In Nelson, a lot of the time we see groundwater assumptions made on desktop studies that don't hold up once the excavator hits the Moutere Gravels. You get water where you didn't expect it. Or you get tight material where a soakage system was planned. That's exactly why the field permeability test, both the Lefranc method for soils and Lugeon for rock, is not optional when you are dealing with retaining structures, cut-and-cover tunnels, or stormwater disposal. Without in-situ data, your dewatering plan is just a guess. We run these tests during the site investigation phase so the design team knows the actual hydraulic conductivity of the ground. For deeper projects we often combine this with CPT testing to get a continuous soil profile and pore pressure picture before placing the test intervals. Nelson's mix of alluvial terraces and weathered Port Hills loess makes local knowledge critical. You need a team that knows when a Lugeon test in the underlying gravels is going to give you more useful data than a surface infiltration test.
A Lugeon test doesn't just measure permeability—it reveals whether rock fractures are open, dilated under pressure, or susceptible to infilling erosion.
Service characteristics in Nelson
Critical ground factors in Nelson
Nelson sits in a high-seismic zone, and the Moutere Gravels have a known potential for liquefaction in places. When you add high groundwater to that equation, you're looking at a serious risk of bearing capacity failure or excessive settlement. Ignoring in-situ permeability means you don't know the drainability of the soil during an earthquake. Pore pressure buildup and dissipation rate—that's a direct input into a liquefaction assessment. We have seen projects where a simple Lefranc test changed the entire foundation strategy from shallow footings to ground improvement, saving the client from a post-construction failure that would have cost ten times the investigation budget. In rock tunneling for water supply or stormwater on the outskirts of town, an untested fracture zone can mean a sudden inrush of water mixed with fines, destabilizing the face. The Lugeon test is your pre-excavation warning system. It tells you exactly where to grout and where you can advance without treatment.
Our services
Our field permeability testing is part of a larger geotechnical investigation package. These are the three core services we deliver alongside the in-situ test to give you a complete geotechnical model.
Lefranc Testing in Soils
Constant and falling head tests in boreholes to determine hydraulic conductivity of alluvial and residual soils. We match the test interval to the stratigraphy, not just arbitrary depths.
Lugeon (Packer) Testing in Rock
Pressurized water tests in N-size or H-size boreholes through a pneumatic packer system. We use the standard five-stage pressure cycle to assess fracture flow behavior and grouting needs.
Soakage & Infiltration Assessment
Combined in-situ testing and analysis for stormwater disposal systems in accordance with Nelson City Council requirements and NZS 4404.
Frequently asked questions
When is a Lugeon test required instead of a Lefranc test?
A Lugeon test is required when the ground investigation encounters bedrock. It measures permeability in fractured rock using a packer system to isolate a specific interval in the borehole. The Lefranc test is for soils and is performed in the open borehole without a packer. In Nelson, many sites transition from terrace gravels into weathered rock, so both tests are often needed in the same borehole.
How long does a permeability test take on site?
A single Lefranc test typically takes 30 to 60 minutes once the test interval is prepared. A full five-stage Lugeon test in rock takes one to two hours per interval, depending on water take and fracture response. We plan the test depths with the supervising engineer to fit within the overall drilling schedule.
What is the cost of field permeability testing in Nelson?
For a standard Lefranc or Lugeon test in Nelson, the cost ranges from NZ$1,120 to NZ$1,660 per test interval. The final cost depends on access conditions, borehole depth, and the number of stages required.