A description is given of the triaxial apparatus in our laboratory, which is capable of achieving the full range of crustal confining pressures (up to 1000 MPa), with an internal heater providing sample temperatures up to 1000°C. Rock samples ranging in diameter between 10 and 20mm can be tested under servo-controlled loading and pore pressure conditions. The apparatus is adapted to enable speeds of 1 MHz acoustic waves to be measured along the cylindrical sample axis during loading, while acoustic emissions can be simultaneously measured, and waveforms are recorded.
Our laboratory has long been engaged in experimental rock deformation studies under crustal conditions (Edmond & Murrell 1973, Ismail 1974, Ismail & Murrell 1976, Murrell & Ismail 1976a,b, Murrell 1985) and in recent years our interest has turned to rock physical property changes caused by deformation (Jones 1988, Main, Meredith & Jones 1989, Sammonds et al 1989). Our current objective is to develop a qualitative and quantitative model of compactive and dilatant rock behaviour caused by deformation, based on experimental studies in which measurements of acoustic wave speed, acoustic emission (rates and amplitude statistics), porosity, pore fluid pressure, and permeability will be used to evaluate compaction and dilatancy. Although dilatancy has been widely studied since the early researches of Brace (e.g. Brace, Paulding & Scholz 1966), Paterson (e.g. Edmond & Paterson 1972) and their colleagues little progress has been made in extending this research to the physical conditions of deeper crustal levels where elevated temperature is a significant factor in rock behaviour. Yet rock dilatancy involving crustal fluids at elevated temperatures is of significant interest both in economic activities and in the geological sciences. In our laboratory we have been active in studies of the role of metamorphic dehydration in rock deformation (Murrell & Ismail 1976, Murrell 1985), but have hitherto been inhibited from producing a detailed model of the processes involved by our inability to measure dilatant volume changes at elevated temperatures. It is this that gave impetus to our initial interest in rock physics. However, the recent development by Paterson and his colleagues at AN.V. (Canberra) (pers. comm. 1986–1989 from M.S. Paterson and G. Fischer) of a servo-controlled pore volumometer has pointed the way to resolve the problem more directly (see also Read et al 1989). It is the measurement of rock physical properties under triaxial loading and elevated temperature conditions that particularly characterizes the currently expanding research in our laboratory, and this has determined the technical characteristics (and particularly the cylindrical geometry) of the apparatus we have been developing. Fuller descriptions are given by Ismail (1974) and Jones (1988).
A block diagram of the apparatus as equipped [or acoustic measurements is shown in Figure 1.
The shell is designed for a maximum operating pressure of 1400MPa using inert gas as a pressurizing medium so that an internal furnace is able to heat the pressurized rock samples to temperatures of l000°C.
