Dunedin's ground profile rarely reads like a textbook. You encounter everything from weathered basalt flows and jointed schist to deep loess deposits, often within the same site. A desk-study permeability estimate won't cut it here. We run Lefranc tests in boreholes and Lugeon tests in fractured rock to give you in-situ hydraulic conductivity values that reflect actual conditions. Basalt joints around Mount Cargill can open up during excavation, and loess permeability near the Taieri Plain shifts dramatically with moisture content. Before designing dewatering or permanent drainage, a test pit investigation often helps confirm the soil fabric, while footing design directly depends on the drainage characteristics you measure in the field.
A Lugeon test reveals not just permeability, but the hydraulic aperture of fractures — a parameter no lab test can replicate.
Methodology applied in Dunedin
Demonstration video
Local geotechnical conditions in Dunedin
Dunedin's volcanic geology creates permeability contrasts that catch out standard designs. The Dunedin Volcanic Group includes massive basalt flows sitting directly on highly fractured scoria layers — you can drill through tight rock and suddenly hit an open conduit carrying significant groundwater. On hillside sites from Maori Hill to Brockville, colluvium overlying schist bedrock often develops perched water tables after prolonged rainfall, destabilizing cut slopes. A Lefranc test in the colluvium might show moderate permeability, but the real risk lies at the soil-rock interface. The Lugeon test quantifies that contrast. Without it, drainage assumptions fail, and retaining walls see hydrostatic pressures they weren't designed for. This is especially critical where slope stability assessments rely on accurate pore-water pressure profiles through the wet winter months.
Our services
Our Dunedin field testing programme covers the full sequence from borehole preparation to hydrogeological interpretation.
Lefranc Testing in Soil and Weathered Rock
Variable-head tests for low-permeability materials; constant-head for higher flows. Conducted within HQ-diameter boreholes following NZGS protocols.
Lugeon Packer Testing in Fractured Rock
Five-stage pressure testing in basalt and schist formations. Digital pressure and flow data logging with real-time Lugeon value computation.
Hydrogeological Interpretation & Reporting
Integration of field permeability data with borehole logs, fracture mapping, and laboratory test results to produce consent-ready hydrogeological reports.
Common questions
When does a site in Dunedin require a Lugeon test rather than a Lefranc test?
The choice depends on the ground conditions encountered during drilling. A Lefranc test suits soil, highly weathered rock, or materials where the borehole wall stands open without casing. Once you hit competent basalt or schist with discrete fractures, the Lugeon packer test becomes the appropriate tool because it isolates specific fracture zones and measures their hydraulic aperture under controlled pressure stages. Many Dunedin sites require both methods within the same borehole as the profile transitions from colluvium into bedrock.
How long does a single Lugeon or Lefranc test take on site?
A single Lefranc test typically requires 40 to 90 minutes depending on whether the ground is fine-grained and needs a longer response period. A full five-stage Lugeon test generally takes 60 to 100 minutes per test interval, including packer inflation, stage stabilization, and deflation. Multiple intervals in a deep borehole can be completed in one day with efficient crew coordination.
What does field permeability testing cost for a Dunedin project?
A single Lefranc or Lugeon test typically ranges from NZ$1,050 to NZ$1,950 depending on borehole depth, number of test intervals, and site access conditions on Dunedin's hillside sections. A full-day programme with multiple tests is more cost-effective per test than mobilizing for a single measurement.
What Lugeon value indicates a need for grouting in Dunedin basalt?
The interpretation follows Houlsby's classification. Lugeon values below 1 Lu indicate tight rock with negligible grout take. Values between 1 and 5 Lu suggest minor fracturing where grouting may be optional depending on the project's water-tightness requirements. Values above 5 Lu indicate open, interconnected fractures that will accept grout and generally warrant treatment for dam foundations, deep excavations, or tunnels in the Dunedin volcanic sequence.