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(b) The following parameters are known for a normally consolidated clay: N = 2.56, λ = 0.16, T = 2.35 and M = 1.15. (i) Estimate the value of void ratio (e) and principal stress difference (q) at failure if an undrained triaxial test was conducted on the clay specimen consolidated under cell pressure (03) of 400 kPa and back pressure of 200 kPa. Sketch the effective stress path of the test on the q-p' plane. (5 marks) (ii) Explain why it is necessary to apply back pressure on the triaxial test specimen. (4 marks) (iii) Estimate the pore water pressure in the clay specimen at failure. (3 marks) (iv) The undrained shear strength (c₂) is equal to half of the principal stress difference at failure. Express cu of normally consolidated clay in terms for I, M, N, λ and mean effective stress after isotropic consolidation (pc). (4 marks) (c) Apart from vane shear tests and triaxial tests, name two other tests (laboratory or field tests) that are commonly used to determine shear strengths of soils. (2 marks) Equation of ICL: v = N - λ ln p' q' = Mp' Equations of CSL: v=r-λln p' 3M sin d' cv 3q' (6p' + q') 6 + M = 0'₁-0'3 o'₁+0'3 = =