SOME OF THE TERMS DEFINED RELATING TO BEARING CAPACITY OF FOUNDATIONS.

It will be useful to define, at this stage, some of the terms relating to bearing capacity of foundations
(refer to Fig. 12.3).

(a) Total Overburden Pressure q0
qo is the intensity of total overburden pressure due to the weight of both soil and water at the base level of the foundation.

Figure 12.3 Total and effective overburden pressures

(b) Effective Overburden Pressure q'0
q'0 is the effective overburden pressure at the base level of the foundation.

(c) The Ultimate Bearing Capacity of Soil, qu
qu is the maximum bearing capacity of soil at which the soil fails by shear.
 
(d) The Net Ultimate Bearing Capacity, qnu
qnu is the bearing capacity in excess of the effective overburden pressure q'0 expressed as

(e) Gross Allowable Bearing Pressure, qa
qa is expressed as

where Fs = factor of safety.

(f) Net Allowable Bearing Pressure, qna
qna is expressed as

(g) Safe Bearing Pressure, qs
qs is defined as the net safe bearing pressure which produces a settlement of the foundation which
does not exceed a permissible limit.
 
Note: In the design of foundations, one has to use the least of the two values of qna and qs.