Experimental investigation and numerical analysis of mechanical behaviour of railway station reconstruction over twin tunnels.

Railway station reconstruction adjacent to existing twin tunnels has been a challenging problem, as the former can impose heavy loads on the latter. As a result, the existing twin tunnels may sustain damage. To address this problem, in this study, a design plan for a railway station reconstruction over twin tunnels was improved by optimising the cross-section form and installing a buffer layer (XPS). Model tests were employed to investigate the mechanical behaviour of a railway station reconstruction over twin tunnels and the earth pressure in the surrounding rock, and an assessment of the safety of the existing tunnel lining was also performed. The numerical modelling was validated by an experiment based on the comparison of reinforcement strain, concrete stress, and failure pattern, particularly, the tensile-shear failure. In addition, the parametric study considering the different stiffness of the buffer layer was presented. These results comprehensively show the optimised design scheme not only addressed the very small clearance ranging from 1.46 m to 3.06 m but also reduced the construction cost including the decrease of concrete. As the stiffness of the buffer layer increases, the tunnel lining bears larger forces. The relatively low 10 MPa elastic modulus of buffer layer was recommended in this project. The valuable ideas, in this study, can potentially be generalized to similar projects for reducing the disturbance from the adjacent construction to the existing tunnels. [ABSTRACT FROM AUTHOR]