Wednesday 05 May 2021 Release time: 09:15 (BST) for 4 hours

 Data sheets attached: 

• Definitions of stress and strain variables

 • Equations of Modified Cam Clay model

Q1

(a) The first sample is isotropically compressed to a normally consolidated state under a cell pressure of 300kPa and a back pressure of 100kPa before being sheared to a critical state in a conventional undrained triaxial compression test, with the cell pressure held constant at 300kPa. Calculate the final critical state values of mean effective stress ?′, deviator stress ?, specific volume v and pore pressure ?. [6]

 (b) The second sample is prepared to an overconsolidated state by isotropically compressing under a cell pressure of 500kPa and a back pressure of 100kPa before isotropically unloading under a cell pressure of 300kPa and a back pressure of 100kPa. It is then sheared to a critical state in a conventional drained triaxial compression test, with the cell pressure held constant at 300kPa and the back pressure held constant at 100kPa. Calculate the final critical state values of ?′, ? and v and the (engineering) volumetric strain during shearing. [7] 

(c) The third sample is prepared to the same normally consolidated state as the first sample i.e. isotropic compression under a cell pressure of 300kPa and a back pressure of 100kPa. It is then sheared to a critical state in an unconventional drained stress path triaxial compression test, in which the axial stress ? ? is held constant at 300kPa while the cell pressure ? ? is reduced, with the back pressure held constant at 100kPa. Determine the resultant gradient of the effective stress path in the ?:?′ plane. Hence, calculate the final critical stat