Abstract: The western Route Project for China’s South-to-North Water Transfer is to divert 2×1010 m3 water annually from the upper of the Yangtze River to the Yellow River, which will bring relief to the drought-ridden northwestern and northern parts of China. Engineering geological investigation has discovered the complicated geological conditions, such as polytype rocks, overgrown folding, numerous north-western fractures and even active fractures, etc., which will have great effect on the slope stability of the high dams, the excavation of tunnels and caves, and earthquake effect, etc. To find out the mechanical properties of these rock masses, several representative sections were chosen to carry out field tests, such as wave-velocity test and large-scale shear test(500 mm?500 mm?350 mm), etc. The means and procedure of field shear test were expounded and the relation curves of shear stress to displacement and normal stress to shear stress have been obtained. And then, the shearing strength and shear strength of rocks obtained from field shear test were compared with laboratory test results through a slope stability analysis. The strength parameters got from field large-scale shear test is of utmost importance to the slope stability analysis and the optimum design.

Key words: rock, field test, mechanical property, shear test, stress, displacement