Civil Engineering Reference
In-Depth Information
Free swelling test
In ISRM (1979b), ISRM (1989a) and ISRM (1999b) simple test setups are suggested
that are intended to measure the free swelling strain occurring when an unconfined
specimen of intact rock is immersed in water. For this purpose, the strains due to swell-
ing are measured in axial and radial directions. However, since unconfined swelling
rocks tend to disintegrate when immersed in water, the strains of the specimen due to
swelling may be non-uniform or it may not even be possible to measure it. This type of
swelling test therefore cannot be recommended to be carried out.
Triaxial swelling test
Triaxial swelling tests that allow intact rock specimens to expand in more than one di-
rection are not standard, and only a few corresponding testing devices are reported in
literature (Özkol 1965, Pregl et al. 1980, Franklin 1984, Yesil et al. 1993).
In the testing devices developed by Özkol (1965), Franklin (1984) and Yesil et al. (1993),
cylindrical-shaped rock specimens are subjected to conventional triaxial loading condi-
tions, that is, the axial strain or stress due to swelling is measured at constant confining
stress. The true triaxial testing apparatus described by Pregl et al. (1980) allows cubic
intact rock specimens after irrigation to swell independently in one, two or three orthog-
onal directions.
14.7
Slake Durability and Disintegration Resistance
Slake durability is a measure of disintegration resistance of rocks, which is influenced,
for example, by structure and microstructure, mineralogical composition, particle
bonds, water content, porosity, permeability and degree of weathering. A reduction in
disintegration resistance, among others, may be a result of water action, of decreasing
capillary tension, of chemical deterioration, of thermic cycles or of wetting and drying
cycles. Many sedimentary rocks, in particular argillaceous rocks, disintegrate to a large
extent or even completely after a short time of being exposed to wetting and drying
cycles without any mechanical impact (Gamble 1971).
The slake durability test, originally suggested by Franklin & Chandra (1972), is in-
tended as an index test to assess the disintegration resistance of intact rock when sub-
jected to wetting and drying cycles. The testing device illustrated in Fig. 14.24 (upper)
consists of a cylindrical test drum comprising a standard sieve of 2 mm mesh size, a
trough in which the drum is placed in such a manner that it can be rotated round a
horizontal axis, and a motor drive capable of rotating the drum at a speed of 20 rpm
(ISRM 1979b, DGGT 2002a).
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