Experimental study on the influence of synchronous grouting in shield tunneling on an upper existing tunnel in sandy soil stratum

During the construction of shield tunnels in sandy strata underpassing existing overlying tunnels, the characteristics of surrounding earth pressure changes and tunnel deformation in the existing tunnel induced by synchronous grouting remain unclear. Through use of a model test device with a geometric similarity ratio of 1:10, synchronous grouting model tests to simulate shield tunnelling were conducted to monitor the flexural deformation, change in diameter, and earth pressure surrounding an existing tunnel. The experimental results indicate that: Excessive grout filling increases earth pressure above the grouting path, with the most significant change occurring at the tunnel bottom; A large grout fill ratio concentrates the existing tunnel's upper deformation zone above the grouting path, causing overall arching deformation, and the flexural deformation at the bottom is larger than that at the top; Under additional grouting loads, the existing tunnel experiences uneven flexural deformation and transverse elliptical deformation specifically above the grouting path; In sandy soil layer, the fill ratio of grouting materials should be reasonably controlled to avoid excessive deformation of the upper existing tunnel caused by overfilling.