| 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. The diameter data together with the hydraulic pressure and the acoustic emissions data and ultrasonic data are analyzed to determine the major and minor stress fields in the media, and also the tensile strength, yield strength, and deformation characteristics of the borehole media. |