Geology Reference
In-Depth Information
chemical reaction was set up between the various rocks used to con-
struct the dam, which resulted in acid pollution of river courses and the
production of hazardous gas, with the death of two workers; at
Pracana Dam, Portugal, the use of reactive aggregate led to rapid
deterioration of the concrete. The latter phenomenon has been
reported from many locations around the world and is associated
with a variety of minerals, including cryptocrystalline silica (some
types of
flint), high-temperature quartz, opal and rock types ranging
from greywacke to andesite. Details of how to investigate whether
aggregate may be reactive and actions to take are given in RILEM
(2003).
MASS SCALE
Mass-scale factors include the distribution of different materials in dif-
ferent weathering zones or structural regimes, as successive strata or as
intrusions. It includes structural geological features such as folds,
faults, unconformities and joints (
Table 4.3).
Discontinuities very
commonly control the mechanical behaviour of rock masses and
some soils. They strongly in
uence strength, deformability and hydraulic
conductivity.
FACTOR
CONSIDERATIONS
EXAMPLES OF ROCK TYPES
SITUATIONS
lithological
heterogeneity
dif
culty in establishing engineering
properties, construction problems (plant
and methodology)
colluvium, un-engineered
ll,
interbedded strong and weak strata, soft
ground with hard corestones
joints/natural
fractures
sliding or toppling of blocks, deformation,
water in
slopes, foundations, tunnels and
reservoirs, nuclear repository
ows, leakage/migration of
radioactive
fluids
faults
as joints, sudden changes in conditions,
displacement, dynamic loads
tunnels, foundations, seismically active
areas
structural
boundaries,
folds,
intrusions
heterogeneity, local stress concentrations,
changes in permeability
all rocks/soils
-
water in
ows
weathering
(mass scale)
mass weakening; heterogeneity (hard in
soft matrix), local water in
all rocks and soils close to Earth
s
surface, especially in tropical zones;
ravelling in disintegrated rock
masses
'
ow, unloading
fractures
hydrothermal
alteration
as weathering, low strength and prone to
collapse especially below water table
generally for igneous rocks especially
near contacts
