This project involved a design and build subsidence remediation scheme for a property in Mahon for a local authority. The initial appraisal identified serious cracking to the rear of the property which was replicated internally in the order of moderate. The Institute of Structural Engineers define ‘moderate’ and ‘serious’ cracking as cracking of between 2 and 5mm and 5 and 15mm in width respectively. The movement was considered to be above the ‘damage threshold’ or ‘serviceability limit’ with loss of airtightness. Further investigation was prescribed to identify the cause and provide a solution to the movement.
This investigation included a drain test / CCTV survey, trial holes and ground investigation. Our Premier Plant 100 series rig has been modified in order to allow the mast to work remotely from the power pack and therefore, completing ground investigation to the rear of a terraced property or other restricted access areas is no problem.
A waste pipe from the kitchen did not discharge between the hopper and the water seal and was allowing water to escape down to the foundations and thereby softening the already vulnerable soft silt at formation level. Therefore, the cause of the movement was attributed to escape of water and the resultant softening of the underlying soils.
A series of micropile supported reinforced concrete ground beams were installed through the rising walls and drypacked on completion.