What Is Soil Permeability ?

What Is Soil Permeability ? Wordnetweb Princeton defines permeability as the properties of an object that can passing by fluid (through osmosis or diffusion). While Wikipedia defines it as: Permeability in fluid mechanics and soil science (usually denoted by ? Or k) is a measure of the ability of porous objects (usually rock) to pass liquid.

Permeability units in international units (SI) is the "m" ^ "2". Another commonly used unit is Darcy (D) or more commonly milidarcy (mD). The equivalent Darcy? "10"? ^ (-12) "M2". Another unit commonly used is "cm2". (1 "m2" = "104 cm2").

Soil Permeability

Soil is a collection of solid particles with interconnected voids. This cavity allows the water to flow in the cavity of a single particle with a higher point to a lower point. The nature of the soil which allows water to pass through the various specific flow rate is called the permeability of the soil. This characteristic comes from the nature of granular soil, although it can be affected by other factors (such as water bound in clay). Thus, different soils will have a different permeability.

Darcy's law

Darcy's law describes the ability of water to flow in the cavities (pores) in the soil and the properties that affect it. There are two major assumptions used in the determination of Darcy's law. The first assumption states that the flow of fluid / fluid in the soil is laminar. While the second assumption states that the land is in a state of saturation.

"? = K.i"

with v = flow velocity (m / s or cm / s) k = coefficient of permeability i = hydraulic gradient
Then it is known that: "v =" "Q" / "At" and i =? H / L, so the Darcy law can be expressed by the equation:

Q = (k.A.t.? H) / L

With A = cross-sectional area of ​​flow (m2 or cm2) t = time fluid along L (seconds)? H = height difference (m or cm) L = length of the area through which the flow (m or cm)

Coefficient of Permeability
Darcy's law indicates that the permeability of the soil is determined by the coefficient of permeability. Basic permeability depends on various factors. At least, there are six major factors that affect the permeability of the soil, namely :

1. Viscosity of the liquid, the higher the viscosity, the soil permeability coefficient will be smaller.
2. Pore ​​size distribution, pore size distribution more equitable, permeability coefficients tend to be smaller.
3. Distribution grain size, more uniform size distribution of grains, permeability coefficients tend to be smaller.
4. Void ratio (void), the greater the ratio of emptiness, soil permeability coefficient will increase.
5. Roughness mineral particles, the coarse mineral particles, soil permeability coefficient will be higher.
6. The degree of saturation of the soil, the more saturated the soil, soil permeability coefficient will be higher.

Determination of coefficient of permeability

There are at least two ways to determine the coefficient of Soil Permeability, ie with fixed head test and falling head test. Test head remained in use for land that has a coarse grain and has a high permeability coefficient. While falling head test is used for fine-grained soil that has and has a low coefficient of permeability.