4.4 The effective stress parameters for a fully saturated clay are known to be c = 15 kN/m² and = 29°. In an unconsolidated-undrained triaxial test on a specimen of the same clay the all-round pressure was 100 kN/m² and the prin- cipal stress difference at failure 170 kN/m². Assuming that the above parameters are appropriate to the failure stress state of the test, what would be the expected value of pore water pressure in the specimen at failure?