Environmental Engineering Reference
In-Depth Information
1970). Intact specimens are tested in uniaxial compression or tension to provide data for
classification and correlations. Other tests include those for flexural strength and triaxial
compressive strength. Applied forces for the various tests are shown in
Figure 3.37.
Rock Masses
Rock-mass strength is normally controlled either by the joints and other discontinuities or
by the degree of decomposition, and the strength parameters described in
Section 3.4.2
here. Strength is measured
in situ
by direct shear equipment or special triaxial shear equip-
ment.
Uniaxial Compressive Strength U
c
(ASTM D2938)
Procedure
An axial compressive force is applied to an unconfined specimen (
Figure 3.38)
until fail-
ure occurs.
Data Obtained
A stress-strain curve and the unconfined or uniaxial compressive strength (in tsf, kg/cm
2
,
kPa) result from the test. Stress-strain curves for various rock types are given in
Table 3.24.
Data Applications
Primarily used for correlations as follows:
●
(Figure 3.1a)
is useful for field measurements of outcrops to correlate variations
in
U
c
. Corrections are available for inclinations from the vertical.
●
Hardness classification —
Table 5.20.
●
σ
d
σ
d
σ
3
σ
N
σ
N
σ
d
σ
d
σ
3
σ
3
(a)
(b)
(c)
(d)
σ
d
σ
d
σ
d
σ
d
(e)
(f)
(g)
(h)
FIGURE 3.37
Common laboratory tests to measure strength of rock cores: (a) uniaxial compression; (b) triaxial compression;
(c) direct shear for soft specimens; (d) direct shear for joints; (e) point load; (f) direct tension; (g) splitting
tension (Brazilian); and (h) four-point flexural.
