Isolated Foundation and Type

Ø  What is Foundation?

·         Foundation is the basic component of structure through which the whole load of structure is transferred to the soil, the solid ground on which foundation is rested, is called foundation bed.

·         Stability is provided by Foundation to the structure, by distributing the load of superstructure to the earth.

·         Strong and well-designed foundation prevent settlement of structure and increase the stability.

 

Ø  Isolated Foundation

·     Isolated foundation or Individual foundation is the type of shallow foundation, (Types of Foundations) which is used for building construction.

·    This foundation is constructed for single column.

·     It is the most economical types of footing, because the column placed at a particular distance.

·   The shape of footing may be square or rectangular or circular.

·   Material used for it may be reinforced or non-reinforced.

·  The size of footing is depended on the safe bearing capacity of soil and load of superstructure come on column.

·  Simply, the size of footing calculated by dividing the total load at the column base by the allowable bearing capacity of soil.

·  On all sides of concrete bed, 15 cm offset is provided. But in case of brick masonry column, 5 cm offset is provided to all four sides.

·  According to load conditions, and the soil bearing capacity and characteristics, the isolated footing having following types.

 

Ø  Types of Isolated Foundation     

1.      Flat, pad, plain or reinforced isolated foundation

2.      Sloped isolated foundation

       3.    Stepped isolated foundation 

1.      Flat, Pad, Plain Or Reinforced Isolated Foundation

ü  It is constructed by plain or reinforced concrete.

ü  Each footing with column constructed independently of others.

ü   The thickness of base is uniform.

ü  It has different shapes of square, circular, and rectangular which is depend upon the loading condition of structure.

ü  At the critical section, the footing helps to minimize the bending moments, and the shearing forces.

ü  It is economical construction because it needs less excavation.

 

2.      Sloped Isolated Foundation

ü  Slope isolated foundation has trapezoidal.

ü  It is constructed with care to achieve top slope of 45 degree across all directions.

ü  In sloped isolated footing, the requirement of reinforcement and concrete is less than the plain isolated footing.

ü  The concrete mix used in the footing must be stiff so that avoiding sustaining viscous deformation.

  

3.      Stepped Isolated Foundation

ü  It is mostly used in residential building.

ü  In this footing construction is done step by step, each step of footing is depend on the another step of footing.

ü  This type of footing was popular previously, but nowadays it is not used more.

 

Ø  Factor Affecting To The Construction Of  Isolated Foundation

ü  The footing is well-organized, and efficient.

ü  The footing is constructed when the capacity of soil is large.

ü  The load of structure is not more on ground, isolated foundation preferred.

ü   When there is a need of distance between the columns, the isolated foundation is constructed.

 

Ø  Use Of Isolated Foundation

ü  For transferring the concentrated load to the soil, isolated foundation is used as shallow foundation.

ü  When columns are placed at distance.

ü  Load of structure is less.

ü  Bering capacity of soil is high.

 

Ø  Advantages Of Isolated Foundation

1.      It is very economical.

2.      It is easy and simple to construct.

3.      Low skilled lobar required.

4.      It needs a less excavation of soil.

 

Ø  Disadvantages Of Isolated Foundation

1.      Round the base of foundation soil should be stable.

2.      For dealing with heavy loads, the footing made wide.

3.      Separate foundation should make different settlement.

Types of Foundation

Introduction 

When we are thinking about any kind of construction like a small house to skyscraper, foundation is base of the construction, foundation is the most important part of the structure, which transferred whole load of structure to the soil safely and provide stability to the structure.

Design of foundation is the most essential part when a structure is designed. After the study of topography, geology, and size of structure and other factors consideration the type of foundation is decided.

Ø What Is Foundation?

·         Foundation is the basic component of structure through which the whole load of structure is transferred to the soil, the solid ground on which foundation is rested, is called foundation bed.

·         Stability is provided by Foundation to the structure, by distributing the load of superstructure to the earth.

·         Strong and well-designed foundation prevent settlement of structure and increase the stability.

 

Ø  Types Of Foundations

On the earth surface different kind of soil, sediment, stones are found. By studying their characteristics, and so many factors geotechnical engineers recognized how these factors affects the structure, and which type of design of structural element should be done.

So there are two type of foundation

1.      Shallow Foundation

2.      Deep Foundation

1.      Shallow Foundation

ü  Shallow foundation is the foundation in which width of foundation is greater than the depth of foundation.

ü  It is more economical than deep foundation because it requires less digging.

ü  Shallow foundation is suitable where the soil can bear the weight of structure at a shallow depth.

ü  Shallow foundation again divided into following types,

Types of Shallow Foundation

A.    Individual foundation and isolated foundation

B.     Combined foundation

C.     Strip foundation

D.    Raft or mat foundation

 A.    Individual Foundation And Isolated Foundation

ü  Individual foundation or isolated foundation is the type of shallow foundation, which is used for building construction.

ü  This foundation is constructed for single column.

ü   It is the most economical type of footing, because the column placed at a particular distance.

ü   The shape of footing may be square or rectangular.

ü  Material used for it may be reinforced or non-reinforced.

ü  The size of footing is depending on the safe bearing capacity of soil and load of superstructure come on column.

ü  Simply, the size of footing calculated by dividing the total load at the column base by the allowable bearing capacity of soil

                   

             B.    Combined Foundation

ü  The combined footing is the combination of a different footing.

ü  It is not differing from the isolated footing, only difference is that one base or footing is sharing weight of two columns.

ü  It happened because the two footing area come very close to each other.

ü  The shape of footing can be rectangular, square trapezoidal.

                    

        ü  The overall distribution of load is uniform.

          C.     Strip Foundation Or Wall Footing Or Continuous Footing

ü  This type of footing is used in load bearing structure, in which wall distributing the load of structure, not the column or pillars and beam.

ü  In this footing, the base of footing is wider than the load bearing wall because the foundation runs the entire length of load bearing wall.

ü  This wider base of footing transferred load safely to soil and provide better stability.

ü  It is made up of reinforced concrete, bricks, etc.

 

  

          D.    Raft Or Mat Foundation

ü  This type of foundation is used when the bearing capacity of soil is weak.

ü  The Mat foundation is spread across the entire area of building.

ü  This foundation is used where load of the structure coming from wall and column is too high.

ü  To prevent settlement of structure this foundation is used.

ü  This is costly structure; this footing is constructed when there is no other type of footing is suitable.

ü  The columns are placed closely to each other.

        ü   It is suitable where ground water table is low.

        1.      Deep Foundation

ü  Deep foundation is used when building on the soft soil and sand which cannot carry the load of structure safely.

ü  Up to getting hard strata, the foundation is deeper.

ü  The foundation is situated at the deep underground or underwater.

ü  For bridges, piers and dams such foundation is used.

ü  Deep foundation gain divided into following types:

Types of Deep Foundation

                E. Pile foundation

                F. Drilled shafts or caissons

                G. Pier foundation

E. Pile Foundation

ü  Pile foundation is the most common type of deep foundation, which is used where the hard strata of soil are deeper, and to carry load of structure the plies are used.

ü  Pile length is more than its cross-sectional area.

ü  Pile transferred load to soil trough friction or bearing.

ü  They are helped to reduce cost of construction.

ü  The types of piles are as follows

a.   Based on their function or use

1.      Sheet piles

2.      Load bearing piles

3.      End bearing piles

4.      Friction piles

5.      Soil compactor piles

b.   Based on the material and construction method.

1.      Timber piles

2.      Concrete piles

3.      Steel piles

4.      Composite piles.

 

 

   F. Drilled Shafts or Caissons

 

ü  A drilled shafts also known as caissons, which is mostly used at the construction of bridge, pier and mostly at the structure over water.

ü  They have the characteristics of floating at a desired location then sunk into the place.

ü  By digging the loose land with an auger up to getting bedrock, sand while digging, hollow steel casing is fixed to prevent the sand or soil from caving, the reinforced mesh rebar is then centered  inside the casing, and then concrete poured. Concrete is filled from bottom to the top of casing, so that all the groundwater out from the top.  Caisson foundation can be done by this way

ü  Also by using mesh grid of rebar filled with concrete, caisson can be constructed on site.

ü  Main types of caissons are as follows:

1)      Open caissons

2)      Pneumatic caissons

3)      Monolithic caissons

4)      Sump caissons

5)      Box caissons

       G. Pier Foundation

ü  The load which is not transmitted by the shallow foundation, for transferring such massive load pier foundation is used.

ü  It is not as deep as piles; it is used in multistory structure.

ü  It transferred load to soil through end bearing.