Civil Engineering Project Management (4th Edition)
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228 <strong>Civil</strong> <strong>Engineering</strong> <strong>Project</strong> <strong>Management</strong><br />
the last 150–225 mm of excavation, any loose material being either removed by<br />
hand labour or rolled back with a light roller before placing of the base course for<br />
a road or blinding concrete.<br />
The presence of springs in a soft formation material exacerbates formation<br />
finishing problems. Usually the specification will require spring water to be<br />
led away by grips or drains to a pump sump which is continuously dewatered<br />
to prevent softening of the formation. If springs are encountered and have not<br />
been anticipated, or the method of dealing with them is not specified or shown<br />
on the drawings, the resident engineer should report the situation to the engineer.<br />
Special measures are often required to deal with springs to ensure safety<br />
of the structure to be built on a formation containing them.<br />
18.3 Haulage of excavated material<br />
For large open excavations, such as when road cuttings have to be made and the<br />
material tipped to form embankments, or for building an earth dam from open<br />
borrow pit areas, the motorscraper is the most economical machine for excavating,<br />
transporting and placing clays and clay-sand mixes. But the gradients<br />
traversed need to be gentle and the motorscraper cannot pick up hard bands<br />
of material or rock, unless ripping beforehand can break up the material sufficiently.<br />
If hard or rocky material has to be excavated, the face shovel loading to<br />
dump trucks has to be used, the trucks commonly having a capacity of 50–60 t,<br />
sometimes larger. However, neither scrapers nor dump trucks can traverse<br />
public roads.<br />
If the excavated material has to be routed off site via public roads to some<br />
dumping area, the excavated material has to be carted away by tipping lorries<br />
licensed for use on the public highway. Tipping lorries have a lesser capacity<br />
than dump trucks, usually in the range 10–30 t. A factor often having considerable<br />
influence when needing to transport material along public roads, is the<br />
reaction of the local road and public authorities who may object to the extra construction<br />
traffic and mud on the roads. If the local authority has also to give<br />
planning permission for dumping spoil on some given land, such permission<br />
may only be granted subject to restriction on the size of lorries used and their<br />
frequency of passage. This situation cannot be left for tenderers to find out; the<br />
employer has to obtain the necessary permissions and the contract must reproduce<br />
exactly the conditions laid down by the planning or other authority concerned<br />
and require the contractor to conform to them. If the restrictions limit the<br />
size and frequency of tipping lorries, the contractor may be forced to temporarily<br />
stockpile excavated material on site and double handle it in order to conform<br />
to his intended programme for construction and the haulage conditions laid<br />
down. This will raise his costs for excavation.<br />
Assuming there are no planning restrictions, the contractor needs to choose<br />
that combination of excavating plant and haulage vehicles which achieves the<br />
required excavation rate at lowest cost. The face shovel or backhoe output must