Case Study

Gillingham WRC – Caisson Shaft

V J Donegan & Co. Ltd delivered the civil engineering works to form Storm Tank No. 2 at Gillingham WRC via a caisson shaft solution, including detailed design, sinking operations, base plug construction and integration with existing site networks. The works provided a MEICA-ready, watertight storage asset to increase the site’s storm resilience and align with Wessex Water’s spill management strategy.

Client Scope

Wessex Water’s upgrade at Gillingham required additional storm storage capacity and compliant tie-ins to the existing process. The civils package comprised the design, supply and installation of a caisson shaft and base, with associated pipework interfaces, safe access, testing and handover documentation.

Details

Client: Wessex Water
Value: £450,000

Services Provided

Segmental Shaft Sinking

General Civil Engineering

Scope of Works

V J Donegan’s solution encompassed:

Detailed design responsibilities
Design of the caisson shaft, temporary works, anti-flotation measures and reinforced concrete base plug, working to provided levels, storage requirements and outline drawings.
Caisson procurement & sinking
Supply of caisson segments/components and sinking in controlled stages with set-out checks, sinkability controls and tolerances to land at design formation.
Base plug / RC works
Construction of an in-situ base plug (anti-flotation) and any jacking collar/upstands required; waterproofing and finishing to specified tolerances.
Connections & interfaces
Pipework connections to existing networks as defined in the Works Information/drawings, including penetrations, collars and reinstatement.
Temporary works & dewatering
Design/check, monitoring and sequencing of temporary works; groundwater and arisings management in line with environmental requirements.
Muck-away & materials management
Handling, classification and off-site disposal of excavated arisings; site housekeeping and segregation.
Quality, testing & handover
ITPs/hold points, watertightness checks (as specified), surveys/as-builts and H&S File submission.

Challenges & how we solved them

Ground & groundwater conditions
Managed sinkability and uplift risks through temporary works design, staged sinking, real-time monitoring and a conservative anti-flotation base plug design.
Live-site interfaces, tight working area
Sequenced deliveries and lifting operations to maintain safe access; coordinated tie-ins to minimise process disruption and protect existing assets.
Tolerances & watertightness
Early set-out verification and template checks for penetrations/ducts; inspection and test plan with hold points at critical stages (sinking milestones, base pour, connections).
Programme certainty under Option A
Activity-based planning aligned with the sinking methodology and concrete cure windows; proactive early-warning culture to protect time risk allowances.

Outcome / Client benefits

A MEICA-ready, watertight caisson storm tank integrated with existing networks, increasing site storm capacity and resilience.
Predictable delivery under NEC3 Option A through a clear Activity Schedule and defined change control.
Clean handover with as-built records, test evidence and an updated H&S File.