Search for underground services — ProQual Awarding Body Occupational Qualification Construction & Building Services Revision
This subtopic covers the essential procedures for locating and avoiding underground services during highways maintenance kerb and channel work. It focuses
Topic Synopsis
This subtopic covers the essential procedures for locating and avoiding underground services during highways maintenance kerb and channel work. It focuses on the correct interpretation of public utility plans, safe site setup, and the systematic use of detection equipment to prevent service strikes, which could cause severe injury, disruption, and financial penalties. Mastery ensures compliance with health and safety legislation and industry best practice.
Key Concepts & Core Principles
- Types of kerbs: half-battered (standard for most roads), bullnose (used at junctions and pedestrian crossings), dropped kerbs (for wheelchair access), and specials (e.g., radius kerbs for curves). Each type has specific dimensions and applications defined in SHW Series 1200.
- Bedding and haunching: Kerbs are bedded on a mortar or concrete base (typically 100mm thick) and haunched with concrete to at least 150mm width on the back face. This provides lateral support and prevents movement from traffic loads.
- Drainage function: Channels (often combined with kerbs as combined kerb and drainage units) collect surface water and direct it to gullies. The gradient and alignment must ensure positive drainage without ponding.
- Setting out: Using string lines, levels, and templates to ensure kerbs are straight, at the correct height, and with consistent gaps (usually 10mm) for jointing. Accuracy is checked with a straightedge and spirit level.
- Jointing and finishing: Joints are filled with a semi-dry mortar mix and tooled to a smooth finish. Expansion joints are required at intervals (typically every 5-10m) to accommodate thermal movement.
Exam Tips & Revision Strategies
- Always cross-reference utility plans with on-site physical markers (e.g., lamp posts, valve covers) to build a more complete picture before using detection equipment.
- When demonstrating searching techniques, narrate your actions clearly to the assessor, explaining why you are choosing specific modes or scanning patterns — this showcases underpinning knowledge.
- In practical assessments, take time to perform a full visual inspection of the area for surface evidence (e.g., patched tarmac, recent excavations) that may indicate hidden services.
- Document all findings meticulously, even those you consider negative; clear records show you have followed a thorough process and can be vital evidence for the assessor.
- Always reference the hierarchy of avoidance: locate, identify, mark, and only then dig with caution.
- During assessments, vocalise your actions when using detection equipment to demonstrate understanding of the processes.
- Check that any service drawings are the most current revisions and that they cover the entire work area.
- If a service cannot be located but is suspected, demonstrate the use of trial holes and physical identification methods.
Common Misconceptions & Mistakes to Avoid
- Assuming that all underground services run in straight lines and at consistent depths, leading to missed shallow or diverted utilities.
- Neglecting to scan the area beyond the planned excavation footprint, thereby missing services that approach from adjacent zones.
- Misinterpreting the difference between passive and active signals on a CAT, resulting in false confidence when only one detection mode is used.
- Failing to check that the signal generator (Genny) is correctly connected to the service and set to the appropriate frequency for the type of line being traced.
- Relying solely on utility plans without verifying the actual location on site, as plans can be out of date or inaccurate.
- Assuming utility plans are fully accurate without verifying scale, date, or missing private services.
Examiner Marking Points
- Award credit for accurately identifying and correctly interpreting a minimum of five utility symbols from provided sample plans (e.g., gas, electric, water, telecoms, fibre).
- Evidence must demonstrate a logical sequence in site preparation: securing the work area, positioning warning signs, and setting up exclusion zones before any excavation.
- Candidate must correctly demonstrate the calibration and functional check of cable avoidance tools (CAT and Genny) before use, explaining the importance of each step.
- Look for a systematic scanning pattern covering the entire work area, not just the immediate dig zone, with clear verbal or written annotation of any located services.
- Answers or practical demonstrations must reference the use of utility plans in conjunction with detection equipment, showing how they correlate to confirm service locations.
- Award credit for accurately cross-referencing utility plans with on-site features to identify service routes, depths, and materials.
- Award credit for demonstrating correct preparation, including exclusion zone setup, appropriate signage, and functional checks of detection equipment.
- Award credit for methodical scanning in both power and radio modes, and for using the Genny to induce a signal on non-conductive services.