Considering the influences of shallow unloading and relaxation rocks, a 3D geo-mechanical model test and 3D nonlinear FEM calculation were carried out to study the global stability of high arch dam and foundation of Xiaowan Project, using different sizes and mechanical parameters of rhombus small blocks. At the same time, the main geological structures and the reinforcing schemes at the dam abutment and dam foundation were simulated.In order to carry out strength-decreasing test, the major weak structural planes were simulated using temperature analogous material. The shallow unloading zone of dam foundation was simulated using dense element. The model tests and calculations showed that the rocks nearby the dam heel and dam toe cracked firstly(corresponding to model test) or appeared plastic zone firstly(corresponding to calculation),affected by the shallow unloading rocks in the process of overloading test,and finally the crack or the plastic zone transfixed nearby the upstream dam heel,which showed the shallow unloading rocks have a certain influence on the stability of dam and foundation.
