---
title: "Define reserve and estimate construction material"
subject: "Engineering Geology II"
chapter: 7
key: "semester_4/engineering_geology_ii:define-reserve-estimation"
source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/define-reserve-estimation
site: BCT Engineering
---

# Define reserve and estimate construction material

Engineering Geology II · Chapter 7: Geology and Construction Materials

- Asked in: 2081 Chaitra, 0.5 marks; 2079 Asoj, 1 marks; 2079 Chaitra, 1 marks; 2077 Chaitra, 1 marks; 2076 Bhadra, 0.5 marks; 2074 Bhadra, 1 marks; 2072 Asoj, 3 marks; 2071 Magh, 3 marks; 2070 Magh, 1 marks; 2069 Bhadra, 3 marks (asked 10 times)
- Video: [Reserve calculation, True thickness|Engineering Geology Numerical|Purbanchal University TU KU PoU](https://www.youtube.com/watch?v=2XgGJZKWdNY) — Civil Engineering Solution Channel
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/define-reserve-estimation
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-7

## Question

Define reserve. Describe how the reserve of construction materials (aggregate) from bedrock and unconsolidated deposits is estimated (major steps).

## Short answer

Reserve: the measured, economically extractable part of a resource. Bedrock aggregate: find true thickness (t = t_v cosδ), calculate volume (area × thickness), deduct losses, then multiply by density for tonnage. Unconsolidated: survey area, measure average workable thickness above water table, subtract overburden, and compute tonnage from bulk density.

## Answer

#### 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: $V = 360{,}000\ \text{m}^3$.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is a reserve?
   A. All material of a kind in the crust, found or not
   B. Material expected only in unexplored areas
   C. Any deposit within 5 km of a project
   D. The part of a resource that is identified and can be extracted economically, legally and with existing technology
   Answer: D. Reserve is a subset of resource that is measured and currently extractable. (Key point: Reserve definition)

2. Which sequence is correct for bedrock aggregate reserve?
   A. Density, then volume, then area, then thickness
   B. Area, true thickness t = tv cos δ, volume A x t, deduct losses, multiply by density
   C. Volume from plan area x dip, then add overburden
   D. Thickness from strike, then sum of recovery factors only
   Answer: B. Volume is area x true thickness, reduced for overburden/waste/recovery, then converted to tonnage by density. (Key point: Bedrock steps)

3. How is a sand and gravel reserve estimated?
   A. Strike length x dip length x cos δ
   B. Borehole depth only, ignoring area
   C. Counting boulders on the surface
   D. Area x average workable thickness from test pits or sections, deducting overburden and the portion below the water table
   Answer: D. Pits/trenches give thickness and quality; volume is area x workable thickness, excluding unusable parts. (Key point: Unconsolidated deposits)

## Related in Engineering Geology II

- [Aggregate reserve: sandstone 300 m, 227 km2](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Areserve-sandstone-227-km2) — Engineering Geology II, chapter 7, asked 2×
- [Aggregate reserve: quartzite 300 m, 437 km2](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Areserve-quartzite-437-km2) — Engineering Geology II, chapter 7, asked 2×
- [Aggregate reserve: sandstone N44W/36, 82 m](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Areserve-sandstone-n44w-36) — Engineering Geology II, chapter 7, asked 2×
- [Aggregate reserve: sandstone N42W/34, 80 m](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Areserve-sandstone-n42w-34) — Engineering Geology II, chapter 7, asked 2×
- [Geomorphology in searching construction materials](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Ageomorphology-construction-materials) — Engineering Geology II, chapter 7, asked 4×
- [Reserve: quartzite apparent dips 1:9 and 1:12, 4.6 km2](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Areserve-quartzite-apparent-dips-area) — Engineering Geology II, chapter 7, asked 2×

## Related in other subjects

- [Estimate, quantity survey, estimated vs actual](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Aestimate-quantity-survey-actual) — Estimating and Costing, chapter 1
- [Factors for selecting construction materials](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Afactors-selection-construction-material) — Civil Engineering Materials, chapter 1, asked 9×
- [Water bound macadam materials and construction](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Awbm-construction-procedure) — Transportation Engineering II, chapter 3, asked 4×
- [Steps of sewer construction](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Asewer-construction-steps) — Sanitary Engineering, chapter 3