Civil Engineering Project Management (4th Edition)

184 Civil Engineering Project Management
should then clearly state which classes of work (i.e. ‘trades’) are not measured
in accordance with the CESMM.
For matters which it is usual to let out to specialist sub-contractors, such as
terrazzo floorings, balustrading, ceramic tiling, etc., either lump sums can be
called for if the drawings and specification define everything required, or
provisional sums can be inserted.
15.7 Some problems of billing
Excavation
Apart from excavation by dredging or for ‘cuttings’; the CESMM distinguishes
only between ‘excavation for foundations’ and ‘general excavation’ (listed in
that order). However, the more logical order should be adopted of billing
general excavation to a stated level (the ‘final surface’ for that item) followed by
excavation for foundations below the ‘final surface’ for the general excavation.
This can result in items referenced ‘E400’ in accordance with CESMM, preceding
those referenced ‘E300’; but these references should not be changed.
If the general excavation has to be taken down to two different levels, that is
to a ‘stepped’ formation, then under the CESMM method it is billed as one
item to the lower of the two ‘final surface’ levels. If an attempt is made to bill
it as two excavation items ‘banded horizontally’, one below the other, sundry
complications occur which are best avoided as they can cause confusion. Nor
should it be taken as two separate items, the depth of each being measured
from ground surface, because it is not excavated in this manner when the areas
are adjacent.
Rock excavation has to be itemized separately from other materials, the volume
of rock being measured independently. Usually neither the quantity nor
the depths at which rock will be encountered will be accurately known; but the
quantity should be estimated on the basis of the geophysical data available.
The latter must be supplied to tenderers to permit them to make their own
judgement as to the depth and extent of rock likely to be encountered.
The definition of ‘rock’ presents difficulties, but it must be stated in the
preamble to the bills of quantities. Geophysical data may occasionally permit
a given ‘rock’ to be defined, but in most cases rock is probably best defined
according to the method of excavation. Unfortunately methods for removal can
vary greatly, but for specification purposes three methods can be distinguished:
• use of explosives;
• use of hydraulic hammers or compressed air-operated tools;
• use of mechanical rippers (in open excavations).
It is usual to combine the first two methods to define rock by defining them
as – ‘Rock is material requiring to be loosened or broken up in situ by use of