Subsidence Works

House Lifters New Zealand lifts, slides and levels houses affected by ground subsidence - including villas, character and heritage houses. Our experienced teams are based in Auckland and Christchurch.

 

Minimising the Risk & Effects of Subsidence

An unlevel house is often caused by subsidence; the ground beneath the foundations sinking, settling or slumping. House relevelling usually also requires partial or full foundation replacement, at a suitable depth. House Lifters is the only New Zealand company providing a complete lifting, sliding and levelling service - which can include replacing foundations, concrete floor slabs, repiling, and ground stabilisation.  

A crucial aspect of House Lifters’ subsidence work is understanding each site’s ground conditions and soil bearing capacity. We can then use the most suitable type of foundation, piles, and if required, ground stabilisation. To help avoid being affected by subsidence, houses need to be built on soil with sufficient bearing capacity (bearing pressure) to support the house and foundations, with less than 25mm of settlement.  

Common Causes of Subsidence

Foundations, Slabs & Piles

House Lifters repairs/replaces house foundations, concrete floor slabs and piles:

  • Shallow & deep foundations
  • All-piled foundations
  • Perimeter concrete foundations (ring foundations)
  • Concrete floor slabs (slab on grade)
  • Concrete piles
  • Screw piles
  • Timber piles

Our experienced teams are based in Auckland and Christchurch. House Lifters is unusual in the industry for also having in-house engineers, designers, and Licensed, Certified builders. We are able to design subsidence solutions for even the most technical projects, including steep hill sites, pole houses, and challenging sections with access issues. 

subsidence

subsidence

Ground Stabilisation

House Lifters can undertake ground stabilisation, strengthening and remediation to lessen the risk or effects of subsidence (and seismic activity – e.g. liquefaction and lateral movement). Methods of improving the strength and bearing capacity of soils can generally be described as: Densification - to increase the soil’s strength and stiffness… Containment - to support and reinforce the soil… And Solidification - to improve the soil’s stability.
House Lifters’ ground stabilisation, foundation and piling options include:

  • Remedial Underpinning
  • Mechanical Slabjacking System 
  • Armadillo™ Foundation System
  • Screw Piles (Ground Screw Anchoring System)
  • Gravel Rafts
  • Retaining Walls

Common Causes of Subsidence

Ground subsidence (sinking, settling or slumping) is usually due to the soil having insufficient bearing capacity (bearing pressure) to carry the load of the house and foundations. Significant changes in soil moisture, e.g. the soil becomes saturated, and/or dries out through drought, can cause the subsoil water pressure (or lack of) to compromise the integrity of foundations, floor slabs and piles, which can take a house out of level.

  • House built on soil types with insufficient bearing capacity (bearing pressure)
  • Insufficient surface and/or sub-surface (subsoil) drainage
  • Drought
  • Earthquakes, seismic activity, liquefaction
  • Volcanic activity
  • High water table
  • Flooding, landslips, excessive runoff
  • Sloping site in high rainfall area
  • Flood-prone site, e.g. near river
  • Earthworks, excavation, exposed banks
  • Removal of vegetation
  • Erosion – e.g. beach frontage, clifftop sites
  • Retaining wall failure/deterioration
  • Natural springs

Houses built on land near waterways are more vulnerable. For example, most of Christchurch city’s urban lowlands is drained swampland with a high water table; made up of coastal and river deposits e.g. sand, shell, gravel, silt, clay and peat.

Soil Bearing Capacity (Bearing Pressure)

New Zealand soils vary widely - from strong rock, to very soft soil. If there any are doubts about ground stability, it is important to consult a geotechnical engineer. Examples of soils which are more likely to subside:

  • Expansive (Reactive) Soils E.g. Heavy clay - expands in winter, shrinks in summer
  • Compressible Soils  E.g. Soft alluvial soils, topsoil, uncompacted loose gravel
  • Allophanic Soils E.g. *Volcanic ash soils - low density, low strength
  • Pumice Soils Sandy/gravelly, low strength, easily erodible
  • Peat Drained peat consolidates & breaks down

 

*Much of Auckland city is built on the Auckland Volcanic Field (AVF), which contains at least 50 volcanoes, and resulting volcanic ash soils. Auckland also has clay soils with widely-varying moisture content.