ABSTRACT
In karst-developed areas, secondary construction disturbances during the excavation of twin shield tunnels with small clear distances can exacerbate the instability of surrounding rock and tunnel structures. This study employs FLAC 3D to construct a three-dimensional numerical model simulating the entire shield machine construction process for twin tunnels. The results show that tunnel structural deformation primarily occurs in the stage between the excavation and grout hardening stages. The newly excavated tunnels exhibit more pronounced horizontal deformation due to the coupled effect of the karst and nearby tunnel. This study compares the impacts of karst location, distance, and size on twin tunnel structural deformation. Karsts of varying diameters located at the top, bottom, and sides of the tunnel inconsistently affect the global deformation of twin tunnels. It should pay more attention to the large-diameter karsts on both sides of the tunnel and small-diameter karsts below it.
