Rock Cycle

1
Rock Cycle Soil Origins

• Magma gt Igneous Rocks
• Intrusive, Extrusive
• Transportation, Erosion, Weathering
• Sediments -gt Sedimentary Rock
• Metamorphism
• Melting to Magma

2
Natural Soil Deposits

• Weathering Process
• Mechanical and Chemical
• Soil Types
• Residual - Formed in-place
• Transported Glacial, Alluvial, Aeolian

3
Soil-Particle Size

• Coarse Grains
• Gravels - typically gt 2 mm
• Sands typically 0.075 2 mm
• Fine Grains
• Silts 0.002 0.075 mm
• Clays typically lt 0.002 mm

4
Particle Size Table 1.1

• MIT Initial classification system
• USDA Textural classification system, agronomy
• AASHTO Classification for road building
  purposes
• USCS Predominant system used for geotechnical
  engineering

5
Clay Minerals

• Silica Tetrahedron
• Silica Sheet
• Alumina Octahedron
• Octahedral Sheet (Gibbsite)
• Different clay minerals built up of varying sheet
  combinations
• Become putty-like in presence of water

6
Clay Minerals

• Kaolinite Large blocky particles
• 15 m2/g specific surface
• Illite flake-shaped particles
• 80 m2/g
• Montmorillonite Very flaky
• 800 m2/g

7
Specific Gravity

• Ratio of unit weight of material to the unit
  weight of water
• Gs (s/(w Ms / Vs (w
• Typically 2.6 to 2.9
• Table 1.2 provides representative values

8
Mechanical Analysis

• Sieve Analysis
• Good to 0.075 mm (200)
• Dry - Mechanical shaker
• Wet Hand separation
• Hydrometer Analysis
• Sedimentation Test
• Good to 1-2

9
Particle-Size Distribution

• Generally plotted on semi-log paper with
  Passing vs. log size
• Provides simple visual aid for describing
  predominant size range and size distribution

10
Table 1.4 Sieve Analysis
11
Size Distribution Curve
12
Size Distribution Curve
13
Visual Interpretations
14
Shorthand Descriptors

• Pxx Percent passing sieve xx
• For example, P200, P1
• Rxx Percent retained on sieve xx
• For example, R200
• Pxx 100 Rxx
• Dxx Diameter for which xx is finer
• For example, D10

15
Size Distribution Curve
P4
30
4
D30
16
Numerical Descriptors

• Effective Size, D10
• Uniformity Coefficient, Cu
• Cu D60 / D10
• Coefficient of Gradation, Cz
• Cz D302 / D60D10

17
Numerical Descriptors

• Coarse Grained Soils
• Gravels
• Well Graded if Cu gt4 and 1ltCzlt3
• Sands
• Well Graded if Cugt6 and 1ltCzlt3