# How Is The Depth Of Foundation Calculated?

Okay, you know I'm an electrical engineer who plays with software. But I'm curious to know how the depth of foundation is calculated. Logically, it should be directly proportional to the height of the construction. But with that logic, super tall structures would need a super deep foundation. π

## Replies

it depends upon various factors like the type of soil, function of the building, wind loads, which earthquake zone the building is to built in, and the depth of underground water table. What I'm wondering is why an electrical engineer needs to know about foundations ? Personally, I'll tell Foundation Engineering is the most boring subject amongst all the civil subjects.. π

Also, I would like to tell you one thing about your logic. Depth does not depend upon height. In fact more height means more loads coming on the soil which means greater area required at the base. strength depends on width of base rather than depth. π
• Kaustubh Katdare
Curiosity, my friend. I'm interested in everything.
Well. Must praise your curiosity then, for starting from the foundations.. π Though I have not been of much help with foundations, Do contact when you reach to the slab level. That's my area of interest.. π Will be waiting.. π
• Kaustubh Katdare
First of all, I don't know what kind of questions I may have about the slab. Happened to pass by a construction site that was preparing the foundation and the question struck my mind.
• Anant Jalgaonkar
Must be Boring for Karan Avad, but let me tell you Foundations are the most tricky part of a structure and thus cannot be ignored by a structural engineer!!! Well Mr. Big K you can refer to any basic soil engineering book and you will get to know how foundation size are determined. For your Curiosity, You must have heard about capacity of soil to take load, foundation sizes are related to the capacity of a particular soil to take load( just a crude explanation for civil engineering rookie). Hope this for now have settled your "Curiosity".
• Kaustubh Katdare
Okay, I didn't know my curiosity would get notice so frequently. Does the shape of foundation also determine the depth? The tallest building - Burj Khalifa has a tripod like base; which I think plays an important role in the stability of overall structure.
• Anant Jalgaonkar
Look the sole idea is to transfer the superstructure load to the substructure and finally to the soil underneath. In burj Khalifa they must have used Pile Foundations that too also at a much greater depth, because it is on sea shore and the soil underneath the structure must be sand, which has a very bed reputation of forming Quick sand condition(Soil losses all its shear strength) with sea water all around. Stiffness of triangle is highest among all available shapes (circle, rectangle etc.) so they might have given a triangular shape at base to the Burj Khalifa. Does the shape of foundation also determine the depth? I am not too sure what you want to ask here. After designing if depth required is 30m (say, for Pile foundation) you need to go that deep.
• Kaustubh Katdare
Okay, gives me enough idea. Pile foundations make sense.
At Mr. Anant Jalgaonkar.. I never said its useless or of any less importance. I said its boring and it was a personal opinion. as such no part of any structure can be ignored not just the foundations. π
• @n@nd

this is how the substructure of burj khalifa looks. The 80,000 sq ft / 7432 sq meter foundation slab and 50-metre deep piling.
To ensure the safety of the design, numerous wind tunnel tests were undertaken.
Building a foundation this large is extremely important because otherwise the tower may sink into the unstable desert sand. There is some rock at the Burj Khalifa site, but it is fragile and saturated with ground water making it incapable of withstanding a lot of weight.
So, large boreholes were dug 164 feet (50 m) deep and then filled with viscous polymer slurry to maintain the stability of the hole. The slurry is denser than water, but lighter than concrete. The concrete, when poured into the hole, displaces the slurry and hardens to form a foundation pile.
• Anant Jalgaonkar
Well to rookie of any field one should not tell his/her opinion.One should be clarifying the questions asked. Otherwise the one who have asked the question will follow a Prejudice!! Anyways my intention was not to hurt anyone...Peace!!!!
• Infinity
The_Big_K
Okay, you know I'm an electrical engineer who plays with software. But I'm curious to know how the depth of foundation is calculated. Logically, it should be directly proportional to the height of the construction. But with that logic, super tall structures would need a super deep foundation. π
Nice Question! Although some people explained it well I would like to add some points. Foundation depth mainly depends on the type of soil stratum(in a broader sense) because it is soil which has to ultimately bear the whole load..... poor chap!πIn soil what we try to avoid is:
1) the settlement of soil due to the application of load
2) Stress failure i.e applied stress gets larger than soil bearing capacity .

I won't go in technical details since you are from electrical(I guess) but I will try to make it clear from an example. Just think do we need foundation at all if in place of soil there was just rocky stratum that too uneven. Not at all π....... so we take the foundation from the load application point to the point where we start getting hard stratum of soil that can support the load. So if you get the hard stratum at just 1 or 2 m below the ground level why we would go for 10 or 20 m long columns! Burj Khalifa's pile foundation depth could have been 1/3rd to 1/2 of present depth if the soil condition had been good.So talking in a broader sense this is done to take care of settlement criteria. But we are still not done.
Now we will check that the soil doesn't fail in stress criteria and to ensure that we end the column with regular size footing such as square, rectangle etc. Footing is important because stress = force/area. here force is constant so we try to distribute this force over a large area to decrease the stress on soil and hence make it less than that of Soil Bearing Capacity.

Conclusion: You might see a multi storey building standing on small columns if the soil stratum is hard(as in most regions of maharashtra....rocky soil) and you might see long piles just to support a single storey building if the soil is bad as hell. for ex. muddy area. But the thing is that Civil Engineers will make it possible to build the structures anywhere you wantπ

PS: Sorry for the long post!
• Kaustubh Katdare
• Mohamed Amir
I would like to say something
when I was young I tried to understand many engineering topics which I never study like the_big_k curiosity ..... and when I grew up and study civil engineering I found out the study most of the time approve the sense of human "subhan allah" for example the deflection of slabs and things like u say eng k is so right sense the tall and huge building require huge foundation so don't let your mind stops ever .even if another field other than electrical ....... my greetings
• Jeffrey Arulraj
Does the one sixth of the height of the building must be the depth of the foundation hold good in very huge structures

I was wondering this when I read about the 2 km tall tower proposed in China if this is true then the foundation must be at least 300 m deep right

Do clarify here
• Manas1gec
@n@nd

this is how the substructure of burj khalifa looks. The 80,000 sq ft / 7432 sq meter foundation slab and 50-metre deep piling.
To ensure the safety of the design, numerous wind tunnel tests were undertaken.
Building a foundation this large is extremely important because otherwise the tower may sink into the unstable desert sand. There is some rock at the Burj Khalifa site, but it is fragile and saturated with ground water making it incapable of withstanding a lot of weight.
So, large boreholes were dug 164 feet (50 m) deep and then filled with viscous polymer slurry to maintain the stability of the hole. The slurry is denser than water, but lighter than concrete. The concrete, when poured into the hole, displaces the slurry and hardens to form a foundation pile.
hiee... do u know any software by which such modelling is done??
• titansComputer
Manas1gec
hiee... do u know any software by which such modelling is done??
Sorry for bumping, but I think Karan has explained that for strong structure it is important how much wide is your footing. Also knowing from somewhere else online I have found that depth of foundation should be 1/3 of the height of building, which is in my opinion is confusing. If you look to Burj Khalifa's foundation depth is 50m deep, where height is 829m, so in this case 1/3 rule of the height of building isn't applied here.

• Ankan Roy
this is the formula for foundation depth! Rankine's formula
• Naseeruddin4
If the height of minaret 30m wat is the depth of foundation
• Naseeruddin4
Jeffrey Samuel
Does the one sixth of the height of the building must be the depth of the foundation hold good in very huge structures

I was wondering this when I read about the 2 km tall tower proposed in China if this is true then the foundation must be at least 300 m deep right

Do clarify here
1/6 height of building by which code
• Jeffrey Arulraj
Naseeruddin4
1/6 height of building by which code
I am noob in Civil designs bro.

I Heard about this 1/6th thing some where not bale to remember it. Pls clarify it here
• ankitsaini
anyone is here whose capable to give the answare of my question.
for what load the ground floor column can be design?
if frame structure looks like that,
• Harissh
Hi friends,

Which type of foundation is best for building,i have a plan to construct 5 floor building,please tell me which building foundation is best and what should be the depth of the foundation.

Regards,
Harish.S
• Harissh
Hi friends,

Which type of foundation is best for building,i have a plan to construct 5 floor building,please tell me which building foundation is best and what should be the depth of the foundation.

Regards,
Harish

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