|It is always prudent to complete ground investigation prior to commencing any foundation related works. This proved true for a proposed extension at the Lough where dynamic probing identified poor ground conditions to 3 metres.
Considering the depth and proximity to the existing dwelling, a micropiled foundation was the preferred solution. 13 nr micropiles, with a Safe Working Load of up to 200kN, were designed by Substruck Ltd. to support a new RC ground beam for the extension. These micropiles were constructed of DYWI® R38-500 hollow bar, installed by simultaneous drill & grout, using a 90mm Ø drill bit. Each micropile was provided with a rock socket 2m in length. One nr micropile was tested by an independent specialist contractor.
In order to protect the existing structure locally, pressure grouting or ground improvement was completed by drilling 40mm boreholes through foundations, 3m from ground level deep, at 18 nr locations, grouting with a neat cement grout with w/c = 0.5 and reinforcing on completion with a H20 reinforcement bar. A total of 1.7 tonnes of cement or 1.4m3 of cement grout was injected over 2 nr phases.
A 500mm wide * 450mm thick RC ground beam was constructed over the micropiles, with load transfer via a 200*200*20mm steel plate fixed to the hollow bar with proprietary locking nuts. Reinforcement consisted of 3 nr longitudinal H16 T&B, 400mm*300mm 8mm Links and 3 nr 12mm L-bars T&B at each corner. Concrete was C28/35 Class XC2.