Permeability and Water Flow in Soils and Sediments

Hilal, Eman Mohammad Ali (1989) Permeability and Water Flow in Soils and Sediments. MSc(R) thesis, University of Glasgow.

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SECTION I Permeability and its measurements. (1) Permeability is defined as the property of a soil which allows the seepage of fluids through its interconnected void spaces. (2) The flow of water through soils is assumed to follow Darcy's law: Q/t = kA H/L where, k = the coefficient of permeability Q = the quantity of water flowing through the soil in time t L = the height of the soil sample A = the area of the cross-section through which the water flows H = the constant head of water (hydraulic head) operating over the height of the soil. (3) Laboratory measurements. The two most common laboratory methods for determining the coefficient of permeability of soils are the following: i) Constant head permeameter. In the constant head test the level of the water is kept constant by addition of water, ii) Variable head permeameter. In this test the level of the water does not remain constant because no water is added to the cylinder containing the sediment. (4) Field measurements. Soil permeability in the field can be measured when the water table is present and when its absent. 4.1 Water table present. Several methods are presently available for the determination of the coefficient of permeability in the field when the water table is present. In my thesis I discussed some of these methods, which are as follows: 4.1.1 Auger hole methods. 4.1.2 Well and pumping method. The determination of the coefficient of permeability is made when water flows through a surface area of 2nrH and when it flows through 2nd. 4.3.1 Multi-layer method. 4.2 Water table absent. Several methods are also available for the determination of the coefficient of permeability in the field when the water table is absent. Some of these methods are as follows: 4.2.1 Particle size method. 4.2.2 Shallow water pumping test. 4.2.4 Pond-Infiltration test. This test, which is an infiltration test over a large area, has been recommended and put into practice to avoid the problem of soil compression which is inherent in core samples. SECTION II Sediment properties influencing permeability. Permeability depends on the characteristics of the soil which are as follows: 1 Particle size. An increase in grain size results an increase in permeability. Two methods for determining the particle size parameters are outlined (I) Graphical analysis. (II) Algebraic analysis. 2 Particle shape. The coefficient of permeability decreases with increasing uniformity of the pore spaces. The effect of particle shape on porosity is discussed using Fraser's experiment. 3 Packing. Permeability is dependent on the packing arrangement, because the tighter the packing density of particles in the soil or sediment the lower its effective porosity and hence the lower its permeability. 4 Void ratio. The void ratio of soils and sediments has an important effect on permeability. When the volume of voids decreases, the permeability also decreases. 5 Composition. Soil composition is of limited importance in the permeability of some soil types such as silts, sands and gravels, but it is of major importance in clays. 6 Fabric. Fabric is one of the most important sediment properties influencing permeability, especially in finegrained soils. Soil samples which are in a flocculated state will have a higher permeability, while the ones in a more dispersed state will have a lower permeability. 7 Degree of saturation. The higher the degree of saturation, the higher the permeability. The relationship between degree of saturation, void ratio and water content have been algebraically solved and illustrated. 8 Biological effects. I have quoted some examples of these effects, such as the effects of intertidal burrowing invertebrates and micro-organisms. SECTION III Soil physics. 1 Water potential. Water is held in the soil against gravitational forces draining water out, or against evaporation of water from the surface of the soil. The energy with which water is held in a soil at any water content is called the water potential. Water flows from where the potential energy is high to where it is low. It moves constantly in the direction of decreasing potential energy. Water potential consists of pressure potential, solute potential and matric potential. The sum of the gravitational potential and the water potential gives the total water potential. 2 Steady state flow in horizontal and vertical direction. In steady state flow, flow characteristics do not change with time, although they may change with location. The rate of flow will depend on the rate of decrease of potential energy in a horizontal and vertical direction. (Abstract shortened by ProQuest.).

Item Type: Thesis (MSc(R))
Qualification Level: Masters
Keywords: Hydrologic sciences, Soil sciences
Date of Award: 1989
Depositing User: Enlighten Team
Unique ID: glathesis:1989-77918
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 28 Feb 2020 12:09
Last Modified: 28 Feb 2020 12:09

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