Traditional scheduling software for the construction industry is dominated by Primavera, Microsoft Project, Power Project and others. All of these solutions provide opportunity to develop a series of activities that are logically connected to provide a sequence of events from project start to finish. While these tools are very powerful, they are designed for the construction of buildings and other facilities (power generating stations, refineries, etc.) and are not adequate for the constructability issues and demands of building a linear project such as a pipeline, rail system or roadway. The definition of a linear project is where a series of crews move, in sequence, along a ROW (right-of-way) during construction.
March charts (also known as Time-Distance charts) have been widely used in linear projects, particularly in Europe and the U.K. This methodology is newer to the Americas, but is rapidly gaining widespread acceptance. March charts are often hand drawn, prepared in Microsoft Excel or in a drawing program such as AutoCAD. Linear planning and scheduling software that automates the development of the plan and progressing is relatively recent (last 15 years or so). Key advantages of march charts are that the schedule are connected to the geography of the ROW and any constructability issues that are important to the project.
The intent of “The concept of linear scheduling” is to provide an overview of how to interpret and use march charts with an emphasis on using some of the linear planning software tools that are currently available. A list of software is provided at the end of this appendix.
Differences between Gantt and March Charts
Gantt charts are familiar to anyone that has planned and scheduled a project. The planner creates a series of activities based on the project execution plan and then logically connects these activities (Finish-Start, Start-Start, Finish-Finish and Start-Finish). Resources can be added to each activity schedule and resource loading can be easily displayed. In order to maintain crew sequencing in a pipeline project the planner would make sure that each activity is connected to its successor by a Start-Start and a Finish-Finish relationship. A typical Gantt chart for a pipeline job is shown in Figure 1.
This Gantt charts clearly shows each activity with the start and end date of each activity. Any progress would be shown on the Gantt chart as the percent complete for each task. The problem with a traditional Gantt chart is that reporting that a bending crew is 45 % complete is quite meaningless because these traditional tools assume that progress is from start to finish and there is no connection between progress and the geography of the ROW. The ability to include crew moves, permitting delays, environmental restrictions and other construction issues is not possible.
A march chart on the other hand displays these same crews as a series of lines moving along the ROW. Each crew is logically connected to its successor with Start-Start and/or Finish-Finish relationships. Completed sections are easily identified with crew moves, crossings and environmental windows clearly visible on a march chart. Using same example, a march chart will clearly display what 45% of the ROW has been completed by the bending crew and how any moves or ROW access issues have impacted the progress.
A typical march chart (Figure 2) in its most basic form shows each crew represented by a different line type. Usually distance along the ROW is horizontal and increases from the left to the right. Time is typically represented vertically, increasing from bottom to top (although it can just as easily be shown increasing top to bottom). It should be noted that the orientation of the time and distance axes is a matter of personal preference and can easily be switched in the software.
The advantage of march charts is immediately obvious as you can easily determine the location of each crew at a particular point in time. Any issues associated with crew productivity rates are also readily apparent. For example, the red arrow in Figure 2 indicates that, based on the productivity of each crew, the lower-in crew will overtake the ditching crew between KP 25+000 and 30+000. This was not obvious in the Gantt chart view (Figure 1).
In a march chart the slope of the activity indicates the relative productivity rate for the crew. The steeper the slope, the slower the crew is moving (because more time is spent and less distance is completed). Non-work periods, such as scheduled days off or work stoppages appear as vertical segments on the crew line. A vertical line indicates that time is passing, but the crew is not moving. Figure 3 shows an example where the grade crew is moving slower (468 m/day) than the Haul and String crew (600m/day) with each crew working a 6 day 10h shift rotation. The green bars across the march chart, and the short vertical jumps in each crew, indicate the day off each week. This march chart shows that grading has to start about 18 days ahead of string in order to keep these crews from overlapping.
The productivity rates that are displayed are calculated automatically by the march chart software based on duration and length of each task.
For clarity and ease of explanation, all of the following examples in this guide will only show a few representative pipeline crews. Typically each crew is assigned to a different layer of the march chart so that the planner can display one or many crews simultaneously by activating the layers.
With a basic understanding of these march chart elements a march chart can be further enhanced to display any other critical elements of your project. These can include the ROW profile, crossings, environmental restrictions and land acquisitions. Other elements such as vegetation type, soil type and rainfall data can also be included on the march chart. The amount and type of information shown on a march chart is determined by the project team.
The ROW profile is important in developing the hydro-test plan and to determine productivity rate changes based on elevation (discussed later in the section on speed profiles). Most profile data (LIDAR or survey) is available in a spreadsheet format and can be easily imported into a profile diagram using the import function of the march chart software to generate the ROW profile as seen below in Figure 4.
Restricted ROW Access
Construction of the pipeline may be hampered by periods when certain parts of the ROW are not accessible. This would include environmental windows for wildlife and rare plants, permitting issues or ROW acquisition delays.
Restricted access periods are easily represented graphically on a march chart by rectangular shapes as shown in Figure 5. Once the impact of a restriction has been evaluated it may be necessary to modify the work plan to avoid working in the restricted area. This can be done by splitting the crews so that the work that is impacted by the restricted area will be completed at a later date once the restricted period is over. Figure 5 illustrated a move for both the grade and string crew to avoid the restricted area. In this example, both crews skip the restricted area (1 day lag to allow for move) and continue to the end of the ROW at 30+000. Once this work is finished, and the environmental restriction has expired, both crews move back to the restricted area and complete it in a reverse lay. The red dashed lines indicate the logical links between each crew segment.
Once the environmental or land restrictions have been established on your march chart the next step is to identify crossings. Crossing types can include foreign utilities, roads, rail or water and are important features to locate on your march chart. The method of crossing will be dependent on the type of crossing. Water crossings usually require an open cut (if permissible under the environmental guidelines) or will utilize a HDD (Horizontal Directional Drill). Most roads and rail crossings utilize some type of bore method while foreign utilities are exposed using a hydrovac. Each type of crossing can be color coded on the march chart for quick and easy identification.
Figure 6 (below) shows a highway (at KP 1+793) shown in grey and a blue river crossing (KP 29+690) on the march chart.
Stockpile locations and Valve Sites
Virtually any information that is important can be inserted into the march chart. The following example (Figure 7) shows the stockpile location (KP 26+102) and the supply zone for this pipe (KP 0+000 to KP 29+655). It is interesting to note that stationary items (such as mainline block valves) can also be shown on a march chart. The two valves shown in Figure 7 are represented by a series of rectangular shapes indicating different stages of installation from civil to mechanical to instrumentation and telemetry.
Risks related to weather events (precipitation amounts, temperatures) are easily evaluated by overlaying meteorological data on the march chart. In the Figure 8 the different shades of blue represent average monthly rainfall amounts. The heaviest amounts of rain occur in the lower right of the march chart (represented by a darker blue). In this example the planner has avoided working in this area during high rainfall amounts thus reducing the risk of heavy rain impacting construction.