Ground investigation - why it pays for your development to have one
So, why should you invest in ground investigation? Philip Thomas, Technical Director discusses the challenges developers may face and the importance of having one.
30 Oct 2020
Ground investigation is often considered as a project overhead typically attracting a fraction of the funding of the overall project spend (0.1 to 0.3%). The exceptionally low level of expenditure on ground investigation fails to recognise the significant risks that are inherent in the ground and the value that a robust ground investigation can bring to the overall project delivery. This disparity was recognised as long ago as 1984 when the National Research Council recommended that a minimum of 3% of the project value should be dedicated to ground investigation.
So, why should you invest in ground investigation? The answer is simple, lower construction costs and greater programme certainty. This is achieved through:
- Early identification of risks allowing proactive management of ground conditions through informed master planning
- Sustainable materials management
- Improved efficiency of design
- Risk reduction/improved cost forecasting
The variance on construction costs within the ground can vary by an order of magnitude, whereas the above ground construction costs are typically predictable within 5 -10%. The importance of understanding your ground conditions is highlighted by the Institution of Civil Engineers who state; 'The ground is the place where things are most likely to go wrong during a construction project and the worse the ground the greater the risk'.
Spotting key opportunities
Proactive management
Early identification of ground conditions and the associated constraints supports a proactive management approach allowing the scheme to be designed to take account of challenging ground conditions increasing scheme viability and reducing ground risk significantly. With sufficient information areas of public open space and low sensitivity structures can be located in the areas of poorest ground conditions, with the high sensitivity structures being located in the lowest risk areas.
Efficient design
Increased data reduces uncertainty allowing efficient design. Where designers are faced with high levels of uncertainty, they are forced to compensate for the lack of a robust ground model with conservative design assumptions which can lead to significant over design of structures. Typically, this will lead to deeper or wider foundations, thicker pavement structures and/or more onerous floor slab design, with associated additional disposal costs for arisings.
Sustainability and materials management
Understanding ground conditions beneath the site can allow for the most sustainable viable solutions to be adopted for the proposed development allowing materials reuse and retention onsite to be maximised and offsite disposal minimised.
Risk Reduction
Risk can be managed, minimized, shared, transferred or accepted, but it cannot be ignored. At some point during the construction process the ground risks will manifest themselves in increased expenditure and/or delays to programme. Where the ground conditions are robustly characterised an appropriate risk register can be developed, and proportionate risk allowances can be set providing viability on likely expenditure and potential programme delays.
What are the key risks?
The key risks from not having a ground investigation can increase your project programme and overall expenditure. In extreme cases, lack of understanding or mismanagement of ground conditions can also lead to third party liabilities, fines/prosecution and a failure to obtain a consent.
Delays, especially where Local Authority consent, Environment Agency or Building Control sign off are required, can lead to significant programme extensions running into many week and months, and can sometimes result in buildings that cannot be lawfully occupied on completion. Additional expenditure associated with abnormal construction activities can be significant, impacting on scheme viability.
Remember, you pay for an investigation whether you have one or not!
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