DERAILMENTS DUE TO LANDSLIDES AND GEOTECHNICAL FAILURE IN CANADA'S RAILWAY SYSTEM

Canada’s railway system traverses a wide variety of terrains and encounters a range of geotechnical conditions. The interaction of these factors together with climatic, and less commonly, seismic forcing, may produce landslides and geotechnical failures that impact on the safety and efficiency of rail operations. The system generally dates from the latter part of the nineteenth or early twentieth century and was therefore constructed before the development of modern geotechnical engineering and engineering geology. Despite this, the system has been quite resilient and has undergone continuous upgrading. Major derailments have occurred, however, resulting in significant loss of life and substantial economic losses (viz. locomotives, rolling stock, track repairs, traffic interruption, and demurrage). The record of derailments related to landslides and geotechnical failure, including the forensic analysis of recent events, shows that they have occurred in four main settings; 1) the failure of fills, 2) the failure of rock cut slopes either by rockfall or rockslide, 3) impact on the track by a natural landslide originating outside the right of way, and 4) trackbed failure by landslide or subsidence due to piping in natural ground beneath it. A review of case histories shows that derailment events are frequently associated with unusual hydrometeorolgical conditions such as heavy sustained rains, torrential downpours, rapid thaws, or rain-on-snow events. They have also been attributable to the effects of animal (e.g., beaver dams) and human activity adjacent to the right-of-way (e.g., irrigation). Further, when the system has been subject to large earthquakes many geotechnical failures have resulted. Fill stability is particularly problematical because the method utilized in original fill construction did not generally involve modern compaction techniques. In addition, the cut-and-fill philosophy used in Canadian railway construction led to the fact that potentially unstable materials (e.g., low-plasticity silt) removed from cuts were used as material for adjacent fills. Mitigation efforts have centred on slope stabilization, avoidance of problem areas through tunneling, protection of the track through defensive structures, a variety of warning systems, maintenance crew education, and the development of slope hazard rating systems.