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

|This simple and quick field test will give you a rough idea of bearing capacity of soil.

**Procedure**

- Excavate a pit of required depth. (preferably equal to the depth of foundation)
- Take a solid ball or square cube of known weight and dimension.
- Drop the ball or square cube several times, from a known height on to the bottom surface of excavated pit.
- Calculate the average depth of impression made several times on the bottom surface of the excavated pit. Let “d” is the average depth of impression.

**Calculation**

Calculate the ultimate resistance of soil ( R ) 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 the solid ball or square cube (in kg)

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

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

Resistance of soil per unit area (in kg/cm^{2}) = R / A

Safe bearing capacity (in kg/cm^{2}) = R / (A * F.O.S)

Where,

F.O.S = Factor of safety

**Notes to Remember**

- F.O.S varies from 2 to 3 depending upon the type of structure and site condition.
- In order to get reliable test result, perform this test on different types of soil and then use your judgment to reach at any conclusion.
- Instead of using solid steel ball or square cube, we can also use CBR test plunger, or Cone (used for cone penetration test)

**Presumptive Bearing Capacity**

The table given below shows the presumptive bearing capacity values for different types of soils. This table will guide you to reach at any conclusion after conducting the test.

Type of Soil / Rock |
Safe / Allowable Bearing Capacity (kg/cm^{2}) |

Rock | 32.40 |

Soft rock | 4.40 |

Coarse sand | 4.40 |

Medium sand | 2.45 |

Fine sand | 4.40 |

Soft shell / Stiff clay | 1.00 |

Soft clay | 1.00 |

Very soft clay | 0.50 |

**Notes to Remember**

- For non-cohesive soils the values should be reduced by 50% if the water table is above or near base of footing.
- These values should be used only for preliminary design. The actual bearing capacity of soil should be calculated as per the standard codes.

**Also Read: How to Calculate Bearing Capacity of Soil On Site Using N-Value**

**Also Read: How to Calculate Bearing Capacity of Soil From Plate Load Test**

Can you help me to understand this:

In Miami, the bedrock is limestone, but it’s highly porous. According to a chart on another table, (limestone in general) has a safe load capacity of 16.5 kg/cm2. So if I dig down to the bedrock to build a skyscraper, assuming a footprint of about 50m x 60m, that multiplies out to a maximum weight of the building to be about 495m kg. That should be about a 50-60 stories tall, else the bedrock won’t support the weight.

Do I understand this correctly, and is this the reason there are no super-tall skyscrapers in Miami?

Is there a way to amend the footing to increase the load capacity?

why bearing capacity of soils effects the design and construction of a building?

a p brick pier 450ms exerts a force of 200k/ns including the mass of the pier. calculate the pressure per metre square on brick pier and the minimum area foundation required if the oil has a bearing capacity of 150k/N per square metre

please sir. I want to know whether safe bearing capacity and allowable bearing capacity are the same.

Good day Sir. I need your help in solving the bearing capacity of soil given LL,PI,moisture content, number of blows,N, from a geotech exploration because it is not stated in the result. Please. Thank you so much. I have a full result if you wanted to see. God bless.

I don’t understand clearly about ‘d’ average depth of impression. Can u explain me please?

I’d like to see if you have an answer for that one. Thanks.

What’s unclear is if you drop your object several times in the same spot or multiple times in one spot. One hint that it might be several separate drops in separate places is that you say, “Calculate the average depth of impression made several times on the bottom surface.” But is that the average of several separate impressions, or the average depth of one impression, if it is not perfectly level?

Seems like dropping a cube would be less accurate, if you can’t ensure that it would land perfectly flat each time. A corner would go in deeper than the whole surface.

Sir what is Normal dry soil bearing capacity ?

I’m Gervas Marco Graduate Eng.I ‘m getting trouble to use your method how times i have to drop the ball?

Dear Suryakanta how are your .?

i am build a residential Apartment , The plot size is 30’x30′ so how i calculate the bearing capacity .Excavation depth 12 foot

thanks a lot, it’s a great help… what will be a recommended size of the cube, if any

How to calculate ground bearing capacity for crawler crane set up?

I am James, when I do this I found that I drop weight 2 times and 3 times are different depth of impact, how to use your formular to calculate the R?

Thank you.

This is the first time i am getting into soil test topic in my life. Nice and clear explanation from u.

We r doing core cutter test

For SBC we can core cutter test ?

So its a compacted soil or clay or gravel will need to give 45000kg/m2 then it’s a safe one for further procedure…

Dear sir:

I need to convert of unit for calculation of bearing capacity

the units for bearing capacity is N/m^2

SBC of every state will be different or it will be same?And will u send me the list of SBC OF EVERY STATE ON MY EMAIL.

msyaser45@gmail.com.

thanks

In the equation the Area ‘A’ is best measured as the area of the impression in the soil.

Dear sir,

Please tell me how to calculate bearing pressure of soil if CBR is known.

Sir, I have a question related to IS 1888 for safe bearing capacity and settlement when the size of the plate is maximum 750 mm?

thanks

can any1 help in doing calulation for improvement of bearing capacity of soil using bamboo

try coconut fruit instead of square cube.

I wants Ur help for calculating sbc by using bamboo

This topic is very interesting and clear to understand how to calculate the soil bearing so I’m very happy

I would like to know more about this article Sir can you help me?

what is safe bearing capacity of soil if corrected spt value is 10.6

My name is kasiraj and my profession is chartered engineer , I want to know The design of footing ,gradebeam and column by using excell spread sheet,can I get that above software

Please I am a builder and I want to be very in structural design and calculations. Can you help

proccedure images

Super duper idea

help me know how to select a good and viable foundation of a storeyed building

needs to know formula for determining soil pressure under r.c ring beam

Site is better for field practical tests and knowldge

how to find foundation of house.

and how can i select foundation of house.