Constructing a home on an active landslide may now be possible after a new house was built in Dorset on a double foundation with jacks to re-level the structure as the ground moves.
Home owners of Crow’s Nest did not want to leave the location after ground movement damaged their old bungalow so looked for an alternative solution.
Geotechnical consultant PCRM partnership and structural designer Eckersley O’Callaghan worked with foundation contractor Bullivant to construct the two part foundation solution.
“The old house was located above the graben of a large translational – slab-like – landslip that, when ground water pressures were high enough, would spill over the Lias Clay cliffs about 300m to the south,” said PCRM partner Peter Chapman. “When movement occurred, the house would be severely distorted as it settled into the graben that opened up between the landslip and the Upper Greensand Formation Outcrop.”
Eckersley O’Callaghan associate Robert Rock said: “The Crow’s Nest is different in that we have accepted ground movement is inevitable. It would have been expensive and disproportionate to prevent or resist it somehow. Instead we have integrated a bold, yet pragmatic, way of responding to nature into the design.
“A shallow piled foundation was used – although these still penetrated into the sand – to carry the loads in the temporary and landslip case. In the permanent condition, the building sits on the ground beams which act as shallow strip foundations.
Deeper piles were discounted because installing at the depths and diameters needed to resist the forces from a landslip would be disproportionate to the building works.”
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Steel cased cast insitu piles were installed by Roger Bullivant for main contractor Mew Developments.
Rock believes that other projects could benefit from the knowledge and acceptance of risk gained through this scheme. “It is the perception of risk to investors, clients, developers that needs to be mitigated through early engagement of a design team to help ensure more cost-effective solutions and structures such as this are realised.
So far monitoring points around the property have not shown any ground movement but Chapman said that a wet winter will put the design to the test.