How Can Developers Avoid Costly Variations in Civil Infrastructure?
One of the biggest causes of costly variations in civil infrastructure projects is loopholes or gaps in the design. If the design is completed to the highest possible standard and best practice, the chances of major variations reduce significantly.
However, variations can never be fully eliminated — some will always occur because certain factors are simply out of anyone’s control at the time of tender.
Please note: the following are just a few examples of typical variation causes. These do not represent the full list, and variations can result from many other factors based on the project scope, site conditions, or client requirements.
🔍 Lack of Ground Investigation Before Tender
If ground investigation is not completed prior to the tender, the tendering party has no way of knowing the following:
Whether the ground is contaminated
If there’s groundwater present
If the ground is collapsing or unstable
Where and how deep the rock layer starts, or what strength the rock is
In such cases, contractors have no choice but to exclude these risks in their pricing — and rightfully so. You cannot price for something you have no data for.
⚠️ Risks from Unknown Existing Services
Designers often include a note in the drawings that existing services may be present, but their location, depth, and condition are unknown.
Naturally, the contractor cannot price for these accurately, so they exclude any risk related to:
Locating existing services
Protecting or working around unknown services
Delays or costs due to unexpected utility clashes
These exclusions are standard and necessary unless proper locating and survey information is available.
🔄 Changes to Design During or After Tender
Another common cause of variation is design revisions that happen after the tender has been submitted.
Examples include:
Pipe diameter changes
Pipe material changes
Introduction of additional fittings or valves
Relocation of manholes, hydrants, or valves due to constructability feedback
Revisions to accommodate site constraints or updated authority comments
These are legitimate variation items because the pricing was based on a different set of design assumptions.
Disclaimer: These examples are provided from a civil estimator’s perspective. Only the design consultant has the authority to make final decisions about pipe sizing, material selection, and layout design. Any input from an estimator should be treated as a professional opinion, not a design directive.
✅ How to Minimise the Impact of Variations
To help reduce variations and their cost impacts, developers should:
Ensure thorough and complete design before tendering
Conduct ground investigation and service locating early
Provide a clear scope of works and avoid ambiguity in tender packs
Share all reports (geotech, groundwater, etc.) with estimators
Use professional estimators who can flag missing items, risks, and exclusions clearly
Be mindful of specification layers — for example, when a developer’s specification is stricter than Sydney Water’s, the higher standard must be followed (e.g., 110mm layer testing vs. 150mm)
📞 For professional estimating services with a real-world approach to variation risk:
WSE Sydney
📧 tenders@watersewerestimatingsydney.com.au
📱 +61 451 404 645