Geology Reference
In-Depth Information
4.3.3.2 Equation 2: environmental factors
Environmental factors, some of which are listed in Table 4.4, including
hydrogeological conditions, should be considered part of the ground
model for a site, but are best reviewed separately from the basic
geology, although the two are closely interrelated. The environmental
factors to be accounted for depend largely on the nature, sensitivity
and design life of structures and the consequence of failure. It is usual
practice to design structures to some return period criterion such as a 1
in 100 year storm or 1 in 1,000 year earthquake, the parameters for
which are determined statistically through historical review. In some
cases, engineers will also want to know the largest magnitude event
that might occur, given the location of the site and the geological
situation. Then some thought can be given as to whether or not it is
possible to make some provision for that maximum credible event. For
earthquakes, for example, a structure might be designed to behave
Table 4.4 Examples of environmental factors that should be considered for a project
FACTOR
CONSIDERATIONS
EXAMPLES OF ROCK TYPES
SITUATIONS
in situ
stresses
high stress:
squeezing,
overstressing,
rockbursts
mountain slopes and at depth, shield areas,
seismically active areas
low stress:
open fractures,
high in
extensional tectonic zones, unloaded zones,
hillside ridges
ows,
roof collapse in tunnels
natural gases
methane, radon
coal measures, granite, black shales
seismicity
design loading, liquefaction, landslides
seismically active zones, high consequence
situation in low seismic zones
in
uenced by
man
unexpectedly weak rocks, collapse
structures
gases and leachate
undermined areas
landfills, industrial areas
groundwater
chemistry
chemical attack on anchors/nails
foundations/materials
acidic groundwater, salt water
groundwater
pressure
effective stress, head driving in
ow,
all soils and rocks
settlement if drawn down
ice
ground heave, special problems in
permafrost/tundra areas, freeze-thaw
jacking and disintegration
anywhere out of tropics
biogenic
factors
physical weathering by vegetation,
rotted roots leading to piping,
insect attack
near-surface slopes
weathered rocks
causing tree collapse
 
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