A RISK MANAGEMENT FRAMEWORK FOR GROUND HAZARDS ALONG CANADIAN NATIONAL RAILWAYS

Transcription

1 A RISK MANAGEMENT FRAMEWORK FOR GROUND HAZARDS ALONG CANADIAN NATIONAL RAILWAYS Tim Keegan, Sr. Geotechnical Engineer, Canadian National Railways, Edmonton, Canada Brian Abbott, Asst. Chief Engineer, Canadian National Railways, Edmonton, Canada Mario Ruel, Sr. Geotechnical Engineer, Canadian National Railways, Montreal, Canada Abstract: Ground hazards associated with rail grades, embankments and cut and natural slopes are a source of risk to railway operations. In 1996 Canadian National Railway (CN) made a strategic decision to adopt a systematic risk based methodology to manage these ground hazards. This paper describes CN s methodology within the framework of CAN/CSA , the accepted Canadian standard for risk management. A description is provided of the primary elements of the strategy including; the CN Rockfall Hazard and Risk Assessment (CNRHRA) system, the Beaver Activity Hazard Assessment (BAHA) system, the Earthquake Notification (EQNS) System, weather reporting systems, and GIS information management systems. 1 INTRODUCTION Historically, railway engineers have faced a unique challenge. Driven to minimize both gradient and horizontal curvature, they have been forced to strike alignments across significant stretches of geomorphically active ground. Ground hazards of concern to railways typically manifest themselves in the form of rockfalls, landslides and hydraulic erosion ( washouts ). Hazards may be triggered by events in the natural environment such as; rainfall, snowfall, ground freezing, movement of surface or ground water, weathering of earth materials and seismic events. The activities of humans and animals, most notably beavers, also play a significant role.

2 As much of the terrain traversed by railways is sparsely populated, resources available to mitigate associated hazards have always been limited. Clearly, there is a need for objective priority setting. A risk management process can provide the necessary framework for decision-makers. This paper provides an overview of the methodologies currently being developed and implemented by CN s geotechnical engineers to identify, analyze, evaluate, and control the risks associated with ground hazards along the railway. The Canadian Standards Association s Risk Management: Guidelines for Decision Makers, CAN/CSA Q (1) provides the framework for this discussion. Terminology and definitions utilized in this paper are consistent with those contained in CAN/CSA Q (1). 2 BACKGROUND In 1996, CN undertook an extensive review of its management of ground hazards. While CN s practices were shown to meet or exceed current railway state-of-practice, the review did identify a growing trend in other industries toward a more systematic risk based approach. In response to this review, a policy decision was made to adopt a risk management system for ground hazards. In 1998, CN s Grade and Slope Stabilization Engineering and Management Protocol was draughted. The protocol began the process of combining the various ground hazard risk management practices into one system. 3 METHODOLOGY The objective of risk management is to ensure that significant risks are identified and that appropriate action is taken to mitigate these risks. According to Head & Horn (2), risk management comprises the logical sequence of: identifying and analyzing loss exposures, examining alternative techniques for dealing with those exposures,

3 selecting the most promising techniques, implementing the chosen techniques, and monitoring the results to verify that the loss exposure has been dealt with most cost effectively. The Canadian Standards Association s Risk Management: Guideline for Decision-Makers, CAN/CSA-Q (1) provides a practical framework for the development of a risk management system. The risk management methodology is developed in an iterative process as illustrated in Figure 1. According to CAN/CSA-Q850-97, risk involves three key issues: the frequency of the loss, the consequence of the loss and the perception of the loss by the affected stakeholder. Figure 1 - Steps in the Q850 Risk Management Decision Making Process Simple Model (1) Note that understanding the perception of loss is deemed to be as important as the frequency or consequence thereof. This stresses the need for risk communication with the stakeholders at every

4 step of the risk management process. The term stakeholder in this context refers to individuals, groups, or organizations who are able to affect, who are affected by, or believe they may be affected by a decision or activity. In the railway s case, primary stakeholders include operating personnel whose duties bring them into proximity with ground hazards. 3.1 Initiation The Initiation step was accomplished when CN made the policy decision to proceed with a risk management process for ground hazards and adopted its Grade and Slope Stabilization Protocol. At that point: issues surrounding ground hazards had been identified, the risk management team was identified, a responsibility matrix was established, and the process of identifying and communicating with stakeholders had begun. 3.2 Preliminary Analysis The next step, Preliminary Analysis, involves the process for ground hazard identification, categorization and characterization. This is followed by the development of risk scenarios for each of the various ground hazard categories. CN currently employs a number of techniques to identify ground hazards: geotechnical field inspections, incident and condition reporting from operating personnel, air photo interpretation, rockslope inspections, and aerial reconnaissance of drainage conditions and anthroprogenic activity.

5 Advancements in remote sensing, analytical GIS, terrain/hazard/risk mapping techniques and other methods are expected to improve the railway s ability to identify ground hazards in the near future. An effective information management system is essential to the success of any risk management strategy. The system is required to maintain a ground hazard inventory and risk information library. Computer based relational databases and GIS applications are ideally suited to this purpose. CN is currently developing such a system to manage ground hazard information related to more than 2000 sites. Information for each identified hazard location includes: a description of the site conditions, the hazard type, the potential trigger conditions, a subjective assessment of the rate of failure, consequence of failure, the latest hazard or risk assessment, the latest priority, and the proposed. With the number and complexity of ground hazards affecting railways, it is necessary to break down the hazards into manageable categories as outlined in Figure 2. Ground hazards are categorized starting with a broad distinction between landslides and erosion. Under the category of landslides, hazards are further divided into the various materials and slope movement types as defined by Cruden and Varnes (3). Snow and ice classifications are included to cover snow avalanche hazards. A distinction is introduced in the earth material types to distinguish between non-cohesive and cohesive or organic soils. This division is made because of the significantly different trigger conditions and failure modes exhibited between these soil types. Because of their propensity for liquefaction, slope failures in saturated non-cohesive materials can present a greater risk to railway operations. The notable exception to this distinction for cohesive soils is the behaviour of high sensitive and quick clays. Under the category of hydraulic erosion a broad distinction is made between erosion resulting from seepage and surface flow. Again, this distinction is made because of the significantly different characteristic of the failures and contributing factors associated with these two mechanisms.

6 Railway Ground Hazard Identification Landslide Hazards Hydraulic Erosion Hazards Rock Debris Earth Snow & Ice Fall Topple Slide Fall Slide Flow Avalanche Seepage erosion Surface erosion Non-cohesive Cohesive and Organic Fall Slide Flow Spread Subsidence Slide Flow Spread Subsidence Figure 2 - Railway Ground Hazard Classification Once categorized, risk scenarios are developed for each hazard or series of hazards. A risk scenario is defined as a sequence of events with an associated frequency and consequence. In the case of the railway, risk scenarios typically involve a combination of one or more ground hazards (condition(s)) and one or more perils. Perils are events that trigger loss. They include; intense rain, floods, high stream flows, rapid snowmelts, rain on snowpack, elevated groundwater seepage, prolonged rainfall, freeze / thaw and seismic activity. i.e. Ground Hazard(s) Peril(s) Loss Loss exposures may include any of the following: personnel loss (illness, injury or fatality), property loss (equipment, commodities, track, roadbed, facilities etc.),

7 liability loss (arising from torts, statutes, and criminal law), environmental loss, and income loss (stemming from train service disruptions and loss of market share). A typical risk scenario might start with the loss of erodible material at the toe of slope due to river erosion (a hazard). This condition may continue resulting in the over-steepening of the overall slope raising the potential for the formation of an earth slide (a new hazard resulting from the river erosion). An intense rainstorm may hit the location (a peril) raising the water pressures in the slope and triggering an earth slide. This earth slide poses a risk to train traffic as the grade beneath the track may slip away and the train may derail resulting in consequent loss. 3.3 Risk Estimation At the Risk Estimation phase, engineers gauge both frequency of occurrence and consequences to screen out risk scenarios that represent the greatest loss exposure. For the railway, risk scenarios involving rockfalls, debris flows, earth slides in silt and fine sand, river erosion and hydraulic erosion attributable to beaver activity and rapid runoff have been identified as being most critical. The common denominators with these risk scenarios are that they occur frequently, without a long warning period and often have severe consequences. An estimate of the risk associated with a given scenario may be based on historical data, models, professional judgement or a combination of methods. Although ideally assessments of the probability and severity of loss are made quantitatively, practicality often dictates the use of qualitative assessments. Estimates of frequency may be based on historical data with the inherent assumption that future conditions will mirror those of the past. Alternatively, the assessor may be able to draw upon published data related to the frequency of the specific perils such as climatic or earthquake events.

8 Where no relevant historical data are available, methods such as fault-tree or event-tree analysis may be used to generate estimates. Consequence is normally measured in terms of the number of injuries, value of property damage, cleanup costs, business loss and environmental impact. Depending on the scenario, accumulated experience may offer some guidance. In the absence of sufficient data, expert judgment must be substituted. The risk estimator must also be aware that, while certain risk scenarios may indicate low risk at individual hazard sites, the aggregate risk to the rail corridor may be high if a series of hazard locations coupled with a high probability of a triggering peril are considered. This is particularly true when considering climatic and earthquake perils. The approach in these cases requires more sophisticated understanding of the peril(s) that triggers the loss. As rockfall and beaver related hazards are of particular concern to railway operations, CN has developed: CN Rockfall Hazard and Risk Assessment (CNRHRA) Abbott et al, (4) and (5) describe the methodology and its application in companion papers. CNRHRA can be described as an event tree analysis whereby the various risk scenarios stemming from rockfall hazards are assigned a subjective probability of derailing a train. Derailment hazard scores (DH) are generated as a relative measure of the total derailment potential attributable to a rockfall off a given slope. The frequency of rockfalls from the slope is estimated subjectively using a prescribed process relying mainly on site evidence. CNRHRA has been in use since 1997 and has become an integral tool for identification, prioritizing and monitoring CN s approximate 1500 rockslopes. In addition, ratings are utilized with the level of rockfall activity to guide rockslope inspection frequency.

9 3.3.2 Beaver Activity Hazard Assessment (BAHA) The BAHA methodology assesses the potential for beaver related activities to disrupt track serviceability by considering factors such as the volume of ponded water, dam condition, topography, and the ability of railway infrastructure to handle a sudden releasement from beaver dam failure. BAHA results, expressed in the form of a numeric rating, guide mitigative efforts that include dismantling hazardous beaver dams, removing nuisance beavers and installing devices to prevent reconstruction. The short-term objective of the system is to reduce risk exposure by effectively prioritizing work to control nuisance beaver activities. In the longer term, the objective is to achieve near 100% control of high-risk dams. 3.4 Risk Evaluation Risk Evaluation is the process by which risks are examined in terms of costs and benefits. Evaluation is aimed at determining whether a given level of risk is acceptable. Pre-determined risk resolution matrices such as that proposed in the Manual for the Development of System Safety Program Plans for Commuter Railroads, American Public Transit Association (6) and shown in Figure 3 may aid in the evaluation and communication of risk. Consideration of the needs and concerns of stakeholders is critical during this phase (1). To this end, CN conducts technical information sessions and town hall meetings to both familiarize operating personnel with issues affecting the integrity of the roadbed and provide an opportunity for feedback. Where resources are limited, the results of the Risk Evaluation phase provide the basis for the establishment of priorities. It is essential that priorities be set and communicated before advancing the process to the next step, Risk Control. CN completes its priority setting exercise in the form of a grade stabilization plan eight months in advance of the year in which the work is to be executed. This lead-time facilitates communication of

10 the plan with stakeholders. It also allows project managers to effectively design the mitigative works, procure regulatory approvals and solicit competitive tenders. Severity Probability Frequent (Likely to occur) Probable (Will occur several times in life of an item) Occasional (Likely to occur sometime in the life of an item) Remote Unlikely but possible to occur in life of item Improbable (So unlikely, it can be assumed occurrence may not be experienced) Catastrophic (Death or permanent total disability, major property damage, or system loss) Critical (Permanent partial disability, temporary total disability, significant property damage or major system damage) Marginal (Minor injury, lost workday accident, minor property damage, or minor system damage) Negligible (First aid or minor medical treatment, or minor system impairment) Unacceptable Unacceptable Unacceptable Unacceptable Unacceptable Unacceptable Tolerable Tolerable Tolerable Figure 3 Risk Resolution Matrix (6) 3.5 Risk Control Risk Control can be defined as any conscious action (or decision not to act) that reduces the frequency, severity, or unpredictability of accidental losses (7). The underlying objective is to reduce the total costs of risk control measures and losses. It involves identifying and evaluating risk control measures for each ground hazard risk scenario that warrants it based on risk levels assessed in earlier steps.

11 The preferred approach is to mitigate the loss exposure proactively. This is almost always the most cost effective when compared against potential derailments or unexpected service disruptions. The general proactive approach may involve, in order of preference: 1. reducing the hazard condition(s) through mitigative stabilization, 2. protecting the track against the hazard by erecting such things as flumes, rock & snow sheds, barriers or catchment nets, or 3. warning trains in the event a hazard is triggered. Warning systems are generally employed when the extent of the hazard practically precludes application of the former two approaches. Warning systems may either be targeted at the occurrence of a hazardous event (i.e. landslide or rockfall) or at the triggering peril (i.e. climatic or seismic event). In the latter case, the objective is to develop systems capable of maximizing both the length of the warning time and the accuracy of the warning. To that end, CN has developed sophisticated notification systems for earthquakes and weather Earthquake notification system (EQNS) More than 1,000 earthquakes are recorded in Canada each year. Since 1994, CN has been working with other railways to develop threshold criteria and appropriate protocols for the response to seismic events. Until recently, the major stumbling block to any response strategy was the lack of real time event notification. To address that issue, CN developed a custom link to the Geological Survey of Canada (GSC) s AUTOLOC system which comprises a network of 53 digital seismograph stations across Canada connected through data processing centres in Sidney, B.C. and Ottawa, Ontario. Earthquake notifications go directly to Rail Traffic Control (RTC) personnel responsible for controlling train movements. Not only does the system provide immediate information relative to the location and magnitude of seismic events, it is programmed to specify response actions commensurate with the earthquake s magnitude. In the case of significant events, train traffic is brought to reduced speeds or halted until the integrity of the corridor can be verified through field inspection.

12 3.5.2 Weather reporting Presently, CN contracts a weather forecasting service to provide operating personnel with customized forecasts together with near real time and antecedent weather reports. Information is disseminated through daily electronic messages. As well, a digital map is fed directly to CN s Network Operation Centre (NOC). Weather alerts and warnings issued by Environment Canada are brought to the immediate attention of the NOC and tracked using the digital map system. CN is collaborating with CP Rail in the development of a significantly enhanced weather reporting system. The contemplated enhancement would involve more refined processing of weather radar precipitation data to provide real time intensity and antecedent rainfall information on a much tighter grid of 1 to 2 kilometres. Using the antecedent rainfall in conjunction with soil moisture characteristics on an accumulative basis would provide an indication of the soil saturation and runoff potential in near real time and with high spatial resolution. Comparing the real time antecedent rainfall with historical data could provide an indication of the significance of the event. From that information, predetermined alert levels and action plans could be developed. 3.6 Action / Monitoring The final phase of the process, Action / Monitoring, comprises the implementation of and monitoring of program results. A comprehensive monitoring process is essential to evaluate the effectiveness of control measure effectiveness. CN uses the assessed risk level to determine monitoring frequency and methodology. Hazards with associated higher risk scenarios are given more attention. Although CN benefits from a relatively long history along its primary corridor, ground hazards are dynamic and new hazard sites can develop. Consequently, it is essential to maintain a system of incident and condition reporting to ensure that new sites are assessed in a timely manner. Finally, the monitoring system must close the loop by feeding information concerning changing hazard levels back into the risk management process starting with Preliminary Analysis.

13 4 CONCLUDING REMARK This paper shows that the Canadian Standards Association s Risk Management: Guidelines for Decision Makers, (1) can be effectively applied to the complex and dynamic risks associated with ground hazards along railways. 5 REFERENCES 1. Canadian Standards Association (1997). Risk management: Guidelines for decision makers, CAN/CSA-Q850-97, 1997., Canadian Standards Association, Etobicoke, Ontario, Canada. 2. Head, G.L. and Horn II, S.H Essentials of risk management, ARM 54, 3 rd Edition, Insurance Institute of America 3. Cruden, D.M., and Varnes, D.J Landslide types and processes, Landslides investigation and, Special report 247, Transportation Research Board, National Research Council, National Academy Press, Washington, D.C., Chapter 3: Abbott, B., Bruce, I., Keegan, T., Oboni, F., & Savigny, W. 1998a. A methodology for assessment of rockfall hazard and risk along linear transportation corridors, 8 th Congress of the International Association for Engineering Geology and the Environment, Vol. II: Abbott, B., Bruce, I., Keegan, T., Oboni, F., & Savigny, W. 1998b. Application of a new methodology for the management of rockfall risk along a railway, 8 th Congress of the International Association for Engineering Geology and the Environment, Vol. II: American Public Transit Association (1997). Manual for the Development of System Safety Program Plans for Commuter Railroads. 7. Head, G.L Essentials of risk control, ARM 55, 3 rd Edition, Insurance Institute of America