The Goodman Jack is a borehole tool used for estimating the deformability of rock masses in-situ. It is designed to be used in 3" (76 mm) boreholes. Two models are available: a twelve piston model for use in hard rock, and a three-piston model for determining the consolidation-time properties of soft rock, soil, and stiff clays.
The Goodman Jack consists of a hydraulic jack with curved bearing plates, LVDT sensors, a displacement indicator, a hydraulic pump with pressure gauge, hydraulic hose, electrical cable, and a coupler for drill rod.
The jack is attached to drill rod and inserted into the borehole. A hand pump is used to create hydraulic pressure in the lines connected to the jack, which in turn activates the pistons and produces a uniform and unidirectional stress field at the bearing plate. The applied hydraulic pressure is measured with a standard Bourdon-type pressure gauge. The deformation of the rock is measured by two linear variable differential transformers (LVDT) and data are displayed by the indicator at the surface. After the test, the bearing plates are retracted by reversed pistons and the jack is withdrawn from the borehole.
The modulus of deformation is calculated using formulae derived empirically from in-situ testing and correction factors that were developed by laboratory testing.