AN IMPROVED ANALYSIS MODEL FOR SHIELD TUNNEL WITH DOUBLE-LAYER LINING AND ITS APPLICATIONS

Based on three kinds of existing numerical models,a new analysis model with lining-segment joint-contact surface replaced by beam-spring-compression bar and spring combined element for shield tunnel with double-layer lining is improved.The problems of radial tension existing on the contact surface between strata and segment and between segment and secondary lining,and shear stress independent on shear displacement in contact surface between segment and secondary lining are solved by application of compression bar element,method of point displacement coupling,etc..The formulas of some critical parameters are given.The influences of contact surface elements number on results are discussed.The mechanical behaviors of Qiantang River tunnel on a high speed railway from Hangzhou to Changsha are studied.The results show that:(1) The bending moment of double-layer lining increases obviously as its thickness increases,and the increasing trend of bending moment keeps basically consistent with that of double-layer lining thickness.(2) The increase of double-layer lining?s thickness has little effect on axial force of double-layer lining.(3) There is no linear relationship between distribution proportions of bending moment on segment and secondary linings and their thickness proportions.The research results have some reference value for the design and analysis of underwater double-layer lining shield tunnel in the future.