中文摘要：

利用基于离散元理论的颗粒流软件PFC3d建立基坑开挖土钉支护的二维颗粒流模型，通过分析有复合土钉墙支护基坑和无复合土钉墙支护基坑数值模型的位移场和应力场，研究复合土钉支护基坑开挖过程的规律和土钉支护的机理．有复合士钉墙支护基坑和无复合土钉支护基坑在变形程度和变形模式等方面存在较大差异．复合土钉墙支护基坑挡墙变形较小，出现“两头小、中间大”的流鼓型变形模式，坑底隆起量和墙后土体沉降量相对于无土钉墙支护基坑均较小．利用土拱效应来分析复合土钉支护机理，认为土钉支护作用的父键是土拱效应，而不仅仅是土钉和土体之间相互拉拔作用．细观机理研究和颗粒流数值模拟为复合土钉墙支护基坑的机理研究提供新的思路和方法．

英文摘要：

A three-dimension soil nails support excavation particle simulation model is established by the software of PFC3d which is based on discrete element method（DEM）. The contrast of deformation and stress during excavation between PFC3d numerical model with and without soil nailing is analyzed in order to investigate laws of excavation with soil nailing and mesoscopic mechanism of soil nailing. Greatdifference exists in deformation mode and level between excavation with and without soil nailing because the effect of soil nailing. The deformation of wall, foundation pit and settlement of excavation with soil nailing is smaller than that without soil nailing. Especially the deformation mode of wall with soil nailing which appears a special mode with small deformation on the top and at the bottom of wall and big deformation in the middle of wall. Finally, the mesoscopic mechanism of soil nailing is analyzed. The pullout contact between soil and nailing is not only factor for the excavation support; the soil arching is the most important factor for the soil nailing wall support excavation. The mesoscopic mechanism and PFC simulation study is expected to be a new approach for soil nailing wall support excavation research.