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**((الخواص الأسـاســيـة للـتـربــة (Basic Characteristics of Soil)**

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**Soil and Soil Engineering**

*The term Soil has various meanings depending upon the general field in which it is being considered. *To a Pedologist (agricultural soil scientist)... Soil is the substance existing on the earth's surface, which grows and develops plant life. *To a Geologist Soil is the material in the thin surface zone within which roots occur, and all the rest of the earth’s crust is termed ROCK irrespective of its hardness. *To an Engineer .... Soil is the un-cemented deposits of mineral and/or organic particles or fragments covering large portion of the earth's crust. 2

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**Ingredients of Soil: The Phase Diagram**

The nature of soil differ from other material, since it composes from three states and they respectively as follows: Solid State, Liquid State, and Gas State. The Phase Diagram In a typical volume of soil there are three components are arranged in a complex mixture: Soil Solids, Water, and Air. To visualize the relationships among the components when performing weight-volume or mass-volume calculations, drawing a phase diagram is recommended. Much like checking equilibrium with a free body diagram in statics, completing and balancing a phase diagram with numerical values of all quantities permits crosschecking the solution. The Figure below shows an element of soil and the corresponding phase diagram.

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**The Soil Phases Diagram**

THE SOIL SYSTEM “PHASE” DIAGRAM AIR WATER SOIL SOLIDS Air pockets

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All solid particles in the element are taken as an equivalent single mass at the bottom of the diagram. Above the solids is the water-also represented as a single equivalent mass-and above that, the air. On the sides of the diagram are variable names; numerical values are entered here during calculations. On the left side are the total volume V, the volume of solids Vs, the volume of water Vw, and the volume of air Va. The combined volume of water and air is the volume of voids Vv . On the right side are shown the total weight M, the weight of solids Ms, and the weight of water Mw. The weight of air is negligible.

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Objectives To compute the masses (or weights) and volumes of the three different phases. Va air Ma=0 Mt Notation M = mass or weight V = volume s = soil grains w = water a = air v = voids t = total Vt Vv Vw water Mw Vs soil Ms Phase Diagram

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Definitions Water content (w) is a measure of the water present in the soil. soil air water Vs Va Ma=0 Ms Mw Mt Vw Vv Vt X 100% Expressed as percentage. Range = 0 – 100+%. Phase Diagram

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**Definitions Void ratio (e) is a measure of the void volume. soil air**

water Vs Va Ma=0 Ms Mw Mt Vw Vv Vt Phase Diagram

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Definitions Porosity (n) is also a measure of the void volume, expressed as a percentage. soil air water Vs Va Ma=0 Ms Mw Mt Vw Vv Vt X 100% Theoretical range: 0 – 100% Phase Diagram

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Definitions Degree of saturation (S) is the percentage of the void volume filled by water. soil air water Vs Va Ma=0 Ms Mw Mt Vw Vv Vt X 100% Range: 0 – 100% Dry Saturated Phase Diagram

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**A Simple Example In this illustration, e = 1 n = 50% S = 50% air water**

soil e = 1 n = 50% S = 50%

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Definitions Bulk density (m) is the density of the soil in the current state. soil air water Vs Va Ma=0 Ms Mw Mt Vw Vv Vt Units: t/m3, g/ml, kg/m3 Phase Diagram

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Definitions Saturated density (sat) is the density of the soil when the voids are filled with water. Submerged density (’) is the effective density of the soil when it is submerged. ’ = sat - w

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**Definitions Dry density (d) is the density of the soil in dry state.**

air water Vs Va Ma=0 Ms Mw Mt Vw Vv Vt Units: t/m3, g/ml, kg/m3 Phase Diagram

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Definitions Bulk, saturated, dry and submerged unit weights () are defined in a similar manner. = g kg/m3 N/m3 m/s2 Specific gravity of the soil grains (Gs) typically varies between 2.6 and 2.8.

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**Testing Times… State whether the following are true or false?**

(a) Dry density is greater than submerged density True (b) In unsaturated soils, water content is always less than 100%. False (c) Larger the void ratio, larger the porosity. True

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**والسلام عليكم ورحمة الله وبركاته**

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