无黏性有限土体主动破坏及土压力离散元分析

建立在半无限土体假定上的朗肯土压力理论和库伦土压力理论，在挡土墙后填土有限的情况下不再适用。针对墙后无黏性填土，采用离散元方法分别对光滑、粗糙墙面平动模式下墙后有限宽度土体主动破坏的过程进行研究，分析了挡土墙运动过程中滑裂带发展、土体位移规律以及墙后水平土压力分布的情况。研究结果表明，墙体光滑情况下，滑裂带呈直线，墙后填土宽高比较小时，可以观察到滑裂带的反射，墙后土体呈多折线破坏模式，滑裂带倾角基本与库伦理论滑裂带倾角相等，且与土体宽高比无关，水平土压力合力受土体宽高比影响亦不大。墙体粗糙情况下，滑裂带呈曲线，反射现象随墙体粗糙程度增加而减弱，滑裂带倾角随土体宽高比增大而减小，最终落于库伦理论滑裂带内侧。此时，存在一临界宽高比，当墙后土体宽高比小于此值时，主动土压力随宽高比增大而增大，大于此值时，主动土压力不受宽高比影响。而无论墙体粗糙与否，墙后土体宽高比越小，达到极限状态所需墙体位移均越小。

DEM study on active failure and earth pressure of cohesionless soil with limited width behind retaining wall

The classical Coulomb and Rankine earth pressure theories are based on the assumption that the soil near a retaining wall are semi-infinite. It is obvious that these theories are no longer suitable for the narrow backfill behind a retaining wall. A series of numerical simulations are conducted by DEM to study the active failure process of limited cohesionless soil with finite width behind a rough and smooth walls. The development of the failure surface, the displacement field of the soils and the distribution of active earth pressure are analyzed. The results show that multiple slip surfaces occur in the backfill if the region behind the smooth wall is narrow enough. The slip surface angle is close to the Coulomb''s theoretical solution, which shows no relation with the width height ratio. This ratio also has little influence on the active earth pressure in this case. In another case, when the wall is rough, the actual shape of failure surface is a curve rather than a straight line. The rougher the wall, the weaker the reflection. The angle of failure surface decreases along with the width height ratio of soils increases. And the failure surface is finally located inside the Coulomb''s failure surface. There exists a critical width height ratio of soils behind the rough wall. The active earth pressure decreases with increases of the ratio if it is smaller than the critical value, but the active earth pressure is independent from the ratio if it is larger than the critical ratio. The smaller the width height ratio is, the smaller displacement of the ultimate equilibrium state will be, regardless of roughness of the retaining wall.