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Note for Soil Mechanics - SM by shweta sharma

  • Soil Mechanics - SM
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Shweta Sharma
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ORIGIN OF SOILS (0 Questions asked from last 6 years of GATE) • • • • Soils are formed from weathering of rocks and decomposition of organic matter. Types of weathering – Physical weathering: by temperature, frost action, abrasion etc. – Chemical weathering: oxidation, carbonation, hydrolysis etc. Different types of soils - Alluvial soil, Black soil (Cotton soil), Laterite soil, Sandy Soil etc. Alluvial soil is formed by river transportation, Black soil by chemical weathering and laterite soil by leaching. SOIL CLASSIFICATION (0 Questions asked from last 6 years of GATE) • • • Classification based on origin and type of soil Residual soil: Soil formed by weathering and is deposited there itself. Transported soil: Soil transported by agents like water, wind, ice, glaciers etc. Types of transported soil and their agents. Types of Soil Alluvial Lacustrine Marine Aeolian (Sane dunes, Loess) Drift Till Colluvial (Talus) Agents of Transportation Rivers Lake Ocean Wind Glacier Melting of glacier Gravitation THREE PHASE DIAGRAM (BLOCK DIAGRAM) (Minimum 1 Question from this topic in every year GATE Exam) • • Unsaturated soil consists of solids, water and air which forms the three phase diagram Basic abbreviations used: V s , V w , V a represents volume of solids, water and air respectively V represents total volume. CivilEnggForAll.com

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V s , V w , V a represents volume of solids, water and air respectively V represents total volume. Vv = Va + Vw V=V a + V w + V s = V v + V s PROPERTIES 1. Void ratio e = V v /V s Remember volume = weight/density (It can be used to solve some problems) - Value of ‘e’ always greater than zero. e coarse grained < e fine grained 2. Porosity (K) or percentage voids η = V v /V 0 < η < 100% Relationship between e and η e = η/(1- η) η = e/(1+e) 3. Degree of Saturation (S r ) S r = V w x 100 / V v 0 ≤ S r ≤ 100% CivilEnggForAll.com

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S r = 0 for dry soil and S r = 1 for fully saturated soil. 4. Air content (a c ) a c = V a /V v a c = 0 for fully saturated soil and a c = 1 for dry soil. Relationship between a c and S r is a c = 1-S r or a c +S r = 1 5. Percentage air voids (η a ) η a = V a x 100/V 0 ≤ ηa ≤ η η a for fully saturated soil and η a = η for dry soil. For dry soil, V w =0 , therefore V v = V a Relationship between η a , η and a c is η a = η x a c DENSITY OF SOLID MASS Bulk Density γ b = W/V = (W W +W S )/V Dry Density γ d = W S /V Density of Solids, γ S = W S /V S (Unit wt. of solids) γ s is constant for given soil, but γ d is not. Saturated density, γ sat = W sat /V CivilEnggForAll.com

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Submerged density (γ sub or γ’) = W sub /V W sub is Submerged Weight of Soil Relationship between γ sub and γ sat is γ sub = γ sat – γ w where γ w is density of water Water Content or Moisture Content W C = W W x 100/W S WC > 0 W W , W S , W represents weight of water, solids and total weight SPECIFIC GRAVITY OF SOLIDS Specific Gravity (G) = γ S /γ w G is measured at 270 C G is usually taken as 2.65 γ S is density of soil solids γ w is density of water Apparent/Bulk/Mass Specific Gravity (G m ) = γ b /γ w γ b is bulk unit weight Gm < G For a given soil, G is constant but G m is not. Relationship between volume of soil, void ratio and dry density. V 1 /V 2 = (1+e 1 )/(1+e 2 ) = γd 2 /γd 1 CivilEnggForAll.com

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