Application of limit equilibrium and shear strength reduction techniques for stability assessment of upstream and downstream slope cuts- A case study ofKhalid-Dijo dam project, Southern Ethiopia

Abstract

Dam failure can occur due to various reasons like structural instability, downstream and upstream slopes instability. The downstream and upstream slope cuts of Khalid-Dijo irrigation dam project has assessed by integrating both limit equilibrium and finite element methods. In this research, limit equilibrium methods such as Morgenstern-Price, Spencer and Janbu corrected methods were utilized. Because those methods are satisfies both force and moment equilibriums. In addition, numerical finite element shear strength reduction method was utilized to compare the analysis results with limit equilibrium methods and validate the analysis. Slide v 6.0 software packages were utilized for limit equilibrium analysis and a phase2 v 8.0 was utilized for finite element analysis. In both methods the analysis was carried out at four anticipated natural conditions (i.e., static dry, static saturated, dynamic dry and dynamic saturated conditions). Slope material (i.e. soil and rock) properties are measured from in situ, laboratory tests and used as input parameters for the analysis to obtain factor of safety and critical strength reduction factor. Those are unit weight, cohesion, angle of internal friction, poison’s ratio, dilation angle and young’s modulus. Thus, the analysis shows that the factor of safety values for limit equilibrium methods and the critical strength reduction factor for finite element method are very close each other for the three slope cuts at all anticipated conditions. The lowest factor of safety and critical strength reduction factor is 1.56 and 2.14 respectively. Thus, it can be concluded that Khalid-Dijo irrigation dam project is safe against upstream and downstream slope cuts failure. The study suggested that the average safety factor values of both methods should be used during the design stage to minimize the risk.