17

The Mohr circles at failure and the corresponding failure envelopes for both series of tests are shown in Fig. Ex. 8.17. In both cases the failure envelope is the line nearest to the common tangent to the Mohr circles. The total stress parameters representing the undrained strength of the clay are:

c = 85 kN/m2; A\ = 0u o/u The effective stress parameters, representing the drained strength of the clay, are:

c' = 20 kN/m2; l/J = 26°

a

Example 8.18 An embankment is being constructed of soil whose properties are c/ = 1071 Ib/ft2, l/J/ =21 0 (all effective stresses), and Y= 99.85 Ib/ft3. The pore pressure parameters as determined from triaxial tests are A =0.5, and B =0.9. Find the shear strength of the soil at the base of the embankment just after the height of fill has been raised from 10ft to 20 ft. Assume that the dissipation of pore pressure during this stage of construction is negligible, and that the lateral pressure at any point is one-half of the vertical pressure.