In Wollongong, you can have competent Hawkesbury sandstone on one block and colluvial silts on the next. We see this every week. A standard borehole log gives you strength. It doesn't tell you how water moves through the fractures. That's why we run field permeability tests using the Lefranc method in soils and the Lugeon method in rock. The data goes directly into the dewatering plan. We do the test. We interpret the result. No extrapolating from grain size curves. AS 1726 gives the framework. Our local experience gives the context. For projects near the escarpment, where the water table responds to rainfall within hours, you need numbers you can trust. A CPT test can map the stratigraphy, but only a Lefranc or Lugeon test measures the mass permeability of the formation.
A permeability value from a disturbed lab sample is a guess. A Lefranc or Lugeon test gives you the mass permeability of the formation as it sits.
Quick answers
When should I specify a Lugeon test instead of a Lefranc test?
Specify a Lugeon test in rock or very stiff cemented materials where you drill with rotary methods and can isolate a test interval with a packer. The rule of thumb: if you need a core barrel to advance the hole, you need a Lugeon test. Use the Lefranc test in soils where the borehole stays open or is supported by a slotted casing and a sand filter. In Wollongong, many sites have a soil profile overlying sandstone, so you'll need both. Lefranc in the upper 3 to 6 metres, Lugeon in the rock below.
How long does a field permeability test take on site?
A single Lefranc test in moderate-permeability soil can be completed in 1 to 2 hours once the test interval is prepared. A Lugeon test in rock typically takes 45 to 90 minutes per 5-metre interval, running all five pressure stages. We always allow time for the test zone to saturate and for flow to stabilise before recording data. In low-permeability materials, the test duration increases because the flow rate takes longer to reach equilibrium.
What does a Lefranc or Lugeon test cost in the Wollongong area?
For a typical investigation in the Wollongong region, a field permeability test ranges from AU$900 to AU$1,770 per test interval. The final cost depends on the depth of the test, the number of intervals required, and the access conditions on site. Mobilisation is additional. We provide a fixed-price quote once we review the borehole logs and the testing depth.
What Lugeon value indicates that rock grouting is needed?
We use the Houlsby interpretation method. A Lugeon value below 3 typically indicates tight rock that does not require grouting. Values between 3 and 10 suggest moderate permeability where grouting depends on the project's water-tightness requirements. A Lugeon value above 10 indicates open fractures and a rock mass that will take grout. For dam foundations and cutoff walls, the acceptance threshold is often set at 3 to 5 Lugeon after grouting.
