A warehouse foundation in the sandy loess of Waikiwi behaves nothing like a retaining wall sunk into the dense gravels near the Oreti River. The difference comes down to one thing: how water moves through the ground. In Invercargill, where perched water tables and layered alluvial deposits are common, a standard desktop estimate of permeability simply does not hold up. We run the Lefranc test in soil and the Lugeon test in rock to get direct measurements of hydraulic conductivity on site. The data feeds straight into dewatering design, basement waterproofing, and excavation planning. For deeper projects where rock mass permeability matters, we often pair the Lugeon test with a CPT investigation to map the transition between soil and weathered bedrock with precision.
A single Lugeon test in fractured greywacke gives more useful data for a basement design than a dozen lab permeability tests on small specimens.
Methodology applied in Invercargill
Local geotechnical conditions in Invercargill
A 3-level carpark excavation on Tay Street hit groundwater at 1.8 metres—exactly where the borehole log had shown a silty sand layer. The contractor had planned a simple sump and pump system, but the inflow rate was three times higher than the desktop estimate. The result was two weeks of delays, a flooded excavation, and a redesign of the temporary works. In Invercargill, the margin between a dry dig and a costly dewatering operation is often just a metre of elevation or a single lens of open gravel. Skipping the field test means guessing the inflow rate. Guessing wrong means pumps running 24/7, sediment management issues, and potential instability at the toe of the cut. The Lefranc test removes that guess. For rock sockets under bridge piers or tower crane bases, the Lugeon test reveals whether grouting is needed before concrete placement. It is a small upfront cost against a very real risk of rework.
Our services
Our permeability testing forms part of a wider site investigation package. We tailor the scope to the project—single test for a residential basement, multiple tests across a site for commercial developments.
Lefranc testing in soil
Borehole permeability measurement at discrete depths using constant or falling head methods. Suitable for alluvial sands, silts, and gravels common across the Southland plain.
Lugeon testing in rock
Pressurised water testing in fractured greywacke or schist using a double packer system. Provides Lugeon values and an assessment of rock mass groutability.
Combined permeability and CPTu profiling
Piezocone testing with pore pressure dissipation to estimate hydraulic conductivity in fine-grained soils, correlated with Lefranc results for full-site coverage.
Quick answers
What does a field permeability test cost in Invercargill?
A single Lefranc test typically ranges from $940 to $1,300 depending on depth and access. A full Lugeon profile over a 25-metre rock socket usually falls between $1,300 and $1,700. The final figure depends on the number of test intervals, the drilling method required, and how far the rig needs to travel. We provide a fixed-price quote after reviewing the borehole plan.
When should I specify a Lugeon test instead of a Lefranc test?
Lefranc is for soil and very soft rock where the borehole wall stays open or can be cased. Lugeon is for competent but fractured rock—typically greywacke in the Invercargill area—where you need to measure flow through joints and fissures under pressure. If the project involves a dam foundation, a deep basement socketed into rock, or grouting design, the Lugeon test is the correct tool.
How long does it take to get results from the test?
The field data is processed as soon as the test is complete. We email the preliminary log and calculated permeability values within 24 hours so the contractor can make decisions on dewatering or grouting. The full interpreted report, including comparison with any lab tests, is delivered within five working days.