HOW TO CALCULATE SAFE BEARING CAPACITY OF SOIL ON SITE?

How to calculate the safe bearing capacity of the soil on the 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

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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.