The drill hole jack designed by Goodman, Harlomoff and Homing and licensed by Slope
lndicator Co., Seattle, USA, has been used in the investigation. 1t consists of two curved
rigid bearing plates of angular width 90 degrees, which can be forced apart by a number
of pistons. The device is used inside an NX size (76 mm diameter) drill hole. Two LVDTs
mounted at either end of the 20 cm long bearing plates measure the displacement. Two
return pistons retract the bearing plates to their original position. The total piston travel
of the equipment is about 12.5 mm and the LVDTs have a linear range of 5 mm. Pressure
of the order of 70 MPa can be applied by the iacls. The volume of rock affected by the
jack is about 0.028 m3 and extends to about 114 mm into the rock away from the drill
hole walls. One problem with borehole deformability tests is that they affect a relatively
small volume of rock and therefore contain an incomplete sample of fracture system
(Goodman 1989). However, the Goodman jack has the unique advantage of giving an
indication of the range of properties of the rock mass remote from the surface at an early
stage of field investigation. A large-scale field test requires drifts and is more expensive
and time consuming. The large-scale field test can be carried out for final construction of
the structure. Goodman jack along with the pump is shown in Fig. 10.4 and Goodman
jack inside a drill hole is shown in Fig. 10.5.