Case Studies: Earthwork Planning

Case Study 1: End-Area vs. Prismoidal Methods

Example

A contractor is estimating the volume of soil to be excavated for a 500 m500 \text{ m} long highway cut. The cross-sectional areas at each 20 m20 \text{ m} station vary significantly because the terrain goes from a flat plain into a sharp, irregular hillside.
The contractor's junior engineer calculated the total volume using the Average End-Area Method, but the senior engineer rejected the calculation and demanded they recalculate using the Prismoidal Formula.
Explain why the senior engineer rejected the Average End-Area Method for this specific terrain.

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Case Study 2: Shrinkage vs. Swell in Mass Haul Planning

Example

A highway contractor is excavating 10,000 cubic meters (bank volume) of dense, undisturbed clay from a cut section. They plan to use this exact volume to fill a 10,000 cubic meter depression (compacted volume) further down the road. The clay has a swell factor of 25% upon excavation and a shrinkage factor of 10% when heavily compacted compared to its original bank state.
Explain why this plan will fail, and calculate the actual volume of compacted fill the cut will produce.

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Solved Problems: Volume Computations

Problem 1: Average End-Area Method (Basic)

Example

A highway route has three consecutive cross-sections spaced 30 m30 \text{ m} apart (L=30 mL = 30 \text{ m}). The areas of the cross-sections are:
  • Station 10+00010+000: A1=45.5 m2A_1 = 45.5 \text{ m}^2
  • Station 10+03010+030: A2=60.2 m2A_2 = 60.2 \text{ m}^2
  • Station 10+06010+060: A3=85.0 m2A_3 = 85.0 \text{ m}^2
Calculate the total volume of earthwork between Station 10+000 and Station 10+060 using the Average End-Area method.

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Problem 2: Prismoidal Formula (Intermediate)

Example

Using the exact same data from Problem 1 (A1=45.5 m2A_1 = 45.5 \text{ m}^2 at 0 m0 \text{ m}, A2=60.2 m2A_2 = 60.2 \text{ m}^2 at 30 m30 \text{ m}, and A3=85.0 m2A_3 = 85.0 \text{ m}^2 at 60 m60 \text{ m}), calculate the total volume across the entire 60 m60 \text{ m} stretch as a single prismoid using the Prismoidal Formula.

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Problem 3: Prismoidal Correction (CpC_p) (Intermediate)

Example

The End-Area volume of a 20 m20 \text{ m} long earthwork segment (L=20 mL=20 \text{ m}) was calculated as 1200 m31200 \text{ m}^3. The end sections are level sections (flat ground). At Station 1, the center height (c1c_1) is 2.0 m2.0 \text{ m} and the top width (w1w_1) is 14.0 m14.0 \text{ m}. At Station 2, the center height (c2c_2) is 4.0 m4.0 \text{ m} and the top width (w2w_2) is 22.0 m22.0 \text{ m}.
Calculate the Prismoidal Correction (CpC_p) and use it to find the true (Prismoidal) volume.

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Problem 4: Borrow Pit Method (Advanced)

Example

A borrow pit is laid out as a 2×22 \times 2 grid of squares, where each square measures 15 m15 \text{ m} by 15 m15 \text{ m}. The grid has 3 rows and 3 columns of stakes (total 9 stakes). The depth of excavation (cut) at each stake in meters is given as follows:
  • Row 1: h1,1=1.2h_{1,1}=1.2, h1,2=1.5h_{1,2}=1.5, h1,3=1.8h_{1,3}=1.8
  • Row 2: h2,1=1.4h_{2,1}=1.4, h2,2=2.0h_{2,2}=2.0, h2,3=1.9h_{2,3}=1.9
  • Row 3: h3,1=1.1h_{3,1}=1.1, h3,2=1.6h_{3,2}=1.6, h3,3=1.3h_{3,3}=1.3
Calculate the total volume of earth excavated from the borrow pit.

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