Geoscience Reference
In-Depth Information
•
Applying a specification provides a better confidence in the properties of the fill.
•
Importing a better quality fill can provide a better consistency than using a sta-
bilised local fill. However, the latter may be more economical and this has to be
factored into the design performance.
Table 17.1
Desirable material properties.
Requirement
Typical
Desirable material property
application
Gravel %
Gravel size
Gradation
Fines
High strength
Pavement
Increase
Increase
Well graded
Reduce
Low permeability
Liner
Reduce
Reduce
Well graded
Increase
High permeability
Drainage layer
Increase
Increase
Uniformly/Poorly graded
Reduce
Durability
Breakwater
Increase
Increase
-
Reduce
17.2 Pavement material aggregate quality requirements
•
Pavement materials are typically granular with low fines content.
•
Larger nominal sizing has the greatest strength, but an excessive size creates
pavement rideabilty and compaction issues.
•
The optimum strength is obtained with a well graded envelope.
•
Some fines content is useful in obtaining a well graded envelope but an excessive
amount reduces the
Table 17.2
Developing a specification for pavement materials.
Nominal
Material
Aggregate quality required
sizing
property
High (Base)
Medium (Sub - Base)
Low (Capping)
Poor
40 mm
% Gravel
20%
20%
20%
20%
>
>
>
<
% Fines
10%
15%
20%
20%
<
<
<
>
30 mm
% Gravel
25%
25%
20%
20%
>
>
>
<
% Fines
15%
20%
25%
25%
<
<
<
>
20 mm
% Gravel
>
30%
>
30%
>
20%
<
20%
% Fines
20%
25%
30%
30%
<
<
<
>
- Natural River gravels may have about 10% more fines than the crushed rock
requirements shown in the table, but 10% to 20% more gravel content.
17.3 Backfill requirements
•
Backfill shall be free from organic or deleterious materials.
•
A reinforced soil structure should have a limit on the large sizes to avoid damage
to the reinforcing material. Water should be drained from the system, with a
limitation on the percentage fines.
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