Experimental Study and Theoretical Analysis of the Effect of Surcharge/Unloading at Both Sides of the Ground Surface on an Existing Shield Tunnel at Different Burial Depths

This paper investigates the impact of surcharge/unloading at both sides ground surface on an existing underground shield tunnel varying burial depths. A large-scale indoor model experiment was conducted to study vertical convergence deformation, settlement, and additional surrounding pressure different depths when occurred surface. The effect depth, surcharge mass, uneven further investigated by theoretical calculation. results indicate that under same conditions, greater depth leads reduced pressure. Unloading can partially reduce deformation but it does not completely counteract preceding surcharge. In cases a symmetrical above tunnel, is symmetrically distributed, with higher pressures arch top bottom lower waist. suggests are vulnerable points require special attention. has most pronounced followed surface, and, finally, smallest from bias load.