# Soil Stress

## Definition - What does Soil Stress mean?

Soil Stress, also known as Geostatic Pressure or Overburden Pressure, is the stress or pressure exerted by the overlying rock or sediments above a depth or formation of interest. It is usually considered to be about 1.0 psi per feet although the value can vary depending on the specific area; hence this value can be considered for approximations. Soil stress is also commonly referred to as geostatic stress.

## Petropedia explains Soil Stress

To estimate the stress on the soil or overburden pressure at any point, it is important to first determine the material density, i.e., the density of rocks and fluids at that point. The equation for estimating the overburden pressure/ soil stress at depth z is given by:

Where,

p(z) = density of overlying rock at depth z

g = acceleration due to gravity

po = datum pressure

There are certain assumptions made while deriving the above equation, such as the acceleration due to gravity is considered to be constant at depth z which is why it is kept outside the integral. However, in actual scenario, acceleration due to gravity will not be constant and changes a little when moved deeper into the earth. The reason for keeping āgā outside the integral part is to practice most near surface applications which need the determination of lithostatic pressure.