ABSTRACT
SHEAR STRENGTH EQUATION IN TERMS OF EFFECTIVE PRINCIPAL STRESSES The principal stresses may be expressed either as total stresses or as effective stresses if the values of pore pressure are known.
If u is the pore pressure developed during a triaxial test, we may write as before
where 0'1 and a 3are the effective principal stresses. The equation for shear strength in terms of effective stresses is
2 2 2 where 2a = 90° + lj)/ Coulomb's equation in terms of effective stresses is
s = C / + (a - u) tan lj)/
(8.37)
Since, 0-+0-0--0-
0--0-0-+0we have 1 3 cosfjJ' =c' + 1 3 tanfjJ'
0--0-+ 1 3 cos(90 + fjJ') tan fjJ' - u tan fjJ'
Simplifying
(8.38)or 1 c' cos f/J' + (03 - u) sin f/J' -(0--0-) -----~---2 1 - 3 f - 1-sin fjJ'
where (a1 - ( 3)f indicates the maximum deviator stress at failure. Eq (8.38) may also be expressed in a different form as follows by considering effective principal stresses
