Soil Bearing Capacity: Significance And Types (2024)

Buildings, dams, bridges, and everything else constructed by civil engineering are all anchored to the ground. The foundation is required so that the weight of the building may be distributed across a wide region of soil.

It is important that the foundation of the building is not going to cut into the soil or cause the building to settle too much. In order to prevent anything like this from occurring, the conventional technique of designing foundations is predicated on the idea of the bearing capacity of the soil.

In this article, we will talk about the bearing capacity of soil, including its importance, different types, and the factors that influence it.

Bearing capacity of soil: What is it?

When subjected to stress from loading, the soil has a tendency to distort. The soil’s ability to resist displacement is influenced by a number of different variables, including its moisture content, relative density, internal friction angle and the way in which force is transmitted to the soil.

The term “bearing capacity of soil” refers to the maximum weight per unit area that soil can support without succumbing or being displaced.

Bearing capacity of soil: Significance

When deciding whether or not a specific soil can withstand the load that the structure imposes on it, the ability of the soil to carry weight is an extremely important factor.

If the soil underneath a building cannot support the weight of the structure being constructed, the structure may become unstable, which can result in fractures and other forms of damage.

As a result, in order to circumvent this problem, the bearing capacity of soil must be taken into consideration while designing the foundation.

Known about: Soil Density

Bearing capacity of soil: Various types

Ultimate Bearing Capacity

The ultimate load that a given soil can support without breaking apart in shear or experiencing an excessive amount of settlement from a building built on top of it is referred to as the ultimate bearing capacity of that soil.

Safe Bearing Capacity

The safe bearing capacity of the soil is the highest force it can sustain without giving way. It’s the number you put into the foundation-planning spreadsheet to account for bearing capacity. A sufficient safety factor is subtracted from the final bearing capacity to arrive at this figure. It is recommended that the safety factor be between 3 and 5.

Allowable Bearing Capacity

It is the total load, including the foundation’s surcharge, over which neither the earth nor the building settles too much. However, designers often ignore this bearing pressure. Whenever there is a chance of failure or an element of the plan’s execution that is unknown, a suitable safety factor is applied.

Bearing capacity of soil: Factors impacting this

The ability of the soil to support weight is affected by a wide variety of factors. These factors are linked to the loads that are applied to the soil and have a significant impact on the bearing capacity of soil.

Foundation width

Soil with little cohesiveness might have its bearing capacity reduced if the foundation is too narrow. In cohesionless soil, where internal friction contributes significantly to soil shear strength, a wider foundation will support a greater load. Soil with infinite depth, consistent shear strength, and cohesive properties may support loads of any width foundation.

Foundation depth

A deeper foundation is necessary for increased bearing capacity. This is most noticeable in cohesive-free soil when the texture is hom*ogeneous. The opposite is true if the foundations are pushed into a poor soil layer, which reduces their carrying ability.

Unless the building is anchored by under-consolidated soil or compressible soil that is vulnerable to wetness, appropriate bearing capacity is typically assured by foundations set at depths where the weight of the structure matches the weight of the displaced soil.

Surcharge and soil weight

One cannot exclude the bearing capacity contribution of water table-influenced surcharge and subsurface soil. Construction, seepage, and elevation issues may be avoided if the water table is kept below the foundation’s base. There will be no effect on the bearing capacity of soil from water table levels below the failure surface.

Spacing between foundations

When designing a foundation, it is advised that a minimum separation between footings that is 1.5 times the width of the foundation be taken into consideration. This will help prevent a loss in the foundation’s carrying capacity.

Dynamic motion and earthquake

The bearing capacity of soil might diminish due to repeated movement, which would raise pore pressure. Earthquakes, vibrating equipment, and several other factors such as transportation, explosion, and pile driving all contribute to cyclic motions.

When pore pressures are higher than the soil confining tension, the foundation soil may become liquefied. The effective stress drops to zero due to liquefaction, leading to significant deformation and a decrease in bearing capacity.

Frost action

Changes in the bearing capacity of soil may occur gradually over time due to frost heave in particular soils that are in proximity to water and are exposed to subzero weather. Materials with a low cohesiveness, such as those made up of a lot of silt-sized particles, are more vulnerable to the effects of frost.

Subsurface voids

The bearing capacity of soil is diminished when subsurface voids are present within a crucial depth under the foundation. The critical depth is determined by the depth at which the pressure exerted by the foundation on the soil is no longer significant.

Collapsible and expansive soils

When the soil is somewhat dry, its sturdiness and bearing capacity may increase significantly, despite its tendency to collapse and expand. However, because of changes in moisture content, the proportion of these soils might shift. As a result, there will be shifts in the structure’s base on a global and regional scale. Soil movement brought on by rain and dry spells may cause long-term, severe damage to buildings.

Potential heave

Consolidometer testing, carried out in line with ASTM D 4546, may reveal the presence of a possible heave. The findings of this test are taken into account when deciding how to prepare the foundation soils so that they are better able to resist or isolate the anticipated soil heave.

Soil reinforcement

The bearing capacity of weak or soft soil may be significantly boosted by the installation of different types of reinforcement in the soil. These reinforcements can take the shape of metal links, strips, arrays, geotextile fabrics, or coarse aggregates.

Seepage and soil erosion

Seepage and erosion of the soil surrounding and beneath foundations may both lower the bearing capacity of the foundation soil and ultimately lead to its collapse.

Bearing capacity of soil: Nine ways to enhance this

There are cases where the soil does not have sufficient safe bearing capacity at a shallow depth, or when it is so low that the resulting footing dimensions are too huge and costly. As a consequence of this, under such situations, and contingent upon the requirements of the site, it becomes essential to enhance the bearing capacity of soil. The following are strategies for enhancing the bearing capacity of soil:

• By raising the foundation’s depth

In most situations, the restricting weight of the underlying material causes the bearing capacity to rise with depth. If the moisture content of the subsurface material rises with depth, as it does with slits, then you should not utilise this technique.

• Through soil drainage

According to the findings, the presence of an excessive amount of water causes sandy soils to lose fifty per cent of their bearing capacity. Because of this, appropriate drains need to be installed in the foundation channel in order to remove any surplus water.

• Through soil compaction

Compaction reduces the amount of space between certain soil particles, which makes those particles less prone to movement. As a result, compaction will indirectly enhance the bearing capacity of soil. When dealing with sandy soils that have a loose texture, compaction of a certain degree may be achieved, notably by the driving of piles or the packing of boulders.

• Constraining the soil

By enclosing the ground with sheet piles, you may prevent any movement of soil that would otherwise occur as a result of the action of load. When sheet piles are pushed together to construct an enclosure, the result is a compacting of the soil particles. As a result, the bearing power will be increased.

These constrained soils might undergo further compaction to achieve a higher degree of strength. This approach is particularly helpful for sandier soils that are present below shallow foundations.

• Expanding the width of the base

When the breadth of the foundation is increased, the bearing area also increases, which results in a reduction in the amount of pressure that is exerted. This technique has restricted use since there is a limit to how much the breadth of the foundation may be extended.

• Replacing deteriorating soils

The substandard soil is excavated first, and then the resulting space is filled with more desirable components such as crushed stone, gravel, sand, or other types of hard materials. After first excavating the foundation trenches to a depth of approximately 1.5 metres, the trenches are then filled with hard material in stages of 30 centimetres each before being rammed.

• Using grout

A suitable number of borings are drilled into the soil carrying layers that have low quality. After that, a concrete grout is injected into the foundation under pressure in order to seal any fractures or crevices that might otherwise impair the bearing capacity of soil. The majority of the time, this approach is used for fissured fractures.

• Through a chemical process

Silica-based chemical solutions are pumped under high pressure. By combining soil particles into a cohesive gel, they may indirectly boost the bearing capacity of soil. However, even if the chemicals are only introduced in minute quantities, the process is still expensive, which is why it costs a lot of money and is only used in certain circ*mstances.

• By means of geotextiles

Strengthening and increasing the bearing capacity of weak soils may be accomplished via the use of this approach. In this particular setting, geotextiles made of coir have shown to be very beneficial.

Bearing capacity of soil: Safe bearing capacity of various soils

FAQs