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ABSTRACT: An experimental study has been undertaken to investigate laboratory verification of the Kaiser effect in rock under different environmental conditions - air dry, saturated in distilled water at different elapsed time after application of the previous stress. The previous stress was applied to a rock specimen, West Australian granite or Gosford sandstone, under uniaxial or triaxial compressive loading. The paper describes some factors influencing on the recollection of the maximum previous stress - elapsed time, water and confining pressure, and suggests the technique to accurately evaluate the previous stress by using the AE signatures in cyclic reloadings of the previously stressed rock. The results of in situ vertical stresses estimated from drilled core rock is also described to show the applicability of the technique to in situ stress measurement. RESUME: Une etude experimentale a ete realise pour verifier en laboratoire I'effet de Kaiser sur des ruches surmises à diverse conditions - air sec, satire en eau distiller à different intervallic de temps après application dune constraint resalable. La constraint resalable a ete applique sur un specimen de roche, un granite d' Australia Occidental our un gores de Gosford, en compression uniaxiale our triaxiale. L'article donne une description de quelques uns des facteurs influançant la recuperation de la constraint resalable maximale - Intervalle de temps, pression d'eau et de confinement, et propose des techniques d'evaluation precise de la constraint originelle en utilisant les signatures AE dans les cycles de remise en charge des ruches prealablement surmises à contraintes. Par ailleurs, les resultats de I' estimation de contraintes verticales in-situ obtenues sur des carottes de sondages sont egalement decrits pour montrer les possibilites de mise en aeuvre de cette technique dans la mesure in-situ des contraintes. ZUSAMMENFASSUNG: Es ist eine experimentelle Untersuchung durchgefuehrt worden, um Laborbestatigung des Kaiser-Effeckts in Fels unter vershiedenen Umweltbedingungen - trocken in Luft, gesattigt in destilliertem Wasser nach vershiedenen Verweilzeiten nach Anwendung vorhergehender Spannung - durchzufuehren. Vorhergehende Spannung wurde auf Felsproben von west-australischem Granit bzw. Gosford-Sandstein unter einachsiger oder dreiachsiger kompressiver Belastung durchgefuehrt. Die Studie beschreibt einige Faktoren, welche die Erinnerung an die maximale vorhergehende Spannung - verstrichene Zeit, Wasser und begrenzenden Druck beeinflussen, und sie schlagt ein Verfahren fuer genaue Bewertung der vorhergehenden Spannung durch Verwendung der AE-Signaturen in zyklischen Neubelastungen des vorher belasteten Felsens. Die Ergebnisse vonVertikalspannungen an Ort und Stelle, geschatzt von gebohrtem Felskern, werden auch beschrieben, um die Anwendbarkeit des Verfahrens auf Spannungsmessung an Ort und Stelle zu zeigen. 1. INTRODUCTION A knowledge of the magnitude and directions of the in situ and induced stresses in a rock mass is an essential concern in underground excavation design. 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 to determine in situ stress, the determination of in situ stress is not an easy task and all suffer from deficiencies and limitations. 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 techniques are that they are deficient for measuring the in situ stress at depth in remote regions which are hard to access from boreholes or mine workings.
- Research Report > New Finding (0.49)
- Research Report > Experimental Study (0.34)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Rock Type > Igneous Rock > Granite (0.47)
- Energy > Oil & Gas > Upstream (0.54)
- Materials > Metals & Mining (0.48)
ABSTRACT: A brittle rock-like material having a wide range of porosity and density, and a medium range of strength has been developed. The compressive strength and tensile strength decreased exponentially with an increase in the porosity under both dry and water saturated conditions. Percentage reduction in strengths due to water saturation increased with an increase in the porosity. The density had an opposite effect on the properties. RESUMÉ: Un materiau fragile et de caractère rocheux avee de fortes variations de porosite et densite et une variation moins importante de resistance a ete cre. Les resistances de cc materiau en extension et en compression decroissent exponentiellement par rapport au porosite, quel que soit le contenu d'eau. Le plus grand le porosite, la plus importantes sont les abaissements de resistances dûes à la presence d'eau. Par contre, une hausse de densite donne lieu à une amelioration des resistances. ZUSAMMENFASSUNG: Es wurde ein Material mit großer Porositat und Diehte und einer mittleren Zerreißfestigkeit entwickelt. Die Druck- und Zugbelastbarkeit fallt exponentiell fuer einen Anstieg in der Porositat, sowohl unter trockenen Bedingungen als auch bei Wassersattigung. Eine prozentuale Reduktion der Zerreißfestigkeit wird durch einen Anstieg in der Porositat verursacht, wahrend ein Anstieg der Diehte den gegenteiligen Effekt hat. 1 INTRODUCTION Porosity and density are two important indicators of strength of rocks, particularly sedimentary rocks. For example, differences in mechanical properties of sandstones and shales from various formations are largely due to differences in porosity and density. For identifying the effect of porosity and density on the strength of rock, it was necessary first to develop a brittle rock-like material which has similar behaviour and strength as a medium-strength rock. The developed rock-like material can also be used for other purposes. Many materials and combinations of materials were used for various types of modelling works. A good classification or model materials was given by Stimpson (1970) based on differences in the components and applications for different purposes. Some of the materials used include Portland cement Mortar, plaste, concrete, pumice, cork, etc. The materials used most frequently are either plaster or cement with various filler materials (Hobbs, 1966; Saucier, 1967; Rosenblad, 1968: Johnston and Choi, 1986; Indraratna, 1990; Gu and Mostyn, 1992: Gu. Jafari and Mostyn, 1993). Plaster and filler materials were the most practical and feasible for modelling brittle rocks (Saucier, 1967). The development of an adequate rock-like material had been a difficult task. The investigations done in this area are valuable but all works represent soft rock with a low unconfined compressive strength (< 8 MPa) and the model materials behave in a brittle manner under low confining pressures only. Rock generally is known as a brittle material and most rocks have a high strength and they behave in a brittle manner even under high values of confining pressure. Further investigations are needed to find a rock-like material with a wide range or porosity, density and a medium range or strength that behaves in a brittle manner similar to rock under a high can lining pressure in triaxial tests. The constituents of plaster (patternstone U), crushed sand, water and borax were selected among different materials to make the model material. The constituent materials greatly affect the technique of modelling and the mechanical properties of the specimens. Crushed sands having different grain sizes from the same rock were tested to find a critical range of grain sizes. Different ratios, by weights, of plaster, crushed sand, water and borax were tried to find critical constituents to model the specimens successfully. Two methods, compacting the mixture of model material.
- North America > United States (0.68)
- Europe > Norway > Norwegian Sea (0.24)