When shallow options work; structural and rating constraints.
Where deep sockets clash with utilities, shallow systems keep HVM performance achievable. We outline viable scenarios, depth limits, and load paths, plus ground-improvement options. Plan coexistence with services (243), integrate drainage (245), and specify fixings/tolerances that survive SAT checks (626, 638). Compare pros/cons to deep options (332) and assemble evidence for submittals (431, 938). 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.
244.1 When shallow is viable
Use when deep sockets clash with services or slabs (243, 216). Maintain HVM bollard clear gaps (232) and confirm the crash rated bollard family offers a certified shallow variant (415).
Shallow bases are appropriate where utility corridors, depth constraints, or existing site constraints prevent standard embedment. The key is equivalence: select a product family/variant whose certificate explicitly covers the shallow foundation class, and design the array to keep the clear-gap within limits.
Check adjacent slabs (PT, suspended) and easements. Where a shallow base crosses a groundwater/soil zone, durability and bearing checks become governing. If approvals are required, note UAE SIRA acceptance of shallow variants for the stated rating and footing class.
| Aspect | What matters | Where to verify |
|---|---|---|
| Performance | System tested as shallow variant | How to read crash ratings |
| Spacing | Pass/fail by clear-gap | Spacing rules |
| Constraints | Clash and depth class mapping | Utility search methods |
244.2 Typical depths & limits
State depth ranges and soil prerequisites (423). Limits inform HVM bollard array spacing and crash rated bollard pass/fail margins (414).
Shallow systems (often rails/plates) typically range ~120–350 mm overall construction depth, but actual limits depend on the certified variant and bearing capacity. In weak subgrades, the governing limit may be serviceability (durability/settlement) rather than ultimate resistance. Keep ULS/SLS checks in one calc pack.
Depth also controls finish interfaces (thresholds, curb faces) and tolerance for paving buildup. Where PT slabs exist, add a strike-avoidance plan and confirm minimum cover above tendons per the engineer’s PT drawings.
244.3 Load path basics
Spread load via rails/plates into concrete sub-slab. Ensure HVM bollard group behavior is checked (331); confirm crash rated bollard anchors match certificate (421).
Shallow bases distribute impact via steel rails/endstops into a reinforced pad or structural topping. The group action of adjacent posts is critical: edge rails and anchors must match the rating-critical dependencies. Do not substitute anchor grades, spacing, or edge distances without equivalence testing or vendor-approved engineering.
Provide continuous reinforcement across the rail footprint and detail anti-uplift where rail reactions go into tension. For suspended slabs, check punching/shear and vibration limits at operating frequency.
244.4 Ground improvement options
Lean mix, micros, or geo-grids increase capacity. These keep HVM bollard layouts intact and make a shallow crash rated bollard credible.
When subgrade CBR is low or the water table is high, consider a lean-mix blinding to seal, geogrid-reinforced base layers to spread load, or micro-piles tied into a thin raft. Each option must be compatible with the certified shallow variant—record any departures and obtain vendor sign-off. Where feasible, prefer methods that improve bearing uniformly rather than introducing point-stiffness that could skew load paths.
244.5 Utilities coexistence
Respect sleeves, offsets, and inspection access (241–243). Coexistence allows HVM bollard lines to hold; keep crash rated bollard fixings outside no-go zones.
Translate survey results into a depth-class layout, maintaining easements and inspection bands around red-zone utilities. Keep any anchors, hold-downs, and rail fixings outside no-go envelopes. Where shared corridors are unavoidable, add protective sleeves and serviceable covers coordinated in the ducting & trench details.
244.6 Drainage around shallow bases
Prevent ponding at plate edges; add outfalls (334, 245). Good drainage protects HVM bollard finishes and crash rated bollard hardware (361–362).
Rail edges can trap water. Provide falls away from plate edges, add outfalls to a drainage strategy, and isolate dissimilar metals. Where bollard heads include seals/caps, specify inspection intervals in the O&M. For automatic variants, keep cable/conduit entries above water lines and route to sumps with maintenance access.
244.7 Fixing & tolerances
Template anchors, verify level/plumb (612, 626). Tight tolerances keep HVM bollard gaps; shallow crash rated bollard rails meet alignment rules (315).
Use factory templates or laser-cut jigs to set anchor grids. Check datums & benchmarks, then verify rail level (± tolerances) before pour or grout. After installation, measure alignment and confirm the in-service tolerances preserve clear-gap. Record checks for SAT (638).
244.8 Pros/cons vs deep
Pros: avoids clashes, faster install. Cons: more concrete, strict detailing. Choose what preserves HVM bollard performance and crash rated bollard certification.
Pros. Minimizes utility diversions, reduces excavation risk, and can accelerate programmes. Often better for heritage or constrained sites.
Cons. Tighter detailing, potential for increased concrete/steel, and heightened sensitivity to subgrade quality and water. May carry stricter maintenance to keep joints and coatings sound.
Use the foundation types comparison to document the trade-offs and confirm the chosen class aligns with rating dependencies.
244.9 Evidence & approvals
Provide calcs, details, and photos (716, 938). Evidence shortens HVM bollard reviews and secures crash rated bollard acceptance (431).
Assemble an evidence pack: certified datasheets, shallow-variant certificates, drawings (plans/sections), rebar schedules, setting-out and tolerance checks, and a test & inspection plan. Include georeferenced installation photos and a concise submission index. For UAE projects, cross-reference SIRA acceptance for the stated rating and footing class.
Related
External resources
- NPSA: Hostile Vehicle Mitigation
- ASTM F2656 Vehicle Impact Test Standard
- BSI Vehicle Security Barriers — Impact Test Specifications
244 Shallow foundations for Crash-Rated Bollards — FAQ
When is a shallow mount foundation acceptable for crash-rated bollards?
When deep embedment clashes with mapped services or structural slabs and the selected product family has a certified shallow variant for the required rating. Confirm spacing/clear-gap, soil/groundwater conditions, and that anchors/rebar match the certificate.
How deep are typical shallow systems?
Common ranges are roughly 120–350 mm overall construction depth, but limits are product- and soil-dependent. Always check the certificate, bearing capacity, and ULS/SLS criteria; PT slabs may further restrict allowable depth.
Do shallow rails affect certification or rating?
Yes. Certification relies on rating-critical dependencies such as rail geometry, anchor grade/edge distances, and concrete/rebar specs. Substitutions require documented equivalence or manufacturer approval to keep the stated rating valid.
What should we do if a shallow base still conflicts with a red-zone utility?
Maintain no-go envelopes and easements. Shift the array if feasible; otherwise add sleeves/protection, adjust plate geometry, or introduce uniform ground improvement. Record decisions and protective details in the submission pack for approval.