🏔️ Embankment Volume Calculator

Trapezoidal Cross-Section Formula

An embankment cross-section is a trapezoid. The area formula is:

Area = ((Top Width + Bottom Width) / 2) × Height

Volume is then:

Volume = Area × Length

This assumes a constant cross-section along the full length. For variable sections, use the prismatoid formula or calculate average end areas.

Fill Factor (Shrinkage)

When you haul material from a borrow pit and compact it in an embankment, it takes up less volume than it did loose. This shrinkage ratio is called the fill factor or shrink factor. Common values:

• Clay: 1.15–1.25 (15–25% more loose material needed)
• Common earth: 1.10–1.20
• Gravel: 1.05–1.15
• Rock fill: 0.70–0.90 (rock actually swells in fill — you need less volume than you'd expect)

Typical Side Slopes

• 2:1 (2H:1V): Standard for road embankments in common earth
• 3:1: Required for embankments that will be seeded/vegetated; flatter is more stable and easier to maintain
• 1.5:1: Used with reinforced fill (geogrids, rock) or when right-of-way is limited
• 4:1 or flatter: Earth dams and levees — stability and seepage control requirements drive flat slopes

Compaction Requirements

Road embankments typically require 95–98% Standard Proctor (ASTM D698) or 95% Modified Proctor (ASTM D1557) in the upper zone. Embankment fill is placed in loose lifts — usually 200–300mm (8–12") — and compacted with a smooth drum or padfoot vibratory roller. Never exceed the maximum lift thickness specified in your geotechnical report.