Two samples of fully saturated, normally consolidated clay were isotropically consolidated to cell pressures of 150 and 300 kPa. The final void ratios were found to be 035 and 0.65, respectively.
(i) For the isotropic normal consolidation line, evaluate N and A. for this clay. (5 marks)
(ii) The specimen that was consolidated to a cell pressure of 300 kPa, was subsequently sheared to failure under drained conditions, at the same cell pressure, and the deviator stress at failure (i.e. at the critical state) was found to be 368 kPa. Determine the value of M for this clay. (7 marks)
(iii) What would be the deviator stress at failure in a drained test for the specimen consolidated to 150 kPa. (8 marks)
2. A series of water content—matric suction measurements have been taken for a saturated silty soil undergoing drying. The filter paper technique was adopted for measuring the matric suction, and the corresponding water contents were obtained in terms of degree of saturation. The results are provided in Table 1. The same soil was then tested for shear strength (at varying matric suctions) in a modified direct shear apparatus, and the results are provided in Table 2.
Construct the soil—water characteristic curve (SWCC) in terms of the BC’, vG2 and FX3 SWCC models and obtain the fitting parameters for each model. (4 marks)
(ii) Plot each SWCC model (along with the actual data given in Table 1) as a separate figure and compare the performance of the three models in terms of goodness of fit. (4 marks) (iii) Obtain the air—entry value using the BC SWCC model. (3 marks) (iv) Obtain the air—entry value for the vG and FX SWCC models using the graphical method. Are the two values different? (4 marks)
(v) Obtain the air—entry value for the vG and FX SWCC models using explicit equations. Are the values different? (4 marks)
(vi) Report an average air—entry value based on your results from Parts (iii) to (v). (3 marks)