When we talk about constructing something – be it a house, a bridge, or any structure – one crucial aspect to consider is the type of soil upon which the foundation rests. The ability of the soil to withstand and support the loads from the structure is termed as its “bearing capacity.”
The ultimate bearing capacity is the maximum pressure at the foundation base where the soil fails. For safety reasons, this ultimate value is divided by a factor to get the “safe bearing capacity” of the soil. This safe value ensures stability and prevents failures.
Before we embark on designing any foundation, it becomes imperative to understand the bearing capacity of the underlying soil. This knowledge allows engineers to tailor the foundation design to the specific soil conditions, ensuring the structure’s stability and longevity.
Various field tests can be conducted to determine the bearing capacity of the soil. However, when time is of the essence or detailed test data is not available, standard safe bearing capacity values for different soil types come in handy.
Below is a comprehensive table providing safe bearing capacity values for different types of soils. These values are crucial for quick decision-making during construction, especially when detailed testing may not be feasible.
| S.No | Type of Soil | Safe Bearing Capacity (kN/m2) |
|---|---|---|
| 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 thumb up to a few centimeters | 50 |
| 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 |
| 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 |
Understanding these values is fundamental for engineers and builders to ensure the strength and stability of structures on diverse types of soils.