4.4 SOME OBSERVATIONS ON TERZAGHI'S BEARING CAPACITY THEORY

It is obvious from Section 4.3 that Terzaghi's bearing capacity theory has been obtained by assuming general shear failure in soil. However for local shear failure in soil, Terzaghi (1943) suggested the following relationships:

Strip foundation ( B/ L=0; L=length of foundation)

Square foundation ( B=I)

Circular foundation ( B=Diameter)

where N _c ?, N _q ? and N _? ? = modified bearing capacity factors c ? = 2 c/3

The modified bearing capacity factors can be obtained by substituting ?? = tan ^?1(0.67 tan ?) for ? in Eqs. (4.32), (4.33), and (4.34). The variations of N _c ?, N _q ? and N _? ? with ? are shown in Table 4.2 and also in Fig. 4.12. Vesic (1973) has suggested that a better form of obtaining ?? for estimating N _q ? and N _? ? for foundations on sand would be as follows