Groundforce Shorco has provided structural support for a deep basement excavation in Chatham, Kent.
The company has supplied its MP50, MP150 and MP250 modular hydraulic props to groundworks specialist Lashi Contractors which is constructing an underground car park for a development of 61 one, two and three-bed apartments at 3 New Road in Chatham.
The development, by Callisto Homes, will comprise two blocks separated by a communal garden. The site was formerly home to a popular nightclub called Krystals.
Groundforce Shorco was initially approached by Callisto and tasked with designing a support solution in partnership with Lashi Contractors and the client’s temporary works designer.
The excavation measures approximately 35m wide by 46m long and reaches a maximum 6m in depth. It is lined with a secant-piled retaining wall topped with a concrete capping beam.
Because the site slopes steeply away from the road, structural support is required on three sides of the basement excavation. The sloping ground also means that the capping beam steps down in line with the surrounding ground as the depth reduces.
“The challenge was how to brace the sides of the excavation with the capping beam at different levels,” says Ken Sandell, area manager (major projects) for Groundforce Shorco.
“Normally we’d brace the props against a waling beam positioned around the perimeter of the excavation, but with the capping beam at various depths, any temporary waling beam would have interfered with the permanent works.”
The solution was to dispense with the waling beam and instead cast corbels into the capping beam for the hydraulic props to bear against, thereby keeping the props above the level of the ground floor slab.
Six Groundforce props were installed as knee-braces across the corners of the excavation. These comprised two 6.5m-long MP150 inner props, with two 14m-long MP250s across the intermediate span, and another two MP250s across the widest span. The longer MP250 props employed 813mm-diameter tubes to maximise stiffness over their 23m length.
Great care was taken by the temporary works team to ensure that the support provided by the Groundforce Shorco equipment ensured maximum stability. Immediately adjacent to the excavation is an existing Victorian property whose shallow foundations could be easily disturbed by any ground movement.
Groundforce Shorco therefore fitted its proprietary wireless load monitoring system to the three knee-braces on the side immediately adjacent to the neighbouring building.
This Senceive data monitoring system comprises an electronic load-cell in the prop’s connecting pin which sends a continuous signal to a remote computer via a 3G gateway module where the exact load acting on the prop can be observed. The system will also send by SMS an early warning to the monitoring station if the load exceeds a pre-set value.
This project marks the first time Lashi Contractor has employed a proprietary support system, says company director Vlad Lashi.
“We’ve used welded steel frames before but this is the first time we have worked with Groundforce,” he says.
Despite the unfamiliarity with the system, Lashi installed the props themselves adds Mr Lashi.
“Groundforce were very helpful, and we found the installation of the props to be a very straightforward process. Everything went smoothly as per the drawings – no dramas!” he adds.
