Abstract: Mechanical parameters of rock and soil at dam foundation are important for the design and stability calculation of dam structure. A large number of granite pegmatite dikes occurs at the dam foundation of Lenggu hydropower station. In view of this, the characteristics of deformation and strength of the dikes were studied by circular rigid bearing plate test and straight shear test. Test results show that stress-deformation curves obtained from bearing plate test are in two shapes, namely straight linear type (or quasi straight linear type) and concave type. The curves of τ-u obtained from direct shear test can be classified into three types brittleness, plasticity and composite type. According to the physical meaning of envelope modulus and secant modulus and the hydraulic project’s characteristics, as well as the representativeness of least square method and optimal slope method in analyzing strength test data, the principle of determining the standard value of rock mass is presented. Finally, mechanical parameters of pegmatite dike at the dam foundation are proposed.

Key words: pegmatite dike, mechanical parameters of rock mass, rock deformation, rock mass strength, Lenggu hydropower station