Class notes of Geotechnical Engineering course I used to teach at UET Lahore. Feel free to download the slide show.
Anyone looking to modify these files and use them for their own teaching purposes can contact me directly to get hold of editable version.
1. 1
Geotechnical Engineering–I [CE-221]
BSc Civil Engineering – 4th Semester
by
Dr. Muhammad Irfan
Assistant Professor
Civil Engg. Dept. – UET Lahore
Email: mirfan1@msn.com
Lecture Handouts: https://groups.google.com/d/forum/2016session-geotech-i
Lecture # 11
27-Feb-2018
2. 2
Two commonly used classification system:
1. Unified Soil Classification System (USCS)
preferred by Geotechnical engineers
2. American Association of State Highway and
Transportation Officials (AASHTO) System
preferred by Transportation engineers
SOIL CLASSIFICATION
3. 3
→ Developed by Casagrande in 1942 for US Army
→ System based on particles < 3 in
→ Uses grain size distribution and plasticity of fines
Three major categories:
coarse-grained soils
fine-grained soils
organic soils
P200 < 50% → Coarse grained soil
P200 ≥ 50% → Fine grained soil
UNIFIED SOIL CLASSIFICATION
SYSTEM (USCS) (ASTM D 2487)
5. 5
Definition of Grain Size
Boulders Cobbles
Gravel Sand
Silt and
Clay
Coarse Fine Coarse FineMedium
300 mm 75 mm
19 mm
No.4
4.75 mm
No.10
2.0 mm
No.40
0.425 mm
No.200
0.075
mm
Use
Atterberg limits
UNIFIED SOIL CLASSIFICATION
SYSTEM (USCS)
UNIFIED SOIL CLASSIFICATION
SYSTEM (USCS)
7. 7
FIG. 1 Flow chart for Classifying Fine-Grained Soil (50% or More Passes No. 200 Sieve)
Fine Grained Soils
8. 8
Group Symbol Group Name
FIG. 1b Flow chart for Classifying Organic Fine-Grained Soil (50% or More Passes No. 200 Sieve)
Fine Grained Organic Soils
9. 9
FIG. 2 Flow chart for Classifying Coarse-Grained Soils (50% or More Retained on No. 200 Sieve)
Coarse Grained Soils
10. 10
Used for fine grained soils to determine whether silt (M) or clay (C)
Below A-line is silt – use symbol M
Above A-line is clay – use symbol C
LL > 50 High plasticity
LL< 50 Low plasticity
PLASTICITY/A-LINE CHART
11. 11
Soil A
Fines = 52% > 50% => Fine-grained soil
PRACTICE PROBLEM #1
20. 20
20
FIG. 3 Flow chart for Classifying Coarse-Grained Soils (50% or More Retained on No. 200 Sieve)
Gravel = 36%
Sand = 54%
Fines = 8%
21. 21
Soil A: D60 = 4.2 mm , D30 = 0.6 mm, D10 = 0.09 mm
Cu = 46.67
Cc = 0.95
Gravel
= 98-62
= 36%
Sand
= 62-8
= 54%
Fines
= 8%
PRACTICE PROBLEM #2
22. 22
22
FIG. 3 Flow chart for Classifying Coarse-Grained Soils (50% or More Retained on No. 200 Sieve)
Gravel = 36%
Sand = 54%
Fines = 8%
Cu = 46.7
Cc = 0.95
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24
FIG. 3 Flow chart for Classifying Coarse-Grained Soils (50% or More Retained on No. 200 Sieve)
Gravel = 36%
Sand = 54%
Fines = 8%
Cu = 46.7
Cc = 0.95
Soil A is classified as [SP-SM: Poorly-graded sand with silt and gravel]
LL = 42
PL = 31
PI = 42-31 = 11
ML
25. 25
Classify the following soils Using Unified Classification
System.
PRACTICE PROBLEM #3
Soil SIEVE LL PI
No. 4 No. 200
(Cumulative % passing)
A 92 48 30 10
B 99 76 60 32
C 80 35 24 2
26. 26
FIG. 3 Flow chart for Classifying Coarse-Grained Soils (50% or More Retained on No. 200 Sieve)
Coarse Grained Soils
27. 27
Used for fine grained soils to determine whether silt (M) or clay (C)
Below A-line is silt – use symbol M
Above A-line is clay – use symbol C
LL > 50 High plasticity
LL< 50 Low plasticity
PLASTICITY/A-LINE CHART
28. 29
Two commonly used classification system:
1. Unified Soil Classification System (USCS)
preferred by Geotechnical engineers
2. American Association of State Highway and
Transportation Officials (AASHTO) System
preferred by Transportation engineers
SOIL CLASSIFICATION
29. 30
→ Classification procedure standardized by ASTM D3282 and
AASHTO M145.
→ Soil rating for subgrade construction.
→ Soils classified into 8 groups (+ several subgroups);
A-1 (best) to A-8 (worst).
→ Organic soils (peat and muck) assigned group A-8.
→ Required tests are sieve analysis and Atterberg limits.
AASHTO Soil Classification
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A4 ~ A7A1 ~ A3
Granular Materials Silt-clay Materials
LL and PI separates silty materials from
clayey materials
LL and PI separates silty materials from
clayey materials (only for A2 group)
AASHTO Soil Classification
(ASTM D3282; AASHTO M145)
A-1 (0)
Group Number Group Index
Example
35% pass No. 200 sieve > 35% pass No. 200 sieve
31. 32
101501.040005.02.035 200200 PIFLLFGI
Partial GI determined from LL Partial GI determined from PI
where
F200 = percentage passing through the No. 200 sieve
LL = Liquid limit, and PI = Plasticity index
GI is rounded off to nearest whole number
(e.g., GI = 3.4 is rounded off to 3; GI = 3.5 is rounded off to 4)
GI = 0, if the equation yields negative value.
GI → Empirical formula used to further evaluate soils within a
group (subgroups)
GROUP INDEX (GI)
32. 33
GI is shown in parentheses after the group symbol,
e.g. A-2-6(3), A-6(12), A-7-5(17)
101501.0 200 PIFGI
GROUP INDEX (GI)
Smaller the GI, better is the soil.
GI of soils belonging to groups A-1-a, A-1-b, A-2-4, A-
2-5, and A-3 is always zero.
GI for soils belonging to groups A-2-6 and A-2-7 is
computed by using the partial formula.
33. 34
Boulders Gravel
Sand Silt and
Clay
75 mm
Coarse
No.10
2.0 mm
No.40
0.425 mm
No.200
0.075
mm
AASHTO Particle Size
Fine
37. 38
Range of LL and PI for soils in groups A-2, A-4, A-5, A-6, and A-7.
AASHTO Plasticity Chart
38. 39
CONCLUDED
REFERENCE MATERIAL
An Introduction to Geotechnical Engineering (2nd Edition)
By R. D. Holtz, W. D. Kovacs and T. C. Sheahan
Chapter #3
Principles of Geotechnical Engineering – (7th Edition)
Braja M. Das
Chapter #5