Study of physico-mechanical properties of weak rock underlaying structure foundations

The foundation of the Ust-Ilim Hydro Power Plant structures includes a thick trappean intrusion underlaid by sedimentary rock. The trappean intrusion is composed of granophyre, ophite and troctolite diabases characterized by the columnar structure with three systems of original fissures. Rock masses adjacent to contact surfaces are of block or slab structure. Rock in these areas as well as in those near to the ground surface are subjected to more intensive weathering and · disintegration. It is characterized by heavy fracturing at which diabase turns into fragments and gruss. The weathering has manifested in the formation of heavily ferruginate d layers (of thickness ranged from 0.5 to 5 cm) of reduced strength along joint faces.