In mid-2000, development approval was granted for a development in Nelson Bay NSW which involved a substantial [approximately 3.5 m deep] excavation in loose & medium dense sands which was immediately adjacent to a residential building. Subsequently, excavation of the basement commenced in early 2003, with the shoring system for the excavation consisting of timber poles with second-hand corrugated metal sheeting affixed by screws to the timber poles. The system of excavation support was certified by a local structural engineer, who was also a lecturer at the Newcastle University.
Later, and as some minor subsidence on the adjoining property occurred during the initial excavations, several complaints were made by the owner of the residential building as to the adequacy of the propose shoring system. Subsequently, several engineers, including two geotechnical engineers, inspected and reported on the partly constructed excavation. These engineers then endorsed the original design, whilst expressing some concerns as to the adequacy of the design.
Subsequently, and as the owner of the residential building was still not satisfied as to the adequacy of the shoring system, SCE was then engaged to inspect the site, and advise on the adequacy of the shoring system.
The results of the SCE investigations were in essence that:
- the shoring system, although certified by others, was structurally inadequate and not fit for purpose;
- the risk associated with excavating the basement was high;
- the shoring system required a ‘complete redesign’ to ensure the stability of the adjoining ground and residential building.
As a consequence, and after the institution of legal proceedings, the local structural engineer agreed to a wholesale revision to the shoring system design, and replaced the timber pole / corrugated metal sheet shoring design with a contiguous pile shoring system.
Subsequently, the basement excavation and supporting system was constructed without incident.