Based on the study of the intrusion

tectonic-hydrothermal action and epigeneaction of the diabase-dikes in the foundation of a high arch dam in the south west of China and the comparison of their own processes of deformation and failure

it is shown that

after hydrothermal alteration

these processes involve tensile crack of dike wall

shear slip and compressive fragmentation under the same environment of tectonic stresses

and thus control the action of planes of weakness

rock mass structure and its mechanical properties associated with the diabase-dike.A brief discussion is given on the effect of diabase-dikes on the stability and deformation of the arch dam foundation.