The ability of the soil to withstand the loads exerted by the foundation is known as its bearing capacity. The ultimate bearing capacity refers to the gross pressure at the foundation’s base, which causes the soil to fail. The safe bearing capacity, on the other hand, is obtained by dividing the ultimate bearing capacity by a factor of safety that accounts for various failure conditions.
Before designing a foundation, it is crucial to determine the bearing capacity of the soil, which can be achieved through several field tests. However, in situations where test data is insufficient or speedy construction is required, standard safe bearing capacity values are available for different soil types.
By utilizing the safe bearing capacity values, construction projects can proceed more quickly without compromising the foundation’s stability. It is important to note that ignoring the bearing capacity of the soil can result in serious consequences, including foundation settlement, tilting, or even collapse. Therefore, accurate determination of the soil’s bearing capacity is crucial for the success and safety of any construction project.
Safe Bearing Capacity values of Different Soils
The table presents the safe bearing capacity values for various types of soils. It indicates the maximum load per unit area that the soil can bear without failure or excessive deformation. The safe bearing capacity is an important parameter to consider during the design and construction of foundations for buildings, bridges, and other structures.
Different types of soils have different safe bearing capacities due to variations in their physical and mechanical properties, such as composition, density, porosity, moisture content, and shear strength. For example, cohesive soils like clay have a lower safe bearing capacity than non-cohesive soils like sand and gravel. Similarly, soft soils like organic and peat soils have a lower safe bearing capacity than hard soils like rock and limestone.
It is important to determine the safe bearing capacity of the soil before constructing any structure to ensure that the foundation can support the load without settling or shifting. The safe bearing capacity values are usually obtained through geotechnical investigations, such as soil tests, borehole logs, and laboratory tests. These values are used to design the foundation type, size, and depth, and to calculate the allowable bearing pressure and settlement.
In summary, the table provides information about the safe bearing capacity of different types of soils, which is a crucial factor in the design and construction of foundations. The safe bearing capacity varies with soil type and properties, and is determined through geotechnical investigations. Engineers and architects use these values to ensure that the foundation can support the load of the structure without failure or excessive deformation.
| S.No | Type of Soil | Safe Bearing Capacity ( kN/m2) |
| Cohesive Soils | ||
| 1. | Soft shale, hard or stiff clay in a deep bed, dry state | 440 |
| 2. | Medium clay readily indented with a thumbnail | 245 |
| 3. | Moist clay and Sand clay mixture which can be indented by thumb pressure | 150 |
| 4. | Black cotton soil/expansive clay ( 50% saturated) in dry state | 130 to 160 |
| 5. | Soft clay indented with moderate thumb pressure | 100 |
| 6. | Very soft clay which can be penetrated with the thump up to few centimetres | 50 |
| Cohesionless Soil | ||
| 7. | Compact gravel/sand and gravel mixture with good resistance against penetration of tools | 440 |
| 8. | Compact and dry coarse sand | 440 |
| 9. | Compact and dry medium sand | 245 |
| 10. | Loose gravel or sandy gravel mixture, dry state | 245 |
| 11. | Fine sand and silt ( consists of dry lumps) | 150 |
| 12. | Loose and dry fine sand | 100 |
| Rocks | ||
| 13. | Hard rocks such as granite trap, diorite etc. | 3240 |
| 14. | Laminated rocks such as sandstone, limestone, etc. | 1620 |
| 15. | Residual deposits of shattered and broken bedrock and hard shale, cemented material | 880 |
| 16. | Soft rocks | 440 |
FAQs
What is bearing capacity of soil?
Soil has a capacity to support the loads that come from a foundation, which is called the bearing capacity of the soil. When the gross pressure at the base of the foundation exceeds a certain limit, the soil fails, and this limit is known as the ultimate bearing capacity. To determine a safe limit for building on the soil, the ultimate bearing capacity is divided by a factor of safety, taking into account different failure conditions. This resulting limit is called the safe bearing capacity of the soil.
What is the bearing capacity of soft rocks?
Soft rocks are known to have a certain capacity to bear weight, which is measured in terms of kN/m2. In this case, it has been determined that the bearing capacity of soft rocks is 440kN/m2. This means that for every square meter of soft rock, it can withstand a weight of up to 440kN, which is a measure of force.
It is important to understand the bearing capacity of soft rocks because it can affect various construction and engineering projects. For example, if a structure is built on soft rock, the weight of the structure must be carefully considered to ensure that it does not exceed the bearing capacity of the rock. If the weight of the structure is too much for the soft rock to bear, it could lead to structural failure or instability.
Knowing the bearing capacity of soft rocks can also help engineers and geologists make informed decisions about where to build certain types of structures. For instance, if a project involves constructing a heavy building, it would be wise to avoid building it on soft rock that has a low bearing capacity. Instead, a more suitable location with harder, more stable rock may be selected to support the structure.
In conclusion, the bearing capacity of soft rocks is an important factor that needs to be taken into account when planning and executing construction and engineering projects. By understanding this capacity, it is possible to prevent potential failures and ensure the safety and stability of structures built on soft rock.
What is the bearing capacity of cohesive soils?
The given information states that cohesive soils such as soft shale, hard or stiff clay in a deep bed, when in a dry state, have a bearing capacity of 440kN/m2. This means that these types of soils are capable of supporting a load of up to 440 kilonewtons per square meter.
On the other hand, black cotton soil or expansive clay, which is only 50% saturated and in a dry state, has a lower bearing capacity compared to cohesive soils. The bearing capacity of black cotton soil/expansive clay ranges from 130 to 160 kN/m2, which means that it can only support a load of up to 160 kilonewtons per square meter at most.
It is important to consider the bearing capacity of soils when constructing any type of structure on them, as the load capacity of the soil affects the stability and safety of the structure. Therefore, understanding the bearing capacity of soils is crucial for ensuring the durability and longevity of any construction project.