Environmental Engineering Reference
In-Depth Information
In most projects, method's specifications become the routine quality control technique,
even if a performance specification has been used for the contract documents. This is the
only practical way of allowing work to proceed without unnecessary delay.
On some projects the owner/engineer will be responsible for the quality control, i.e. the
inspection, testing and assessing whether the required quality standard has been achieved,
and will have the authority to require additional work to achieve the standard or to reject
the non conforming work. The owner/engineer in these projects will also be responsible
for quality assurance, i.e. that the quality control standards are valid for the dam, that the
specified tests are being implemented and correctly performed, that the quality control
plan is working and that records and reports are verified and maintained.
On other projects the quality control aspect may be incorporated into the contract and
be the contractor's responsibility. This can be quite satisfactory provided that the contract
documents clearly define the level of inspection and testing required and the standards to
be adopted and that the inspection and testing group are given authority by the contractor's
management to enforce the standards. Often the testing will be subcontracted to a special-
ist geotechnical consultant. This assists in maintaining the independence of the inspection
and testing group from the main contracting staff.
Whichever method is adopted, testing and QA procedures cannot replace experience
visual inspection and commonsense changes to specifications, methods and control when
they are needed.
14.4.3
Quality control
(a)
Inspection
Inspection must always form a critical part of a quality control plan. The field and lab-
oratory testing program should be seen first as establishing the methods required to
achieve the required quality, then ensuring that the quality is being maintained and as
a definitive, quantifiable means of rejecting substandard work. It is clearly impractical
to test the whole of the completed product so one must rely on visual inspection to
maintain overall quality.
It is important that the inspectors are properly trained and briefed on the implica-
tions of substandard work. It is also important to recognise that inspectors will often
be needed in the borrow areas, as well as on the embankment, so that unsuitable mate-
rial can be rejected before it reaches the embankment.
(b)
Testing
Most testing which is carried out is for quality control, i.e. to ensure that the require-
ments of the specification are being met. The selection of areas or materials for testing
may be done in either of two ways:
- Selecting those areas which are judged by the supervisor/inspector to be least likely
to meet the specification. This can assist in reducing the quantity of testing and, if
the testing shows acceptable performance, should ensure the overall adequacy of
the construction work. It does, however, require independent and experienced
supervisors;
- Selecting test areas at random, at the minimum recommended frequency. This will
yield test results which better reflect the overall condition of the construction work,
as the biased sampling of the first alternative is avoided.
The latter method is better suited to establishing statistical limits to the testing,
allowing recognition of the fact that there is a statistical sampling error and that,
within a large mass of earth and rockfill, the failure of a small proportion of the mate-
rial to meet the basic specification criteria will not affect overall performance (pro-
vided the failures are not representative of poor compaction for example adjacent a
conduit or wall).
