Dublin-based Howard Building Contractors found itself facing a delicate problem when employed to build a new house on a vacant plot in Blackrock, Co. Dublin.
The major challenge of the scheme was the construction of a 70m2 basement within 2.5m of a neighbouring property. Furthermore, due to the stiff nature of the ground in the area, the effects of vibration on nearby properties during the installation of the sheet piles was a potential problem. The contractor employed Groundforce, a specialist excavation support company, to provide a solution.
"Groundforce proposed a number of solutions to cater for the problem on this site but the one we chose was to auger the ground before driving the sheet piles,” comments James Howard, company managing director. Following the piling activity, a complete temporary works solution was provided, comprising of shallow profile GFi interlocking sheet piles, selected to help reduce the overall plan dimensions, together with lateral support provided by a medium duty Maxi Brace modular frame braced with HSK80 hydraulic cross struts.
Augering the ground before driving sheet piles is a common practice on major projects but is seldom encountered on small building projects such as domestic house-building.
The technique involves sinking a helical screw into the ground along the perimeter, where the sheet piles are to be driven. This breaks up the soil and changes its condition from cohesive to non-cohesive. With the soil loosened, the sheets can be driven with far less resistance and hence greatly reduce vibration.
To further reduce the risk due to vibration, Groundforce also supplied a real-time vibration monitor throughout the piling operation.
Groundforce technical sales manager Joseph Lenihan commented: "Basement construction is becoming popular once again, especially in the Dublin area, and it is therefore vital to ensure excavation designs incorporate the correct support solutions.
With space becoming a premium and due to planning restrictions, more and more domestic and commercial clients are looking to construct down where possible. It is great to see projects such as these going ahead once again and it is an encouraging sign of the times.
The full package solution provided by Groundforce made what could have been a major headache a simple, straightforward procedure, says James Howard.
“This was our first job with Groundforce, and we were very satisfied,” said Mr Howard. “Not only did they provide a solution to the vibration problem, but more importantly, they provided a full health and safety package too.”
This comprised the company’s Edgesafe barrier system and Premier Laddersafe entry system for deep excavations.
The Groundforce equipment was on site for approximately eight weeks during excavation and construction of the basement. The new house is now out of the ground and is due for completion by the summer.