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Introduction_to_Soil_Mechanics_Suvadeep_De.pptx

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Introduction_to_Soil_Mechanics_Suvadeep_De.pptx

  1. 1. Soil Mechanics Topic: Phase Analysis of Soil Presented by, Suvadeep De (13001320032)
  2. 2. Introduction to Soil Mechanics The term ‘soil’ according to engineering point of view is defined as the material, by means of which and upon which engineers build their structures. And Soil Mechanics is a branch of Civil Engineering involving the studies about the properties and behaviour of soils in the action of various forces and its applications as an engineering material.
  3. 3. Formation of Soil Soil is formed due to the weathering of rocks by physical and chemical processes. Exposed parts of rocks and decayed by that processes and coarse aggregates are made. That aggregates then are transferred to another places by physical carriers and mixed with various organic and inorganic things and then it turned into the thick level, that’s soil.
  4. 4. What’s Phase Diagram? The diagrammatic representation of different phases separated in soil mass is called as phase diagram. If the soil is partially saturated (air, water, and solid included), that diagram is called Three Phase Diagram. And if the soil is completely saturated (water and solids) or completely dry (air and solids, eg.- oven dried soil), that’s called Two Phase Diagram.
  5. 5. Three Phases of Soil and its Diagram Soil mass is generally referred to as three phase system because it consists of solid particles, liquid and gas. Where, Wa= Weight of air part Ww= Weight of water part Ws= Weight of solid part Va= Volume of air part Vw= Volume of water part Vs= Volume of solid part
  6. 6. Two Phase Diagrams of Soil Completely Saturated Soil Completely Dry Soil
  7. 7. Volumetric Ratios (1) Void ratio, e= Volume of Voids/volume of solids = vv/vs (2) Porosity, n%= (Volume of voids/Total volume of soil)x100% = (Vv/Vt)x100% (3) Degree of Saturation, S% (0–100%)= (Volume of water/Volume of voids)x 100% =(Vw/Vv)x100% (4) Water Content, (W%)= (Weight of water/Weight of solid part)x100% = (Ww/Ws)x100%
  8. 8. Soil Unit Weights Unit weight or weight density of soil refers to its weight per cubic meter volume Unit= KN/m3 1. Dry unit weight, γd= weight of soil solids/total volume of soil= Ws/Vt 2. Total/Bulk/Wet/moist unit weight, γ = Total weight of soil/Total volume of soil = Wt/Vt = (Ws+Ww)/Vt Or, γ = (Ws/Vt) + (Ww/Vt) = γd+(Ww/Vt)
  9. 9. 3. Saturated Unit Weight γsat = (Weight of solid + weight of water)/Volume of soil= (Ws+Ww)/Vt = Total weight of saturated soil/Vt 4. Submerged/ Buoyant Unit Weight When the soil is submerged in the water, water pushes the soil particles upwards, that force is called Buoyant force. γ’= γsat- γw Or, γ’= (Ws)sub 𝑉𝑡 where, (Ws)sub= Submerged soil solids weight =Ws (in air)–weight of solid displaced by water
  10. 10. Relations Between the Properties 1. Specific Gravity, Gs= 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑠𝑜𝑖𝑙 𝑠𝑜𝑙𝑖𝑑𝑠 𝑜𝑓 𝑎 𝑣𝑜𝑙𝑢𝑚𝑒 𝑊𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑎𝑡 4℃ 𝑜𝑓 𝑠𝑎𝑚𝑒 𝑣𝑜𝑙𝑢𝑚𝑒 = 𝑈𝑛𝑖𝑡 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑠𝑜𝑙𝑖𝑑 𝑈𝑛𝑖𝑡 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 𝑎𝑡 4℃ = γ𝑠 γ𝑤 = 𝑊𝑠 𝑉𝑠 .γ𝑤 as,( γs= 𝑊𝑠 𝑉𝑠 ) 2. Relation between e and n: e= 𝑛 𝑛−1 ; n= 𝑒 1+𝑒 3. Relation between e ,S, W, and Gs: S.e=W.Gs as W= 𝑉𝑤 𝐺𝑠 𝑉𝑠 4. Relation between γ, e, S and Gs: γ= 𝑆𝑒+𝐺𝑠 1+𝑒 γw
  11. 11. Example The moist unit weight of a soil is 19.2 kN/m2. Given that G, 2.69 and w = 9.8%, determine a. Dry unit weight b. Void ratio c, Porosity d, Degree of saturation. Ans. γ= 19.2 KN/m3 Gs= 2.69 W= 9.8%= 9.8 100 γw= 9.81 KN/m3 S.e= 9.8 100 x2.68 ≅ 0.264 Gs = γ𝑠 γw = 2.69x9.81= γs = 26.4 KN/m3 γ= ( 𝑠𝑒+𝐺𝑠 1+𝑒 ) γw => 19.2= ( 0.264+2.69 1+𝑒 ) x 9.81 =>1+e= 1.51 => e= 0.51 ∴ S = 0.264 𝑒 = 0.264 0.51 = 0.52 ∴ n = 𝑒 1+𝑒 = 0.51 1.51 =0.34.
  12. 12. Conclusion of Soil Phase Analysis Soil analysis has proved to be very useful in both agriculture and horticulture. In the forest, however, soil analysis has seldom proved to be of consistent value. In part this is because the perennial roots of trees, together with their mycorrhizae, seem able to access forms of nutrient elements not accessible to short-lived arable plants so the chemical soil extractants developed for agriculture may not be appropriate. Perhaps more significant, however, is that over time tree roots can exploit all the rooting volume available to them.

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