The aim of this paper are the relations between static and dynamic indexes of rock deformation at great depths on the basis of laboratory geomechanical studies under conditions of high pressure and temperature. In the studies the high-capacity MTS-815 Rock Test System with a thermo-pressure cell and recording the ultrasonic waves was used. The tested were six types of rocks, subjected to triaxial compression with confining pressure 0 to 90MPa and temperature 22 to 120°C. The tests shown variable dynamics of increase of the wave velocity (Vp) with an increase of pressure. Therefore the wave velocity in sedimentary rocks can reach the value close to velocity characteristic for granite under low pressure. The comparison of the longitudinal wave velocity (Vp) and the phases of deformation indicates main increase of velocity in the phase of compaction and in the phase of elasticity. The wave velocity reaches its maximum value near the threshold of absolute dilatancy but with discrepancies, depending on the lithology and depth modeled by pressure and temperature.
Rock features at great depths are identified mainly by geophysical methods where lithological layers, tectonic structures and engineering parameters are established on the basis of measuring the velocity of seismic waves. However, wave velocity registered at the given depth is not an unequivocal feature of lithology, and thus of geomechanical properties of the rocks at the unknown conditions (Birch 1961,Wolarowich et al. 1964). Seismic wave velocity depends on the stress and temperature and in the given rock is variable at the various depths (Wepfer & Christensen 1991). Therefore the appropriate correlation of seismic data with geomechanical parameters, requires detail research, the importance of which was clearly stated by Barton (2000, 2007), as a key topic for rock engineering courses of research.
The range of fluctuations in geomechanical and geophysical properties determination under varying conditions of temperature and pressure was tested in a laboratory on a lithologicaly well-identified rocks from various regions of Poland. Samples were subjected to compression strength tests under triaxial conditions, during which the changes in longitudinal wave velocity were simultaneously recorded. The aim of the study was to link dynamic parameters describing the characteristics of the rocks obtained in geophysical studies, with parameters characterizing their mechanical properties, obtained in static laboratory compression tests. Thus, the properties of rocks at the stress and temperature modeling the conditions of increasing depth, were being determined in two separate research ways. Further, the comparative data and correction factors, necessary in identification of rock massive behaviour at a great depths, have been acquired.
