Case study Machynlleth

Scheme Summary
Heavy flooding washed away the ground from the edge of the stream to the house taking with it a large majority of the fill and foundations from under the house. Site investigation works established solid ground conditions at 2-metres below the top of the existing stone foundation and that approx. 35m3 of ground had also been washed away.

The repair solution was designed to be undertaken in two phases, Phase one – structural repairs to the property and Phase two repairs to the garden and stream banks.

Prior to commencing the scheme consutations were held with Ceredigion County Council Land Drainage/Flood & Coastal Management/ Planning Liasion Officer and the necessary permission granted.

Scheme Solution
In order to remove the risk of ‘differential movement’ between the exposed area and the remaining “as built” section of the property, it was agreed to underpin the complete front elevation. The sequence of underpinning was designed to allow the neighbouring pins to cure before excavations were undertaken for the pins adjacent to them.

The design included a mechanism to release hydrostaic pressure, this included 50mm underground pipes laid at 500mm centres through the underpins to alliveate hydrostic pressure behind the wall and discharge it into 110mm pies falling towards and discharging into back into the stream. Future flood protection to the property was provived by the installation of 24 stone filled gabion baskets and strategically placed rock armour.

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