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Railway Alignment and Track Criteria in Extreme Climatic Conditions Carolyn Fitzpatrick, Canarail, Montreal, Canada. Serge Bourdin, Systra, Paris, France. Introduction During the last two years the authors have had the challenging experience of designing railway alignment and track structure for two widely disparate climatic zones, presenting extreme environmental conditions which will have a significant impact on both the construction and maintenance of a viable railway line. In both cases the design has been required to handle the transportation of bulk minerals in the most cost effective manner possible; this demands track geometry, and a track structure, capable of handling the heavy axle loads and long trains that are essential for an efficient bulk-haul operation. At one end of the spectrum over two hundred and fifty kilometres of railway line has been designed to traverse the An Nufud, the second largest area of true desert in the Kingdom of Saudi Arabia. The design has had to contend with a large area of active dune development and, at certain times of the year, the periods of intense blowing sand. At the other extreme, over two hundred kilometres of potential railway line have been evaluated for the northwest of Canada’s Baffin Island, an area that lies between 400 - 600 km north of the Arctic Circle, a zone of continuous permafrost. Sand Behaviour in Dune Regions Highway construction through dune areas has allowed the Kingdom’s Ministry of Transportation to develop considerable expertise in the design of roads which minimizes the tendency for blowing sand to accumulate on roadways. Many of their geometric criteria for highways are designed to ensure a smooth air flow that does not slow the wind transported sand, and thus prevents its deposition. The mechanics of sand movement in the wind is a function of the grain size of the sand. In most “dune” fields the smaller, lighter grains of sand that are easily transported by the wind, are not significantly present, having been blown away many eons ago. The predominant sand movement is of medium sized grains in quite moderate winds. When the combination of grain size and wind velocity reaches a point that is known as the “fluid threshold” a grain of sand is lifted and carried in the direction of the wind. When the effects of gravity eventually result in the grain of sand falling back to earth, the force of its impact will often result in the grain bouncing back up into the wind or throwing other grains into the air, to be carried forward on the wind. Between 75% and 80% of the sand moving in dune areas has a diameter in the 0.1 mm to 0.5 mm range; grains with diameters of 0.15 mm or less are the most vulnerable to movement in the wind. Sand particles of a diameter greater than 0.5 mm make up the remaining 20% to 25% of the sand moving through dune areas. These grains are generally too heavy to be lifted by most winds but are pushed slowly forward by a combination of the effect of the wind and the impact of the smaller grains as they fall out of the wind. Further forward movement of the sand occurs when the sand accumulation at the crest of a dune exceeds the natural angle of repose of the sand and the crest falls down the leeward face of the dune under the effect of gravity. Even though these types of sand movement effect only the loose surface of the sand, that is usually no more than 3 cm deep, the effects cannot be taken lightly; depending upon grain size, a 30 km per hour wind is capable of moving a tonne of sand across a one metre line in a day and a half 1 or a 48 km per hour wind is capable of moving a tonne of sand across a one metre line in a half day2 1 Bagnold, R. A. 1941. The Physics of Blown Sand and Desert Dunes London, Chapman and Hall 2 Sharp, Robert P. 1963. Kelso Dunes, Mojave Desert, California. Geological Society of America Bulletin, Vol.77, No.10, pp. 1045-1073.

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An effective approach to the control of active dunes has been to stabilize the windward side of a dune by immobilizing the sand on its surface and thus preventing the slow forward movement of the crest of the dune in the direction of the wind. This effectively creates a sand trap on the leeward side of the dune, the crescent shape of the leeward side of the dune slowly fills with sand until a tear drop shaped, aerodynamically stable, dune has been created. During the period that the dune is building up to its final, stable, form it acts as a very effective sand trap and areas that are immediately down-wind of the dune are not subject to the deposition of wind blown sand; however once the final stable form of the dune has been reached, and even though the dune has been prevented from encroaching on a selected site, the site will ultimately be exposed to wind blown sand. Strip stabilisation can also be used to destabilize and lower or eliminate a dune formation when it is installed parallel to the prevailing wind. One of the original approaches to stabilizing the windward side of dunes was the application of blankets, or strips, of crude oil, crude oil blends and emulsified asphalts. These techniques have fallen out of favour on the basis of justifiable environmental concerns and stabilization is now undertaken with gravel blankets and the judicious installation of sand fences perpendicular to the predominant wind direction. Although very effective for stabilizing dunes, sand fences do need frequent maintenance since as each installation is buried by the sand it is trapping it needs to be increased in height. Whatever provisions are put into place to control or eliminate dunes, sand will still drop out of the wind and accumulate wherever wind velocities drop below the rate needed to keep the sand grains airborne and moving. Any irregularity in the ground profile, that interrupts the laminar flow of the wind, will be prone to the accumulation of sand. Hence much of the work of the designer is to create profiles that do not impede the flow of the wind over the new surfaces created by the project or to deliberately create areas, in none critical zones, that will encourage the deposition of sand. Typical dune formation with active crest

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Design Considerations for a Sandy Desert The Ministry of Transport of the Kingdom of Saudi Arabia has developed a set of criteria for highway design that focuses on the primary objective of not disturbing the laminar flow of the wind and thus encouraging the smooth flow of any windborne sand over and away from the highway. The paved highway presents a smoother surface to the wind than the desert floor; so there is a tendency for the wind speed to increase as it passes over the highway itself, thus helping to keep the road surface free of sand. Normal design procedures encourage this process by lifting the road surface above the desert floor and maintaining laminar air flow across the formation by using gentle side slopes on the elevated fill. The Ministry of Transport’s design criteria for highways in zones subject to blowing sand and active dunes recommends:

- Locating an alignment to the windward side of large dunes, - Aligning the project parallel to the predominant wind direction, - Maintaining grade lines above the elevation of upwind topography, - Avoiding cuts through upwind slopes, and - Controlling curvature so that super-elevation does not exceed 5%.

The Ministry also requires that: - Cut slopes shall be at 1:10 or flatter - Fill slopes shall be 6:1 or flatter when the height of the fill does not exceed 4 m., and - Depths of cut in active dunes shall not exceed 4m.

Both curve radius and gradient requirements for a railway are far more limiting than those for a highway, particularly when the alignment design needs to satisfy a heavy haul bulk transportation operation and the Government of Saudi Arabia’s requirement that the alignment should be suitable for a future 250 kilometre per hour passenger operation. In any given area active dunes tend to stabilize at a common elevation and the optimal position for limiting the effects of blowing sand is to be as close to the crest of the dunes as possible. When this is combined with the recommended side slopes and applied to a railway design, limited to a two kilometre wide predefined corridor, the results are unacceptably high earthwork volumes, which are dominated by the fill requirements between the dune formations. The project design team therefore developed criteria that provided an engineered solution to the control of earthwork volumes which also provided an adequate level of control for sand intrusion. Essentially criteria for cuts were developed that could be used to generating the significant volumes of material needed in the high fills between dunes. Since the materials produced are, to a large extent single sized cohesionless sands, techniques to confine the sand core with can outer shell, or blanket, of cohesive material were developed. These were approved by the Ministry of Transport.

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The overriding consideration in the design of the sub-grade has been to subject the railway track to as little sand encroachment as possible; however Mother Nature will not be so kind as to provide uniform and steady wind directions nor level surfaces and the sand control requirements will vary considerably from site to site. In addition, unlike a highway, railway track does not present a smooth surface to the prevailing wind; the presence of the rail itself will act as a barrier and result in some sand dropping out of the wind. In areas where the general topography and natural obstructions result in the wind regularly carrying sand onto and over the track the railway design anticipates a regular maintenance operation to manage ditch and dyke type sand traps along the right-of-way in critical areas, such as has already been successfully implemented by the Saudi railway organisation on its existing lines. Consideration is also being given to leaving a clear space beneath the rail by not completely filling the cribs and allowing the wind to keep the sand moving over the surface of the track. To some extent the passage of long and relatively fast (80kph) trains will tend to blow the finer grained sand away from the rails when it has accumulated there, however techniques to minimise the tendency of sand infiltration into the ballast are presently being examined. These include; a ballast gradation that specifically includes a larger portion of the smaller particle sizes than normal; a top dressing of ballast that is entirely composed of smaller particle sizes, and; the use of a proprietary product that anchors the surface of the ballast, closing its pores to small particles but does not affect the ballast’s natural elasticity and holding power. At the outset of the project, concern was expressed over the range of the daily temperature variation in the desert region and the possible effects this may have on; the potential for track buckling; and a reduction of the service life of the fasteners. A five year temperature record taken in a part of the desert close to the proposed railway shows an absolute temperature range of 51ºC which is less than that experienced on many railways around the world. The maximum temperature range recorded in any one 24 hour period is less than 23ºC which is very similar to that experienced by many North American railways during parts of the spring and fall. The Phenomena of Permafrost Railroads have been constructed in permafrost regions for more than 100 years. As early as 1895, the Russians started building the first Trans-Siberian Railway, in total this was 9,446 km long, 2,200 km of which was over permafrost. In the late 1970s the Russians initiated another project to construct the 3,500 km BAM Railway in Siberia of which 2,500 km is on permafrost. The 756 km Alaska Railway, in the United States, was built in 1904 with 384 km in a region of permafrost. In Canada, five railways have been built in areas with permafrost; the earliest was the Hudson Bay Railway (Omnitrax) which was completed in 1910. Approximately 611 km of the 820 km route was over permafrost. In China, several railways run through permafrost areas. The new Golmud-Lhasa section of the Qinghai-Tibet Railway will be 1,142 km long; 1,110 km are under construction; and 550 km cross areas of continuous permafrost and 52 km of discontinuous permafrost. This construction started in Golmud (Qinghai Province, China) in June 2001 and will take six years to reach Lhasa, Tibet. A large research program with the objective of defining the best construction techniques for regions with permafrost has been carried out. Both experimental and numerical approaches have been used and Canarail has been fortunate to be able to review some of the available literature as part of the process of developing recommendations for applicable construction techniques. A fundamental aspect of dealing with permafrost is to understand that not all permafrost is the same nor does it behave in the same way. Different soil types also behave differently when subjected to permafrost. Other than being continuous or discontinuous, which is self explanatory, permafrost is generally divided into two principle categories:

- Cold permafrost, here the temperature remains below -1° C, and the permafrost tolerates the introduction of considerable heat without thawing, and

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- Warm permafrost, here the temperature remains just below 0° C and the addition of very little additional heat may induce thawing.

Soil or ground types that are important to identify and differentiate between are:

- Thaw-stable, here the permafrost is in bedrock; well drained, coarse-grained sediments such as glacial outwash gravel, and many sand and gravel mixtures. When the permafrost thaws any consequent subsidence or settlement is minor and foundations remain essentially sound.

- Thaw-unstable, here the permafrost is in poorly drained, fine grained soils, especially silts and clays, which generally contain large amounts of ice. The result of thawing can be loss of strength; excessive settlement; and soil containing so much moisture that it flows.

- Ice-rich soil which has 20% to 50% of visible ice. The mean annual air temperature (MAAT) is a commonly used measure of both climatic conditions and climate change. The MAAT of the Tibetan Plateau (4,000 m above sea level) where the Qinghai-Tibet Railway runs, is around - 4.2ºC to - 5.2ºC depending on the exact location, whereas the MAAT in Baffin Island is -17ºC with a summer mean of - 1.5º and a winter mean of - 31ºC. The Mean Annual Ground Temperature (MAGT) of the Tibetan Plateau varies between 0.9ºC to - 1.6 ºC with a permafrost table from 1.9 to 2.5 m below the ground surface. The MAGT in Iqaluit varies from - 9.9ºC to - 7ºC with a depth to the permafrost table of 5 m (measured between 1988 and 1999). Typical Baffin Island Topography

Baffin’s lower temperatures result in permafrost that is typified as continuous and “cold”. In many respects this may well prove to be advantageous since most railways that currently operate through areas of permafrost report that their greatest problems occur during the spring “thaw” in zones of transition between continuous and discontinuous permafrost and between “cold” and “warm” permafrost. However the premise that a railway on Baffin Island will not have to cope with transition zones is probably a little

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over-optimistic since the presence of large bodies of water can produce interesting effects, not least of which are Taliks. A Talik is a body of unfrozen ground which occurs in a permafrost area due to local anomalies in thermal, hydrological, hydrogeological, or hydrochemical conditions. Several large bodies of water and more than one sizeable river are found close enough to the potential railway alignment that the presence of Taliks, and their possible association with areas of “warm” permafrost is anticipated. A serious area of concern in this environment is that of global warming; permafrost is particularly sensitive to climate change and global warming has generally more impact in Arctic areas and other cold regions than other places. The response of Taliks, and the areas immediately surrounding them, to climate change will be an important input factor to the construction criteria through these sensitive areas. The most frequently used method of construct on permafrost (often called “build and maintain”) is to build a structurally adequate, but thermally inadequate, embankment. Designers simply accept that excessive embankment movements are going to occur and accept that maintenance and rehabilitation will be required when these movements do occur. This approach is both acceptable and economic for most road construction, but the acceptable limits of deviation for railway geometric standards are quite narrow in comparison with those of roads, and railway embankment movements must be kept as small as possible to permit the retention of the necessary geometry. The natural thermal state and underground ice conditions are the most important factors influencing roadbed stability in regions with permafrost. When the principle design objective is to ensure embankment stability, the fundamental engineering principle is to choose a roadbed structure, appropriate to the local ground conditions, which will not trigger a degradation of the permafrost. Design Considerations for an Arctic Desert Several different design and construction approaches have been developed, to a large extent these methods either attempt to prevent heat absorption into the embankment or generate cooling effects to offset the effects of heat absorption. Some of the most widely used and/or studied measures are:

- protection of side slopes with crushed rock to reduce the heat absorption; - increase of ventilation through the embankment by using coarsely crushed rock in the

embankment; - embedding heat pipe into the embankment; - reduction of the heat absorbed by the embankment by shading it with awnings; - reduction of the flow of absorbed heat through the embankment with a thermal-insulation barrier; - increase of ventilation through the embankment using ventilation duct s installed through the

embankment; - increase of the insulating effect of the embankment itself by raising and widening it.

The effectiveness of these measures depends on the type of permafrost: “warm” permafrost or “cold” permafrost. For example, insulating material acting as a thermal barrier in the embankment, can reduce the amplitude of annual ground temperature variations, which delays the thawing of the permafrost because the insulating material absorbs more heat than it releases. The use of insulating materials in cold permafrost areas seems effective to a certain degree, but its long-term effectiveness is reduced in “warm” permafrost areas. Proactive designs to limit cooling down is necessary in “warm” permafrost areas, but in “cold” permafrost areas passive methods are more likely to be both sufficient and long-term efficient. In “cold” permafrost areas, the method most commonly used to protect embankments from settlement is to use a gravel fill layer that is thick enough to contain the active layer. When the Mean Annual Ground Temperature is around the freezing point, i.e. in “warm” permafrost, this becomes uneconomical because the thickness of gravel required to keep the soil frozen is too large. The study of the techniques used to encourage or maintain the cooling of the roadbed in the permafrost region of the Qinghai-Tibet Plateau has shown that the behaviour and the deformation of the embankment may vary between the side of the embankment that faces the sun and the side that remains

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in the shade. This differential behaviour has to be considered in the embankment design if good track alignment is to be maintained. The overriding factor for construction in this region is the protection of the integrity of the permafrost layer. Many of the construction techniques that have been developed for the roads of the far north focus on the successful dissipation of the heat accumulating in the “blacktop” of the road surface from solar gain, fortunately this effect is far less pronounced on railway track and techniques that are more specifically suitable to railway construction were identified. A major objective was to identify those techniques that had the potential to reduce the impact of the spring “thaw” that railways, such as the Hudson Bay line to Churchill, regularly have to contend with in transition zones between continuous and discontinuous permafrost and thaw-stable and thaw-unstable soils. Experience with road construction in the far north of Quebec, facing Baffin Island, is that a deep fill of crushed rock or gravel is usually sufficient to prevent the thaw of permafrost. Based on the knowledge that the region in question was generally typified as a “cold” permafrost region the base assumption, used for the development of pre feasibility costs, was that the common approach of blanketing the active layer with a sufficiently large embankment would be adequate in zones that were not excessively “thaw unstable”. The required thickness of the protective layer depends on the thickness of the active layer, the type of material available for the protection layer and the air and ground temperatures (MAAT and MAGT), and consequently varies along the longitudinal axis of the line. At the prefeasibility stage sufficient data on the field conditions was not available to fully define the technical characteristics of the protective layer and the assumption was made that on average the protective layer would be:

- 3 m thick with an average width of 20 m at the toe of slope; and - constructed form locally available gravel or crushed rock .

Smaller sizes of crushed rock (50-80 mm for example) has better heat shield qualities in warm seasons, whereas bigger sizes have better cooling effects in the cold seasons. The cold winter temperatures combined with the use of small sized crushed stones or gravel will, to a large extent, eliminate the need for the active cooling of the embankment.

Consideration was given to the possibility that some specific areas will require particular methods to counteract permafrost thaw (proactive design), including sunny side slope protection with crushed stone, and air ducts. In addition, and knowing that reaching a stable thermal state is a quite long process, it has been assumed that the protective layer would be installed during the winter, since this appears to be the best constructing method to maintain the soil mass under crushed rock embankments in a frozen state. The materials needed to complete the embankment to its design height could conceivably be added in the next year, and allow track laying to be completed in the same year. These assumptions have allowed the development of prefeasibility level construction costs but in the next phase, it will be essential to study the temperature ranges, soil conditions, depth of active permafrost

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layer and the potential for the development of Taliks in the areas considered for the railway alignment. It will also be important to check the forecasted temperature increase on Baffin Island. Permafrost is sensitive to climate change and global warming has generally more impact in Arctic areas or in cold regions than in other places. Given the usual long term useful life that is predicted for railways it will also be important to assess the selected methods for their continuing ability to maintain the stability of the roadbed under climate change. Evidently the major concern at this stage of the project has been to identify construction techniques that will ensure a stable, all -season roadbed, however investigations into local geology and climate has indicated that there will be few problems relating to the track itself. Locally available rock presents good characteristics for the production of ballast and experience with timber in the relative dry and cold climate indicates the potential for a long service life for timber ties. Other materials for ties will be investigated during the next stages of the project, but more in view of potential savings in the cost of transportation of materials than in improving potential service life. One potential problem that will be the subject of some intensive investigation and research is the potential effects of the wide temperature range that is experienced over the year . In a 50 year data record an extreme maximum of 34ºC and an extreme minimum of -50.6ºC has been recorded in the area concerned. However it is evident from the records that the higher temperatures are usually not of a particularly long duration, nevertheless it is going to be crucial that an appropriate rail laying temperature is defined and that precautions are included in the final track design to prevent track buckling and rail pull-aparts. Conclusion During the progress of both these projects design approaches were developed that built upon the experience of modern highway construction and the operating experience of existing railways in similar zones to develop appropriate railway construction criteria. The result has been designs that should reduce, or even eliminate, some of the railway maintenance and operational problems that are presently considered fundamental to those zones. In Saudi Arabia the final definition of the preferred techniques for the control of sand on, and in, the track will wait for a better understanding of the “local” effects on wind patterns and sand behaviour in the deep cuts. Similarly on Baffin Island an intensive investigation of the permafrost conditions in the selected rail corridor will be undertaken before the final design for construction is embarked upon. However, in both cases possible approaches have been defined as have the possibilities for specific testing.