|Client:||London Borough Council Uxbridge|
|Consultant Engineer:||McAdam Design|
|Main Contractor:||Farrans Construction (Design & Build)|
|Dimensions:||40m long and up to 4m high|
Description of Works
Farrans Construction was the main contractor working on a design and build framework to construct the new primary school for the London Borough Council of Uxbridge. As part of these works a retaining wall was required to support a road and car parking adjacent to the school.
The retaining wall, which was 40m long and up to 4m high was originally designed as a traditional reinforced concrete retaining wall. In early January 2014 Richard McCullough the design coordinator for Farrans Construction approached Retain Solutions Ltd to value engineer alternative solutions.
As part of the feasibility analysis Retain engineers produced several separate suitable options and costs for consideration, including a modular block retaining wall, Greenface, their vegetated reinforced soil solution, Permacrib, their timber crib wall and lastly a stone filled gabion retaining wall.
The client specified the gabion wall, and Retain carried out detailed design including calculations and drawings for the approval of the engineer, McAdam Design. The specification proposed by Retain was the superior welded mesh gabion with a 4mm diameter wire front and rear face to provide a more robust face. Selected stone was imported and hand placed inside the gabion to provide a fair face finish.
The gabion wall was built in May 2014 within one week on site, ahead of programme and on budget. The client and Farrans project manager, David Bolton, was impressed with the final solution and approached Retain to redesign a small amphitheatre adjacent to the play area to provide a similar finish to the completed gabion wall.
Retain`s Chartered Engineer Ciaran McGurk was able to design a three tiered circular amphitheatre using standard 4mm welded mesh gabion baskets. These standard units were modified on site to provide the semi-circular structure. Retain also designed, supplied and fitted the wooden seating on the three tiers. The process from original proposal to completion on site was less than 3 weeks, and included original sketch for approval, full design and procurement to construction on site.
As the school was to be handed over for the start of September, Ciaran McGurk was approached by David Bolton to review and provide a solution which had arisen when trying to complete the road works adjacent to the site boundary. The new road was located approximately 1.5m below the existing ground. We were unable to regrade the ground as a line of trees, and their roots had to remain undisturbed. The actual working space was restricted to 600mm, which meant that there was insufficient space for a reinforced concrete, gabion or crib wall. Retain surveyed the area and were able to design a mass gravity structure using Allan block, split faced blocks backfilled with “no fines” concrete which was placed behind the existing kerb and only required minimal disturbance of the cut embankment adjacent to the trees. All works were completed for the handover to allow the school to open, as planned, in September 2014.
This contract showcased:
- Our experience and ability on Design & Build Contracts
- Design substitution of original consultant design with more economical solution
- Provision of 4 different design solutions all with differing benefits for the design and build team
- Design of a bespoke gabion solution utilising a stiffer front face. This resulted in a more robust design which was easier to build.
- Following completion of the original contract with budget and timescale two new projects on the same site were discussed.
- The first additional project involved the design and build of an architectural feature using gabions to provide a semi-circular amphitheatre with wooden seating.
- From design to completion this took 3 weeks.
- The need for the second project arose as handover was required for the school handover in September 2014. The main contractor identified a need for embankment retention at the entrance.
- Again the process from Design to Construction was very short.
- Modular block with “No fines” concrete back fill was specified by Retain and completed in time for the September school handover
- Partnership with main Design & Build contractor ensured the timely handover
- Partnership with the main Design & Build contractor led to two further mutually beneficial contracts.