The safe bearing capacity of soil refers to the maximum load that can be applied to the soil without causing shear failure. It is a crucial factor in foundation design for structures. The safe bearing capacity depends on various factors such as soil type, moisture content, and the type of structure.
The safe bearing capacity of soil varies with its type. Here are approximate values:
1. Rock: 100 tons per square foot or more.
2. Hard Gravel and Dense Sand: 20 – 25 tons per square foot.
3. Stiff Clay and Gravel: 10 – 15 tons per square foot.
4. Loam and Silt: 2 – 8 tons per square foot.
Soft Clay: 1 – 4 tons per square foot.
Safe bearing capacity of soil is the capacity of soil that supports the structural load of building and it transfer all coming load safely into the The Ground without any structure failure or settlement is known as safe bearing capacity of soil.
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All structural dead and live load of slab, beam and wall verticaly transfer to column via column beam joint, column transfer all coming load to the foundation and Foundation safely transfer all load to bed of soil. Now questions is how much different types of soil resist load of super structure without structural failure or settelement.
What is safe bearing capacity of soil? In geotechnical civil engineering, safe bearing capacity is the capacity of soil to support the structural loads applied to the ground. The bearing capacity of soil is define as the maximum average contact pressure between the foundation and the soil which should not produce shear failure in the soil.
There are two types of bearing capacity of soil:- 1) Ultimate bearing capacity and 2) Allowable bearing capacity. The ultimate bearing capacity is the theoretical maximum pressure which can be supported without failure. Allowable bearing capacity is the ultimate bearing capacity divided by a factor of safety.
When we are starting our any new project preliminary first test should be done is soil bearing capacity test, it is essential to find out bearing capacity of soil that resist the applied load. It is pressure develop between Foundation and surrounding soil which are contact with Foundation.
Safe bearing capacity of different types of soil
There is different types of soil available in India and other countries and all different types of soil have different soil bearing capacity. Any structural design, foundation size and Foundation depth should be decided considering the soil bearing capacity in that region.
What is the unit of bearing capacity of soil? The bearing capacity of soil is the maximum load per unit that can support any structure without structural failure and settlement, the bearing capacity of soil measured in unit kN/m2 and kg/cm2.
Safe bearing capacity of hard rocks:- It has strong bearing capacity, it can provide structural support without any shrinkage or swelling. Hard rocks is made of igneous and metamorphic rocks like granite and basalt. It is distinguished from sedimentary rocks because they are typically more difficult to broken. Safe bearing capacity of hard rock like Granite and basalt is about 33kg/cm2 (3300kN/m2).
Safe bearing capacity of soft rocks:- sedimentary rocks are are called as soft rock, common sedimentary rocks include sandstone, limestone, and shale. These rocks often start as sediments carried in rivers and deposited in lakes and oceans. When buried, the sediments lose water and become cemented to form soft rock. Safe bearing capacity of soft rock like limestone and sandstone is about 4.5kg/cm2 (450kN/m2).
Safe bearing capacity of sandy soil:- sandy soil have good bearing capacity, it consists of coarse sand,medium sand and find sand according to particle. it is light, more durable, it absorbs water but do not swell in size making constant volume. Bearing capacity of sandy soil ranging between 2.45kg/cm2 to 4.45kg/cm2, for fine sand, it could be 4.45kg/cm2 (445kN/m2), for coarse sand, it could be 4.40kg/cm2 (440kN/m2) and for medium sand, it could be 2.45kg/cm2 (245kN/m2).
Safe bearing capacity of loam soil:- Loam is the best soil type for construction due to its ideal combination of silt, sand, and clay. It combines the best of all their qualities into the ideal balance for supporting a foundation. Loam generally does not shift, expand, or shrink drastically and handles the presence of water very well. Safe bearing capacity of loam soil ranging between 0.8kg/cm2 to 2.7kg/cm2 (80 – 270kN/m2 depending on alluvial, loam , sandy loam and sandy clay loam.
Safe bearing capacity of clay soil:-Very fine soils like clays and silts typically have lower bearing capacities, it could be ranging between 0.5kg/cm2 to 1kg/cm2 (50kN/m2 to 100kN/m2).
Safe bearing capacity of black cotton soil:– Black cotton soil swells during rainy season and cracks in summer due to shrinkage. These shrinkage cracks are 100 mm to 150 mm wide and 0.5 m to 2 m deep. Swelling creates upwards pressure on the structure and shrinkage creates downward pull. It results into cracks in foundations wall and roof. Hence foundation in black cotton soil need special care. Safe bearing capacity of black cotton soil ranging between 1.3kg/cm2 to 1.60kg/cm2 (130 – 160kN/m2).