Intrusive UXO Survey

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Why do I need an Intrusive UXO Survey?

An Intrusive UXO Survey makes sure that a project can be quickly and efficiently checked for deep buried unexploded bombs (UXO/UXB) so that development can continue safely.

On projects where a risk of encountering UXO/UXB has been assessed, and where deep intrusive groundworks such as piled foundations are planned (more than 4 meters below ground level) – an Intrusive Magnetometer Survey will provide detection and clearance ahead of individual pile locations, clusters and boreholes.

This survey method provides detection of items of ordnance at depths not achievable by Non-intrusive UXO Survey methods, or in ground conditions which have gross surface ferro-contamination. This survey method is a reliable way of minimising UXO risk on Brownfield land projects.

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What is an Intrusive UXO Survey?

It’s a process where a magnetometer probe is pushed into the ground by specialist survey equipment using hydraulic pressure, and we survey a column of soil to detect for deep buried unexploded bombs (UXO/UXB).

As the magnetometer probe is pushed into the ground, a ‘real-time’ display of the magnetometer reading is fed back to the survey engineer present.

This allows for a check of both ferrous anomalies directly beneath the probe (the probes have look-ahead capability), and for any horizontal deviation of the probe (detected by inclinometers in the probe body) so that if necessary the survey can be terminated or corrected.

Each survey position provides a column of clearance down to an assessed maximum bomb penetration depth (which for generic London clay can be up to 12m below ground level), and we can often check multiple pile locations per survey – reducing the overall number of surveys required.

An Intrusive UXO Survey is normally carried out before planned piling works and can be deployed from several different platform configurations to suit specific projects (large, small, restricted access – on ground, rail or overwater).

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How are the survey results communicated back to the client?

Real-time data logs are saved and processed by our in-house geophysical team, and advanced software analysis creates a false-colour survey map showing all identified ferrous targets and anomalies which model (in size and shape) as potential UXO/UXB.

The reports present the results clearly and concisely, and we explain any potential risks to you, and if needed – outline any further specialist support required.

Any anomalies identified during the survey that have similar characteristics to UXO/UXB, can either be investigated (and excavated) or avoided – depending on the client’s requirements.

“1st Line Defence understands our business and requirements and have been able to assist in reaching practical and swift solutions to potential UXO threat. We have found 1LD to be knowledgeable in their specialist field, and they have always been helpful, pragmatic and professional in their approach to the work they have done for CGL to date. We would certainly use 1LD again on future projects where UXO services are required.“

Technical Director, CGL

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Frequently Asked Questions

Browse the most commonly asked Intrusive UXO Survey questions or contact us if you have a specific enquiry

Intrusive UXO Survey

Mitigate risk before ground works commence with an Intrusive UXO Survey

Can an Intrusive UXO Survey be used on a ‘brownfield’ site?

Yes – an Intrusive UXO Survey can be used on a ‘brownfield’ site. The surveys can even be deployed near existing piles / sheet piling (although the diameter of clearance will be reduced). In some circumstances, it maybe necessary to ‘pre-drill’ through hard post-war Made Ground close to surface in order to facilitate the survey.

Can an Intrusive UXO Survey be used to provide UXO clearance ahead of deep piling work?

Yes – an Intrusive UXO Survey is perfectly suited for this job, and we offer a wide range of different Intrusive Survey rigs – small, large, tracked wheels etc. We will have a solution for even the toughest, muddiest and complex sites around – we are experts in our field!

Will the UXO risk on my site be reduced by having an Intrusive UXO Survey?

Yes – an Intrusive UXO Survey is designed to reduce the risk of encountering buried unexploded bombs by physically pushing a magnetometer cone into the ground. Generally, an Intrusive UXO Survey is used to provide clearance to max bomb penetration depth on the main areas where deep intrusive ground works will take place – for example piling and boreholes etc. Once clearance has been given the UXO risk has been reduced to as low as reasonably practicable (ALARP). However, if development plans change, any new areas planned for development would need to be investigated to make sure that all risks have been negated.

How deep does an Intrusive UXO Survey need to go to detect unexploded bombs (UXBs)?

Larger German unexploded bombs (such as the 500kg), can be found up to 12-14m below ground level in certain ground conditions. However, the survey only needs to provide clearance to the assessed ‘maximum bomb penetration depth’ at each particular site / location. The depth that a UXB can reach depends largely on the underlying geology / ground conditions. The denser the ground, the less deep an unexploded bomb will penetrate. This depth can be assessed using site-specific borehole logs, or by a UXO Specialist once on-site.

What happens if the Intrusive UXO Survey highlights a potential risk on my site?

If an Intrusive UXO Survey identifies a potential ordnance risk (sometimes referred to as an ‘anomaly’ or ‘pUXO’), there are generally two options. If viable, the anomaly could be left in the ground undisturbed (the foundation design could be changed, the area avoided etc.). If this is not possible, it is usually recommended that the anomaly is physically investigated. 1st Line Defence can provide UXO Specialists to undertake the investigation / excavation to determine the nature of the anomaly and confirm any potential threat.

What would happen if an unexploded bomb (UXB) or an item of UXO is found on my site?

If a suspected item of UXO or a UXB is discovered by our UXO Specialists on-site, they will implement set incident management procedures to make sure the item is dealt with safely and appropriately. This will depend on factors such as the nature of the item, its condition, its depth, the location it is found and whether is it live or inert. 1st Line Defence can dispose of the item or will arrange for its disposal / removal so that works can resume as quickly as possible.

From survey data, can you immediately tell if a buried object is an item of UXO or something else?

When conducting an Intrusive UXO Survey it is not possible to confirm the nature of an anomaly without physical investigation. Specialist software allows us to model the approximate size and depth of buried ferrous objects – and targets of interest can be selected for further investigation (based on the assessed risk / likelihood of encountering certain types of weaponry in the area). For example, if the historic Risk Assessment only identifies a potential risk from large German UXBs, we would concentrate only on items which model above a certain volume – reducing the number of targets of interest. For Non-Intrusive Surveys, it is often the case (where there are many potential targets in an area) that a recommendation would be made to initially investigate only a percentage of the total as part of a risk reduction exercise.

What would happen if you have conducted an Intrusive UXO Survey and it identified an object with similar characteristics to an unexploded bomb (UXB)?

If the planned ground works will not disturb the object or its close surroundings, the object can be left untouched. If that is not a viable option, the object would require investigation by a UXO Specialist to determine whether it’s a UXB or not – and whether it’s live or inert. If the item is found to be live, the site will be put in emergency response until the threat has been removed. If the item is found to be inert, it will be safely removed so that ground works can proceed safely.

When trying to detect a UXB, do you search for both ferrous and non-ferrous targets?

German high explosive (HE) bombs dropped during WWII had thick iron casings, and can be readily detected with a magnetometer. Smaller, mainly non-ferrous bombs such as incendiary bombs (which cause fire not an explosion) generally had very low ground-penetrating ability and are less likely to be found buried deep in the ground. Most other types of UXO commonly encountered in the UK also have significant ferrous content. Where we are working on sites where we expect to find items with low or no ferrous content, we can change our primary search / survey instrument.

What information do you require from a client to undertake an Intrusive UXO Survey?

Our team will guide you through exactly what is required for an Intrusive Survey to be undertaken, including questions about the suitability of the site – terrain, ground cover etc. In general, we will require the following information:

Copy of a UXO Risk Assessment, risk level and type of risk (Allied / German).

Detailed instructions about any proposed intrusive ground works – boreholes, trial pits, piling, strip foundations etc.

Information about any size or weight sites restrictions for large vehicles.

Full site address and postcode.

How long does it take to complete an Intrusive UXO Survey?

This depends on factors such as terrain, ground types, site access and number of positions that need to be investigated. However, as a rough guide, in good ground conditions, we can undertake an average of 20 surveys per day.

How do I order an Intrusive UXO Survey?

To order and book an Intrusive UXO Survey, call us on +44 (0) 1992 245020, email info@1stlinedefence.co.uk or use our contact form and we will get in touch to discuss your request.

How much does an Intrusive UXO Survey cost?

For 1st Line Defence to provide an accurate quote for an Intrusive UXO Survey, we need to review a copy of the UXO Risk Assessment for your site and get a better understanding of any planned intrusive ground works, boreholes and piles etc. The number of piles and their layout are the biggest determining factors – as well as whether or not ‘pre-drilling’ is required. To discuss your project and how we can support you, call us on +44 (0) 1992 245020, email info@1stlinedefence.co.uk or use our contact form and we will get in touch.