Failure mechanism of slopes reinforced with soil nails by three-dimensional finite element analysis by Man, Tong Man AO Thesis Supervisor: Dr. Wan-Huan Zhou Geotechnical and Structural Engineering ABSTRACT Soil nailing is a simple and economical slope stabilization technique, which is particularly useful for strengthening the new-cut or existing slope. The finite element method (FEM) with shear strength reduction method (SRM) is widely used to investigate the factor of safety of the slope, however, it is only have limited study to the stability analysis and the failure mechanism of the soil-nailed slope by using FEM and SRM. In this study, stability of a three-dimensional soil-nailed slope is analyzed using the shear strength reduction method. Finite element analysis is carried out using numerical program, ABAQUS, to simulate slope sliding failure of the three-dimensional soil-nailed slope model. Moreover, a series of analysis was conducted to study the influence of three different soil nail head’s modeling techniques (i.e., the soil nail connected to the steel plate (nail head), soil nail connected to the shotcrete and no nail head) and dilation angle on stability of soil-nailed slope and stabilizing mechanism. The normal and shear stress on the top, bottom and side surfaces of the soil nails were examined. It is shown that the factor of safety of soil-nailed slope is determined by both the computation convergence and the appearance of a clear potential sliding surface. The presence of the soil nail head affect the safety factor and axial force taken by the soil nail significantly. The difference between the soil-nailed head connecting to nail plate and shotcrete is small. An increase in dilation angle increases the axial force taken by the soil nail and hence factor of safety of slope significantly. It is found that, when the slope approaches to failure, the shear stress along the nails at lower locations is fully mobilized, yet the shear stress along the upper soil nails is not. The maximum axial force in the bottom soil nail is three times of that of the upper soil nail. The results show that the failure sliding surface according to the plastic strain contour is close to the locations of maximum axial force in the soil nails. It is clearly shown that the normal stress beyond the critical slip surface increases differently due to the constrained dilation of the surrounding soil at different depths of the slope. Soil nail located at the bottom is the most sensitive to the soil deformation in the slope and it contributes more resistant force for the slope stability.