This article explores the critical path method (CPM) as a cornerstone of effective project scheduling, control, and delay management. Referring to AACE International Recommended Practices, PMI-SP standards, and global protocols, it emphasizes accurate logic, appropriate level of detail, and practical execution plan with resource allocation alignment. It also covers root cause analysis, critical delay quantification, and strategies for identifying and mitigating project delays. Key focus areas include out-of-sequence work, float path analysis, and delay reasons identification for proposing successful mitigation measures. This framework can enable proactive planning, improve schedule integrity, and support defensible claims empowering project professionals to maintain control over complex, time-sensitive project environments.
Key Points:
• Critical Path Method
• Update and Changes
• Float Paths Analysis
• Delay Root Causes
• Mitigation Actions
1- WHAT IS CPM?
CPM (Critical path method): is sequencing of scheduled activities to determine the minimum duration of a project. It uses forward and backward calculations.
Critical path is the longest sequence of tasks in a project plan that must be completed on time (with no margin/ float) in order to meet the project deadline. If there is a delay in any task on the critical path, then your whole project will be delayed.
Although some projects have only one critical path, other projects may have multiple critical paths.
Critical path and sub-paths
Prior planning, the execution plan, and other drivers should be checked:
Strategy & Methodology: Execution Plan/Formal Written Program. The execution plan should be a dynamic document, which is revised and updated as conditions/scope change.
Typical major categories of a good execution plan include:
· What is the scope of work? How is the work to be executed?
· What is the expected quality of the project?
· Contract strategy and requirements · Permitting and licensing
· Detailed Engineering · Procurement program
· Resource analysis (crews, productivity … etc.) · Cash flow limitations
Pre-planning Drivers
Constructability and construction pre-planning are often used interchangeably.
-Constructability is largely concerned with the technology and methods of installation (Constructability assessments should occur periodically).
-Pre-planning deals with the scheduling of resources, organization, site access, and infrastructure.
-Both are intended to reduce time and costs by considering alternative design and/or installation methods.
Many factors are involved, such as:
· Physical site conditions/ logistics/ weather.
· Restraints of procurement/ material delivery.
· Economics of crew sizes and supporting resources.
· Existing or temporary plant operations, regulatory requirements, etc.
Construction Driven Scheduling as Key to CPM Program assuming that it has been developed on a best economic basis in engineering and material deliveries.
Level of Detail Required for CP
This depends on project size and level of control required (ref: AACEI 37R-06):
Level 0: This is the total project as a single bar spanning from project start to finish.
Level 1: This represents the schedule for the project by its major components. A combination of Level 0 schedules for each component project.
Level 2: Each schedule component is further subdivided for Level 2. For example, utility systems are further subdivided into water, electrical, gas, storm drainage and sanitary systems, etc. Milestones are normally included (Scope priorities).
Level 3: The first level that a meaningful critical path network can be displayed and the CPM schedule can be used to monitor and manage (control) the overall project work.
Levels 4-X: The level of schedule subdivision continues to whatever is appropriate detail for the user. When operating at more detailed levels, the planners generally work with segments of the total schedule.
Often the project "rolling schedule" includes a "look-ahead" period of time (30–180 days) and a "look-back" at recent completed work periods.
Types of Relationships
The schedule contains preferential logic (i.e., sequencing which is not based on physical or safety considerations) and resource assumptions.
Three types:
1- Soft logic: discretionary
2- Hard logic: mandatory
3- Resource dependency
Productivity and Duration Calculation
The activities durations are calculated due to the quantity of work, estimated productivity of the driving resource, and resources assigned:
Activity duration = quantity / (productivity of crew * no of crews)
Location affects the Productivity
A major point to be made and emphasized is that productivity on the same type of work varies significantly from location to location within a country and from country to country. That variation is caused by many factors, which may be grouped as follows:
- Variability-Sociological (Area) Factors. Some variation can be attributed to differences: local work ethic, level of mechanization, the education and training levels of workers, the climate, the organized labor situation, and urban vs. rural factors.
- Variability-Location Factors. As location varies, so do these factors: · Weather patterns, · Access, · Availability of skills, · Availability of logistical support, · Trafficability of site, · Attitude of nearby communities, · Transportation network & · Local economy
- Impact of Disturbance on Performance. Finally, these factors are most completely in the hands of management to control: · Site layout for construction, · Support equipment availability, · Technology/methodology used, · Crew balance, Materials availability and quality, · Tool availability and quality, · Safety program, · Degree of planning, · Vendor performance & · Control of interruptions
Activities durations should be continuous, not interrupted by other activities
NON-SCHEDULE PLANNING ITEMS
Typically, these methodologies are not specially itemized in the schedule, but are critical functions of the project that need to be planned out for project success.
These methodologies include, but are not limited to:
· Design interface & execution plans · Site access plan
· Temporary facilities plan · Crane and heavy lift plans
· Placement of cranes · Engineered and long lead material plans
· Owner provided material planning · Packaging, handling, storage, and logistics plans
· Emergency reaction plans · Other such specific purpose plans
It is important for planning of these logistic methodologies to ensure smooth construction operations.
The result of this logistics planning will be efficient and productive construction operations to support the overall project schedule and potentially reduce cost.
2- Critical Path Calculation
Scheduling is the process that converts the project's work execution plan into a detailed road map, which if followed and adjusted to account for change and/or delay as it may occur, will assure timely project completion.
Forward and Backward Pass. The forward pass through the network determines each activity's ES and EF and the project's duration or the earliest date a project can finish. The backward pass through the network determines each activity's LS and LF as well as providing a basis for calculating Float values for each activity.
Factors Affect the Calculation
The critical path and float values of uncompleted work activities in CPM schedules change over time affected by Calendars, Constraints, Lags & Leads, Open end & Dangling Activities, Resource Limits, Retaining Logic of remaining durations, Out-of-sequence Activities, Variance in productivity, and Change of scope of work.
Workdays and Calendar Days
Work-Days and Calendar Days. The calculated dates are shown in consecutive calendar days. This calculation is used for all examples. However, it must be understood that many projects are worked on a five-day work week with weekends and certain recognized holidays not normally planned as working days. These nonworking days must be accounted for in the total project duration.
Most contracts that stipulate contract time, do so in total calendar days, including weekend and holidays; regardless of the workday calendar used in the CPM schedule model.
Computerized scheduling applications allow for setting calendars and automatically accounting for weekends and holidays. Also, multiple calendars may be necessary to model the work schedules of the engineering staff (working a five day work week); whereas procurement may be modeled on a seven day work schedule (calendar basis) and work at the site is on a two week fortnight basis (a rotation of ten work days followed by four non-work days).
AACE RP 29R-03 of delay analysis: The only way to avoid gaps, discontinuities, and work-day conversions is to use only one calendar consisting of a seven-day week.
Lags between Activities
• Some relationships need waiting (lag) or overlapping (lead) period.
• The duration which should be embedded in the relationship should be defined based on the logic.
• The use of such dependency should be limited and used only when needed like the curing duration or similar cases.
Long lags can be avoided by Replacing Lag by an Activity.
Milestones & Constraints
The start and finish of certain activities, at times, must be constrained in order to represent what will actually occur. For example, based on network logic, the installation of a pump is scheduled to begin on September 17, but the actual pump delivery from the vendor is not scheduled until October 23.
There are seven major types of constraints:
· Start-on · Start-no-earlier than · Start-no-later than · Finish-on · Finish-no-earlier-than · Finish-no-later-than · As late as possible
Each of the above constraints affects the schedule differently depending on network logic.
Total Float Indicator:
- Positive Float: Project/Activity in good situation
- Zero Float: Project/ Activity is critical
- Negative Float: Project/ Activity is delayed
Negative float is a situation that occurs when performing an activity even on its early dates, fails to meet the project's imposed finish date or other constraints.
Out of Sequence Approaches
•The scheduling options are whether retained logic (preferred for hard logic domination) or progress override (preferred for soft logic domination)
•The retained logic method is conservative. It keeps the predecessors' links applicable for the remaining of any started activity which means activities can be Interruptible
•One the other hand, the progress override method breaks the predecessors for any started activity and keep them proceed continuously until finish
•The update methodology can be submitted to be consented initially or later on including duration type, percentage type, scheduling approach, logic change justification and so on
Open End Checks
•All activities should be linked from start and from finish as well
•The sequence can go by linking successors for all activities then review any missing logical link
•The open end or dangling activities should be revisited to link with the most appropriate relationship
Resource Limits
The resource leveling process helps to manage resource constraints by optimizing the use of resources in a project. It involves adjustments to activities' start and end dates which can affect the critical path.
Neutralization & Simplification
The policy of the AACE RP is to be 'software neutral'. This means that procedures and recommendations are made without regard to the brand or version of software used for analysis.
Case Study – Housing Complex
(5 buildings, 3 substations and external works)
In terms of CPM calculations, there are multiple paths in the program as follows:
- Longest Path: At least one continuous critical path from start to finish
- Critical Path: Total float is equal or less than zero
- Float Path: The linked activities with no free float in between
The above is the longest and critical path of the baseline going from the substructure of certain buildings to the superstructure, finishing and closing. This can be sorted by float paths in the following step:
The same longest path is fount that it includes two float paths as follows:
Still, there are Sub-Paths and Near Critical Paths to be checked as follows:
Critical Paths Checks
-Contractual dates and milestones
-Logical sequence of work, types of relationships, and durations of the activities to be aligned with the required/available resources
-Common Sense and Expert Judgment / Actual Observance and forecasting in case of updates
3- Changes and Progress Update
Reasons for Updating. Four major reasons a schedule should be updated regularly are to:
· Reflect current project status
· Keep the schedule as an effective management tool
· Document performance
· Provide documentation to plan for changes and support delay analysis.
The following steps are generally performed during the update process:
· Gather all current information with routine priorities.
· Identify and plan for any changes to the work which affect activity duration, logic, work scope, and others.
· Input these changes into the project schedule (any additional work or delay should be coded appropriately to reflect "unforeseen" or "delay" work activity).
· Recalculate the project schedule.
· Issue updated schedule to all interested parties.
Update Longest Path (TF -86)
At the same time, the update has many other critical paths apart from the longest path (not like the baseline). These critical paths need to be checked.
Update Critical Paths (-ve TF)
4- Float paths analysis
General Principles - 29R-03
The critical path and float values of uncompleted work activities in CPM schedules change over time.
Source Validation Protocols (Baseline, As-built & Update)
Forensic Schedule Analysis – Recommended Practice 29R-03
1- Baseline
A. Cons: Compliance with the contract - Assumed level 3 schedule.
B. Investig.: Correct data date "NTP" with no progress - At least one continuous critical path from start to finish - Relationships - Full scope - Basis of all milestones - Any contract violation - Calendar working days - Software used.
C. Enhanc.: Each activity to be 0.5% to 5% of contract value - Separate as per responsible party - Add activities to enhance the level of detail - Divide act.s based on progress records.
D. Special: Summarization - De-statusing update - Software ver.
2. As-built
A. Cons: Accuracy & reliability are never perfect, so the data to be agreed between parties - The driving activities are called controlling not critical and to be checked from CPM logic and subjective opinion of percipient witnesses.
B. Investig.: Actual dates vs data date - Using the most reliable source/ interviews if possible - Changes in IDs & scope - Check critical and near critical act.s (10% sampling) - Accuracy of dates of significant activities to be 1 working day, and other activities to be 5 days.
3. Updates
B. Investig.: Consistency of dates along the updates - Change in longest path/ controlling activities.
Update Permissible Changes
The progress and actual dates to be reflected with adjustments of minor re-sequencing and remaining durations with respect to the original estimates, without changingthe scope of work or contractual constraints. Anyway, such changes should be recorded and attached in a change log.
Remaining Work Sequence
- The schedule update should reasonably reflect the work plan in effect and the actual conditions at the time of the update.
- The contractor may elect to revise the remaining duration status of every activity in
the schedule to the remaining duration status evidenced at the time of the forecasted end of the delay.
- Activities partially performed out-of-sequence will still exist as successors to the impacted activity, but their remaining durations will be reduced to reflect the work performed during the event period. It may be necessary to modify relationships in consideration of retained logic.
Float Paths Analysis
- Identify the most delayed activities at every measuring point.
- Review the planned logic and evaluate any likely changes based on contemporaneous evidence.
- Be focused on the critical path and sub-critical paths or on key events and activities only, to reduce both the cost and the complexity of the analysis.
- Work plans involving physical process steps dependent upon earlier work being completed (serial in nature) will likely be harder to mitigate.
5- Forecasting & Delay Root Cause Analysis
Periodic Forecasts and Planning. A forecast is a prediction, or an estimate, of future conditions and events based on factual information and observable trends, professional judgment, and documented assumptions available at the time of the evaluation.
Why Plans Fail?
Because of various factors and circumstances, projects may not succeed. Some of the oversights which might lead to failure include:
· Failure of the project team to understand and fully comprehend the scope of the project and/or the attendant risks.
· Failure or poor execution by the project team in developing and implementing a comprehensive plan.
· Failure by the project team to revise the plan when major changes have been identified and incorporated into the scope of work.
· Failure of the major stakeholders (owner, underwriter, and bonding company) to financially support the project as programmed, thus, delaying or stopping the work. And,
· Failure of the project team to develop essential non-planning methodologies during project development and execution.
Root Cause Analysis
When delays occur, identifying why they happened is critical.
🔧 RCA Techniques:
• 5 Whys: Simple questioning technique
• Ishikawa/Fishbone Diagram: Visual cause mapping
• Pareto Analysis: Focus on high-impact causes
• Timeline/Change Log Reviews: Reconstruct events
6- Mitigation Strategies
1- Resources Issues
-Shortage in Manpower: Extra crews and labors
-Overtime (temp) or double shifts
-Idle Equipment: Ensure maintenance and sufficient operators
-Nonproductive Resources: Supervision and training
-Lumpsum work with incentives program
-Delay in engineering works: Technical team increase/support
-Material takes long for installation: Check alternatives
2- Cash-flow Issues
-Cash flow enhancement by expediting payment process
-Improve the review/payment time of IPCs
-Advanced payment increase
-Pay material on site
-Payment to subcontractors and suppliers directly
3- Management Issues
-Methodology of application
-Training and adding more skilled labors
-Enhance Supervision workforce or skills
-Get the site ready early to decrease time losses
-Sequence and logistics solutions
-Management Rearrangement
-Site layout and choosing weather suitable working hours
Technical Schedule Compression
In case of exceeding the contractual finish date, the planning team applies the compression techniques:
1- The activities duration can be decreased by increasing the resources as practicable according to law of diminishing returns. This is called crashing/ crunching
2- The second technique is called fast tracking by overlapping the activities which cause a risk of potential rework
The delay mitigation is a duty of the contractor but without extra cost. If the employer requested acceleration with extra cost. The cost should be agreed or as the case may be
7- Mitigation Actions Effectiveness and deciding forward
Reporting of Performance
The scenarios can be one of the following:
• Performance is improving and recovering delays
• Improvement is not sufficient, and more actions are required
• Plan B/C/D – Apply the effective solution
• Recovery is not enough: Acceleration is required
Further Actions (Potential Decisions):
-Micromanagement of contractor resources
-Direct payment/management of subcontractors
-Descope based on the capacity of the contractor or type of work
-Termination after grace periods and re-award to another contractor
Recommendations
- Plan with consideration of the completion/close out activities and the risk mitigation plans to be prepared
- Check the root causes of delays or poor performance to effectively recover/mitigate them
- Focus on the project success with win-win situation to work in a collaboration with all parties
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Mohamed Hegazy
Project Control Manager
Yanbu
magedkom@yahoo.com------------------------------