Geotechnical Engineering

DHARM

SHALLOW FOUNDATIONS 625

V R

H

e b

Base

area

b×L

x=3—–eb 2

e

—–eb 2

(a) Elevation of footing

(b) Soil pressure

e>—b 6

No pressure

between soil

and footing in

this zone

Fig. 15.16 Footing subjected to moment-resultant force

outside the middle-third of the base

Also, qmax =

V

A

b

be

4

36 −

L

N

M

O

Q

P ...(Eq. 15.11)

where A = bL.

Equation 15.9 reveals that the maximum soil pressure is merely twice the average pres-

sure produced by V acting on the area xL.

Moment about both axes

When moments act simultaneously about both axes, for example when a vertical load acts at
an eccentricity with respect to both the axes, as shown in Fig. 15.17, the soil pressure is given
by the following equation:

q =

V

A

Mc

I

Mc

I

bb

b

LL

L

±±. ...(Eq. 15.12)

This is under the assumption that the entire base is under compression.

V

Mb

L

DA

CB

z

z

e=M/Vbb

e=M/VLL

V

ML

b L

Probable zone of zero pressure

if the computed soil pressure

at C appears to be negative

P

Fig. 15.17 Footing subjected to moments about both axes