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Landslides and Road Deactivation
Landslides and Road Deactivation
Terry Rollerson, Mike Wise, Terry Rollerson, Mike Wise,
Denis Collins, Wilson Muir,Denis Collins, Wilson Muir,
Russ Wong, Tom MillardRuss Wong, Tom Millard
IntroductionIntroduction
We have seen a number of landslides We have seen a number of landslides associated with road deactivationassociated with road deactivation
We need to identify where this is occurringWe need to identify where this is occurring We need to prevent or minimize future We need to prevent or minimize future
occurrencesoccurrences
Topics of DiscussionTopics of Discussion
Study approachStudy approach Types of road deactivation landslidesTypes of road deactivation landslides Contributing factorsContributing factors PreventionPrevention Real Life ExamplesReal Life Examples ConclusionsConclusions
Study ApproachStudy Approach
Compilation of road deactivation landslide Compilation of road deactivation landslide occurrencesoccurrences
Site visits to a selected sample of the Site visits to a selected sample of the landslideslandslides
Compilation of data and analysis to Compilation of data and analysis to determine the most common relationships determine the most common relationships between road deactivation and landslidesbetween road deactivation and landslides
Landslide Inventory ApproachLandslide Inventory Approach
Document as many landslides as possibleDocument as many landslides as possible Visit a selected sample of landslidesVisit a selected sample of landslides Link landslides to terrain typesLink landslides to terrain types Link landslides to deactivation techniquesLink landslides to deactivation techniques Assess contributing factors where feasibleAssess contributing factors where feasible Assess likelihood of prevention or non-Assess likelihood of prevention or non-
preventionprevention
Landslide Data - “on-site”Landslide Data - “on-site”
type of deactivationtype of deactivation type of landslidetype of landslide slope positionslope position slope gradientslope gradient terrainterrain soil typesoil type slope morphologyslope morphology
down slope down slope environmental effectsenvironmental effects
contributing factorscontributing factors preventable / not preventable / not
preventablepreventable signs of incipient signs of incipient
failure (slumping, failure (slumping, tensions cracks)tensions cracks)
Types of road deactivation related landslidesTypes of road deactivation related landslides
Fill slope failures in areas of no deactivationFill slope failures in areas of no deactivation Failures below x-ditches (fill / native slope)Failures below x-ditches (fill / native slope) Failures in partial pull back - residual fillsFailures in partial pull back - residual fills Failures in partial pull back with x-ditchesFailures in partial pull back with x-ditches Failures in partial pull back at gulliesFailures in partial pull back at gullies Cut slope failure (all types of deactivation?)Cut slope failure (all types of deactivation?)
Contributing FactorsContributing Factors
Overloading of native slope by residual fillsOverloading of native slope by residual fills Oversteepening of fill materialsOversteepening of fill materials Concentration of water by ditch lines and x-Concentration of water by ditch lines and x-
ditchesditches Delivery of water from cut slope seepage Delivery of water from cut slope seepage
sites or gullies by x-ditches to residual fillssites or gullies by x-ditches to residual fills Loss of toe support (cuts in deep materials)Loss of toe support (cuts in deep materials)
PreventionPrevention
Deactivate the entire road systemDeactivate the entire road system Full pull back (reconturing) on slopes >60%Full pull back (reconturing) on slopes >60% Outsloping rather than x-ditching where Outsloping rather than x-ditching where
slopes below the road are >50% to avoid slopes below the road are >50% to avoid concentration of road drainageconcentration of road drainage
Trenching of x-ditches to native ground Trenching of x-ditches to native ground when draining seepage sites or surface when draining seepage sites or surface stream channels (remove all residual fill)stream channels (remove all residual fill)
Real Life - 1Real Life - 1
Situation:Situation: Lower roads deactivated but not the back end Lower roads deactivated but not the back end
Contributing factorsContributing factors Short-term planning / decisionsShort-term planning / decisions Oversteepening, overloading and drainageOversteepening, overloading and drainage
PreventionPrevention Proper planning / assessment and deactivation Proper planning / assessment and deactivation
from the back end outfrom the back end out
Real Life - 2Real Life - 2
Situation:Situation: Partial pull back Partial pull back
Contributing factorsContributing factors OversteepeningOversteepening OverloadingOverloading
PreventionPrevention Full pull back where safety is not compromisedFull pull back where safety is not compromised Blasting in isolated locations may be feasibleBlasting in isolated locations may be feasible
Real Life - 3 Real Life - 3
Situation:Situation: Partial pull back with x-ditches Partial pull back with x-ditches
Contributing factorsContributing factors Oversteepening and overloadingOversteepening and overloading Additional waterAdditional water
PreventionPrevention Full pull back where safety permitsFull pull back where safety permits Trench x-ditches to native ground Trench x-ditches to native ground
Real Life - 4Real Life - 4
Situation:Situation: X-ditches only, landslides on 50-60%+ slopes X-ditches only, landslides on 50-60%+ slopes
below roadsbelow roads Contributing factorsContributing factors
Excess water diverted onto slopeExcess water diverted onto slope PreventionPrevention
Outsloping or very very frequent x-ditchesOutsloping or very very frequent x-ditches Partial pull back &/or decompactionPartial pull back &/or decompaction
Real Life - 5Real Life - 5
Situation:Situation: Cut slope failure above partial pull backCut slope failure above partial pull back Same as with no deactivation - fairly rareSame as with no deactivation - fairly rare
Contributing factorsContributing factors loss of toe supportloss of toe support
PreventionPrevention Leveling top of partial pull backLeveling top of partial pull back In most cases not preventableIn most cases not preventable
Real Life - 6Real Life - 6
Full pull backFull pull back No landslides but may get minor sediment No landslides but may get minor sediment
redistributionredistribution
Lesson learned: The right technique in the right placeLesson learned: The right technique in the right place Always deactivate the back end, even if the Always deactivate the back end, even if the
costs seem highcosts seem high Full pull back on slopes > 60% (50%?)Full pull back on slopes > 60% (50%?) Trench to native ground at seepage sites and Trench to native ground at seepage sites and
surface drainage channels on slopes > 50%?surface drainage channels on slopes > 50%? Disperse water when slopes below > 50%Disperse water when slopes below > 50%
Next Steps Next Steps
If you feel the prescription is not right say so, If you feel the prescription is not right say so, or do moreor do more
If you see new landslides on or immediately If you see new landslides on or immediately below deactivated roads take a closer look, below deactivated roads take a closer look, let us knowlet us know
If you see slumping or tensions cracks on a If you see slumping or tensions cracks on a section of deactivated road, do the samesection of deactivated road, do the same
We will continue investigating these eventsWe will continue investigating these events
Contact us at:Contact us at:
Vancouver Forest Region Vancouver Forest Region 2100 Labieux Road 2100 Labieux Road Nanaimo, B.C. , V9T 6E9 Nanaimo, B.C. , V9T 6E9
fax - 250-751-7198 fax - 250-751-7198 e-mail: e-mail:
[email protected]@gems4.gov.bc.ca [email protected] [email protected]
Conceptual frequency plot of deactivation landslide typesConceptual frequency plot of deactivation landslide types
0
2
4
6
8
10
12
14
16
18
No deactivation
X-ditches
Partial pull back
Partial/x-ditch
Cut slope
Full pull back
Road / Slope GeometryRoad / Slope Geometry
Road deactivation landslide reportRoad deactivation landslide report
Location MapDeactivation type Date of slideYour name Fax/e-mailCompany/agency PhoneOptional:Initiation slope angle Surficial MaterialLength TerminusWidth Photos
