The stability and safe operation of any underground excavations has been the prime concern of underground mine engineers. One of the most important parameters to obtain for underground mine planning is the in-situ principal stresses determination. The problems with the in-situ stress determination, particularly in Indonesia, so far have been associated with technology availability, cost efficiency and complexity in performing the in-situ test in remote regions. However, an indirect method with less cost to determine the in-situ principal stresses which is attributed to the use of Acoustic Emission (AE) method has been used by many and proven to be reliable as experienced at an underground gold mine in Indonesia. This paper therefore emphasizes on the technique development of AE test on 6 cored rock specimens retrieved from a reasonably large size core rock sample with different directions encompassing three-component principal stresses. The large size core rock sample had orientation of N58OE/- 4O and was drilled from the AB Tunnel of the Underground copper mine of PT. Freeport Indonesia. Based on the stress level at which the Kaiser effects were detected the in-situ stresses at the AB tunnel was subsequently predicted as follows σ1 =41.4 MPa; σ2 = 18 MPa; σ
Underground mining engineers have been very much concerned with the safe operation of any underground excavations. Prior to making up underground mine planning in-situ principal stresses acting at the interest region should have been obtained. However, the problems with the in-situ stress determination, particularly in Indonesia, so far have been associated with technology availability, cost efficiency and complexity in performing the in-situ test in remote regions. Underground excavation will obviously create induced stress in its near field domain that will be greater than the original in-situ stress, and even will also alter the stress direction. In the last three decades, in-situ stress measurements have been very important issues in the rock mechanics field in Indonesia, since the values obtained from these measurements can help the rock mechanics engineers to analyze the stability of an underground excavation in a better confidence so that safe operation can be achieved. An alternative method for determining the stress-state at depth, remote areas, and without creating induced stress, is to take advantage of the so-called Kaiser Effect of acoustic emission (AE). This phenomenon, termed Kaiser Effect suggests that previously applied maximum stress might be detected by stressing a rock specimen to the stress level where there is a substantial increase in AE activity. Based on the Kaiser Effect, the previous stress can be estimated from the curve of AE activity under monotonically increasing stress, which is referred to the Uniaxial Loading Method (ULM). AE is concerned with a transient elastic wave energy generated by rapid micro-crack growth within a material. The micro-crack propagation is a ubiquitous phenomenon associated with brittle fracture, and has provided ample evidence regarding the failure process in rock.
