2. Soil Classification

Question 1

Grain size and distribution

Mixture of grains

Answer 1

Grains + pores

Grains = solid particles
Pores = air, water

Question 2

Grain size and distribution

classification over …

Answer 2

Mixture of grains

• GS distribution
• plastic deformation (fine grains)

Question 3

Grain size and distribution

Determine GS distribution

(4)

Answer 3

1. Estimate (eye, fingers)
2. Sieving (sand, gravel)
3. Settling analysis (clay, silt)

4 Laser-based measurements

Question 4

Grain size and distribution

Grain size classes

Answer 4

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

Question 5

Grain size and distribution

Sieving analyses

Answer 5

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

Question 6

Grain size and distribution

Settling analyses, generell

Answer 6

• utilizing Stokes Law

- measure density of fluid at given time intervals

Question 7

Grain size and distribution

Settling analyses, formula

Answer 7

Coarse grains sink faster than small ones

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

Question 8

Grain size and distribution

What product is sorting?

Answer 8

product of depositional processes

Question 9

Grain size and distribution

What characterise sorting and GS?

Answer 9

the geotechnical properties

Question 10

Grain size and distribution

One GS dominant?

Answer 10

poorly graded

very well sorted

Question 11

Grain size and distribution

Several GS present

Answer 11

well graded

poorly sorted

Question 12

Grain size and distribution

wanted properties of well graded soils

Answer 12

lower pore space (usually)

-> less affected by compaction

Question 13

USCS: Symbols of classification

Dominant grain size

• gravel
• sand
• silt
• clay
• organic

Answer 13

G = gravel

S = sand

M = silt

C = clay

O = organic

Question 14

USCS: Symbols of classification

Sorting

• poorly graded
• well graded
• high plasticity
• low plasticity

Answer 14

P = poorly graded

W = well graded

H = high plasticity

L = low plasticity

Question 15

USCS: Symbols of classification

Differentiation between coarse and fines

Answer 15

D_50 larger or smaller than 0.063 mm

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

Question 16

USCS: Symbols of classification

G
S
M
C
O

Answer 16

G = gravel

S = sand

M = silt

C = clay

O = organic

Question 17

USCS: Symbols of classification

P
W
H
L

Answer 17

P = poorly graded

W = well graded

H = high plasticity

L = low plasticity

Question 18

USCS classification

Uniformity coefficient
Gravel/Sand

Answer 18

C_du = D_60 / D_10

Question 19

USCS classification

Curvature
Gravel/Sand

Answer 19

C_cd = D_30^2 / (D_10*D_60)

Question 20

USCS classification

guideline 1. step: GS distribution

Answer 20

1. Determine dominant GS:

Gravel/Sand

Silt/Clay

Question 21

USCS classification

guideline 2. step: sorting

• if Gravel/Sand
• if Silt/Clay

Answer 21

Gravel/Sand
-> estimate or analyse GS distribution

Silt/Clay
-> determined Atterberg limits

Question 22

USCS classification

guideline 3. step: Plasticity
if Gravel/Sand

Answer 22

calculate

Uniformity coefficient = C_ud

Curvature = C_cd

Question 23

USCS classification

guideline 3. step: Plasticity
if Silt/Clay

Answer 23

Atterberg limits:

liquid limit
plastic limit
shrinkage limit

Question 24

USCS classification

Liquid limit

Answer 24

= Water content required to fill gab after 25 drops

Graph: Water content vs. Number of drops

Question 25

USCS classification

Plastic limit

Answer 25

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

Question 26

USCS classification

plasticity index (%) formula

Answer 26

PI = LL - PL

Question 27

USCS classification

plasticity index (%) meanings

Answer 27

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

Question 28

Components

What occurs?

Answer 28

silikates!

Carbonates

Organic material

Clay minerals

Question 29

Components

effect of Carbonates

Answer 29

• sensitive to acidic water

- may increase stability

Question 30

Components

effect of Organic material

Answer 30

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

Question 31

Components

effect of clay minerals

Answer 31

• swelling potential, expansion

anhydrite to gypsum

Question 32

Components: measurement

Calcium carbonate content

Answer 32

with:
Calcium carbonate content chamber

quantitative

1 g dried soil treated with HCl in sealed chamber

pressure of CO2 amount of Carbonate

Question 33

Components: measurement

Organic matter content

Answer 33

with:
Loss on ignition

LOI = Wi-Wf/Wi*100

Wi = initial weight
Wf = final weight after burning over 550°C for ~4h

Question 34

Components: measurement

Clay minerals

Answer 34

X-ray diffraction (XRD)