Techniques to Reduce the Environmental Impacts and Costs of Road Construction A Results Based Study. Other authors: Ron Neden, P.Eng. & Freeman Smith, P.Geo. of Terratech Consulting Ltd. James Schwab, R.P.F., P.Geo. Of B.C. Ministry of Forests. Acknowledgements. Skeena Cellulous
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Other authors: Road Construction Ron Neden, P.Eng. & Freeman Smith, P.Geo. of Terratech Consulting Ltd.James Schwab, R.P.F., P.Geo. Of B.C. Ministry of Forests
West Fraser Timber
FRBC and FII
BC Ministry of Forests
Silvicon Services Ltd
Silvatech Consulting Ltd
BGC Engineering Ltd
Terrain Attributes Road Construction
Slope (up and down)
Slope Profile (Shape)
Fill Slope Length & Angle
Fill Type (R, SM, GP, etc)
Wood in fill
Configuration of wood in fill
Cracks in Road
Etc.FIELD DATA INCLUDED
Kalum Forest District
Statistical analysis conducted by Dr. Robert Balshaw, Ph.D.
Concave or Convex 55N/6L
Escarpment or Straight (52)
<2.15 m (42)
>2.15 m 2N/8L
Good or Acceptable 10N/0L
Poor or None (32)
Rapid or Well 18N/7L
Moderate or imperfect 2N/5L
Airphoto 60 Kleanza River
This means that although many factors may contribute to a landslide, only one factor causes the slope to fail.
Creek flowing out of bedrock near original toe of fill
Road Drainage Systems
Existing legislation requires the maintenance of natural surface water flow paths. This has gone a long way to reducing the incidence of all landslide activity within the forest land base.
Detailed assessments and planning of road drainage systems is typically limited to terrain class IV and V (potentially unstable and unstable terrain)
Drainage issues on moderate to gentle terrain and on non-status roads and trails continue to contribute to landslide activity downslope of these areas
Detailed assessments of development related impacts on natural site drainage should be conducted upslope of all moderately steep to steep slopes or potentially unstable and unstable slopes
“Little is documented about the potential for increased mass failures from roads resulting from decay of buried organic material that has been incorporated into road fills or landings during road building. Anecdotal evidence is abundant that failures occur predictably after decay of the organic material.”Gucinski et al, (2001) states:
The failure plane of all the landslides noted in this study was either within the C horizon soils or along the bedrock surface.
No failure planes were noted within the fill materials
In other words, the native soils beneath the fill failed.
Failure Plane in C horizon soils not in fill categories:Sample cross-section 1
Base Case Model
Upper slope perched
Lower slope perched
Mid slope perched
115% fillslope angle
Bulk density of lightweight fill varied from about 15.5kN/m3 to 8.5kN/m3
Base Case Model Used For Soil Suction Analysis
The past use of wood in forest road can be considered as a reinforced soil structure as woody material was often included in the road fills
In some cases, the woody material was included as layers known as puncheon
Take a brief look back a millennium or more
Section of Great Wall of China built 200 B.C.
Currently, steel and plastics (geotextiles and geogrids) are most commonly used to constructed reinforced soil structures
Based on Assumed Site Conditions with very limited subsurface data
Horizontally Continuous Layers of wood reinforcement (puncheon)
Original ground surface
Well Compacted Mineral Soil Fill
Wood Reinforced Soil
FoS = 1.25 with out consideration for soil suction
Can the incidence of road fillslope landslides be reduced?
Can forest road construction practises be improved and/or economized?
Can both be done at the same time?
THE BEGINNING Steep to Steep Slopes