Environmental Engineering Reference
In-Depth Information
Which of these two methods is adopted is also related to the specification limits
used, and whether the supervisors are given any latitude in accepting material which
falls below the specification.
For example, if earthfill is specified to have a density ratio in excess of 98%, with a
water content optimum minus 1% to optimum plus 1%, it would be reasonable in
most cases to accept an area which has tested at 97% density ratio, OWC
2%, as
this will still yield a low permeability fill. However, one would almost certainly reject
an area which has tested at 95% density ratio, at OWC
3%, as this will give a more
permeable, erodible fill.
Similarly, if a relatively low compaction standard is set at (say) 95% density ratio,
no “failures” should be accepted.
The authors' opinion is that it is desirable to establish such guidelines in the design
stage of a project and to detail them in the specification either in a descriptive or a sta-
tistical form. Alternatively, a rigid specification limit may be set, but the site supervi-
sion staff should be advised as to the degree of flexibility which can be used in
applying the specification.
The question of how many tests should be carried out on earth and rockfill is vir-
tually impossible to answer, as it is interrelated to the specification standards, the
competence of the contractor and the inspectors and the site conditions (e.g. variabil-
ity of materials, climate).
ICOLD (1986b) gives some useful examples of minimum frequency of testing
required for some large fill dams in USA, Austria, India, Canada and Italy.
Tables
ing specified for the random fill zone in Winneke Dam by the Melbourne and
Metropolitan Board of Works and for the earthfill in the Ranger Mine Tailings dam (a
zoned earth and rockfill dam).
(c)
Reporting
It is important that a complete record should be kept of all construction operations.
These are invaluable in the event that repairs or modifications are required, if
the embankment is to be raised in the future and for surveillance during the life of the
dam. Records are also important in respect to contractual and insurance claims.
The reporting should include:
- Plans and specifications, including amendments and work as constructed;
- Final construction report written by the engineer;
- Monthly progress reports and reports on technical meetings;
- Reports from dam review panel if one is appointed;
- Laboratory test reports, including clear definition of location and level of samples
tested, and differentiating between original tests and retests after failures;
- Daily reports by all supervisory personnel and inspectors in the form of diaries.
These should concern adequacy of progress and comments on decisions;
- Photographs taken on a regular basis to show placement and compaction of earthfill,
filters and rockfill.
The authors have been involved in a major dam foundation failure where daily reports
and photographs proved invaluable.
14.4.4
Influence of non technical factors on the quality of embankment dams
In the Casagrande volume (Hirschfield and Poulos, 1972), Professor Ralph B. Peck high-
lighted some of the “facts of life” relating to the influence of non technical factors on con-
struction of embankment dams. Professor Peck points out that many shortcomings in
dam engineering relate to the attitudes and actions of the owner, designer, contractor and
