# HOW TO CALCULATE SAFE BEARING CAPACITY OF SOIL ON SITE?

This simple and quick field test will give you a rough idea of ​​the carrying capacity of the soil.

## Process

1. Dig a pit of required depth. (preferably equal to the depth of the foundation)
2. Take a solid ball or square cube of known weight and dimension.
3. Drop the ball or square cube several times on the bottom surface of the excavated pit from a known height.
4. Calculate the average depth of the raid several times over the bottom surface of the excavated pit. Let “d” be the average depth of the impression.

## calculation

Calculate the ultimate resistance (R) of the soil using the formula given below.

r = (w * h) / d

Where,

R = ultimate resistance of soil (in kg)

d = Average depth of impression (in cm)

w = weight of solid ball or square cube (in kg)

h = Height (in cm) of falling of solid ball or cube

If “A” is the cross-sectional area of ​​a solid steel ball or cube, the soil resistance per unit area is calculated using the following formula.

Soil resistance per unit area (in kg/cm)2) = r / a

Safe Bearing Capacity (in kg/cm)2) = R / (A * FOS)

Where,

FOS = Factor of Safety

### notes to remember

1. The FOS varies from 2 to 3 depending on the type of structure and site conditions.
2. To get reliable test results, perform this test on a variety of soil types and then use your judgment to reach a conclusion.
3. Instead of using solid steel ball or square cube, we can also use CBR test plunger, or cone (used for cone penetration testing)

## presumptive bearing capacity

The table below shows the estimated bearing capacity values ​​for different soil types. This table will guide you to reach any conclusion after conducting the exam.

 soil/rock type Safe / Acceptable Bearing Capacity (kg/cm.)2, Rock 32.40 soft stone 4.40 coarse sand 4.40 medium sand 2.45 fine sand 4.40 soft shell / hard clay 1.00 soft clay 1.00 very soft clay 0.50

### notes to remember

1. Values ​​for non-adhesive soils should be reduced by 50% if the water level is above or near the base.
2. These values ​​should only be used for the initial design. The actual bearing capacity of the soil should be calculated as per the standard code.

Read also: How to calculate bearing capacity of soil at site using n-value

Also read: How To Calculate Soil Bearing Capacity From Plate Load Test

Er. Mukesh Kumar

Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.