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 long highway cut.
The cross-sectional areas at each 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 apart (). The areas of the cross-sections are:
- Station :
- Station :
- Station :
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 ( at , at , and at ), calculate the total volume across the entire stretch as a single prismoid using the Prismoidal Formula.
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Problem 3: Prismoidal Correction () (Intermediate)
Example
The End-Area volume of a long earthwork segment () was calculated as .
The end sections are level sections (flat ground).
At Station 1, the center height () is and the top width () is .
At Station 2, the center height () is and the top width () is .
Calculate the Prismoidal Correction () 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 grid of squares, where each square measures by .
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: , ,
- Row 2: , ,
- Row 3: , ,
Calculate the total volume of earth excavated from the borrow pit.
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