Have You Ever wondered what is Bearing Capacity of Soils.

BEARING CAPACITY OF SOIL & SUITABILITY OF FOUNDATION

It is very known fact that all structures whether they are buildings, dams, bridges etc. are built on soils. Foundation of each structure must required transfer its load on large area of soil. So, that the foundation every structure should be so designed that the soil below does not fail in shear nor there is the excessive settlement of the structure. Our method of foundation design is based on the concept of bearing capacity.

The Soil tends to deform when stressed due to loading. The soil deformation depends upon factors like water content, bulk density, angle of internal friction and the manner in which load is applied on the soils

“The maximum load carrying capacity of soil per unit area which the soil or rock can carry without yielding or displacement is termed as the bearing capacity of soils”The Soil properties like density shear strength permeability etc., affect the bearing capacity of soil. Normally, Dense sand will have more bearing capacity than loose sand as unit weight of dense sand is more than loose sand.If the bearing capacity of soil is sufficient to take load of structure at shallow depth, then a shallow foundation is provided and the option for shallow are combined footing, Isolated footing or strip footing. In case when soil immediately below the structure does not have the adequate bearing capacity deep foundations are provided. Pile, piers or well are the options for deep foundations. For type of soil which is liable to differential settlement or where there is a wide variation in loading between adjacent columns Mat or Raft foundation are most suitable.

Different Type of Soil and Their Safe Bearing Capacities and Suggested Foundations.

A) Soil Type : Rock

No.	Type of Rock/Soil	Safe Bearing Capacity KN/m²	Minimum Depth of Foundation (m)	Type of Foundation
1.	Rock without lamination and defects granite & diorite	3240	0.6	Spread Footing
2.	Laminated rock, as sand stone or lime stone in sound condition	1620	0.75	Spread Footing
3.	Residual deposits of shattered and broken bed rock and shale	880	0.90	Spread Footing
4.	Soft rock	440	1.20	Spread Footing

B) Type of Soil: Non – Cohesive Soils

No.	Type of Rock/Soil	Safe Bearing Capacity KN/m²	Minimum Depth of Foundation (m)	Type of Foundation
1.	Gravel, Sand and gravel compact and offering high resistance to penetration when excavated tools	440	1.2	Spread Footing
2.	i) Coarse compact and dry sand ii) Medium compact and dry sand	440 245	1.2 1.2	Spread Footing
3.	Fine Sand, Silt	150	1.2	Spread Footing & Combine Footing
4.	Loose gravel or sand gravel mixture, loose coarse to medium sand dry	245	1.5	Spread Footing & Combine Footing
5.	Fine Sand	100	1.8	Spread Footing & Combine Footing

BEARING CAPACITY OF SOIL & SUITABILITY OF DIFFERENT FOUNDATION

C) Type of Soil: Cohesive Soils

No.	Type of Rock/Soil	KN/m²	Minimum Depth of Foundation (m)	Type of Foundation
1.	Soft shale, hard or stiff clay in deep dry bed	440	1.5	Spread Footing & Combine Footing, strip footing
2.	Medium clay, readily indented with a thumb nail	245	1.8	Combined or Mat Footing
3.	Moist clay and sand clay mixture which can be indented with slight thumb pressure	150	1.8 to 3m depth various depending on moisture movement zone	Combined or Mat Footing
4.	Soft clay indented with moderate thumb pressure	100	3	Deep (Pile) foundation
5.	Very soft clay which can be penetrated several centimetres with thumb	50	5	Pile Foundation