While, taking the initiative to lay the foundation for a new house, building or structure, it is crucial to take careful measures beforehand. Amongst these, enhancing the soil’s bearing capacity tops the list.
It is essential to improve the bearing capacity of the soil before initiating any sort of construction, as the stability of any structure depends upon its foundation, and the foundation depends upon the soil.
In this blog, Graana.com, Pakistan’s smartest property portal, features an in-depth guide on the bearing capacity of the soil, and the methods employed to boost it for the sake of building a safe structure over its surface.
What is the Bearing Capacity of Soil?
To put it simply, the extent to which soil can support the structure built over it is called the bearing capacity of the soil. The bearing capacity of soil is essentially dependent on its type, density and shear strength.
Aside from that, how deep the structure is embedded into the ground also affects its bearing capacity.
Significance of Bearing Capacity of Soil
If the bearing capacity of the soil is high, it will be able to withstand more pressure and load, which is a good sign. On the other hand, if the bearing capacity of the soil is low, the structure built over it is bound to collapse sooner or later.
Allowable Bearing Capacity of Soil
The allowable bearing capacity of the soil is the total weight the soil can endure without coming across shear failure or surpassing the acceptable amount of settlement.
The allowable bearing capacity should always be less than the ultimate bearing pressure as it considers the settlement of the soil, along with the weight needed to bring about shear failure.
How to Improve the Bearing Capacity of Soil?
In case the soil does not provide sufficient bearing capacity, Safe bearing pressure can be improved using the following methods:
- Increasing the depth of the foundation
- Draining the soil
- Compacting the soil
- Confining the soil
- Replacing the poor soil
- Using grouting material
- Stabilising the soil with chemicals
Increasing the Depth of the Foundation
One of the simplest ways to upgrade the bearing capacity of soil is to increase the depth of the structure’s foundation. The bearing capacity increases as we go deeper into the soil, making it more compact.
However, this method is only applicable for granular types of soil, also known as cohesionless soil, for instance, gravel and sand. In some cases, with the increase in the depth, the soil becomes damp; if that happens, this method won’t be applicable.
Moreover, this method is quite expensive, as the cost of construction is directly proportional to the depth of the foundation.
Draining the Soil
As the water content in the soil increases, its bearing capacity decreases, as it lessens the cohesive properties of the soil. Supposing that the soil is sandy, its bearing capacity might reduce to about 50%.
To deal with this issue, a popular method of drainage is implemented. Also, in this method, the drains are placed in the foundation channel, from where the excess water is drained off using pipes.
Compacting the Soil
Compacting the soil minimises the gaps between soil particles, thus, making them less likely to displace. Also, it indirectly enhances soil bearing capacities.
Numerous methods are used to compact the soil, some of which have been stated below.
- Scattering the pieces of glass, stones, or commonly used sand, and afterwards, pressing them into the trench beds.
- By using a roller suitable to the type of soil to move at a definite speed.
Confining the Soil
In this method, an enclosure is formed with the help of sheet piles which help compact particles of soil, resulting in improved bearing capacity of the soil. Once the soil is confined, it is further compacted to achieve even higher strength.
Moreover, this method is particularly helpful for shallow foundations.
Replacing the Poor Soil
Firstly, the poor-quality soil is removed by digging a trench of about 1.5 m in depth. After that, the trench is filled up with hard materials like sand, gravel, stone etc.
Using Grouting Technique
If the soil under the foundation has pores, cracks or fissures etc., grouting is applied. In this procedure, the problematic strata of the soil are hardened by pumping the cement grout in it and filling up any fissures and cracks, which would otherwise bring down the bearing capacity of the ground.
To ensure that the cement grout is distributed evenly, the ground is bored and drain pipes are penetrated into the soil to inject the grout.
Stabilising the Soil with Chemicals
To provide added strength to soft soils at deep depths, chemical compounds like silicates of calcium chloride are injected into the ground. These compounds react with soil particles to form a gel-like mass, which results in enhanced bearing capacity of the soil. This technique is known as chemical stabilisation.
Although these chemicals are not used in abundance, the method has proven to be very expensive. This is why it is only applied in rare cases.
Increasing the Width of the Foundation
The load of the structure is evenly divided into all parts of the foundation. If the area of the foundation is increased, the weight on each part will then decrease. Thus, if the bearing capacity of the soil is weak, this technique can be employed.
However, this method has its limitations, as the foundation can not be improved permanently.
This blog covers in-depth information on the bearing capacity of the soil, along with the methods used to improve it. For more information, visit Graana’s blog.