Geoscience Reference
In-Depth Information
Table 1.8 ( Continued )
Development
Test spacing
Approximate depth of investigation
Dams
25 m to 50 m
2
height of dam, 5 m below toe
or of slope 3 m into bedrock below
toe whichever is greater. Extend to
zone of low permeability.
×
Canals
100 m to 200 m
3 m minimum below invert level
or to a zone of low permeability.
Culverts
1 Borehole
2 B-4 B but below base of
20 m width
One at each end
compressible layer.
<
20 m-40 m
One at each end and 1 in
40 m
the middle with maximum
spacing of 20 m
between boreholes
>
Car Parks
2 Bhs for
50 parks
2 m below formation level.
<
3 Bhs for 50-100
4 Bhs for 100-200
5 Bhs for 200-400
6 Bhs for
>
400 parks
Monopoles and
At each location
0 m to 20 m high: D
4.5 m
=
transmission
20 m to 30 m high: D
=
6.0 m
towers
30 m to 40 m high: D
7.5 m
=
40 m to 5 0m high: D
9.0 m
=
60 m to 70 m high: D
10.5 m
=
15.0 m
Applies to medium dense to dense
sands and stiff to very stiff clays.
Based on assumption on very lightly
loaded structure and lateral
loads are the main considerations.
Reduce D by 20% to 50% if hard clays,
very dense sands or competent rock.
Increase D by
70 m to 80 m high: D
=
30% for loose sands
>
and soft clays.
N* Inferred SPT value.
RQD-Rock Quality Designation.
H-Height of slope.
D-Depth of investigation.
Ensure boulders or layers of cemented soils are not mistaken for bedrock by
penetrating approximately 3m into bedrock.
Where water bearing sand strata, there is a need to seal exploratory boreholes
especially in dams, tunnels and environmental studies.
Any destructive tests on operational surfaces (travelled lane of roadways) needs
repair.
In soft/compressible layers and fills, the SI may need to extend BHs in all cases to
the full depth of that layer.
Samples/Testing every 1.5m spacing or changes in strata.
Obtain undisturbed samples in clays and carry out SPT tests in granular material.
 
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