Pressure Grouting to Extension in Cork City

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A local builder employed Substruck Ltd. to design and construct an underpinning scheme to address foundation movement to a rear extension in Glasheen. This extension was built about ten years ago!!!!  

The cracking was typical of subsidence in an extension where a vertical crack forms between both components; the crack being wider at the top as the extension rotates away from the original structure.

A trial hole showed that the extension was founded on a well-constructed foundation but at insufficient depth. Dynamic probes identified poor resistance to depths of up to 3 metres. However, as the soils were non-cohesive, a pressure grouting or ground improvement solution would be appropriate.

Pressure grouting involves pumping a neat cementitious grout through boreholes formed through the foundation and into the underlying soils. The grout will fill voids, increase strength and reduce compressibility to stabilise the structure. The grout is very mobile and whilst following the path of least resistance, travels through the voids providing both compaction and densification, therefore increasing the bearing capacity of the soil. Grouting was completed at 12 nr locations over two phases. The builder completed the remaining works.

Foundations to extensions to dwellings are not always afforded the respect they deserve – homeowners should always ensure to employ competent persons to complete the works. The added protection of a consulting engineering firm is always money well spent.