A landscaped courtyard within a multi-residential complex in the Sydney suburb of Lane Cove had partially collapsed, caused by a sinkhole that had formed underneath.
The 2-storey development, comprising of 13 apartments with basement parking and storage, is constructed of load bearing masonry, with concrete blockwork perimeter walls in the basement and a suspended concrete floor above. The upper level extends beyond the basement, creating a ‘void zone’ between the perimeter blockwork wall and the adjacent natural rock supporting wall.
Over time, heavy rain soaked into the property’s lawns and slowly migrated the ground towards the void area. This also washed out the soil beneath the courtyard, causing it to progressively erode and form a sinkhole.
In the first instance, Ace Body Corporate Management engaged ACOR Consultants to investigate and propose solutions to this problem. ACOR Consultants worked with the Mainmark team to develop a cost effective and suitable solution. Ace Body Corporate Management contracted Mainmark to undertake the entire remediation project including void filling, sealing the blockwork wall and adding new drainage to mitigate further soil subsidence.
Mainmark leveraged its extensive industry expertise, innovative solutions and partnerships with sub-contractors to complete all facets of the project, providing a one stop shop for the client.
Mainmark delivered an engineered solution to complete the plumbing works, void wall sealing and void filling. Terefil®, an advanced structural lightweight polymer cementitious fill, was used to fill and support the void area, improve the ground stability and reduce exposure to further erosion.
The key objective was to fill the void zone between the back of the basement perimeter blockwork wall and the natural rock supporting wall, to minimise the risk of future washouts and sinkholes.
The client was seeking an all-in-one solution from a single provider to manage the entire scope of works, including void filling, void sealing of the blockwork and plumbing. A lightweight void fill solution was required to minimise pressure on the perimeter blockwork wall, while also providing load bearing capacity to the pavement above. The solution also needed to circumvent site access difficulties and be delivered using a nonintrusive method to avoid disruption to residents.
Mainmark implemented a comprehensive ground engineering and drainage remediation solution, coordinating plumbers and blockwork sub-contractors to fix the issue of surface water ingress from the upper courtyard.
After overseeing the installation of a new drainage system, a camera was used to inspect the pipes to ensure they were fully operational. Mainmark then lined the block wall with a geofabric membrane and pumped 83m3 of Terefil through three core-drilled injection sites to fill the void.
Mainmark used a permeable form of Terefil to ensure water in the filled void zone could freely drain to the newly installed agricultural drains at the base of the void, minimising the risk of future hydrostatic pressure build-up. Terefil has an engineered load bearing compressive strength and a wet density that is more than 50% lighter than traditional grout, reducingpressure on the void’s retaining walls.
Despite difficult access and large volumes of cementitious material to be delivered, Mainmark’s Terefil® installation is non-invasive, causing minimal disruption to residents.
As Terefil is highly-flowable, it can be pumped over long distances which helps to overcome site access issues. Its lower pumping pressures also help to reduce the risk of damage to nearby pipes and other in-ground structures.
The Terefil solution is easily-placed, self-levelling, and does not require pre-loading or compaction. It simply flows into spaces to fill voids with zero bleed and is environmentally inert.
Terefil was a cost-effective alternative to expensive, traditional void-filling methods such as aggregate or granular fills. The solution has provided the residents with much-needed reassurance that the basement supporting walls and the ground above the void zone are now stable.
David Hairman from Ace Body Corporate Management commented, “The owners pass on their sincere thanks for the way the Mainmark team has worked. Despite having to access their courtyards to carry out the job, Mainmark was very discreet and sensitive to the needs of the owners and residents. They are really impressed!”
Project Resources & Downloads
Terefil® Used To Fill Void At Lane Cove Residential Complex
Print At Home Crack Gauge
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Permeation Grouting Stabilises Randwick Development
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