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.