2016 -2017 Soil Mechanics Lectures Third Year Students Includes: Soil Formation, Basic Phase Relationship, soil classification, compaction, Consistency of soil, one dimensional fluid flow, two dimensional fluid flows. Soil Mechanics Lectures /Coarse 1-----------------------------2016-2017-------------------------------------------Third year Student 2 Soil Mechanics Lectures /Coarse 1-----------------------------2016-2017-------------------------------------------Third year Student 3 Soil Mechanics Lectures /Coarse 1-----------------------------2016-2017-------------------------------------------Third year Student Chapter One Soil Formation and Basic-Relation ships Soil Is any uncemented or weakly cemented accumulation of mineral particles formed by weathering of rocks, the void between the particles containing water/ or air. Weak cementation can be due to carbonates or oxides precipitated between the particles or due to organic carbonates or oxides precipitated between the particles or due to organic matter. Depending on the method of deposition, soils can be grouped into two categories: 1- Residual soils: The soils which remain at the place of disintegration of parent rock. 2- Transported soils : The soils, which carried away from their place of disintegration to some other place by transporting agencies. The transporting agencies may be classified as: i) Water ii) wind iii)gravity iv) Ice So in general soil is formed from disintegration of rocks over laying the earth crust. rain wind Weathering Which are usually results from atmospheric processes action on the rock at or near the earth surface. 4 Soil Mechanics Lectures /Coarse 1-----------------------------2016-2017-------------------------------------------Third year Student 1- Mechanical (Physical weathering): All type of actions that cause a disintegration of the parent rocks by physical means such as, gravity, wind and water. The product of this type is rounded, sub rounded or granular, its products called coarse grained soil e.g. (gravel and sand ) they present in nature in a single grain structure . Coarse grained soil • Sand & Gravel • Cohesion less soil • It properties are the same as parent rock. 2- Chemical weathering All types of chemical reactions that occur between the minerals of the rock and the environment (air, water ---et.) and will end up by disintegration of parent rock into fine grain particles; these products have different properties from the parent rock. They present in nature as a lumps of number of plate like particles. The physical property of this product does not reflect the same properties of the parent rocks. Fine grained soil • Silt and clay • Cohesive material • Its properties do not reflect the same properties of the parent rocks. Soil Gravel , Dia Sand Silt Clay > 2 ͡͡ ͕̾͝ ≤ Dia: equivalents diameter (mm) 5 Soil Mechanics Lectures /Coarse 1-----------------------------2016-2017-------------------------------------------Third year Student Clay minerals: There are two basic structure units that form types of the minerals in the clay: a) Tetrahedral Unit : Consists of four oxygen atoms (or hydroxyls, if needed to balance the structure) and one silicon a tom. Elevation Tetrahedral sheet ھ رات ا ي وا ة ان + 4 ت ان ا#و"! . b) Octahedral Unit (consist of six hydroxyl ion at apices of an octahedral enclosing an aluminum ion at the center). 6 Soil Mechanics Lectures /Coarse 1-----------------------------2016-2017-------------------------------------------Third year Student Formation of Minerals The combination of two sheets of silica and gibbsite in different arrangements and condition lead to the formation of different clay minerals such as : 1- Kaolinite Mineral : This is the most common mineral is the kaolin. The structure is composed of a single tetrahedral sheet and a single alumina octahedral sheet as shown in figure below: 1- Strong Hydrogen Bond So not affected by water 2- And its also called China clay 3- 2- Illite has a basic structure consisting of two silica sheets with a central alumina sheet. There is a potassium bond between the layers. 3- Montmorillonite unit: The basic structural unit is similar to that of Illite. Highly affected by water ون دة '& ال ا#$ Highly affected by water with high shrinkage and Swell and it is called expansive soil. ودة ظر ھذه ا ا طق ا راو و ا راو 7 Soil Mechanics Lectures /Coarse 1-----------------------------2016-2017-------------------------------------------Third year Student Clay Particle –water relations: In nature every soil particle is surrounded by water. Since the centers of positive and negative charges of water molecules do not coincide, the molecules behave like dipoles. The negative charge on the surface of the soil particle therefore attracts the positive (hydrogen) end of the water molecules. More than one layer of water molecules sticks on surface with considerable force decrease with increase in the distance of the water molecule from the surface. The electrically attracted water surrounds the clay particle is known as the diffused double-layer of water. The water located within the zone of influence is known as the adsorbed layer as shown in figure: Clay Particle Diffuse double layer Adsorbed water layer surrounding a soil particle Clay structures: 1) - Dispersed structure 2) - flocculated structure 8 Soil Mechanics Lectures /Coarse 1-----------------------------2016-2017-------------------------------------------Third year Student Distinguish between flocculated and dispersed structures Flocculated Dispersed More strength Lower strength Permeability is higher permeability is less Low compressibility higher compressibility Basic Relationships: Weight Wt = Ww + Ws Volume Vt = Vv + Vs = Va + Vw + Vs Where : total weight of soil ̷̴ Total Volume Weight of water ͐/ ∶ ̷̷ ∶ : Volume of Void : Weight of solid ͐1 ̷̳ : Volume of air Weight of air 0 ͐ ̷̡ ∶ ≈ Volume of water ͐2 ∶ : Volume of Soild ͐. 9 Soil Mechanics Lectures /Coarse 1-----------------------------2016-2017-------------------------------------------Third year Student 1- Unit Weight – Density = ̴̡̯̬̚ ̷̴̧̨̥̩ ̷̴ ˫̳̯̩̬ = ̴̡̯̬̚ ̶̵̯̬̭̥ ̴̜ 2- Water content % % = ÍÍ =ÃÍ ́¹ ∗ ̊̉̉ ÅÈ ă¹ ∗ ̊̉̉ ÍÉ ÃÉ 3- Void ratio , e vΤ e = vΡ 4- Porosity (n%) ÌÌ Ä% = ∗ ̊̉̉ ÌÊ 5- Air content A% Ì· % = ∗ ̊̉̉ ÌÊ 6- Bulk Density (total density), ûÊ ρ Λ² = ΢ Τ² 7- Dry density , ÃÉ ( ̌ Á½ ûºÈÏ = ½Ã⁄ ¹Ã ) ÅÈ ( ̌) ÌÊ Ã 8- Dry unit weight ( íºÈÏ ) ÍÉ ̌ íºÈÏ = (Áª⁄ à ) ÌÊ 9- Specific gravity , £É 10 Soil Mechanics Lectures /Coarse 1-----------------------------2016-2017-------------------------------------------Third year Student ûÉ ÃÉ⁄ÌÉ ÃÉ £É = = = ûÍ ûÍ ÌÉ∗ûÍ íÉ ÍÉ⁄ÌÉ ÍÉ ( its value range between 2.6- 2.85) £É = = = íÍ íÍ ÌÉ∗íÍ 10- Solid Density, ûÉ ÃÉ , ÍÉ ûÉ = íÉ = ÌÉ ÌÉ Some Useful Correlation: 1- S.e = £É. ă¹ 2- » Ä = ̊ͮ» 3- Ä » = ̊ͯÄ 4- = Ä(̊ − É) 5- »ͯă∗£É = ̊ͮ» 6- £É(̊ͮă) £É(̊ͮă) ûÊ = ̊ͮ» ûÍ ÅÈ íÊ = ̊ͮ» íÍ 7- £ÉͮÉ∗» £ÉͮÉ∗» ûÊ = ̊ͮ» ûÍ ÅÈ íÊ = ̊ͮ» íÍ 8- £Éͮ» £Éͮ » ûÉ = ̊ͮ» ûÍ ÅÈ íÉ = ̊ͮ» íÍ 9- £É £É ûºÈÏ = ̊ͮ» ûÍ ÅÈ íº = ̊ͮ» íÍ 10- û»¼¼. = û́ = ûÉ·Ê − ûÍ 11- £Éͯ̊ í»¼¼ = í́ = ̊ͮ» íÍ Some typical values of void ratio, moisture content in a saturated condition, and dry unit weight for soils in a natural state are given in the following table: Table 1- Void ratio, Moisture Content, and Dry Unit Weight for some Typical Soils in a Natural State. Type of Soil Void ratio Natural moisture Dry unit weight , íº content in a ( saturated state (%) Áª ⁄Ã̌) Loose uniform 0.8 30 14.5 sand Dense uniform 0.45 16 18 sand 11 Soil Mechanics Lectures /Coarse 1-----------------------------2016-2017-------------------------------------------Third year Student Loose angular- 0.65 25 16 grained silty sand Dense angular- 0.4 15 19 grained silty sand Stiff clay 0.6 21 17 Soft clay 0.9-1.4 30-50 11.5-14.5 Note: the weight of one kilogram mass is 9.806 Newton 1 kg = 9.806 N Example- 1: In its condition a soil sample has a mass of 2290 g and a volume of 1.15*10 -3 m3. After being completely dried in an oven the mass of the sample is 2035g. The value of Gs for the soil is 2.68. Determine the bulk density, unit weight, water content, void ratio, porosity, degree of saturation and air content. Solution: = ͦ.ͦͭͤ ͧ " / = ͥ.ͥͩ∗ͥͤ w = 1990 ͛͟⁄ ͡ = 1.99 (w Unit weight , " ͧ ͧ = = 1990∗9.8 = 19500 ͈⁄ ͡ = 19.5 ͈͟⁄ ͡ Water content , 2 ͦͦͭͤͯͦͤͧͩ ! = . = ͦͤͧͩ = 0.125 ͣͦ 12.5% ́.(1 + !) / = 2 1 + ͙ 2.68(1 + .125) 19.5 = ∗ 10 1 + ͙ e = 0.538 Porosity, n= ͤ.ͩͧͬ ͥͮ = ͥ.ͩͧͬ = 0.3490 ~0.35 ͍. ͙ = ́..! Degree of saturation , S= ͤ.ͥͦͩ∗ͦ.ͪͬ ͤ.ͩͧͬ = 62.267% Air content, A = n (1- S) = 0.35( 1-.62)= 0.132 12 Soil Mechanics Lectures /Coarse 1-----------------------------2016-2017-------------------------------------------Third year Student Example 2: a moist soil has these values : ͯͧ ͧ , m = 13.95 kg , ͐ = 7.08 ∗ 10 ͡ ! = Determine: 9.8 %, ́. = 2.66. by soild? , , ͙ , ͢ , ͍( %), ͙ͪͣͩ͠͡ ͙ͣ͗͗ͩͤ͘͝ ͖ͭ ͕͙ͫͨͦ ͕͘͢ ͙ͪͣͩ͠͡ ͙ͣ͗͗ͩͤͧ͘͝ Solution: ͡ 13.95 ͧ = = = 1970.3 ͛͟/͡ ͐ 7.08 ∗ 10 ͯͧ `ĪĘħ ͥͭͫͤ.ͧ &" = ͥͮ h = ͥͮͤ.ͤͭͬ = 1794.4 (w ́. = 2 1 + ͙ ͦ.ͪͪ e = 0.48 1794.4 = ͥͮ ∗ 1000 ͙ 0.48 ͢ = = = 0.324 1 + ͙ 1.48 S.e = S. 0.48 = 2.66 * 0.098 S = 54.3% ́. ! (Ħ 1794.4 = (Ħ = w ͡. = 12.7 ͛͟ ħ ͫ.ͤͬ∗ ͥͤ ͡2 = ͡ − ͡. ͡2 = 13.95 − 12.7 = 1.25 ͛͟ (Ī ͥ.ͦͩ ͧ ∴ ͪ2 = = = 0.00125 ͡ `Ī ͥͤͤͤ (Ħ (Ħ = ͥͦ.ͫ = 0.00478 ͧ ͪ. = ͪ. = ͡ Ħ`ĪĪ Ħ`Ī ͦ.ͪͪ∗ͥͤͤͤ Example 3:In the natural state, a moist soil has a volume of 0.0093 ͧ and weighs 177.6 ͡ N. The oven dry weight of the soil is 153.6 N. If . Calculate the moisture ́. = 2.71 content, moist unit weight, dry unit weight, void ratio, porosity and degree of saturation.