Reasons for collapsing of foundation
There are several reasons for collapsing of foundation which range from poor soil condition, structural faults etc. Given below, some of the major causes for collapsing of foundation :-
1. Collapsing of Foundation because of surpassing the bearing strength of soil
2. Collapsing of Foundation because of withdrawn of moisture from Soil all of a sudden
3. Collapsing of Foundation because of differential or unequal settlement
4. Collapsing of Foundation because of uneven progress and pattern of construction
5. Collapsing of Foundation because of movement of adjacent soil.
Collapsing of Foundation because of surpassing the bearing strength of soil:-
Ultimate bearing strength means ultimate load intensity that a soil can bear devoid of any shear failure of the Soil. The size of the footing with regard to length, breadth and diameter, is primarily based on the bearing strength.
A foundation/ footing of a structure must contain adequate size in order that the intensity of load directing via that footing from the structure to the soil below should not raise the bearing strength of that soil. If the bearing strength of soil is low or load operating is heavy and the size of the footing is relatively small than actual requirement then the load intensity (i.e. load per unit area say KN/sq.m. etc.) conveyed on the soil may be greater as compared to the bearing strength of the soil, for this reason a shear failure of soil will occur.
To provide perfect footing size, the safe bearing strength rather than ultimate bearing strength should be applied to obtain margin of safety against any accidental loading as well as abnormal behavior of the soil due divergence in its bearing strength. Safe bearing strength is nothing but ultimate bearing strength divided by a appropriate factor of safety usually varying from 2 to 4.
Collapsing of Foundation because of withdrawn of moisture from Soil all of a sudden :
It is one of the most crucial factors that should not be neglected. Moisture withdrawn occurs in the following ways :-
a) By draining water from the adjacent well through pump
b) By dewatering adjacent Pond
c) Reduction of ground water table close to the ground previously.
Since the soil usually comprises of soil solid, water and air and super structural load on soil is carried by the both soil solid and pore water, as soon as the pore water is withdrawn, it will produce voids inside the soil system around and at the bottom of the foundation soil that leads to subsidence of the soil together with supporting structure. As a result, the collapsing of foundation happens.