考虑环境荷载作用的膨胀土边坡挡墙侧向土压力研究

Research on lateral earth pressure acting on retaining wall in expansive soil considering influences of environmental load

为明确干燥蒸发过程中膨胀土边坡挡墙侧向土压力的变化规律,提出简单有效的侧向土压力预测方法。首先,基于非饱和土力学双应力变量理论,分析脱湿过程中不同深度土体单元的应力状态,阐明膨胀土收缩变形对挡墙侧向土压力的影响机制和膨胀土中裂隙的发育机理,提出膨胀土开裂深度的计算方法;其次,假定膨胀土的增湿膨胀变形和脱湿收缩变形完全可逆,通过叠加法建立干燥蒸发条件下挡墙侧向土压力的计算模型;最后,考虑吸力和挡墙粗糙度的影响,改进朗肯土压力理论,建立4种工况下的挡墙主动土压力计算模型。研究结果表明:膨胀土中裂隙的发育由表及里,先竖后横,且开裂深度可由土体含水状态确定;在干燥蒸发条件下,挡墙侧向土压力的分布可根据吸力变化曲线计算得到,利用所建立的计算模型得到的预测值与工程实测值吻合良好;主动土压力受膨胀土脱湿程度和挡墙面粗糙度的影响,与脱湿程度呈负相关,与挡墙面粗糙度呈正相关,4种工况下主动土压力均可由土体的工程性质结合吸力变化曲线计算得到。

In order to clarify the changing law of lateral earth pressure acting on retaining walls in expansive soil during evaporation process,a simple and effective lateral earth pressure predicting method was established.Firstly,based on the theory of dual stress state variables in unsaturated soil mechanics,the stress states of soil elements at different depths during evaporation process were analyzed and the influencing mechanism of expansive soil shrinkage deformation on lateral earth pressure and the development mechanism of cracks in expansive soil were explained.A calculation method for estimating crack depth of expansive soil was proposed.Secondly,assuming that the expansion deformation and shrinkage deformation of expansive soil were completely reversible,a calculation model capable of prediction the lateral earth pressure acting on the retaining wall upon evaporation was established through superposition method.Finally,considering the influences of suction and retaining wall roughness,the Rankine earth pressure theory was modified,and active earth pressure calculation models under four conditions were established.The results show that the cracks develop from the surface to inside,and it develops first vertically and then horizontally in expansive soil.The crack depth can be determined by the water content variations of the soil.The lateral earth pressure acting on the retaining wall during evaporating can be calculated according to the variations of suction profile.The predicted value obtained by the established calculation model is in good agreement with the measured results in the field.Active earth pressure is negatively correlated with the degree of dehumidification but positively correlated with the roughness of retaining wall surface.The active earth pressure for all four scenarios can be determined using the engineering properties of soil and suction profile.