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.%砾石土地层是一种较为特殊的地质环境,其复杂的物质结构及力学性质在隧道工程中引起了广泛的关注.利用一种随机多边形生成法建立砾石土地层;横断面开挖采用删除隧道周围部分颗粒模拟地层损失的方法;纵断面开挖采用设置支护墙体并后退的方法,以此开展横断面不同含石量和不同隧道埋深条件下地层位移、颗粒微观转动及受力分析;纵断面不同含石量条件下地层位移、开挖面支护压力的研究.结果表明:1)开挖造成的砾石颗粒位移显示地层受扰动的范围随着碎石土地层含石量增高而逐渐缩小;2)支护压力的变化趋势随着模拟开挖面支护墙体后退先大幅下降后趋于稳定,且含石量越低,支护压力越大;3)随着隧道埋深的增加,地表最大沉降值减少,且二者之间呈线性关系.
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