Abstract: An improved single-fracture method and apparatus for determining the ambient stress state and material properties of underground media includes, in one aspect, an expandable probe having high-strength steel shells with longitudinally extending, tooth-like ridges to create a maximum friction engagement with the borehole boundary. The single fracture method establishes a force-balance between the probe expansion pressure and the underground stress vector acting perpendicular to the single fracture plane, whereby the expansion pressure and stress vector are related by a proportionality constant (n).

Abstract: An apparatus for measuring in situ stresses surrounding an active earthquake fault and forecasting shallow earthquakes includes a network of monitoring stations, each operating a respective borehole assembly for measuring in situ lateral stresses. The monitoring stations are arrayed along a recognized fault plane and arranged to straddle the fault plane, so that lateral stress readings may be obtained throughout the ground media surrounding the fault zone. All of the monitoring stations communicate with a central data-gathering facility, so that real-time analysis of changes in lateral stress orientation and magnitude surrounding the fault zone may be undertaken, and the results used to forecast forthcoming seismic events. Each borehole probe assembly includes a trio of single fracture expansion probes operated periodically, reiteratively, and automatically to expand against the borehole wall and determine the principal maximum and minimum lateral stress vectors in the underground media.

Abstract: A method and apparatus for measuring ambient stress states and material properties in underground media includes a borehole probe having a cylindrical tube formed of soft, elastic polymer material secured about a central mandrel. An upper end cap assembly removably secures the probe to a service module to provide high pressure hydraulic fluid and sensor connections. A distal end cap seals the tube to the mandrel, so that hydraulic pressure causes diametrical expansion of the tube. The end cap includes an annular seal formed of elastic polymer material and helical springs that are embedded therein in the circumferential direction. The interiors of the helical springs are filled with steel pins or balls to prevent deformation of the springs. High strength fibers are bonded in the outer surfaces of the annular seal and oriented longitudinally to permit radial expansion of the seal assembly without hydraulic leakage or extrusion of the soft polymer of the cylindrical tube.

Abstract: A method and apparatus for mechanized, stress control mining includes the process of continuously cutting and advancing a broad mine face to form a mine opening having a low aspect ratio and an envelope of ambient stresses in the earthen media that protects the roof and floor from failure. At the advancing face the roof is supported by the apparatus of the invention, a superlifting stress control machine. The stress control machine comprises a plurality of support column assemblies, each capable of lifting up to 10,000 tons. The support column assemblies are arrayed at the mine face, and are interconnected by telescoping hydraulic arms so that individual support columns may be unloaded and translated with respect to the operating, anchored support columns. Alternatively, the column assemblies may be mounted in groups on tracked vehicles for high mobility.

Abstract: A borehold probe includes a soft outer plastic cylinder secured to a central mandrel and inflatable by hydraulic pressure conducted therethrough to impinge upon the sidewall of a borehole with controlled pressure. A plurality of LVDT diameter sensors is secured to the probe in planes perpendicular to the axis thereof and spaced angularly thereabout. A plurality of acoustic transducers is also secured to the exterior of the probe to monitor acoustic emissions as well as to survey the earthen media with ultrasonic emissions. The cylinder inflation pressure is increased gradually to exceed both the tensil strength of the media and also the principal stress therein to initiate fracture of the media surrounding the borehole. The cylinder is then deflated to unload the fractured media, and gradually reinflated to first elastically deform the fractured media and then re-expand the fractures previously created.

Abstract: A device for determining microscopic motion in static creep and dynamic oscillation between two objects by measuring relative displacement between the two objects connected by a metal wire includes a linear variable differential transformer disposed within a cylindrical housing. One end of the housing includes an extendable tubular member which is joined to one of the objects, The other end of the housing includes a fitting for securing a wire extending to the other object. The core of the linear variable displacement transformer is supported by a pair of spider diaphragms disposed on opposite sides of the transformer. The tubular member is connected by an extension spring to one of the diaphragms, while the wire retaining fitting is connected by a universal joint to the other diaphragm. The diaphragms provide high axial compliance so that the core may undergo microscopic displacement in concert with the displacement between the two objects.

Abstract: A borehole stress property measuring system for in situ determination of stress states as well as material properties of soil and rock media includes two axially aligned adjacent cylindrical members disposed in a borehole. One cylindrical member is provided with at least four pair of diametrically opposed pistons which are hydraulically actuated to impinge on the borehole wall under various pressure loading conditions. The pairs of pistons are axially spaced and angularly offset, each from the other, so that accurate measurement of the outward extension of the pistons under various pressure loading conditions reveals such material properties as elasticity, isotropy, compressibility, and the like. The second cylindrical member includes expandable four-quadrant pressurizing chambers to apply differential pressure to and simultaneously measure deformation of the borehole boundary for determining the existing stress conditions in the underground media.

Abstract: This instrument is a portable field device that quickly determines microscopic creep velocity by measuring relative displacement between two objects connected by a metal wire. The device consists of a micro-creepmeter probe and recorder. The probe includes a linear variable differential transformer disposed within a cylindrical housing which is secured to one of the objects with a multi-directional ball joint fitting. An extendable piston rod slidably disposed within the housing is secured to the other object by means of a dual wire arrangement, which is also used to electronically compensate for temperature effects from solar radiation and variable wind. The transformer core is attached to the inner end of the piston rod and is translated axially by the piston rod through the sensing field of the linear variable differential transformer. A pair of linear ball bearings holds the piston rod free from axial friction within the cylindrical housing.

Abstract: An underground excavation method which reduces or eliminates the need for roof supports includes the cutting of one or more slots in a radial direction ahead of the advancing underground excavation. The plane of the slot is disposed perpendicular to the tangential stress that is expected around the prospective opening, so that the tangential stress is removed prior to the excavation of the opening, eliminating the potential damage to the boundary. The stress envelope finally formed after the excavation is radially expanded by the advanced slots, and can be made to stress-relieve the ground surrounding the excavation by controlling the length, number, and orientation of the advanced slots. The stress-relieved ground may be utilized as lining material by solidification with cement grouting or very limited anchor bolting.