Page 153 - Civil Engineering Project Management, Fourth Edition

Civil Engineering Project Management
138
16. Glass sheet or metal tray (for mixing in added moisture to sample).
17. 19mm sieve (from Item 4 above).
18. A 1-litre glass graduated measuring cylinder (for measuring volume of
surface-wet material over 19mm sieved out).
The compaction test and in situ density test are important for earthworks con-
struction. The former indicates the maximum density and optimum moisture
content of fill material achieved under ‘standard’ compaction; the latter shows
the density of fill achieved. Specifications often require fill as placed to achieve
90 or 95 per cent of the maximum density obtained under one of the compaction
tests stipulated; the 4.5kg hammer test being used for road construction, the
2.5kg test for other earthworks. For road works a CBR test is often essential to
check design assumptions for the strength of sub-grade. For accuracy this is
normally carried out in the laboratory using standard equipment as set out in
BS 1377 but in situ tests can also be done as a ready check on soil strength.
A small unconfined compression testing apparatus for testing the shear
strength of 38mm diameter undisturbed clay samples is a useful addition to
the site laboratory in certain circumstances. This machine is cheap, easy-to
operate and gives a useful indication of variations of clay strength, as for road
making, etc. The results given by it are not, however, adequate for design
purposes. The triaxial compression testing machine would be used for testing
soils for design purposes; but this is a sophisticated piece of apparatus, not
suitable for site control purposes unless a full-scale soils laboratory has been
set up on site under the direction of a properly qualified geotechnical engin-
eer. It is also useful to have some standard 100mm diameter sampling tubes
on site, to prevent a delay in getting such tubes when an excavation reveals
material that needs to be tested.
Provided proper briefing has been given by an experienced geotechnical
engineer concerning the techniques of testing to be followed, the foregoing
apparatus should permit a useful range of quality control tests to be carried
out on site. Most other tests that might be required, such as consolidation,
permeability and triaxial compression tests, must be regarded as advanced
laboratory tests to be carried out by trained technical staff.

12.12 Site layout considerations

Haulage roads

The roads within the site have to be planned and designed by the contractor.
Lengthy roads may be required to take excavated material to a dumping
ground, or from a borrowpit to the construction site. They exclude any traverse
over public roads. The design of such roads is related to the type of excavat-
ing machinery the contractor proposes to use. Motorized scrapers and balloon
tyred wheeled loaders can pass over hard to moderately soft ground and will