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Geotechnical Engineering–II [CE-321]
BSc Civil Engineering – 5th Semester
by
Dr. Muhammad Irfan
Assistant Professor
Civil Engg. Dept. – UET Lahore
Email: mirfan1@msn.com
Lecture Handouts: https://groups.google.com/d/forum/geotech-ii_2015session
Lecture # 15
25-Oct-2017](https://image.slidesharecdn.com/15-181020124920/85/Geotechnical-Engineering-II-Lec-15-16-Schmertmann-Method-1-320.jpg)
Geotechnical Engineering-II [Lec #15 & 16: Schmertmann Method]
- 1. 1 Geotechnical Engineering–II [CE-321] BSc Civil Engineering – 5th Semester by Dr. Muhammad Irfan Assistant Professor Civil Engg. Dept. – UET Lahore Email: mirfan1@msn.com Lecture Handouts: https://groups.google.com/d/forum/geotech-ii_2015session Lecture # 15 25-Oct-2017
- 2. 2 SCHMERTMANN (1978) METHOD From elasticity theory; 𝜀 𝑣 = ∆𝑞 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 theory + model studies for vertical strain in sands below foundation as function of depth Semi-empirical approach 𝑆 𝑒 = 𝜀 𝑣 ∙ ∆𝑧
- 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 = ∆𝑞 𝐸𝑠 𝐼𝑣 ∙ ∆𝑧𝑆 𝑒 = 𝜀 𝑣 ∙ ∆𝑧 Correction Factors 𝐶1 = 1 − 0.5 𝑞 𝑣𝑜 ∆𝑞 𝐶2 = 1 + 0.2 log 10𝑡 Where, qVO = soil overburden pressure at base of foundation (kN/m2) t = Elapsed time (years) 𝑆 𝑒 = ∆𝑞 𝐸𝑠 𝐼𝑣 ∙ ∆𝑧 ∙ 𝐶1 𝐶2 ?Next slide
- 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) at depth B/2 Strip (Plain Strain) 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 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. 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. 10 Practice Problem #6 B = 2.5 m D = 2.0 m Strip Foundation Influence zone Down to 4B
- 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)