Geology Reference
In-Depth Information
MATERIAL SCALE
The material scale is that of the intact soil and rock making up the site.
It is also the scale of laboratory testing, which is usually the source of
engineering parameters for design. Typical factors to review are given
in Table 4.2. They include the chemistry, density and strength of the
various geological materials and contained
fluids making up the geo-
logical pro
le. Hazards might include adverse chemical attack on
foundations or ground anchors, liquefaction during an earthquake,
swelling or low shear strength due to the presence of smectite clays,
abrasivity or potential for piping failure. Inherent site hazards asso-
ciated with geology include harmful minerals such as asbestos and
erionite. Granitic areas, phosphates, shale and old mine tailings are
sometimes linked to relatively high levels of radon gas, which is esti-
mated to cause between 1,000 and 2,000 deaths each year in the UK
(Health Protection Agency). Talbot et al. (1997) describe investiga-
tions for radon during tunnelling. Gas hazards are especially impor-
tant considerations for tunnelling and mining but are also an issue for
completed structures, as illustrated by the Abbeystead disaster of 1984
when methane that migrated from coal-bearing strata accumulated in
a valve house and exploded killing 16 people (Health and Safety
Executive, 1985). These are all material-scale factors linked to the
geological nature of the rocks at a site.
Locating sources for aggregate, armourstone and other building
materials is often a task for an engineering geologist. Other than the
obvious considerations of ensuring adequate reserves and cost, one
must consider durability and reactivity, and this will involve geological
characterisation and probably testing. Two examples in Chapter 7
relate how adverse material properties of sourced
fill and aggregate
material
led to severe consequences. At Carsington Dam, UK, a
Table 4.2 Examples of material-scale factors that should be considered for a project
FACTOR
CONSIDERATIONS
EXAMPLES OF ROCK TYPES/SITUATIONS
mineral
hardness
mineral
chemistry
abrasivity, damage to
drilling equipment
reaction in concrete
oxidation
silica-rich rocks and soils (e.g. quartzite,
flint, chert)
olivine, high temperature quartz, etc.
pyrites
mudrocks, salts, limestone
acids
swelling, squeezing
dissolution
low friction
-
clay-infilled discontinuities, chlorite coating
loose, open
texture
collapse on disturbance or
overloading,
liquefaction, piping, low
shear strength
poorly cemented sandstone, completely weathered
rocks(V);loess;quickclays
 
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