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(OP)
Hello all

I was wondering if anyone could help me with the following load bearing capacity problem:-

I have worked out that I have a safe soil bearing capacity of 1238kN/m^2

The area of my foundation is 5.883m^2

The total load I am applying to my foundation is 2420kg.

Just based on this information how would I know if I have exceeded my safe bearing capacity of the soil???

I am struggling with the units and not really sure how to work it out??

Any help will be greatly appreciated.

Thank you.

Replies continue below

### RE: Safe Load Bearing Capacity

#### Quote (I have worked out that I have a safe soil bearing capacity of 1238kN/m^2)

Allowable bearing stress calculation is not a precise value so, 1238 kN/m2 should be rounded 1200 kN/ m2. This value could be for rock and 1200 kN/m 2 literally 1200 kPa ,that makes 1.2 Mpa or 12 kg /cm2...

If The area of your foundation is 5.883m^2, ( around 2.4X 2.4 m ...) the thickness should be around 0.5 m. and the own weight of the ftg should be = 5.883*0.5*2.5=7.35 tons or 73.5 kN ...

Your total load for the design of foundation is 2420kg. or 2.42 tons or 24 kN....

Better to look worked examples for foundation design handbooks..

### RE: Safe Load Bearing Capacity

(OP)
Hi HTURKAK

I am still not any the wiser.

Just to clarify the safe soil bearing capacity is 1238kN/m^3, rounded to 12000 kPa as per your response.

The weight of the foundation is 73.5kN as per your response.

The load I am applying to the foundation is 2420kg.

So the total load acting on the soil is 73.5kN + 2420kg and this load is applied over an area of 5.883m^2.

But I still dont know if I exceeded the safe soil capacity?

### RE: Safe Load Bearing Capacity

Please show you you came up with 1238 kPa (kN/m2) for safe bearing capacity (based on settlement (safe bearing pressures which may be less than safe bearing capacity which is based on shear??). Unless I am off base , 1238 kPa is equivalent to 1.24 MPa. Are you on rock? For certainly MPa is not soil as was stated. . .

Secondly, I have never seen a foundation "area" to such accuracy. In real construction foundation dimensions in L and B can be off by as much as 75 to 100 mm - what would this do to your area? Reality vs "bookish".

Computers/calculators can be "so precise" . . .

### RE: Safe Load Bearing Capacity

(OP)
Hi BigH

Thanks for the response.

The soil type is dense gravel with a friction angle of 30 degrees. I used terzaghi bearing capacity theory to come up with the figure of 1238kN/m^2.

The figures do not represent reality.

I am having trouble in understanding when i have exceeded my safe soil bearing capacity.

If I have a safe soil bearing capacity of 1238kN/m^2 and I apply a load of say 2420kg + 73.5kN over an area of 5.883m^2 how would I know whether or not I have exceeded the safe bearing capacity of 1238kN/m^3 - This is the bit i am struggling with.

Can you shed any light?

Thank you.

PS the units for my safe bearing capacity should be kN/m^2.

### RE: Safe Load Bearing Capacity

Employ some high school maths.... Then you'd ask if (2420*9.81/1000+73.5)/5.883<=1238kN/m2? Unsure if you have applied any load factors or not, but consider those if required. Substitute numbers as the thread evolves regarding how you've determined the bearing capacity...

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