Enhancing project outcomes through the early consideration of constructability
Adrian Vesnaver Bellwether Group
Abstract:
Constructability is the extent to which a project design is optimised to ensure the project can be constructed and maintained practically and efficiently, while meeting project objectives. This could include project life cycle objectives for cost, time, quality, WHS and environmental management (Transport for NSW 2017, p.9).
Experience has shown that the ability to reduce project costs through identifying issues and addressing them is much greater early in the life of a project. Much of this opportunity to reduce project costs is lost once the construction contract is out to tender (Transport for NSW 2017, p.6).
Thus, an effective constructability process throughout the design phase can be of great benefit in subsequent stages.
A constructability review or assessment is one of the established methods for integrating design and construction phases, taking construction knowledge and experience into consideration in the early stages of a project’s lifecycle. A secondary purpose is to ensure that construction flexibility and innovation are not unnecessarily constrained by the design documentation. This will maximise opportunities to reduce costs by innovation during construction (Transport for NSW 2017, p.4).
This paper will introduce the benefits of incorporating constructability considerations as part of the design process. This will include a brief introduction to the concept of constructability. It will then examine and compare the constructability processes and procedures of several major jurisdictions within Australia
The paper will illustrate some of the major constructability issues commonly overlooked in design, using several project examples to demonstrate the implications and impacts where constructability is not adequately incorporated or considered during the design phase.
Keywords: constructability, design, project lifecycle, infrastructure
1 Introduction
The Queensland State Government has identified investment in road and transport infrastructure as a key priority to support jobs and business in the community during the current economic recovery period, allocating $27.5 billion under the Queensland Transport Roads Investment Program over the next four financial years (The State of Queensland (Department of Transport and Main Roads) 2021, p.5).
Local government is also investing in infrastructure with Queensland councils spending a combined total of $4.3 billion in 2020 on replenishing and/or constructing new assets to meet community needs (The State of Queensland (Queensland Audit Office) 2021, p. 25).
The Grattan Institute’s analysis of all projects valued at $20 million or more and built over the past 20 years showed the actual costs exceeded the promised costs by 21 per cent (Terril, Emslie &
Moran 2020, p.3). Cost overruns that are a consequence of unnecessarily high actual costs are problematic because they pose large avoidable costs, as well as distorting the planning process (Terril, Brendan & Danks 2016, p.4).
Consideration of constructability during project planning and design process can identify potentially avoidable issues which may impact the final outturn costs.
2 Constructability during planning and design
Transport for NSW (2017, p.9) guidelines for constructability assessment defines constructability as the extent to which a project design is optimised to ensure the project can be constructed and maintained practically and efficiently, while meeting project objectives. This could include project life cycle objectives for cost, time, quality, WHS and environmental management. While related, it augments the existing design assessments, durability assessments, value management and risk management processes. Its purpose it is to reduce construction and maintenance whole of life costs.
Experience has shown that the ability to reduce project costs through identifying issues and addressing them is much greater early in the life of a project as illustrated in Figure 1. Much of this opportunity to reduce project costs is lost once the construction contract is out to tender (Transport for NSW 2017, p.6). Thus, an effective constructability process throughout the planning and design phases can be of great benefit in subsequent stages.
Figure 1 Cost of change compared to potential savings over the project lifecycle
These benefits include (Transport for NSW 2017, p.5):
• Direct benefits:
▪ Design, construction, and maintenance costs are reduced by producing economical design and avoiding re-design during construction and operation
▪ Construction planning is made easier
▪ Construction schedules may be reduced
▪ Product quality is improved
• Indirect benefits:
▪ Building a collaborative project development and construction team committed to project goals
▪ Cross disciplinary training of project team members
▪ Transfer of expertise and knowledge from other projects
▪ Increased innovation in design and construction.
One such approach to incorporating constructability into the planning and design process is through a constructability assessment. This is a formal examination of design documentation and site conditions to achieve the early identification of issues related to construction and maintenance (Transport for NSW 2017, p.9).
The primary purpose of a constructability assessment to optimise the design to ensure the project can be constructed and maintained practically and efficiently, which will assist in meeting the project life cycle objectives. A secondary purpose is to ensure that construction flexibility and innovation are not unnecessarily constrained by the design documentation. This will maximise opportunities to reduce costs by innovation during construction (Transport for NSW 2017, p.4).
Constructability assessments are typically conducted using two methods, a constructability workshop or a constructability review/audit. Transport for NSW (2017) technical procedures for constructability assessment define each as follows:
• Constructability workshop – A workshop meeting held to assess constructability issues for the project design and documentation
• Constructability review/audit – A desktop examination of the constructability issues for a project design.
A constructability workshop typically involves a group of project stakeholders meeting to identify and assess constructability issues. Before the actual workshop, participants examine the design documentation and ideally attend a site inspection. At the workshop, the participants discuss issues and make recommendations and record them in a constructability assessment issue register. It is important that the workshop process is structured and led by a facilitator possessing the requisite skills, experience, and subject matter expertise to ensure the workshop objectives can be achieved.
In contrast, a constructability review or audit typically involves a single reviewer, or small number of subject matter experts, completing a desktop examination of the project design and documentation.
It is normally conducted by a person who is independent of the design team and is experienced in design, construction, and maintenance issues. The reviewer identifies issues, makes
recommendations, and records them in a constructability assessment issue register.
Deliverables from both processes may also include a constructability workshop or review/audit report.
Both also have relative advantages and disadvantages, and the selection of the method to employ on a project is dependent upon several factors such as its size, complexity, timeframe, level of design definition, interfaces, and project stakeholders. A summary of these is provided in Table 1.
Table 1 Advantages and disadvantages of constructability assessment methods
Constructability Workshop Constructability Review/Audit
Advantages
• Involves project stakeholders, encourages collaboration and different points of view
• Likely to identify a broader range of potential issues and opportunities
• Generates feedback and discussion
• Good for complex multi-disciplinary problems
• Often cheaper than a workshop
• Permits a comprehensive analysis of the issues and identification of potential solutions
• Suited to checklists
• Doesn’t require organisation
Disadvantages
• Potentially higher cost
• Participants can get side tracked on non-constructability issues
• Insufficient time and information to focus on potential solutions
• Not suited to checklists
• Requires coordination of multiple parties
• Can often be viewed as a ‘box ticking’
exercise
• Potentially limited by the experience and knowledge of the reviewer
• Doesn’t involve broader project stakeholders
There are multiple procedures for undertaking constructability assessments defined by various road authorities and other government entities throughout Australia. The most comprehensive the author has encountered is the Transport for NSW (2017) Technical Procedure ILC-MI-TP0-620 Constructability Assessment. This is part of an integrated suite of project management
documentation developed by Transport for NSW which also provides technical procedures for other related aspects including health and safety in design, value management, and risk management. ILC- MI-TP0-620 provides a comprehensive range of documentation including:
• Guidelines and procedures for conducting constructability assessments and workshops
• Reporting templates
• Constructability checklists which cover many issues and incorporate approximately 250 questions
• Example documentation.
ILC-MI-TP0-620 mandates either constructability workshops or reviews at various stages of a project’s design life cycle depending on its value, which is summarised in Table 2. Smaller projects (<$2 million) typically only require a review at the later design stages, while major projects (>$10 million) undertake reviews and workshops throughout the design process. Constructability issues are assessed utilising a constructability assessment issue register (Transport for NSW, 2017) and include:
• General issues
• Program and staging
• Widening works
• Site investigations
• Environmental issues
• Earthworks and pavements
• Stormwater drainage
• Kerbs
• Public utilities
• Bridges and structures
• Noise barriers
• Safety barriers
• Landscaping
• Urban design
• Road signs, furniture, footpaths, cycleways, driveways, and fencing
• Construction contract documents
• Work adjacent to railways
• Intersection and traffic control signal design.
Not all issues are assessed at each design stage, with a greater level of detail and interrogation being required as the design definition progresses. A constructability assessment workshop or review report is produced together with the constructability assessment issue register as part of the process.
Constructability workshop facilitators and reviewers are required to have a minimum of ten years of relevant industry experience and membership or demonstrated eligibility for membership with Engineers Australia. They must also demonstrate knowledge and capability in operational
constructability experience and providing specialist constructability advice for road infrastructure construction projects, and detailed understanding of NSW Government constructability processes, construction contracts and specifications (Transport for NSW 2020, p. 40).
Table 2 Transport for NSW requirements for constructability assessments
Design stage
Type of constructability assessment Major Project
(>$10m)
Minor Project ($2- 10m)
Small Project (<$2m)
Option selection Checklist
20% concept design Workshop Workshop or review
80% concept design Review
20% detailed design Workshop
80% detailed design Review Workshop or review Review
Contract documentation Review Review Review
Source: Transport for NSW (2017), p. 12-13
In Queensland, the Department of Transport and Main Roads outline their requirements for constructability assessments as part of the engagement and management documentation provided within the Consultants for Engineering Projects manual (The State of Queensland (Department of Transport and Main Roads) 2021).
Unlike Transport for NSW, the Department of Transport and Main Roads primarily utilises a desktop constructability audit rather than interactive workshops. The audits comprise of the following (The State of Queensland (Department of Transport and Main Roads) 2021, p. 31):
• The constructability audit is used on projects to provide a detailed analysis of:
▪ Provision for traffic (including side tracking, detours and so on.)
▪ Provision for pedestrians
▪ Evaluation of the impact of PUP relocation (including impact of delays)
▪ Construction safety (road users and construction workers)
▪ The feasibility of the proposal (can it be constructed)
▪ Can the project to be economically constructed?
• The auditor is required to be a Registered Professional Engineer Queensland with over ten years of experience in road construction of projects of similar scope to the project and be independent from the design team.
• The review is presented in a similar format to a road safety audit and must identify the schedule item, the issues to be examined, the project, the reviewer, the date of review and have a section to identify that the issue has been checked and another section for comments.
Table 3 provides an overview of the Transport and Main Roads requirements for constructability audits at different design stages. Audits are generally only required to be conducted during preliminary and detailed design, with constructability only considered as part of the risk analysis during to the options analysis and business case.
Table 3 Queensland Department of Transport and Main Roads requirements for constructability audits
Design stage Functional specification reference
Requirement
Options analysis C7521 OA12 & OA13 No audit/review – consider as part of risk analysis
Business case C7522 BC12 & BC13 No audit/review – consider as part of risk analysis
Preliminary design C7523 PD10 Constructability Review Detailed design C7524 DD26 Constructability Audit and
Construction Program
Source: Analysis of requirements in The State of Queensland (Department of Transport and Main Roads)Consultant for Engineering Projects functional specifications.
In comparison to Transport for NSW, the Transport and Main Roads constructability audit:
• Is narrower in scope and somewhat simplified
• The procedures and processes are not as comprehensively defined
• Doesn’t utilise workshops and only occurs once during each design stage unless there is a specific project exception or requirement.
Regardless of whether a workshop or audit is adopted when undertaking a constructability assessment, it is imperative that the personnel involved think like a construction contractor and consider how each element of the works would be built.
3 Common constructability issues overlooked during design
Both Transport for NSW and Queensland Department of Transport and Main Roads outline a range of areas required to be considered as part of a constructability assessment. Table 4 highlights common constructability issues that are often overlooked during the project planning and design phase. This has been derived from the author’s experience gained initially in project based construction roles, and then subsequently in bid management for civil contractors and as a constructability advisor for client authorities and designers.
Table 4 Common constructability issues to consider during planning and design
Issue Consideration Elements
Site and access Adequacy of the contract site and provision of access for construction and maintenance
• Required site facilities
• Location of site facilities
• Stockpile & laydown areas
• Site access and egress
• Adjoining property access
• Temporary access Traffic
management
Feasibility and extent of traffic management
• Traffic staging, detours, etc.
• Pedestrians and cyclists
• Lane widths and configuration
• Delineation and barriers
• Construction speed limits
• Working hours Temporary
works
Feasibility and extent of temporary works
• Temporary pavements
• Propping, shoring and retention
• Formwork and falsework
• Space proofing
• Erosion and sediment control Utilities Impacts on major utilities and utility
provider procedures
• Existing utilities and potential conflicts
• Relocation and protection works
• Timeframes and approvals Flexibility and
innovation
Scope for construction flexibility and innovation
• Will it restrict a contractor’s methodology?
• Potential alternative methodologies
• Earthworks mass haul
Issue Consideration Elements External
interfaces
External interfaces and parties • Other projects
• Government departments
• Adjoining stakeholders – Residents, businesses, schools, etc.
• Public transport Quality, WHS
and
environmental issues
Management of product quality, WHS and environmental issues
• Inspection and testing requirements
• Early loading or trafficking
• Can it be safely constructed?
• Water quality, flora, fauna, dust, noise, vibration, etc.
• Construction footprint Weather
impacts
Delays and other impacts due to weather
• Flooding
• Maintaining stormwater drainage
• Exposure of earthworks and pavement works to weather
• Wet/dry season Program and
milestones
Effects of the program, milestones and staging on planning of the works and resources
• Program constraints
• Preload / surcharge timeframes
• Seasonal constraints Resource
availability
Availability and suitability of
materials, suppliers, contractors, and subcontractors
• Quarry/borrow locations and suitability
• Long-lead items
• Local market capability and capacity
• Specialist scopes of work
4 Examples of constructability issues identified during design
4.1 Traffic management constraints and barrier working widths
Most infrastructure projects generally have interfaces with existing roads and public traffic. This can occur along the length of the entire works for projects such as road upgrades, or at limited interface locations such as access crossovers for works within an existing facility.
In Queensland, the requirements for works on roads at static worksites is governed by Part 3 of the Queensland Guide to Temporary Traffic Management (QGTTM) (The State of Queensland
(Department of Transport and Main Roads) 2021). The QGTTM is a supplement to the Austroads Guide to Temporary Traffic Management (AGTTM), with Part 3 (Nguyen 2021) covering static worksites. Together they provide information about the context and components of designing temporary traffic guidance schemes such as number of lanes, lane widths, speed limits, edge clearances and safety barriers.
To minimise safety risks to both the travelling public and construction workers, temporary road safety barrier systems are often used to delineate the construction works from traffic. Road safety barriers are not rigid and will be subject to a potentially large dynamic deflections depending on the system, creating a hazardous area immediately behind the barriers as depicted in Figure 2.
Figure 2 Dynamic deflection and hazardous area behind a safety barrier system (AGTTM Part 3, Figure 5.4)
It’s surprising the proportion of designers encountered by the author who aren’t familiar with the requirements of the QGTTM and the impacts of the dynamic deflection of a temporary road safety barrier system on the amount of working room available to conduct construction activities. This potentially results in increased cost due to additional construction stages or traffic controls required to safely undertake the works within a more constrained space than was anticipated during design.
Figure 3 shows an example of a typical staging cross section issued as part of the tender design for a road widening project. The purpose of the staging was to demonstrate that adequate width was available to safely construct a temporary pavement under traffic behind a temporary safety barrier.
The design was based on the following assumptions:
• 60kph temporary speed limit during construction
• Cross section located on a radius 200m curve
• T-LOK concrete safety barrier system utilised to delineate the work zone.
The designer assessed that a nominal width of 3.11m was available to construct the temporary pavement as shown in Figure 3. While this is narrow, it would allow a wide enough corridor for small plant to safely operate.
However, during the interrogation of the proposed staging as part of tender estimate process the construction contractor identified several traffic management constraints that should have been recognised and addressed early in the design process during a constructability assessment:
• A minimum lane width of 3m is required for a temporary speed limit of 60kph together with a 0.5m lane widening due to the radius of the curve being less than 250m (Table 2.5 AGTTM Part 3) giving a total travel lane width of 7.0m, not 6.42m as shown on the typical cross section.
• A minimum horizontal clearance to the existing and temporary road safety barrier systems of 0.5m is required from each travel lane (Table 5.1 QGTTM Part 3), rather than the shy line widths of 0.3m and 0.65m shown on the typical cross section.
• T-LOK concrete safety barrier system requires a working width of 1.82m (The State of Queensland (Department of Transport and Main Roads) 2021, p.109) to accommodate the footprint of the barrier and the dynamic deflection from an impact, rather than the safety barrier width of 0.8m shown on the typical cross section.
Figure 3 Typical staging cross section prepared during detailed design for a road widening project showing initial assumed width available for construction (top) and the actual width available (bottom) once traffic management constraints were considered.
After incorporating the traffic management constraints under the QGTTM and AGTTM, the amount of available construction width reduced from 3.11m to 1.46m as shown in Figure 3. The smaller width was insufficient to accommodate the necessary construction plant safely. The impact to the project was that the temporary pavement works could not be completed behind barriers under traffic during the day, and that closures of the adjacent traffic lane were required. Due to the traffic volumes on the road and impact to traffic flow, lane closures were only permitted to occur at night which increased the costs of the project, resulting in an unforeseen cost overrun.
A constructability assessment conducted by an assessor experienced in construction staging and temporary traffic management requirements would have identified this issue during the design, prior to the drawings being issued for tender. This would have enabled the additional costs to be incorporated into the project budget, or potential modification of the design to be investigated to mitigate the issue.
This example highlights the importance of ensuring working width requirements for temporary road safety barrier systems and temporary traffic management constraints are considered during the design phase.
4.2 Temporary works footprint requirements
The permanent works footprint is often the primary focus during the design process and is typically the final output which is detailed on the design drawings. Consideration of the working room and footprint required for temporary works during construction is often overlooked and can have a big impact on whether it is possible to construct the permanent work elements within the given site constraints.
Figure 4 shows an initial concept design for a proposed retaining that was to be constructed adjacent to an existing two lane local arterial road as part of a duplication project. The purpose of the retaining wall was to provide the median separation between the two ultimate opposing carriageways at completion which would sit at different levels. The existing road was located on the high side, with the duplicated lanes on the low side to be constructed first. Following switching of westbound traffic onto the new duplicated lanes, the retaining wall would be constructed with the existing pavement on the high side remaining to provide a carriageway for eastbound traffic and local access for adjoining properties during this stage.
A typical cross section (Figure 5) was prepared by the designer to assess whether there was sufficient available width to accommodate the temporary works for the construction of the new retaining wall and permit eastbound traffic to utilise the existing pavement on the high side. The designer assumed:
• 40kph temporary speed limit during construction
• Transport and Main Roads precast concrete barriers utilised to delineate the work zone
• 1:1 temporary earthworks batter from the rear of the retaining wall base slab.
The designer determined that there would be a 3.0m width available which would be sufficient to accommodate eastbound traffic and construct the retaining wall within the median.
A constructability review of proposed design and construction staging for the retaining wall was conducted and identified several issues.
The review identified that while the remaining width of 3.0m for eastbound traffic achieved the minimum lane width required under Table 2.5 of AGTTM Part 3 for a 40kph speed limit, it did not
allow for the 0.3m edge clearance to the traffic lane from the temporary road safety barrier system as required under Table 5.1 of QGTTM Part 3. This in itself was not a fatal flaw for the design, as the width of the base slab at the critical cross section could be reduced to accommodate the additional room required.
The critical issue identified during the constructability review, was that the designer had not considered the footprint and impacts of the temporary works required to construct the retaining wall base slab:
• Presence of a 300mm deep down-turned shear key at the rear of the base slab requiring additional excavation and extending the temporary batter further back into the existing pavement.
• Allowance of a an additional 100mm depth for concrete blinding beneath the base slab and potential over excavation further pushing back the temporary batter.
• Additional width of 1000mm at the rear of the base slab to accommodate the formwork and falsework system necessary to construct the slab and allow sufficient width for construction personnel to safely access.
• Working width of 800mm (The State of Queensland (Department of Transport and Main Roads) 2021, p.100) required to accommodate the precast concrete barrier and associated dynamic deflection.
After incorporating the footprint and impacts of the temporary works, the amount of available width to accommodate eastbound traffic reduced from 3.0m to 1.6m as shown in Figure 5, which is
significantly less than the 3.3m required under QGTTM Part 3.
The impact to the project was that the retaining wall would require extensive temporary retention in the form of sheet piling to be installed along the rear of the wall during construction to enable it to be completed under traffic. Due to the shallow rock level present in this location, temporary anchors and whaler beams would also be required to restrain the top of the sheet piles as sufficient toe embedment depth could not be achieved. The inclusion of this temporary retention added considerable cost to the project, and potentially required negotiation of subterranean trespass agreements with adjacent property owners depending upon the length of the temporary anchors.
An alternative design utilising permanent bored piles in combination with a ground beam, in lieu of a base slab for the critical sections of the retaining wall was developed. This revised design enabled the wall to be constructed without restricting traffic at a greatly reduced cost and was ultimately adopted.
This example highlights the importance of ensuring the temporary works requirements and the associated construction footprint are considered during the design phase.
Figure 4 Proposed initial concept design detail for reinforced concrete retaining wall to separate opposing traffic lanes
Figure 5 Typical cross section prepared by designer to demonstrate width available for eastbound traffic during construction of a retaining wall. The top image shows the markup of the designer indicating sufficient remaining width, while the bottom includes the necessary temporary works identified during the constructability review, indicating insufficient remaining width for eastbound traffic to utilities the existing pavement at the top of the retaining wall.
4.3 Engagement of stakeholders as part of the constructability assessment process
The design of roads through steeply sloping terrain often includes high cut batters with multiple catch benches. To ensure long term slope stability and prevent drilling and erosion or scour of the batter face, catch drains are generally constructed on the high side of cuttings at the top of the batters (Austroads 2018, p. 55). Batter drains or chutes are then used to convey run-off from the catch drains at the top of the cutting and benches, down the slope of the cut butter for discharge into the roadway table drain or piped drainage system (Austroads 2018, p. 54).
Figure 6 shows a typical cross section from a detailed design for the upgrade of an existing narrow unsealed road through a section of steeply sloping terrain. The cut batters were steepened to minimise the extent of the batters up the steep slopes and volume of excavation required. Catch drains were also detailed along the tops of the cuttings and are shown in an extract from the three- dimensional federated digital design model in Figure 7.
Figure 6 Typical cross section from the detailed design of a road upgrade through steeply sloping terrain
Figure 7 Three-dimensional visualisation from the federated digital design model. (Left) Road formation, cut batters and benches and catch drains at tops of cut batters; (Right) Batters hidden showing piped batter drain arrangement highlighted.
Batter drains or chutes can comprise of either an open shaped channel, or an enclosed piped drainage system (Austroads 2018, p. 54). In this example, the batters of the cutting were too steep for an open channel down the batter face to be used, and a pipe drainage system was detailed (Figure 7) based on the Transport for NSW standard drawing R0230 for a pipe culvert batter drain cut into a batter (Figure 8).
Figure 8 Typical elevation for a pipe culvert batter drain cut into a batter (extract from Transport for NSW 2017, Standard Drawing R0230 Stormwater Drainage Series – Batter Drains – Pipe Culvert in Cut Batter)
Several potential constructability and maintenance issues were identified with the design of the batter drain during the constructability assessment workshop conducted as part of the 20 per cent detailed design review.
The construction of the batter drains would conflict with the sequencing of the earthworks for the excavation of the cutting. Typically, earthworks cuttings of this size are constructed from the top down, whilst stormwater pipes are laid from downstream to upstream – i.e., from the bottom of the cutting in this instance. This meant the construction of the batter drain would need to be completed after the excavation of the cutting. At this stage there would be limited access across steep slopes for plant, equipment, and personnel to safely access the catch berm and top of the cutting to construct the batter drains. Personnel would be exposed to a significant risk of working at height, with limited high order control measures available to be implemented.
An additional potential issue identified was the backfilling and compaction of the excavated trench for the batter drain culverts. Use of granular backfill material would be erodible and likely result in scour and erosion of the batter above the culvert creating an ongoing future maintenance issue over the life of the road. A bound backfill material or mass concrete could have been used, but would have been costly to construct, result in a disruptive visual impact to the appearance of the batter, and potentially lead to the scour and erosion occurring at the interface between the backfill and the adjacent in-situ material on the cutting face.
The asset maintenance stakeholders at the constructability assessment workshop also identified that the batter drain culverts would introduce additional maintenance issues and risks, such as access and working heights, be potentially prone to blockages, and result in scour and erosion of the batter faces if overtopped.
A separate constructability workshop was held to identify potential design solutions to improve the constructability and maintenance of the batter drains. The constructability adviser proposed a
solution based on previous experience, which was adopted by the Queensland Department of Transport and Main Roads on the D'Aguilar Highway between Moore and Blackbutt, approximately 100km northwest of Brisbane as part of the Blackbutt Range Reconstruction. The solution involved the reconfiguration of the cut batter profiles and benches to act as longitudinal batter drains at much reduced grades compared to transverse batter drains. An example of the approach undertaken on the Blackbutt Range Reconstruction project is shown in Figure 9 with a three- dimensional visualisation from the updated federated digital design model incorporating the longitudinal batter drains shown in Figure 10.
Figure 9 Example of longitudinal batter chutes on the D'Aguilar Highway between Moore and Blackbutt in Queensland, constructed as part of the Blackbutt Range Reconstruction project (Google Maps 2021)
Figure 10 Three-dimensional visualisation from the federated digital design model showing the reconfigured batter profiles to enable the use of longitudinal batter drains
The proposed design solution identified and developed as part of the constructability assessment process for the project provided many constructability and maintenance benefits compared to the initial design:
• Safer to construct as the catch and batter drains could be undertaken as part of the bulk earthworks and trimming operations for the excavation of the cut batters when access and the risk of working at heights was significantly reduced
• Significant reduction to project cost and time by avoiding the need to construct several complex drainage structures separately from the main stormwater drainage works
• Elimination of potential future maintenance issues associated with:
▪ Erosion and scour of the cut batter faces
▪ Reduced flow velocities within the batter drains
▪ Reduced risk of blockages
• Safer access for future maintenance activities, with the batter drains potentially also able to be used as access for maintenance personnel to the cut batter benches.
This example highlights the importance of ensuring relevant stakeholders are engaged as part of the constructability assessment process during the design and planning phase to identify potential constructability and maintenance issues. It also reinforces the importance of involving experienced constructability advisers with practical construction experience that can think like a construction contractor and draw on knowledge of both potential issues and design solutions.
5 Conclusion
This paper has introduced the benefits of incorporating constructability considerations early in a project’s planning and design process. These include both direct benefits such as reduced cost and time, improved planning and product quality, and indirect benefits such as collaboration, cross disciplinary training, transfer of knowledge and increased innovation.
Constructability assessments provide the opportunity to consider how the works will be constructed and identify potential impacts. It augments the existing design assessments, durability assessments, value management and risk management processes to reduce construction and maintenance whole of life costs. It is imperative that the personnel involved think like a construction contractor and consider how each element of the works would be built, and the likely issues that could arise.
Constructability workshops and desktop reviews/audits are two common methods used to conduct constructability assessments. Both have relative advantages and disadvantages, and the selection of the method to employ on a project is dependent upon several factors such as its size, complexity, timeframe, level of design definition, interfaces, and project stakeholders. Whichever method is used, it is critical to ensure key project stakeholders are consulted.
A brief introduction of the approaches to the constructability assessment process of two Australian road authorities has also been provided. Transport for NSW provides a comprehensive and detailed technical procedure with supporting documentation for use by professional services contractors engaged on its transport infrastructure projects. Locally, the Department of Transport and Main Roads uses constructability audits during the preliminary and detailed design stages to ensure constructability issues are considered as part of the design process.
Based on the author’s experience, the most common constructability issues overlooked during design are generally related to space proofing for traffic management constraints and temporary
works. Several practical examples were provided demonstrating the potential impacts of failing to consider these issues early during the planning and design for a project.
The ability to influence positive project outcomes and reduce project costs through identifying issues and addressing them is much greater early in the life of a project. This opportunity is lost and
becomes more costly as a project progresses, particularly once a construction contract is out for tender. As the volume of infrastructure works increases due to the economic recovery response to COVID-19 and preparation for Queensland to host the 2032 Summer Olympics, the consideration of constructability early in the project life cycle will be critical to providing positive outcomes and ensuring construction and whole of live cost savings are achieved.
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