Abstract:

The gravel stratum is a kind of unique geomaterial of which the properties are distinctively different from wellknown fine particle soils (e.g. clay, silt and sand). Hence it should be paid more attention to tunnel engineering. The gravel stratum model is established by random polygon in PFC2D; the horizontal crosssection of the tunneling project is simulated by deleting the particles around the tunnel; the longitudinal crosssection of the tunneling project is excavated by setting a support wall and stepping backward; and then the strata displacement micro movement of particle and contact force among particles are analyzed under different gravel contents of horizontal crosssection and different tunnel buried conditions; finally, the strata displacement and support stress on excavation support are analyzed under different gravel contents of longitudinal crosssection. The microanalysis results show that: 1) The tunnelingcaused subsurface movement decreases with increasing of gravel contents. 2) The support pressure variation undergoes two stages, i.e. support pressure declines sharply in the first stage and then tends to stable in the second stage. The lower the gravel content, the higher the support pressure. 3) The maximum ground surface settlement decreases with the buried depth of tunnel increasing, which shows linear relationship.

Key words: gravel soil, discrete element method (DEM), PFC2D, shield tunneling, random polygons