Soil Mechanics Quiz 2

Dry Soil

Soil with two phases: solid soil particles and pore air.

Fully saturated soil

Soil with two phases: solid soil and pore water.

Unsaturated soil

Soil with three phases: solid particles, pore water, and pore air

Void ratio

Measure of void as a fraction of SOLID soil volume: e = Vv/Vs

Porosity

Measure of void as a a percentage of soil volume: n=Vv/V x 100%

Equation for relationship between void ratio and porosity

n=\frac{e}{1+e}

Degree of saturation

Percent of void space filled by water: S_{r}=\frac{V_{w}}{V_{v}}\cdot100\%

Water content (moisture content)

MASS amount of water present in the soil relative to solid soils: w=\frac{M_{w}}{M_{s}}\cdot100\%

Soil particle density

The density of ONLY SOLID soil mass to volume: \rho_{s}=\frac{M_{s}}{V_{s}}

Specific gravity’s usage with density

Gs serves as the ratio of solid soil density to the water density: \rho_{s}=G_{s}\rho_{w}

Bulk/total density

Total mass over total volume. Changes when degree of saturation changes: \rho=\frac{M}{V}

Saturated density

Density of the soil when the voids are completely water: \rho_{sat}=\frac{M}{V}

Dry density

Density of soil that is completely dry (still has air, but air has mass 0): \rho_{d}=\frac{M_{s}}{V}

Effective density

Used to calculate effective stress below the water table, accounting for the water’s buoyancy. \rho^{\prime}=\rho_{sat}-\rho_{w}

Unit weight

The weight per unit volume of soil: \gamma=\rho g

Soil classified as sand has what range of unit weight?

17-23 kN/m³

Soil classified as clay has what range of unit weight?

11-21 kN/m³

Relationship to get from dry unit weight to total unit weight

Using water content w: \gamma=\gamma_{d}\left(1+w\right)

Relationship to get from void ratio to porosity

Using the equation backwards: e=\frac{n}{1-n}

Water content and void ratio to degree of saturation

S_{r}=\frac{wG_{s}}{e}

Relationship of water weight to total unit weight

\gamma_{d}=\frac{G_{s}\gamma_{w}}{1+\frac{G_{s}w}{S_{r}}}

Density index/Relative density

Density of a soil relative to its common range of density: I_{d}=\frac{e_{\max}-e}{e_{\max}-e_{\min}}\cdot100\%