PBA was commissioned by Jayen Civil Engineering Ltd to look at value engineering a design of foundations and retaining works as part of the works to provide a new substation for their client, Jersey Electric.
The substation was required at Westmount Gardens, on the west side of St Helier in Jersey. This is an area of sloping ground that was the site of a former quarry from which andesite bedrock was extracted. The quarry had been infilled in the early 1900s using ash from the waste incinerator on Jersey.
The new substation was essential to secure existing supplies to around 13,000 customers in the area, as well as future proof the network to meet the increasing demand for electricity.
The proposed substation was planned to be constructed on a level platform, which would be formed by cutting into the hillside necessitating an excavation up to 15 metres deep. This excavation would require support in the temporary situation before the permanent works could be constructed to form the retaining works to support the ground. The permanent retaining structure was originally designed to be a large reinforced concrete retaining wall which would include tension piles to resist overturning moments.
We developed a design for the retaining wall that would incorporate the temporary support works into the permanent solution to stabilise the cutting and provide the retaining structure that would form the back of the substation building and side support to the remaining site area.
Once in service, the new substation will remove the pressure on existing infrastructure and service around 70-80% of St Helier’s demand.