基坑设计的杆系–荷载–弹簧模型荷载取值及变形和稳定性分析的若干问题和研究建议

作为当前基坑设计主流方法，杆系–荷载–弹簧模型还有几个问题没有解决。围护结构上的水土压力的统一计算方法，论证水土压力统一计算理论的合理性。目前为杆系–荷载–弹簧模型设计方法所构造的安全系数可能不足以覆盖基坑的所有破坏模式；建立新的控制基坑稳定的安全系数以及对既有安全系数进行改造以使其能够考虑尺寸效应是基坑研究的重要任务之一。目前基坑设计方法考虑安全系数对基坑变形的影响，与常规的安全系数的概念不同，这一点基坑研究时要引起注意。提出一个考虑圆形基坑的杆系有限元算法，建议一个被动区土体弹簧的双刚度模型，可以在用杆系有限元分析时考虑圆形基坑的尺寸效应和长条形基坑土方开挖的空间效应，为基坑研究指出一些方向。

SEVERAL ISSUES ON DEFORMATION AND STABILITY ANALYSIS OF BAR-LOAD-SPRING MODEL OF FOUNDATION PIT DESIGN AND RECOMMENDATIONS

As the present main design method of excavation engineering，the bar-load-spring model，naturally induces several problems which need to be solved. A unified calculation method of the pressure on the supporting structure considering the soil-water interaction is presented，which is more reasonable in the load calculation. Since safety factors system based on the bar-load-spring theory may not be enough to incorporate all the failure modes of foundation pits，new safety factors controlling stability of foundation pits and existing safety factor modified to reflect the size effect should be recommended. Current excavation design method took the influence of safety factor on deformation into account，which was different from the idea of traditional safety factors. Two bar system FEMs such as the bar-load-spring model of circular pits and double stiffness model of soil spring at the passive zone are proposed，which can consider size effect of circular pits and space effect of soil excavation divided into block in strip foundation. Some future research directions on excavation are pointed out.