Case Analysis of Damage and Treatment of Existing Upper Bridges Caused by Shield Tunnel Construction

Based on the background of the shield tunneling under existing bridges in a entrance/exit section tunnel in the central and southern regions, the characteristics and mechanisms of settlement deformation of bridge pile foundation and bridge diseases caused by the construction of 4-line shield tunnel are analyzed. In terms of the characteristics of pile foundation settlement and bridge diseases, it is proposed to use post grouting for pile foundation, UHPC for bridge deck to increase the section, and self compacting concrete for capping beams to increase the section. Laboratory tests were carried out by drilling the core before and after grouting, analyzing the effect of post-grouting on strengthening soil strength. The results show that: 1) Compared with the access segment tunnel, the buried depth of the section tunnel is larger, and the distance between the piles and the section tunnel is smaller, so the pile settlement on both sides of the section tunnel is larger. 2) Due to the differential settlement of pile foundation, compared with the articulated pier, the load increment of the consolidated pier is larger and the circumferential cracks appear in the consolidated pier. 3) Post grouting causes a decrease in the water content and void ratio of the soil around the pile, while increasing the compression modulus, cohesion, internal friction angle, and standard penetration blow count. The maximum increase in strength of silt is achieved, with a 100% increase in the number of standard penetration tests for silt. The improvement of soil strength can effectively increase the bearing capacity of pile foundations.