Examples & Applications: Earthwork Profiling
Cross-Sections
Example 1: Area by Coordinate Method
Problem: Calculate the cross-sectional area of a fill section using the coordinate method. The coordinates of the vertices relative to the centerline (where is horizontal offset and is vertical elevation from a datum) are given as follows: .
Solution:
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Example 2: Volume by Average End Area Method
Problem: A segment of a highway requires excavation (cut). The cross-sectional area at station () is . The cross-sectional area at station () is . Calculate the volume of earthwork using the Average End Area method.
Solution:
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Example 3: Prismoidal Formula Calculation
Problem: Using the same stations from Example 2, suppose a detailed mid-section survey at station reveals the true mid-area is . Calculate the volume of earthwork using the more accurate Prismoidal formula.
Solution:
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Example 4: Applying Prismoidal Correction
Problem: A road segment is long. Station 1 has a top width and a centerline height . Station 2 has a top width and a centerline height . Calculate the Prismoidal Correction ().
Solution:
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Mass Haul Diagram
Case Study 1: Balancing Cut and Fill
Scenario: A contractor is analyzing a highway project. The initial section ( to ) requires significant cut through a hill. The middle section ( to ) crosses a valley requiring fill. The final section ( to ) is mostly flat, requiring minor fill.
Analysis:
- Mass Diagram Construction: The contractor plots accumulated volume. The curve rises from station to a peak at (indicating surplus excavation). From , the curve falls until it crosses the horizontal zero axis at .
- Balance Point: The intersection of the curve with the zero axis at means that all the material excavated from the hill ( to ) is exactly enough to fill the valley ( to ). No external soil needs to be imported or exported for this segment.
- Borrow Pit Required: However, from to , the curve continues to fall below zero. This indicates a deficit. The contractor must find a "borrow pit" (an off-site source of soil) to complete the final segment.
Case Study 2: Calculating Overhaul Costs
Scenario: The contract specifies a freehaul distance of . For any material moved beyond this distance, the contractor is paid an overhaul rate of $$2.50100\text$).
Analysis:
- Diagram Review: The mass diagram shows a balance line drawn at a length of (representing the total haul distance between the centers of mass of a cut and fill segment).
- Freehaul vs Overhaul: The first of the haul is free. The remaining distance is the overhaul distance: , which equals stations.
- Volume Determination: The vertical difference between the balance line and the peak of the mass diagram within that segment gives the volume to be moved, say .
- Cost Calculation: The overhaul cost is the volume multiplied by the overhaul distance (in stations) multiplied by the rate: 10,000\text{ m}^3 \times 3\text{ stations} \times \2.50 = $75,000$.