中文摘要：

基坑开挖过程中坑内土体处于竖向卸荷状态，而土体在卸荷过程中是普遍存在残余应力的。为了分析土体卸荷引起残余应力对基坑被动区土压力及强度的影响，进行砂的静力模型加卸载试验，通过试验得到砂在卸荷过程中应力变化规律，即在卸荷初期砂中应力几乎不变，在荷载完全卸除后仍存在残余应力。通过分析影响土中残余应力的因素，建立归一化参数——残余应力系数ξ和卸荷比R之间的函数关系，结合坑内土体的受力特点，建立基坑被动区残余应力的计算公式。结合既有试验成果，提出利用考虑残余应力的竖向土压力和加载时的静止侧压力系数来计算基坑被动区土压力的方法。建立考虑残余应力的基坑被动区抗剪强度计算方法，并与室内试验结果进行对比，验证方法的正确性。

英文摘要：

The soils inside a foundation pit undergo vertical unloading during excavation, which almost always causes residual stress. In order to study the impact of residual stress on the passive pressure and shear strength of soils, a static model loading-unloading test using sands is conducted. Experimental results show that the stress in sands does not reduce at the initial stage of unloading and there is residual stress even after the load is completely removed. Using normalizations of factors that affected the distribution of residual stress, a function between the residual stress coefficient sc and unloading ratio R is established. Base on the characteristics of soils, a formula for calculating the residual stress of foundation pit is proposed. The calculated shear strength in passive zone agrees well with the measured values.