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The construction process of twin tunnels is very complex, and the different construction schemes will cause obviously different mechanical behaviour, so it is necessary to make an analysis of the optimum construction schemes for a twin tunnel. In this paper, a finite-element forward analysis and back analysis program for twin tunnel is established, which can simulate the construction process under the three-heading construction method and benching tunneling construction method, the settlement of crown and ground, stress of the middle wall and the stability of the surrounding rock are analysed and compared with back-analysed parameters of the surrounding rock, then the advantages of the two methods are compared and a practical construction scheme optimised., The construction process of twin tunnels is very complex, and the different construction schemes will cause obviously different mechanical behaviour, so it is necessary to make an analysis of the optimum construction schemes for a twin tunnel. In this paper, a finite-element forward analysis and back analysis program for twin tunnel is established, which can simulate the construction process under the three-heading construction method and benching tunneling construction method, the settlement of crown and ground, stress of the middle wall and the stability of the surrounding rock are analysed and compared with back-analysed parameters of the surrounding rock, then the advantages of the two methods are compared and a practical construction scheme optimised.

Based on the background of crossing-river twin-tube shield tunneling in Shanghai, a 3D FEM model of a twin-tube shield tunnel to withstand water pressure was developed and the whole excavating and supporting process simulated by the elasto-plastic finite element method. Circumstance with different tunnel distance was analyzed, and the research emphases the interaction rules between the two tunnels. The reasonable parameter of tunnel distance was drawn, which can be the references for optimum design. The internal force, deformation of antecedent-building tunnel and load applying to it were monitored during the course of construction. Monitored results and optimum results of numerical simulation were compared and analysed. The significant results obtained provide a better understanding of the twin-tube tunnel excavation process and will be helpful in similar constructions in the future., Based on the background of crossing-river twin-tube shield tunneling in Shanghai, a 3D FEM model of a twin-tube shield tunnel to withstand water pressure was developed and the whole excavating and supporting process simulated by the elasto-plastic finite element method. Circumstance with different tunnel distance was analyzed, and the research emphases the interaction rules between the two tunnels. The reasonable parameter of tunnel distance was drawn, which can be the references for optimum design. The internal force, deformation of antecedent-building tunnel and load applying to it were monitored during the course of construction. Monitored results and optimum results of numerical simulation were compared and analysed. The significant results obtained provide a better understanding of the twin-tube tunnel excavation process and will be helpful in similar constructions in the future.

To investigate the mechanical behaviors of steel fibre reinforced concrete (SFRC) segments which are firstly used in the test section of the Shanghai Rail Transit Project Line 6, and to propose some useful suggestions for design and construction, a numerical analysis and field test are conducted. The contents of this study involve: (1) the behaviors of the segments against the jacking force, (2) the occurrence and development of cracks, the distribution of stress and strain of segment body, and (3) the distribution of stress and strain in circumferential joints of lining. The results show that safety against the jacking force of shield and the distribution of tensile strain in segment body and joint meet the requirement of design and construction. No cracks have been found in segments under the construction load. This indicates that the steel fibre provides the concrete of the segment with an improved crack resistance. It should be noticed that, although there is no cracks, the maximum tensile strain of rabbets of circumferential joints is much larger than the critical strain of the concrete. It is suggested that the rabbets should be reinforced in design., To investigate the mechanical behaviors of steel fibre reinforced concrete (SFRC) segments which are firstly used in the test section of the Shanghai Rail Transit Project Line 6, and to propose some useful suggestions for design and construction, a numerical analysis and field test are conducted. The contents of this study involve: (1) the behaviors of the segments against the jacking force, (2) the occurrence and development of cracks, the distribution of stress and strain of segment body, and (3) the distribution of stress and strain in circumferential joints of lining. The results show that safety against the jacking force of shield and the distribution of tensile strain in segment body and joint meet the requirement of design and construction. No cracks have been found in segments under the construction load. This indicates that the steel fibre provides the concrete of the segment with an improved crack resistance. It should be noticed that, although there is no cracks, the maximum tensile strain of rabbets of circumferential joints is much larger than the critical strain of the concrete. It is suggested that the rabbets should be reinforced in design.