Mathematical Applications: Index Properties

Calculating porosity, void ratio, and unit weight of rock and soil samples.

Example

Problem 1: Basic Porosity Calculation

A cylindrical rock core sample has a total volume (VtV_t) of 150 cm3150 \text{ cm}^3. After drying, the volume of the solid mineral grains (VsV_s) is determined to be 135 cm3135 \text{ cm}^3. Calculate the porosity (nn) and the void ratio (ee) of the rock sample.

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Example

Problem 2: Void Ratio from Porosity

A highly fractured sandstone aquifer has a tested porosity (nn) of 28%28\%. Calculate its void ratio (ee) and determine the volume of solids (VsV_s) if the total volume of the sample is 1 m31 \text{ m}^3.

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Example

Problem 3: Calculating Unit Weight

A piece of unweathered granite has a total volume (VtV_t) of 0.05 m30.05 \text{ m}^3 and weighs 1.3 kN1.3 \text{ kN} in its natural state. The porosity (nn) is known to be 2%2\%. Assuming the voids are completely dry, calculate the dry unit weight (γd\gamma_d) and the specific gravity of the solid minerals (GsG_s). The unit weight of water (γw\gamma_w) is 9.81 kN/m39.81 \text{ kN/m}^3.

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Case Studies: Engineering Properties of Rock Types

Analyzing the practical implications of different rock formations on civil engineering projects.

Example

Case Study 1: Igneous Rocks - Tunneling through Basalt

A deep highway tunnel is being excavated through a massive formation of young, extrusive basalt. Engineers must assess the rock mass properties to design the excavation method and primary support system.

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Example

Case Study 2: Sedimentary Rocks - Foundation on Shale

A heavy bridge pier must be founded on a thick, horizontal bed of dark grey marine shale. The structural loads are significant, and strict settlement limits apply to the bridge deck.

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Example

Case Study 3: Metamorphic Rocks - Slope Stability in Slate

A new railway alignment requires a deep, open cut (30 m30 \text{ m} high) through a mountain composed entirely of slate. The regional tectonic forces have steeply tilted the foliation planes of the slate.

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