Holdenhurst WRC – Tank 13 & 14 Access Bridge
A 60-metre modular access bridge, fabricated in-house and installed across two live outlet channels in a single day.
The Brief
Woodhams delivered the Tank 13 & 14 steelwork package as part of the AMP7 Phosphorus Removal and Storm scheme at Holdenhurst Water Recycling Centre for Wessex Water — a major treatment upgrade on a live operational site in Bournemouth.
The scope was a new 60m access bridge and walkway spanning the Tank 13 and 14 outlet channels, providing permanent safe access along the channels for operation, inspection and maintenance.
Working over open channels on a live site meant the installation had to be planned to keep work at height, and time spent over the water, to a minimum. The steelwork also had to accommodate dimensional variation in the existing tank walls and clashes with existing pipe supports — conditions that could not be fully surveyed before fabrication began.
The Solution
Modular fabrication and in-house build. Woodhams designed and fabricated the bridge as ten individual 6m modular sections, giving a continuous 60m run across the two outlet channels. Each section was formed from a galvanised steel frame in grades S275 and S355, fitted with 41/100 open-mesh flooring and mesh infill handrailing, together with the stair and ladder access, landings and self-closing safety gates required to complete the walkway. All steelwork was fabricated entirely in-house at Woodhams’ own facility, giving the team full control over quality, tolerances and programme.
Building up at low level. Each section — typically 490 to 500kg — was fabricated, galvanised and then assembled and fitted out in the site laydown area, complete with flooring and handrailing, before being craned into place. Building the sections up on the ground meant the bulk of the fit-out was carried out safely at low level rather than over the open outlet channels, reducing work at height and improving both safety and quality.
Detailing for tolerance. The steelwork was deliberately detailed slightly narrower than the channel openings, with adjustable supports, so that dimensional variation in the existing tank walls and clashes with existing pipe supports could be taken up accurately on site. The structure could absorb the tolerances of the existing tanks without rework.
Transportation and installation. Once each section had been fitted out and checked, the units were transported across the live site and lifted into their final position on the channel walls using mobile craneage. Careful lift planning and sequencing allowed the sections to be landed and connected efficiently, with base plates fixed down using resin anchors and adjustable supports set to suit the existing structure. Thanks to the modular, pre-fitted approach, Woodhams installed the full 60m bridge in a single day, followed by three days of secondary works and snagging to complete connections, access components and final adjustments.
Access, safety and compliance. The bridge was designed and delivered in line with Wessex Water standards and the WIMES 9.02 specification for permanent access fabrications, together with the Wessex Water amendment to WIMES 9.02 and DS 220 access and protection requirements. All steelwork was hot-dip galvanised to BS EN ISO 1461 for long-term durability in the wastewater environment, and fabricated and erected to Execution Class 2 in accordance with BS EN 1090. The open-mesh flooring, mesh infill handrailing, stairs and self-closing gates provide a safe, compliant and durable access route for operational and maintenance teams.
The Result
Woodhams fabricated and installed a continuous 60m galvanised walkway across the Tank 13 and 14 outlet channels, with the full bridge installed in a single day and secondary works and snagging completed over the following three days.
By fabricating the bridge in-house and building it up as pre-fitted modular sections, Woodhams was able to offer real buildability benefits to the project. The modular approach moved the majority of the flooring and handrailing installation off the live channels and down to ground level, reducing work at height and improving both safety and quality. Detailing the steelwork with adjustable supports and slightly reduced widths meant the structure could absorb the tolerances of the existing tanks without rework on site, giving a fast, controlled installation that minimised time spent working over and around the operational treatment process.
The completed structure provides Wessex Water with safe, durable and compliant permanent access along the channels, delivered with minimal disruption to the live site.
Project Gallery
