Stabilizing a Steep Driveway Slope with Riprap

A steep hillside beside a driveway (over 45°) eroding toward the pavement needs more than loose rock. Riprap (6–10″ diameter stone) alone will not hold on slopes steeper than 45°.

Proper Riprap Installation (≤45° Slopes)

1. Clear all vegetation; compact subgrade to match surrounding undisturbed soil density.
2. Excavate a keyway trench at the toe of the slope to anchor the stone.
3. Lay non-woven geotextile fabric on the compacted slope.
4. Place 6″ of sand or fine gravel over the fabric as a bedding layer.
5. Place riprap minimum 9″ thick (two stone layers).
6. Bury fabric edges at top and key into toe trench.
7. Install a drain at the slope base if water collects.
8. Plant shrubs at the crest to reduce surface runoff velocity.

If Slope Exceeds 45°

Riprap will slump. Options:

• Terrace with retaining walls (segmental block, stone, or timber).
• Soil nail wall with shotcrete facing.
• Engineered geogrid-reinforced slope.

Consult a geotechnical engineer or licensed landscape architect for slopes >45° adjacent to a driveway.