188 Testing techniquesanisotropic and so an essential feature of such a device must be the ability
to both apply load and measure displacement in different radial directions.
One of the best of these types of device is the Goodman Borehole Jack,
shown in Fig. 11.12 together with example results. The ability to estimate
the modulus, varying both the position and direction of application of the
load, is a major advantage.
The development of this, and other similar, devices has not been without
difficulties. A salutory paper published by Heuze and Amadei (1985) lists
the interpretative problems encountered by several investigators and
documents the evolution of the Goodman jack. For example, imagine
estimating the overall rock mass modulus from a series of measurements
made on a borehole wall, often in close proximity to discontinuities. There
will be a range of moduli values as the jack alternately measures within
intact rock blocks and at locations where discontinuities intersect the
borehole wall.
A similar circumstance occurs with a plate loading test conducted either
on a surface rock exposure or underground. In this test, a large steel plate
is set on a cement grout pad and loaded, usually by the application of dead
weights or by means of a hydraulic ram reacting against an opposing
tunnel wall or a system of rock anchors, as illustrated in Fig. 11.13. A
force-displacement curve can be generated from the hydraulic pressure
3-D hydraulic hole line
effect effiFiency dia. pressure change
\ \ AQ'
Ecalc 0.86. 0.93. D. &. K(v,P),
diameter
change ratio angle
which, for full contact (P = 45") in an
NX-borehole, reduced to (English units):
Ecd,,(psi) = 2.40. h~(~~) AQ, (psi). K(v)
Figure 11.12 The Goodman Borehole Jack and example results.