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Mine Project Scheduling: PERT, CPM and CCPM

In the earlier chapter we discussed the project planning issues and influencing parameters. In this chapter we will describe methods for developing and presenting project time schedules. In this chapter, we will also describe how Critical Path Method (CPM) based project cost optimization can be made. We will also discuss how the new technique, Critical Chain Project Management    (CCPM) has evolved as a new tool for project scheduling.

Projects need to be performed and delivered under certain constraints. Traditionally, these constraints have been listed as scope, time, and cost. This is also referred to as the Project Management Triangle, where each side represents a constraint. One side of the triangle cannot be changed without impacting the others. A further refinement of the constraints separates product 'quality' or 'performance' from scope, and turns quality into a fourth constraint.

The time constraint refers to the amount of time available to complete a project. The cost constraint refers to the budgeted amount available for the project. The scope constraint refers to what must be done to produce the project's end result. These three constraints are often competing constraints: increased scope typically means increased time and increased cost, a tight time constraint could mean increased costs and reduced scope, and a tight budget could mean increased time and reduced scope.

A schedule consists of a list of a project's terminal elements with intended start and finish dates.

Scheduling is an important exercise in engineering, where it can have a major impact on the productivity of a process. The purpose of scheduling is to minimize the production time and costs, by telling a production facility what to make, when, with which staff, and on which equipment. Project scheduling aims to maximize the efficiency of the operation and reduce costs.

Before a project schedule can be created, a project manager should typically have a work breakdown structure (WBS), an effort estimate for each task, and a resource list with availability for each resource. A WBS is a fundamental project management technique for defining and organizing the total scope of a project, using a hierarchical tree structure. A WBS defines a set of planned outcomes that collectively and exclusively represent 100% of the project scope. At each subsequent level, the sub nodes of a parent node collectively and exclusively represent 100% of the scope of their parent node. A well-designed WBS describes planned outcomes instead of planned actions. Outcomes are the desired ends of the project, and can be predicted accurately; actions comprise the project plan and may be difficult to predict accurately. When not available, it may be possible to create something that looks like a schedule, drawn from the work having similar history. They can be created using a consensus-driven estimation method .The reason for this is that a schedule itself is an estimate: each date in the schedule is estimated, and if those dates do not have the approval and acceptance of the people who are going to do the work, the schedule will be inaccurate.

One important principle of WBS is 100% Rule. The Practice Standard for Work Breakdown Structures (Second Edition), published by the Project Management Institute (Project Management Institute ,2006) defines the 100% Rule as follows:

The 100% Rule...states that the WBS includes 100% of the work defined by the project scope and captures ALL deliverables – internal, external, and interim – in terms of the work to be completed, including project management. The 100% rule is one of the most important principles guiding the development, decomposition and evaluation of the WBS. The rule applies at all levels within the hierarchy: the sum of the work at the “child” level must equal 100% of the work represented by the “parent” and the WBS should not include any work that falls outside the actual scope of the project, that is, it cannot include more than 100% of the work… It is important to remember that the 100% rule also applies to the activity level. The work represented by the activities in each work package must add up to 100% of the work necessary to complete the work package. (p. 8)

If a planner attempts to capture any action-oriented details in the WBS, he/she will likely include either too many actions or too few actions. Too many actions will exceed 100%. of the node ( parent) scope and too few will fall short of 100% of the node's scope. The best way to adhere to the 100% Rule is to define WBS elements in terms of outcomes or results. This also ensures that the WBS is not overly prescriptive of methods, allowing for greater ingenuity and creative thinking on the part of the project participants. The project planning starts with scheduling. There are few important scheduling formats.

Overview of Scheduling Formats

There are three methods for displaying time schedules: bar charts, milestones, and network diagrams. Bar charts portray the time schedule of activities or tasks, and milestone charts portrays the schedule of selected key events: Network diagrams portray activities, events, or both and explicitly depict their interdependency with predecessors and successors. Time-scaled tasks with explicit task interdependency linkage schedule (linked Gantt charts) portray both interdependency and the time sequence. The best choice for one may depend on what kind of complexities one is facing in a specific situation.