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Site Maximization: Creating Reinforced Steepened Slopes

Geotechnical Engineering

Reinforced Steepend Slopes Diagram

A steepened slope is an engineered system constructed of soil reinforced with horizontal layers of geosynthetics (geotextiles and/or geogrids).  The reinforcement allows the slope to be constructed at an angle much steeper (typically steeper than 2H:1V) than would be feasible using unreinforced soil.  Steepened slopes can be economical alternatives to retaining walls where there is room to accommodate a steep slope instead of a retaining wall.

Uses of steepened slopes:

  • Alternatives to retaining walls
  • Construction of new embankments
  • Widening of existing embankments
  • Repair of failed slopes
  • Steepened bridge abutments
  • Dam slope repair and retrofitting of dams
  • Avoiding encroachments on wetland areas and other restrictive boundaries

Steepened slopes can provide significant cost savings by:

  • Eliminating the expense of retaining wall facing elements
  • Facilitating the use of a wider quality (non-select) fill soils
  • Reducing the amount of borrow fill required compared to an unreinforced slope
  • Use of on-site materials instead of importing select soils

Steepened reinforced slopes should be designed by a geotechnical engineer familiar with the site conditions, soil types that will be used, and experienced in the design of geosynthetic reinforced steepened slopes.  Some of the considerations that should be evaluated in the design of steepened slopes include:

  • Desired geometry (based on restrictive boundaries or property lines)
  • Internal, external and compound slope stability analyses
  • Slope face reinforcement
  • Loading and performance requirements
  • Subsurface stratigraphy and groundwater
  • Engineering properties of the on-site soils and proposed imported borrow fill soils
  • Subsurface and surface water control

An economic analysis of a reinforced steepened slope versus a conventional flatter slope should consider:

  • Cut and/or fill quantities
  • Angle of slope
  • Cost of select versus non-select soils
  • Cost and availability of right-of-way, if applicable
  • Erosion protection
  • Aesthetics
  • Ability to maintain and/or repair the slope face

Finally, the following problems should be avoided in design and construction of reinforced steepened slopes:

  • Improper design parameters – sometimes designs are developed with assumed soil parameters which do not correspond to the on-site soils, or the proposed borrow soils
  • Inadequate subsurface and surficial drainage
  • Lack of global slope stability analyses
  • Insufficient compaction of the soils, especially near the slope face
  • Poor workmanship and/or use of wrong materials
  • Lack of construction monitoring and quality control
  • Insufficient vegetation which can lead to erosion and slope face instability

We hope that this “Lessons Learned” is helpful to you in your next project.

ECS Corporate Services, LLC