Abstract:The EPB shield model of Ф800 mm was used in laboratory test to study the soil disturbance induced by the shield tunneling in the upper-soft and lower-hard ground. The corresponding model of discrete element method (DEM) was established to investigate the over excavation quantitatively and other information about the disturbed ground. When tunneling is in the hard rock, the settlement surface is sector shaped,orienting towards the soft soil. When tunneling is in the soft soil, the settlement surface is funnel shaped. The surface settlement of the upper-soft and lower-hard ground is smaller than that of homogeneous soft soil,while the subsurface settlement is much larger than that of soft soil. The width parameter of subsurface settlement trough K increases exponentially along the gravitational direction,and the width parameter gets larger as the ratio of hard rock to whole tunnel face gets smaller. For the same depth,K of the upper-soft and lower-hard ground is smaller than that of the homogeneous soil. The larger proportion of hard rock the tunnel face has,the proportion of the excavated soft soil contained in the muck differs more from its theoretical value. The maximum horizontal displacement occurs at the point of inflection of vertical settlement trough.
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