Preloading without vertical drains Notes | EduRev

: Preloading without vertical drains Notes | EduRev

 Page 1


Objectives_template
 Module 4:Preloading and vertical drains 
 Lecture 12:Preloading without vertical drains 
 
 
The Lecture Contains: 
Preloading and sand drains
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_1.htm [10/11/2011 4:25:52 PM]
Page 2


Objectives_template
 Module 4:Preloading and vertical drains 
 Lecture 12:Preloading without vertical drains 
 
 
The Lecture Contains: 
Preloading and sand drains
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_1.htm [10/11/2011 4:25:52 PM]
Objectives_template
 Module 4:Preloading and vertical drains 
 Lecture 12:Preloading without vertical drains 
 
 
Preloading and sand drains
Preloading without vertical drains:
Settlement calculations: 
Figure shows the case where a soft, normally consolidated foundation is preloaded. With earth fill exerting a 
pressure  
equivalent to a future building with a raft foundation.
     
Initial void ratio 
where water content
 specific gravity of soil solids
 compression index 
 = initial vertica pressure
 
After 90% of this settlement has taken place, the surcharge is removed and construction of the building 
begins. 
Figure 12.1
 
 
 
 
 
 
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (1 of 2) [10/11/2011 4:25:52 PM]
Page 3


Objectives_template
 Module 4:Preloading and vertical drains 
 Lecture 12:Preloading without vertical drains 
 
 
The Lecture Contains: 
Preloading and sand drains
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_1.htm [10/11/2011 4:25:52 PM]
Objectives_template
 Module 4:Preloading and vertical drains 
 Lecture 12:Preloading without vertical drains 
 
 
Preloading and sand drains
Preloading without vertical drains:
Settlement calculations: 
Figure shows the case where a soft, normally consolidated foundation is preloaded. With earth fill exerting a 
pressure  
equivalent to a future building with a raft foundation.
     
Initial void ratio 
where water content
 specific gravity of soil solids
 compression index 
 = initial vertica pressure
 
After 90% of this settlement has taken place, the surcharge is removed and construction of the building 
begins. 
Figure 12.1
 
 
 
 
 
 
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (1 of 2) [10/11/2011 4:25:52 PM]
Objectives_template
 
Figure 12.2
 
 
 
 
 
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (2 of 2) [10/11/2011 4:25:52 PM]
Page 4


Objectives_template
 Module 4:Preloading and vertical drains 
 Lecture 12:Preloading without vertical drains 
 
 
The Lecture Contains: 
Preloading and sand drains
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_1.htm [10/11/2011 4:25:52 PM]
Objectives_template
 Module 4:Preloading and vertical drains 
 Lecture 12:Preloading without vertical drains 
 
 
Preloading and sand drains
Preloading without vertical drains:
Settlement calculations: 
Figure shows the case where a soft, normally consolidated foundation is preloaded. With earth fill exerting a 
pressure  
equivalent to a future building with a raft foundation.
     
Initial void ratio 
where water content
 specific gravity of soil solids
 compression index 
 = initial vertica pressure
 
After 90% of this settlement has taken place, the surcharge is removed and construction of the building 
begins. 
Figure 12.1
 
 
 
 
 
 
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (1 of 2) [10/11/2011 4:25:52 PM]
Objectives_template
 
Figure 12.2
 
 
 
 
 
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (2 of 2) [10/11/2011 4:25:52 PM]
Objectives_template
 Module 4:Preloading and vertical drains 
 Lecture 12:Preloading without vertical drains 
 
 
Preloading & Sand drains
Upon reloading the foundation soil, the final settlement  of the building (Exerting a pressure  could 
be expressed in terms of reloading index 
 
The  curve was assumed to show a distinct break at the original overburden pressure of the 
normally consolidated soil element, this means the overburden pressure was assumed to be equal to the 
pre consolidation pressure. For soil samples obtained in the pre consolidation pressure   has to be 
deduced using Casagrande’s graphical procedure.
Figure 12.3
                                AB - secondary consolidation under overburden pressure. 
                                BC- primary consolidation due to surcharge. 
                                CD-secondary consolidation due to surcharge.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_3.htm [10/11/2011 4:25:53 PM]
Page 5


Objectives_template
 Module 4:Preloading and vertical drains 
 Lecture 12:Preloading without vertical drains 
 
 
The Lecture Contains: 
Preloading and sand drains
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_1.htm [10/11/2011 4:25:52 PM]
Objectives_template
 Module 4:Preloading and vertical drains 
 Lecture 12:Preloading without vertical drains 
 
 
Preloading and sand drains
Preloading without vertical drains:
Settlement calculations: 
Figure shows the case where a soft, normally consolidated foundation is preloaded. With earth fill exerting a 
pressure  
equivalent to a future building with a raft foundation.
     
Initial void ratio 
where water content
 specific gravity of soil solids
 compression index 
 = initial vertica pressure
 
After 90% of this settlement has taken place, the surcharge is removed and construction of the building 
begins. 
Figure 12.1
 
 
 
 
 
 
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (1 of 2) [10/11/2011 4:25:52 PM]
Objectives_template
 
Figure 12.2
 
 
 
 
 
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_2.htm (2 of 2) [10/11/2011 4:25:52 PM]
Objectives_template
 Module 4:Preloading and vertical drains 
 Lecture 12:Preloading without vertical drains 
 
 
Preloading & Sand drains
Upon reloading the foundation soil, the final settlement  of the building (Exerting a pressure  could 
be expressed in terms of reloading index 
 
The  curve was assumed to show a distinct break at the original overburden pressure of the 
normally consolidated soil element, this means the overburden pressure was assumed to be equal to the 
pre consolidation pressure. For soil samples obtained in the pre consolidation pressure   has to be 
deduced using Casagrande’s graphical procedure.
Figure 12.3
                                AB - secondary consolidation under overburden pressure. 
                                BC- primary consolidation due to surcharge. 
                                CD-secondary consolidation due to surcharge.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_3.htm [10/11/2011 4:25:53 PM]
Objectives_template
 Module 4:Preloading and vertical drains 
 Lecture 12:Preloading without vertical drains 
 
 
Consolidations under Structural fill with Surcharge 
Assume a highway embankment is placed on highly compressible soil. The expected amount of final 
settlement can be at the top of the embankment.
?     How much extra surcharge  has to be applied for a given time t in order to produce  of 
the final settlement  under the embankment load P alone?
Step1  
 
calculate   for an assumed q.
These are the final settlement due to embankment loading alone and embankment plus surcharge.
Step 2  
 
(settlement under p+q at time +)
Step 3 
 
 
Step 4 
 
find 
Step 5 
 
Step 6 
 
increase q; if  decrease q repeat the calculation till  
Example 12.1 
 
A land reclamation project requires 3m sand & gravel fill to be placed in a deposit with 
the following profile. Ground water level at the surface
Soft silty clay     
 
 
 
 
 
 
 
 
 
file:///D|/Dr.patra/ground_improvement_techniques/lecture12/12_4.htm (1 of 2) [10/11/2011 4:25:53 PM]
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