Review of Soil Mechanics I

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Review of Soil Mechanics I

• Prof. Jie Han, Ph.D., PE
• The University of Kansas

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Outline of Presentation

• Introduction
• Soil Particle Size Distribution
• Index Properties
• Soil Classification
• Water Flow in Soil

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Introduction
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Soil Mass
Air
Solids (or particles or grains)
Liquid
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Formation of Soil

• Weathering
• Break down rock into small pieces by mechanical
• and chemical processes
• Transportation of weathering products
• - Residual soil stay in the same place
• - Glacial soil formed by transportation and
• deposition of glaciers
• - Alluvial soil transported by running water
  and
• deposited along streams
• - Marine soil formed by deposition in the sea

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Soil Particle Size Distribution
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Textural Soil Classification
Soil name
Particle Size (mm)
U.S. Sieve No.
Boulders
gt 300
Cobbles
300 - 75
Gravel
Coarse
3 - 3/4 in.
75 - 19
Fine
3/4 in. to No. 4
19 - 4.75
Sand
No. 4 to No. 10
Coarse
4.75 - 2.00
No. 10 to No. 40
Medium
2.00 - 0.425
Fine
0.425 - 0.075
No. 40 to No. 200
Clays and silts
lt 0.075
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Soil Particle (Grain) Size Analysis

• Sieve analysis
• Suitable for particle size gt 0.075mm
• Hydrometer analysis
• A sedimentation method and used for particle
• size lt 0.075mm

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Sieve Analysis
Dry weight of soil Retained
of Soil Retained
Cumulative of Soil Passing
Cumulative of Soil Retained
Pan
10
Hydrometer Test
0
R reading
L
60
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Definition of D10, D30, D50, and D60
100
0
20
80
60
40
(Cumulative) Percent of Retained
(Cumulative) Percent of Passing (Finer)
40
60
20
80
D30
D10
D50
D60
100
10
1
0.1
0.01
0.001
Particle Size (mm) log Scale
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Coefficients of Uniformity and Curvature
Coefficient of uniformity
Coefficient of curvature
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Type of Gradation Curves
Well-graded particle sizes over a wide range
Poorly-graded particle sizes within a narrow
range
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Example of Gradation Curves
0
100
Poorly-graded
20
80
Well-graded
60
40
(Cumulative) Percent of Retained
(Cumulative) Percent of Passing (Finer)
40
60
Gap graded
20
80
100
10
1
0.1
0.01
0.001
Particle Size (mm) log Scale
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Index Properties
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Volume - Weight Diagram
Va
Air
Vv
Liquid (water)
Vw
Ww
V
W
Ws
Solid
Vs 1
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Index Properties
Porosity
Void ratio
Degree of saturation
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Degree of Saturation of Sand
Condition of sand
Degree of Saturation ()
Dry
0
Humid
1 - 25
Damp
26 - 50
Moist
51 - 75
Wet
76 - 99
Saturated
100
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Index Properties
Water content
Unit weight of soil
Dry unit weight of soil
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Typical Values of Void Ratio and Unit Weight
Soil description
Dry unit weight(pcf)
Void ratio
Saturated unit weight(pcf)
Uniform sand
Silty sand
Clean, well-graded sand
Silty sand and gravel
Sandy or silty clay
Well-graded gravel, sand, silt, and clay mixture
Inorganic clay
Colloidal clay (50lt2?)
(NAVFAC DM 7.1, 1982)
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Index Properties
Unit weight of water
Unit weight of solids
Specific gravity of solids
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Weight-Volume Relationship
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Relative Density
emax maximum void ratio emin minimum void
ratio e0 void ratio of the soil in place
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Qualitative Description of Degree of Density
Dr ()
Description
0 - 15
Very loose
15 - 50
Loose
50 - 70
Medium
70 - 85
Dense
85 - 100
Very dense
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Consistency of Soil - Atterberg Limits
Stress
Strain
Shrinkage limit, SL
Plastic limit, PL
Liquid limit, LL
Liquid
Solid
Semisolid
Plastic
Moisture content
Plastic index, PI
Strength and modulus decrease
Compressibility increases
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Liquid Limit Test
35mm
300
LL
Moisture content ()
20
Penetration (mm)
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Plastic Limit Test
Defined as the moisture content at the soil
crumbles when rolled into threads of 1/8 in
(3.2mm) in diameter
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Plasticity and Dry Strength of Soil
Plasticity
PI()
Dry strength
Field test on air-dried sample
Non-plastic
0 to 3
Very low
Falls apart easily
Slightly plastic
3 to 15
Slight
Easily crushed with fingers
Medium plastic
Difficult to crush
15 to 30
Medium
Highly plastic
gt 30
High
Impossible to crush with fingers
(Sowers, 1979)
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Soil Classification
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Soil Classification Systems

• AASHTO (the American Association of State
  Highway and Transportation Officials)
• USDA (the United States Department of
  Agriculture)
• USCS (the Unified Soil Classification Systems

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USCS Soil Classification

• Fine-grained soils
• 50 or more passes No. 200 sieve
• Coarse-grained soils
• 50 or more is retained on No. 200 sieve
• Highly organic soils
• has fibrous to amorphous texture

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Symbols in the USCS System
Prefix
G ? Gravel S ? Sand M ? Silt C ? Clay O ?
Organic Pt ? Peat
Suffix
W ? Well-graded P ? Poorly-graded M ? Silty C ?
Clayey L ? Low plasticity H ? High plasticity
Examples (the first letter to define general soil
type others are modifiers)
GP ? Poorly-graded gravel GC ? Clayey
gravel SW-SM ? Well-graded sand with silt CL-ML ?
Low plasticity silty clay OH ? High plasticity
organic clay or silt
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Soil Classification