Understanding Bearing Capacity of the Soil
The ability of soil to withstand loads applied to the ground above is known as bearing capacity. The main factors influencing it are the soil’s density, shear strength, and type. The bearing capacity of the soil also varies with the load’s embedment depth; the deeper the load is, the higher the bearing capacity.
Moreover, if the soil’s bearing capacity is insufficient, the ground can be strengthened, or the load can be distributed over a wider area. For instance, this can be achieved with foundations constructed of reinforced concrete.
Different Types of Soil Bearing Capacity
Ultimate Bearing Capacity
The maximum weight that a particular soil can sustain before settling too much or shearing apart under a structure constructed on top of it is known as the soil’s ultimate bearing capacity.
Allowable Bearing Capacity
The maximum force that soil can withstand without exceeding allowable settlement limit is known as its allowable or safe bearing capacity. This is the value that you enter into the spreadsheet for foundation planning in order to account for bearing capacity.
Techniques for Calculating Bearing Capacity
The following is a list of the different techniques used to calculate the bearing capacity:
- Plate Bearing Test
- Presumptive Analysis
- Centrifuge Test
- Penetration Test
- Analytical Methods
- Modern Testing Methods
How Can the Soil’s Bearing Capacity Be Increased?
By Deepening the Foundation
The bearing capacity typically increases with depth due to the underlying material’s constraining weight. However, you shouldn’t use this method if the subsurface material’s moisture content increases with depth.
By Means of Soil Drainage
Some studies indicate that sandy soils lose half of their carrying capacity when there is an abundance of water present. To eliminate any excess water, the foundation channel needs to have the proper drains constructed.
Through Compacting the Dirt
Due to compaction, certain soil particles become less prone to movement when there is less space between them. Therefore, the compaction will increase the soil’s bearing capacity.
By Constraining the Soil
Sheet piles can be used to enclose the ground and stop any soil movement that might otherwise happen due to load action. The soil particles are compacted as sheet piles are forced together to create an enclosure. The bearing capacity will rise as a result.
Increasing the Base’s Width
There is a decrease in the amount of pressure applied as the foundation’s width is expanded since it increases the bearing area. However, there is a limit to how far the foundation’s breadth can be expanded, so, this technique’s applications are restricted.
Replacing Soils
If the soil has deteriorated, it is advised to replace it. First, the upper layer of the soil is removed by excavating it, and then more suitable elements like sand, gravel, stone, and other hard materials are added to the empty space.
Applying Grout
A sufficient number of borings are bored into the soil, and concrete grout is forced into the foundation to fill up any crevices or cracks that could otherwise reduce the soil’s ability to support weight.
Safe Bearing Capacity of Various Soils
No. | Soil Type | Safe Bearing Capacity in kN/m2 |
Cohesive Soils | ||
1. | Sand clay and moist clay | 150 |
2. | Black cotton soil | 130-160 |
3. | Stiff or rigid clay in a deep bed | 440 |
4. | Medium clay | 245 |
5. | Soft clay | 100 |
6. | Very soft clay | 50 |
Cohesionless Soil | ||
7. | Gravel and sand mixture | 440 |
8. | Dry and compact sand | 440 |
9. | Sandy gravel | 245 |
10. | Fine sand and silt | 150 |
11. | Dry and loose sand | 100 |
Rocks | ||
13. | Hard rocks | 3240 |
14. | Laminated rocks | 1620 |
15. | Broken and shattered bedrock and hard shale | 880 |
16. | Soft rocks | 440 |