A single-storey dwelling located in regional New South Wales had suffered differential settlement due to past mining activity.about the back of their house sinking and that considerable damage might occur if left unchecked. A large crack had formed in one of the walls and cracks had appeared along the ceiling cornice of three separate rooms. The damage indicated that the entire back section of the house was subsidising relative to the rest of the building.
The region is known for its coal and when coal is extracted from the ground, the land above can become unstable and ‘sink’, which is commonly referred to as mine subsidence. This subsidence can compromise the structural integrity of buildings built on top of the subsided land.
Remediation of the home required a staged approach over several years. In 2013, Mainmark applied Teretek® engineered resin as a temporary solution to address 150mm subsidence identified at the property.
In 2017, after an unused mine void located nearby was filled, the property experienced further settlement of up to 220mm across the entire home. It was essential to rectify this subsidence, to ensure the home was level, including aligning the pavement steps, drainage and pipe grades to within tolerance, to prevent further structural damage to the home.
Over time, further re-levelling work was required to complete the final stage of remediation. Mainmark was engaged by the building contractor in February 2018 to assess the site and identify a solution that would re-level the building to within allowable tolerances.
Mainmark recommended the use of JOG Computer-Controlled Grouting technology (JOG), which is commonly used to re-level large and complex structures, to help prevent any additional ground movement from occurring, and further support and re-level the building.
Mainmark was required to provide an effective solution that would lift and level the structure evenly and accurately across a large area of the home.
It was important to raise the entire structure back towithin Building Code of Australia tolerances on behalf of the project client and the property owner.
Mainmark utilised JOG, an advanced grouting technology for re-levelling and strengthening ground beneath structures using computer-controlled cement grout injection.
JOG was recommended for the property because it is non-invasive, highly accurate, and uses multiple lifting points with finite control, to effectively and gently float the building back into position. JOG is an extremely precise method for stabilising soils, consolidating weak ground and lifting foundations to deliver specific, engineered outcomes, regardless of complexity.
Level correction was achieved using JOG to raise the single-storey home by a maximum of 183mm, without
the need for invasive, labour intensive excavation. The cementitious grout was delivered to the target depths via narrow injection ports placed into 25mm to 40mm diameter holes which were core drilled into the floor.
The injection process was carefully controlled via a central computer unit. Re-levelling was undertaken contemporaneously across the entire house, including the garage, to ensure that the lifting resulted in level tolerances across the slab were in line with all relevant building codes and guidelines.
Re-levelling and re-supporting a home using JOG
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Mainmark Ground Engineering Pty Ltd
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