Define reserve and estimate construction material

Reserve

A reserve is the part of a resource that has been identified (measured) in quantity and quality and can be extracted economically, legally and with existing technology at the time of the estimate. Hence a reserve is a subset of a resource. For construction materials, the reserve is the volume or tonnage of usable aggregate, sand or gravel of acceptable quality that can actually be quarried.

Reserve of aggregate from bedrock

1. Select the site: using topographic and geological maps and a field survey; identify the rock type, outcrop and quality (strength, durability, specific gravity, abrasion).
2. Determine the quarry area: map the boundary (strike length $\times$ dip length, or plan area $A$), excluding settlements, forests, rivers and roads.
3. Determine the attitude and thickness: measure strike and dip from outcrops, and the vertical thickness $t_v$ from boreholes or section lines; compute the true thickness

$$t = t_v\cos\delta$$

4. Compute the volume: $V = A \times t$ when $A$ is measured on the bed (strike length $\times$ dip length), or $V = A \times t_v$ when $A$ is the plan area.
5. Deduct losses: overburden, weathered rock, waste bands, unusable rock and set-back zones; apply a recovery factor (e.g. 0.7 to 0.9).
6. Compute tonnage: mass = $V\times$ density (bulk density of rock, about 2.6 to 2.7 t/m³).
7. Classify: as measured, indicated or inferred according to the spacing of data.

Reserve of sand, gravel and boulders (unconsolidated deposits)

1. Locate river terraces, floodplains, fans and moraines from topographic maps, aerial photos and geomorphology.
2. Survey the deposit area (grid or cross-sections) and dig test pits, trenches or drill holes at regular spacing to measure the thickness and the depth to the water table.
3. Take samples for grading, fines, organic and clay content, and quality tests.
4. Calculate $V =$ area $\times$ average workable thickness (or use the cross-section/prismoidal method), deducting the overburden and the portion below the groundwater level.
5. Multiply by the bulk density to get the tonnage, and deduct the percentage of oversize and fines.

Example: area 150 m x 150 m, thickness 16 m: $V = 360{,}000\ \text{m}^3$.