This General Report requested by the Organisers attempts to describe the state-of-the-art as perceived by the Reporter in the area of the determination of rock properties at great depth by physical methods. The paper focuses on laboratory studies of rocks under physical conditions simulating those crustal conditions in which a rock may be modelled as a cracked solid through which fluids may percolate. Current and upcoming developments in the study of compaction and dilatancy in such rocks under triaxial loading are summarised, and the intimate relation between rock mechanics and rock physics is brought out. An important special aspect of this study is the transition from cataclastic to plastic behaviour, which coincides with the elimination of dilatancy and probably of seismic activity. The paper also discusses the need for a strong parallel focus on crustal stress measurement, which is the missing link in the application of rock mechanics and rock physics to many engineering and Earth science problems, particularly in the context of plate tectonics theory, which has facilitated the systematic ordering of knowledge about the Earth's crust and its properties, processes, and evolution.
With increasing knowledge of the origin, processes, and properties of the Earth's crust, and increasing engineering and technological capacity to extract minerals and heat energy from great depths, there is naturally a growing desire to measure and understand the properties of rocks and rock masses at these depths. The concepts and theories of plate tectonics have in recent years enabled our knowledge of the crust to be ordered in a fundamental and systematic way more suited to useful physical and chemical modelling (e.g. see Bott 1982, Turcotte & Schubert 1982, Meissner 1986). This has stimulated a new interest in the nature, processes, origin and properties of the lower parts of the continental crust (e.g. see Dawson et al 1986), which are being increasingly probed, by electrical deep sounding methods (Haak & Hutton 1986), deep seismic reflection profiling (Meissner 1986, Matthews 1986, Smithson 1986), (which provide both rock samples and opportunities for close range measurements at great depths, see Raleigh 1985 and Behr et al 1987). Field studies by geophysical and geological methods enable the properties of the crust and of rock masses within the crust to be determined and measured, but this is dependent on a good understanding of rock properties at the crystal, grain, and atomic scales. The latter properties have to be determined in the laboratory, based on the laws of physics and chemistry. The subject of the present paper is the determination of rock physical properties in the laboratory within the perspectives of this Symposium.
Advances in laboratory techniques are enabling measurements to be made of rock physical and chemical properties under simulated crustal conditions corresponding to increasingly greater depths. Indeed it is now possible to simulate most crustal conditions, though there are very few laboratories at present that are fully equipped for measurements on rock samples under simulated conditions of great depth.
