SSC JE Civil Engineering 23-Mar-2021 Shift 1 Paper

Concepts:
Several unit weights are used in Soil Mechanics. These are the bulk, saturated, dry, and submerged unit weights.
The bulk unit weight is simply defined as the weight of soil under existing conditions per unit volume of soil sample.
$\mathrm{\gamma }\mathrm{b}=\frac{\mathrm{totalweight}}{\mathrm{Volume}\mathrm{of}\mathrm{Soil}\mathrm{mass}}$
The dry unit weight, ${\mathrm{\gamma }}_{\mathrm{d}}$ ­ is defined as the weight of soil mass under dry conditions to the total volume of soil sample. When all the voids are filled with air the bulk unit weight is identical to the dry unit weight,${\mathrm{\gamma }}_{\mathrm{d}}$. It is givenas:
$\mathrm{\gamma }\mathrm{d}=\frac{\mathrm{Dry}\mathrm{Weight}\mathrm{of}\mathrm{soil}\mathrm{sample}}{\mathrm{Volume}\mathrm{of}\mathrm{Soil}\mathrm{mass}}$
The submerged unit weight is the unit weight of soil mass when is fully submerged in water. It is given as:
${\mathrm{\gamma }}_{\mathrm{sub}}={\mathrm{\gamma }}_{\mathrm{sat}}-{\mathrm{\gamma }}_{\mathrm{w}}$
Note:
The relation between bulk, saturated and dry unit weights can be expressed as:
1. $\mathrm{\gamma }\mathrm{b}=\frac{\left(\mathrm{G}+\mathrm{Se}\right){\mathrm{\gamma }}_{\mathrm{w}}}{1+\mathrm{e}}$
2. $\mathrm{\gamma }\mathrm{d}=\frac{{\mathrm{\gamma }}_{\mathrm{b}}}{1+\mathrm{w}}$
3. porosity, $\mathrm{n}=\frac{\mathrm{e}}{1+\mathrm{e}}$
4. ${\mathrm{\gamma }}_{\mathrm{sat}}=\frac{\left(\mathrm{G}+\mathrm{e}\right){\mathrm{\gamma }}_{\mathrm{w}}}{1+\mathrm{e}}$