Design-Build Project Schedule Development and Management - Design-Build for Water and Wastewater Projects - page 242

resource-loading the schedules and performing resource-constrained scheduling, by the
utilization of multiple calendars and by the use of start/finish external constraints. These
more dynamic schedules add a great amount of complexity to the CPM computations. For
example, tasks are no longer just critical or noncritical; tasks can now be start critical with
finish noncritical, start noncritical with finish critical, reverse critical, and noncontinuous.
Furthermore, the critical path is no longer likely to be continuous from NTP to substan-
tial completion (de la Garza and Kim 2009; Kim and de la Garza 2003, 2005).
In a discontinuous critical path, there are tasks that are reported as noncritical, hence
with positive TF, but in actuality such TF is a miscalculation due to discontinuities in the
critical path and hence overstated. The difference between the theoretical but overstated
TF and the real TF is known as phantom float . Schedulers and consumers of scheduling
information must be aware of these idiosyncrasies while interpreting project information
so as to avoid making decisions and reaching conclusions with flawed information, even
if this information is produced by commercial software.
A viable as-planned schedule should be the result of an iterative scheduling process.
To be valid and useful, the as-planned schedule (i.e., the baseline schedule) for a DB water
or wastewater project should
• Reflect the intended sequence of work
• Reflect job-specific constraints
• Include design development and regulatory approval (permitting)
• Include owner-furnished items
• Include adequate review times for submittals
• Include interim milestones
• Follow prescribed sequence of construction
• Have the right level of detail
• Include procurement activities and specifically consider long-lead equipment and
materials
• Include the work of subcontractors and/or multiple prime contractors
• Have adequate task durations
• Have means and methods (i.E., Logic relationships) that are consistent with best
practices
• Include facility startup and commissioning activities
• Account for weather and other calendar-driven constraints
• Not sequester float
The as-planned schedule must reflect the design-builder's true intentions for per-
forming the work.
The Project Control Process
Maclean (1993) summarized the main objectives of project controls as follows: “If you
can't measure it, you can't improve upon it. If you don't measure it, you won't even try to
improve it.” The overall function of the project control process is to monitor the actual
execution of the project to predict the impact of deviations from the baseline schedule.