ABSTRACT In order to study the reinforcement effect of the broken soft rock tunnel after pre-grouting in the shallow buried section, the construction is carried out smoothly and safely. Based on the Hongshi River tunnel with sleeve valve grouting, a three-dimensional finite element model is established and passed through the site. Test and monitoring measurements compare and analyze the reinforcement effect before and after grouting. The comprehensive analysis shows that after the surface grouting treatment, the strength and integrity of the surrounding rock are obviously improved, the permeability of the rock mass is reduced, the arching ability of the stratum is enhanced, and the overall stress characteristics of the tunnel support structure are greatly improved. The maximum axial pressure value of the initial support was reduced by nearly 20%, and the maximum axial tensile force was only half of the original; the maximum positive bending moment of the initial support was reduced by 58%, and the maximum negative bending moment was reduced by 29%; The trend of change with the surrounding convergence is basically the same, about 70% of the total deformation is completed within the first 10 to 15 days, and the deformation is basically completed at 20 to 25 days. And the numerical calculation is consistent with the field test results, the grouting effect is very significant, which can provide some reference for similar projects. Keywords: shield tunnel; pit excavation; sandy gravel strata; anti-floating stability measures; numerical modelling

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