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(a) Vane shear tests (VST) were carried out at a project site to determine the undrained shear strength (C₂) of clay in the field. (i) Assuming uniform mobilization of soil strength at the two ends of the vane, prove that cu of the clayey soil can be obtained by the following equation: D T Cu == K where K = - (1 + 3H) лD²H 2 where T = applied torque, D = diameter of vane and H = height of vane. (4 marks) (ii) The maximum torque applied at the test was 12.5 Nm, with vane diameter of 38 mm and height of 76 mm. Estimate the cu of the clayey soil. (1 mark) (iii) Correction factors are usually applied to shear strength derived from vane shear tests. Give two reasons why cu obtained by VST may be different from those obtained from triaxial tests. (2 marks)