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Quan%ta%ve Risk Analysis of Linear Infrastructure from Geotechnical Proper%es to Societal Impacts (Analyse quan%ta%ve des risques des infrastructures linéaires allant de propriétés géotechniques aux impacts sociaux)
Heather Brooks, PE -‐ Ph.D. Candidate and Guy Doré, PhD, ing. -‐ Professor Genie Civil, L’Université Laval, Québec, Québec
References Baecher & Chris@an (2003). Reliability and Sta-s-cs in Geotechnical Engineering. Chichester, West Sussex, England: John Wiley & Sons, Inc.
Banerjee & DiPa (1991). Reliability Analysis of Thaw-‐Induced Pore Pressures, Journal of Cold Regions Engineering, 5(3), 125-‐141.
Public Safety Canada (2011). All Hazards Risk Assessment -‐ Methodology Guidelines.
Risk Analysis Process and Research Plan
Figure 1. Public Safety Canada Risk Evalua@on Process (Public Safety Canada, 2011)
Preliminary Event Tree Analysis for Embankments on Permafrost
Project Needs • Infrastructure in the North is supported by permafrost.
• Popula@ons and business interests are increasing in the North.
• Road, rail and airport infrastructure are significant travel and shipping methods.
• Climate change is adversely effec@ng permafrost.
• Public money is limited and must be spent wisely.
Project Objec%ves • Building an objec@ve tool to analyze risks to these infrastructures based on measurable data
-‐ Following the process outlined in Figure 1 and presented to the right in Risk Analysis and Research Plan
• Providing guidance to effec@vely use this tool in the infrastructure decision making process
2. Risk Event Descrip%on • Determine engineering calcula@on process for each node
• Determine inputs, outputs and defini@ons of failure for each node
• Example: thaw sePlement
-‐ calculate thaw depth (Modified Berggren Equa@on)
-‐ calculate thaw strain for soil (Thaw Consolida@on Theory or empirical data)
3. Risk Analysis • R = P x C
-‐ R = Risk
-‐ P = Probability/Likelihood of Failure
-‐ C = Consequence of Failure
• Qualita@ve -‐ P & C are scalar values from a ra@ng system
• Quan@ta@ve -‐ P & C are calculated from available data
• Calculated for each event tree node
Problems of Embankments on Permafrost
Subsurface Voids in the Embankment (Dempster Hwy)
Localized Thaw SeTlement (Dempster Hwy)
Thermal Erosion Induced Kars%ng (Alaska Hwy)
Subsurface Massive Ice -‐ Ice Wedge (Alaska Hwy)
Tension Cracking from Lateral Embankment Spreading (Alaska Hwy)
Thermal Erosion in a Drainage Ditch (Alaska Hwy)
Addi@onal problems include retrogressive thaw slumps, ac@ve layer detachment failures, and culvert problems.
1. Iden%fy the Risk Events • Iden@fy all possible failure modes of embankments on permafrost (photos to the leg)
• Map failure modes into an event tree (nodes)
5. Risk Treatment • Take ac@on on risks
-‐ Redesign or reconstruct high risk sec@ons
• Manage Infrastructure
-‐ Rank high risk areas
-‐ Allocate repair money
-‐ Design infrastructure inspec@on plan 4. Risk Evalua%on • Rank risk of each node of the event tree
• Map highest risks along the infrastructure
3b. Consequence Assessment • Economic -‐ Costs to communi@es & businesses
-‐ Direct -‐ Costs to repair, reconstruct or maintain the infrastructure
-‐ Indirect -‐ Costs businesses & communi@es due to infrastructure closure
• Environmental -‐ Poten@al impacts from failures
• Societal -‐ Poten@al impacts to people
-‐ Injuries & Fatali%es -‐ Direct impacts to people injured or killed from an infrastructure failure
-‐ Health & Safety -‐ Indirect impacts to people from failures; road closure requiring airligs of people to another hospital
3a. Likelihood Assessment • Uncertainty Defini%ons (Baecher & Chris@an, 2003)
-‐ Aleatory -‐ Random varia@on
-‐ Epistemic -‐ Sample & measurement bias; the difference between the engineering model & reality
• Determine the equa@ons for uncertainty for the analysis process at each node (Banerjee & DiPa, 1991)
-‐ Start at input uncertain@es
-‐ Build up uncertainty equa@ons at each level of the calcula@on process
• Calculate probability of failure for each node compared to a cri@cal value (defini@on of failure)
Acknowledgements Special thanks to Chantal Lemieux from Université Laval and Ouranous for allowing me to present my poster in English.