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NIRE Annual Report
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 1999

Rock Stress Measurement Using Rock Cores by the AE Method

Fracture Mechanics and Explosives Division
Safety Engineering Department
Objectives
Reliable evaluation of in situ stress is an important step in the analysis and design of underground excavations, particularly for evaluating the stability of underground structures to prevent failure or collapse of underground openings. Although a number of techniques have been proposed and developed, the main deficiency of established techniques such as over coring method or hydraulic fracturing method is that they are usually expensive and time consuming. Other shortcomings of the technique are that they are deficient for measuring the in situ stress at depth in remote regions.
As an alternative, AE (Acoustic Emission) method has been studied at NIRE for years to develop the technique for in situ stress determination with reasonable accuracy and without large cost spending and time consuming. This report briefly shows the applicability of the AE method to measurement of in situ stresses.
Results
The rock cores have been collected from various places and various depths up to nearly 1000 m from the surface in collaboration with several institutions such as JNC, Kyusyu University, Western Australian School of Mines, University of NSW, Monash University, gold mines in Australia, zinc and lead mine in Japan, and coal mines in Japan and Australia. Also, the AE method has been applied to various types of rock materials from soft sedimentary rock to igneous or metamorphic rock. And, all the results from the AE method was compared with those from over coring method or hydraulic fracturing method as well as over burden pressure estimated from rock density and the depth in order to evaluate the accuracy of the AE method. Consequently, we reached the conclusion that the AE method developed by NIRE should be practically applicable to in situ stress determination in any depth up to 1000 m and in any rocks of which uniaxial strength is more than 5 MPa. Fundamental researches, however, will be still required to understand the mechanism of stress memorization in rock. Fig. 1 is an example of the result of principal stresses determined by the AE method in comparison with over coring method. As shown in this figure, stress orientation is well consistent with each other. Also, the magnitude of the principal stresses from the AE method agreed well with those obtained by over coring method. For instance, maximum principal stress determined by the AE method was 10.5 MPa and 9 MPa by over coring method.
Fig.1
Fig. 1. Plots of Principal stresses
Selected Publications
1) In-situ rock stress measurement from rock cores using the acoustic emission method and deformation rate analysis, Geotechnical and Geological Engineering, Vol.17, pp.1-26, 1999.

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