2. Soil Classification Flashcards
Grain size and distribution
Mixture of grains
Grains + pores
Grains = solid particles Pores = air, water
Grain size and distribution
classification over …
Mixture of grains
- GS distribution
- plastic deformation (fine grains)
Grain size and distribution
Determine GS distribution
(4)
- Estimate (eye, fingers)
- Sieving (sand, gravel)
- Settling analysis (clay, silt)
4 Laser-based measurements
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
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)
Grain size and distribution
Settling analyses, generell
- utilizing Stokes Law
- measure density of fluid at given time intervals
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) )
Grain size and distribution
What product is sorting?
product of depositional processes
Grain size and distribution
What characterise sorting and GS?
the geotechnical properties
Grain size and distribution
One GS dominant?
poorly graded
very well sorted
Grain size and distribution
Several GS present
well graded
poorly sorted
Grain size and distribution
wanted properties of well graded soils
lower pore space (usually)
-> less affected by compaction
USCS: Symbols of classification
Dominant grain size
- gravel
- sand
- silt
- clay
- organic
G = gravel
S = sand
M = silt
C = clay
O = organic
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
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
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)
