THE MAGAZINE FOR THE DRAINAGE, WATER & WASTEWATER INDUSTRIES
SPECIAL WORKS
the excavation, explains Ms Herd: “The excavation was about 5.250m deep and the ground conditions were fantastic – you couldn’t have better ground conditions, really, so the lateral loads were not massive.”
This was just as well because, with the concrete chamber already installed, Groundforce Shorco had to provide a bracing design that transferred the loads from the sides of the excavation to the chamber itself.
Groundforce Shorco produced the temporary works design for CHAP Civils and these were passed to ESD for approval.
Akil Jasm, chief engineer for Groundforce Shorco, said: “We were expecting very high loads, to be honest, but when the contractor started to dig we soon realised that the ground was better than we first thought.”
“But the fact that the access chamber had already been installed made the job very challenging, so we had to find a bespoke solution which was not only safe but also provided adequate room for the installation of the pipework. Also, we needed to ensure that the integrity of the concrete chamber was not compromised due to the loads coming on to the tank from the props. Although the ground conditions were good, there were earth embankments behind the sheet piles and the sides were not self-supporting.”
The design utilised Groundforce Shorco’s modular propping system. Two levels of hydraulically-adjustable Mega Brace beams were ranged along all sides of the sheet-piled excavation and the corresponding sides of the concrete chamber.
These were supported by a combination of MP50, MP60 and MP150 props to
brace the sides of the excavation. Mega fixed extensions were installed against the concrete chamber to uniformly spread the load on the concrete chamber rather than fixing the props directly on to the chamber. This would have subjected the chamber to high concentrated or point loads.
To provide as much working room as possible, Groundforce decided to use a single prop on the eastern side, resulting in 6.7m long unsupported span. Here, Groundforce Shorco used one of its 150 tonne-capacity MP150 hydraulic props to brace the lower level of Mega Brace beams. The top of the excavation was braced with one MP50 prop - a 50 tonne- capacity unit.
The rest of the excavation was braced with 10 MP60 props - three pairs along the north side and the other two pairs to the western side.
FOLLOW US
November 2024 |
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