Page 190 - Civil Engineering Project Management, Fourth Edition

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Programme and progress charts
does not give a false impression of progress the following adjustments are
advisable:
• The ‘target’ cost should include the contingency money provided. A lower
line at the base of the graph can show this contingency money and the
expenditure against it, thus revealing where any exceedance of the target
is due to excess contingency money spent.
• If there is a major item of expenditure incurred late in the contract (such as for
supply and installation of plant), the value of this should also be excluded,
or be plotted separately as an additional line.
• The cumulative valuations plotted monthly should not include retention
money deducted, nor payment on account for materials on site, nor reim-
bursement of increased costs of wages and prices.
Although such a progress chart is not exact, it is a good indicator of progress.
Usually the plot of valuations forms an S-curve, having its steepest inclination
during the central part of the contract period when productivity should be
at its greatest. As a consequence, if the plotted line of valuations does not rise
above the straight line sometime during the middle period of the contract, then
almost certainly the contract will finish late.
One advantage of a progress chart of this kind is that, when an employer
needs an estimate of future rates of expenditure, this can be estimated by
sketching in an S-curve of the type shown and reading off the monthly rates
of expenditure it implies, less any retention money held back.
Some standard conditions of contract, such as those of FIDIC (see Section 4.3)
require the contractor to produce a cash-flow forecast along with his programme
for construction. It must be remembered, however, that a cash-flow from interim
payments does not necessarily represent construction progress, because deduc-
tions are made for retention and additions may be made for advance payments
(if any), and materials delivered to site.
Similar types of cumulative output chart can be applied to specific types of
work. One for concrete work to different structures is shown in Fig. 14.4. The
horizontal bands show to scale the amount of concrete to be placed in each
structure. The cumulative amount of concrete placed month by month can be
plotted for each structure, and their total shown separately. Such a chart is
useful for indicating where slow progress is occurring.
For a mainlaying contract the type of progress chart shown in Fig. 14.5 can
be used. It is self-explanatory. The profile of the main may have to be shown
in a condensed form; it also shows where specials are required.

14.5 Network diagrams and critical path planning

A network ‘diagram’ has been referred to in the preceding section. It lists each
activity required to complete a project giving each a reference and estimated
duration – usually in weeks. An assumption is made concerning the order in