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Shear Strength of soil and Tests on soil
The document discusses the shear strength of soil, detailing its importance in construction, failure modes, and methods of investigation such as unconfined compression and direct shear tests. It outlines the factors influencing shear strength, including cohesion and the angle of internal friction, along with various testing procedures. Examples provide calculations for determining soil cohesion and internal friction based on experimental data.
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Overview of shear strength, failure types, and its importance in construction, emphasizing design and stability.
Different methods for investigating soil shear strength including unconfined compression and direct shear tests.
Introduction to triaxial compression test setup and parameters for assessing soil strength.
Analytical details of data from triaxial compression tests, focusing on cohesive soil strength.
Discussion on variations in shear test procedures, highlighting UU, CU, and CD tests.
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Similar to Shear Strength of soil and Tests on soil
Shear Strength of soil and Tests on soil
- 1. Shear Strength ofSoil COSC 323: Soils in Construction
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- 5. Shear Strength dueto Sliding Friction Normal Force N Shearing Force S Failure Plane
- 6. Shear Strength dueto sliding friction Sliding Force Normal Force
- 7. Shear Strength dueto sliding friction Normal Force Sliding Force
- 8. Shear Strength dueto Sliding Friction Normal Stress vs. Shear Stress Normal Stress (s) Shear Stress (f) 10 kPa (=kN/m2 ) 6 kPa 20 kPa 12 kPa 30 kPa 18 kPa
- 9. Shear Strength dueto Sliding Friction Normal Stress (s) ShearStress(s) Angle of internal friction (f) φσ φσ σ φ tan tan tan += = = cs s s
- 10. Coulomb Equation :tan : : :c : φ φ σ s Effective intergranularnormal pressure (perpendicular to the shear plane) Shear strength Cohesion (Strength gained from the ionic bound between grain particles) Angle of internal friction (Strength gained from internal friction resistance) Coefficient of friction φσ tan+= cs
- 11. Shear strength ofsoil • Soil cannot resist tension • Soil can resist compression. • For excessive compression failure occurs in the form of shearing along the internal surface within the soil • Structural Strength of soil = f ( soil’s shear strength) • Shear Strength – Soil’s ability to resist sliding – Important for • foundation design • Lateral earth pressure calculations • Slope stability analysis
- 12. Methods of investigatingshear strength • Unconfined compression test (for cohesive soil) • Direct shear test • Triaxial compression test • Vane test (for soft clay) • Standard penetration test (for cohesionless soil) • Penetrometer test
- 13. Unconfined compression test 2 uq c= Soil Specimen uq uq cohesion: strengthecompressivunconfined: c qu
- 14. Example • A clayeysoil subjected to an unconfined compression test fails at a pressure of 2540 lb/ft2 (i.e., qu = 2540 lb/ft2 ). What is cohesion of this clayey soil?
- 15. Direct Shear Test NormalLoad Sharing Force Sharing Force Normal Load Sharing Force Sharing Force Soil Specimen
- 16. Direct Shear Test SoilSpecimen Normal Load Sharing Force Normal Stress ShearStress c Normal Stress = Normal load / the specimen’s cross-sectional area Shear stress = Shearing Force / the specimen’s cross- sectional area The graph can be used to determine the given soil’s shear strength for any load Problem: Shear failure is forced to occur along a predetermined plane, which is not necessarily the weakest plane of the soil specimen tested. Test with different Normal Load φ φ: angle of internal friction c: cohesion
- 17. Example • A seriesof direct shear tests was performed on a soil sample. Each test was carried out until the soil specimen experienced shear failure. The test data are listed next. What is soil’s cohesion and angle of internal friction? Specimen Number Normal Stress (lb/ft2 ) Shearing Stress (lb/ft2 ) 1 604 1522 2 926 1605 3 1248 1720
- 18. Triaxial Compression Test Wrapthe specimen with rubber membrane
- 19. Triaxial Compression Test Enclosethe specimen in a chamber filled with water
- 20. Triaxial Compression Test s3 Applya specific pressure using water s3 s3 s3
- 21. Triaxial Compression Test s3 s3 p∆ Applya vertical load and increase until the specimen fails Use different lateral pressure, conduct the same experiment s3 s3 p∆
- 22. Triaxial Compression Test s3 p∆ p∆s3 : Minor principal stress Dp : Deviator stress at failure axial = (Load at failure / cross-sectional area) s3 s3 s3
- 23. Triaxial Compression Test s3 p∆+=31 σσ s3 : Minor principal stress Dp : Deviator stress at failure axial = (Load at failure / cross-sectional area) s1 = s3 + Dp; major principal stress How to obtain cohesion and angle of internal friction? s3 p∆+= 31 σσ
- 24. Triaxial Compression Test s3s3 s3 s3 s3s3 s1=s3+Dp s1= s3+Dp Before After
- 25. Triaxial Compression Test (s1)1 (s3)1(Dp)1 Normal Stress First Test ShearStress A B
- 26. Triaxial Compression TestShearStress SecondTest (s1)1 (s3)1 (Dp)1 (s3)2 (Dp)2 (s1)2 Normal Stress A B C D
- 27. Triaxial Compression TestShearStress NormalStress (s1)1 (s3)1 (Dp)1 (s3)2 (Dp)2 (s1)2 Strength Envelop A B C D
- 28. Triaxial Compression Test c F ShearStress NormalStress (s1)1 (s3)1 (Dp)1 (s3)2 (Dp)2 (s1)2 Strength Envelop A B C D
- 29. Example • Gien – Triaxialcompression tests on three specimens of a soil sample were performed. Each test was carried out until the specimen experienced shear failure. The test data are tabulated as follows: • Required – The soil’s cohesion and angle of internal friction Specimen Number Minor Principal Stress (kips/ft2 ) Deviator Stress at Failure (kips/ft2 ) 1 1.44 5.76 2 2.88 6.85 3 4.32 7.50
- 30. Example Specimen Number Minor Principal Stress (kips/ft2 ) Deviator Stress atFailure (kips/ft2 ) Major Principal Stress (kips/ft2 ) 1 1.44 5.76 7.2 2 2.88 6.85 9.73 3 4.32 7.50 11.82
- 31. Example 0 2 46 8 10 12 14 2 4 6 8
- 32. Example 0 2 46 8 10 12 14 2 4 6 8
- 33. Example 0 2 46 8 10 12 14 2 4 6 8
- 34. Example 0 2 46 8 10 12 14 2 4 6 8
- 35. Example 0 2 46 8 10 12 14 2 4 6 8 4 2 2 1 /9.0 26 4 2 tan 4 2 tan ftkipc = = = = − φ φ φ
- 36. Variations in ShearTest Procedures • Unconsolidated Undrained (UU) – Q test • Consolidated Undrained (CU) • Consolidated Drained (CD) – S test