(Solved): b) A saturated clay sample was taken from a site at a depth of \( 4 \mathrm{~m} \) from the origin ...

b) A saturated clay sample was taken from a site at a depth of \( 4 \mathrm{~m} \) from the original ground level and was tested for an oedometer test. The clay layer has a saturated unit weight of \( 20 \mathrm{kN} / \mathrm{m}^{3} \) and the specific gravity of the soil is \( 2.70 \). The results of the test were shown in Table Q3(b). Table Q3(b): Consolidation test results i) Plot the e-log \( \alpha_{1}^{\prime} \) curve and determine the preconsolidation stress using the Casagrande's method. Given the final thickness and final moisture content of the sample were \( 17.90 \mathrm{~mm} \) and \( 57 \% \) respectively. A semi-log scale graph paper is attached in Appendix 2 and to be submitted together with your answer script. \( (\mathrm{CO} 2-\mathrm{PO} 2)(\mathrm{C} 4) \) (8 marks) ii) Determine the compression index and swelling index of the consolidated soil. \( (\mathrm{CO} 2-\mathrm{PO} 2)(\mathrm{C} 4) \) (4 marks) iii) The preconsolidation status of a soil can be described using the overconsolidation ratio (OCR). Determine the overconsolidation ratio (OCR) of the tested clay sample and define the preconsolidation status obtained based on clay stress history. \( (\mathrm{CO} 2-\mathrm{PO} 2)(\mathrm{C} 4) \) \( (6 \) marks)