Surficial Slope Instability and the Potential Contribution of Erosion Control Practice

Civil and Geotechnical Engineering design practice primarily considers general slope stability, with surficial slope stability addressed with less design rigour. Long term surficial slope stability is commonly accomplished with vegetation in the form of grass lined slopes, where detailing of same is accomplished by the slope stability engineer, a vegetation specialist or an erosion control practitioner.

When removing in-situ organic material pre-construction, there is common misconception that topsoil replaced post-construction must be equal to, or greater than the depth of the original topsoil. Little, if any attention is given to examining the vegetation establishment capacity of the civil grade. Common practice is to place topsoil on top of civil grade with typically insufficient detailing considering mechanical sloughing or organic leaching. With increased slopes, more compacted subgrades and less compacted topsoil, there comes increased likelihood of surficial slope instability.

This paper examines surficial slope instability where design detailing may be a contributing factor to long term surficial slope instability; where instability is found within days, months, years or even decades.

Further, this paper expands on the potential contribution of the erosion control industry where commonly delivered ‘Best Management Practices’ may contribute to surficial slope instability.
Evidence will be brought to support discussion around less topsoil and greater diligence in design detailing, to cause long-term sustainable root establishment in the civil grade for more robust grass liner protection of engineered infrastructure.