Settlement and Causes of Settlement

 

Settlement

It is a vertical downward displacement of the structure due to decrease in the volume of soil mass on which it is built .

IN other way , the sinking of a structure due to downward displacement of the soil below is termed as settlement . It is one of the most important problems which a civil engineer encounters in his life time . There is hardly a single structure which does not undergo settlement , so proper attention should be given to the design and execution of structures .

Settlement is of following types :

 1.Uniform settlement

2.Differential settlement

3.Tilt

 

Different Type of Settlement

1.Uniform settlement :It the settlement of structure due to soil displacement is even ,It is known as uniform settlement .

 

Uniform Settlement

It may be noted that if the settlements of all the footings of a simple building are uniform ,then there is no damage to the building.

 

2. Differential Settlement : If the settlement of the structure  due to soil movement is uneven, it is termed as differential settlement or non uniform settlement. This settlement  is more  dangerous as it causes damage to the structure partially or as whole.

Differential Settlement

The amount or differential settlement can be calculated by measuring the difference of settlements, between any two adjacent column.

3. Tilt : It is type of non uniform settlement. Tilt is defined as angular distortion or rotation of a structure, about its base. The leaning tower of Pisa in Italy built during 14th century is typical example of tilt. It is 179 feet in height and its top is out  of plumb by 20 feet. It occurs when the structure is unevenly loaded or when the soils are non uniform. 

Tilt

DIFFERENT CAUSES OF SETTLEMENT

Settlement of soil is caused due to a number of reasons. Few important causes from civil engineering point of view are as follows :

I.        Excavation of earth near a structure.

II.      Vibrations in coarse grained soil such as; pile driving, blasting etc in the vicinity.

III.    Consolidation of soil.

IV.    Lowering of water table.

V.      Landslides, surface erosion and other earth movements.

VI.    Under the action of moving vehicles, trains and other types of loads.

VII.  Mining operations, tunnel construction and other changes in the vicinity.

VIII. Thermal changes i.e swelling and shrinkage of soils especially in clay.

IX.    Burrowing animals.

X.      Structural collapse of soil (i.e when the load is higher than the shearing strength of soil).