In soil nailing

soil nails have the functions of reinforcement and anchorage

and the forces and deformations are changed with the construction process. On the base of the stability analysis

it is reasonable to calculate the soil nail forces by the incremental method. In soil nailing

according to the interaction between the soil and nails and the characteristic of soil nail forces at the slip surface

the upper-bound method can be used in the calculation of soil nail forces. In the calculation by the upper-bound method

the incremental coefficients of soil nail forces are decided based on the kinematical velocity field and the relationship between the forces and displacements of the soil nails. In every excavation of the cut

the energy equation of upper-bound method is used to obtain the dissipation power by the soil nails. According to the power dissipated by the soil nails and the incremental coefficients

the incremental forces of soil nails are calculated. Then

the total soil nail forces are obtained by the accumulation of the whole excavations. At last

an engineering case is presented

and the calculation results by upper-bound method are compared with other methods. The comparisons show that the upper-bound method here is effective and exact.