Records, GPR, CAT, trial pits—when and how to use.
Utility intelligence drives feasibility for HVM bollard arrays and crash-rated bollard foundations. Start with desktop records and statutory requests, then select GPR/EM with the right accuracy class. Plan trial pits, use consistent mark-out conventions, and log evidence that flows into clash decisions (243), shallow-base choices (244), and drainage (245). Tie permits and safety controls to MS/RAMS (721–722) and ITP (714). Include one-sentence context that naturally links upward to the parent hubs (this section and the chapter hub). Add SIRA context with a link to SIRA Bollards (UAE) when relevant. Link installation pages only if helpful: What to Expect and Installation Guide.
Important: This is a general guide. For live projects we develop a tailored
Method Statement & Risk Assessment (MS/RA) and align with authority approvals (e.g., SIRA) where in scope.
241.1 Desktop study sources
Pull base maps, as-builts, and statutory records. Note gaps for site proving (242). Early utility intel steers HVM bollard routes and whether a crash rated bollard needs shallow foundations (244).
Begin with recent as-built drawings, GIS base maps, and utility search portals to assemble a first “conflicts map.” Record obvious risk zones—corridors full of ducts, chambers, or PT slabs—and flag unknowns for proving. This desktop picture shapes early array sketches in arrays & spacing and helps decide if you should bias toward shallow systems (244) near service-dense frontages (234).
Annotate each source with date, accuracy, and disclaimers. Where records conflict, capture both and add an assumptions register entry so later proving and witness procedures aren’t derailed by surprises.
| Aspect | What matters | Where to verify |
|---|---|---|
| Performance | Tested system (bollard + footing) | Crash standards overview |
| Operations | Duty, fail-state, safety devices & measures | Installation Guide |
241.2 Statutory undertaker requests
Submit marked plans with clear extents and dates. Track replies and disclaimers. Outcomes gate HVM bollard excavation (611) and crash rated bollard socket viability (332).
Issue a clean red-line plan showing proposed arrays and excavation envelopes, with scale, north arrow, and date. Log each undertaker’s response, SLA, and “no liability” clauses. Where utilities refuse to mark private services, plan additional proving (242) before freeze dates in the ITP. Negative responses or “records not held” should trigger design buffers (241.6) and a resurvey point (241.9).
If working under UAE authority approvals, add a short note in the submission index and link to SIRA Bollards (UAE) for reviewers unfamiliar with HVM utility-depth constraints.
241.3 GPR & EM methods
Pick GPR for non-metallics, EM for conductive runs (242). Combined surveys prevent HVM bollard clashes and narrow crash rated bollard base choices (422).
HVM layouts often sit above mixed services: water, telecoms, LV/MV, and drainage. Ground-Penetrating Radar (GPR) detects non-metallic routes and voids, while Electromagnetic (EM) locators and a Cable Avoidance Tool (CAT) trace conductive services. Commission both where feasible, then reconcile anomalies on a single plan per overlay standards (936) so selection in depth & utilities choices (422) is evidence-led.
Note site factors that degrade signals—reinforced slabs, saturated ground, or steel street furniture—and book proving pits (241.4) where GPR “low confidence” bands overlap proposed deep sockets (332).
241.4 Trial pits & permits
Hand-dig/scan first; permit, barricade, and photograph (716). Findings confirm HVM bollard set-out (612) and de-risk crash rated bollard pours (624).
Adopt a “scan—hand dig—verify” routine: CAT sweep and GPR first, then hand-dig with insulated tools inside a marked exclusion zone. Use a Permit to Work (PTW) and method statement controls from MS format (721) and risk assessment (722). Photograph each exposure with a wide→detail set and a depth scale, then close with suitable backfill and plates. Feed verified depths to setting-out (612) and pour planning (624).
241.5 Mark-out conventions
Use color codes/arrows, depth notes, and dates (934). Clear marks keep HVM bollard spacing accurate (232) and protect crash rated bollard cages (621).
Adopt a simple legend: color by utility type, arrows for flow, text for depth (e.g., “TEL 0.6 m 2025-10-22”). Date every mark-out and initial the surveyor. Avoid painting over expansion joints or heritage paving (316). Transfer marks to a controlled ducting/trench detail (934) and keep a photo/redline logbook (937) so later shifts (241.9) are auditable.
241.6 Accuracy classes
Record confidence bands (e.g., PAS128). Lower class = bigger buffer. Buffers affect HVM bollard centers and crash rated bollard edge distances (331).
Document the survey’s accuracy class (e.g., QL-D desktop, up to QL-A verified by exposure). Use the class to set design buffers: reduce clear-gap claims in clear-gap calculations (322) and increase edge distances for foundations (331). Where classes vary across a frontage, note it in the ITP hold points and schedule proving ahead of concrete works.
241.7 Evidence logging
Geo-tag photos, sketches, and plan overlays (716, 248). Evidence accelerates HVM bollard reviews and crash rated bollard approvals (938).
Standardize filenames and embed EXIF GPS/time. Pair each photo set with a keyed plan (936) and upload to the submission pack (938). This speeds client and authority reviews, and supports later handover (639). Use the evidence templates (916) to keep captions, depths, and utility types consistent.
241.8 Safety controls
Adopt LOTO, CAT/Gen checks, and exclusion zones (723). Controls protect HVM bollard crews and the future crash rated bollard asset.
Before any cut or dig, brief a toolbox talk (723), confirm zero-energy with LOTO (725), and verify with CAT/GEN checks. Maintain barriers around open pits, protect reinstated surfaces, and log near-misses (727). Good controls prevent service strikes and safeguard long-term reliability of the installed system.
241.9 When to resurvey
Rescan after design shifts or conflicting finds (216, 617). Updated proofs keep HVM bollard drawings honest and crash rated bollard depth picks valid (422).
Trigger a resurvey when layouts change, new utilities appear, or excavation reveals conflicts. Update the “key plan” and notify stakeholders via the change log (718). Close the loop by re-issuing affected drawings in the submission index (917) and adjusting foundation choices in 422.
Related
External resources
- NPSA — Hostile Vehicle Mitigation
- FEMA 426 / DHS — Reference Manual
- BSI — Impact Test Specifications (overview)
241 Utility Search Methods — FAQ
What’s the practical difference between GPR, EM, and a CAT scan?
GPR “sees” changes in subsurface materials (good for non-metallic pipes and voids). EM detects electromagnetic fields from conductive services. A CAT is a field EM receiver used to quickly trace and avoid live cables; it complements, not replaces, a full survey.
When do we need trial pits if we already have PAS 128 survey data?
Use trial pits at high-risk locations (e.g., deep sockets, congested corridors) or where the accuracy class is below QL-A. Trial pits verify depth/position before setting-out and concrete pours.
How do survey accuracy classes change our foundation choice?
Lower confidence means bigger buffers. You may shift bollard centers, move to a shallow foundation class, or relocate arrays to avoid services. Record the rationale in the ITP and change log.
What should be in the evidence pack for utility proving?
Geo-tagged photos (wide→detail), marked plans with dates/depths, survey class notes, and any trial-pit logs. File them against the submission index so reviewers can trace decisions.