Geology Reference
In-Depth Information
modelling and could be done using PFC3D (Itasca). Whilst the largely
intractable geological characterisation nature of the problem would
remain, the problem could probably be resolved parametrically in a
similar way and with a similar level of success for prediction as the
Hoek-Brown model for fractured rock masses.
Mixed soil and rock deposits include sedimentary deposits like collu-
vium and glacial boulder clay, but also some weathered rocks. As for
assessing shear strength, there are considerable dif
culties for sam-
pling and testing and there can also be signi
cant problems for con-
struction (e.g. Weltman &Healy, 1978). The conservative position for
design is to take the strength and deformability of the matrix as
representative of the mass, but allowance might be made for the
included stiffer and stronger clasts by rational analysis, perhaps
backed up by numerical modelling.
Crushed rock and quarried or dredged sand and gravel are important
materials used in making concrete and construction generally, perhaps
as
fill. Rock is also used as armourstone, for example, in protecting
earth dams fromwave action or for forming harbours. It is also cut and
polished as dimension stone to be used as kitchen work surfaces or as
cladding on the outside of prestigious buildings. Engineering geologists
are often required to identify sources of aggregate, either from existing
quarries but sometimes from new borrow areas in the case of sand for
reclamation or new quarries for a remote project such as a road. Some
of the properties that are important for their use are the same as in
much of geotechnical design: strength, unit weight and porosity, but
there are other properties that need to be tested speci
cally.
5.9.1 Concrete aggregate
For concrete, the aggregate must be sound, durable and chemically
stable. Materials to be avoided include sulphates (e.g. gypsum and
pyrites), clay and some silicate minerals such as opal and volcanic
glass, which can cause a severe reaction and deterioration of the
concrete if present in the wrong proportions (see case example of
Pracana Dam in
Chapter 7).
Tests are available and should be used
to ensure that the aggregate being sourced is suitable. These include
mortar bar tests whereby a test mix of concrete is formed and observed
to see if it expands with time. Other factors might include the need for
light- or heavy-weight concrete,
fire resistance and overall strength.
Concrete mix design for a large project may require a research
