Bearing Capacity of Soil

We knew that the main function of the foundation is transmitted the load to the soil which received from structure either building, bridges, dam, etc.,

A foundation will be design based on the soil stability and different types of load. The soil stability has calculated through the bearing capacity of the soil and it is the very important factor in designing the depth of foundation.

So in this post, we are going to discuss the bearing capacity of the soil and how it could be calculated in the field.

What is bearing capacity of Soil?

The capacity of the soil that supports the structural load to the ground without any shear failure or settlement is called safe bearing capacity of the soil.

bearing capacity of soil

 The safe bearing capacity of soil formula

The safe bearing capacity of soil = Ultimate bearing capacity (UB)/Area x Factor of Safety

What is meant by the Ultimate bearing capacity of the soil

When the soil displacement starts at a point is called ultimate bearing capacity.

  Ultimate bearing capacity of soil = Wxh/d

Let us explain in easiest way!…

A 1.5 Liter water bottle can accommodate 1-litre water it is called as Safe bearing capacity. At the same time it can able to store 1.5-litre water and can’t be able to store more than 1.5 litres is called Ultimate bearing capacity.

The safe bearing capacity of soil has calculated by Drop Weight method for the small structure at the field.

Drop Weight Method

  1. First, excavate the pit at the required depth.
  2. Take a solid square cube of know weight and dimension.
  3. Then drop the cube from known height for several times.
  4. Measure the average depth of impression made by the square.

bearing capacity of soil

 

The dimension of the Cube – 15cmx15cmx15cm    Weight (W) – 1 Kg     Area – 225 Sqcm      h – 150cm

Average Depth – 0.6cm (d1+d2+d3)/3

The factor of Safety (FOS) – 2 (Generally it will be the range 2 to 3)

Ultimate bearing capacity = 1 x 150/0.6

                                          = 250 Kg

Safe bearing capacity = 250/15 x 2

                                   = 8.33 Kg/Sqcm

Here we listed some Bearing capacity soils with Values

SISoil TypeCapacity KN/Sqm
1Hard rock - Granite,Dionite3236
2Sand Stone, Lime Stone1618
3Residual deposits of Shatters & broken bed rock883
4Soft Rock441
5Gravel Sand441
6Coarse Sand, Compact & Dry441
7Coarse Sand, Compact & Dry441
8Fine Sand & Silt245
9Loose Gravel98
10Fine Sand, Loose & Dry98
11Hard Clay451
12Medium Clay245
13Moist Clay147

Here we illustrated the bearing capacity calculation just for your knowledge and the actual design should be calculated as per IS code specification. You may refer the calculation of minimum depth of shallow foundation.

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