主动与被动状态下墙体侧向位移近似计算

极限状态下墙体侧向位移对土压力计算和支挡结构设计影响显著。根据Rankine变形体和Coulomb刚塑体模型，将墙后土体变形分别当作单剪和直剪试验中试样的剪切过程，以达到极限剪切变形（剪应变或单位长度剪切位移）作为进入主被动状态标准，构建了土体变形与墙体位移的几何关系，提出了反映土体变形与强度特性，同时考虑静止时初始应力状态影响的墙体极限侧向位移近似计算模型。分析表明：土体极限剪切变形、滑移区范围、初始应力状态是影响墙体极限位移的核心要素，其中极限剪切变形占据主导作用，是导致不同颗粒组成及密实程度土体进入极限状态所需墙体位移差异显著的主要原因，而主被动区范围不同和因静止土压力系数 1引起的初始剪切变形，则是被动状态墙体位移远大于主动的关键因素；算例中主动与被动状态下墙体位移与墙高之比分别介于0.5‰～13.2‰和?0.4%～?5.2%，且主动状态下细粒土墙体位移大于粗粒土，计算结果与工程经验及相关文献模型试验基本一致。

Calculation of wall displacement to reach active or passive earth pressure state

The movement of wall plays an important role in the calculation of lateral earth pressure and the design of retaining structure. Regarding the process of backfill approach active or passive pressure state as the shearing process of soil sample in simple shear test or direct shear test, the backfill process reaches active or passive earth pressure state when the soil deformation equals to the ultimate value (shear strain in the simple test or shear displacement per unit length in the direct shear test). Based on the geometric relationship between the soil shear deformation and wall displacement, the theoretical calculation method of wall displacement required to reach active or passive earth pressure is provided, where the soil stress-strain behavior and initial stress state are considered. The analysis indicates that the magnitude of needed wall displacement to reach active or passive earth pressure is controlled by soil ultimate shear deformation, the range of active or passive zone, and the initial earth pressure state. The first factor is the most important among them, which contributes to variation of wall displacement among different soils. The wall displacement in passive state is greater than that in active state, because the range of passive zone is larger than that of active zone. The theoretically calculated wall displacement attaining active state is about 0.5‰~13.2‰ H (where H is the height of the wall), of which the non-cohesive soil is larger than the cohesive soil. As to the case of passive state, the wall displacement is ?0.4%~?5.2% H. The theories are concordant with the model test results from relevant literatures.