Independent Geotechnical Design Engineers
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info@bylandengineering.comTemporary Works Design for Embankment Dam Improvements
Byland Engineering worked in partnership with Alan Auld Engineering to design temporary works for Bentley, main contractor engaged by United Utilities to build improvements to a water supply reservoir embankment dam at Lower Coldwell, near Colne, in Lancashire. Lower Coldwell Reservoir is situated in the historically landslip prone Catlow Brook valley in the western Pennines. The dam is 120m long and up to 20m high and it is formed of earthfill shoulders with a central puddle clay core. It was built between 1881 and 1884.
The permanent works comprise the construction a new wave wall and side crest overflow weir and an overflow channel and stilling basin together with modifications to the embankment downstream slope and to mechanical devices for flow control. The new overflow channel is a reinforced concrete trough-like structure built in the dam mitre and along the downstream toe.
The main temporary works concern was to provide a safe and efficient support system to the 7m deep excavation required to accommodate the overflow channel construction. Steel sheet piles propped internally at 1, 2 or 3 levels were chosen, the propping arrangement being strongly influenced by the available toe-in achievable by the steel sheet piles driven into the Lower Coal Measures / Millstone Grit bedrock beneath the embankment fill and superficial soils.
Bylands’ contribution to the temporary works was as follows : 1) Geotechnical analysis of the support system and sizing of steel sheet piles and ground anchorages, 2) Analysis of the temporary stability of the embankment downstream slope and of other slopes required for construction operations, 3) Design of working platforms for heavy tracked plant, 4) Feasibility designs for soil nailed slopes, 5) Feasibility designs for tied back steel sheet pile walls.