Stress Distribution Trough Soil - Part 03

Stress Isobars

Isobars of the vertical stress under footing are developed based on the Boussinesq Equation. Pressure isobars, developed to estimate the vertical stress under a squire and a strip footing, is given below.

Newmark developed the equation to estimate the pressure under a corner of a squire footing loaded with a pressure of q0

 

 

Where,

qv = stress increment

q0 = loaded pressure

M = B/Z

N = L/Z

V = M² + N² + 1

V1 = (MN)² 

  

Above equation we can expressed in terms of a stress influence factor Iz

 

Iz = Influence factor – Non dimensional parameter  ( we can obtain this from tables given N and M)

This table is, stress influence factors (Iz) beneath a corner of a rectangular loaded area,

M = B/Z

N = L/Z

Note : M and N interchangeable 

Any internal point within a loaded area may be considered by dividing the loaded area into rectangles with the point under consideration is a common corner and using the method of superposition to add the stress caused by each rectangular area.