Field Tests - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 471

give an indication of whether the rock behavior is time-dependent. The test pressure
p should not fall below 0.2 MPa during the test to ensure permanent contact of the
LFJ with the slot wall (ISRM 1986).

Figure 15.11 Sawing of slot for an LFJ (Wittke 1990)

The test results are plotted in the form of p versus s curves. These are evaluated under

the assumption that the rock mass is homogeneous and its stress-strain behavior is elas-
tic and isotropic. Young's modulus then can be calculated at each deformeter as follows
(Loureiro-Pinto 1981, DGEG 1984a, ISRM 1986):

Δ

(15.17)

where K has the dimension of length and depends on the number of LFJs and the po-
sition of the deformeters. Since the tensile stresses induced at the slot's edges can cause
tensile cracks of depth d (Fig. 15.10, lower) leading to an increase in

s, K is also de-
pendent on d. The K values for LFJs of 1.25 m length and 1 m width given in cm (when
Δ

Δ

s is measured in cm) are provided by Loureiro-Pinto (1981) as a function of the num-
ber of LFJs, the position of the deformeters and the depth of the tensile cracks. Corre-
sponding values for LFJs of other dimensions must be provided by the manufacturer.