SHEARING STRENGTH OF GRANULAR SOILS Notes | EduRev

: SHEARING STRENGTH OF GRANULAR SOILS Notes | EduRev

 Page 1


NPTEL- Advanced Geotechnical Engineering 
 
Dept. of Civil Engg. Indian Institute of Technology, Kanpur                                                                           1 
 
Module 4 
Lecture 24 
Pore water pressure and shear strength - 8 
Topics 
1.3.7 Unique Effective Stress Failure Envelope 
1.3.8 Unique Relationship between Water Content and Effective Stress 
1.3.9 Vane Shear Test 
 
1.3.7 Unique Effective Stress Failure Envelope 
When Mohr’s envelope is used to obtain the relationship for normal and shear stress at failure (from triaxial 
test results), separate envelopes need to be drawn for separate preconsolidation pressure,   
 
. This is shown 
in Figure 4.34. For a soil with a preconsolidation pressure of   
  
    
 
  
 
    
    
; similarly, for a 
preconsolidation pressure of   
  
    
 
  
 
    
    
. 
 
 
Figure 4.34 
Page 2


NPTEL- Advanced Geotechnical Engineering 
 
Dept. of Civil Engg. Indian Institute of Technology, Kanpur                                                                           1 
 
Module 4 
Lecture 24 
Pore water pressure and shear strength - 8 
Topics 
1.3.7 Unique Effective Stress Failure Envelope 
1.3.8 Unique Relationship between Water Content and Effective Stress 
1.3.9 Vane Shear Test 
 
1.3.7 Unique Effective Stress Failure Envelope 
When Mohr’s envelope is used to obtain the relationship for normal and shear stress at failure (from triaxial 
test results), separate envelopes need to be drawn for separate preconsolidation pressure,   
 
. This is shown 
in Figure 4.34. For a soil with a preconsolidation pressure of   
  
    
 
  
 
    
    
; similarly, for a 
preconsolidation pressure of   
  
    
 
  
 
    
    
. 
 
 
Figure 4.34 
NPTEL- Advanced Geotechnical Engineering 
 
Dept. of Civil Engg. Indian Institute of Technology, Kanpur                                                                           2 
Henkel (1960) showed that a single, general failure envelope for normally consolidated and preconsolidated 
(irrespective of preconsolidation pressure) soils can be obtained by plotting the ratio of the major to minor 
effective stress at failure against the ratio of the maxi um consolidation pressure to the average effective 
stress at failure.  
1.3.8 Unique Relationship between Water Content and Effective Stress 
There is a unique between the water content of a soil and the effective stresses to which it is being subjected, 
provided that normally consolidated specimens and specimens with common maximum consolidation 
pressures are considered separately. This can be explained with the aid of Figure 4. 35, in which a Rendulic 
plot for a normally consolidated clay is shown. Consider several specimens consolidated at various 
confining pressures in a triaxial chamber; the states of stress of these specimens are represented by the 
points             located on the isotropic stress lines. When these specimens are sheared to failure by 
drained compressions, the corresponding stress paths will be represented by lines such as                . 
During drained tests, the moisture contents of the specimens change. We can determine the moisture 
contents of the specimens during the tests, such as  
 
  
 
    as shown in Figure 4.35. If these pointsof 
equal moisture contents on the drained stress paths are joined, we obtain contours of stress paths of equal 
moisture contents (for moisture contents  
 
  
 
   ). 
 
 
 
 
Figure 4.36 and 4.37 show the stress paths for equal water content for normally consolidated and 
overconsolidated Weald clay. Note the similarity of shape of the stress paths for normally consolidated clay 
in Figure 4.36. For overconsolidated clay, the shape of the stress path gradually changes, depending on the 
overconsolidation ratio. 
     Figure 4.35  Unique relationship between water content and effective stress 
Page 3


NPTEL- Advanced Geotechnical Engineering 
 
Dept. of Civil Engg. Indian Institute of Technology, Kanpur                                                                           1 
 
Module 4 
Lecture 24 
Pore water pressure and shear strength - 8 
Topics 
1.3.7 Unique Effective Stress Failure Envelope 
1.3.8 Unique Relationship between Water Content and Effective Stress 
1.3.9 Vane Shear Test 
 
1.3.7 Unique Effective Stress Failure Envelope 
When Mohr’s envelope is used to obtain the relationship for normal and shear stress at failure (from triaxial 
test results), separate envelopes need to be drawn for separate preconsolidation pressure,   
 
. This is shown 
in Figure 4.34. For a soil with a preconsolidation pressure of   
  
    
 
  
 
    
    
; similarly, for a 
preconsolidation pressure of   
  
    
 
  
 
    
    
. 
 
 
Figure 4.34 
NPTEL- Advanced Geotechnical Engineering 
 
Dept. of Civil Engg. Indian Institute of Technology, Kanpur                                                                           2 
Henkel (1960) showed that a single, general failure envelope for normally consolidated and preconsolidated 
(irrespective of preconsolidation pressure) soils can be obtained by plotting the ratio of the major to minor 
effective stress at failure against the ratio of the maxi um consolidation pressure to the average effective 
stress at failure.  
1.3.8 Unique Relationship between Water Content and Effective Stress 
There is a unique between the water content of a soil and the effective stresses to which it is being subjected, 
provided that normally consolidated specimens and specimens with common maximum consolidation 
pressures are considered separately. This can be explained with the aid of Figure 4. 35, in which a Rendulic 
plot for a normally consolidated clay is shown. Consider several specimens consolidated at various 
confining pressures in a triaxial chamber; the states of stress of these specimens are represented by the 
points             located on the isotropic stress lines. When these specimens are sheared to failure by 
drained compressions, the corresponding stress paths will be represented by lines such as                . 
During drained tests, the moisture contents of the specimens change. We can determine the moisture 
contents of the specimens during the tests, such as  
 
  
 
    as shown in Figure 4.35. If these pointsof 
equal moisture contents on the drained stress paths are joined, we obtain contours of stress paths of equal 
moisture contents (for moisture contents  
 
  
 
   ). 
 
 
 
 
Figure 4.36 and 4.37 show the stress paths for equal water content for normally consolidated and 
overconsolidated Weald clay. Note the similarity of shape of the stress paths for normally consolidated clay 
in Figure 4.36. For overconsolidated clay, the shape of the stress path gradually changes, depending on the 
overconsolidation ratio. 
     Figure 4.35  Unique relationship between water content and effective stress 
NPTEL- Advanced Geotechnical Engineering 
 
Dept. of Civil Engg. Indian Institute of Technology, Kanpur                                                                           3 
 
\ 
 
 
 
 
 
 
Figure 4.36  Weald-clay normally consolidated. (Note:        
 
         
 
) (Redrawn after 
D. J. Henkel, The Shearing Strength of Saturated Remolded Clays, Proc. Research Conference 
on Shear Strength of Cohesive Soils, ASCE, 1960) 
Figure 4.37 Weald-clay normally consolidated: maximum consolidated pressure      
     
 
        
 
) (Redrawn after D. J. Henkel, The Shearing Strength of Saturated 
Remolded Clays, Proc. Research Conference on Shear Strength of Cohesive Soils, ASCE, 
1960) 
 
Page 4


NPTEL- Advanced Geotechnical Engineering 
 
Dept. of Civil Engg. Indian Institute of Technology, Kanpur                                                                           1 
 
Module 4 
Lecture 24 
Pore water pressure and shear strength - 8 
Topics 
1.3.7 Unique Effective Stress Failure Envelope 
1.3.8 Unique Relationship between Water Content and Effective Stress 
1.3.9 Vane Shear Test 
 
1.3.7 Unique Effective Stress Failure Envelope 
When Mohr’s envelope is used to obtain the relationship for normal and shear stress at failure (from triaxial 
test results), separate envelopes need to be drawn for separate preconsolidation pressure,   
 
. This is shown 
in Figure 4.34. For a soil with a preconsolidation pressure of   
  
    
 
  
 
    
    
; similarly, for a 
preconsolidation pressure of   
  
    
 
  
 
    
    
. 
 
 
Figure 4.34 
NPTEL- Advanced Geotechnical Engineering 
 
Dept. of Civil Engg. Indian Institute of Technology, Kanpur                                                                           2 
Henkel (1960) showed that a single, general failure envelope for normally consolidated and preconsolidated 
(irrespective of preconsolidation pressure) soils can be obtained by plotting the ratio of the major to minor 
effective stress at failure against the ratio of the maxi um consolidation pressure to the average effective 
stress at failure.  
1.3.8 Unique Relationship between Water Content and Effective Stress 
There is a unique between the water content of a soil and the effective stresses to which it is being subjected, 
provided that normally consolidated specimens and specimens with common maximum consolidation 
pressures are considered separately. This can be explained with the aid of Figure 4. 35, in which a Rendulic 
plot for a normally consolidated clay is shown. Consider several specimens consolidated at various 
confining pressures in a triaxial chamber; the states of stress of these specimens are represented by the 
points             located on the isotropic stress lines. When these specimens are sheared to failure by 
drained compressions, the corresponding stress paths will be represented by lines such as                . 
During drained tests, the moisture contents of the specimens change. We can determine the moisture 
contents of the specimens during the tests, such as  
 
  
 
    as shown in Figure 4.35. If these pointsof 
equal moisture contents on the drained stress paths are joined, we obtain contours of stress paths of equal 
moisture contents (for moisture contents  
 
  
 
   ). 
 
 
 
 
Figure 4.36 and 4.37 show the stress paths for equal water content for normally consolidated and 
overconsolidated Weald clay. Note the similarity of shape of the stress paths for normally consolidated clay 
in Figure 4.36. For overconsolidated clay, the shape of the stress path gradually changes, depending on the 
overconsolidation ratio. 
     Figure 4.35  Unique relationship between water content and effective stress 
NPTEL- Advanced Geotechnical Engineering 
 
Dept. of Civil Engg. Indian Institute of Technology, Kanpur                                                                           3 
 
\ 
 
 
 
 
 
 
Figure 4.36  Weald-clay normally consolidated. (Note:        
 
         
 
) (Redrawn after 
D. J. Henkel, The Shearing Strength of Saturated Remolded Clays, Proc. Research Conference 
on Shear Strength of Cohesive Soils, ASCE, 1960) 
Figure 4.37 Weald-clay normally consolidated: maximum consolidated pressure      
     
 
        
 
) (Redrawn after D. J. Henkel, The Shearing Strength of Saturated 
Remolded Clays, Proc. Research Conference on Shear Strength of Cohesive Soils, ASCE, 
1960) 
 
NPTEL- Advanced Geotechnical Engineering 
 
Dept. of Civil Engg. Indian Institute of Technology, Kanpur                                                                           4 
1.3.9 Vane Shear Test 
The field vane shear test is another method of obtaining the undrained shear strength of cohesive soils. The 
common shear vane usually consists of four thin steel plates of equal size welded to a steel torque rod. To 
perform the test, the vane is pushed into the soil and torque is applied at the top of the torque rod. The torque 
is gradually increased until the cylindrical soil of height H and diameter D fails. The maximum torque T 
applied to cause failure is the sum of the resisting moment at the top,  
 
      
 
  of the soil cylinder, plus 
the resisting moment at the sides of the cylinder,  
 
.  
 
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