshows that the oretical prediction results is in accordance with the measured results, so it can be used forthe engineering practice.