Managing water to protect pits and foundations.
Groundwater can derail pits and sockets if unmanaged. Assess groundwater early (423), choose sumps or wellpoints, and secure discharge permits. Size pumps with standby capacity, control silt, and mitigate uplift/float risks for HVM bollard pits (334, 245). Define monitoring and shutdown procedures, and file records/approvals that roll into commissioning readiness and authority submittals (631, 717, 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.
614.1 Assessing groundwater
Check levels/seasons and inflow rates (423). Assessment drives HVM bollard pit design (334).
Start by reviewing seasonal trends, nearby water bodies, and recent dewatering on adjacent plots. Confirm the groundwater effects (423) through site logs and trial pits; record the static level and a simple bail test to estimate inflow. Tie the findings to foundation selection (e.g., foundation types 332) and the drainage concept (334). Where uncertainty persists, assume the credible worst case for sizing and approvals.
Document soil permeability, anticipated infiltration capacity estimates, and utilities constraints (see 617 Utility Conflicts). These inputs steer whether a simple pit sump is enough, or a perimeter drawdown via wellpoints is needed.
| Aspect | What matters | Where to verify |
|---|---|---|
| Performance | Tested system (bollard + footing) | Global crash ratings |
| Design | Drainage strategy & soil data | Drainage for HVM/Crash-Rated Bollards |
| Execution | Sumps/wellpoints method | Excavation/Drainage/Ducting |
614.2 Sumps & wellpoints
Choose method by drawdown depth. Systems keep crash rated bollard works dry.
Use a local sump with automatic pumps when inflow is modest and soils are cohesive enough to stand with shoring (see 613 Excavation & Shoring). Where the water table sits above formation level or inflow is continuous through granular soils, a wellpoint system provides even drawdown. Keep intakes away from utility protection zones and ensure any shallow foundations are coordinated with the dewatering geometry.
Protect pit edges and maintain safe access; dewatering can induce settlement. Re-check set-out and levels before cages or sleeves are fixed (see 626 Datum & Alignment Checks).
614.3 Discharge routes & permits
Secure legal outfalls and silt control (218, 245). Compliance shields HVM bollard sites.
Confirm your lawful discharge point (storm sewer, temporary settlement tank, or tanker off-haul) and obtain the necessary authority submittals (717). Many jurisdictions require suspended solids limits; deploy silt socks/baskets or lamella tanks before discharge (see 245 Drainage strategy). In the UAE, align with environmental and municipal rules and, where the scope touches security assets, note any SIRA implications with a concise pointer to SIRA Bollards (UAE).
614.4 Pump sizing & standby
Size duty/standby with alarms. Sizing prevents crash rated bollard flooding.
Estimate peak inflow (trial-pit bail rate × safety factor) and select a duty pump with head to overcome hydrostatic head plus line losses. Add a witness script for alarm/failover tests. Provide a fully valved standby on the same header or specify a SLA for rapid swap-out. Protect power with an RCD/RCBO and safe cable routing (see 514 Electrical Supply & Protection).
614.5 Silting & filtration
Install socks, tanks, or filters. Filtration protects HVM bollard equipment.
Use silt socks/baskets at outfalls and keep sump strains clear to prevent pump damage. Where fines are high, add a settlement tank or bag filter and monitor clarity using a simple turbidity tube. Route clean water away from pits to prevent recirculation. Coordinate with long-term drainage (334) and any equipment sumps (see 616 Drainage Pits/Sumps for Equipment).
614.6 Slab uplift/float risks
Check buoyancy against pour timing (333). Checks keep crash rated bollard bases seated.
Before pouring, confirm the concrete weight (plus rebar and any ballast) exceeds uplift from groundwater at seasonal high. Perform a quick buoyancy check using water level, pit footprint, and formation depth; if margin is low, delay the pour, deepen the formation, or add temporary hold-downs. Tie this to 333 Design checks and note any drain-down time assumptions in the pour plan.
614.7 Monitoring regime
Log levels/flows and turbidity. Monitoring proves HVM bollard controls work (716).
Adopt a simple log: water level vs datum, pump run hours, estimated flow, and clarity checks. Capture geo-tagged photos of sump levels pre- and post-pour (see 937 Photo/Redline Logbook) and store evidence to the 716 Evidence Capture Standards. For automatic systems nearby, protect panels and cabling from spray and ensure health pings remain green during works.
614.8 Shut-down procedures
Safe stop, isolate, and secure hoses. Procedures avoid crash rated bollard washouts.
Shut down with a clear sequence: cut inflow near source if possible, stop pumps, isolate valves, and secure discharge hoses to prevent back-siphon. Install a backflow preventer (NRV) where outlets are below flood risk levels. Update the 631 Pre-Commission Checklist so reinstatement works don’t trap water in sleeve annuli or service ducts.
614.9 Records & approvals
File permits, logs, and maps (938). Records speed HVM bollard approvals.
Maintain a concise pack: permit/NOC copies, dewatering layout (sumps/wellpoints), log sheets, discharge test results, and as-built updates. Index them per 938 Submission-Pack Guidance and roll forward into closeout (e.g., 736 Handover Pack Index). This reduces queries at 638 SAT/Witness Procedure and supports any environmental inspection.
Related
External resources
- NPSA HVM — risk context & site planning
- FEMA 426 — site & building protection
- BSI — vehicle security barrier test specifications
614 Dewatering & Groundwater — FAQ
How do I decide between a sump and a wellpoint system?
A sump with auto-pumps works when inflow is modest and the excavation can stand with shoring; wellpoints suit granular soils or when the water table sits above formation and continuous drawdown is required. Choose based on inflow tests, soil type, and the target drawdown depth.
What permits are typically required to discharge dewatering water?
Most authorities require a discharge permit or NOC that sets limits for suspended solids and where you can discharge (e.g., storm sewer or tankering). Include silt control and submit logs/results in your submission pack to speed approval.
How do I prevent slabs or sockets from floating during a pour?
Check buoyancy: ensure the weight of fresh concrete and steel exceeds uplift from groundwater at seasonal high. If margins are low, deepen formation, stage the pour, add ballast/hold-downs, or maintain temporary dewatering until concrete gains strength.
What should I monitor during dewatering?
Log water level vs datum, pump hours, approximate flow, and clarity/turbidity. Add geo-tagged photos and keep evidence against the ITP. Monitoring proves controls work and helps resolve queries at SAT/witness stages.