What is minimum depth of foundation & Rankine formula, hi guys in this article we know about minimum depth of foundation & Rankine formula, depth of footing, depth of Shallow & pile foundation and What is the standard depth of foundation as per IS code.

Foundation is important structure in civil engineering work in construction of building formation of Dams, Bridge factories and industrial building. Main function of footing is it safely transfer load acting on it to the bed of soil.

Depth of foundation generally depend on two factors soil load bearing capacity and types of foundation. Load bearing capacity of poor soil has greater depth of foundation and load bearing capacity strong soil have less less of foundation.

There is two types of foundation shallow type and deep type, generally Shallow Foundation is provided in the soil which have higher load bearing capacity and pile Foundation is provided in the soil which have less load bearing capacity.

But question is what is minimum depth of foundation? For a small residential building It is customary practice to place the foundation of a simple footing at a minimum depth of 1.50m (5 feet) from ground level or at least 1.50 times the width of footing. In cold climates the depth of footing is Kept at a minimum of 1.50m below surface because of possible frost action.

**Minimum depth of foundation(shallow/pile)**

Basically the depth of foundation depends upon type of foundation or type of soil. How type of foundation affect depth of foundation. ?

As we know depth of deep Foundation is higher then shallow foundation. Deep Foundation are provided in special case like,-water logged area,poor soil bearing capacity & Special type of structure.

So if you provided deep Foundation depth of foundation will be different compare to shallow foundation.

**How Type of soil affect depth of foundation?**

As we know all soil type has a different characteristics. If soil bearing capacity of that soil is higher then it will reduce depth of foundation. weak soil for example Black cotton soil,poor sandy soil is increase depth of foundation.

1.5m (5 feet) is minimum depth of foundation used for small scale construction, in simple footing it will be 4 feet and for shallow foundation it is 5 feet.

Depth of deep foundation depend on applied load on structure If the load on foundation is 500KN, minimum depth is 3.5m to 4.5m, If the load on foundation is in the range of 2000KN to 3000KN, minimum depth for pile foundation is 6.0m to 20.0m with pile caps.

Now question is what is minimum depth of foundation? their answer will be following:

● Ans. 1.5m is minimum depth of foundation for small scale residential building.

Now question is what is depth of Shallow Foundation? Their answer will be following:

● Ans. 1.5m to 2.5m is depth of Shallow Foundation used in construction civil engineering

Question is what is depth of pile foundation? Their answer will be following:

● Ans. 3.5m to 20m is depth of pile Foundation depend on load acting on it.

**Minimum depth of foundation as per IS code**

Minimum depth of foundation as per IS 1080-1982 is 50cm from Ground Level and as per Rankine’s theory Minimum depth of foundation =p/w (1-sin Φ /1+sin Φ) 2 where p=gross bearing capacity w =density of soil Φ =angle of response of soil. But in practice, the foundation depth is kept at 0.90m or even more.

**Rankine’s formula for depth of foundation**

Depth of foundation formula is calculated according to Rankine theory.

As per Rankine’s theory Minimum depth of foundation =p/w (1-sin Φ /1+sin Φ)^2

where p=gross bearing capacity

w =density of soil

Φ =angle of response of soil.

Ranking considered the equilibrium of soil element one immediately below the foundation and other just beyond the edge of footing. When the load on putting increases and approaches a value.