Information on in situ rock stresses is valuable in numerous discipline like mining engineering, civil engineering, petroleum engineering and geology. Especially in rock mechanics adequate and accurate stress measurement is extremely important to evaluate the stability of rock mass in underground excavations. A variety of methods have been developed and used in attempts to determine in situ stresses in rock mass, most popular currently are Bore hole overcoring and Hydraulic fracturing. Both methods have certain limitations very costly, time consuming and interpretation of data may become very difficult in some time. Due to these factors, use of these methods are not extensive. An alternative method of using Acoustic Emission technique on drilled core rock to determine in situ stress has been proposed by various researchers in the recent past. In this paper we try to evaluate the possibility of using Acoustic Emission technique to measure in situ stress using the Kaiser Effect, which characteristics AE rate increase in an increasing stress exceeds the previous maximum stress. The rock cores from a recently drilled vertical exploratory bore hole of 315 metre depth in the Hunter Valley, NSW, Australia were used in the laboratory environment to evaluate the vertical in situ stress condition. And also to evaluate the time dependency of Kaiser effect, rock cores from another bore hole of 400 metre depth drilled in Newcastle, NSW, Australia area nearly 2 years ago were investigated. All tests were conducted in uniaxial compression condition using a servo controlled hydraulic testing machine with two acoustic emission sensors, and employing the AE instrument MISTRAS 2001 system.
- There was significant correlation between the overburden pressure (estimated from the depth) and Acoustic Emission of the Kaiser Effect
- The time lag of two years does not deter to evaluate the critical in situ stress condition. Rock can recollect the in situ stress condition reasonably well (within ± 10%).
- Rock cores collected from near to the surface i. e. -100 m and above does not show enough Acoustic emission activities, that could be due to nature of the rock moisture content and weathering condition of the rock in this zone.
- Further research work in this promising area is suggested.
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