土钉支护施工阶段土钉轴力的计算分析

Analysis of nail tensile forces during construction of soil nailing

土钉支护的形成过程对其受力和变形有直接影响。结合土钉支护边开挖、边支护且开挖在前的施工特点,定义开挖影响面以反映土体开挖时边坡滑动趋势的变化,与开挖影响面相交处的土钉在土体开挖时轴力增加最多。开挖土压力表示以开挖影响面为边界的土块体产生的土压力,由相邻两步开挖土压力之差求得挖土引起的不平衡力。增加的土钉轴力在平衡此不平衡力的同时,维持着边坡稳定。据此,以开挖影响面及其土钉轴力增量为主要研究对象,提出了施工阶段土钉轴力的分析方法。该方法在求得土钉轴力最大值及其作用位置的同时,还给出了土钉轴力沿钉长方向的分布。应用此方法对法国CLOUTERRE项目1号墙足尺试验进行了计算,结果表明:计算与测试结果吻合良好。

The construction process has an important effect on the behavior of the soil nailing. Based on the feature that the soil excavation precedes the nail installation and the facing construction in each step, excavation influential surfaces （EIS--the most likely slip surface when the latest excavation surface remains temporarily unsupported and the nails are not yet installed） is defined where the increments of nail tensile forces are the largest. The concept of excavation earth pressure （EEP---the earth pressure is supported by nails and acted by the soil block where the EIS is the edge during the excavation） is presented in the calculation of the unbalanced forces during the construction of soil nailing. Taking EIS and the increments of nail tensile forces as the main research objects, an analytical method is proposed to calculate the soil nail forces along the nails in different excavation phases according to the two functions of nails--to remain the slope balance and stable. By means of this method, the location and magnitude of the maximum tensile forces during the construction are estimated. The calculated nail forces of Experiment 1 of CLOUTERRE Project by this method agree fairly well with the experiment data.