基坑围护结构增量计算法的改进

就围护桩（或围护墙）加内支撑这一基坑支护形式而言，基于弹性地基梁理论的增量法是其围护结构内力和变形计算的常用方法。合理计算荷载增量是该方法实施的关键之一。目前，该法的荷载增量主要由土压力增量和挖除土体弹性抗力释放的反力增量两部分组成。根据弹性地基梁和增量法的基本原理，结合基坑施工过程，综合分析得出：荷载增量除上述两部分外，还应包括开挖面以下土体因开挖面下降、水平抗力系数降低而引起的土体弹性抗力部分释放的反力增量；开挖面以下围护桩（或围护墙）任意点的这部分反力增量等于该点在上一工况下的侧向位移与开挖侧土体水平抗力系数的比例系数m和本工况挖除土体厚度的乘积。工程实例理论计算结果和实测结果的对比分析表明，与传统增量法相比，采用改进增量法，围护桩（或围护墙）侧向位移的计算值与实测值更加接近，计算结果更加符合工程实际。

Improvement of incremental calculation method of retaining structure for foundation pit

In terms of support form for foundation pit, the most common calculation method of internal force and displacement of retaining piles (or enclosure wall) plus internal bracings is incremental method, which is based on the theory of beam on elastic foundation. Reasonable calculation of load increment is the key to implement this method. At present, the load increment of this method mainly consists of earth pressure increment and reaction increment released by the excavated soil elastic resistance. Based on the basic principle of the method of beam on elastic foundation and incremental method, combined with excavation construction process, the following conclusions were drawn through the comprehensive analysis. In addition to the above two parts, the load increment also included reaction increment by soil elastic resistance released, which was partially caused by the decrease of the excavation face and the reduction of the horizontal resistance coefficient. The reaction increment of random point of the retaining piles (or enclosure wall) in this part that below the excavation face was equal to the product of the lateral displacement of this point in the previous working condition and the proportional coefficient of the soil horizontal resistance coefficient (m) , and the excavated soil thickness in the current working condition. The comparative analysis of theoretical calculation results and measured results of engineering examples show that: compared with the traditional incremental method, utilizing the load increment mentioned in this paper to do load increment calculation (the improved incremental method) yields a value of lateral displacement of retaining piles (or enclosure wall) that is much closer to the measured value. The calculation result is more in line with the engineering practice.