Page 206 - Civil Engineering Project Management, Fourth Edition

Civil Engineering Project Management
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Thrust blocks for pipelines have to be constructed against vertically cut
undisturbed ground. It avoids argument if items for thrust blocks to dimen-
sions shown on the drawings are followed by an extra-over item for trimming
sides of excavation adjacent to thrust blocks to the vertical, including any back-
filling between a thrust block and the vertical excavated face with concrete.
Under the CESMM thrust blocks are measured per cubic metre inclusive of
concrete, formwork, reinforcement, etc. For large pipes requiring major blocks
it may be better to deviate from the standard method by treating these blocks
as structures in their own right.
Earthwork construction

Earthwork construction is measured as the net volume as placed. The source
of the filling should be stated. All information available about the nature of
the proposed fill material should be supplied to tenderers so they can make
their own estimate of the bulking factor of loose filling, its weight per unit
volume loose and when compacted, etc. When the filling is to be obtained
from a borrow pit, information concerning the extent and characteristics of
the borrow pit material and its location should be provided in the tender
documents.
If specified material for filling is to be obtained from selected material from a
borrow pit, the removal or set aside of unsuitable material from the borrow pit
has to be included in the rate for filling. It may also be necessary to include
re-handling of the unsuitable material in order to put it back into the borrow pit.
It is impracticable to measure the unsuitable material because some may be
worked around and left in situ. Hence it is important to define what the rates for
placing filling obtained from a borrow pit are to cover. Failure to include any
necessary double-handling of unsuitable material can result in a large claim for
extra payment from the contractor. It is advisable to give separate items for
stripping overburden from the borrow pit, and an item for reinstatement of
the borrow pit. The specification should set out all the requirements needed
for reinstatement which it should then be possible to bill as a lump sum item for
pricing. One point to note is that when ‘suitable material’ has to be taken from
a borrow pit, it may be helpful to specify instances of ‘unsuitable material’ also.

Concrete

Concrete in situ is measured in the CESMM as two operations: (i) supply
according to various quality grades; and (ii) the placing of concrete according
to its location in beams, columns, slabs, etc. This suits the modern practice
in the UK and similar developed countries where widespread use is made
of ready-mix concrete delivered to site. The totals of concrete in the various
grades must therefore sum the same as the relevant placing items per grade.