Soil Replacement

New Zealand’s dense urban areas tend to be located on alluvial plains and in coastal regions. In these coastal areas, buildings sit on sandy, shifting soils. The combination of liquefiable ground and density in these regions means that over 50% of New Zealand’s population is exposed to moderate and higher liquefaction susceptibility. Additionally, 25% of the population is exposed to high or very high liquefaction susceptibility.

Buildings in these areas could be impacted during seismic activity, with many variables determining the exact behaviour of a structure on liquefiable ground. These include the depth and stiffness of the structural foundation, magnitude of contact pressure, and the intensity of ground motion. The seismic response of the structure and soil, thickness and properties of liquefiable soil layers, and the non-liquefiable crust are other factors that could impact how liquefaction affects buildings.

Terefil is a Mainmark technology to create a lightweight cellular concrete. Cellular concrete has found extensive use in construction and civil engineering applications due to being lightweight while still retaining good compressive strength.

Terefil is created when a foaming agent is added to a cementitious slurry, forming a large number of air bubbles within the mixture. These air voids give cellular concrete its characteristic low density. This makes it much lighter than traditional concrete, and its highly fluid nature makes it easy to uniformly fill areas around pipes and other obstacles.

“Mainmark played a major part in the successful completion of the Redevelopment of Wainuiomata High School carried out over 4 main stages from 2021 to 2024.

The designers picked Terefil (a lightweight cellular concrete) as a substitute for traditional ground improvement methods. The process for installation, and the completion rates that Mainmark were able to produce were very well communicated. The Mainmark team provided an awesome service. Completing the filling operations with an average of 100-130m3/ day as promised, which was largely dependent on the capacity of the local grout supplier. They brought plenty of experience to the table and did everything that they said they would. 

Overall, Naylor Love were impressed. Terefil is a self-levelling and self-compacting product, making it easy to meet the level requirements through the raft construction, also the final site level. Mainmark’s quality assurance measures also ensured that the specified strength and compaction requirements of the raft was consistently achieved throughout the project. The results of which were clearly communicated through to Naylor Love in a timely fashion throughout the construction.

We were very happy with both the team on site and the team behind the scenes and wouldn’t hesitate to recommend them for future projects.”

James Prestney

Quantity Surveyor Team Leader at Naylor Love 

Mainmark and Tetra Tech carried out numerical modelling to compare the performance of an unimproved soft soil site to both gravel raft and Terefil raft solutions.

The modelling takes into account the thickness and density of the Terefil, as well as site specific variables like the depth of groundwater.

Results show that a Terefil raft performs twice as well as a reinforced gravel raft. Additionally, the Terefil raft was able to reduce differential settlement at only half the thickness of the reinforced gravel raft.

If you would like a copy of this modelling for your future project, get in contact with us today and one of our Technical Sales Managers will be in touch with further information.