Key considerations when building a stable structure on a difficult site


24 February 2021

Australia and New Zealand are lands of diverse topography, with thousands of communities situated in areas where hills, slopes, embankments and elevations are prevalent. And while that may mean stunning views and natural light for those wishing to live on an elevated site, it raises significant challenges for builders and engineers who must consider the ground terrain and other geotechnical issues.

As a ground engineering specialist, we have seen many examples of challenging building sites, including an elevated property in Parramatta, NSW. A retaining wall between a home and an adjacent public park collapsed shortly after construction. The residence was situated on a very steep slope with a high retaining wall on the property boundary. Mainmark was responsible for backfilling approximately 40m3 behind the new wall with Terefil®, a structural, lightweight, cementitious based fill.

As traditional concrete or fill materials were unfeasible for this project, due to the heavy load they would have placed on the wall, Terefil provided a unique lightweight yet structural solution that allowed the engineers to reduce the wall’s thickness. Terefil’s fully permeable formulation also ensured the wall complied with the engineered specifications for full water drainage.


While sites that feature slopes, cliffs and other scenarios where there is a steep drop in ground levels can make the construction process more complex, they are not impossible for engineers and builders to overcome. The key is to identify the site’s soil and ground bearing conditions to help select the right solution to manage the issue. Here are some common considerations when building on sloping or elevated building sites.

What are the solutions?

Mainmark has a range of products and solutions to help overcome the challenges of building or remediating structures on sloping or elevated sites. In many cases, they can also help avoid the need to use invasive ground remediation processes, such as traditional underpinning and piling, and avert costly repairs down the track should structural damage occur due to poor ground conditions.

Teretek®, Terefil®, and Permeation Grouting are just a few solutions that Mainmark uses to help overcome the complexities of remediating buildings on sloping sites with unfavourable soil conditions.


Teretek is an expanding polyurethane resin mix which is injected through small tubes into the ground beneath the footings. It is ideal for strengthening and re-levelling settled and uneven ground using a process that is likened to keyhole surgery. The application is completed in a fraction of the time compared to conventional re-levelling methods and causes minimal disruption to the site.

Terefil is a lightweight, specialist cementitious fill with a uniformly distributed matrix of air bubbles allowing it to flow into places where other cementitious fills may be unable to reach. Terefil can be supplied as either a permeable or an impermeable cementitous mix, to meet specific project requirements, allowing project engineers to manage ground water flows. It is typically used to backfill load bearing retaining walls, fill voids and sinkholes, and abandon pipes and shafts. Terefil is environmentally inert, cost-effective and uses much less water than traditional options such as cellular lightweight concrete or foam concrete methods.

Permeation Grouting is a commonly used technique for turning granular soils into a solid mass while filling cracks, joints, and other ground defects in non-cohesive conditions. The solution is ideal for resolving ground settlement and subsidence or rectifying other ground problems, such as voids, in locations with soft granular soil or sandy ground conditions.

The secret to building on difficult sites is to design and construct with the appropriate materials for the site conditions, to ensure that a buyer’s ‘house on the hill’ dream is a safe and long-term reality.  Mainmark’s experience and product range provides the designing engineer with targeted solutions to address the demands of the site.




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