Engineering design for tunnelling dewatering treatment: flow estimation, treatment-train sizing, equipment selection and discharge-consent compliance.
The application overview — scope, treatment process and benefits.
On-site pilot trials confirm performance and set dosing and media-change rates.
Pre-assembled, relocatable treatment equipment for construction sites.
The parent hub for construction and quarry dewatering treatment.
Designing dewatering treatment for a tunnel drive starts with an honest estimate of how much water will arrive and how dirty it will be, then sizes each unit operation for the peak while keeping good turn-down. This guide sets out the design basis, the flow and quality parameters we work to, the treatment train and the monitoring needed to satisfy a discharge consent.
What We Size The Plant For
The governing case for a tunnel plant is the combined peak: natural groundwater ingress plus construction process water (probe drilling, grouting return, wheel-wash and invert cleaning). We work with the geotechnical team to bracket ingress from packer tests and the ground investigation, add the process-water schedule, and apply a contingency for fissure crossings. The plant is then sized for that peak but specified to turn down to base flow without short-circuiting the clarifier.
Both the peak and the diurnal average are fixed so pumps, clarifier rise rate and dosing all hold up across the range.
Design TSS, pH and any contaminant ceilings are set from the GI and previous land-use desk study.
Modular clarifier cells and variable-speed dosing keep performance at low flow between fissure crossings.
Typical Tunnelling Dewatering Values
Indicative figures we use for early sizing — always confirmed by site sampling and the ground investigation.
| Parameter | Typical Range | Treatment Driver |
|---|---|---|
| Combined flow | 10–200 m³/h | Pump and clarifier sizing |
| Suspended solids | 500–5,000 mg/L | Grit removal + clarification |
| pH (cement-affected) | 9–12 | Acid / CO² correction |
| Discharge TSS consent | ≤ 30–50 mg/L | Filtration polishing |
| Discharge pH consent | 6–9 (typical) | Closed-loop pH control |
| Hydrocarbons | site-specific | Carbon / oil separation |
Unit Operations In Sequence
A buffer tank smooths the swings between fissure crossings so dosing and clarification see a steady load.
Cyclones drop out sand before it reaches pumps and plates.
Charge neutralisation and flocculation grow settleable floc from colloidal rock flour.
Inclined plates achieve a high settling area for compact TSS removal.
Closed-loop dosing holds the final pH inside consent.
Media or disc filters polish to the discharge TSS limit.
Proving The Discharge
Specified for This Duty
Coarse and fine screens remove debris, formwork waste and timber that would otherwise blind pumps and settlement plant.
View EquipmentHydrocyclones and sand traps strip abrasive sand and grit to protect pumps, valves and downstream media.
View EquipmentHigh-rate inclined-plate settlers achieve a large settling area in a small footprint for rapid TSS reduction.
View EquipmentAutomated acid/alkali dosing brings high-alkalinity or acidic groundwater within consent before discharge.
View EquipmentInline coagulant and polymer dosing destabilises colloidal fines so they settle or filter out reliably.
View EquipmentMultimedia and pressure filters polish settled water down to low single-figure NTU for tight consents.
View EquipmentBack to the Application
Send us your flow and water-quality data and we will propose a sized, compliant treatment train.
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