Book in your FREE, no-obligation site inspection. Contact us today for peace of mind.

Quick Enquiry Call Us

Search

If you cant find what you’re after please don’t hesitate to contact us.

Select Region

Please select the global region website you'd like to view.

Asia
Japan

Quick Enquiry

Submit your enquiry using our online form and include a brief message about the type of issues you are experiencing. One of the Mainmark experts will contact you as soon as possible.

Hidden
This field is for validation purposes and should be left unchanged.

Soil Replacement

Terefil Raft for Liquefiable Sites

Overview

The effects of seismic activity on liquefiable ground

Improving ground conditions in areas with soft, compressible, or liquefiable soils.

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.

The Effect of Liquefaction on Buildings & Infrastructures

There are a number of ways liquefaction can affect a building and its connecting infrastructure, including:

  • Reduced bearing capacity due to the associated reduction in soil strength
  • Subsidence associated with shear deformation, cyclic ratcheting, lateral spreading and ground re-levelling, and reconsolidation
  • Surface ejection of soil and water (sand boils)from beneath or around foundations
  • Heave of ground bearing floor slabs and buoyancy of buried pipes, tanks, chambers and basements
  • Horizontal displacement and stretching of the footprint and foundation with lateral spreading.

Terefil is a Mainmark technology to create a lightweight cellular concrete.

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.

Terefil® lightweight raft

Terefil can be used as a soil replacement method, one of the principle methods to improve the ground’s seismic performance and resistance to liquefaction. In this ground improvement application, Terefil is used to create a lightweight cellular concrete 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. The replacement method can be applied to both sands and silts.

The soil replacement method involves the removal of the insitu liquefiable soil, and replacement with a non-liquefiable material. It is useful for treatment of shallow liquefiable layers or creating a mat of engineered uniform fill to support lightweight structures. 

Numerical Modelling

Mainmark has carried out numerical modelling to compare the performance of an unimproved site to both a gravel raft and Terefil raft.

The results show that the 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

Largest decrease in differential settlement (2 x compared to gravel raft)
Largest decrease in total settlement
Mitigation from liquefaction damage
Load decrease in underlying soils
Half the excavation depth compared to a gravel raft

Gravel Raft

Decrease in differential settlement
Mitigation from liquefaction damage
Load increase compared to natural ground
No reduction in total settlement

No Raft

No load reduction on sub base soils
Largest total settlement
Largest differential settlement
No mitigation from liquefaction damage

Key Benefits of a Terefil Raft

Cost Effective

Save on excavation time and disposal costs compared to traditional methods.

Minimal Distruption

No vibration and can be set up 30 -60m away from excavation.

Save Time

The entire raft poured in one day. Save construction time and overall build timeline

Decreases Differential Settlement

Decreases differential settlement and can be designed to mitigate primary consolidation settlement.

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. 

Terefil® Raft Ground Improvement used in the rebuild of Christchurch

The replacement of weak surface soil with dense granular fill has been a common method of ground improvement used in the rebuild of Christchurch, following the 2011 Christchurch earthquake. Ground improvement trials undertaken by EQC in 2013 proved that this method was effective at mitigating differential subsidence for lightweight structures.

This also reduces the weight on the underlying soils and provides an engineered fill material with consistent strength and stiffness properties.

Need help?

Need Help With A Project? Contact Us Today

Talk to an expert

Contact us about your project

Step 1

Submit your enquiry using our online form. Include a brief message about the type of problem you are experiencing.

Step 2

One of our expert team members will be in touch to schedule a site inspection that suits you.

Hidden
This field is for validation purposes and should be left unchanged.

Whitepapers

Resources & downloads

The Use Of Terefil Rafts To Control Static Settlement Under Building Loads

© 2024 The Mainmark group of companies. ‘Mainmark®’, ‘Terefil®’, ‘Terefirm®’ and ‘Teretek®’ are trademarks of the Mainmark group of companies.

Mainmark Ground Engineering (NZ) Ltd

Residential

Commercial

Solutions

Seismic

About Mainmark

Our team

Careers

Contact

Technologies

Media & Press

News

Awards

Privacy Policy

Terms and Conditions

Created by Codex