A novel in situ stress meter was developed at James Cook University, Australia. It is based on the recovery principle where tangential stress relief created by cutting an axial slot into the wall of a borehole generates strains that are measured with a sensor. Field tests with a prototype and an early commercial instrument were conducted at the Underground Research Laboratory in Pinawa, Manitoba. Although the results looked promising, the commercial instrument had some design related shortcomings. Additional laboratory tests were carried out at the Rock Mechanics Laboratory at École Polytechnique de Montreal with a modified unit which gave results that demonstrated the viability of the method for in situ stress measurements.
Un instrument de mesure de contraintes a ete developpe à l"Universite James Cook, Australie. Il base sur le principe de recuperation où le relachementde la contrainte tangentielle à proximite d"une fente creee axialement dans 1a paroi d"un trou de forage engendre des deformations qui sont mesurees à l"aide d"un capteur. Des essais avec un prototype ainsi qu"avec un modèle commercial ont ete effectues dans le Underground Research Laboratory à Pinawa, Manitoba. Les resultats initiaux ayant montre certaines anomalies, il a ete decide de realiser certaines verifications de l"appareil au laboratoire de mecanique des roches de l"École Polytechnique de Monteal. Les resultats obtenus ont demontre la validite de la methode pour la mesure des contraintes in situ.
Ein neuartiges Gebirgsspannungs Messungsverfahren wurde an der James Cook Universitat, Australien entwickelt. Es arbeitet auf dem Prinzip der Normalisierung des Spannungszustandes welcher sich in einer tangentialen Entspannung des Gesteins direkt nebeneinem Schlitz, der in die Wand eines Bohrloches geschnitten wird, auswirkt. Die dadurch entsehende Dehnung wird mit einem Tangentialen Dehnungsgeber gemessen. Teste mit einem Prototypen und einem Produktions Modell wurden in dem Underground Research Laboratory, Pinawa Manitoba durchgefuehrt, welche gewisse Design Mangel im Produktions Modell aufzeigten, obwohl im Gesamten die Teste vielversprechend waren. Zusatzliche Labor Teste mit einem modifizieten Instrument in der École Polytechnique, Montreal, Quebec, gaben ausgezeichnete Resultate und haben die Einsatzfahigkeit dieser Methode unter Beweiss gestellt.
The purpose of this paper is to present results from stress measurements field trials and laboratory measurement simulations using a novel in situ stress meter developed at James Cook University, Australia. It is based on the recovery principle where, by cutting an axial slot into the wall of a borehole, total tangential stress relief is achieved adjacent to the slot. The resultant strain is then measured by a calliper type strain sensor. The novel method"s advantages are the instrument"s recoverability and its non reliance on overcoring.
Results of comparative field tests with a prototype in Australia were in reasonable agreement with other measurements, and good results were also obtained in some mines in Canada (Kanduth and Germain, 1990).
Noranda has now obtained a commercially manufactured slotting instrument from Interfels, Germany. The purpose is to use it for affordable pre mining stress measurements as well as routine monitoring of stress change in Noranda"s mines. To evaluate the instrument"s performance, initial field tests were carried out at the Atomic Energy of Canada Underground Research Laboratory (URL) in Pinawa, Manitoba.
The stress state at this location has been measured extensively by a variety of methods.
