Introduction
EC Engineers was engaged by a national insurance company regarding a property on the Sunshine Coast which had identified concerns regarding the dwelling’s concrete stumps and level differentials. Our services were engaged to conduct a forensic engineering investigation which entailed a site inspection and hydraulic level survey to investigate the cause and extent of damages to the subfloor’s concrete stumps.
Methodology
The methodology used entailed an internal inspection firstly by our Forensic Engineer. The internal inspection found cracking to internal walls or ceiling linings. We then moved our inspection to the exterior of the dwelling to investigate any external damages and inspect the subfloor area. The external inspection identified varying degrees of spalling (spalling is when the reinforcement steel within the concrete begins to rust placing pressure on the concrete leading to detachment of concrete). Additionally, sections of timber flooring were observed to have timber rot, water staining and mould present to the timber floorboards and bearers/joists.
To better investigate the extent of possible movement to the dwelling, a hydraulic level survey was conducted to the dwellings internal lower-level floor area. The purpose of conducting a hydraulic floor level survey throughout the dwelling was to measure the extent of any possible floor level differentials. The measurements taken from the floor level survey are used to formulate a contour profile of the house, which is often used as an indicator of the cause of the foundation movement.
The results of the floor level survey conducted at this property, indicated differential foundation movement has occurred throughout the dwelling. The variance in the floor levels as measured across the internals of dwellings floor was found to be approximately 50 mm.
Solution/Outcome
It was determined that the property was constructed on clay-based soils meaning it is susceptible to natural seasonal ground movement. The dwelling displayed evidence consistent with settlement and seasonal foundation movement. The dwelling’s clay-based soil foundations have sustained movement over a long-term duration. The evidence from our site inspection indicated that the seasonal foundation movement throughout the foundations had generated stresses which have propagated throughout the dwellings floor structure leading to level differentials.
In addition to the foundation movement, it was determined that the concrete stumps were experiencing spalling or concrete cancer. The stumps had reached the end of their service life. In summary, it was recommended that the stumps and concrete strip foundations were replaced and a scope of works report was provided to outline the requirements for this from an engineering perspective.
