Remediating collapsed retaining walls on building sites

Published on Monday, February 12th, 2018

East Side Village being constructed in the city of Calgary. Major develpoment project in progress

As construction companies look to utilise every inch of land when planning new developments, retaining walls are becoming an even more integral part of site works. Indeed, many projects are featuring increasingly high retaining walls to maximise their construction outcomes. 

As retaining wall heights increase, so too does the potential impact of a wall collapsing.  The issue can put lives at risk and expose ajoining properties to significant structural damage, as was the case in November last year, when the retaining wall at a multi-storey development site in south-east Queensland collapsed causing serious structural damage to neighbouring buildings and the evacuation of residents. 

The higher the wall, the more likely things can go wrong and issues can escalate if gas, power or water pipes are affected. Drainage is also important.  If water can’t escape from behind the wall it will create pressure which can increase the wall’s lateral load from 800kg to 1800kg per metre of height (based on the lateral load of non-cohesive soil versus saturated non-cohesive soil). This can create a precariously dangerous situation.

In emergencies, a fast remediation process is required to re-stabilise the area.  This process can often require substantial excavation and backfilling, yet in situations where time is critical, traditional backfill materials, such as concrete and aggregate, can be cumbersome to use, particularly if the site is hard to access or on steep sloping ground. 

This is where solutions such as our Terefil® lightweight cementitious fill, and Teretek® resin injection, can benefit engineers and builders when there is a need to backfill, remediate or support a retaining wall quickly without compromising its structural integrity or strength.

Terefil, which is available in permeable or impermeable form to suit specific site conditions, is ideal as a backfill for retaining walls during construction or after a new wall has been built.  It forms a stable block without disturbing or redirecting natural water flow and its light weight minimises pressure on the wall when compared to heavier granular fills. Once in place, Terefil can withstand heavy loads, including large machinery and vehicular traffic, to allow construction works to continue.

The Terefil formulation is highly flowable.  Its pumpability is able to reach more than 620 metres and can be placed at 70 cubic metres per hour.  Terefil is also environmentally inert, uses much less water than traditional cemititious fill solutions and, is extremely cost effective.  Sampling and compression tests carried out to Australian Standard AS1012.9 confirms Terefil’s permeability is in the range of 0.53cm to 0.087cm per second and has a compressive strength from 0.5 to 0.6 MPa, once it has cured.

Teretek engineered resin also provides an immediate solution for stabilising a partially collapsed retaining wall or where there is a need to increase the strength of the ground and reinforce the toe of a retaining wall. 

Teretek is a two-in-one innovation that delivers both ground improvement and re-levelling.  When injected into retaining walls, the resin components mix together and expand, strengthening and re-supporting the wall’s footings without the need for any undue demolition or excavation.  Teretek can also be used as backfill or to consolidate any fill material to help protect and strengthen a newly rebuilt retaining wall.

In the event of a retaining wall collapse, our team of engineers can assess a site’s individual requirements and tailor a fast and cost effective solution.


By James O’Grady

James O’Grady is the Sales and Business Development Manager at Mainmark. He is a civil engineer with 25 years’ experience in structural engineering, construction materials and ground treatment.

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