Page 205 - Civil Engineering Project Management, Fourth Edition

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Measurement and bills of quantities
explosives or hydraulically operated rock hammers or compressed air-operated
rock breaking equipment before being removed’. From the contractor’s point of
view this is not entirely satisfactory since it would exclude payment for rock
he can get out with a suitably powerful digger able to cope with hard bands,
albeit with difficulty and at a slow rate, involving substantial extra cost. Hence
mechanical ripping forms a third category which may warrant separate meas-
urement where hard bands of material are encountered that cannot be broken
up by scrapers or the normal bucket excavator, but do not qualify as rock.
Measurement of rock excavated for valuation is not easy; it is best done by a
member of the resident engineer’s staff and the contractor’s staff viewing the
excavation together in order to agree on the rock volume.
Working space

Contractors often claim payment for additional excavation to provide working
space, despite the fact that most contracts and methods of measurement clearly
state that only the volume vertically above the limits of foundations will be
measured for payment. Therefore if some exterior tanking or rendering to a
basement is required, it is advisable to repeat in the item for this that the con-
tractor must allow in his rates for any working space he requires.

Pipelines

Trench excavation for pipelines is covered piecemeal in Classes I, K and L of
the standard method (Class J covers provision of fittings and valves). Trench
excavation to pipe invert level is included in the supply, laying and jointing of
pipes per linear metre in Class I. Excavation below that for bedding is included
in the supply and placing of bedding material, also per linear metre, in Class L.
Extra excavation for manholes is included in the rates for manhole construc-
tion in Class K. Rock is an extra item payable per cubic metre in Class L. All
pipework excavation items include backfilling.
Excavation of joint holes is not specifically mentioned so needs to be speci-
fied as included in the rates.
If the standard method of measurement is not used, it can prove simpler to
take excavation (including backfilling) separately from pipe supply and lay-
ing. The maximum and average depth of trench, including any depth required
for bedding, is stated for any given length of pipeline and is taken for payment
per linear metre. Excavation for joint holes should be stated as not measured
but included in the rate for trench excavation. The drawings should show the
standard trench widths taken for payment, and the depth of any bedding.
Rock is paid for as an extra over per cubic metre within the payment limits, the
rate to include for overbreak and backfilling thereof. Bedding, haunching and
surrounding are measured per linear metre for supply and placing.