The document discusses soil texture and grain size distribution. It defines different soil types based on particle size, including gravel, sand, silt and clay. Various classification systems are used to categorize soils based on predominant particle sizes. The size of particles in a soil can range widely, from boulders larger than 60mm to clay particles smaller than 2 micrometers. The grain size distribution of a soil, including metrics like D10, D30 and D60, impact its engineering properties such as permeability and compressibility.

1. Soil Classification

2. 2
Soil Texture

3. 3
Soil Texture
The texture of a soil is its appearance or “feel”
and it depends on the relative sizes and shapes
of the particles as well as the range or
distribution of those sizes.
Coarse-grained soils:
Gravel Sand
Fine-grained soils:
Silt Clay
0.075 mm (USCS)
0.06 mm (BS) (Hong Kong)
Sieve analysis Hydrometer analysis

4. 4
1.2 Characteristics
(Holtz and Kovacs, 1981)

5. 5
Grain Size and Grain Size
Distribution

6. Take note!!!
The sizes of particles that make up soil vary
over a wide range. Soils are generally called
gravel, sand, silt, or clay, depending on the
predominant size of particles within the soil. To
describe soils by their particle size, several
organizations have developed particle-size
classifications.

7. Particle Size Distribution
boulders > 60mm
60mm > gravel > 2mm
2mm > sand > 60 m
60 m > silt > 2 m
2 m > clay
Each class may is sub-divided into coarse, medium and fine.
for sand:
2mm > coarse sand > 600 m
600 m > medium sand > 200 m
200 m > fine sand > 60 m
Classification boundaries either begin with a '2' or a '6'.

8. Soil-Particle Size Classification

9. 9
Grain Size
4.75
Unit: mm (Holtz and Kovacs, 1981)
USCS
BS
0.075
2.0 0.06 0.002
USCS: Unified Soil Classification
BS: British Standard

10. • Data often presented as Particle Size Distribution Curves with
logarithmic scale on X-axis
Particle Size Distribution (continued)
• S - shaped - but some conventions of curves going left to right,
others, the opposite way around
sand
siltclay

11. A Problem
• clay is used both as a classifier of size as above, and also to define
particular types of material.
• clays exhibit a property known as cohesion
(the "stickiness" associated with clays).
General Properties
• Gravels ----- permeability is of the order of mm s-1.
• Clays ----- it is 10-7 mm/s or less.
• Compressibility of the soil increases as the particle size decreases.
• Permeability of the soil decreases as the particle size decreases.
Particle Size Distribution (continued)

12. 12
Sieve Sizes
(Das, 1998)
(Head, 1992)

13. 13
Grain Size Distribution (Cont.)
Coarse-grained soils:
Gravel Sand
Fine-grained soils:
Silt Clay
0.075 mm (USCS)
0.06 mm (BS) (Hong Kong)
•Experiment
Sieve analysis Hydrometer analysis
(Head, 1992)

14. 14
Grain Size Distribution (Cont.)
Log scale
(Holtz and Kovacs, 1981)
Effective size D10: 0.02 mm
D30: D60:

15. 15
Grain Size Distribution (Cont.)
• Describe the shape
Example: well graded
•Criteria
•Question
What is the Cu for a soil with
only one grain size?
2
)9)(02.0(
)6.0(
)D)(D(
)D(
C
curvatureoftCoefficien
450
02.0
9
D
D
C
uniformityoftCoefficien
2
6010
2
30
c
10
60
u


mm9D
mm6.0D
)sizeeffective(mm02.0D
60
30
10



)sandsfor(
6Cand3C1
)gravelsfor(
4Cand3C1
soilgradedWell
uc
uc




16. 16
Answer
•Question
What is the Cu for a soil with only one grain size?
D
Finer
1
D
D
C
uniformityoftCoefficien
10
60
u 
Grain size distribution

17. SAMPLE PROBLEM
1. For a soil with D60 =0.42mm, and D30 =0.21mm, and
D10 =0.16, calculate and the coefficient of gradation.
Sol’n;
CU =D60 /D10 =0.42mm/0.16mm=2.625
CC = (D30 )2 /(D10 )(D60) =(0.21)2 / (0.16)(0.42)=0.66

18. 2. The following are the results of a sieve analysis:
US Sieve
No.
Mass of Soil Retained on
Each Sieve (g)
Opening Commulative
Mass
% Passing
4
10
20
40
60
100
200
PAN
0
18.5
53.2
90.5
81.8
92.2
58.5
26.5
4.75
2.0
.850
.425
.250
.150
.075
0
18.5
71.5
162.2
244
336.2
394.1
421.2
100
95.608
82.977
61.491
42.070
20.180
6.434
0
a.) Determine the percent finer than each sieve size and plot a grain-
size distribution curve.
b.) Determine D10 , D30 and D60 from the grain-size distribution curve.
c.) Calculate the uniformity coefficient, Cu.
d.) Calculate the coefficient of graduation, Cc.

19. Grain-size distribution curve
0
20
40
60
80
100
120
0.01 0.1 1 10

20. Solution
c.) Cu = D60 /D10 =0.4/0.12= 3.33
d.) CC = (D)2/(D60)(D10) =1.01

21. 3.The particle-size characteristics of a soil are given in the
table.
Sieve no. Opening % Passing
4
10
20
40
80
200
4.75
2.00
0.850
0.425
0.180
0.075
100
90
64
38
18
13
Calculate the uniformity coefficient ( Cu) and
coefficient of gradation ( Cc).

22. Sol’n:
Cu= D60/ D10= 0.73/0.019= 38.421
Cc = (0.29)2 / (0.73)(.019)=0.063

23. 23
Grain Size Distribution (Cont.)
• Engineering applications
 It will help us “feel” the soil texture (what the soil is) and it will
also be used for the soil classification (next topic).
 It can be used to define the grading specification of a drainage
filter (clogging).
 It can be a criterion for selecting fill materials of embankments
and earth dams, road sub-base materials, and concrete
aggregates.
 It can be used to estimate the results of grouting and chemical
injection, and dynamic compaction.
 Effective Size, D10, can be correlated with the hydraulic
conductivity (describing the permeability of soils). (Hazen’s
Equation).(Note: controlled by small particles)
The grain size distribution is more important to coarse-grained soils.

24. 24
Particle Shape
 Important for granular soils
 Angular soil particle  higher friction
 Round soil particle  lower friction
 Note that clay particles are sheet-like.
Rounded Subrounde
d
Subangular Angular
(Holtz and Kovacs, 1981)
Coarse-
grained
soils

25. Thank you!!!