Laboratory Tests - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 436

Figure 14.18 Arrangement of specimen in the shear box (ISRM 1975a)
Shear and normal force must be measured independently using load cells. Normal stress
is calculated from the applied normal force F N as
(14.48)
Shear stress acting in the shear plane is calculated from the applied shear force F S as
(14.49)
If information about deformability of the discontinuity is required, devices such as
electric transducers must be installed to measure the specimen's shear and normal
displacements. If lateral displacements of the specimen are possible, these should
be measured as well.
The measured displacements normally include the displacement of the discontinuity
and in addition those of the intact rock and the encapsulating material. Thus, the dis-
placements of the intact rock and the encapsulating material must be eliminated in
order to obtain the displacement of the discontinuity alone. Alternatively, the displace-
ments may be recorded using a measuring frame that is doweled at the specimen just
above or below the discontinuity (Leichnitz 1981, DGEG 1988).
Various types of laboratory direct shear testing devices are reported in literature
(Krsmanovic & Langof 1964, Bernaix 1969, Kutter 1971, Goodman & Onishi 1973,
Crawford & Curran 1981, Leichnitz 1981, Sun et al. 1985, Erban 1986, Barla et al. 1990,
Jiang et al. 2004). As an example, Fig. 14.19 shows a test apparatus developed at the
University (RWTH) of Aachen (Erban 1986).