Civil Engineering Reference
In-Depth Information
With the exception of anhydrites, which swell because of chemical
incorporation of water to form gypsum, swelling is most pronounced in
rocks that contain abundant clay minerals (montmorillonite having the
greatest volume change, with other clay minerals such as illite and kaolinite
being much less susceptible to volume change), or clay-sized particles of
other minerals. Some common materials that swell are shales, claystones
and mudstones, where the swelling is directly proportional to the amount
of clay minerals, especially montmorillonite, that are present.
Swelling is commonly a slow process, primarily because of the fine grain
of the minerals that are prone to swelling. The permeability of such minerals
is low, and penetration of water of any origin takes considerable time.
Swelling is likely to be accelerated if the construction process brings water
in contact with a soil, which is capable of swelling.
2.4.3 Typical ground parameters for tunnel design
Due to the many influences that determine the ground behaviour and the
disparity that often exists between this and the properties of the individual
soils/rocks it is not possible to determine binding parameters for a rock or
soil type, i.e. it cannot be put into any 'Standard'. However, some typical
values are provided in the following tables. These provide the reader with
a 'feel' for the magnitudes of the values involved with certain parameters.
TYPICAL ROCK AND SOIL PARAMETERS
Tables 2.9 to 2.12 provide some typical values for the strength and
deformation characteristics of rocks, generic hardness classes, and some
strength and permeability values for soils respectively.
Table 2.9
Strength and deformation characteristics of some typical rocks (after
Reuter 1992 and, Klengel and Wagenbreth 1987)
Ground
Compressive strength (MPa)
E (MPa)
Basalt
160-400
48000-105000
Dolomite
50-180
32000-100000
Gabbro
80-345
75000-120000
Gypsum
9-40
10000-29000
Granite
100-300
37000-72000
Chalk
20-240
16000-90000
Sandstone
10-290
6000-71000
Rocksalt
20-30
16000-24000
Slate
20-210
23000-85000
Concrete C20/25
25 (cube crushing strength)
a
29000
Note: (a) For the influence of the shape of the specimens on the compressive strength see
uniaxial compression test
