Assessment of Risks Involved
•Hazard, or Likelihood of Failure
•Consequences of Failure/Values at Risk
(Infrastructure and Environment)
Range of Management Options
•Do Nothing or Adapting to Slide
•Move Facilities, Protection Measures
•Stabilization Measures
Stabilization Measures
(What is adequate and cost-effective)
•Maintenance--Slide Removal
•Use of Vegetation, Drainage
•Slope Modification
•Gabions, Small Walls, Buttresses
•Reinforced Fills, Deep Patch Repairs
•Designed Retaining Structures
•Piles, Anchors, Soil Nails, Etc.
Use of Vegetation for Slide PreventionUse of Vegetation for Slide Prevention
and Slope Stabilizationand Slope Stabilization
SummarySummary
• Use commonly stable cut and fill slope angles
• For failures, assess why a site failed
• Find the least expensive, effective stabilization
measure
• Consider use of drainage and vegetation
• Use structures where necessary. Analyze and
design significant structures!
• Place structures on a solid foundation
Gordon Keller, PE, GEGordon Keller, PE, GE
Geotechnical EngineerGeotechnical Engineer
grkeller@fs.fed.usgrkeller@fs.fed.us
gordonrkeller@gmail.comgordonrkeller@gmail.com
Editor's Notes
Large earth movement
Potential solutions:
Do nothing, minimize road standard and live with slide too big to stabilize cost effectively
Lower grade
Abandon and relocate
Depending on the geology one could also consider a compound cut, a steeper cut in the more competent material (rock) and a flatter slope is the less competent (soil)
Suggested cutslope ratios
Rock buttress at toe on FHWA project on Tahoe National Forest
Erosion of cut slopes can be greatly mitigated by the use of vegetation, here using grass, works quite well on 3 meters (9 feet) or less near vertical cuts
Can also provide a wider catchment area w/o fencing
Missed a spring during construction, did not account for ground water. What are possible alternatives to resolve fill slope failures. The first, if you can, is to realign the road “shift the alignment” into the cutslope. Here the new centerline would be in the present ditch shifting the downhill edge of roadway off the failed material into stable material. The cutslope and alignment would have to be modified.
Last few noted about fills, dumping of waste
This earlier sliver fill photo
Small retaining wall. Posts driven into stable material a few feet, support the horizontal members. This project in Vicforests, Australia
Photo of timber facing and using geogrid as reinforcement and showing backfill material. Backfill can be native, need to design for the planned backfill material if it is dry enough to be properly compacted.
Here is a welded wire wall using the welded wire to “retain” the backfill but also used as the face of the wall
Using geogrids as the reinforcing mats
Gravity structure important to have firm foundation and base typically 70% of wall height
Or tires, this a tire faced wall again with geogrid reinforcing elements as tie-backs
Other fill-slope repair options
Soil nails 10 to 20’ in length shot into the surface, spaced 3 to 5’ centers
Typical retining wall problems: Nedd a firm foundation, especially gravity type structures
Inadequate foundation, here due to scour