Laboratory Tests - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 441

Figure 14.21 Swelling test according to Huder & Amberg (1970)

The swelling strain index test described in ISRM (1979b) and DGEG (1986) can be
considered as a special case of the swelling test according to Huder & Amberg (1970)
with only one stress level. In this test, the specimen is subjected to a small axial load
specified as F = 3 kPa (ISRM 1979b) or F = 5 kPa (DGEG 1986). After irrigation of
the specimen the axial strain is measured as a function of time until no further increase
in axial strain occurs. The maximum axial strain at the end of the test is referred to as
the “swelling strain index” (ISRM 1979b).
In the swelling pressure index test the specimen is initially loaded by a small axial stress
specified with 5 kPa (DGEG 1986), 10 kPa (ISRM 1979b) or 25 kPa (ISRM 1989a,
ISRM 1999b) and then irrigated. Subsequently, the axial strain due to swelling is not
allowed to occur, that is, small amounts of axial strain are compensated for by increas-
ing stepwise the axial force during the test (ISRM 1979b, ISRM 1989a, ISRM 1999b).
Alternatively, the rigid frame with the loading unit is locked after initial loading of the
specimen (DGEG 1986). During the test the axial force due to swelling at constant
volume of the specimen is recorded as a function of time. The test can be terminated
when no further increase in axial force is measured. The corresponding axial stress σ z0

is referred to as the “swelling pressure index” (ISRM 1979b).

Since the swelling parameters K q and σ q0 cannot be determined by swelling strain index

tests and swelling pressure index tests, respectively, these tests should only be carried out
in order to complement swelling tests according to Huder & Amberg (1970). Swelling
strain indices and swelling pressure indices can then be used to cross-check the results
of swelling tests according to Huder & Amberg (1970) obtained at low and high axial
stress levels.