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New Zealand
Overview
The Better Alternative to a Gravel Raft
Improving ground conditions in areas with soft, compressible, or liquefiable soils.
New Zealand has a complex geology including soft, compressible and liquefaction-prone soils. In recent years, New Zealand has experienced a growing demand for ground improvement due to increasing population and urbanisation. This has resulted in an increase in the construction and retrofit of buildings and infrastructure, which need suitable foundations to ensure their long-term durability and safety.
Soil replacement involves the excavation and removal of unsuitable soil and its replacement with engineered fill material. This method is effective for improving ground conditions in areas with soft, compressible, or liquefiable soils. Mainmark uses Terefil to create lightweight, cellular concrete rafts prior to building construction, which aids in offsetting the structure’s weight.
Terefil raft performs twice as well as a gravel raft at reducing differential settlement of the house, while only needing to be half the thickness.
Terefil Raft
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Largest decrease in differential settlement (2 x compared to gravel raft)
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Largest decrease in total settlement
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Mitigation from liquefaction damage
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Load decrease in underlying soils
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Half the excavation depth compared to a gravel raft
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Gravel Raft
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Decrease in differential settlement
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Mitigation from liquefaction damage
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Load increase compared to natural ground
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No reduction in total settlement
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No Raft
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No load reduction on sub base soils
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Largest total settlement
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Largest differential settlement
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No mitigation from liquefaction damage
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Terefil is a Mainmark technology to create a lightweight foamed or cellular concrete.
Foamed 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 foamed concrete its characteristic low density. The lower density makes it much lighter than traditional concrete, while its highly fluid nature makes it easy to uniformly fill areas around pipes and other obstacles.
In a ground improvement application, Terefil is used to create a lightweight raft prior to building construction. Weak, compressible or liquefiable soils are excavated to a designed depth and replaced with foamed concrete. This reduces the weight on the underlying soils and provides an engineered fill material with consistent strength and stiffness properties.
Testimonial – Redevelopment of Wainuiomata High School using Terefil Cellular Concrete
“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
Terefil® light-weight raft numerical modelling
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.
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Mainmark Ground Engineering (NZ) Ltd
