Abstract: Geomechanical model testing is a key approach to studying the safety and stability of a cemented sand-gravel (CSG) dam. However, displacements of a tested model dam are relatively small and the overturning trend of the dam is usually difficult to capture, so its compression failure interval and overload safety factor (or ultimate safety factor in failure stage) cannot be determined with enough accuracy. To overcome this problem, we conduct geomechanical tests on a model CSG dam, and measure strains in the dam foundation and at the dam surfaces and surface displacements at the downstream dam face. The overload safety factor Kp of the model dam are estimated in the range of 4.6 ~ 6.2. To determine this factor accurately, first we use the catastrophe theory to fit a quadratic polynomial to the model test data, and then the fitted values and instability discriminant are used to finalize its values－an accurate Kp range of 6.0 ~ 6.2. This method solves the accuracy problem in calculation of the overload safety factor of a geomechanical model CSG dam, and helps promote its development and application.

Key words: hydraulic structure, geomechanical model test, cemented sand-gravel (CSG) dam, catastrophe theory, failure criterion