Model Test Study on Ground Settlement and Arching Evolution Induced by Super-Large-Diameter Shield Undercrossing an Existing Tunnel

Super-large-diameter shield undercrossing beneath an existing tunnel induces ground disturbance, influencing both the tunnel and the ground surface. As a key manifestation of ground response, soil arching plays a critical role. Using a self-developed shield tunneling simulation platform, we conducted model tests of a super-large-diameter tunnel undercrossing an existing tunnel, considering different volume loss ratios and tunnel spacings. Measurements of surface settlement, subsurface deformation, and earth pressure on the existing tunnel were obtained. Results indicate that surface settlement is dominated by volume loss ratio and modulated by tunnel spacing. High loss combined with small spacing may trigger surface collapse. Digital image correlation (DIC) captures settlement fields and reveals the soil arching evolution. The existing tunnel alters stress transfer paths, forming a stable arch at the front edge and an unstable arch at the rear edge. The ground disturbance induced by shield tunneling leads to significant changes in the earth pressure acting on the existing tunnel, and the pressure responses also corroborate the evolution of the surrounding soil arching. These findings provide insights for the deformation control and safety assurance in super-large-diameter shield tunneling.