Japan is situated in one of the most activecrustal zones in the world. The country’sextremely diverse topography andgeology combine to create generallyunstable conditions, including frequentearthquakes. The weather, too, can beunmerciful, bringing heavy rain and snow.It is not surprising that a wide variety ofnatural disasters strike different parts ofJapan each year.The nationwide rail network needsprotection from natural disasters. Thisarticle looks at efforts taken by Japaneserailways, and research conducted by theRailway Technical Research Institute(RTRI), to prevent damage caused byheavy rain and snow, gale-force winds,major earthquakes and other naturaldisasters.
Geology and Weather—Formidable Forces
The earth’s crust is divided into more than10 plates of different sizes. The plates risefrom submarine ridges, move laterally ata speed of 1 to 10 cm per year, then sinkinto oceanic trenches. The Japanesearchipelago is located along severalplate boundaries. As Figure 1 shows, theJapanese islands are subjected totremendous stresses caused by thecollision of four massive plates.The archipelago’s configuration wasdetermined by these forces. Violentupthrusts throughout the entire island chainduring the Quaternary period, about 2million years ago, produced topographicalfeatures with generally steep gradients, andgeological formations of faulted, weak rockthat extends far below the surface. Japanis still subject to great crustal stresses todayas the many active volcanoes and frequent
earthquakes indicate. As a result, Japan’sgeological makeup is quite different fromthat of many continental areas where strataoften date back to pre-Mesozoic times andthe land is relatively stable.Rain and snowfall are heavy in Japanbecause it stretches from the monsoonclimate zone to the sub-arctic. Meanannual precipitation (total rainfall andsnowfall) is about 1700 mm, or twice thatof much of Europe and the USA. Andbecause Japan’s landmass is elongatedand narrow, with steep mountain ranges,there is a relatively high tendency—fourtimes greater than in Europe and theUSA—for rain and meltwater to washaway the ground. Weathering and erosionresult in extensive surface degradation,causing frequent landslides and otherdisastrous events.
Natural Disasters and TheirImpact on Railways
Figure 2 shows the number of times since1966 that natural disasters (not includingearthquakes) have damaged railway tracksin Japan. About 30 years ago, there wereabout 8000 incidents annually. But thisfigure has declined substantially sincethen, to stand at about 1000 incidentsnow.Figure 3 shows a breakdown of differentnatural forces that have interrupted trainoperations over the last 10 years. Flooddamage caused by typhoons andlocal ized downpours occupies aprominent position, followed by stormand snow damage.Steps to mitigate the effects of naturaldisasters have helped reduce the numberof times railway operations have beeninterrupted, but natural forces still causederailments and accidents that kill andinjure passengers each year, so furthermeasures are required.
Railway Technology Today 10 (Edited by Kanji Wako)
Minimizing the Effect of Natural Disasters Tatsuo Noguchi and Toshishige Fujii
Eurasianplate
Okhotskplate
Kuriltrench
Pacificplate
Japantrench
Izu-Ogasawaratrench
Philippinesea plate
Ryukyutrench
Nankai trough
Figure 1 Japan’s Proximity to Four Tectonic Plates and Plate Movement
To limit the impact of natural disasters onrailway operations, we need to be able topredict time, location, and type. But weare dealing with natural phenomena thatare extremely hard to predict accurately,even with today’s advanced technology.So Japanese railways have concentratedtheir efforts on achieving safety anduninterrupted operations by combiningthe following three types of measures:
• Strengthening infrastructureand installing protection devicesRailways try to mitigate the forces ofnature and prevent track damage in anumber of ways, part icular ly bystrengthening infrastructure. Tracks forshinkansen and other lines laid in therelatively recent past are generallydesigned to withstand the forces of nature.However, most conventional lines werebuilt decades ago and have many sectionsthat cannot withstand natural forces.
Figure 4 Typical Train Operation Controls
1000
10
20
30
40
50
60
70
80
200 300 400 500
Accumulated rainfall R (mm)
Ho
url
y ra
infa
ll r
(m
m/h
)
Operation suspendedSpeed regulatedPast records of disasters
These sections are being reinforcedgradually.Typical measures, discussed later in moredetail, include slope protection, erectionof avalanche fences and wind barriers, andseismic reinforcement of infrastructure.These measures are the most effectivepossible but would be prohibitivelyexpensive if applied to every section ofevery track, explaining why priority is givento track sections that are at most risk ofnatural disasters.
• Train operation controlsWhen natural forces are strong enough toindicate the possibility of damage to trackor trains, trains are run at slower speedsor operations are suspended. Indicesindicating accumulated rainfall (absoluterainfall) and hourly rainfall (rainfallintensity) are generally used to expressboth of these factors in combination.Figure 4 gives an example of trainoperation controls applied to reduce therisks associated with rain. Rainfallamounts and indices indicating reducedspeeds and interrupted service are shown.Rising river indices are based on actualwater levels, wind indices are based oninstantaneous wind speed, and seismicindices are based on the seismic motionat ground level. The important questionregarding these train operation controlsremains; how to determine the values thatgovern operations? In actual practice,they are determined through experience,taking into account data from previousdisasters.
• Disaster detectionIf natural forces create conditions that couldinterfere with train operations, systems canquickly detect these conditions to stop thetrain and prevent damage. For example,devices are installed to detect rock falls andavalanches, and the Urgent EarthquakeDetection and Alarm System (UrEDAS) hasbeen developed. Both are discussed below.In some cases, one can detect signs that
warn of future trouble—for example, apartial land slippage or changes inunderground water level can indicate animminent landslide. We can use measuringdevices to predict and detect such anoccurrence. But the installation of suchdev ices and measurements andobservations require significant manpowerand expense, so these devices are installedonly in a limited number of locations.
Safeguarding Trains fromHeavy Rainfall
Heavy rain can seriously disrupt railservices. Rainwater can flood tracks,wash away ballast and collapse slopes(e.g. embankment slopes, cut slopes, andnatural slopes). Flooding rivers can scourbridge and revetment foundations. Rockfalls are another serious problemencountered on slopes, although theydo not necessarily occur during heavyrainstorms.Various preventive structures are installedalong the track to prevent these problems(Fig. 5). Such structures are often the most
effective, but, as previously mentioned,they require huge expense. Anotherreason why they are not the answer toevery problem is that they are not disaster-proof if the natural force is stronger thanthe design force. This means that we mustalso use train operation controls and,where necessary, detection devices evenafter erection of protective structures.Slope failure is the most common problemassociated with heavy rainfall, so measuresto prevent rain damage begin by preventingslope failure. However, before decidingwhich preventive measure would be mosteffective, we must first evaluate how muchrainfall will trigger a slope collapse.Preventive structures and train operationcontrols will be effective countermeasuresto heavy rainfall only if we can make sucha prediction with a high degree ofexactitude.To increase prediction accuracy, RTRIrecently devised a new risk estimationmethod for slope failure during heavyrainfall. Risk estimations are made forthree types of slope failure: embankmentcollapse, surface collapse on cuttings, and
Figure 5 Major Structures to Prevent Damage by Landslides and Flooding
Cut slope protectionRock catch wall
Rock catch fenceRestraining piles
Rock catch net
Rock shed
Embankment slope protection
Anti-scour protection
Figure 6 Critical Rainfall Curve
1000
10
20
30
40
50
200 300 400
Accumulated rainfall R (mm)
Ho
url
y ra
infa
ll r
(m
m/h
)
Area of probability ofslope failure occurrence
Deep collapse
Safe area
Embankment collapse
Surface collapse
Current operationcontrol threshold
deep collapse on cuttings. The estimatedslope failure risk value is expressed usingthe term ‘critical rainfall’.Figure 6, which indicates both hourly andaccumulated rainfall, plots sample resultsobtained through this risk estimationmethod. The critical rainfall curveindicates withstanding force, with thehighest withstanding force in the upperright of the figure. When the actual rainfallis more than the values plotted on thecurve, the risk of collapse is great. Thisrisk estimation method has already beenadopted by the JR group of companies,which are now using it to estimate slopefailure risks.The extent to which a soil slope collapsesis closely related to the amount of rain,but this is not necessarily the case withfalling rocks, which may fall even duringfine weather. Train operation controls aretherefore not very effective in preventingdamage caused by fal l ing rocks.Protective barriers and detection devicesare more effective. Such devices consistof cables laid near track areas where thereis a risk of falling rocks. When a cable issevered by a falling rock, an alarm isactivated and the train is stopped.
Safeguarding Trains fromHeavy Snowfall
Snow can seriously interfere with trainoperations. Trains may be stopped by snowaccumulating on the tracks and turnouts,or by drifting snow or avalanches.Avalanches and snow drifts can derail atrain, snow can damage rolling stock, snowadhering to rolling stock may fall off whilethe train is in motion and cause an accident,and railway structures may collapse underthe weight of snow.A number of structures can be erected toprevent these and other problems (Fig. 7).The snow can also be removed before itbecomes a serious nuisance using rotarysnowplows or Russel (pushing) snowplows.In addition, winter schedules can be
56 Japan Railway & Transport Review 23 • March 2000
devised to permit the alternate use ofsnowplows and trains on the same track.Train operat ion controls can beimplemented on a phased basis, dependingon the amount of snow on the tracks andsnow removal conditions.Avalanche risk is evaluated from the airusing helicopters, and on the ground duringpatrols. When an avalanche is anticipated,especially during the snowmelt season,special surveillance measures are taken toprotect rail operations. A different problemis seen in tunnels—freezing of leakingwater. To prevent this, structures equippedwith thermal insulators are being developedand installed.The following measures are taken toprotect shinkansen from snow damage. Inthe case of the Tokaido Shinkansen line,sprinklers spray water on ballasted trackduring snowfalls. This makes snow wet,otherwise it would fly up when trainsspeed by, and prevents snow fromadhering to rolling stock.The Tohoku and Joetsu shinkansen lines runthrough areas subject to greater snowfalls.Ballasted track sections are shorter there,and rolling stock is designed to inhibit snowadherence. Viaducts on the TohokuShinkansen line have been constructed towithstand snow depth equivalent to theannual return in a 10-year period. On theJoetsu Shinkansen line, water sprinklersmelt snow on track sections in the plainsand on long, tunnel-free sections inmountainous areas. Snow sheds and snowshelters have been constructed over shortersections between tunnels.
Figure 7 Major Structures to Prevent Snow Damage
Testing avalanche detection and alarm system at Shiozawa Snow Test Site. Pole in middle for avalanche detection (RTRI)
Cornice fence
Avalanche
fence
Avalanche protection forest
Stepped
terrace
Avalanche fence
Snow shed
Snow melt
Snow run off ditch
Snow fence
Avalanche deflecting
structure
Avalanche wedge
Guy supported
structuresSnow fence
Snow retaining wall
Avalanche breakingstructure
Interruption of rail services caused by heavy snow (RTRI)
RTRI is now developing an avalanchedetection and alarm system for railwaytracks. We have completed basic researchon a system that will be extremelyaccurate in detecting the occurrence ofavalanches and evaluating their size, andthat will issue alarms when required. Ourprototype experiments have indicated thatthe system can perform these functionsand we have every reason to believe thatit will be put to practical use soon.
Safeguarding Trains fromGale-force Winds
The greatest danger posed to a train bygale-force winds is derailment. Wind issaid to have caused 29 derailments duringthe more than 120 years of rail transportin Japan.Other external forces also come into play,especially lateral inertia force andcentrifugal force. These external forcescan combine with gravitational force toexert a pressure that is directed towardthe leeward side of the wheels. Thispressure pushes the wheels away fromtheir point of contact with the rails,causing the train to derail (Fig. 8).One way to prevent this is to reduceaerodynamic forces acting on rolling stock.Another way is to measure wind speeds
Figure 8 External Forces on Rolling Stock and Critical Conditions forOverturn (typical)
Storm
Lifting forceSide force
Moment
Lateral inertia force
Centrifugal force
Coupler force
Resultant of
external forces
and gravity
Gravity
Typical wind barrier (JR Hokkaido) Wind-tunnel test on aerodynamic forces of gale-force winds on rolling stock (RTRI)
58 Japan Railway & Transport Review 23 • March 2000
with trackside anemometers, and to stoptrain operations on wind-prone tracksections when wind speeds indicate a needto do so. The first approach involvesinstallation of wind fences or windbreaks.The second approach involves use of trainoperation controls, which generally stopservices when the instantaneous windspeed reaches 30 m/s, or 25 m/s in areaswhere even greater caution is warranted.Once the train is halted, operationguidelines call for it to stay halted for a full30 minutes, and then to proceed only ifconditions indicate that wind speeds aredropping.RTRI is conducting wind-tunnel tests todetermine the extent to which variousrolling stock shapes, and the variousshapes of structures like bridges andembankments, can determine the intensityof wind-generated aerodynamic forcesagainst moving rolling stock. We are alsoexamining wind conditions along tracksect ions to discover the var iouscharacteristics of wind. The results of thisresearch will be used to establish safe andeffective train operating control norms.
Figure 9 Principle of Urgent Earthquake Detectionand Alarm System (UrEDAS)
UrEDAS warning
P-wave arrival S-wave arrival
Initial tremor Main shock
Time
Acceleration warning
Safeguarding Trains fromEarthquakes
Japan is one of the most earthquake-pronecountries in the world. A recent exampleis the Great Hanshin Earthquake thatstruck the Kobe region in January 1995,causing considerable damage to railwayinfrastructure, including the San’yoShinkansen line.Measures to protect railways fromearthquakes include: (1) strengtheninginfrastructure and equipment so that theycan withstand the anticipated earthquakemotion; and (2) stopping the train as soonas an earthquake occurs, in order tominimize damage.The second measure involves installationof trackside seismometers and theapplication of train operation controls.The controls vary according to detectedseismic motion. Train operation controlsgenerally call for reduced speed when theearthquake acceleration is between 40and 79 gals, and a rapid stop when theacceleration is 80 gals or greater. Theobjective is to prevent the train fromentering a zone that has been damagedby an earthquake. But the problemremains that the train must travel somedistance while the ground is shaking
before coming to a complete halt. Thus,this type of precaution may be inadequate,especially in the case of a fast shinkansen.To address this issue, RTRI developed theabove-mentioned Urgent EarthquakeDetection and Alarm System (UrEDAS),which is designed to detect earthquakeforces more rapidly and transmit alarmsmore accurately. As Figure 9 shows, thesystem detects an earthquake by pickingup small seismic waves called P-waves,which are the first to reach the Earth’ssurface. The system then immediatelyestimates the epicenter and the magnitudeof the earthquake, and then uses this datato determine risk levels. If the risk is great,the system transmits alarms to areas thatcould be affected. The object here is tohalt trains, or at least reduce their speed,before the main shock arrives and causesdamage. When UrEDAS was first installedin 1992, it covered the entire TokaidoShinkansen line. It has now been installedon all shinkansen tracks.The other earthquake countermeasure—s t rengthening in f ras t ructure andequipment—follows seismic designstandards established by the Japanesegovernment. Work has been carried outto increase the earthquake resistance ofnew structures and equipment, and of
Viaduct collapsed during Great Hanshin Earthquake (RTRI)
existing structures and equipment in areaswhere it is thought a major earthquakecould strike.However, the motion of the 1995earthquake in the Kobe area greatlyexceeded any earthquake movementexpected at the time. Therefore, RTRIrevised its seismic design principles. Twonotable results of this revision are: (1) inthe past, any study of extremely strongearthquake motion focused on interplateearthquakes, but consideration is now alsogiven to earthquakes along inland activefaults; and (2) structural design is based onthe principle that structures must notcollapse during an earthquake even thoughthey may sustain damage. Decisionsregarding structural seismic capacity arebased on each structure’s importance.
Toshishige Fujii
Mr Fujii joined JNR in 1974 after completing a postgraduate science
course at Hokkaido University. He held a variety of posts in the Track
& Structure Department before becoming Chief Researcher in the
Geotechnical Engineering Laboratory of RTRI in 1987. He is currently
Chief Research Engineer in the Meteorological Disaster Prevention
Group.
Kanji WakoMr Kanji Wako is Director in Charge of Research and Development at the Railway Technical Research Institute (RTRI). He joined JNR in 1961 after graduating in engineering from Tohoku
University. He is the supervising editor for this series on Railway Technology Today.
Tatsuo Noguchi
Mr Noguchi joined JNR in 1973 after graduating in geology from
Tohoku University. He left the Structure Maintenance Section of JNR
Head Office in 1987 to join the newly formed Railway Technical
Research Institute (RTRI) where he is now General Manager of the
It is impossible to prevent an act of Godfrom inflicting damage on railwayinfrastructure, but appropriate measurescan make infrastructure less vulnerable.First, for any protective measure to beeffective, railways must always remainaware of conditions on and near theirtracks, and must take appropriate stepswhenever there is a risk of disaster.Japanese railway companies inspect theirtracks and equipment on a regular basis,and information obtained from theseinspections is used when devisingprotective measures. Inspections areconducted mainly by engineers, but newtechniques, such as remote sensing, have
also been used recently.Effective train operation controls requirecontinuous and accurate assessment ofmeteorological conditions. Over the years,this has meant trackside installation of raingauges, anemometers and other devices.In some cases, such devices can now beaccessed online, making it possible tocollect data in real time. Greater precisionis also achieved using data from Japan’sMeteorological Agency. We must alsoincrease the reliability of technologies usedto predict natural disasters, and developother effective and economical means tosafeguard railways from the forces of nature.RTRI is conducting serious research totackle these issues. �
Seismometer (left) installed at UrEDAS site (middle) and data processing unit at Seismic Data & Analysis Center (Photos: RTRI)
