Safe Load Bearing Capacity

[MatthewMansfield]

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.

 

[HTURKAK]

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....

Check your quantities and units...

Better to look worked examples for foundation design handbooks..

 

[MatthewMansfield]

Hi HTURKAK

Thank you for your response.

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?

 

[BigH]

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" . . .

 

[MatthewMansfield]

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.

 

[Agent666]

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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