This trial hole was completed as part of a subsidence investigation project on behalf of Cork City Council in December 2018. It identified a traditional strip foundation founded at 0.95m with a projection of 0.33m-0.44m and a thickness of 0.3m.
The local gully was found to be installed incorrectly resulting in a continual escape of water from the first day of construction!! There was no actual pipe installed between the gully and the hopper!!! The presence of water was evident in the subsoil and leakage could be observed when water was placed in the gully!!!
In many cases, a crowbar is used by the designer to prise the ground locally to give an indication of the bearing capacity of the soil. There isn’t a lot of science to this procedure but if the crowbar can be easily pushed into the soil for its full length, then this would be a cause for concern!!!!!!!!!!
To provide some science to the bearing capacity of the soils, a dynamic probe was employed which showed very little resistance at formation level and to a depth of about 2.5m with no value exceeding N10H=1 before bedrock was encountered between 3 and 4 metres. For Dynamic Probe Heavy, values of N10H=1 in till are indicative of bearing pressures of less than 20kN/m2!!!!!
A window sample showed that the building was founded on very soft SILT; Homebond recommend great care in the design of foundations in such soils.
The design to address this problem was a reinforced concrete raft, needled through the rising walls, and supported by 20 nr R38-500 DYWI® micropiles drilled one metre into rock with a SLS of 100kN, with each needle dry-packed on completion with a proprietary non-shrink grout. All works were designed, constructed, tested and certified by Substruck Ltd.