Abstract: The state of stress in a rock mass surrounding a borehole (21) can be estimated by measuring the initial dimensions of the borehole, cutting a cone-shaped opening extending outwardly from the borehole having a bottom wall (44), and cutting a conical slot (45) from the bottom wall (44) of the cone-shaped opening outwardly from the borehole at an angle to the axis of the borehole. The release of stress on the rock between the borehole and the conical slot results in a change in the dimensions of the borehole. An apparatus for carrying out the measurements includes one or more cutting arms (27) pivotally mounted to a main support housing (26) and capable of being rotated thereon while being pivoted outwardly to cut the cone-shaped opening.

Abstract: Measurements of the deformability of deep rock masses are made by positioning a borehole jack (20) having opposed bearing plates (22, 24) in a borehole at a position at which measurements are to be made, and driving the pressure plates (22, 24) apart to displace the walls of the borehole. A lateral displacement probe (30) is mounted between the pressure plate surfaces in position to detect and measure displacements of the wall of the borehole at points lying on a diameter perpendicular to the direction of the resultant of the equal and opposite forces applied by the pressure plates (22, 24) to the wall (21) of the borehole. The lateral displacement probe (30) includes probe tips (35) that are biased firmly against the wall (21) of the borehole to move inwardly or outwardly therewith. A displacement transducer provides an output signal transmitted to the surface which is indicative of the displacements of the probe tips (35).

Abstract: Rock stress in a borehole wall is determined in situ by obtaining an initial strain reading of the wall, relieving the strain by fracturing the wall from within the borehole with a hydraulic jack, obtaining a releived strain reading, and using the two strain readings to determine stress. The jack comprises a pair of diametrically opposed loading members for applying a self-equilibrating pair of forces to opposite quadrants of the wall, and a pair of diametrically opposed piston members for impressing a set of friction strain gauges against the remaining quadrants. The piston members are pivotally mounted to the jack to allow the strain gauges to conform to the shape of the wall. The jack is first located at the preselected region of the borehole and the loading members are separated until they contact the wall to stabilize the jack in the borehole. The pistons are operated to move the strain gauges into firm abutment with the wall to obtain the initial strain reading.