Laboratory Tests - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 447

metals and highway aggregates, such as the testing method using the Los Angeles
machine (ISRM 1978b). Others are model tests using original tools that are rather
expensive and therefore are not suitable for standard testing procedures. In addi-
tion, approaches to determine abrasiveness by means of an index value are suggest-
ed, in which the index is defi ned as a combination of mineral content and rock me-
chanical parameters such as unconfi ned compressive strength and tensile strength
(Schimazek & Knatz 1970, Schimazek & Knatz 1976, Ewendt 1989, Plinninger
2002, Plinninger 2008, Plinninger 2010). An overview of currently used methods of
determining abrasiveness of rock is given in Plinninger & Restner (2008).
At present, the most accepted method for determining the abrasiveness of intact rock
is the C erchar a brasiveness i index test (CAI test). “Cerchar” stands for “ c entre d' e tudes
et r echerches de char bonnages de France”. It was in this institute that the test was orig-
inally performed (CERCHAR 1986). Two types of testing devices are in use today,
which are referred to as the “Cerchar apparatus” and the “West apparatus”.

The original layout, the Cerchar apparatus (CERCHAR 1986), consists of a vice, hold-
ing a cubical or cylindrical rock specimen and of a hand lever that is directly connected
with the fi xing of the testing pin made of steel (Fig. 14.26, upper). This steel pin has a
cone-shaped tip (Fig. 14.27, left). During the test, the steel pin loaded with a force of
70 N applied by a weight of 7 kg is scratched over the rock surface by moving the lever
with a velocity of 10 mm/s.
The West apparatus also consists of a vice and a steel pin loaded with 70 N. The vice
holding the specimen is slid below the pin, using a hand crank (West 1989). In contrast
to the Cerchar apparatus, the testing velocity of 1 mm/s is ten times lower. Figure 14.26
(lower) shows the West apparatus used in the laboratory at WBI.
The diameter d c of the truncated cone caused by wear of the conical steel pin (Fig.
14.27, right) should be measured at least in two directions parallel and perpendicu-
lar to the direction of movement with a reading accuracy of 0.02 mm and then the
arithmetic mean is taken. The test should be repeated several times on the same
sample and in each case a new pin should be used and the direction of movement on
the test specimen should be changed (West 1989, Plinninger et al. 2003). The C erchar
a brasiveness i index (CAI) is calculated from the arithmetic means obtained from

n individual tests:

(14.54)

Plinninger et al. (2003) and Käsling et al. (2007) propose to test at least fi ve specimens,
prepared from each sample. Intact rocks exhibiting a schistosity or bedding should be
tested both parallel and perpendicular to the structure planes (Käsling et al. 2007).