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The constant head permeability test is conducted for
coarse grained soils
silty soils
clayey soils
organic soils
coarse grained soils
The constant head permeability test is specifically designed for coarse-grained soils (such as sand and gravel) which exhibit high permeability. Because these soils allow water to flow through them at a significant rate, a steady supply of water can maintain a constant hydraulic head throughout the test duration.
The constant head permeability test is specifically designed for coarse-grained soils (such as sand and gravel) which exhibit high permeability. Because these soils allow water to flow through them at a significant rate, a steady supply of water can maintain a constant hydraulic head throughout the test duration.
k=AthQLтАЛ тАФ Coefficient of permeability where k is permeability, Q is volume, L is length, A is area, t is time, and h is head.
Water from a reservoir flows through a cylindrical sample of soil under a constant pressure head maintained by an overflow mechanism. The volume of water collected over a known time interval is measured, allowing for the calculation of the coefficient of permeability using Darcy's law. The method assumes laminar flow conditions through the soil pores.
Suitable for soils with k>10тИТ3┬аcm/s.
Requires a constant supply of water to keep the head steady.
The hydraulic gradient i is kept constant throughout the test.
Not suitable for clays due to extremely low flow rates.
Simple to perform for granular materials.
Allows for direct measurement of volume over time.
Inaccurate for soils with low permeability (clays/silts).
Requires significant volume of water for testing.
Dam foundation studies.
Drainage design for granular embankments.
| Feature | Constant Head | Falling Head |
|---|---|---|
Soil Type Suitability | Coarse-grained (Sand/Gravel) | Fine-grained (Clay/Silt) |
For fine-grained soils like silts and clays, the falling head permeability test is used because the flow rate is too slow for steady-state measurement.
The constant head apparatus ensures that the pressure gradient remains uniform, which is only measurable when the discharge is sufficiently large.
A is correct тАФ The constant head permeability test is used for soils with high hydraulic conductivity such as coarse-grained soils.
Always remember the threshold: Constant Head is for high permeability (k > 10тБ╗┬│ cm/s) and Falling Head is for low permeability (k < 10тБ╗┬│ cm/s).