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Geomorphotechnical Map for Railway Mainline Infrastructure Improvement. A case study from Romania

La cartographie géomorphologique pour l’amélioration de l'infrastructure des grandes lignes de chemin de fer. Une étude de cas en Roumanie
Bogdan Mihai, Robert Dobre et Ionuţ Săvulescu
p. 79-90

Résumés

L'amélioration des grandes lignes de chemin de fer dans les secteurs critiques à forte déclivité et sujets aux catastrophes naturelles est un objectif difficile à atteindre avec les projets de génie civil. L’ article analyse un secteur du réseau ferroviaire roumain (8 km de grande ligne), dont les caractéristiques techniques anciennes (huit secteurs présentant des courbes avec un rayon compris entre 170 et 250 m et de fortes déclivités comprises entre 25-27 ‰) a limité l'efficacité de la circulation ferroviaire. La source principale d'accidents est la réactivation des glissements de terrain qui ont interrompu le trafic pendant des mois. La carte géomorphotechnique se concentre sur les travaux de génie civil considérés comme un indicateur des secteurs où la géomorphologie est un facteur limitant du développement. Cette carte a été validé par des données de terrain et par l'analyse d'un diagramme géotechnique. Notre objectif est d'identifier et de cartographier l'infrastructure ferroviaire et les travaux de génie civil en interrelation avec la morphodynamique actuelle, à une échelle multitemporelle. Le résultat est une carte d’usage pratique pour trouver des solutions d'amélioration de la circulation, étant donné que cette section fait partie de la branche Sud du IVème corridor paneuropéen reliant l'Europe Centrale à la Turquie et la Grèce.

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Notes de la rédaction

Article soumis le 12 juillet 2013, accepté le 14 février 2014 ?

Texte intégral

The authors brought an equal contribution for this paper. These researches received a financial support in the framework of the project TD coordinated by Robert Dobre (2007-2009). The authors are grateful to the Romanian Railways (CFR) authority which provided different technical documentation.

Introduction

1Developing rail transport is one of the main priorities on the agenda of European Union Countries since mid 1990s, when the Pan-European Corridors were established as development axes (Eurostat, 2007). The need to find better and sustainable solutions, both for passengers and freight, led to an increased competition in the field, all for the purpose of increasing the market percentage accounted for by rail transportation (Wheat and Nash, 2006).

2Western Europe entered a new era of high speeds and interoperability between transport systems, as such, railway mainline development planners need to find a way to implement western standards throughout Eastern Europe as well. In terms of viability upgrading the existing rail infrastructure depends on the overall environment features and on the involved socio-economic factors.

3One of the most restrictive factors to consider in infrastructure planning is geomorphology together with geological features, land cover and economical limitations. This environmental feature offers the support for the transport infrastructure (passive relationship). Engineering works represent the response to the active relationship between infrastructure and morphodynamics (Cavallin et al., 1994). Environmental Impact Assessments (EIA; Panizza and Fabbri, 1995; Panizza et al., 2003; Lundkvist, 2005) represents the instrument geomorphologists use in their effort of identifying sustainable solutions for transport infrastructure development. With the help of these EIAs, engineers could further improve their understanding of particularities to consider and therefore provide better technical solutions (Gares et al., 1996; Alcantara-Ayala, 2002; Fell et al., 2008).

4EIAs focused road/railroad–related literature was pretty scarce over the last two decades. Yet, the papers that do include EIAs demonstrate an outstanding interest for finding best hazard mitigation solutions so as to improve slope management: H. Kienholz and P. Mani (1994) in Switzerland’s Alps, A.S. Al-Homoud and T. Tubeileh (1997) and A.S. Al-Homoud and Y. Masanat (1998) in the Jordanian deserts, A.M. Youssef et al. (2009) on Egypt’s Red Sea Coast, M. Cardinali et al. (2002), P. Budetta (2004), F. Guzzetti et al. (2004) and B. Palma et al. (2011) in the Umbria and Campania Regions of Italy, C. Jonasson and R. Nyberg (1999) and M. Lundkvist (2005), in Northern Scandinavia, M. Seppälä (1999) in Finland, J. Bonachea et al. (2005) in Northern Spain, P. Jaiswal et al. (2010) in Southern India.

5In the Romanian literature there are also a few papers to consider, providing mainly regional approaches. G. Posea (1969a, 1969b) analyzes the interrelationship landslides-railway/roads along the mountainous sector of Buzau’s River Valley. N. Popescu et al. (1969) contributed also to a better understanding of slope stability and engineering works studying the road along Cerna Valley in the Southern Carpathians. V. Surdeanu (1975) undertook landslide surveys along a road across the Eastern Carpathian’s flysch area, and P. Urdea (2000) published interesting data on the geomorphological risk induced by events such as avalanches, debris flows and rockfalls along the Alpine road crossing Fagaraș Mts, Southern Carpathians. M. Ielenicz et al. (1996) and M. Dinu (1999) used geomorphological mapping when analysing the impact of landslides upon different secondary railway sectors. V. Ilinca (2009) undertook dendro-geomorphologic investigations so as to identify and assess geomorphic hazard along the national road along Lotru Valley, Southern Carpathians.

6Recent regional geomorphological studies included EIAs of transport infrastructure, B. Mihai (2005) in the Timiș Mountains, R. Dobre (2011), along Prahova Valley. Both contributions evaluated the impact of existing trans-Carpathian railways and roads background on which assumptions were made with respect to possible designs for a motorway connecting Bucharest to Brașov (IVth Pan European Corridor).

7The current study represents an integrated geomorphologic approach to a specific practical problem occurring along a railway mainline sector in Romania. By this study we intended to obtain a detailed mapping of the inter-relationship railroad infrastructure - morphodynamic features (mainly landslides) and a quantitative understanding of the co-dependence geomorphologic limitations, railway infrastructure and rail traffic, to help engineers and regional planners in finding traffic improvement solutions for the sector under study: Bucharest-Timișoara mainline, part of the Southern branch of the IV Pan European Corridor (connecting Germany, Austria and Hungary to Turkey and Greece).

Study area

8The study area is represented by a sector where the required transport connection was only possible through remarkable technical solutions (part of the Romanian Railways network: CFR Bucharest-Rosiorii de Vede-Craiova-Timisoara). The section under study develops between Balota railway station (km 345 from Bucharest Nord) and Erghevita railway stop (km 351+400 m) on a total length of 6.40 km.

9The studied railway section is located in the south-western part of Romania, in the Oltenia Historical Region (Mehedinti County) overlaying the Getic Piedmont (fig. 1).

10The railroad crosses the cuesta escarpment forming the western border of Getic Piedmont, further the structural plateau of this geomorphologic region, reaching-onto Danube River’s top terraces in Drobeta-Turnu Severin Depression (Stroe, 2003; Badea, 2010). The area is known by a dynamic drainage network because a local subsidence phenomenon features the depression along the Danube River (Stroe, 2003; Enciu, 2007). This process creates favourable conditions for stream cutting and capture phenomena. This entire dynamic feature superposes on active slide bodies.

11A relief index of 150-170 m characterizes these scarps, where gullies and torrential valleys shape a hilly glacis-slope and old landslides alternate with alluvial cones.

12The geology of the area is mainly made up of soft rocks: fine sands, fine and coarser gravels intercalated with clay lenses (Enciu, 2007; Badea, 2010).

13Built in 1875, part of the Pitești-Vârciorova main railway, the sector under study was famous for being part of the former route of the Orient Express, connecting Paris to Constantinople (Popescu et al., 1994; Bellu, 1999).

14The railway configuration in Balota-Erghevita sector (8.4 km) is unique in Romania with its eight narrow curve sectors, with local gradients of 25-27‰ (Iordănescu and Georgescu, 1986). Since 1875, when the Bucharest-Pitești-Craiova-Vârciorova was inaugurated, the technical solution remained almost the same, although the railway was modernized in the framework of its electrification (1969-1970). The curvature radius of the rail track is the same as that from the 1880s, measuring between 170 and 280 m. Two sectors have different features: the Balota railway station with five tracks and the section between km 348+500 and km 350, with double track for traffic safety purposes (around the Valea Alba railway stop). There is also a service railway track used only to avoid the derailment of railway vehicles between km 349-km 350.

15The project is the result of the railway building policy in Romania during the 1870s, when an Austrian company (StEG – Staatse-Eisenbahn-Gesellschaft) had the charge of building the railroad and of assuring its maintenance (Botez et al., 1977). The relief index between Balota and the Danube River floodplain is 237 m on only 9-10 km distance (Balota-Drobeta-Turnu Severin). The railway section with narrow curves and no tunnel is about 19 km with a local gradient of 20-25 m/km. Lithological features are represented by sand, gravels and clay (Pliocene and Quaternary of Getic Piedmont).

16This technical inadequate solution (Pop, 1984; Iordănescu and Georgescu, 1986) needed a lot of energy for uphill traction of trains with steam engines (3-4 units) and an important risk for downhill traction (train derailment is common), a fact which hasn’t changed since the age of steam trains (Pop, 1984) when the Orient Express only reached a maximum 45 km/h in this area (Popescu et al., 1994).

17The time for crossing this section (8.4 km) is limited to 13-17 minutes (uphill and downhill) for all passenger trains, as the average speed limit is 30-40 km/h (according to the latest timetable). This time is usually longer because technical stops and temporary limitations occur. The delay is of 10-15 minutes at the Balota railway station in both directions.

18Another issue to address is the frequent derailment of railway vehicles which knew a few critical points throughout the entire period of service (from inauguration up to present).

19Over the years this section faced constant technical problems translated into speed limitations (20-30 km/h) but the latest event, a massive landslide (2010.02.20), interrupted the traffic for almost 4 months and destroyed the lines and the overhead.

20The latest engineering works along this sector were built during the 1970s, after the electrification, while an efficient management of these developments dates since the end of 1980s.

21In 1994, this sector became part of the Southern Branch of the IVth Pan European Corridor (fig. 1): Arad-Timișoara-Caransebeș-Drobeta Tr.Severin-Craiova-Vidin. This railway mainline will provide a shorter connection between Hungary (Central Europe) and Bulgaria, Turkey or Greece in the Balkans. Along with the inauguration of the Calafat-Vidin railway bridge (2014-2015) across the Danube, this transport connection is expected to boost its traffic values and European importance.

22In this context, this difficult railway section will be the subject of a complex modernization project with the financial support of European Union. To this purpose, planners need to understand and take properly into consideration the two main restrictions of this area: topography and railway line configuration. The morphodynamics of the area includes events such as landslides, known for their destructive power, triggered by the snow melting during the spring and by heavy rainfall during summer. To these, the usual technical limitations (dilatation of rails, train safety stops) add up decreasing train speed to merely a few kilometres per hour. Being the main railway connection between Bucharest and Timișoara, whatever works to be undertaken along this section need to rely on an Environmental Impact Assessment.

Fig. 1 – Balota-Erghevita Railway Section along mainline 100, in Southwestern Romania.
Fig. 1 – Le secteur de la grande ligne ferroviaire no100, Balota-Erghevita, au sud-ouest de la Roumanie.

Fig. 1 – Balota-Erghevita Railway Section along mainline 100, in Southwestern Romania.Fig. 1 – Le secteur de la grande ligne ferroviaire no100, Balota-Erghevita, au sud-ouest de la Roumanie.

Materials and methods

23The approach combines the cartographic method with the quantitative analysis in the context of an integrated applied geomorphological study. The aim of combining these methods is to provide a spatial vision of the problems and then to evaluate the relationship between morphodynamic processes and railway infrastructure. A vision over the analysis can be provided as the integration between GIS mapping and modeling with the special diagrams.

24Geomorphic mapping is one of the traditional methods in relief analysis (Demek et al., 1972) which can be easily and successfully improved in the context of the new digital techniques used in GIS environment (Gustavsson et al., 2006, 2008).

25The analysis requires a special type of geomorphic map, showing in the same frame morphodynamic features (landslide bodies, gullies etc.), railway infrastructures (railway track, overhead/catenary, signals, different railway marks etc.) and engineering works, as an expression of the inter-relationship between morphodynamics and railway traffic infrastructure.

26R. Dobre et al. (2011) presented the new approach of the geomorphotechnical map, for scientific debate in order to prepare a tool for railway building engineers in the context of mainline modernization process along the IVth Pan European corridor in Prahova Valley (from Bucharest to Brasov).

27The map provided for the study area is a totally upgraded version of the above mentioned map. It includes also remote sensing data into the background together with railway track parameters. All these data were obtained from different sources and have a different topology (tab. 1).

28According to table 1, data sources were different. The geomorphotechnical map was designed with a selection of digital layers after building the topological models (Kemp, 2008).

29Map drawing and design was done in ArcGIS 10.0 desktop, using the specific overlay tools. The data frame focused the amount of data on both sides of the railway track, providing also the national and European highway (DN6/E70, from Bucharest to Timisoara and Belgrade).

30The themes of the geomorphotechnical map are a selection of data layers in the formula of a special map to be transferred to engineering geologists and railway engineers.

31Beyond the cartographic representation, it was necessary to build a quantitative correlation of the geomorphic and engineering parameters, in order to show how the relationship between slope morphodynamics and railway infrastructure is important. Then it is also useful to investigate if engineering works along the railway section have an adequate position and to focus on the critical points where natural hazards and traffic problems (e.g. derailments) might occur.

32This approach was not focused on simple statistic dataset development, because regression analysis (Boradaille, 2003) offers only a synoptic view on the study area and not a focus on the real problems of rail traffic limitations and possible improvement solutions.

33A solution is a special geomorphotechnical diagram. This representation provides a spatial and correlative vision over the geomorphic and technical parameters along the investigated railway sector. Using the official kilometric marks and divisions, it is possible to cut the railway into continuous gradient sections and to superpose of different features: active and inactive landslides, active gullies and torrents, engineering works from cuts and embankment to gabions. This diagram can replace the classical statistic approach, because it offers a spatial vision over the relationship between slope morphodynamics and the technical issues along the railroad sector.

Tab. 1 – Digital data used for the geomorphotechnical map of Balota-Erghevita area.
Tab. 1 – Données numériques utilisées pour la carte géomorphotechnique de la zone Balota-Erghevita.

Data

Data source

Topology

Features (resolution, time coverage)

Linear erosion features

Field mapping

Line

June 2011, compared with orthophoto from

July 2005

Scarps (landslide,

gully)

Topographic map

Orthophoto

Field mapping

GPS survey

Line

Multitemporal data from topographic map (1975) scale 1:25000 and orthophoto (2005) scale 1:5000, resolution 0.5 m

Landslide bodies

Field mapping

GPS survey

Polygon

June 2011, compared with orthophoto from

July 2005

Slope deposits

Field mapping

Geological maps

Polygon

June 2011, compared with geological maps of 1968 (Romanian Geological Institute), scale 1:200000

Glacis, alluvial fan

Field mapping

Geological maps

Polygon

2011, compared with geological maps of 1968 (Romanian Geological Institute), scale 1:200000

Wetland

Field mapping

Orthophoto

Polygon

June 2011

Springs

Field mapping

GPS survey

Point

June 2011

Railway embankment/cut/half cut and bridge

Topographic map 1:5000

Field mapping

GPS survey

Polygon

June 2011, update of topographic map 1:5000 (IGFCOT București, 1975)

Other engineering works (retention wall, gabion, drainage channel etc.)

Field mapping

GPS survey

Line

June 2011

Engineering works damaged by morhpodynamic processes

Field mapping

GPS survey

Line

June 2011

Railway track

Topographic map 1:5000

Field mapping

Line

June 2011

Catenary portal 25kv/50Hz

Orthophoto

Line

July 2005, validated 2011

Curvature radius of railway track (labeled)

Technical data

(CCCF railway documentation)

Line Point

1986

Railway signals

Field mapping

GPS survey

Point

June 2011

Railway marks (speed regime, gradient, third track)

Field mapping

GPS survey

Point

June 2011

Roads and poweline

Orthophoto

Line

June 2005

Built-up area (railway station and building, houses, farms etc.)

Orthophoto

Polygon

June 2005, validated 2011

Contour lines, heights

Topographic map

Line

Point

1975, 10 m interval

Map background

Orthophoto

from ANCPI

Bucharest database

Raster

0.5 m resolution, scale 1:5000, natural colors processed in grayscale, July 2005

Results

34The analysis of the geomorphotechnical map for this sector brings new data about the geomorphic conditions, the railway transport infrastructure, through the interface of the engineering works layer. Figure 2 is an expression of this relationship, in the context of two different situations: a poor slope morphodynamics control and an efficient control of the morphodynamic processes. The first case, rail traffic superposes with special limitations on active landslide bodies where severe speed decrease, delay and accidents can occur (Fig. 2A). The second case corresponds to inactive landslide bodies with maintained engineering works providing a higher safety level for rail traffic (Fig. 2B).

35The map from figure 3 (original scale 1:5000) covers a limited surface of 5-6 km2 and allow a synoptic analysis of the railway infrastructure together with its geomorphic background. The map legend has four parts: morphodynamic features, engineering works, transport infrastructure and other features.

36Morphodynamic features (morphodynamic processes and landforms) are the limiting factor of this railway section improvement.

37For technical purposes, our map (fig. 3) selected only the morphodynamic features with a practical importance. It is important to separate the active features (landslides, gullies, slope cuts) as well as the dormant features from the non-active (indicated by retention walls superposed on half-cuts).

38Field geomorphic mapping from June 2011 brought new data about landslides. Old landslide scarps were identified on the topographic map from 1975 (1:5000) and updated from orthophotos (July 2005). These scarps are inactive and are difficult to be mapped in forested area. Six landslide bodies are crossed by the railway line, while other occurs in and around the Erghevita village.

39Only one body at km 349+500, is the subject of efficient slope drainage works and retention wall system building, while the other are dormant with possibilities of sudden re-activation. The map provides also the point at which the railway embankment was broken by the sudden landslide of February 20, 2010, when a train was passing before (between km 345+740- km 345+755).

40A complete mapping of scarps provided other useful data in a multitemporal formula (1975 and 2005). These landforms confirm the dynamics of landslidings and gully erosion, in the context of the reforestation of some slopes. Fields check of these features (June 2011) identified these scarps as non-active and protected by forest.

Fig. 2 – Two complementary situations regarding the relationship geomorphic factors, engineering works, railway traffic on the Balota-Erghevita sector of mainline 100.
Fig. 2 – Deux situations complémentaires concernant la relation entre les facteurs morphodynamiques, les travaux d’ingénierie civile et le trafic ferroviaire sur le secteur Balota-Erghevita de la grande ligne n° 100.

Fig. 2 – Two complementary situations regarding the relationship geomorphic factors, engineering works, railway traffic on the Balota-Erghevita sector of mainline 100. Fig. 2 – Deux situations complémentaires concernant la relation entre les facteurs morphodynamiques, les travaux d’ingénierie civile et le trafic ferroviaire sur le secteur Balota-Erghevita de la grande ligne n° 100.

A: Railway sector destroyed by slope failure on February 20, 2010 at km 344+740 (photo by S. Carablaisa, February 2010). B: Stabilized landslide controlled with complex works for drainage and stabilization, close to Valea Alba railway stop. The Intercity Train from Timișoara to Bucharest has a speed limit of 20-25 km/h within this sector.
A : Secteur ferroviaire détruit par un glissement, le 20 février 2010 au km 344 +740 (photo S. Carablaisa, Février 2010). B : Glissement de terrain inactif contrôlé par des travaux complexes de drainage et de stabilisation, à proximité de l’arrÍt ferroviaire de Valea Alb„. La vitesse du train Intercités à partir de Timisoara jusqu'à Bucarest est limitée à 20-25 km /h.

Photos by I. Savulescu and R. Dobre, June 2011.
Photos de I. Savulescu and R. Dobre, juin 2011.

Fig. 3 – Geomorphotechnical map of Balota-Erghevita area, together with legend. Orthophoto from ANCPI Bucharest database (July 2005).
Fig. 3 – Carte géomorphotechnique de la zone Balota-Erghevita, avec la légende. Orthophotographie de ANCPI Bucarest (Juillet 2005).

Fig. 3 – Geomorphotechnical map of Balota-Erghevita area, together with legend. Orthophoto from ANCPI Bucharest database (July 2005).Fig. 3 – Carte géomorphotechnique de la zone Balota-Erghevita, avec la légende. Orthophotographie de ANCPI Bucarest (Juillet 2005).

41Technical features for railway traffic are shown in detail on the map. This increases the technical significance of the cartographic information: gradient mark boards (20-25‰), speed limit boards, signalling devices, supplementary rail sectors (anti-derailment). This data can help the understanding of the limitations within the studied railway sector.

42The relationship between railway gradient and the railway traffic speed limit is an exponential regression function (fig. 4). The significant relationship (R2=0.87) was obtained on the basis of an extended data sampling. Data from the study area was sampled at 500 m intervals, using the technical specifications for train traffic from the Romanian National Railway Company (CFR Infrastructure Service) as well as the speed limiting boards along the rail (field check). The number of points was limited for obtain a relevant result as the studied sector in only about 8 km long. For this reason we decided the introduction of similar data samples from another mainline, crossing the Carpathian (mainline 300: Ploiesti Vest-Brasov). The mainline is a sector of the IVth Pan European Corridor which is partly modernized since 2011 (Bucharest to Sinaia), having similar problems as the study area (speed limitations on great slope gradient). The regression diagram allows the drawing of gradient-to-speed thresholds in order to define the technical difficulties introduced by the topographic profile to the railway traffic.

43The geomorphotechnical diagrams (fig. 5) is an explanation of the geomorphotechnical map. It is structured in two modalities of representation.

44Figure 5 a is a simple profile of the railway mainline sector, extended to the larger area it belongs to. The length of this graph is extended for an increasing relevance purpose, and superpose on a representative section between two main railway stations or Inter City train stops (in our case from Strehaia and Drobeta-Turnu Severin). This profile is built on the base of the detailed Digital Elevation Model and shows the configuration of the topographic features crossed by the mainline. This simple diagram shows the speed limitations of railway traffic according to the technical specifications. In order to characterize the sector, it was possible to provide in the same representation the present-day and the potential speed limit regimes. There are three technical solutions for decreasing the travel time between stations. All of them show an important contribution of landform configuration and morphodynamic features: rail sector gradient decrease (from 25‰ to 15‰), the increase of rail curvature radius in selected sectors (up to 250 m) and the widening of the railroad (from 40 m to 60 m where possible).

45Figure 5B focuses on the study area (solid line in fig. 5A). The diagram replaces the classical statistic representations by a seven level band shaped diagram, offering the spatial position of geomorphotechnic features. Kilometric marks together with stream network crossings are used for spatial orientation.

46The diagram’s first level confirms the high gradient values along the narrow curvature radius sectors (up to 25‰). This parameter is fully correlated with derailment points occurring to the end of the high gradient curve. These points are documented by historical evidences and railway technical reports and need a special technical analysis.

47Morphodynamic factors cover the second and third sections of the diagram in figure 5B. Landslide bodies (active: 15-16% of the sector, dormant processes: 13-14%) crossed by railroad are drawn against the railway sector and correspond to the lowest sector where deforested slopes occur around the villages. Active and dormant landslides have almost the same occurrences because the landslide bodies are the result of long-time slope processes with local reactivation on the background of active gully erosion. It is also interesting to notice the narrow configuration of the landslide bodies along the railroad, as their occurrence is strongly influenced by the drainage network configuration (bodies develop within catchments).

48The diagram in figure 5B shows a complex relationship between engineering works, the railway mainline and landslides. The total length of these works is about the same with the railway sector (6.47 km) and this means that the railroad is totally dependent on the technical slope developments and drainage facilities (all embankments, cutting and retention works have longitudinal drainage channels at the basement).

49Another feature is that all these engineering works concentrate in segments without landslide bodies and active gullies. They show that in 1970, when the mainline sector was electrified, slope processes where stabilized after a good forest recovery process.

Fig. 4 – The relationship between railway gradient and the railway traffic speed limit.
Fig. 4 – Relation entre la pente de la voie de chemin de fer et de la limite de la vitesse de circulation ferroviaire.

Fig. 4 – The relationship between railway gradient and the railway traffic speed limit.Fig. 4 – Relation entre la pente de la voie de chemin de fer et de la limite de la vitesse de circulation ferroviaire.

Fig. 5 – The geomorphotechnical diagram.
Fig. 5 – Le diagramme schématique géomorphotechnique.

Fig. 5 – The geomorphotechnical diagram. Fig. 5 – Le diagramme schématique géomorphotechnique.

A: Correlative diagram showing the relationship between mainline, slope declivities, slope processes and engineering works. B: Railway sector profile showing the speed limitations differences on homogenous slope gradient segments. Reference points: PM=railway switch control point (simple to double track); DTSM= Drobeta Turnu-Severin Marfuri railway station; Drobeta TS= Drobeta Turnu-Severin main station.
A : Schéma montrant les relations entre les grandes lignes, les déclivités, les processus de pente et les travaux de génie civil. B : Profil du secteur ferroviaire montrant les limites de vitesse différenciées sur des segments de pente homogène. Les points de référence: PM= point ferroviaire de contrôle de commutation (simple à double voie) ; DTSM=gare de Drobeta Turnu- Severin Marfuri ; Drobeta TS=gare de Drobeta Turnu-Severin.

Discussion

50The cartographic and the quantitative analysis results display the technical and environmental (geomorphic) limitations of the studied railway mainline section. As the map has a qualitative role, the graphs in figure 5 confirm that topographic difficulties, together with landslide hazards are the control factors of the railway traffic. The poor technical solution, a cheaper one since the railway was built (1875) still needs a big energy, time and expertise consumption. All of these entered the equation of a future sustainable development project.

51The analysis results, together with other data from the railway safety documentations and reports and train timetable data for passenger traffic (1970-2011), help us to define three discussion topics. These are the following:

  • Natural hazards mapping, analysis and management along the mainline sector.

  • Railway traffic safety problem along the studied railway sector.

  • Sustainable solutions for railway traffic improvement and infrastructure development.

The natural hazards

52The natural hazards are an old problem along this section. The railway section technical were not the most suitable ones. According to the historical data (Botez et al., 1977) the landslide and gully erosion problem is known since the railway section was built by the Austrian StEG company (1875).

53Geological data (Enciu, 2007) confirm a difficult situation to manage for the engineering geologists. Clay and gravel lenses maintain good conditions for increasing gully erosion. All direct tributaries of the Danube River are short streams with high gradients of longitudinal profile. There are good conditions for upstream erosion and stream channel cutting after summer heavy rainfall episodes and after short time snow melting periods (3-7 days in February-March). Stream channel density has values of more than 4-5 km/km2 on these slopes in the context of an intensive grazing around the village situated to the west of the study area (Stroe, 2003).

54The field documentation of the event from February 20, 2010, confirmed that deep-seated landslides can start even in forested areas when the clay lenses and gravel receive water from rapid snow melting episodes.

Railway traffic safety

55The railway section configuration introduced a permanent risk for rail vehicles derailment in some characteristic points. The Balota-Erghevita section is considered as one of the most difficult from the entire Romanian railway network system.

56The accident report archive from the CFR specialized service is the source for the 2005-2011 period. The basic problem is related to the derailment of wagons during the speed increase of trains downhill. We can establish critical points along this mainline section by integrating the geomorphotechnical map with the the geomorphotechnical diagram and data from geotechnical measurements to be done in the future. They are related to the narrowest curves sectors superposed on high declivities. These parameters are an important limitation for railway traffic improvement along time. Present-day speed limits are 30-40 km/h. This means they are lower than at the beginning of this railway mainline (45 km/h for the Orient Express; Popescu et al., 1994).

57Derailment risk zones are superposing the downhill sides of the narrowest curves, where brake systems can fail on wet tracks after heavy rainfall or snowmelts. This is the reason the trains have limited length and weight (passenger and goods).

58There are two documented derailment points on the geomorphotechnical map (fig. 3). For space reasons we did not provided all these places on the map, but we have selected the points with the most notable incidents in the history of this railway section.

59The technical intervention is also limited within the forested sectors of the mainline (about 60% from the total length) and the single track line. Engineer train and rail track measurement units are usually supplied for rapid intervention and relief purpose in Balota or Valea Alba railway stations.

Sustainable solutions for railway traffic improvement and infrastructure development

60During the last decade all efforts in this respect were focused on the mainline 300, which is a part of the IVth Pan European traffic corridor (Budapest-Arad-Brașov-Bucharest-Constanta). The modernization projects are still developing along the Prahova Valley mainline (Brașov to Bucharest). For the study area, the future modernization projects are now on paper.

61The main achievement will be the opening of the Danube bridge from Calafat (Romania) to Vidin (Bulgaria), which is an important step to open a new Pan European Corridor, from Arad to Timișoara, Drobeta Turnu-Severin (a new modern railway station opened in 2011), Craiova to Vidin, Mezdra and Sofia (and then to Varna or Istanbul or Thessaloniki).

62The opening of this so-called “Southern Branch” of the IVth Pan European Corridor needs important investments for traffic infrastructure. Special attention has to be focused on this section, in order to allow a normal and efficient traffic in time and to limit the waiting of trains in railway stations.

63Landslide hazards and other problems can only be controlled by an efficient management of the slopes crossed by the railway infrastructure. A double railway cannot be built on the basis of the existing one because the soft rocks (sand, gravel, marls) and the slope profile/gradient do not allow the widening of the embankments and other engineering works. All of these works can be modernized with new technologies but the railway will remain a simple track one.

64The building of a tunnel is a difficult task in this soft lithology, although it is not impossible with the present-day technologies. A sustainable solution might focus on searching a possibility for a new variant for the railway track of the mainline. This could be with a simple configuration and a continuous slope profile. This possible project would increases the distance from Balota to Drobeta Turnu-Severin with only 4.5 km, but the hazard management issues together with the rail traffic management would improve. The reason is the use of more stable slopes and top of terraces, closer to the Danube River.

65The search of a sustainable solution in order to “repair” or to “improve” the past technical solution must be a priority for engineers and planners. This contact area between two Pan European corridors (IV South Branch and IX-the Danube Rivers) will help the combined transport development (rail to fluvial, fluvial to rail and road) which develops in Drobeta Turnu-Severin and Orșova ports area, separated by the Porțile de Fier Dam (Iron Gates Dam) on the Romanian-Serbian border. Improving the rail traffic conditions in a sustainable formula will attract the road freight traffic to this new infrastructure. This is another current problem within this area, because the national highway (DN 6/E 70) is often blocked in Balota area by heavy traffic.

Conclusion

66The combination between the cartographic analysis (geomorphotechnical map) and the statistical approach brings interesting data regarding the relationship between the railway infrastructure and the geomorphic background. For the study area these are efficient tools in evaluating how sustainable the technical solutions of the past could be in the context of a new Pan European Corridor’s development.

67This approach proposes an informative tool for engineering projects and offers an overview of the problems and of the critical points in railway infrastructure improvement. Emerging problems can be identified on special maps (geotechnical maps and slope engineering map) and then investigated in detail by different specialists.

68Our approach must be continued with the analysis of landslide susceptibility and hazards. For this purpose, a special GIS application needs more data, including geotechnical information (not sufficient at this moment).

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Annexe

Version française abrégée

Le développement du transport ferroviaire est l'une des principales priorités de l'agenda des pays de l'Union Européenne depuis le milieu des années 1990, lorsque les corridors paneuropéens ont été créés comme des axes de développement (Eurostat, 2007). La nécessité de trouver des solutions meilleures et durables, à la fois pour les passagers et le fret, a conduit à une concurrence accrue dans ce domaine, dans le but d'augmenter le pourcentage de marché détenu par le transport ferroviaire (Wheat et Nash, 2006).

L’Europe de l'Ouest est entré dans une nouvelle époque, celle de la grande vitesse et de l'interopérabilité des systèmes de transport. Les planificateurs du développement des grandes lignes ferroviaires doivent trouver un moyen de mettre en œuvre les normes occidentales des infrastructures de chemin de fer dans toute l'Europe de l'Est. En termes de viabilité, la modernisation de l'infrastructure ferroviaire existante dépend de l'ensemble des caractéristiques de l'environnement et des facteurs socio-économiques.

Un des facteurs les plus restrictifs à prendre en considération dans la planification de l'infrastructure est la géomorphologie. Le relief est un fondement pour l'infrastructure et il est lui-même affecté par les travaux de génie civil et par l'infrastructure elle-même (Cavallin et al., 1994).

Des évaluations d'impact environnemental (EIA) (Panizza et Fabbri, 1995 ; Panizza et al., 2003 ; Lundkvist, 2005) sont réalisées par les géomorphologues qui cherchent des solutions durables pour le développement des infrastructures de transport. Leurs travaux de recherche peuvent améliorer la compréhension des spécificités du terrain et donc offrir de meilleures solutions techniques (Gares et al., 1996 ; Alcantara-Ayala, 2002 ; Fell et al., 2008.).

Les objectifs de l’article sont la réalisation d'une cartographie détaillée de l'infrastructure des chemins de fer en interrelation avec les caractéristiques morphodynamiques des tronçons étudiés (principalement des glissements de terrain) et une compréhension quantitative des limites géomorphologiques en co-dépendance avec l'infrastructure ferroviaire et le trafic ferroviaire.

La carte géomorphotechnique que nous proposons comme outil d’aménagement et d’entretien des infrastructures ferroviaires offre une synthèse des caractéristiques morphodynamiques du terrain, de l’infrastructure des chemins de fer et des travaux de génie civil. Cette carte a été réalisée à l'aide d'un SIG, après des levés de terrain à grande échelle, combinés avec l'utilisation de cartes topographiques et d'orthophotographies. L'échelle multitemporelle de la carte apporte des informations spatiales sur le potentiel des processus morphodynamiques, qui peuvent limiter le développement de l'infrastructure. Un exemple est donné par la cartographie de la configuration des glissements de terrain (niches d'arrachement...) qui affectent l’infrastructure.

L’approche graphique des problèmes de relation entre la morphodynamique des versants, l’infrastructure et les travaux spécifiques de génie civil permet d'identifier les secteurs critiques le long de la grande ligne, là où les travaux sont insuffisants et où on a besoin de développer des études géomorphotechniques et géotechniques.

Les résultats peuvent aider les ingénieurs et les planificateurs régionaux à trouver des solutions d'amélioration du trafic dans le secteur de l'étude, la grande ligne Bucarest - Timișoara faisant partie de la branche sud du corridor paneuropéen IV reliant l'Allemagne, l'Autriche et la Hongrie à la Turquie et la Grèce.

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Table des illustrations

Titre Fig. 1 – Balota-Erghevita Railway Section along mainline 100, in Southwestern Romania.Fig. 1 – Le secteur de la grande ligne ferroviaire no100, Balota-Erghevita, au sud-ouest de la Roumanie.
URL http://geomorphologie.revues.org/docannexe/image/10525/img-1.png
Fichier image/png, 2,4M
Titre Fig. 2 – Two complementary situations regarding the relationship geomorphic factors, engineering works, railway traffic on the Balota-Erghevita sector of mainline 100. Fig. 2 – Deux situations complémentaires concernant la relation entre les facteurs morphodynamiques, les travaux d’ingénierie civile et le trafic ferroviaire sur le secteur Balota-Erghevita de la grande ligne n° 100.
Légende A: Railway sector destroyed by slope failure on February 20, 2010 at km 344+740 (photo by S. Carablaisa, February 2010). B: Stabilized landslide controlled with complex works for drainage and stabilization, close to Valea Alba railway stop. The Intercity Train from Timișoara to Bucharest has a speed limit of 20-25 km/h within this sector.A : Secteur ferroviaire détruit par un glissement, le 20 février 2010 au km 344 +740 (photo S. Carablaisa, Février 2010). B : Glissement de terrain inactif contrôlé par des travaux complexes de drainage et de stabilisation, à proximité de l’arrÍt ferroviaire de Valea Alb„. La vitesse du train Intercités à partir de Timisoara jusqu'à Bucarest est limitée à 20-25 km /h.
Crédits Photos by I. Savulescu and R. Dobre, June 2011.Photos de I. Savulescu and R. Dobre, juin 2011.
URL http://geomorphologie.revues.org/docannexe/image/10525/img-2.png
Fichier image/png, 2,4M
Titre Fig. 3 – Geomorphotechnical map of Balota-Erghevita area, together with legend. Orthophoto from ANCPI Bucharest database (July 2005).Fig. 3 – Carte géomorphotechnique de la zone Balota-Erghevita, avec la légende. Orthophotographie de ANCPI Bucarest (Juillet 2005).
URL http://geomorphologie.revues.org/docannexe/image/10525/img-3.png
Fichier image/png, 8,3M
Titre Fig. 4 – The relationship between railway gradient and the railway traffic speed limit.Fig. 4 – Relation entre la pente de la voie de chemin de fer et de la limite de la vitesse de circulation ferroviaire.
URL http://geomorphologie.revues.org/docannexe/image/10525/img-4.png
Fichier image/png, 1,6M
Titre Fig. 5 – The geomorphotechnical diagram. Fig. 5 – Le diagramme schématique géomorphotechnique.
Légende A: Correlative diagram showing the relationship between mainline, slope declivities, slope processes and engineering works. B: Railway sector profile showing the speed limitations differences on homogenous slope gradient segments. Reference points: PM=railway switch control point (simple to double track); DTSM= Drobeta Turnu-Severin Marfuri railway station; Drobeta TS= Drobeta Turnu-Severin main station.A : Schéma montrant les relations entre les grandes lignes, les déclivités, les processus de pente et les travaux de génie civil. B : Profil du secteur ferroviaire montrant les limites de vitesse différenciées sur des segments de pente homogène. Les points de référence: PM= point ferroviaire de contrôle de commutation (simple à double voie) ; DTSM=gare de Drobeta Turnu- Severin Marfuri ; Drobeta TS=gare de Drobeta Turnu-Severin.
URL http://geomorphologie.revues.org/docannexe/image/10525/img-5.png
Fichier image/png, 2,3M
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Référence papier

Bogdan Mihai, Robert Dobre et Ionuţ Săvulescu, « Geomorphotechnical Map for Railway Mainline Infrastructure Improvement. A case study from Romania », Géomorphologie : relief, processus, environnement, vol. 20 - n° 1 | 2014, 79-90.

Référence électronique

Bogdan Mihai, Robert Dobre et Ionuţ Săvulescu, « Geomorphotechnical Map for Railway Mainline Infrastructure Improvement. A case study from Romania », Géomorphologie : relief, processus, environnement [En ligne], vol. 20 - n° 1 | 2014, mis en ligne le 01 janvier 2016, consulté le 21 octobre 2017. URL : http://geomorphologie.revues.org/10525 ; DOI : 10.4000/geomorphologie.10525

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Auteurs

Bogdan Mihai

University of Bucharest – Faculty of Geography – 1, Nicolae Balcescu Blvd., 010041 Bucharest, Sect. 1, Romania (bogdan@geo.unibuc.ro).

Robert Dobre

University of Bucharest – Faculty of Geography – 1, Nicolae Balcescu Blvd., 010041 Bucharest, Sect. 1, Romania (dobrotel@yahoo.co.uk).

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Ionuţ Săvulescu

University of Bucharest – Faculty of Geography – 1, Nicolae Balcescu Blvd., 010041 Bucharest, Sect. 1, Romania (savulescu@geo.unibuc.ro).

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