WMM vs. WBM Roads: Key Differences and Applications | Civil Works and Solutions

1. Introduction

In geotechnical and hydrogeological investigations, evaluating the permeability of rock formations is essential, particularly when assessing grouting needs, seepage potential, or foundation suitability. The Lugeon test, a widely used method for measuring rock permeability through water pressure testing in boreholes, is often adapted into a more compact form—the Micro-Lugeon Test—to suit small-scale or low-budget projects where full-scale testing may not be feasible.

This article provides an overview of the micro-lugeon test, its methodology, applications, and advantages for small-scale construction and infrastructure projects.

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2. What is a Micro-Lugeon Test?

The micro-lugeon test is a scaled-down version of the standard Lugeon test, used to determine the water permeability of rock or fractured zones over shorter intervals and at lower injection volumes and pressures. It is typically performed in small-diameter boreholes (less than 50 mm), often drilled for soil nails, mini-piles, small retaining structures, or tunneling support in constrained areas.

The test measures the rate of water absorption (in Lugeon units)—defined as liters per minute per meter of test section under a pressure of 10 bars (1 MPa).

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3. Methodology

Test Setup:

• Borehole Drilling: Depths typically range from 5–20 meters depending on the application.
• Packer Installation: Single or double packers isolate a test zone (usually 1–3 meters long).
• Water Injection: Water is pumped at controlled pressure (often 3 to 10 bars) into the isolated section.
• Flow Measurement: The inflow rate is measured at a stable pressure over a defined time (usually 10 minutes).

Calculations:

$$\text{Lugeon Value} = \frac{\text{Water injected (L/min)}}{\text{Test length (m)}}$$

Lugeon values help classify rock as:

• <1 LU – practically impervious
• 1–5 LU – low permeability
• 5–10 LU – moderate permeability
• >10 LU – high permeability

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4. Applications in Small-Scale Projects

Micro-lugeon testing is particularly suitable for:

• Retaining wall and slope stabilization projects
• Microtunneling or trenchless technology
• Anchor and soil nail design
• Dam toe drainage assessments
• Foundations for small buildings or bridges in rocky terrains

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5. Advantages

• Low Cost and Simple Equipment: Requires only basic pressure testing apparatus and manual or portable pumps.
• Rapid Execution: Can be completed within hours for each borehole section.
• Minimal Disturbance: Ideal for urban or constrained sites with limited access.
• Targeted Data Collection: Offers high-resolution permeability profiles, especially useful for localized seepage zones.

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6. Limitations

• Limited to shallow depths and small-diameter boreholes
• Not suitable for intact massive rocks without fractures
• Requires calibration and pressure control to avoid false readings due to air entrainment or tool leakage

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7. Conclusion

The micro-lugeon test is a practical and efficient tool for permeability assessment in small-scale geotechnical investigations. While it doesn't replace full-scale Lugeon testing in large dams or tunnels, it offers a cost-effective alternative where high-resolution, localized data is sufficient. As geotechnical design becomes more data-driven, micro-lugeon testing ensures that even small projects can achieve a rigorous understanding of subsurface hydraulic behavior.