Shear Strength of Soils Final (Complete)

Shea hearr Str Stre eng ngth th of Soi oils ls CE2112 Soil Mechanics Nationa tio nall Unive niv ersity rsi ty of Singa ing apore por e Department of Civil iv il and Env Envir iron onmental mental Eng Engin ine eering ri ng

Shea hearr Strength Strength of Soil oils s : Introd ntroductio uctio n

Wh at is i s St St r en g t h? • Po w er t o Res i s t Fo r c e -

cons co nsid ide ered red in Civ Civil il Eng Engin ine eering ri ng • Concre oncrete te Stre trength ngth • Ste tee el Stre trength ngth

Introd Introduct uction ion - 1

Shea hearr Strength Strength of Soil oils s : Introd ntroductio uctio n

Wh at is i s St St r en g t h? • Po w er t o Res i s t Fo r c e -

cons co nsid ide ered red in Civ Civil il Eng Engin ine eering ri ng • Concre oncrete te Stre trength ngth • Ste tee el Stre trength ngth

Introd Introduct uction ion - 1

Shea hearr Strength Strength of Soil oils s : Introd ntroductio uctio n

oncrete te Cube ubes s • Concre • Ty p i c al l y c u r ed f o r 28 d ay s • A  Ap p p l y ax axii al l o ad u n t i l t h e • The ma maxi ximu mum m stress s tress o a ar ea a e concre e cube cu be ca can n sust su sta ain be b efo fore re it c r u s es s n o w n as s  ___________________ (e.g.. compre compr essive stre strength ngth (e.g  ________________________  ___________________ ay c o m p r es s v e s r_____ en g . Introd Introduct uction ion - 2

Shear Strength of Soils : Introductio n

• Steel bar specimen

• Subject the steel bar specimen to tensile pulling at its two ends. • Stress-strain curve looks like this:

yield strength

Introduction - 3

Shear Strength of Soils : Introductio n

Loading Piston

• • Cylindrical Soil Specimen, e.g. 76 mm , 2:1 aspect ratio ___.

water  pressurized _____. •

er ca s ress s app e o e so specimen by controlling the  ___________________________. movement of the loading piston

• Force on the loading piston and the movement of the piston is measured and recorded. The data is processed to obtain the stress-strain curve. Introduction - 4

Shear Strength of Soils : Introductio n

Two Im ortant As ects of Geotechnical Problems (a) Deformation/Consolidation • Covered by Prof Lee. • This course provides you with some simple tools to make preliminary settlement / deformation calculations • Difficult and challenging topic in practice • Very experienced engineers may come up with different predictions for deformation / • Material effects : variability, complex stressstrain relationshi elastic- lastic res onse • Dependent on modulus (gradient of stress-strain c urve) ,

c

s

• Geometrical effects : 2D and 3D Introduction - 5

Shear Strength of Soils : Introductio n

Two Im ortant As ects of Geotechnical Problems (b) Stability (or Failure) • Dependent on Soil Strength • Soil strength is highly variable, even within same s te • Collapse (may or may not happen) • Loss of Stability

• Excessive deformation

Introduction - 6

Shear Strength of Soils : Response of Soils to Load Appli cations

When the applied loads are small: Soil stresses are low, deformations are small Stability of the soil structure typically not a problem When the applied loads are large: Soil stresses are high, deformations are large Stability of the soil structure may become a problem Failure may occur 

Introduction - 7

Shear Strength of Soils : Response of Soils to Load Appli cations

In geotechnical engineering, FAILURE can have different ‘meanings’: In extreme case, we have collapse. In more general cases, we have limiting conditions (not necessarily complete breakdown) beyond which the soil structure cannot be used.

Introduction - 8