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Geotechnical Engineering-II [Lec #15 & 16: Schmertmann Method]

Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.

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Geotechnical Engineering-II [Lec #15 & 16: Schmertmann Method]

  1. 1. 1 Geotechnical Engineering–II [CE-321] BSc Civil Engineering – 5th Semester by Dr. Muhammad Irfan Assistant Professor Civil Engg. Dept. – UET Lahore Email: Lecture Handouts: Lecture # 15 25-Oct-2017
  2. 2. 2 SCHMERTMANN (1978) METHOD From elasticity theory; πœ€ 𝑣 = βˆ†π‘ž 𝐸𝑠 𝐼𝑣 Where, eV = vertical strain Dq = net foundation contact pressure (kN/m2) ES = Modulus of elasticity of sand (Young’s Modulus) (kN/m2) IV = Strain influence factor for soil beneath foundation Settlement Where, Dz = Thickness of compressible layer Semi-empirical approach οƒ  theory + model studies for vertical strain in sands below foundation as function of depth Semi-empirical approach 𝑆 𝑒 = πœ€ 𝑣 βˆ™ βˆ†π‘§
  3. 3. 3 SCHMERTMANN (1978) METHOD C1 = Correction factor to compensate for the effects of foundation depth (or embedment) C2 = Correction factor for creep and other time dependent deformations 𝑆 𝑒 = βˆ†π‘ž 𝐸𝑠 𝐼𝑣 βˆ™ βˆ†π‘§π‘† 𝑒 = πœ€ 𝑣 βˆ™ βˆ†π‘§ Correction Factors 𝐢1 = 1 βˆ’ 0.5 π‘ž π‘£π‘œ βˆ†π‘ž 𝐢2 = 1 + 0.2 log 10𝑑 Where, qVO = soil overburden pressure at base of foundation (kN/m2) t = Elapsed time (years) 𝑆 𝑒 = βˆ†π‘ž 𝐸𝑠 𝐼𝑣 βˆ™ βˆ†π‘§ βˆ™ 𝐢1 𝐢2 ?Next slide
  4. 4. 4 SCHMERTMANN (1978) METHOD Strain Influence Factor (IV) Square foundations (L/B = 1) Strip foundations (L/B > 10) Max. Stress below footing (IVP) Square (Axisymmetric) οƒ  at depth B/2 Strip (Plain Strain) οƒ  at depth B q = foundation contact pressure q’vo = overburden pressure at foundation level Dq = net foundation pressure s’vp = soil overburden pressure at depth for Ivp (B or B/2)
  5. 5. 5 Practice Problem #5 A square footing 3 m by 3 m is resting on a sand deposit shown in the figure. Assuming the modulus of elasticity of the sand to be equal to 2.5qc, determine the elastic settlement of foundation 5 years after construction using Schmertmann method.
  6. 6. 9 Practice Problem #6 The results of a CPT sounding performed at a site are shown in figure. The soils consist of young normally consolidated sands with interbedded silts. The groundwater table is at a depth of 2.0 m below the ground surface. A 375 kN/m load is to be supported on a 2.5 m x 30 m footing to be founded at a depth of 2.0 m in this soil. Use Schmertmann’s method to compute the settlement of this footing soon after construction and the settlement 50 years after construction. Use Es = 2.5 qc; g = 17 kN/m3 (above WT), and g = 20 kN/m3 (below WT)
  7. 7. 10 Practice Problem #6 B = 2.5 m D = 2.0 m Strip Foundation Influence zone οƒ  Down to 4B
  8. 8. 12 CONCLUDED REFERENCE MATERIAL Foundation Analysis and Design (5th Ed.) Joseph E. Bowles Chapter #5 Principles of Geotechnical Engineering (7th Ed.) Braja M. Das Chapter #11 Essentials of Soil Mechanics and Foundations (7th Ed.) David F. McCarthy Chapter #10 (Schmertmann Method) (Timoshenko & Goodier Method) (Modified Mayerhof Method)