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 foamed or cellular concrete.
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. 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® light-weight raft
Terefil can be used in the 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 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 dense uniform ground to support lightweight structures.