Short Notes: Foundations | Short Notes for Civil Engineering - Civil Engineering (CE) PDF Download

 Page 1


     
CHAPTER – 10 
FOUNDATIONS 
 
Every structure consists of two parts. (1) Foundation and (2) Super 
structure. The lowest artificially prepared parts of the structure which are 
in direct contact with the ground and which transmit the loads of the 
structure to the ground are known as Foundation or Substructure. The 
solid ground on which the foundation rest is called the “foundation bed” 
or foundation soil and it ultimately bears the load and interacts with the 
foundations of buildings. 
10.1 Objects of foundations: 
 Foundations are provided for the following purposes 
1) To distribute the total load coming on the structure on large 
area. 
2) To support the structure 
3) To give enough stability to the structures against various 
distributing forces such as wind, rain etc. 
4) To prepare a level surface for concreting and masonry work. 
The general inspection of site of work serves as a good for 
determine the type of foundation, to be adopted for the proposed 
work and in addition, it helps in getting the data w.r.to the 
following items. 
i) Behavior of ground due to variations in depth of water 
table 
ii) Disposal of storm water at site 
iii) Nature of soil by visual examination 
iv) Movement of ground due to any reason etc. 
Page 2


     
CHAPTER – 10 
FOUNDATIONS 
 
Every structure consists of two parts. (1) Foundation and (2) Super 
structure. The lowest artificially prepared parts of the structure which are 
in direct contact with the ground and which transmit the loads of the 
structure to the ground are known as Foundation or Substructure. The 
solid ground on which the foundation rest is called the “foundation bed” 
or foundation soil and it ultimately bears the load and interacts with the 
foundations of buildings. 
10.1 Objects of foundations: 
 Foundations are provided for the following purposes 
1) To distribute the total load coming on the structure on large 
area. 
2) To support the structure 
3) To give enough stability to the structures against various 
distributing forces such as wind, rain etc. 
4) To prepare a level surface for concreting and masonry work. 
The general inspection of site of work serves as a good for 
determine the type of foundation, to be adopted for the proposed 
work and in addition, it helps in getting the data w.r.to the 
following items. 
i) Behavior of ground due to variations in depth of water 
table 
ii) Disposal of storm water at site 
iii) Nature of soil by visual examination 
iv) Movement of ground due to any reason etc. 
 Foundations                                                                        
  
10.2  Bearing capacity: The ability of the foundation material, 
weather soil or rock to carry loads safely. 
Methods of determine the bearing capacity of soil: 
The bearing capacity of soil is determined by any one of the 
following methods 
(i) Method of loading 
(ii) Method of dropping a weight 
I. Method of loading 
Procedure to carry out the test: 
1. A square pit of required size is excavated upto 5 times the 
side of steel plate to be used. At the centre of pit, square hole 
is dig, which is same ratio to that of breadth to depth of pit. 
2. The bottom of the hole is made level 
3. The steel plate is put up in the hole and then platform is 
prepared as shown in fig 10.1. 
 
Fig 10.1  Method of loading 
Page 3


     
CHAPTER – 10 
FOUNDATIONS 
 
Every structure consists of two parts. (1) Foundation and (2) Super 
structure. The lowest artificially prepared parts of the structure which are 
in direct contact with the ground and which transmit the loads of the 
structure to the ground are known as Foundation or Substructure. The 
solid ground on which the foundation rest is called the “foundation bed” 
or foundation soil and it ultimately bears the load and interacts with the 
foundations of buildings. 
10.1 Objects of foundations: 
 Foundations are provided for the following purposes 
1) To distribute the total load coming on the structure on large 
area. 
2) To support the structure 
3) To give enough stability to the structures against various 
distributing forces such as wind, rain etc. 
4) To prepare a level surface for concreting and masonry work. 
The general inspection of site of work serves as a good for 
determine the type of foundation, to be adopted for the proposed 
work and in addition, it helps in getting the data w.r.to the 
following items. 
i) Behavior of ground due to variations in depth of water 
table 
ii) Disposal of storm water at site 
iii) Nature of soil by visual examination 
iv) Movement of ground due to any reason etc. 
 Foundations                                                                        
  
10.2  Bearing capacity: The ability of the foundation material, 
weather soil or rock to carry loads safely. 
Methods of determine the bearing capacity of soil: 
The bearing capacity of soil is determined by any one of the 
following methods 
(i) Method of loading 
(ii) Method of dropping a weight 
I. Method of loading 
Procedure to carry out the test: 
1. A square pit of required size is excavated upto 5 times the 
side of steel plate to be used. At the centre of pit, square hole 
is dig, which is same ratio to that of breadth to depth of pit. 
2. The bottom of the hole is made level 
3. The steel plate is put up in the hole and then platform is 
prepared as shown in fig 10.1. 
 
Fig 10.1  Method of loading 
     
4. The amount of initial load is decided according to the type of 
the soil to be tested 
5. A level is planted to note the setting of steel plate w.r.to the 
permanent benchmark. 
6. The load is to be kept on platform till the settlement of the 
ground ceases or stops 
7. The load is increased by a suitable amount, usually 0.5 tonnes 
and the procedure is continued 
8. The recording of results is carried out in the following 
proforma. 
Date and 
time of 
taking 
reading 
 
Load 
 
Increase in 
settlement 
 
Total settlement 
 
Remarks 
 0.5 
tonne 
 
 
 
 
1.0 
tonne 
a 
b 
c 
- 
 
a1 
b1 
c1 
a 
a+b 
a+b+c 
- 
 
a+b+c+a1 
a+b+c+a1+b1 
a+b+c+a1+b1+c1 
 
 
 
settlement 
ceases 
 
 
settlement 
ceases 
9. The settlement of the ground will be fairly is proportion to the 
load upto a certain limit, when the bearing power of soil 
exceeded, the settlement will be out of the proportion. 
10. The bearing capacity and safe bearing capacity of soil are 
calculated by using the following  
Page 4


     
CHAPTER – 10 
FOUNDATIONS 
 
Every structure consists of two parts. (1) Foundation and (2) Super 
structure. The lowest artificially prepared parts of the structure which are 
in direct contact with the ground and which transmit the loads of the 
structure to the ground are known as Foundation or Substructure. The 
solid ground on which the foundation rest is called the “foundation bed” 
or foundation soil and it ultimately bears the load and interacts with the 
foundations of buildings. 
10.1 Objects of foundations: 
 Foundations are provided for the following purposes 
1) To distribute the total load coming on the structure on large 
area. 
2) To support the structure 
3) To give enough stability to the structures against various 
distributing forces such as wind, rain etc. 
4) To prepare a level surface for concreting and masonry work. 
The general inspection of site of work serves as a good for 
determine the type of foundation, to be adopted for the proposed 
work and in addition, it helps in getting the data w.r.to the 
following items. 
i) Behavior of ground due to variations in depth of water 
table 
ii) Disposal of storm water at site 
iii) Nature of soil by visual examination 
iv) Movement of ground due to any reason etc. 
 Foundations                                                                        
  
10.2  Bearing capacity: The ability of the foundation material, 
weather soil or rock to carry loads safely. 
Methods of determine the bearing capacity of soil: 
The bearing capacity of soil is determined by any one of the 
following methods 
(i) Method of loading 
(ii) Method of dropping a weight 
I. Method of loading 
Procedure to carry out the test: 
1. A square pit of required size is excavated upto 5 times the 
side of steel plate to be used. At the centre of pit, square hole 
is dig, which is same ratio to that of breadth to depth of pit. 
2. The bottom of the hole is made level 
3. The steel plate is put up in the hole and then platform is 
prepared as shown in fig 10.1. 
 
Fig 10.1  Method of loading 
     
4. The amount of initial load is decided according to the type of 
the soil to be tested 
5. A level is planted to note the setting of steel plate w.r.to the 
permanent benchmark. 
6. The load is to be kept on platform till the settlement of the 
ground ceases or stops 
7. The load is increased by a suitable amount, usually 0.5 tonnes 
and the procedure is continued 
8. The recording of results is carried out in the following 
proforma. 
Date and 
time of 
taking 
reading 
 
Load 
 
Increase in 
settlement 
 
Total settlement 
 
Remarks 
 0.5 
tonne 
 
 
 
 
1.0 
tonne 
a 
b 
c 
- 
 
a1 
b1 
c1 
a 
a+b 
a+b+c 
- 
 
a+b+c+a1 
a+b+c+a1+b1 
a+b+c+a1+b1+c1 
 
 
 
settlement 
ceases 
 
 
settlement 
ceases 
9. The settlement of the ground will be fairly is proportion to the 
load upto a certain limit, when the bearing power of soil 
exceeded, the settlement will be out of the proportion. 
10. The bearing capacity and safe bearing capacity of soil are 
calculated by using the following  
 Foundations                                                                          
  
Bearing capacity of soil in tones/m
2
 
    Maximum load 
   = -------------------------------- 
    Area of steel plate 
Safe bearing capacity of soil in tones/m
2
 
    Bearing capacity of soil 
   = --------------------------------------- 
           Factor of safety 
 
Note:  
1) This method can also be used for confirming the known bearing 
power of a soil 
2) The loading should applied without shock 
3) Dial gauges or deflect meters to record the settlement instead of 
level & staff for the accuracy upto 0.02mm 
4) The zero corrections should be deducted from the observed 
settlement to get actual settlements zero correction is the 
settlement due to adjustment of soil particles under the action of 
loading 
5) The bearing capacity of sandy soil and gravelly soil is affected to 
the extent of 50% by presence of water table. Water should be 
pumped out before placing the steel plate 
6) The results obtained by this method are fairly accurate and 
reliable. 
Page 5


     
CHAPTER – 10 
FOUNDATIONS 
 
Every structure consists of two parts. (1) Foundation and (2) Super 
structure. The lowest artificially prepared parts of the structure which are 
in direct contact with the ground and which transmit the loads of the 
structure to the ground are known as Foundation or Substructure. The 
solid ground on which the foundation rest is called the “foundation bed” 
or foundation soil and it ultimately bears the load and interacts with the 
foundations of buildings. 
10.1 Objects of foundations: 
 Foundations are provided for the following purposes 
1) To distribute the total load coming on the structure on large 
area. 
2) To support the structure 
3) To give enough stability to the structures against various 
distributing forces such as wind, rain etc. 
4) To prepare a level surface for concreting and masonry work. 
The general inspection of site of work serves as a good for 
determine the type of foundation, to be adopted for the proposed 
work and in addition, it helps in getting the data w.r.to the 
following items. 
i) Behavior of ground due to variations in depth of water 
table 
ii) Disposal of storm water at site 
iii) Nature of soil by visual examination 
iv) Movement of ground due to any reason etc. 
 Foundations                                                                        
  
10.2  Bearing capacity: The ability of the foundation material, 
weather soil or rock to carry loads safely. 
Methods of determine the bearing capacity of soil: 
The bearing capacity of soil is determined by any one of the 
following methods 
(i) Method of loading 
(ii) Method of dropping a weight 
I. Method of loading 
Procedure to carry out the test: 
1. A square pit of required size is excavated upto 5 times the 
side of steel plate to be used. At the centre of pit, square hole 
is dig, which is same ratio to that of breadth to depth of pit. 
2. The bottom of the hole is made level 
3. The steel plate is put up in the hole and then platform is 
prepared as shown in fig 10.1. 
 
Fig 10.1  Method of loading 
     
4. The amount of initial load is decided according to the type of 
the soil to be tested 
5. A level is planted to note the setting of steel plate w.r.to the 
permanent benchmark. 
6. The load is to be kept on platform till the settlement of the 
ground ceases or stops 
7. The load is increased by a suitable amount, usually 0.5 tonnes 
and the procedure is continued 
8. The recording of results is carried out in the following 
proforma. 
Date and 
time of 
taking 
reading 
 
Load 
 
Increase in 
settlement 
 
Total settlement 
 
Remarks 
 0.5 
tonne 
 
 
 
 
1.0 
tonne 
a 
b 
c 
- 
 
a1 
b1 
c1 
a 
a+b 
a+b+c 
- 
 
a+b+c+a1 
a+b+c+a1+b1 
a+b+c+a1+b1+c1 
 
 
 
settlement 
ceases 
 
 
settlement 
ceases 
9. The settlement of the ground will be fairly is proportion to the 
load upto a certain limit, when the bearing power of soil 
exceeded, the settlement will be out of the proportion. 
10. The bearing capacity and safe bearing capacity of soil are 
calculated by using the following  
 Foundations                                                                          
  
Bearing capacity of soil in tones/m
2
 
    Maximum load 
   = -------------------------------- 
    Area of steel plate 
Safe bearing capacity of soil in tones/m
2
 
    Bearing capacity of soil 
   = --------------------------------------- 
           Factor of safety 
 
Note:  
1) This method can also be used for confirming the known bearing 
power of a soil 
2) The loading should applied without shock 
3) Dial gauges or deflect meters to record the settlement instead of 
level & staff for the accuracy upto 0.02mm 
4) The zero corrections should be deducted from the observed 
settlement to get actual settlements zero correction is the 
settlement due to adjustment of soil particles under the action of 
loading 
5) The bearing capacity of sandy soil and gravelly soil is affected to 
the extent of 50% by presence of water table. Water should be 
pumped out before placing the steel plate 
6) The results obtained by this method are fairly accurate and 
reliable. 
      
 
II. Method of dropping a weight: 
 In this method, a substance of known weight is dropped 
from a known height as shown in 10.2. The depth of impression 
made by the weight on the soil is noted. Then the bearing 
capacity of the soil is worked out as follows. 
 
Fig 10.2 Method of Dropping Weight 
 Ultimate resistance of soil 
   w x h 
  R=   ------------- 
      d 
 
where  R – Resistance of soil 
 A – cross section area of the substance 
 h  - Height 
 w -  weight of substance