Optimization of Grouting Reinforcement Mass Parameters for Shield Under-passing Buildings in Sandy Stratum

Objective Grouting reinforcement is a common measure to reduce disturbance on existing buildings during tunnel construction. It is essential to focus on the design of GRM (grouting reinforcement mass) parameters in the engineering. Appropriate GRM parameters are crucial to ensure reinforcement effectiveness and reduce project costs. Therefore, it is necessary to optimize and analyze these parameters based on practical engineering conditions. Method Taking the tunneling project of Wuyi Overpass Station to Xinxiu Park Station interval on Nanning Rail Transit Line 5 as example, the under-passing construction is classified by the position relation between existing buildings and tunnel. Numerical calculations are used to optimize the GRM cross-sectional parameters, and the stress mechanism of the GRM is analyzed. On-site grouting reinforcement is carried out according to the parameter optimization results to validate the effectiveness of GRM parameter optimization. Result & Conclusion Under-passing construction is divided into three categories: under-passing directly beneath buildings, side-passing Type I buildings, and side-passing Type II buildings. For the first one, the GRM should extend into the micro-disturbance area by approximately 1 m, with a grouting thickness of 6 m. For the second and third, the GRM should extend approximately 4 m beyond the close tunnel side and penetrate 4 m into the micro-disturbance area on the far tunnel side, with a thickness of 6 m. The stress mechanism of the GRM can be simplified to anchor beams at both ends when under-passing directly beneath buildings and to cantilever beams when side-passing buildings. Monitoring results demonstrate that optimizing the GRM parameters can effectively control building deformation.