IntroductionIn my last July 2021 article, I provided a summary of the common delay analysis methods in the industry and in my August 2021 article, I explained the factors to consider when selecting and implementing the delay analysis methods. In my October 2021 article, I started sharing my experience on the common delay analysis methods in the industry, taking guidance from AACE International (AACE International) Recommended Practice No. 29R-03 (“AACE RP29R-03”), AACE International Recommended Practice No. 52R-06 (“AACE RP52R-06”) and the Society of Construction Law (SCL) Delay and Disruption Protocol (SCL 2nd Protocol). I covered the following the following methods:
- The Impacted As Planned Method,
- The Time Impact Analysis Method, and
- The Time Slice Window Analysis.
- The As Planned versus As Built Windows Analysis,
- The Retrospective Longest Path Analysis, and
- The Collapsed As Built Analysis.
As-Planned versus As-Built Windows Analysis (ASAB-WA)Brief Description This method is considered to be an “Effect & Cause” analysis in that it does not simulate the impact of the delay event(s) (i.e. it is an observational method). The method starts by determining the as built critical path “contemporaneously” in windows and then identifying the delay periods at that point in time (the “Effect”). The analysis then attempts to link the delay to the claimed event(s) (the “Cause”). It is important to note that this method differs from the As Planned versus As Built method, in that it is performed in windows and determines the contemporaneous critical path, while the As Planned versus As Built analysis is performed statically and grossly (i.e. one window) and determines the retrospective as built critical path. There are other terms which refer to the same basic method, including:
- Windows Analysis
- Contemporaneous analysis method
- Contemporaneous period analysis
- Snapshot analysis
- 3.2 Periodic (Fixed Periods)
- 3.2 Periodic (Variable Windows)
- A baseline program. This program does not have to be logic linked or produced using a software tool.
- As built data – doesn’t necessarily have to be in a program format. There is no requirement to have any contemporaneous program.
- Identify the contemporaneous as built critical path in windows.
- Compare the as built critical path to the baseline and determine the actual critical delay periods.
- Delay Event 1 (DE1): Lack of access to activity A, 3 days (days 1 to 3 inclusive), and
- Delay Event 2 (DE2): Lack of client supplied material 2 days (days 6 and 7).
ASAB-WA-Window 1In the second window, the analyst would determine that the critical path moved to Activity D and that the commencement of the activity was delayed by 4 days. However, 3 days out of these 4 days were identified in the previous window (2 days of critical delay and 1 day of float). Therefore, there is only 1 day of critical delay in this window. After investigation, the analyst would link this delay to Delay Event DE2.
ASAB-WA-Window 2In the third window, the analyst would determine that the critical path remains in Activity D and observes that there is 1 day of further delay to the commencement of Activity D (because of Delay Event DE2). However, the analyst would also observe that Activity G is now on another critical path in this window, with 4 days of delay to the completion of the activity. However, 1 of these days occurred in the first window without causing critical delay and only 1 day out of the remaining three days would cause critical delay when compared to the delays of the previous window. This 1 day delay is not linked to any of the delay events and may be concurrent with delay event DE2.
ASAB-WA-Window 3In the fourth and final window, the analyst would observe that there are three critical paths driven by Activity C, D and G. The forecast of activities D and G remained as per the previous window and therefore there is no more critical delay observed in the window. Activity C suffered from 5 days of overall delay to its completion. However, none of these delays caused critical delays to the overall completion date (because of the float created by the other critical paths).
- Window 1: Delay event DE1 caused two days of critical delay on days 2 and 3,
- Window 2: Delay event DE2 caused 1 day of critical delay on day 6,
- Window 3: Delay event DE2 caused 1 day of critical delay on day 7. However, the contractor’s progress delays caused 1 day of concurrent critical delay on the same day 7.
- Window 4: No further critical delay was observed.
Retrospective Longest Path Analysis (RLPA)Brief Description This method is considered to be an “Effect & Cause” analysis in that it does not simulate the impact of the delay event(s) (i.e. it is an observational method). The method starts by creating an as built program and determining the as built critical path “retrospectively”. The analysis then identifies the critical delay periods comparing key dates along the as-built critical path against corresponding planned dates in the baseline program (the “Effect”). The analyst then investigates the project records to determine what events might have caused the identified critical delay (the “Cause”). The analysis is usually performed using programs and software tools. There are other terms which refer to the same basic method, including:
- As Planned versus As Built method
- Bar chart analysis
- As Built bar chart method
- 3.1 Gross
- A baseline program. The program does not have to be a logic-based program.
- As built program. The program does not have to be a logic-based program.
- Identify the retrospective as built critical path,
- Compare the as built critical path to the baseline and determine the actual critical delay periods.
RLPA-As Built Program
The first path goes through activities A, B and C. The start of activity A was delayed by 3 days (days 1, 2 and 3). Activity B was delayed by the same three days. Activity C was delayed by further 6 days, three of which were caused by the knock-on effect of the previous activities A and B
RLPA-As Built Critical Path 1 AnalysisThe second critical path goes through Activities A, D and E. There is an overall of 5 critical days delay on the path. These delays are caused by delay events DE1 (3 days) and DE2 (2 days) as follows:
RLPA-As Built Critical Path 2 AnalysisThe third path goes through activities F and G. Activity F is delayed by 1 day and Activity G is delayed by four days, one of which is caused by Activity F delays. These delays are not linked to any of the claimed delay events.
RLPA-As Built Critical Path 3 AnalysisEffectively, there are three critical paths on the project. The Retrospective Longest Path analysis looks backwards at the paths, identifies the as built critical path and ignores the contemporaneous critical path, which may be different (e.g. the critical paths identified in the previously analysed methods, in windows). The decisions relating to the longest path and critical delay period requires professional judgment and has a subjective element. For example, it may be argued that the true longest path was going through Activities F and G which were not impacted by any of the delay events. In this case, the contractor may not get any extension of time.
RLPA- Summary of As Built Critical Paths (highlighting path not impacted by Delay Events)The contractor may argue that the critical path was going through activities A, D and E, which were impacted by Delay Events 1 and 2. In the Retrospective Longest Path Analysis, the project is reviewed in one window and therefore the critical paths are likely to be treated equally. Therefore, the Retrospective Longest Path method in this instance would be vulnerable to arguments that the full 4 days of delay to the completion (i.e. day 8 to day 12) was concurrent
Collapsed As-Built Analysis (CAB)Brief Description This method is considered as a “Cause & Effect” analysis in that it does simulate the impact of the delay event(s) (i.e. it is a modelled method). The method starts by reviewing or creating an as built program “retrospectively”. The analysis then models the impact of the delay events on the as built program. The retrospective critical path is determined and the critical delay periods are identified by extracting the delay events from the as built program (the “Effect”). The method is sometimes performed in windows. There are other terms which refer to the same basic method, including:
- But-for analysis
- Modified as built
- Time impact technique
- Forensic scheduling
- But-for-Backward Analysis
- Collapsing technique
- Impacted as built
- As built less delay analysis
- As built subtracting impacts
- Modified but-for
- Apportionment Delay Method
- 8 Single Simulation (Global and stepped extraction)
- 9 Multi Simulation (Fixed periods and stepped extraction))
- As built program. The program needs to be logic-based so that it can simulate the critical path but for the delay events.
- A selection of delay events to be modelled on the as built critical path.
- Review or create the as built program,
- Model the delay events on the as built program,
- Extract the delay events and assess the resulting critical path,
- Determine the critical delay periods.
CAB – As Built ProgramThere are two delay events to analyse. The as built program can be collapsed once (two events at the same time) or in windows (1 event each time). For the purpose of this case study, I will analyse the delay in two windows. The As Built program finished on day 12. But for Delay Event DE2, the project would have completed on the same day 12 i.e. delay event DE2 did not cause critical delay.
CAB- As Built Program – DE2 ExtractedSimilarly, but for Delay Event DE1, the project would have completed on the same day 12 i.e. delay event DE1 did not cause critical delay.
CAB- As Built Program – DE1 and DE2 ExtractedAs has been determined in the iterative methods such as Time Impact Analysis and Time Slice Windows Analysis, the order of the delays is crucial in determining the delay events that impacted the actual critical path. The Collapsed As Built method identifies that after you remove DE1 and DE2, the maximum entitlement to an EOT is only 3 days (i.e. day 9 to day 12). This is because the Collapsed As Built method demonstrates that Activity C would not have been completed until at least day 9 – even after DE1 and DE2 had been removed. If we take out that the critical path of activities F and G, the critical delay caused by Delay Events DE1 and DE2 would be 3 days only (day 12 minus 9). This is because the Collapsed As Built CAD method demonstrates that Activity C wouldn’t have been completed until at least day 9 – even after DE1 and DE2 had been removed. Therefore, the Collapsed As Built method in this instance would be vulnerable to arguments that the full 4 days of delay to the completion (i.e. day 8 today 12) was concurrent.”
Summary and RecommendationIn this article and the previous one, I summarised the key delay analysis methods in the industry and linked the Society of Construction Law Delay and Disruption protocol’s 6 key methods with the AACE International’s 9 retrospective forensic scheduling groups. In practice, the selection of the delay analysis method requires professional judgment of the analyst considering the factors which I discussed in my previous articles. In my next Articles, I’ll discuss the approach I follow personally including the identification of the critical path, analysing the delays and structuring the delay report.
Disclaimer: This article is intended to provide an update on the current industry practice in terms of delay analysis. However, it does not in any way constitute any type of legal or professional advice. Delay Article 1: https://www.astonconsult.net/delay-analysis-what-is-the-most-appropriate-method/  Delay Article 2: https://www.astonconsult.net/delay-analysis-methods-factors-to-consider/  Delay Article 3: https://www.astonconsult.net/delay-analysis-methods-simplified-1-2/  2nd Edition, February 2017  SCL 2nd Protocol, 11.5 (d)  Delay Article 3: https://www.astonconsult.net/delay-analysis-methods-simplified-1-2/  This example scenario will be used for the 6 methods discussed in this article  While the figures identify the remaining activities as though it had been calculated by software (in the same manner as Time Slice Analysis), the order, logic and criticality of these remaining activities are the analyst’s view and interpretation of the remaining activities using their knowledge of the project, judgement and experience  Changing the window period will likely change the result (e.g. daily windows may demonstrate that the progress delay was not critical).  SCL 2nd Protocol, 11.5 (e)  SCL 2nd Protocol, 11.5 (f)  Delay Article 3: https://www.astonconsult.net/delay-analysis-methods-simplified-1-2/