Laboratory Tests - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 405

(14.4)

(14.5)

(14.6)

(14.7)

where m is the bulk mass including the pore-water and V s is the solid or grain volume
of the sample, g = 9.81 m/s2 is the acceleration due to gravity and ρ w = 1000 kg/m3 is the

density of water at standard conditions.

Water content
The water content of intact rocks can be of practical importance since the deformabil-
ity and strength, particularly those of soft rocks, exhibit a considerable dependency on
water content (Colback & Wiid 1965, Vutukuri et al. 1974, Lashkaripour 1998, Nick-
mann 2007, Plinninger et al. 2008). Coating in wax or a metal foil coated with plastic or
storage in a metal box is required after extraction of the sample to maintain the natural
water content (Section 13.5.1).
Either drill cores or irregular shaped pieces of intact rock are suitable as samples. A
representative sample should comprise at least ten specimens, each having a mass of
not less than 50 g and a minimum dimension of 10 times the maximum grain size. The
sample is placed in a container with cap having the mass A. Then, the mass B of the
sample plus container is weighed. Subsequently, the cap is removed and the sample is
dried to constant mass at a temperature of 105°C. Afterwards, the sample with cap is
cooled down in a desiccator for 30 minutes. Finally, the mass C of the container and the
dried sample is weighed and the water content is determined as (ISRM 1979b)

(14.8)

It should be noted that w does not contain the water that may be present in isolated
pores or the capillary bounded water for rocks containing clay minerals.

Dry density
The dry density ρ d of intact rocks that do not swell or disintegrate when oven dried or

immersed in water can be determined by the “caliper and saturation method” as well as
the “saturation and buoyancy method” (ISRM 1979b).