Soil Properties - I. Amit Prashant. Indian Institute of Technology Gandhinagar. Short Course on. Geotechnical Aspects of Earthquake Engineering

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Soil Properties - I Amit Prashant Indian Institute of Technology Gandhinagar Short Course on Geotechnical Aspects of Earthquake Engineering 04 08 March,

1 Soil Properties - I Amit Prashant Indian Institute of Technology Gandhinagar Short Course on Geotechnical Aspects of Earthquake Engineering March, 2013 Regional Soil Deposits of India Alluvial deposits Desert Soils Laterites and lateritic soils Black cotton soils Marine deposits Boulder deposits 2 1

Soil: A Complex Material Particulate Media Three Phase

Effective Stress Pressure Dependency Transient Response

Particle Shapes and Sizes Sands and Gravels Particle Size >

2 Soil: A Complex Material Particulate Media Three Phase Relationship Volume Change Characteristics Principal of Effective Stress Pressure Dependency Transient Response Highly on-linear Response Spatial Variability Others 3 Particle Shapes and Sizes Sands and Gravels Particle Size > 75 mm Clays Size > 2 mm 17 mm Rounded Subrounded Subangular Angular 2 mm 4 2

3 Soil Groups Based on its Particle Size Clay minerals Cohesive soils on-clay minerals Granular soils or Cohesion less soils Clay Silt Sand Gravel Cobble ine Medium Course ine Course Boulder Grain size (mm) ine grain soils Coarse grain soils 5 Grain Size Distribution Poorly Graded Well Graded Gap Graded 6 3

4 Three Phases in Soils S : Solid Soil particle W: Liquid Water (electrolytes) A: Air Air Vv Void ratio, e V s Air Water r a r w Solid r s 7 Particle Assemblage: Void Ratio 8 4

5 Relative Density e max D r = 0% emax e Dr e max e min Void ratio, e e 0%<D r <100% e min D r = 100% 0 9 Atterberg Limits The presence of water in fine-grained soils can significantly affect associated engineering behavior, so we need a reference index to clarify the effects. 10 5

6 Typical Values of Atterberg Limits (rom Mitchell, 1993) 11 Plasticity Chart L M H 12 6

7 Sensitivity Strength ( undisturbed ) S t Strength ( disturbed ) Unconfined shear strength w > LL Clay particle Water 13 Thixotropy Loses strength when remolded; Gains strength while at rest Structure re-adjusts when left undisturbed S Thixotropic Strength Ratio S A R 14 7

8 Axial orce, Deformation, Axial orce, Compressibility and Time Effects Time 1 k Displacement Time 15 Model of Contact riction: Rigid Plastic W T f W T f Shear orce, T f Tf m..tan n Displacement 16 8

9 Effective stress w hs w Area = 1 Total Stress Area h s s h w s h w Effective Stress Area h h h. h.. s s w w s m. m. s s Water Pressure u. h w w. h. h s s w s. h. h s s w w. h w m. w.tan u.tan 17 Effective Stress Profile in Soil Deposit 18 9

Example Determine the effective stress distribution with depth if the water table is 2 m below ground surface Steps in solving effective stress problems: 38 evaluate distribution of total head with

10 Example Determine the effective stress distribution with depth if the water table is 2 m below ground surface Steps in solving effective stress problems: 38 evaluate distribution of total head with depth subtract elevation head from total head to yield pressure head calculate distribution with depth of vertical total stress subtract pore pressure (=pressure head x γ w ) from total stress ailure Criteria for soils.tan n n 20 10

11 Interlocking Effect Particle riction Glue Particle Interlocking Glue Increase in riction angle due to Interlocking Effect s Particle-to-Particle riction angle on-linearity due to reduced interlocking with increase in normal stress 21 Cohesion and Cementation Effect Glue.tan n c.tan n c 22 11

12 Effect of density or void ratio emax e Relative Density, Dr e e max min Increase in D r 23 Effect of Pre-compression history Overconsolidation Ratio, or Peak Shear Strength as ailure Increase in OCR vo OCR v or varying OCR but constant vo Maximum overburden stress ever induced OCR constant for each line 24 12

13 Volume Change or Evolution of Pore Water Pressure During Shearing Initially loose configuration Drained Shearing Slow Loading Contractive Undrained Shearing ast Loading Increase in Pore Water Pressure Initially loose configuration Dilative Decrease in Pore Water Pressure 25 q Stress strain behavior of soils Drained / Slow Loading Undrained / ast Loading q q q ve V V q Contraction ve u q ve q Total and effective Stress Path p ' Dilation ve q 26 p ' Effective Stress Path 13

Stress Strain Curve for soils q Peak Shear Strength Strain hardening zone Softening zone Zone of instability Elastic zone irst yield point Steady State Shear Strength q q

14 Stress Strain Curve for soils q Peak Shear Strength Strain hardening zone Softening zone Zone of instability Elastic zone irst yield point Steady State Shear Strength q q 2G max 2G G max = Maximum Shear Modulus G = Secant Shear Modulus q 27 Strain Dependent Shear Modulus Linear Elastic Model onlinear Elastic Model Include Plasticity % 28 14

15 Transient Effects on structures lood Oil Tank lood 29 Transient Effects on structures b = 18 k/m 3 ; sat = 20 k/m 3 ' = 18º (CU test) 10 m Top line of water seepage m 1 18 m 1 Under ilter 10 m 30 15

16 Spatial Variability of soil strata 1 Bore Holes Thank You 32 16

Soil Properties - II

Soil Properties - II Amit Prashant Indian Institute of Technology andhinagar Short Course on eotechnical Aspects of Earthquake Engineering 04 08 March, 2013 Seismic Waves Earthquake Rock Near the ground