Civil Engineering Reference
In-Depth Information
Table 2-3
continued
Guideline values for permeability coefficient kf
f
Soil
k
f
m/s
Soil
k
f
m/s
10
-2
10
-7
to 10
-11
Coarse river gravel
Silty clay, clay
10
-3
to 10
-4
10
-9
to 10
-10
Coarse gravel, river
gravels and coarse sand
Clay, greasy
10
-3
to 10
-4
10
-8
to 10
-9
Sand
Clay, silty
10
-4
to 10
-5
10
-9
to 10
-10
Fine sand
Loess, disturbed
10
-4
to 10
-7
10
-9
to 10
-10
Fine sand and silt
Mud
10
-5
to 10
-8
Silt
Bentonite
0.0033 mm/year
The coefficient of permeability
k
f
is dependent on soil type, grain composition, size
of the individual pores and the pore volume or consolidation density. This value is a
decisive for the selection of a suitable process of dewatering including compressed air,
for the calculation of groundwater lowering and the assessment of the suitability of the
undisturbed ground for grouting. It can be generally stated that soils with a permeability
coefficient
k
f
of greater than 10
-4
m/s are permeable, less than 10
-6
m/s are semi-perme-
able and less than 10
-8
m/s can be considered (nearly) impermeable [105].
2.3
Engineering geology and rock mechanics investigations
General.
Geological engineering and rock mechanics investigations and the design and
construction of underground cavities always have to be considered in relationship to
each other. Design work should therefore be performed as a close cooperation between
the responsible specialists for geology, rock mechanics, design and construction, and
this cooperation should start at an early stage of preliminary investigations. This is fol-
lowed by a description of the tasks and methods of engineering geology and rock me-
chanics investigations. More detailed information can be found in the relevant publica-
tions.
Binding guidelines for such investigations that are applicable for all cases can scarcely
be given since ground conditions can vary widely from case to case. The aim of engi-
neering geology and rock mechanics investigations is the assessment of the conditions
below ground for construction purposes, entailing the creation of documents for safe
and economical construction of the structure (selection of process) including the speci-
fication of construction measures for temporary and permanent support and lining of the
rock cavity. At the preliminary design stage, suitable methods should be used to deter-
mine whether the planned structure is feasible in the intended location including consid-
eration of technical and economic questions. It is important to find out which particular
underground conditions and rock properties are of decisive significance. In the further
course of processing the project design, the geological and rock mechanical conditions
in the project area are determined more precisely and documents are produced for the
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