The aim of this study is to better understand the mechanics of backfill grouting effects of shallow shield tunnels in sandy cobble stratum from a microscopic perspective.A series of numerical simulations were performed by using the fluid-coupled discrete element method (DEM) and such observations as follows can be made.Backfill grouting can obviously influence the stress redistribution after tunnel is excavated, the soil arch height is lowered and thus the loosened zone gets smaller, and grouting can significantly reduce the maximum ground settlement, alter the displacement field distribution.