What are Clearance Surveys?
Clearance surveys are critical before any digging, drilling, or borehole works where utility networks intersect or sit close to your construction area (e.g., pipelines, power cables, telecom ducts, gas mains, water and sewer services).
The UK suffers an estimated ~60,000 accidental strikes on buried utilities each year, with total direct and indirect costs of ~£2.4 billion annually, with the average direct cost per strike ~£3,371, and indirect costs can be ~29× higher. Planning with validated utility data (like “PAS 128” and predig searches) is a primary mitigation.
Interlocks Surveys identifies and accurately maps the underground utilities in and around the proposed or existing infrastructure—so you can set safe standoffs, meet regulatory and engineering standards, and avoid costly, dangerous utility strikes.
What a Clearance Survey includes
A clearance survey (service avoidance or borehole clearance survey) scopes the proposed excavation or drilling locations using Ground Penetrating Radar (GPR), Electromagnetic Locating (EML) and “Drainage surveys” to accurately map below-ground infrastructure. We work to “PAS 128:2022” methodology—progressing from Type D/C records and reconnaissance through Type B detection to accurately detect and record the position of existing utilities in the proposed location.
Picture from our Stansted Airport project
What we do on site
- Carry out a “Utility Survey” to detect and trace electric, gas, water, telecoms and fibre using EML and GPR, marking positions and depths on the ground around the proposed clearance location
- Lift all utility manholes and covers to inspect and carry out and “drainage surveys” required
- Measure and record GPS coordinates and position for all located assets and survey control
- Map separation distances (horizontal and vertical) between existing services and your proposed works or borehole
- Provide design-ready outputs aligned for coordination with “Engineering Surveys”, “Setting Out” and “CCTV Drainage Surveys”
Deliverables
- Digital drawings (DWG/PDF) with PAS 128 Quality Levels and symbology
- GPS/GNSS coordinates for assets, boreholes and exclusion zones
- Separation measurements to proposed alignments, excavation limits and exclusion zones
- 3D Revit models of utility locations
Reducing risk with a Utility Clearance Survey
- Before excavation, trenching, piling or borehole drilling – especially in corridordense or poorly recorded sites – clearance data lets you set hand-dig only zones, mechanical standoffs, and diversion decisions with confidence
- Compliance & safety: HSE guidance makes clear that damaged underground electrical cables can cause fatal or severe injuries from electrical arcs and burns; planning, up-to-date plans, detection, and controlled excavation are required near live services.
- Tender and programme certainty: Referencing a “PAS 128” clearance survey in your specification standardises scope, methods and deliverables -improving data quality, reducing rework and disputes.
Why it works
On a recent city centre project, our surveyors identified an uncharted service at 0.65 m depth, 0.90m from a proposed drainage run.
Actions: The client was made aware of this straight away, and later presented the deliverables of all data found on site.
Outcome: the client carried out a QLA trial hole and verified the route and depth of the unknown, which later turned out to a redundant 11Kv cable. This led to modification of the design, shifted the trench by 0.8 m and set hand-dig only within 1.0 m of the cable, and enforced a ≥ 500 mm mechanical standoff.
Result: zero strikes, no extension to traffic management, and programme maintained.
Why choose Interlocks for Clearance & Borehole Surveys?
- Experienced surveyors skilled in tracing and mapping complex corridors
- Advanced technology: “GPR”, EML, “CCTV”
- Comprehensive deliverables: ground markings, GPS measurements, and digital CAD plans as standard
- Risk mitigation: identify obstacles early to prevent H&S incidents, service outages, and avoidable project costs
