Bicester STW Growth

Envolve was awarded the Civil Works package which primarily comprised of the Design and Build of a new Activated Sludge Process Lane (ASP), Final Settlement Tank (FST), Flow Split Chamber and associated cross site pipework.

Envolve competitively tendered the Design Package, and awarded it to Hydrock Consulting Engineers. envolve together with their design partners carried out a Value Engineering exercise on the Outline Design and identified a series of areas where the tender concept could be rationalised, simplified and developed, to arrive at an optimum design. The permanent design was developed alongside the temporary works designs, ensuring a ‘whole project’ approach to design.

Flexible, waterproof joints between the existing ASP lanes and the new lane were designed to allow the new structure to remain water-tight whilst accommodating the predicted 10mm settlement. Envolve worked closely with the Hydrock Geotechnical engineer to achieve an optimal batter design for the bulk dig , carrying out ‘live’ ground investigations as the bulk dig proceeded ensuring no more material was removed than absolutely necessary.

The original tender concept for the FST was to replace the virgin ground material down to the underlying limestone bedrock, incorporating a 1m thick stone layer and 2m mass concrete anti-floatation plug underneath the FST structure. This would have generated over 1500m3 of un-necessary muck away and used over 1000m3 of concrete as deadweight against floatation, as well as 1000t of structural fill. Envolve and Hydrock pursued a tension pile solution, utilising 47No piles bored down into the limestone. These piles anchored the FST to the bedrock and generated good environmental savings as well as being a more cost effective solution.

The piles were constructed over a 2 week period before the RC structure commenced. Anchor nuts and load plates connected the base slab to the piles ensuring anti-floatation resistance and also facilitated a thinner base slab. The modified design proved successful, especially considering the proximity to the adjacent lake and the risk of installing a 6m deep cofferdam within a few metres of the bank that was mitigated through challenging the initial design concept.

The Design and Build model proved very successful at Bicester STW. Our client was ensured the best possible price, whilst best practice environmental and quality procedures were maintained. The Design programme was extremely tight, with Start on Site within 2 months of being awarded the contract. The envolve design team worked very closely with the MWHT Design team to ensure timely issue and approval of drawings and calculations.

• Safety: Outstanding H&S standards
• Quality product that met the design brief
• Time: Project delivered on programme.
• Cost: Excellent commercial management, project delivered on budget, CEs tightly controlled.

“The exceptional work you have done penetrates deep into the wider conversations” – Simon Wright, MWHT Director

“I just wanted to drop you a note to compliment all of your efforts with respect both SHEQ performance and programme performance to date” – Paul Bresnan, MWHT Managing Director

“The project has been so successful so far which makes the operational world easier. Great work, thank you” – Amanda Smith, Operations Manager, Thames Water