基坑开挖反压土作用机制及其简化分析方法研究

分析了反压土与支护结构相互作用的机制。在此基础上，基于弹性抗力法，结合天津市一些工程经验，建立了考虑反压土影响时支护结构内力和变形的计算方法，并结合工程实例进行比较分析。分析结果表明，反压土高度不变时，随着反压土的坡度减小或反压土宽度的增大，支护结构的最大位移和最大弯矩都逐渐减小；当反压土的坡度减小到一定值或顶宽增大到一定的程度时，支护结构的最大位移和最大弯矩不再减小而趋于一个定值。反压土土质条件对反压土的作用的发挥有着显著作用。开挖前进行良好的降水，开挖过程中注意不要扰动反压土，并对反压土做好良好的护坡，防止雨水侵入土坡，这些措施均有助于保证反压土作用的充分发挥。必要时，可考虑对反压土进行注浆加固。工程实测表明本文建议方法的计算结果与工程实测结果较吻合，并表明在开挖面积较大的基坑工程中，条件适当时，采用基坑内侧预留反压土的方法可不需设置水平支撑，可节约大量基坑支护投资，并缩短工期，具有良好的经济效果。

A study of mechanism of earth berm and simplified analysis method for excavation

The interaction between the earth berm and the retaining structure is analyzed. A simplified method is proposed to consider the effect of earth berm on the retaining pile based on the principle of elastic-reaction method. Calculating results show that with the same earth berm height, the displacement and bending moment of retaining pile can be reduced with the decrease of grade of earth berm or the increase of width of earth berm. But finally they will remain constant when certain grade of earth berm or width of earth berm is reached. The soil condition of earth berm also plays an important role for earth berm to reduce the displacement and bending moment of retaining pile. Well dewatering before excavation, protection of earth berm from being disturbed during excavation and prevention of earth berm from rain during and after excavation are important for earth berm to work. The earth berm can be treated with grouting or DMM when necessary. Case histories show that the results obtained by the suggested method agree fairly well with the field measured data. The application of earth berm in a large excavation project, where horizontal supporting system is no longer necessary, can save considerable cost and reduce construction period.