The paper presents the results of physical (geomechanical) model investigation of fractured rock behavior for validating the overall stability of openings excavated in the rock massif for a power house of a hydropower plant. Three types of tests were performed by geomechanical modeling to investigate the strength and stability of the opening for the power house, integral shear resistance of rock mass and limiting strains developed in the rock surrounding the opening. The experimental modeling studies proved useful for obtaining the reliable and comprehensive data on the behavior of the rock massif around underground openings with the massif actively weakened by fractures.
Geomechanical models are generally made as block assemblies capable of describing basic structural features of a rock massif, mechanical parameters of rock and stress state of the rock mass portion encompassing the openings (Kuznetsov,1968; Glushikhin,1991). To assess the strength and stability of rock massif enclosing large-scale underground openings for a powerhouse and transformer room, three types of tests have been performed for specifying a number of design decisions for full-scale structures. The studies were made for the Rogun hydraulic scheme on Vaksh river in Tadjikistan, the construction of which was practically stopped in 1993. The design of the hydraulic scheme assumed to incorporate a 335m high earth-and-rockfill dam and underground powerhouse.
The laboratory tests of equivalent material models and theoretical evaluations have been performed for the assessment of the stress-strain state, strength and stability a of rock massif incorporating underground openings for machine and transformer rooms of a hydro powerplant. The measurements were made in bore holes by unloading procedure developed at the Institute for Underground Surveying (VNIMI)-strain measurements on the face of a bore hole during drilling of a core sample (Belik, 1958).