Numerical simulation analysis of tunnel backfill grout based on DEM-FDM coupling and particle inlet

Abstract

Shield tunnel backfill grouting is vital to stabilize tunnel settlement at a later stage; however, most shield tunnel backfill grouting designs lack a complete theoretical reference, and numerical simulations of the grouting process are rarely conducted. This study presents the fundamental theories of grout diffusion and pressure variation for backfill grouting during shield construction. Moreover, the numerical simulation methods coupled with discrete element methods(DEM) and finite difference methods(FDM) are achieved to simulate the process of grout injection from the grouting hole into the shield tail gap and generate grout pressure on the surrounding rock. The diffusion state of the grout in the shield tail gap and the squeezing effect on the surrounding rock under two shield tail disengagement modes are analyzed, as well as the impact of various grouting pressure on the surface settlement. The results indicated that the grout diffusion in the shield tail gap can be divided into three stages: the stage of diffusion with each grouting hole as the starting point, the stage of interconnection and contact of the grout injected in each grouting hole, and the final gap filling stage. Each of the three stages can be described using the proposed equation. During the grouting process, the grout is injected into the shield tail gap at a certain pressure, but the grout diffuses slowly to both sides and upwards, which causes a rapid rise of the principal stresses in the soil around the tunnel. After grouting is complete, the grout pressure gradually dissipates and stabilizes, and the principal stress decreases. In addition, backfill grouting can reduce surface settlement, but it does not affect its distribution width.

Keywords

Shield tunnel / Backfill grouting / Discrete element / Finite difference / Particle generator

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