Techniques to Reduce the Environmental Impacts and Costs of Road Construction A Results Based Study

1. Techniques to Reduce the Environmental Impacts and Costs of Road Construction A Results Based Study

2. 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

3. Acknowledgements Skeena Cellulous West Fraser Timber FRBC and FII BC Ministry of Forests Robert Balshaw Silvicon Services Ltd Silvatech Consulting Ltd BGC Engineering Ltd

4. QUESTIONS • 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?

5. LOOKING BACKAT PAST RESULTS • Past road practises -- What did not work ? • Why? • What worked? • How can we build upon it?

6. STUDY DESIGN • Focused on road fillslope landslides • Existing roads constructed across slopes greater than 50% (based on TRIM mapping) • Past road construction and management techniques

7. HOW • Collect terrain and road attributes at sites where fillslope landslides occurred; and • Collect the same attributes at similar sites where landslides had not occurred. • Compare the data sets statistically • Determine what combinations of terrain and road construction attributes contribute to fillslope landslides; and by default • What combination of terrain and road construction attributes do not contribute to fillslope landslides

8. DATA COLLECTED INCLUDED • Existing topographic, road, bedrock and surficial geology data; • Interpreted information from aerial photographs; and • Field data

9. Terrain Attributes Slope (up and down) Surficial Material Aspect Drainage Bedrock Type Slope Profile (Shape) Etc. Road Attributes Fill Width Fill Slope Length & Angle Fill Type (R, SM, GP, etc) Ditch Condition Wood in fill Configuration of wood in fill Cracks in Road Deactivation? Etc. FIELD DATA INCLUDED

10. STUDY AREA STATISTICS Kalum Forest District • Coastal Western Hemlock Biogeoclimatic Zone • 158,000 hectares • 1079 km of forest roads • 196 km or 18% located on moderately steep to steep slopes (based on TRIM data) • Williams; West Copper; Kleanza; Legate-Chimdemash; and West Kalum

11. STUDY AREA Kalum Forest District

12. Road lengths

13. RESULTS OF STUDY • Field data collected at 40 landslide sites and 89 null site (non landslide sites) • Distribution of terrain slopes where data was collected is as follows:

14. Natural slope down

15. STATISTICAL ANALYSIS • Bivariate Analysis • Logistic Regression Model Statistical analysis conducted by Dr. Robert Balshaw, Ph.D.

18. Exploratory Classification Tree from Logistic Regression Model Natural Landslides No (113) Yes 2N/14L Concave or Convex 55N/6L Slope Profile Escarpment or Straight (52) <2.15 m (42) Perch Height >2.15 m 2N/8L Good or Acceptable 10N/0L Ditch Condition Poor or None (32) Rapid or Well 18N/7L Drainage Class Moderate or imperfect 2N/5L

19. Natural Instability

20. Slope profile

21. Perch height

22. Ditch condition

23. Drainage class

24. WHAT DID NOT WORK? Airphoto 60 Kleanza River

25. Although there can be many factors that give rise to landslide activity, there is only one trigger (Wieczorek, 1996). This means that although many factors may contribute to a landslide, only one factor causes the slope to fail.

26. Landslide triggers can be grouped into one of four categories: • Increased loading on the slope • Removal of material from the toe of the slope • Vibration loading (such as earth-quake or man-caused vibration) • Increased pore water pressure

27. Slide trigger

28. Blocked Seepage Creek flowing out of bedrock near original toe of fill

29. WHAT DID NOT WORK? Road Drainage Systems

30. WHY? • Inappropriate location of culverts • Inadequate number and in some cases size of culverts • Inadequate culverts maintenance • Lack of maintenance • Lack of deactivation • Concentration of surface and seepage water flows • Inadequate ditching and ditch maintenance • Inadequate control of seepage water

31. CAN THIS BE IMPROVED? YES 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.

32. HOWEVER Detailed assessments and planning of road drainage systems is typically limited to terrain class IV and V (potentially unstable and unstable terrain) and Drainage issues on moderate to gentle terrain and on non-status roads and trails continue to contribute to landslide activity downslope of these areas

33. THEREFORE: 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

34. WHAT DID WORK? • Over 80% of all sites (landslide and null site) incorporated wood material into the road construction • Statistically, there is a 70% probability that the simple presence or absence of wood in fill has no influence on fillslope landslide activity

35. Forest Roads: A Synthesis of Scientific Information “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:

36. Is this really an issue?

37. Wood in fill

38. Is this an Issue?

39. Cracks

40. Observation 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.

41. Failure Plane in C horizon soils not in fill Sample cross-section 1

42. Fillslope Stability Analysis • Parametric Study to look at: • Influence of location of perch fill • Height of perch fill • Influence of pore water pressures • Weight (density) of fill • Influence of soil matrix suction

43. Base Case Model Base Case Model

44. Comparative Model Used For Existing Fillslope Stability Upper slope perched Lower slope perched Mid slope perched

45. RESULTS OF LIMIT EQUILIBRIUM ANALYSES OF SLOPE STABILITYInfluence of the location of the perch fill and height of perch fill

46. Conclusion • Location of perch on slope has little influence on the stability for shallow fills • Location of perch on slope has greater influence on stability for deeper fills • Influence of water has an order of magnitude greater influence

47. Light Weight Fill Stability Model 115% fillslope angle

48. RESULTS OF LIMIT EQUILIBRIUM ANALYSES OF SLOPE STABILITYInfluence of Density of Fill on Slope Stability Bulk density of lightweight fill varied from about 15.5kN/m3 to 8.5kN/m3

49. Conclusion • Reducing the density of the fill has little influence on the stability of the slope

50. Base Case Model Base Case Model Used For Soil Suction Analysis