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 (x,y)(x, y) of the vertices relative to the centerline (where xx is horizontal offset and yy is vertical elevation from a datum) are given as follows: (0,5),(10,5),(15,0),(15,0),(10,5)(0, 5), (10, 5), (15, 0), (-15, 0), (-10, 5).
Solution:

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Example 2: Volume by Average End Area Method

Problem: A 100 m100\text{ m} segment of a highway requires excavation (cut). The cross-sectional area at station 10+0010+00 (A1A_1) is 45 m245\text{ m}^2. The cross-sectional area at station 11+0011+00 (A2A_2) is 65 m265\text{ m}^2. 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 10+5010+50 reveals the true mid-area AmA_m is 50 m250\text{ m}^2. 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 100 m100\text{ m} long. Station 1 has a top width w1=20 mw_1 = 20\text{ m} and a centerline height h1=4 mh_1 = 4\text{ m}. Station 2 has a top width w2=30 mw_2 = 30\text{ m} and a centerline height h2=6 mh_2 = 6\text{ m}. Calculate the Prismoidal Correction (CpC_p).
Solution:

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Mass Haul Diagram

Case Study 1: Balancing Cut and Fill

Scenario: A contractor is analyzing a 5 km5\text{ km} highway project. The initial section (00 to 1.5 km1.5\text{ km}) requires significant cut through a hill. The middle section (1.51.5 to 3 km3\text{ km}) crosses a valley requiring fill. The final section (33 to 5 km5\text{ km}) is mostly flat, requiring minor fill.
Analysis:
  • Mass Diagram Construction: The contractor plots accumulated volume. The curve rises from station 00 to a peak at 1.5 km1.5\text{ km} (indicating surplus excavation). From 1.5 km1.5\text{ km}, the curve falls until it crosses the horizontal zero axis at 3 km3\text{ km}.
  • Balance Point: The intersection of the curve with the zero axis at 3 km3\text{ km} means that all the material excavated from the hill (00 to 1.5 km1.5\text{ km}) is exactly enough to fill the valley (1.51.5 to 3 km3\text{ km}). No external soil needs to be imported or exported for this segment.
  • Borrow Pit Required: However, from 3 km3\text{ km} to 5 km5\text{ km}, 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 500 m500\text{ m}. For any material moved beyond this distance, the contractor is paid an overhaul rate of $$2.50percubicmeterstation(whereastationisper cubic meter-station (where a station is100\text$).
Analysis:
  • Diagram Review: The mass diagram shows a balance line drawn at a length of 800 m800\text{ m} (representing the total haul distance between the centers of mass of a cut and fill segment).
  • Freehaul vs Overhaul: The first 500 m500\text{ m} of the haul is free. The remaining distance is the overhaul distance: 800 m500 m=300 m800\text{ m} - 500\text{ m} = 300\text{ m}, which equals 33 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 10,000 m310,000\text{ m}^3.
  • 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 = $75,000$.