Assessment of soil nailing performance by using finite element and finite difference methods

The field performance of a geotechnical structures including its failure mechanism should be evaluated in detail before construction in order to minimize the possibility of potential failure. In this paper, the application of soil nailing system is documented in a detailed based on case study in the north of Tehran, Iran. The total excavation depth for a 15 storey residual building wall brought the cut face close to 12 m. The diameter of nails was 28 mm and their lengths were varied between 8 to 10 m with inclination of 7 degree to the horizontal plane. A series of numerical modelling was conducted to evaluate the deformation during the excavation process using finite difference method (FDM - FLAC 2D) and finite element method (FEM - PLAXIS 2D). In the modelling process, the pattern of wall deflection was simulated with shotcrete facing. A good agreement has been observed between the results of both methods when the pattern of deformation in the first and the last steps of excavation were simulated. Based on the maximum vertical displacement of shotcrete facing, calculated by two methods, the results obtained by FEM were closer to the field measurement. However, a good agreement has been observed between the values of factor of safety which were calculated by FLAC 2D and PLAXIS 2D, for different stages of excavation.