(Solved): QUESTION 4 (33 marks) A consolidated undrained (CU) triaxial test was perform ...

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QUESTION 4 (33 marks) A consolidated undrained (CU) triaxial test was performed on a specimen of saturated overconsolidated clay with a cell pressure of \( 400 \mathrm{kPa} \) and a back pressure of \( 150 \mathrm{kPa} \). At failure, the total vertical stress on the sample was \( \left(1000+\frac{\Omega}{2}\right) k P a \). Assuming \( c^{\prime}= \) \( \left(25+\frac{\Omega}{10}\right) k P a \) and \( \varphi^{\prime}=28^{\circ} \) for the sample, (a) Plot the effective stress and total stress Mohr circles at failure, and also the failure line on the same plot. (6 Marks) (b) Determine the total pore water pressure in the sample at failure. (4 Marks) (c) Calculate the effective normal stress and the shear stress on the failure plane. (4 Marks) (d) At failure, what angle (between 0 and 90 degrees) would the failure plane make with the horizontal? (3 Marks) (e) How much is the Skempton parameter \( A \) at failure \( \left(A_{f}\right) \) for this test? (4 Marks) (f) Plot the total stress path (TSP) and effective stress path (ESP) on a p-q diagram for this test. (6 Marks) (g) A sample of this clay is taken from a different depth where it is known that the undrained shear strength is \( c_{u}=120 \mathrm{kPa} \). The sample is then subjected to a direct shear test in which a normal stress of \( (200+\Omega) k P a \) is applied to the sample, and then immediately after application of this normal stress, the sample is sheared quickly. What is the pore water pressure in the sample at failure? (6 Marks)