Moisture movement is soil and its permeability
As it is known from the scientific facts that ground water
in the soil moves inside it if it is exposed to a difference in the water level
on both sides of it and through its mass, and this difference in the water
level is called hydrostatic pressure. And that the water
movement is rapid and noticeable if the soil is sandy, and slow if the soil is silty or clayey
cohesive.
As an example of this
and a statement of this movement, if we dug at a site for the purpose of
implementing foundations for a facility and the drilling extends below the
groundwater level at the site as a result, hydrostatic pressure will be generated on the drilling wall, the maximum value of which will
be at the level of the drilling bottom. And this pressure (the
weight of the water column is above the bottom level Drilling) It causes the movement of water to flow into
the hole from both sides and the bottom of the drilling, as shown in the figure
below.
- Soil Permeability.
The speed of water movement
in the soil depends on several factors:
- The soil permeability,
which is the characteristic that relates to the free movement of water through its
grains.
- the amount of Hydraulic gradient, which is the amount of the hydrostatic pressure relative to the distance the water move in the soil.
Thus, the phenomenon of water movement in the soil is
expressed by a law known as the Darsy EQ law, which is
V = K * I
Where,
V = the velocity of water in the soil m/s
K = the soil permeability coefficient CM/S
I = Hydraulic gradient
This, given the
velocity of water in the soil, it is possible to calculate the amount of water
accumulated in a certain area, which is called water discharge
Q = V * A
Q = Discharge
in units of length cubed per unit time
V = the velocity of water in the soil
A = Cross sectional area in units of length squared
- Measuring Soil Permeability.
We can measure soil permeability by two methods:
- Constant Head Test.
The same relative elevation of the top of the water column (head pressure) remains over the sample throughout the test. It is a valid test for soils with a high rate of flow like sands and gravels, but also some clay soils.
- Falling Head Test.
Allows the head to decrease as water infiltrates the sample, diminishing the pressure over the course of the test. Falling head methods are generally limited to fine-grained soils.