Choosing deep/shallow around real underground constraints.
Utilities often dictate foundation depth. This page sets a clear path for choosing deep sockets versus shallow slabs/rails, weighing structural trade-offs, drainage constraints, and review/approval implications. We show mitigation options when clashes are found (241–243, 335) and how to present evidence, costs, and programme impacts. Link decisions to shallow foundations (244), foundation types (332), rating-critical dependencies (421), and as-built proof (731, 938) for HVM bollard projects. 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.
422.1 Deep vs shallow decision
Select deep sockets where feasible; choose shallow slabs/rails when utilities clash. Decision must keep HVM bollard energy paths equivalent to the certified crash rated bollard (244, 332).
Start by confirming the embedment depth required by the certified system. Deep sockets resist overturning through depth and soil fixity; shallow rails/slabs spread load across a wider footprint to bypass services. The chosen option must preserve the certified crash rating and permitted clear-gap rules.
Where corridors are service-dense, a shallow solution (e.g., precast or cast-in-place rail module) can be selected if the vendor provides certificate evidence or an approved equivalence. If deep is feasible without affecting utilities, it often remains the simplest path for buildability and inspection.
| Aspect | What matters | Where to verify |
|---|---|---|
| Performance | System equivalence (bollard + footing) | How to read ratings |
| Dependencies | Depth, geometry, group stiffness | Rating-critical dependencies |
| Constructability | Utility avoidance, access, curing | Foundations, concrete & alignment |
422.2 Utilities conflict options
Prove services, then reroute, sleeve/protect, or adopt shallow solutions. The chosen path must not widen HVM bollard clear gaps or undermine the crash rated bollard base (241–243, 335).
Follow a search → detect → prove & classify sequence. Use PAS 128 techniques (GPR/EM) and trial pits to obtain positive identification. Then either reroute the service (preferred if feasible), provide engineered protection/sleeving, or shift to a tested shallow rail/slab detail that keeps the defended line intact.
When adopting a shallow system, maintain clear-gap and array geometry; do not “weave” around services in ways that create drive-throughs. If in Dubai, reference SIRA expectations early for approvals and witness points.
422.3 Structural trade-offs
Shallow bases spread load; deep sockets anchor rotation. Document how the HVM bollard still meets penetration/deflection proven for the crash rated bollard (331–333).
Deep sockets rely on depth to resist base rotation and form a plastic hinge in the post above ground. Shallow rails/slabs build group stiffness across multiple posts to achieve comparable moment resistance. Your calculations should show comparable penetration and residual set to the tested article; include soil class and any punching shear checks for slabs over utilities.
422.4 Approval implications
Note authority permits and witness expectations for changed bases. Clear rationale keeps HVM bollard submittals defensible against crash rated bollard evidence needs (133–134, 938).
Changing from deep to shallow (or vice-versa) can trigger revised permits, witness procedures, and updated drawings. In UAE contexts, engage SIRA early to align on evidence and witness points; provide a concise base-equivalence note with cross-references to certificates and calculations.
422.5 Cost & programme impacts
Compare excavation, reroutes, precast lead-times, and traffic management. A transparent plan avoids late HVM bollard downgrades of the crash rated bollard scope (855, 338).
Itemize service diversions, night-work, traffic management, precast fabrication, and float for authority review. Shallow rails can reduce deep excavation but introduce lead-time and lifting/plant costs; deep sockets may be cheaper if utilities are sparse. Use the Programme & Phasing page and Value engineering guidance to keep scope on track without performance downgrades.
422.6 Drainage constraints
Bases must integrate sumps/outfalls; water floatation can defeat sockets. Drainage-first keeps HVM bollard reliability and the crash rated bollard foundation durable (245, 334).
Design sumps/outfalls sized per Drainage Sump Sizing, add weep holes and backflow protection, and verify hydrostatic uplift for chambers and sockets. In high groundwater, include a buoyancy check and, if required, ballast or tie-downs to prevent socket floatation. Poor drainage leads to corrosion, misalignment, and failed SAT.
422.7 Evidence for reviewer
Provide utilities surveys, base calcs, and certificate links showing equivalence. Evidence bridges HVM bollard geometry to the crash rated bollard test (431, 414, 444).
Bundle a reader-friendly pack: utilities detection results, trial-pit photos, set-out with depths, foundation calculations, and the relevant certificate pages. Cite any equivalency caveats and link evidence & documentation pages. Make it easy to trace assumptions back to the tested configuration.
422.8 As-built proof requirements
Submit photos, set-out surveys, cube tests, and depth checks. Proof that the HVM bollard matches the approved crash rated bollard base (626, 716, 731).
Capture datum & alignment checks, pour records/cube tests, depth/cover photos with scale, and a redline as-built. A photo standard plus a short conformance note streamlines SAT and handover.
422.9 Example selection matrix
Matrix columns: utilities risk, programme, drainage, approvals, cost, and compliance. Scoring shows why the chosen HVM bollard base preserves the crash rated bollard performance (235, 339).
Rate each option 1–5 across the columns, weight “compliance/equivalence” highest, and document the winning choice with a signed decision record. Cross-link to the Purpose/Tier Matrix and Decision Flow so reviewers can follow the logic.
Related
External resources
422 Depth & utilities choices for Crash-Rated Bollards — FAQ
How do I decide between a deep socket and a shallow rail/slab?
Confirm utility positions first. If a deep socket clashes, choose a tested shallow rail/slab that preserves rating, clear-gap, and group stiffness. Document equivalence with calculations and certificate references.
Will a shallow foundation change my project approvals?
Possibly. A change of base can trigger revised permits, authority review, and SAT witness points. In Dubai, consult SIRA early and include a concise base-equivalence note in the submission.
What drainage details prevent socket floatation and corrosion?
Size sumps/outfalls, add weep holes and backflow protection, and check buoyancy where groundwater is high. Provide ballast or tie-downs if needed and record evidence during SAT.
What proof should be in the as-built pack?
Surveyed depths/offsets, trial-pit photos, pour/cube records, alignment checks, and redlined drawings—enough to show the installed base matches the approved foundation detail.