Clear the path. With certainty.

A site-wide surface magnetometry survey provides area coverage but cannot guarantee that every individual pile position to full foundation depth is clear. Borehole clearance uses a downhole magnetometer probe to scan each specific pile location from surface to the assessed maximum bomb penetration depth (typically 12 metres in soft ground), providing point-specific assurance before the piling rig engages. This is the definitive check that protects the piling crew and the pile driving equipment.

For each borehole or pile position, the first metre is hand-excavated to remove near-surface clutter and establish a clean entry point. A downhole magnetometer probe is then lowered into the hole at one-metre intervals, logging magnetic data at each stage. If no significant anomalies are detected at any depth, that position is signed off as clear and the piling crew can proceed immediately. The process is typically programmed to run directly ahead of the piling rig, keeping the critical path moving.

As a general guide, an experienced operative using a downhole magnetometer can clear between 20 and 40 positions per day on a straightforward site with clear access. Where anomalies are encountered and require investigation, progress slows, but real-time feedback from the probe means decisions can be made immediately without waiting for off-site data processing.

If the probe detects a significant ferrous anomaly, drilling at that position stops and the finding is logged. The UXO engineer will recommend either relocating the pile within the structural engineer's tolerance, or initiating a Target Investigation: a supervised excavation to identify the object. The vast majority of anomalies prove to be innocuous, but each must be assessed before work resumes at that position.

Yes, and this is often the most cost-efficient approach. A combined magnetometer-and-piezocone probe surveys UXO risk and ground geotechnical properties simultaneously in a single pass, producing both a UXO clearance log and soil stratigraphy data. This avoids the need for separate mobilisations and is particularly valuable on projects where ground investigation and UXO assessment are both at an early stage.

Each cleared position receives an individual borehole clearance log, and a summary clearance report is produced at the end of the programme. These documents confirm that UXO risk has been managed to ALARP at each signed-off location and are accepted as the standard record for piling contractors, structural engineers, geotechnical consultants, and CDM documentation. They form part of the site's permanent health and safety file.