Improving Ground Stability

Understanding the unique soil types in various regions is vital for constructing foundations that can effectively account for soil subsidence, compression, and movement. This is where Mainmark, a ground engineering and asset preservation company, excels.

Established in 1989 following the Newcastle earthquake, Mainmark quickly emerged as a local leader in providing tailored earthquake repair and remediation solutions. 

The company’s specialised grouting techniques and commitment to continuous innovation and development of non-invasive technologies for void filling, re-levelling, and ground improvement have propelled it to become the global ground engineering and asset preservation company it is today. Mainmark offers intelligent and economical solutions across all residential, commercial, mining, and infrastructure sectors.

Mainmark’s commitment to excellence and family values has driven its growth over the past 35 years. With an extensive portfolio of projects across Australia, New Zealand, Japan, and the United Kingdom, Mainmark has earned a global reputation for delivering innovative solutions to iconic projects worldwide. 

This has established them as an internationally recognised and award-winning ground engineering organisation.

Mainmark offers diverse ground improvement solutions tailored to address various geological challenges. Their services span from in-situ injection techniques beneath existing structures to ground replacement for new construction, ensuring robust and effective ground improvement solutions for all types of construction projects. With their innovative approaches, Mainmark ensures long-term durability and resilience for buildings and infrastructure. 

One product of particular note is Terefil, which is designed for a range of purposes.

Lightweight cellular technology

Terefil is a unique and innovative technology from Mainmark that creates lightweight cellular concrete that can be applied as a proven method for improving ground conditions by excavating and removing unsuitable soils and replacing them with engineered fill materials with enhanced mechanical properties. This approach is particularly effective in soft, compressible, or liquefiable soils.

Cellular concrete boasts lower density than other fill materials, ranging from 500 to 1500 kilograms per cubic metre. This starkly contrasts the 1800 to 2400 kilograms per cubic metre found in traditional engineered fill or concrete alternatives.  

As a ground improvement application, Terefil is used to create a lightweight raft before building construction commences. Weak, compressible or liquefiable soils are excavated to a designed depth and replaced with Terefil. This reduces the weight on the underlying soils and provides an engineered fill material with consistent strength and stiffness properties.

Features and Benefits  

Terefil’s lightweight yet strong nature makes it an ideal soil replacement solution. Numerical modelling has also shown that a Terefil raft performs twice as well as a reinforced gravel raft while only requiring half as much excavation.

Because Terefil is stronger and denser, less weight is placed on the underlying soils. This provides an engineered fill material with consistent strength and stiffness across the raft. It is also designed to flow and be pumped over long distances. Terefil can be pumped over hundreds of metres if required, getting into any hard-to-reach places.

With this flexibility, Terefil cuts construction time and the overall build timeline. It achieves this by being produced and placed at up to 50 cubic metres per hour. There is also no need to compact Terefil. It is self-consolidating, which eliminates the need for heavy earthmoving equipment and mechanical compaction. This further increases the time and financial savings available to end users.

High School Re-Development 

How has Terefil been utilised? It’s been used in a growing number of infrastructure projects. This includes a recent high school redevelopment, which required ground improvement to reduce weight on the soft soils and expected static settlements. Concerns also existed about vibration during the installation of traditional methods, which could damage the existing neighbouring buildings and potentially induce soil liquefaction due to the cyclic loading from the compaction equipment.

To address these challenges, a cellular concrete soil replacement solution was chosen for its lightweight nature and strength, meeting the necessary density and strength requirements. The ground improvement works, carried out in four stages, allowed the new buildings to be added without increasing the risk of static settlement, reducing build time and costs. Mainmark successfully completed the ground improvement stages, ensuring stability for the new structures.

Substation Ground Improvement 

Another example of Terefil being used was in a regional area undergoing significant growth. It was transforming from a rural region into a bustling suburban district with commercial and residential developments. This growth necessitated the construction of a new substation to supply electricity to an estimated 7500 dwellings and a large proposed commercial development. 

As a result, the town needed to build a new substation. It was designed around the grid-connected Tesla Powerpack used at another substation. The substation was located between a residential area and a main water and wastewater pump station site. 

Geotechnical investigations revealed weak soil conditions, necessitating the installation of lightweight rafts to provide a stable platform and prevent subsidence. Mainmark was contracted to install three lightweight concrete Terefil compensation rafts, which were identified as the ideal solution due to their superior structural fill capabilities and minimal site disruption. 

The project required precise planning to meet specific weight, depth, and measurements, ensuring the combined weight of the rafts, structure, and equipment did not exceed the undercut soil’s capacity. Mainmark worked closely with engineering consultants, overcoming access challenges and ensuring worker safety. The project was completed over eight days, covering 665 cubic metres, providing a much faster solution compared to traditional methods.