Estimating Sheet

# How to work out the standard depth of foundation

Construction Software This civil engineering article focuses on how to determine standard depth of foundation from ground level in a building. The depth of foundation is settled on the basis of the following factors :-

1. Type of soil
2. Ground water table
4. Bearing strength
5. Density of soil

The depth of foundation can be determined by applying the Rankine’s formula as follow :-

D = P /W x (1 – sinθ) / (1 + sinθ)2

Here, D stands for least depth of foundation in meter.

P stands for total load on foundation or load of structure in KN/m2.

W stands for unit weight of soil or density of soil.

θ stands for Angle of repose or internal friction of soil.

Given below, the angle of repose and unit weight for different types of soils :-

Angle of repose - Unit Weight

Dry Sand = 25 to 35 degree - 16 KN/m3
Moist Sand = 30 to 35 degree - 18 KN/3

### Also Read: Common types of foundations for buildings

Wet Sand = 15 to 25 degree - 19 KN/m3

As for instance, assume the load of structure, density of soil and angle of repose as follow :-

Load of structure (p) = 300 KN / m2
Density of soil = 18 KN/m3
Angle of repose = 30 degree

After putting all these data into the above mentioned formula, we get the following result :-

D = 300 / 18 (1 – sin300) / (1 + sin300)2 = 1.85 meter (it is obtained through a calculator)

So, the standard depth of foundation = 1.85 meter

Video Source: Civil Engineer Deepak Kumar 