This paper presents a new, deep-hole dilatometer technique, intended for determination of rock deformability and in-situ stresses. The borehole instrument consists of four parts; a sleeve" a pressure intensifier, a linear displacement transducer and a pressure transducer. As the membrane is inflated against the rock wall, a pressure-volume curve is recorded. From the linear part of this curve the deformability of the rock is calculated. Further pressurization will lead to the initiation of axial fractures in the borehole wall. This is recorded as an abrupt change in slope of the pressure-volume curve. To date, the work has comprised development of the instrument and laboratory testing in blocks of granite and, diabase. Test results are in good agreement with results obtained by uniaxial compression tests.
Cette communication présente une nouvelle technique de pressiométrie à grande profondeur, concue pour déterminer la déformabilité des roches et leur état de contraintes in-situ. L''instrument pour trous de forage se compose de quatre éléments: une membrane gonflable en caoutchouc, un amplificateur de pression, un lecteur de pression, et un lecteur de déplacements linéaires. Au fur et à masure que l''on gonfle la membrane contre la roche encaissante, une courbe pression-volume est enregistrée. La partie linéaire de cette courbe permet de calculer la déformabilité de la roche. Une augmentation de la pression provoque l''initiation de fractures axiales dans la roche, ce qui se traduit sur la courbe par une brusque rupture de pente. Jusqu''à présent, les travaux ont porté sur la mise au point de l''équipement et sur des tests de laboratoire sur blocs de granite et de diabase. Les resultats obtenus sont cohérents avec ceux obtenus par tests de compression uniaxiale.
Dieses Referat stellt eine neue Tiefloch-Dehnungsmesstechnik für die Bestimmung von Gesteinsdeformierbarkeit und Spannungen vor Ort ver. Das Bohrloch instrument besteht aua vier Teilen, der Hülse, dem Druckverstärker und den Messwertumformern für Linearverdrängung und Druck. Beim Aufblasen der Membrane an der Gesteinswand wird eine Druck-Volumenskurve festgehalten. Aus dem linearen Teil dieser Kurve wird die Deformierbarkeit des Gesteins berechnet. Weitere Beaufschlagung der Membrane mit Druck führt zu anfänglichen Axialfrakturen in der Bohrlochwand. Diese sind als plötzliche Änderung der Neigung der Druck-Volumenskurve merkbar. Bis he ute hat die Arbeit die Entwicklung der Instrumente und Laborversuche mit Granit und Diabas umfasst. Die Versuchsergebnisse stehen in guter Übereinstimmung mit den Ergebnissen einachsiger Verdichtungstests.
The concept of using an inflatable membrane in boreholes for measuring deformation properties was introduced. by Kögler in 1933. The development continued with Lois Ménard, who invented the pressuremeter. In 1957 the first pressuremeter for soil engineering was taken into use. Panek et al. (1964) developed a borehole cell called the Cylindrical Pressure Cell (CPC) for determining the modulus of rigidity of rock. The CPC system had, however, some, problems. One of these was that the copper membrane that was pressurized inside the borehole underwent permanent deformation during each test. Hustrulid and Hustrulid (1975) improved the system, the calibration and data reduction procedure, and called the new system the Colorado School of Mines (CSM) cell. Ozdemir and Wang (1981) further improved the CSM cell. Our sleeve is a further development of the CSM cell. The sleeve fracturing system offers the possibility of determining two rock parameters in-situ in one and the same test. The system is first pressurized to a level where no axial fractures are initiated. From the linear part of the pressure volume curve the modulus of rigidity of the rock mass is determined. If the Poisson''s ratio of the rock is known or can be estimated, the elastic modulus (E) can be calculated. By increasing the pressure further, two axial fractures are induced and a sleeve breakdown pressure (Pb) is recorded. The direction of the fractures indicates the direction of maximum stress in a plane perpendicular to the axis of the borehole. By conducting a second pressurization and recording the pressure for reopening the fracture and knowing the tensile strength (T) of the rock mass the magnitude of principal stresses can be determined by using equation (1). In this paper we present the design of the sleeve fracturing system and the methods for determination of rock mass modulus and rock stresses. Results from testing blocks of granite and diabase are presented and future development are described.
The pressuremeter is Widely used for investigating static and cyclic strength and deformation properties of soils. The use of the pressuremeter in rock is, however, very limited. There are two main reasons for this;
difficulties with constructing rubber membranes which can withstand such high pressures, and
low system stiffness.
When testing in hard rock (E > 60 GPa) the stiffness of the system becomes so dominant that it is impossible to observe any difference in stiffness for various rock types.
