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Geotechnical Engineering-II [Lec #20: WT effect on Bearing Capcity)

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 #20: WT effect on Bearing Capcity)

  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: mirfan1@msn.com Lecture Handouts: https://groups.google.com/d/forum/geotech-ii_2015session Lecture # 20 17-Nov-2017
  2. 2. 2 Case I Groundwater table is located at a distance D above the bottom of the foundation. Case-I  BNNDcNq qfcult 5.0 1. Modify γDf term as γ(Df – D) + γsub.D 2. Modify 0.5γBNγ term as 0.5γsubBNγ Where, γsub = γsat - γw EFFECT OF GROUNDWATER TABLE ON BEARING CAPACITY
  3. 3. 3 Case II Groundwater table is located at the foundation base.  BNNDcNq qfcult 5.0 1. No change to γDf term. 2. Modify 0.5γBNγ term as 0.5γsubBNγ Where, γsub = γsat - γw Case-II EFFECT OF GROUNDWATER TABLE ON BEARING CAPACITY
  4. 4. 4 Case III Groundwater table is located at a depth D below the foundation base.  BNNDcNq qfcult 5.0 1. No change to γDf term. 2. Use γav in the third term; γav = γ (for D > B) γav = 1/B [γD + γsub (B – D)] (for D ≤ B) γsub = γsat - γw Case-III EFFECT OF GROUNDWATER TABLE ON BEARING CAPACITY
  5. 5. 5 Practice Problem #5 Compute the factor of safety against a bearing capacity failure for the square spread footing shown in figure with the groundwater table at Position A. Some time after construction, the water table rises to Position B. Compute the new factor of safety against bearing capacity failure
  6. 6. 8 Terzaghi (1943) developed the theory for continuous/strip foundations (simplest, 2D problem).  BNNDNcq qfcult '5.0''  Contribution of: Shear strength Surcharge Soil self- weight  sBNNDsNcq qfccult '5.0''  General form of Terzaghi’s Bearing Capacity Theory sc and sγ → shape factors TERZAGHI’S BEARING CAPACITY THEORY
  7. 7. 9  BNNDNcq qfcult '5.0''  TERZAGHI’S BEARING CAPACITY THEORY
  8. 8. 10 Practice Problem #6
  9. 9. 12 GENERAL BEARING CAPACITY EQUATION
  10. 10. 13 GENERAL BEARING CAPACITY EQUATION
  11. 11. 14 Practice Problem #7
  12. 12. 16 Practice Problem #8
  13. 13. 18 CONCLUDED REFERENCE MATERIAL Foundation Analysis and Design (5th Edition) Joseph E. Bowles Chapter #4 Principles of Geotechnical Engineering (7th Edition) Braja M. Das Chapter #16

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