2. Soil Classification Flashcards by Temja Tohr

Grain size and distribution

Mixture of grains

Grains + pores

Grains = solid particles
Pores = air, water

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Grain size and distribution

classification over …

Mixture of grains

GS distribution
plastic deformation (fine grains)

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Grain size and distribution

Determine GS distribution

(4)

Estimate (eye, fingers)
Sieving (sand, gravel)
Settling analysis (clay, silt)

4 Laser-based measurements

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Grain size and distribution

Grain size classes

Coarse gravel 20 mm –63 mm
Medium gravel 6.3 mm –20 mm
Fine gravel 2 mm –6.3 mm
-----------------------------------------  
Coarse sand 630 μm –2 mm
Medium sand 200 μm –630 μm
Fine sand 63 μm –200 μm
-----------------------------------------  
Coarse silt 20 μm –63 μm
Medium silt 6.3 μm –20 μm
Fine silt 2 μm –6.3 μm
-----------------------------------------  
Clay < 2 μm

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Grain size and distribution

Sieving analyses

different sized meshes
Weight amaount of soil in each sieve -> percentual per grain class
from coarse (top) to fine (bottom)

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Grain size and distribution

Settling analyses, generell

utilizing Stokes Law

- measure density of fluid at given time intervals

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Grain size and distribution

Settling analyses, formula

Coarse grains sink faster than small ones

W_s = sqrt( 8/3 * (rho_p-rho_f) * g * r / (rho_f*C_D) )

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Grain size and distribution

What product is sorting?

product of depositional processes

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Grain size and distribution

What characterise sorting and GS?

the geotechnical properties

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Grain size and distribution

One GS dominant?

poorly graded

very well sorted

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Grain size and distribution

Several GS present

well graded

poorly sorted

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Grain size and distribution

wanted properties of well graded soils

lower pore space (usually)

-> less affected by compaction

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USCS: Symbols of classification

Dominant grain size

gravel
sand
silt
clay
organic

G = gravel

S = sand

M = silt

C = clay

O = organic

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USCS: Symbols of classification

Sorting

poorly graded
well graded
high plasticity
low plasticity

P = poorly graded

W = well graded

H = high plasticity

L = low plasticity

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USCS: Symbols of classification

Differentiation between coarse and fines

D_50 larger or smaller than 0.063 mm

> domination of sand/gravel or clay/silt
> clay/silt = class acc to plastic deformation

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USCS: Symbols of classification

G
S
M
C
O

G = gravel

S = sand

M = silt

C = clay

O = organic

USCS: Symbols of classification

P
W
H
L

P = poorly graded

W = well graded

H = high plasticity

L = low plasticity

USCS classification

Uniformity coefficient
Gravel/Sand

C_du = D_60 / D_10

USCS classification

Curvature
Gravel/Sand

C_cd = D_30^2 / (D_10*D_60)

USCS classification

guideline 1. step: GS distribution

Determine dominant GS:

Gravel/Sand

Silt/Clay

USCS classification

guideline 2. step: sorting

if Gravel/Sand
if Silt/Clay

Gravel/Sand
-> estimate or analyse GS distribution

Silt/Clay
-> determined Atterberg limits

USCS classification

guideline 3. step: Plasticity
if Gravel/Sand

calculate

Uniformity coefficient = C_ud

Curvature = C_cd

USCS classification

guideline 3. step: Plasticity
if Silt/Clay

Atterberg limits:

liquid limit
plastic limit
shrinkage limit

USCS classification

Liquid limit

= Water content required to fill gab after 25 drops

Graph: Water content vs. Number of drops

USCS classification Plastic limit

= Water content where a thin thread of solid (3-4 mm) breaks apart at a diameter of 3.2 mm

USCS classification plasticity index (%) formula

PI = LL - PL

USCS classification plasticity index (%) meanings

``` 0 non plastic 1-5 slightly plastic 5-10 low plasticity 10-20 medium plasticity 20-40 high plasticity > 40 very high plasticity ```

Components What occurs?

silikates! Carbonates Organic material Clay minerals

Components effect of Carbonates

- sensitive to acidic water | - may increase stability

Components effect of Organic material

- sinking in - higher compaction level - lower shear strength - oxidation! e. g. peat layers etc. horror

Components effect of clay minerals

- swelling potential, expansion anhydrite to gypsum

Components: measurement Calcium carbonate content

with: Calcium carbonate content chamber quantitative 1 g dried soil treated with HCl in sealed chamber pressure of CO2 amount of Carbonate

Components: measurement Organic matter content

with: Loss on ignition LOI = Wi-Wf/Wi*100 ``` Wi = initial weight Wf = final weight after burning over 550°C for ~4h ```

Components: measurement Clay minerals

X-ray diffraction (XRD)