Project: Waste Water Treatments Works at Hyndburn
Customer: United Utilities
Main Contractor: HMB Alliance
In 2003 the HMB Alliance were upgrading Hyndburn WwTW at Great Harwood, as part of a £10 million water treatment project. This required a 14.0m long, 3.0m wide, 10.0m deep trench to carry large pipe runs from the main settlement tank.
Aside from the high loadings generated by the fairly poor ground conditions (granular fill with a mid-level water table) and the huge depth, the excavation had another problem – it took a turn through 45º at the centre.
HMB Alliance had come up with a sheet pile design utilising Larssen piles and had intended to design and install bespoke welded steel frames to accommodate the bend in the trench. However, the cost implications and anticipated difficulty of installation of a welded frame – particularly on such a short time scale – urged HMB to seek a better option.
MGF used HMB’s frame loads to design ‘back to back’ bays of hydraulic Heavy Duty Tank Brace. The pinned joints at the corners meant that the usual internal angle of 90o for rectangular frames could be articulated and increased to 112.5º thus accommodating the overall bend of 45º. As the frame loads at lower levels were very high, the lower frames were twinned up, but there was no need for any additional cross strutting and the customer had almost 7.5m of clear working room in the pit.
The equipment was easy to install and, due to its available adjustment, it allowed for slight deviations in actual on site dimensions compared with those designed.
The solution was much safer and more cost effective than a welded frame option and also greatly reduced the risk and magnitude of any deflections or ground movement.
Working space was kept to a maximum, with the only obstructions being the return legs of Heavy Duty Tank Brace cutting across the bend.
Download the full case study PDF here: HMB Alliance.pdf