CASE STUDIES
systems where the installation process involves the shifting or tilting of the box plates, causing the width of the trench to vary which in turn allows the soil to move.
While excavation of the trench continues, Murphy is using Groundforce Shorco’s MP150 hydraulic struts to support the UTX chamber excavation. This excavation will facilitate construction of a 12m-deep insitu concrete chamber which will house valves and washout equipment essential to allow Severn TrentWater tomaintain the watermain.
Measuring 15.2mx 13mx 9.5mdeep, this excavation is lined with 10m-long Larssen sheet piles and supported by Mega Brace hydraulic waling beams and fourMP150modular hydraulic props. The props are installed as knee-braces, spanning the corners of the excavation and braced against each other in the middle of the waling beams.
This excavation comprises two rectangular bays adjacent to each other and braced at the interface withMega Brace units.
Themain challenge was the poor ground conditions, with landfill over bedrock and the uncertain location of underground services, including the existing water main. There are also overhead power
FOLLOW US
cables and a large embankment that cannot be disturbed due to the risk of undermining structures built on top of it.
Therefore, instead of pre-driving sheets to full depth, Groundforce Shorco proposed using a “dig-and-drive”method whereby sheets are driven a short distance into the ground which is then excavated in stages to allow the identification of buried obstacles before the sheet piles encounter them.
In each excavation, large servicesmust be avoided, and soMurphy has installed Groundforce Shorco’s End Closure Panels above the services to prevent any soil entering these locations.
Murphy also employed Piletec’s new side-grip excavator-mounted vibrating piling hammer to install the sheet piles, with Piletec providing on-site training for the excavator operators in how to use the new device.
The great advantage of this new hammer is that it enables the use of sheet piles that are longer than the reach of the excavator. The hammer’s linear side- clamping systemalso results in amore efficient clamping load transfer.
With the UTX chamber now fully supported and progress on the trench excavation progressing quickly,Murphy will soon be ready to excavate the
second UTX chamber on the opposite side of the proposed railway line where Groundforce Shorco also proposes to provide structural support.
The new pipelines will then be reconnected to the existing watermain on the western side of the railway inside another large excavation, known as the UPT chamber.
“The watermakes a 90° turn here where itmeets the existing pipeline and we have to install what’s known as a thrust- block. This will resist the force imposed by the volume of water turning that corner otherwise the pipeline will fail,” explains SamWoodyatt.
Groundforce Shorco was involved at an early stage in the design process, allowing themto fully assist with solving the challenges of the project.
“Groundforce Shorco were very helpful. They turned designs around very quickly and I was in direct contact with Zoe [Holmes, design engineer] at all times,” saysMrWoodyatt.
“They were instrumental in helping us to minimise the amount ofmaterial excavated.We are on a landfill site and all arisingsmust be disposed of in a licensed tip, which is very expensive and less environmentally friendly,” commentsMr Woodyatt.
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