How to select the best delay analysis technique?

You would think that with the progress made in software and communication, construction projects would have become more streamlined and efficient.  However, according to Bent Flyvberg of Saïd Business School, with delay and cost overruns affecting more than 90% of the world’s infrastructure projects, the problems of delays and cost overruns occurring are becoming, more, rather than less of a problem. 

These delays and cost overruns ultimately lead to disputes between the contractor and the client, leading to the parties looking to apportion blame and ensure that they are put back into the position they were, before such delays occurred.

To apportion the causative acts the contractor (normally) or the client, would use a delay analyst to ascertain what went wrong.  For any delay analyst, the starting point in deciding which methodology to use to assess any delay and its impact, is determined by reference to the following criteria (extracted from the Society of Construction Law Protocol (2^nd Edition 2017) (“Protocol”) :

• to review the relevant contract conditions;  (However, almost all standard forms of contract are silent on this point)
• the nature of the causative events;
• the nature of the project;
• to ensure a proportionate approach, the value of the project or dispute;
• the time available;
• the nature, extent and quality of the records available;
• the nature, extent and quality of the programme information available; and
• the forum in which the assessment is being made.

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The Protocol has dropped its recommendation to use “Time Impact Analysis” in all circumstances and now provides a table that classifies delay analysis methods in several ways.

The table is reproduced below:

The Protocol classifies the way in which the critical path is determined and has sub-divided this into three types: “prospectively”, “contemporaneously”, and “retrospectively”.

Why the Protocol deems the critical path as important, is that it is only delays which lie on the critical path that can delay completion and thus qualify for an extension of time.  The Protocol (Guidance Part B: Core Principle 11; para 11.4 (d))defines as follows:

“Criticality is determined in one of three different ways.  Purely prospective critical path assessments adopt the perspective evident at the outset of the project only and take no account of progress achieved. Contemporaneous critical path assessments adopt an evolving perspective over the course of the works and take account of the effect that both historical progress and changes in the strategy for the future prosecution of the works have on predicted criticality. Retrospective critical path assessments adopt the perspective evident at the end of the project (or window of time)”.

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Below we shall look at how the SCL classify how the critical path is determined and the different types of delay analysis techniques, what their strengths and weaknesses are as well as when best to use each technique during the construction stage.   

Each of these six techniques have their own characteristics, strengths and weakness:

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1.     Impacted As-Planned Analysis: 

This delay analysis technique is prospective in its methodology. It predicts the effect of a certain delay, by inserting the event on a model of the original baseline programme to determine the impact of those activities. It does not take into consideration the actual progress on works made.

Strengths:

• Relatively simple to understand and prepare; and
• No progress of actual works is required as it is solely dependent upon the baseline programme.

Weaknesses:

• It assumes that the baseline was correct;
• Does not take into consideration actual progress of works made;
• Not reliable should the matter escalate to dispute resolution, as it does not take into account sequence changes;
• Difficult to assess concurrent delays as they are easily overlooked;
• Cannot be used for complex projects; and
• Used to quantify potential delays rather and actual.

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2.     Time Impact Analysis: 

This delay analysis technique is a contemporaneous method.  It takes into account the progress and timing of delay events impacting the works.   This method requires reliable records, including as‐built data to update the programme, including an up-to-date and reliable baseline programme being integral for its function (hence, if detailed and regular progress data is not available, then this method can be very difficult to use).

Strengths:

• Was the preferred method of the SCL protocol
• Takes into consideration changes to the critical path as they occur on the project
• Takes the contractor’s delays and slow progress into account
• Demonstrates cause and effect
• Most effective when undertaken in real-time over the course of the project
• Requires several sources of schedule information to perform

Weaknesses:

• It begins with an assumption as to the causes of the delay
• Best utilised when the project is ongoing, therefore has a limited timeframe to be used
• Requires reliable and consistent CPM schedule updates throughout the project
• Time consuming to undertake
• Requires considerable degree of expertise and technical knowledge

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3.     Time Slice Window Analysis:

It is a contemporaneous method also known as time slice analysis.  The time slice relies on the analysis of contemporaneous progress information is considered to be dynamic because it considers the dynamic nature of the critical path.  The time slice analysis breaks the construction period into separate time slices and examines the effects of delay as the delays occur.

Strengths:

• Relies on contemporaneous records of the programme updates
• Relatively simple to perform
• Accounts for non-excusable delay
• Effective at dealing with a large number of delay events
• Can use different methodologies in each window so the analysis is relevant to the activity
• Yields the most reliable results
• Accurate

Weaknesses:

• Requires significant time and effort since it requires a large amount of information and the schedule needs to be periodically updated
• May not be appropriate for projects that lack strict administrative procedures and updated schedules
• Expensive
• Can be time consuming
• Contemporaneous basis, but no future changes considered
• Can produce theoretical results unless properly implemented

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4.     As-Planned vs. As-Built:

This delay analysis technique is a contemporaneous method.  This is the most basic method of delay analysis and is quick and easy to use and prepare.  No changes are made to the programme as it is a straightforward comparison between the planned versus the actual performance of the works.  This method therefore requires an as‐built programme and accurate as-built records.

Strengths:

• Very simple to execute and easy to understand
• It is inexpensive to execute
• Can be performed with basic information available
• Conclusions are supported by as-built records

Weaknesses:

• As-built programme required
• As-built sequence must relate to the as-planned sequence to show activity method variances
• It does not deal with the matter of consequential delays or of the re-sequencing of works
• It cannot deal with showing concurrency or parallel delays

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5.     Longest Path Analysis:

This delay analysis technique is a retrospective method to determine the as-built critical path.  The delay analyst must develop the detailed as-built programme then trace the longest continuous path backwards from the actual completion date to determine the as-built critical path.  The incidence and the critical delay are then determined by comparing key dates along the programmes critical path against planned dates on the baseline programme.  The delay analyst then investigates the project records to identify the events which might have caused the critical delays.

Strengths:

• It accounts for non-excusable delays
• It does not require complete programme updates

Weaknesses:

• It ignores any re-sequencing and/or mitigation methods that may have been used
• It produces theoretical results

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6.     The Collapsed As-Built (CAB) (or But For):

This delay analysis technique is a retrospective method also known as the But For method.  The CAB is traditionally carried out on a single-base as-built programme, relying on a simulation of a “what if” scenario based not on the contractors’ intentions, but rather the contractor’s actual sequences and durations.  The CAB uses the opposite approach to the Impacted As Planned, as the Impacted As Planned takes an additive approach, which involves inserting delays into a planned sequence, the CAB takes a deductive approach.

Strengths:

• Relies on an as-built programme
• Can be suitable where a baseline or updated programme are defective
• Does not require a baseline programme
• Does not require progress updates

Weaknesses:

• It can identify as-built periods as compensable delay
• Requires subjective assumptions when recreating the CAB model for analysis
• Constructing as-built logic is subjective
• Ignores resequencing and mitigation
• Complicated method/difficult to execute and time consuming

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In conclusion to the above and having looked at each of the delay analysis techniques and highlighting their strengths and weaknesses, I shall identify below when each technique is best used during the construction stage:

• Impacted as planned is best used at the beginning of the project.
• Time impact analysis is best used during the course of the project.
• Windows analysis is best used during the course of the project.
• As-built vs. as-planned is best used at the end of the project.
• Collapsed as built is best used at the end of the project.

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