Precedence Networks - Construction Project Scheduling and Control - page 93

in one of two common ways. A third method, using the Linear Scheduling Method,
will be discussed in Chapter 11.

1. The stair-type relationship : In this method, each activity is divided into two or
more parts (Figure 5.3): After Excavation I is complete, both Excavation II
and Subbase I can start. Once Subbase I is finished, Subbase II and Pipe I can
start (probably Excavation III as well), and so on. This method is well known
and widely acceptable. It is popular for projects such as heavy construction
(highway, utilities, etc.) in which activities are few but large and have long
durations. It is customary to divide the activities of these projects into phases,
steps, or “subactivities.” The main drawbacks of this method are the increase in
the number of activities and the confusing similarity of their titles. For instance,
in the example shown in Figure 5.3, a 5-activity project became a 15-activity
project.
2. The precedence diagramming method : The project can alternatively be repre-
sented as shown in Figure 5.4. The activities in this network have SS relation-
ships. This means Subbase cannot begin till Excavate has started, Lay Pipe

Figure 5.3 Stair-type schedule for utility pipe installation project

0, 6 0, 7 0, 4 0, 3 0, 2

Compact
2

Excavate
6

Subbase
7

Lay Pipe
4

Backfill
3

Figure 5.4 Precedence diagram, for utility pipe installation project, using start-to-start
relationships with no lags