Angle of repose is the steepest angle at which a granular material can be piled without slumping under its own weight. Cut slopes and embankments designed steeper than this angle, without additional retention measures, are working against the material's natural stability rather than with it. This tool compares a proposed slope angle against typical repose angles for common soil and rock types.
Why This Matters for Cut and Fill Design
A slope surveyed and mapped via topography survey gives the exact existing angle, which is the starting point for any earthwork or embankment design decision. Designing a slope steeper than the material's angle of repose without retaining structures or soil stabilization measures invites slope failure, especially after rain saturates the material and reduces its internal friction.
| Material | Typical Angle of Repose | Notes |
|---|---|---|
| Soft clay (wet) | 20-25° | Highly sensitive to moisture, needs gentle slopes |
| Silty soil | 28-32° | Moderate stability, monitor after rainfall |
| Dry sand | 33-37° | Stable when dry, loses cohesion when saturated |
| Compacted fill | 35-40° | Depends heavily on compaction quality |
| Angular gravel/rock fill | 40-45° | Most stable of common fill materials |
What This Tool Does Not Replace
Angle of repose is a simplified stability indicator, not a full geotechnical slope stability analysis. Real slope design accounts for water table, seismic loading, soil cohesion beyond simple friction, and layered soil profiles. This tool is useful for a quick sanity check during early planning, before a proper construction survey and geotechnical investigation inform final design.
Cut slope on a construction site, the physical result of angle-of-repose decisions made at design stage.
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