Working across Auckland’s diverse topography, our team frequently observes that the combination of volcanic ash soils, residual clay from Waitemata Group sandstone, and high seasonal rainfall creates recurrent slope instability. Before any development on hillsides, we conduct a thorough landslide assessment that integrates surface mapping with subsurface exploration. In many cases, the initial walkover reveals tension cracks or perched water tables that demand deeper investigation using calicatas exploratorias to expose the failure plane directly. This hands-on approach ensures we capture the real geometry of the slip surface rather than relying solely on assumed models.
A single tension crack at the crest of a slope can indicate a failure plane 8-10 metres deep — catching it early saves millions in remediation.
Methodology and scope
Our landslide assessment methodology follows the New Zealand Geotechnical Society guidelines, particularly the 2016 Slope Stability and Landslide Risk Assessment practice note, which is mandatory for Resource Consent applications in Auckland Council areas. The process typically includes:
Geomorphological mapping and historical aerial photo review to identify past movement
Subsurface investigation using test pits, hand augers, or machine drilling depending on access
Laboratory testing of shear strength parameters (direct shear, triaxial) on undisturbed samples
Limit equilibrium and finite element stability analysis using SLOPE/W or Slide software
For deep-seated rotational failures, we combine this with monitoreo-taludes using inclinometers to track movement rates over time. When debris flows are a concern, we run runout modelling calibrated to local terrain — a step that often surprises clients unfamiliar with Auckland’s rapid infiltration behaviour on weathered rock.
Technical reference image — Auckland
Local considerations
Comparing the North Shore’s steep volcanic slopes with the soft alluvial flats of South Auckland, the failure mechanisms shift dramatically. In areas like Takapuna or Devonport, shallow translational slides dominate due to thin soil cover over basalt. Down south near Manukau, deep-seated rotational failures in the Tauranga Group clay can extend 6-8 metres below grade. Our landslide assessment must account for these contrasts because a generic analysis misses local triggers — like the perched water tables that form after three consecutive days of rain exceeding 80 mm, a pattern Auckland experiences regularly in winter.
Review of historical aerial photos, lidar data, and council records to identify past landslides and define the landslide inventory for your site.
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Subsurface Investigation (Test Pits & Boreholes)
Machine-excavated test pits up to 4 m deep to expose failure surfaces, plus boreholes with undisturbed sampling for laboratory shear strength testing.
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Stability Analysis & Modelling
Limit equilibrium analysis (Morgenstern-Price, Spencer) and finite element modelling (RS2) to calculate factor of safety under static, seismic, and rainfall scenarios.
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Monitoring & Remediation Design
Installation of inclinometers, standpipes, and surface markers; design of drainage, soil nailing, or retaining walls to stabilise the slope.
Applicable standards
NZS 4404:2010 (Land Development and Subdivision Infrastructure), NZGS 2016 – Slope Stability and Landslide Risk Assessment Practice Note, AS/NZS 1170.2:2011 (Structural design actions – wind actions for slope interaction), NZS 4402 (Direct Shear Test of Soils Under Consolidated Drained Conditions)
Frequently asked questions
When is a landslide assessment required in Auckland?
Auckland Council typically requires a landslide assessment for any development on land with a slope steeper than 15 degrees, or where the property is within a known landslide-prone area as identified in the District Plan. It is also mandatory when applying for Resource Consent for subdivision or building on hillsides.
How much does a landslide assessment cost in Auckland?
The cost varies depending on site complexity, but for a typical residential slope in Auckland you can expect to pay between NZ$1,530 and NZ$5,700. This includes the desktop study, field investigation, laboratory testing, and a formal report with stability analysis.
What is the difference between a landslide assessment and a geotechnical investigation?
A geotechnical investigation is broader and covers all soil and rock properties for foundation design. A landslide assessment is a focused study that specifically evaluates slope stability, failure mechanisms, and risk of movement. In practice, the two often overlap — a landslide assessment includes geotechnical testing of the failure surface materials.
Location and service area
We serve projects across Auckland and its metropolitan area.
