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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 # 3
13-Sep-2017](https://image.slidesharecdn.com/3-180930132623/85/Geotechnical-Engineering-II-Lec-3-Direct-Shear-Test-1-320.jpg)
Geotechnical Engineering-II [Lec #3: Direct Shear Test)
- 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 # 3 13-Sep-2017
- 2. 2 DETERMINATIONOFSOILSHEARSTRENGTH (c, φ or c’, φ’) Laboratory tests on representative samples Field tests Direct shear test Unconfined compression test Triaxial shear test Simple shear test Torsional ring shear test Plane strain triaxial test Laboratory vane shear test Laboratory fall cone test Vane shear test Torvane Pocket penetrometer Fall cone Pressuremeter Static cone penetrometer Standard penetration test Assignment: Brief intro of each
- 3. 3 z σv σv σhσh Before construction Representative soil sample z σv + Δσ σhσh During and after construction σv + Δσ FIELD STRESS CONDITIONS
- 4. 4 Step 1 Application of initial stress condition σv σv σh σh Representative soil sample from site 0 00 0 Step 2 Application of disturbing/structural load σv + Δσ σhσh σv + Δσ t σv σv τ τ LAB SIMULATION OF FIELD CONDITIONS
- 5. 5 DIRECT SHEAR TEST - Schematic Illustration - t tan cf P
- 6. 6 Components of Shear Box Preparation of Sand specimen Porous Plates DIRECT SHEAR TEST - Specimen Preparation -
- 7. 7 Leveling the top surface of specimen Specimen preparation completed Pressure plate DIRECT SHEAR TEST - Specimen Preparation -
- 8. 8 Step 1: Apply a vertical load to the specimen and wait for consolidation Porous Plates Pressure Plate Steel BallP Proving ring to measure shear force F Soil Specimen DIRECT SHEAR TEST - Test Procedure -
- 9. 9 P Pressure plate Steel Ball Proving ring to measure shear force F Porous Plates DIRECT SHEAR TEST - Test Procedure - Step 2: Lower box is subjected to a horizontal displacement at a constant rate
- 10. 10 Shear Box Loading frame to apply vertical load Dial gauge to measure vertical displacement Dial gauge to measure horizontal displacement Proving ring to measure shear force DIRECT SHEAR TEST
- 11. 11 sampleofAreasectional-Cross (P)forceNormal stressNormal sampleofAreasectional-Cross (F)surfaceslidingat thedevelopedresistanceShear stressShear t Cross-sectional area of the sample changes with the horizontal displacement DIRECT SHEAR TEST - Calculations - t tan cf hBAA oC . Ac = Corrected Area Ao = Original Area B = Width h = Sample Deformation
- 12. 12 DIRECT SHEAR TEST - Calculations - DDG constant = 0.01mm/div Proving Ring constant = 0.8lb/div Weight of Hanger = 8 lb 15 ounce = 8.94lb Normal Load = 20lb Total Normal Load = 28.94lb Sample# Normal Load, N Horizontal D/R Horizontal Displacement, ∆H Col#3×L.C Corrected Area, Ac =A0-b∆H Load Dial Reading Horizontal Shear Force, F Col#6×PRC Normal Stress, σn=N/AC Shear Stress, τ=F/AC (lb) (mm) (cm2 ) (lb) (kN/m2 ) (kN/m2 ) 1 2 3 4 5 6 7 8 9 2 28.94 0 0.0 36.00 0.0 0.0 35.77 0.00 28.94 20 0.2 35.88 17.0 13.6 35.89 16.87 28.94 40 0.4 35.76 21.0 16.8 36.01 20.91 28.94 60 0.6 35.64 23.0 18.4 36.13 22.97 Sample Calculations
- 13. 13 tf1 Normal stress = 1 How to determine shear strength parameters c and ? Shearstress,t Shear displacement tf2 Normal stress = 2 tf3 Normal stress = 3 Shearstressatfailure,tf Normal stress, Mohr – Coulomb failure envelope DIRECT SHEAR TEST - Analysis of Results - t tan cf
- 14. 14 DIRECT SHEAR TEST - Stress ~ Strain Relationships - Shearstress,t Shear displacement Dense sand/ OC clay tf Loose sand/ NC clay tf Dense sand/OC Clay Loose sand/NC Clay Changeinheight ofthesample ExpansionCompression Shear displacement
- 15. 15 DIRECT SHEAR TEST ON CLAYS Failure envelopes of clay from drained direct shear tests Shearstressatfailure,tf Normal stress, ’ Normally consolidated clay (c’ = 0) • Horizontal displacement applied at a very slow rate to allow dissipation of pore water pressure • One test would take several days to finish Over-consolidated clay (c’ ≠ 0)
- 16. 16 INTERFACE TESTS ON DIRECT SHEAR TEST APPARATUS • Friction angle between soil and structural material (concrete, steel, wood, etc.) • Used in many foundation design and retaining wall problems t tan af c Where, ca = adhesion, = angle of internal friction Foundation material Soil P S Foundation material Soil P S
- 17. 17 DIRECT SHEAR TEST -- Advantages & Disadvantages -- Advantages Relatively simple and quick test. Interface strength parameters can be determined. Disadvantages Failure occurs along predetermined failure plane. Area of the sliding surface changes as the test progresses. Non-uniform distribution of shear stress along failure surface. Reliable ‘mostly’ for granular soils only.
- 18. 18 ANGLE OF REPOSE The steepest angle to which a loose granular material can be piled without slumping. Angle of repose ≈ Friction angle
- 19. 19 CONCLUDED REFERENCE MATERIAL Principles of Geotechnical Engineering – (7th Edition) Braja M. Das Chapter #12 Geotechnical Engineering – Principles and Practices – (2nd Edition) Coduto, Yueng, and Kitch Chapter #12 Essentials of Soil Mechanics and Foundations – Basic Geotechnics – (7th Edition) David F. McCarthy Chapter #11