Time

4.3.1. Baseline schedule

Time management for projects revolves around the project schedule. Activities identified at the lowest level of the WBS are loaded into scheduling software and sequenced in their logical order. Constraints or dependencies related to each activity (if necessary) are identified, the resources necessary to complete them (personnel, material, consumables, equipment or contracts) are assigned (using the project’s cost breakdown structure, see Section 4.4.1), a work schedule (e.g. hours or days per week) is set up for each resource, and a resultant schedule produced.

Key milestones that identify the start or end of specific activities are identified. The project schedule needs to reflect all of the work associated with delivering the project on time, including elements not being funded directly by the project.

Schedules are typically represented via Gantt or Programme Evaluation and Review Technique charts, which are graphic representations of the project’s activities, the time it takes to complete them and the sequence in which they should be done. Project management software is typically used to create these analyses. A sample Gantt chart is provided in Fig. 15.

Summary schedules showing lower levels of detail can be derived from the integrated project schedule (the most detailed level of the schedule). Figure 16 illustrates the concept. Any vendors and contractors working on the project may have their own particular schedules; however, these need to be strongly linked to the project’s master schedule. Ideally all work groups would work off the same schedule and use the same software tools.

Scheduling and scheduling levels for NPP projects are further discussed in section 3.5 of IAEA Nuclear Energy Series No. NP‑T‑2.7 [2] and the PMI has issued a schedule practice standard [106]. The National Aeronautics and Space Administration (NASA) has produced a detailed schedule management handbook [107] that contains numerous examples and lessons learned.

Once the initial schedule has been prepared, it needs careful analysis to ensure that it is realistic and optimized.

Some typical activities in this area include reviewing the project’s critical path, resource levelling and running

‘what if?’ scenarios.

Critical path method (CPM) analysis is the process of looking at all of the activities that are to be completed, and calculating the ‘best line’ — or critical path — to take so that the project is completed in the minimum amount of time. This path would have no intrinsic ‘float’ (i.e. time that any task in a path could be delayed without causing a delay in the overall project). The method calculates the earliest and latest possible start and finish times for project activities and estimates the dependencies among them to create a schedule of critical activities and dates.

Analysis of the schedule and resequencing of some activities can often reduce critical path dependencies. Higher risk activities can often be moved earlier in a schedule to allow greater time for mitigation without impacting on the critical path.

FIG. 15. Simple example Gantt chart for the design phase of a project.

FIG. 16. Scheduling levels (reproduced from Ref. [2]).

Any resource has capacity limits; that is, a project cannot apply an infinite number of personnel or other resources to complete a task in zero time. Resource levelling is the process of reviewing the sequence of activities to ensure that excessive demand is not put on resources at any point in time. If resources are available only in limited quantities, then the timing of activities can be changed so that the most critical activities have the first priority for the resources.

A process known as the critical chain method also addresses resource availability. Activities are planned to use their latest possible start and finish dates. This adds extra time between activities, which can be used to help manage work disruptions. Critical resources need not be just personnel; key construction equipment such as heavy transport and lift equipment can also be critical and require careful scheduling and planning.

‘What if’ scenario analysis examines the effects of different scenarios on a project. Simulations are run, often using Monte Carlo methods, to determine the effects of various adverse, or harmful, assumptions on the project.

Projects can then measure and plan for the risks posed in these scenarios.

4.3.2. Project milestone and schedule management

Project milestones as derived from a project schedule are a typical project communication and control tool.

Project managers often publish lists of key milestones and use metrics such as percentage of milestones completed on time as a project performance indicator. Such milestone completion rates are often regularly reviewed by senior management and may even be tied to bonus schemes for project team members.

Once the initial project schedule has been prepared and finalized it becomes the baseline schedule for the project. Project progress (e.g. activity completion, project costs) is then measured against this baseline. The baseline is not updated unless a specific change to it is approved, often in the context of a new project phase or superseding release of funds.

Project progress requires regular (often daily or twice daily during construction and commissioning) updating to ensure that the status of the work is known, resources utilized are recorded, future resource needs are reforecast if needed, and work groups understand and can plan for upcoming activities. Data for these updates can come from formal and informal sources. These can include work groups inputting progress directly into computer systems, cost and schedule analysts inputting data received during team meetings or direct contact with work group representatives. Figure 13 of IAEA Nuclear Energy Series No. NP‑T‑2.7 [2] illustrates a typical flow of information in gathering data for schedule updating.

Once updated, schedules need analysis to identify potential issues. These can include missed or delayed activities or deliverables, over or under allocation of resources, or the potential for missing future milestones or cost increases. The reasons for any of these occurrences need to be investigated and schedule adjustments made as required. These can include adjustments to assessed resources, changing duration estimates, tasks and dependencies or updating workforce development plans. Any new risks should be identified via project risk management processes (see Section 4.9).

4.3.3. Impact of late deliverables

Late deliverables can have a negative impact on a project that goes well beyond their simple effect on schedule and cost. Secondary effects such as errors, rework, activity resequencing, overtime, delay time, expediting or design changes caused by one or more late deliverables can exacerbate their initial effects and lead to further schedule delays. Such changes can place undue pressure on the project safety, quality, cost and schedule. Furthermore, with the additional strain placed on meeting these goals, extra pressure is also placed on the individuals, teams and organizations involved in a project [108].

Late deliverables can include such items as:

● Engineering documents, approvals or responses to requests for information;

● Engineered equipment;

● Bulk materials;

● Fabricated materials;

● Prefabricated assemblies;

● Permits (including regulatory authorizations or licences);

● Project plans;

● Human resources;

● Utilities and infrastructure (e.g. roads, utility tie‑ins);

● Construction equipment.

Some of the above can be due to or produced by other separately managed projects.

The CII has produced a number of publications related to the impact of late deliverables on construction projects, including a guide that can help to identify and weight potential risks associated with late deliverables [108]

and a number of case studies [109]. Identified risks can be incorporated into a project’s risk register.

Of the ten late deliverable categories studied by the CII, the following were found to be the most prevalent groupings, in terms of both severity and commonality [108]:

● Engineering documents, reviews and approvals;

● Speciality equipment and materials (i.e. engineered equipment, prefabricated materials and fabricated assemblies).

This would indicate that special attention to the impacts of engineered and speciality items on projects is of particular importance. Of particular note is the need to not overestimate the level of experience and capacity of a typical engineering organization to meet an aggressive project schedule, and the need to only use cost and schedule predictions for speciality items that have been confirmed by individuals in the supply chain who have consulted with suppliers and contractors.

4.3.4. Schedule metrics and schedule risk analysis (SRA)

A common metric to monitor schedules is the schedule performance index (SPI). SPI is a ratio of the earned value of a project to its planned value (PV). If the SPI is less than one, it indicates that the project is potentially behind schedule to date, whereas an SPI greater than one indicates that the project is running ahead of schedule.

Refer to Section 4.1.4.2 for more details on EVM.

Schedule risk analysis (SRA) is similar to a traditional CPM analysis (see Section 4.3.1) except that rather than each activity having a single duration value, it has a range of durations that including a minimum duration, maximum duration and most likely duration. Monte Carlo risk analysis is then done on the schedule by running it thousands of times, sampling values from the defined ranges of each activity with each run.

These results from such analysis will provide confidence ranges for the end date of the project. These can offer dates ranging from 0% confidence (P0) to 100% confidence (P100). In many projects P75 or P80 dates are regarded as acceptable forecasts with any residual risks identified. A useful output from such an exercise is the quantitative identification of the riskiest areas of a project’s schedule, allowing for the possibility of risk mitigation.

Additionally, the risk analysis tool can often be linked to a project’s cost model so that the impact of any schedule delays can be reflected on a project’s cost estimate.