Transcript Landslides and Road Deactivation

Landslides and Road
Deactivation
Terry Rollerson, Mike Wise,
Denis Collins, Wilson Muir,
Russ Wong, Tom Millard
Introduction
We have seen a number of landslides
associated with road deactivation
 We need to identify where this is occurring
 We need to prevent or minimize future
occurrences
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Topics of Discussion
Study approach
 Types of road deactivation landslides
 Contributing factors
 Prevention
 Real Life Examples
 Conclusions
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Study Approach
Compilation of road deactivation landslide
occurrences
 Site visits to a selected sample of the
landslides
 Compilation of data and analysis to
determine the most common relationships
between road deactivation and landslides
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Landslide Inventory Approach
Document as many landslides as possible
 Visit a selected sample of landslides
 Link landslides to terrain types
 Link landslides to deactivation techniques
 Assess contributing factors where feasible
 Assess likelihood of prevention or nonprevention
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Landslide Data - “on-site”
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type of deactivation
type of landslide
slope position
slope gradient
terrain
soil type
slope morphology
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down slope
environmental effects
contributing factors
preventable / not
preventable
signs of incipient
failure (slumping,
tensions cracks)
Types of road deactivation
related landslides
Fill slope failures in areas of no deactivation
 Failures below x-ditches (fill / native slope)
 Failures in partial pull back - residual fills
 Failures in partial pull back with x-ditches
 Failures in partial pull back at gullies
 Cut slope failure (all types of deactivation?)
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Contributing Factors
Overloading of native slope by residual fills
 Oversteepening of fill materials
 Concentration of water by ditch lines and xditches
 Delivery of water from cut slope seepage
sites or gullies by x-ditches to residual fills
 Loss of toe support (cuts in deep materials)
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Prevention
Deactivate the entire road system
 Full pull back (reconturing) on slopes >60%
 Outsloping rather than x-ditching where
slopes below the road are >50% to avoid
concentration of road drainage
 Trenching of x-ditches to native ground
when draining seepage sites or surface
stream channels (remove all residual fill)
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Real Life - 1
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Situation:
 Lower
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roads deactivated but not the back end
Contributing factors
 Short-term
planning / decisions
 Oversteepening, overloading and drainage
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Prevention
 Proper
planning / assessment and deactivation
from the back end out
Real Life - 2
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Situation:
 Partial
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pull back
Contributing factors
 Oversteepening
 Overloading
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Prevention
 Full
pull back where safety is not compromised
 Blasting in isolated locations may be feasible
Real Life - 3
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Situation:
 Partial
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pull back with x-ditches
Contributing factors
 Oversteepening
and overloading
 Additional water
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Prevention
 Full
pull back where safety permits
 Trench x-ditches to native ground
Real Life - 4
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Situation:
 X-ditches
only, landslides on 50-60%+ slopes
below roads
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Contributing factors
 Excess
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water diverted onto slope
Prevention
 Outsloping
or very very frequent x-ditches
 Partial pull back &/or decompaction
Real Life - 5
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Situation:
 Cut
slope failure above partial pull back
 Same as with no deactivation - fairly rare
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Contributing factors
 loss
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of toe support
Prevention
 Leveling
top of partial pull back
 In most cases not preventable
Real Life - 6
Full pull back
 No landslides but may get minor sediment
redistribution
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Lesson learned: The right
technique in the right place
Always deactivate the back end, even if the
costs seem high
 Full pull back on slopes > 60% (50%?)
 Trench to native ground at seepage sites and
surface drainage channels on slopes > 50%?
 Disperse water when slopes below > 50%
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Next Steps
If you feel the prescription is not right say
so, or do more
 If you see new landslides on or immediately
below deactivated roads take a closer look,
let us know
 If you see slumping or tensions cracks on a
section of deactivated road, do the same
 We will continue investigating these events
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Contact us at:
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Vancouver Forest Region
 2100
Labieux Road
 Nanaimo, B.C. , V9T 6E9
fax - 250-751-7198
 e-mail:
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 [email protected]
 [email protected]
Conceptual frequency plot of
deactivation landslide types
18
16
14
12
10
8
6
4
2
0
No deactivation
X-ditches
Partial pull back
Partial/x-ditch
Cut slope
Full pull back
Road / Slope Geometry
Road deactivation landslide report
Location
Deactivation type
Your name
Company/agency
Optional:
Initiation slope angle
Length
Width
Map
Date of slide
Fax/e-mail
Phone
Surficial Material
Terminus
Photos