Abstract
A three-dimensional twin tunnels scale model was established utilizing the discrete element method (DEM) with PFC3D. This model aims to investigate the displacement (in horizontal and vertical directions) and deformation of the first tunnel lining in four different cases which the clear distance of twin tunnels are 5, 10, 15 and 20 m during the second tunnel construction process. The numerical results indicate that the clear distance between twin tunnels and the distance between the measurement points of the first tunnel and the excavation area of the second tunnel are two most critical factors that influence the displacement and deformation of the first tunnel lining. Meanwhile, the soil arching effect, gravity, water pressure and lateral pressure also have an impact on the behavior of the first tunnel. The maximum disturbance of horizontal and vertical displacements occurred in the time points of finishing of the second tunnel. However, the horizontal displacement of the first tunnel is much more sensitive to the vertical displacement. The first tunnel turns to the right and down in direction while having an anticlockwise rotation (φ) during the process of construction of the second tunnel. In addition, the displacement and deformation of the lining of the first tunnel are critical to monitor, and the necessary precautions should be taken to decrease the risk of craze. In conclusion, the influence of the second tunnel excavation on the first tunnel lining could be neglected when their distance is more than 15 m.
Highlights
With the increase in transportation demand encountered in large cities, it is necessary to construct twin tunnels in the metro system
First stage: the horizontal displacements of Tunnel 1 lining increase with time domain when t is less than 0.085 s, which means the Tunnel 1 lining are gradually moving to the right direction
Third stage: when t = 0.095 - 0.135 s, the horizontal displacements generally decrease, which implies that the particles around Tunnel 1 are moving back to the left direction
Summary
With the increase in transportation demand encountered in large cities, it is necessary to construct twin tunnels in the metro system. Three-dimensional DEM modelling of twin tunnels is needed to assess the impact of adjacent tunnel constructional on an existing adjacent tunnel In view of these issues, there is still very limited knowledge of the displacement and deformation of an existing tunnel lining induced by later near distance tunneling, especially for the microscopic mechanism analysis by DEM method. To better understand the macro- and micro- mechanism of the lining of first tunnel during the construction process of the second tunnel using shield construction method, in this paper, a three-dimension DEM model has been conducted In this model, the horizontal and vertical displacements and deformation of Tunnel 1 lining in four different cases have been discussed. The numerical results provide a reference for the distance of shield construction twin tunnels in cross section
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
