FOUNDATION-ANALYSIS-AND-DESIGN Notes | EduRev

: FOUNDATION-ANALYSIS-AND-DESIGN Notes | EduRev

 Page 1


FOUNDATION ANALYSIS AND DESIGN 
 
Module 1 
(Lecture 2) 
GEOTECHNICAL PROPERTIES OF SOIL AND OF 
REINFORCED SOIL 
Topics 
1.1  SOIL CLASSIFICATION SYSTEMS 
1.2 AASHTO System  
? Unified System 
? Examples and Solutions 
     1.3 HYDRAULIC CONDUCTIVITY OF SOIL  
     1.4 STEADY-STATE SEEPAGE 
     1.5 FILTER DESIGN CRITERIA 
     1.6 EFFECTIVE STRESS CONCEPT 
 
 
 
 
 
 
 
 
Page 2


FOUNDATION ANALYSIS AND DESIGN 
 
Module 1 
(Lecture 2) 
GEOTECHNICAL PROPERTIES OF SOIL AND OF 
REINFORCED SOIL 
Topics 
1.1  SOIL CLASSIFICATION SYSTEMS 
1.2 AASHTO System  
? Unified System 
? Examples and Solutions 
     1.3 HYDRAULIC CONDUCTIVITY OF SOIL  
     1.4 STEADY-STATE SEEPAGE 
     1.5 FILTER DESIGN CRITERIA 
     1.6 EFFECTIVE STRESS CONCEPT 
 
 
 
 
 
 
 
 
FOUNDATION ANALYSIS AND DESIGN 
SOIL CLASSIFICATION SYSTEMS 
Soil classification systems divide soils into groups and subgroups based on common 
engineering properties such as grain-size distribution, liquid limit, and plastic limit. 
The two major classification systems presently in use are (1) the AASHTO 
(American Association of State Highway and Transportation Officials) Systems and 
(2) the Unified Soil Classification System (also ASTM), the AASHTO classification 
system is used mainly for classification of highway subgrades. It is not used in 
foundation construction. 
      AASHTO System 
The AASHTO Soil Classification System was originally proposed by the Highway 
Research Board’s Committee on Classification of Materials for Subgrades and 
Granular Type Roads (1945). According to the present form of this system, soils can 
be classified according to eight major groups, A-1 through A-8, based on their grain-
size distribution, liquid limit, and plasticity indices. Soils listed in groups A-1, A-2, 
and A-3 are coarse-grained materials, and those in groups A-4, A-5, A-6, and A-7 are 
fine-grained materials. Peat, muck, and other highly organic soils are classified under 
A-8. They are identified by visual inspection. 
The AASHTO classification system (for soils A-1 through A-7) is presented in table 
8. Note that group A-7 includes two types of soil. For the A-7-5 type, the plasticity 
index of the soil is less than or equal to the liquid limit minus 30. For the A-7-6 type, 
the plasticity index is greater than the liquid limit minus 30. 
For qualitative evaluation of the desirability of a soil as a highway subgrade material, 
a number referred to as the group index has also been developed. The higher the value 
of the group index for a given soil, the weaker will be the soil’s performance as a 
subgrade. A group index of 20 or more indicates a very poor subgrade material. The 
formula for group index, ???????? , is  
???????? = ( ???? 200
- 35)[0.2 + 0.005( ???????? - 40)] + 0.01( ???? 200
- 15)( ???????? - 10)      
[1.23]    
Where  
???? 200
= percent passing no 200 sieve, expressed as a whole number  
???????? = liquid limit  
???????? = plasticity index  
 
 
 
Page 3


FOUNDATION ANALYSIS AND DESIGN 
 
Module 1 
(Lecture 2) 
GEOTECHNICAL PROPERTIES OF SOIL AND OF 
REINFORCED SOIL 
Topics 
1.1  SOIL CLASSIFICATION SYSTEMS 
1.2 AASHTO System  
? Unified System 
? Examples and Solutions 
     1.3 HYDRAULIC CONDUCTIVITY OF SOIL  
     1.4 STEADY-STATE SEEPAGE 
     1.5 FILTER DESIGN CRITERIA 
     1.6 EFFECTIVE STRESS CONCEPT 
 
 
 
 
 
 
 
 
FOUNDATION ANALYSIS AND DESIGN 
SOIL CLASSIFICATION SYSTEMS 
Soil classification systems divide soils into groups and subgroups based on common 
engineering properties such as grain-size distribution, liquid limit, and plastic limit. 
The two major classification systems presently in use are (1) the AASHTO 
(American Association of State Highway and Transportation Officials) Systems and 
(2) the Unified Soil Classification System (also ASTM), the AASHTO classification 
system is used mainly for classification of highway subgrades. It is not used in 
foundation construction. 
      AASHTO System 
The AASHTO Soil Classification System was originally proposed by the Highway 
Research Board’s Committee on Classification of Materials for Subgrades and 
Granular Type Roads (1945). According to the present form of this system, soils can 
be classified according to eight major groups, A-1 through A-8, based on their grain-
size distribution, liquid limit, and plasticity indices. Soils listed in groups A-1, A-2, 
and A-3 are coarse-grained materials, and those in groups A-4, A-5, A-6, and A-7 are 
fine-grained materials. Peat, muck, and other highly organic soils are classified under 
A-8. They are identified by visual inspection. 
The AASHTO classification system (for soils A-1 through A-7) is presented in table 
8. Note that group A-7 includes two types of soil. For the A-7-5 type, the plasticity 
index of the soil is less than or equal to the liquid limit minus 30. For the A-7-6 type, 
the plasticity index is greater than the liquid limit minus 30. 
For qualitative evaluation of the desirability of a soil as a highway subgrade material, 
a number referred to as the group index has also been developed. The higher the value 
of the group index for a given soil, the weaker will be the soil’s performance as a 
subgrade. A group index of 20 or more indicates a very poor subgrade material. The 
formula for group index, ???????? , is  
???????? = ( ???? 200
- 35)[0.2 + 0.005( ???????? - 40)] + 0.01( ???? 200
- 15)( ???????? - 10)      
[1.23]    
Where  
???? 200
= percent passing no 200 sieve, expressed as a whole number  
???????? = liquid limit  
???????? = plasticity index  
 
 
 
FOUNDATION ANALYSIS AND DESIGN 
Table 8 AASHTO Soil Classification System 
General 
classification  
Granular materials (35% or less of total samples passing no. 200 
sieve) 
 A-1 A-2 
Group 
classification  
A-1-a A-1-b A-3 A-2-4 A-2-5 A-2-6 
Sieve analysis 
(%) passing) 
      
No. 10 sieve  50 
max 
     
No. 40 sieve  30 
max 
50 max 51 max    
No. 200 sieve  15 
max  
25 max  10 max 35 max 35 max 35 max 
For fraction 
passing No. 40 
sieve 
      
Liquid limit (LL)    40 max 41 min 40 max 
Plasticity index 
(PI) 
6 max  Nonplastic  10 max 10 max 11 min 
Usual type of 
material  
Stone fragments, 
gravel, and sand 
Fine sand  Silty or clayey gravel and sand  
Subgrade rating     Excellent to good 
       
General 
classification  
Silt-clay materials (More than 35% of total sample passing no. 
200 sieve) 
Group 
classification  
A-4 A-5 A-6 A-7   
    A-7-5
a
   
    A-7
b
   
Page 4


FOUNDATION ANALYSIS AND DESIGN 
 
Module 1 
(Lecture 2) 
GEOTECHNICAL PROPERTIES OF SOIL AND OF 
REINFORCED SOIL 
Topics 
1.1  SOIL CLASSIFICATION SYSTEMS 
1.2 AASHTO System  
? Unified System 
? Examples and Solutions 
     1.3 HYDRAULIC CONDUCTIVITY OF SOIL  
     1.4 STEADY-STATE SEEPAGE 
     1.5 FILTER DESIGN CRITERIA 
     1.6 EFFECTIVE STRESS CONCEPT 
 
 
 
 
 
 
 
 
FOUNDATION ANALYSIS AND DESIGN 
SOIL CLASSIFICATION SYSTEMS 
Soil classification systems divide soils into groups and subgroups based on common 
engineering properties such as grain-size distribution, liquid limit, and plastic limit. 
The two major classification systems presently in use are (1) the AASHTO 
(American Association of State Highway and Transportation Officials) Systems and 
(2) the Unified Soil Classification System (also ASTM), the AASHTO classification 
system is used mainly for classification of highway subgrades. It is not used in 
foundation construction. 
      AASHTO System 
The AASHTO Soil Classification System was originally proposed by the Highway 
Research Board’s Committee on Classification of Materials for Subgrades and 
Granular Type Roads (1945). According to the present form of this system, soils can 
be classified according to eight major groups, A-1 through A-8, based on their grain-
size distribution, liquid limit, and plasticity indices. Soils listed in groups A-1, A-2, 
and A-3 are coarse-grained materials, and those in groups A-4, A-5, A-6, and A-7 are 
fine-grained materials. Peat, muck, and other highly organic soils are classified under 
A-8. They are identified by visual inspection. 
The AASHTO classification system (for soils A-1 through A-7) is presented in table 
8. Note that group A-7 includes two types of soil. For the A-7-5 type, the plasticity 
index of the soil is less than or equal to the liquid limit minus 30. For the A-7-6 type, 
the plasticity index is greater than the liquid limit minus 30. 
For qualitative evaluation of the desirability of a soil as a highway subgrade material, 
a number referred to as the group index has also been developed. The higher the value 
of the group index for a given soil, the weaker will be the soil’s performance as a 
subgrade. A group index of 20 or more indicates a very poor subgrade material. The 
formula for group index, ???????? , is  
???????? = ( ???? 200
- 35)[0.2 + 0.005( ???????? - 40)] + 0.01( ???? 200
- 15)( ???????? - 10)      
[1.23]    
Where  
???? 200
= percent passing no 200 sieve, expressed as a whole number  
???????? = liquid limit  
???????? = plasticity index  
 
 
 
FOUNDATION ANALYSIS AND DESIGN 
Table 8 AASHTO Soil Classification System 
General 
classification  
Granular materials (35% or less of total samples passing no. 200 
sieve) 
 A-1 A-2 
Group 
classification  
A-1-a A-1-b A-3 A-2-4 A-2-5 A-2-6 
Sieve analysis 
(%) passing) 
      
No. 10 sieve  50 
max 
     
No. 40 sieve  30 
max 
50 max 51 max    
No. 200 sieve  15 
max  
25 max  10 max 35 max 35 max 35 max 
For fraction 
passing No. 40 
sieve 
      
Liquid limit (LL)    40 max 41 min 40 max 
Plasticity index 
(PI) 
6 max  Nonplastic  10 max 10 max 11 min 
Usual type of 
material  
Stone fragments, 
gravel, and sand 
Fine sand  Silty or clayey gravel and sand  
Subgrade rating     Excellent to good 
       
General 
classification  
Silt-clay materials (More than 35% of total sample passing no. 
200 sieve) 
Group 
classification  
A-4 A-5 A-6 A-7   
    A-7-5
a
   
    A-7
b
   
FOUNDATION ANALYSIS AND DESIGN 
Sieve analysis (% 
passing) 
      
No. 10 sieve        
No. 40 sieve        
No. 200 sieve  36 
min 
36 min 36 min  36 min   
For fraction 
passing No. 40 
sieve  
      
Liquid limit (LL) 40 
max 
41 min  40 max  41 min   
Plasticity index 
(PI) 
10 
max  
10 max 11 min  11 min    
Usual types of 
material  
Mostly silty soils Mostly clayey soils  
Subgrade rating   Fair to poor    
a
 If PI =LL-30, it 
is A-7-5. 
      
b
 If PI>LL-30, it 
is A-7-6. 
      
When calculating the group index for a soil belonging to groups A-2-6 or A-2-7, us 
only the partial group index equation relating to the plasticity index: 
???????? = 0.01( ???? 200
- 15)( ???????? - 10)       [1.24] 
  
The group index is rounded to the nearest whole number and written next to the soil 
group in parentheses; for example, 
???? - 4 ? ? ? 
|
Soil group
 
(5)
?
 
Group index
  
 
 
Page 5


FOUNDATION ANALYSIS AND DESIGN 
 
Module 1 
(Lecture 2) 
GEOTECHNICAL PROPERTIES OF SOIL AND OF 
REINFORCED SOIL 
Topics 
1.1  SOIL CLASSIFICATION SYSTEMS 
1.2 AASHTO System  
? Unified System 
? Examples and Solutions 
     1.3 HYDRAULIC CONDUCTIVITY OF SOIL  
     1.4 STEADY-STATE SEEPAGE 
     1.5 FILTER DESIGN CRITERIA 
     1.6 EFFECTIVE STRESS CONCEPT 
 
 
 
 
 
 
 
 
FOUNDATION ANALYSIS AND DESIGN 
SOIL CLASSIFICATION SYSTEMS 
Soil classification systems divide soils into groups and subgroups based on common 
engineering properties such as grain-size distribution, liquid limit, and plastic limit. 
The two major classification systems presently in use are (1) the AASHTO 
(American Association of State Highway and Transportation Officials) Systems and 
(2) the Unified Soil Classification System (also ASTM), the AASHTO classification 
system is used mainly for classification of highway subgrades. It is not used in 
foundation construction. 
      AASHTO System 
The AASHTO Soil Classification System was originally proposed by the Highway 
Research Board’s Committee on Classification of Materials for Subgrades and 
Granular Type Roads (1945). According to the present form of this system, soils can 
be classified according to eight major groups, A-1 through A-8, based on their grain-
size distribution, liquid limit, and plasticity indices. Soils listed in groups A-1, A-2, 
and A-3 are coarse-grained materials, and those in groups A-4, A-5, A-6, and A-7 are 
fine-grained materials. Peat, muck, and other highly organic soils are classified under 
A-8. They are identified by visual inspection. 
The AASHTO classification system (for soils A-1 through A-7) is presented in table 
8. Note that group A-7 includes two types of soil. For the A-7-5 type, the plasticity 
index of the soil is less than or equal to the liquid limit minus 30. For the A-7-6 type, 
the plasticity index is greater than the liquid limit minus 30. 
For qualitative evaluation of the desirability of a soil as a highway subgrade material, 
a number referred to as the group index has also been developed. The higher the value 
of the group index for a given soil, the weaker will be the soil’s performance as a 
subgrade. A group index of 20 or more indicates a very poor subgrade material. The 
formula for group index, ???????? , is  
???????? = ( ???? 200
- 35)[0.2 + 0.005( ???????? - 40)] + 0.01( ???? 200
- 15)( ???????? - 10)      
[1.23]    
Where  
???? 200
= percent passing no 200 sieve, expressed as a whole number  
???????? = liquid limit  
???????? = plasticity index  
 
 
 
FOUNDATION ANALYSIS AND DESIGN 
Table 8 AASHTO Soil Classification System 
General 
classification  
Granular materials (35% or less of total samples passing no. 200 
sieve) 
 A-1 A-2 
Group 
classification  
A-1-a A-1-b A-3 A-2-4 A-2-5 A-2-6 
Sieve analysis 
(%) passing) 
      
No. 10 sieve  50 
max 
     
No. 40 sieve  30 
max 
50 max 51 max    
No. 200 sieve  15 
max  
25 max  10 max 35 max 35 max 35 max 
For fraction 
passing No. 40 
sieve 
      
Liquid limit (LL)    40 max 41 min 40 max 
Plasticity index 
(PI) 
6 max  Nonplastic  10 max 10 max 11 min 
Usual type of 
material  
Stone fragments, 
gravel, and sand 
Fine sand  Silty or clayey gravel and sand  
Subgrade rating     Excellent to good 
       
General 
classification  
Silt-clay materials (More than 35% of total sample passing no. 
200 sieve) 
Group 
classification  
A-4 A-5 A-6 A-7   
    A-7-5
a
   
    A-7
b
   
FOUNDATION ANALYSIS AND DESIGN 
Sieve analysis (% 
passing) 
      
No. 10 sieve        
No. 40 sieve        
No. 200 sieve  36 
min 
36 min 36 min  36 min   
For fraction 
passing No. 40 
sieve  
      
Liquid limit (LL) 40 
max 
41 min  40 max  41 min   
Plasticity index 
(PI) 
10 
max  
10 max 11 min  11 min    
Usual types of 
material  
Mostly silty soils Mostly clayey soils  
Subgrade rating   Fair to poor    
a
 If PI =LL-30, it 
is A-7-5. 
      
b
 If PI>LL-30, it 
is A-7-6. 
      
When calculating the group index for a soil belonging to groups A-2-6 or A-2-7, us 
only the partial group index equation relating to the plasticity index: 
???????? = 0.01( ???? 200
- 15)( ???????? - 10)       [1.24] 
  
The group index is rounded to the nearest whole number and written next to the soil 
group in parentheses; for example, 
???? - 4 ? ? ? 
|
Soil group
 
(5)
?
 
Group index
  
 
 
FOUNDATION ANALYSIS AND DESIGN 
Unified System 
The Unified Soil Classification System was originally proposed by A. Casagrande in 
1942 and was later revised and adopted by the United States Bureau of Reclamation 
and the Corps of Engineers. This system is presently used in practically all 
geotechnical work. 
In the Unified System, the following symbols are used for identification. 
Symbol  ???? ???? ???? ???? ???? ???????? ???? ???? ???? ???? 
Descripti
on  
Grav
el  
San
d  
Sil
t  
Cla
y  
Organ
ic silts 
and 
clay  
Peat 
and 
highl
y 
organ
ic 
soils  
High 
plastici
ty  
Low 
plastici
ty  
Well 
grad
ed  
Poorl
y 
grad
ed 
The plasticity chart (figure 1.7) and table 9 shows the procedure for determining the 
group symbols for various types of soil. When classifying a soil be sure to provide the 
group name that generally describes the soil, along with the group symbol. Tables 10, 
11 and 12, respectively, give the criteria for obtaining the group names for coarse-
grained soil, inorganic fine-grained soil, and organic fine-grained soil. These tables 
are based on ASTM Designation D-2487. 
Table 9 Group Symbol for Soil According to the Unified Classification System 
[Based on Material Passing 3-in. (75-mm) Sieve] 
Major division  Criteria  Group symbol  
Coarse-grained soil  ???? 200
< 5, ???? ???? = 4, 1 = ???? ???? = 3 
GW 
???? 200
> 50 ???? 200
< 5, ???? ???? < 4, and
/or ???? ???? not between 1 and 3 
GP 
Gravelly soil ???? 4
> 0.5 ???? 200
 ???? 200
> 12, ???????? < 4, or 
Atterberg limits plot be low 
A line (figure 1.7) 
GM 
 ???? 200
> 12, ???????? < 7, and 
Atterberg limits plot on or 
above A line (figure 1.7) 
GC 
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