The Coulomb's limit equilibrium theory is modified to study the active earth pressure on retaining walls in non-limit state. It is considered that the earth pressure on a retaining wall is due to the thrust of a sliding wedge of soil between the back of the wall and a plane which passes through the bottom edge of the wall. The basic equations are formulated by considering the equilibrium of the forces on a thin-layer element of the wedge. By using the equilibrium equations of the moments on the entire wedge, the lateral coefficient of earth pressure, the earth pressure distribution along the wall back, the resultant force of earth pressure and its action point are obtained. The effects of the internal frictional angle of the backfill, the frictional angle between the wall and the backfill and the displacement ratio of the wall on the lateral coefficient of earth pressure, the earth pressure, the resultant force of earth pressure and its action point,and the overturning stability of the retaining wall are investigated. The proposed method is compared with experimental data. Evaluation of the influence of the displacement ratio of the wall on the overturning moment indicates that if they are designed according to the limit equilibrium theory, it would be dangerous for the overturning stability of the retaining wall with an active translational movement in non-limit state.%改进库仑极限平衡理论,用于非极限状态主动土压力的研究,认为挡土墙土压力是由墙后填土在平衡状态下出现的滑动楔体所产生.在该滑动楔体上沿竖向取水平薄层作为微分单元体,通过作用在单元体上力的平衡条件,建立挡土墙非极限状态主动土压力基本方程,并结合整个滑楔体的力矩平衡条件,由此得到对应不同内摩擦角、墙土摩擦角和挡土墙位移比的侧土压力系数,将其用于水平微分单元法求解刚性挡土墙平移模式下非极限状态主动土压力,得到挡土墙土压力和合力作用点的理论公式.分析填土内摩擦角、墙土摩擦角和挡土墙位移比对土侧压力系数、土压力强度、土压力合力、土压力合力作用点的影响,并与模型试验数据进行比较.另外,通过探讨位移比对挡土墙倾覆力矩的影响,认为采用极限平衡理论计算平动模式下刚性挡土墙主动非极限状态时的抗倾覆稳定性偏于危险.
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