The Critical Path Method (CPM) - Construction Project Scheduling and Control - page 48

2. Location/floor/segment : Activities occurring in different locations must be
separated.
3. Size/duration : For large activities or those with large quantity, it is better to
divide the activities into smaller portions. For example, excavation activities
can bes divided into smaller activities by grid or depth. For linear excavation,
this can be divided by stations or 100-foot segments. This helps in measuring
the work's progress during execution. As mentioned earlier, this can be a
contractual requirement.
4. Timing/chronology : Sometimes a portion of the work may be delayed purposely
by the contractor. For example, a portion of the slab on grade (SOG) for a
building may be delayed until the end of the project because the area is being
used as storage. Such a portion must be considered as an activity by itself.
5. Responsibility/trade : Schedulers must break down portions of work that are
done by different parties (e.g., subcontractors, crews). In case of a schedule
variance, it is important to indicate who is responsible for the variance.
6. Phase : This can be a division made by the designer based on certain criteria,
such as timing, location, or other aspects.
7. Contractual restrictions : In many contracts, especially government contracts,
there is an upper limit to the duration of an activity, which, in turn, limits the
size of that activity. Such a limit usually ranges from 14 to 30 days.
8. Level of confidence in the duration : The scheduler should use the “divide and
rule” principle: whenever the scheduler's confidence in the duration of a cer-
tain activity is not high enough, the activity must be broken down into smaller
activities so that the confidence level increases.
Tip Box 4.1
Never combine two activities if they are measured differently, performed at different
locations, performed during different time periods, or performed by different crews.
The preceding eight factors underscore the difference between the cost estima-
tor's and the scheduler's mentality in breaking down the project into activities. For
example, to the estimator a slab on grade in the project is a slab on grade, no matter
where or at what time it was placed. To the scheduler, it does matter.
The level of the details in breaking down the project into activities depends also
on whether the schedule is a preliminary or a final, detailed schedule. In a typical
preliminary schedule, it is normal to see a small number of major activities; each one
represents a work package, assembly, or some activities that are grouped based on a
particular criterion. Later on, when the design is completed, these major activities are
broken down into minor activities, so a schedule with 50-70 activities can explode
into one with 800-1,500 activities.