Many retaining walls are designed with slopes above. Slopes above a wall are okay, but there are limits to the steepness of slopes that must be considered.
In static designs, the maximum unreinforced slope above any wall cannot exceed the friction angle of the soil used to reconstruct the slope.
In seismic designs, the maximum unreinforced slope above any wall cannot exceed the friction angle of the soil used to reconstruct the slope minus the seismic inertial angle. The seismic inertial angle is determined by the soils engineer for that specific project site.
If the desired slope above exceeds either of the two limits above, the designer must analyze the slope above in a global stability program and provide slope reinforcement as required.
For any wall having a slope above greater than 3:1, and/or any slope with poor soils or walls with seismic requirements, it is recommended that the designer call for the slope to be reconstructed with stabilizing geogrid layers. These layers typically match the standard grid lengths in the wall along with their spacing.
The soil within the slope must also follow proper lift and compaction parameters within the geotechnical recommendations. For more, see (ref. BP, Chapter 12.3-6)
Allan Block is working to achieve our industry initiative of Zero Wall Failures. With our Best Practices Manual and experience in the industry we are trying to expand the knowledge base for the design of segmental retaining walls (SRW's) by communicating and educating the professionals in the industry. To see the full Best Practices Manual, visit allanblock.com to download today and keep an eye out for more industry Best Practice recommendations here.