The Lostock Sustainable Energy Plant (LSEP) is an Energy from Waste plant located on the footprint of an old now demolished power station within the existing TATA Chemicals plant near Northwich, Cheshire.
When complete the facility will export 69.9MW of electricity into the national grid using residual waste, the waste material remaining once materials that can be recycled have been removed, as a fuel.
P J Edwards were appointed on this project to design and build the required piled foundations on the project which included a large diameter secant wall box to allow excavation of the main waste bunker, and in excess of 1400no. smaller diameter bearing piles.
Design
Design support for this project was provided by our design partners Byrne Looby and Partners with whom P J Edwards have a long standing relationship both in Ireland and the UK. By access to the depth of experience and knowledge within the combined PJE and Byrne Looby teams, substantial cost and programme benefits were able to be realised.
These included reduced propping requirements for the deep waste bunker box, and the use of reduced pile diameters for the bearing piles when compared to the original scheme outline design carried out by the client. More design efficiencies were also driven by the ability to carry out a suite of preliminary load testing in advance of the main works.
Waste Bunker
The waste bunker consisted of 160 linear metres of secant wall to form a watertight enclosed box with approximate plan dimensions of 58m long by 22m wide. The wall was formed by interlocking 1200mm diameter primary and secondary piles, drilled to depths of 22m to allow a subsequent 14m deep excavation. To allow unhindered excavation of the waste bunker box the wall was designed with an external top prop only which was provided by the diaphragm action of a thick RC slab around the perimeter of the box.
To maximise speed of installation, and achieve a very high verticality tolerance, the piles were installed using a combination of PJE's two largest rigs, namely the Llamada P240 in CFA mode and the Mait HR420-800 in rotary mode. Both of these rigs weigh in at 130t and can generate drilling torques in excess of 40Tm.
As the ground conditions in this area had a water table above the base of the excavation, additional 1200mm diameter tension piles were also required to resist any hydrostatic uplift that the base of the box would encounter once sealed.
Bearing Piles
Bearing piles for the scheme varied from 450mm diameter up to 750mm diameter, and typically up to depths of 15m to found into the underlying bedrock.
All bearing piles were installed using CFA techniques with a variety of rigs from PJE's internal fleet.
In addition to pile installation, PJE also utilised one of their Mait HR260 rotary rigs to remove old deep building foundations which were uneconomical to remove using traditional demolition techniques.
The wall and bearing piles were installed over multiple visits between December 2020 and July 2023.