SSC JE Civil Engineering 30-Oct-2020 Shift 2 Paper

Concept:
Compression Index: For normally consolidated soil, the slope of void ratio (e) v/s logarithm of effective stress (log $\mathrm{\sigma }{’}_{\mathrm{v}}$ ) curve is called compression index.
Mathematically compression index is given by,
${\mathrm{C}}_{\mathrm{C}}=\frac{{\mathrm{e}}_1-{\mathrm{e}}_2}{\log \left(\frac{{\mathrm{\sigma }}_2}{{\mathrm{\sigma }}_1}\right)}$
where ${\mathrm{e}}_{\mathrm{1}}$ = void ratio at effective stress ${\mathrm{\sigma }}_1\prime$ and ${\mathrm{e}}_{\mathrm{2}}$ = void ratio at effective stress ${\mathrm{\sigma }}_2\prime$
Calculation:
$0.28=\frac{{\mathrm{e}}_1-{\mathrm{e}}_2}{\log \left(\frac{21.6}{12}\right)}$
∴ Δe = 0.28 × 0.255 = 0.0715