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How It Works
A permeameter is a lab device that pushes water through a soil sample under a known hydraulic head. By measuring the flow rate, sample length, cross-sectional area, and head difference, you can calculate the permeability coefficient K using Darcy's law. K tells you how easily water moves through the material -- critical for landfill liner design, well construction, and drainage engineering.
The formula is Q = K × A × Δh / ΔL, and it can be rearranged to solve for any of the five variables.
Example Problem
Water flows at 0.0002 m³/s through a soil sample with A = 0.05 m², ΔL = 0.3 m, and Δh = 1.2 m. What is K?
- K = Q × ΔL / (A × Δh) = 0.0002 × 0.3 / (0.05 × 1.2)
- K = 0.00006 / 0.06 = 0.001 m/s
A K of 10−3 m/s corresponds to coarse sand or gravel -- highly permeable.
Frequently Asked Questions
What is Darcy's law used for in environmental engineering?
Darcy's law describes groundwater flow through porous media. Environmental engineers use it for well design, contaminant transport modeling, landfill leachate analysis, and sizing of drainage systems.
What are typical permeability values for different soils?
Gravel: 10−2 to 1 m/s. Sand: 10−5 to 10−2 m/s. Silt: 10−9 to 10−5 m/s. Clay: 10−12 to 10−9 m/s. Clay liners for landfills must have K below 10−9 m/s.
What is the difference between a constant-head and falling-head permeameter?
A constant-head permeameter maintains a steady water level and works best for coarse soils with high permeability. A falling-head permeameter lets the water level decline over time and is more accurate for fine-grained soils with low K values.
Related Calculators
- Unconfined Well Calculator -- apply Darcy's law to radial flow toward a pumping well.
- Solid Waste Calculator -- estimate landfill percolation through the soil cover.
- Rainwater Collection Calculator -- design catchment systems that interact with soil infiltration.
- Darcy's Law Calculator — calculate groundwater flow velocity from permeability data.
- French Drain Calculator — design subsurface drainage using soil permeability results.
- Length Unit Converter — convert sample dimensions between metric and imperial units.