This informal CPD article, ‘What is a UXO survey?’, was provided by Brimstone Site Investigation, who are Explosive Ordnance Disposal (EOD) experts dedicated to the safe removal and disposal of Unexploded Ordnance (UXO) across the United Kingdom and around the globe.
An unexploded ordnance (UXO) survey explores beneath the surface and detects buried ferrous objects, such as unexploded wartime bombs. The survey is often a follow up activity to a UXO risk assessment and is undertaken before ground intrusion works take place on sites across the UK that have a moderate or high UXO risk.
These surveys ensure the safety of construction workers and can prevent expensive, unexpected costs and delays further down the line. Different projects will have varying requirements, ground types and budgets, which is why UXO surveys come in two key forms, intrusive and non-intrusive.
Non-Intrusive UXO Surveys
A non-intrusive survey uses state-of-the-art equipment in a drone, towed or pushed method, clearing large areas down to 6m in depth. This type of survey is suitable for greenfield sites or sites where shallow ground intrusions are planned.
A push-cart is a five-channel system suitable for small to medium-sized areas. It is usually carried out by a specialist two-person team and involves manually pushing the system across the area of land being surveyed.
A non-intrusive survey in a towed format uses an eight-channel gradiometer and is ideal for larger areas. Again, this is usually carried out by a two-person team and features an all-terrain vehicle towing the sensors across the site.
Finally, a drone is perfect for surveys in areas where a push-cart or towed-array system cannot reach! Drone systems can survey up to five times as many hectares in a single day compared to the push-cart system, bringing costs down. Regardless of which survey method is used, they all collect technical data which is used to detect ferromagnetic anomalies.
Intrusive UXO Surveys
An intrusive survey involves deploying a Cone Penetrometer Testing Rig to your site. These rigs can survey single pile positions or clusters for any deep intrusive works. For large scale excavations, they can provide a site-wide matrix clearance, offering a complete survey solution to a maximum depth of 25m across a large area.
The rigs are box-like containers mounted on a crawler undercarriage. They work by using hydraulic pressure to push a hardened metal cone into the soil. The cone penetrates up to 20m below grow level, where it uses magnetometry to sense rogue objects.
A key benefit of intrusive surveys is that they can be deployed to brownfield sites or sites with areas of made ground (sites that would usually be unsuitable for a non-intrusive survey). In addition to this, greater depths can be achieved with this system when compared to the non-intrusive methods. Like non-intrusive surveys, data is collected and then analysed for any anomalies.
What happens next?
Once the data has been collected, it will be assessed by a geophysicist. They will check for anomalies and data characteristics against signatures for unexploded ordnance. If an anomaly models the characteristics of an item of UXO, these might need to be investigated further by a UXO engineer. If no anomalies are found, you can continue with peace of mind that your groundwork can be carried out safely and that you have mitigated the risk of UXO.
We hope you found this article helpful. For more information from Brimstone Site Investigation, please visit their CPD Member Directory page. Alternatively, you can go to the CPD Industry Hubs for more articles, courses and events relevant to your Continuing Professional Development requirements.