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ACEM-Rail 265954 D1.1 State of Practice

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SEVENTH FRAMEWORK PROGRAMME

THEME SST.2010.5.2.1.

Automated and cost effective railway infrastructure maintenance

Automated and Cost Effective Maintenance for Railway

Contract: 265954

D1.1 Report on the state of practice of railway infrastructure

maintenance

Deliverable number D1.1Work Package number WP1: State-of-art of maintenance in Railway & Other Industries

Task Task 1.1

Revision 0

Due date 2011/02/28 Submission date 2011/02/25

Distribution Security PU Deliverable type R

Reviewer F.G. Benitez, N. Caceres, L. Romero (US)

AuthorsN. Jimenez, A. Barragan, P. Cembrero, F. G. Benitez, N. Caceres, F.Schubert, A. Simroth, Cesare Santanera

Partners CEMOSA, US, FRAUNHOFER, DMA

Verification F. Schubert (Fraunhofer)

Approval (coord.) N. Jimenez (CEMOSA)


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Table of Contents

1. INTRODUCTION..........................................................................................................................9

1.1 BASIC CONCEPTS AND DEFINITIONS .............................................................................................. 91.2 MAINTENANCE CLASSIFICATION ................................................................................................. 101.3 MAINTENANCE COSTS .................................................................................................................. 111.4 MAINTENANCE TECHNIQUES ....................................................................................................... 131.5 MAINTENANCE PLANNING AND SCHEDULING ............................................................................. 14

2. RAILWAY INFRASTRUCTURE MAINTENANCE..............................................................15

2.1 GENERAL MAINTENANCE ASPECTS.............................................................................................. 152.2 ORGANIZATION OF THE RAILWAY SECTOR ................................................................................ 16

2.2.1. The liberalization of the Railway sector in the European Union...................................................................172.2.2. Models for the organization of the rail sector................................................................................................17

2.2.3. Interoperability and safety in the EU.............................................................................................................192.3 INSPECTION AND MAINTENANCE OPERATORS ............................................................................ 212.4 RAILWAY INFRASTRUCTURE.THE TRACK .................................................................................. 22

2.4.1. Superstructure ..................................................... ........................................................... ............................... 232.4.2. Substructure......................................................... ........................................................... ............................... 31

2.5 TRACK DEGRADATION AND FAILURE .......................................................................................... 342.5.1. Superstructure ..................................................... ........................................................... ............................... 342.5.2. Substructure...................................................................................................................................................45

2.6.TRACK MAINTENANCE AND RENEWAL .............................................................................................. 482.6.1. Superstructure ..................................................... ........................................................... ............................... 482.6.2. Substructure...................................................................................................................................................55

3 TRACK MEASUREMENT ....................................................................................................59

3.1 MEASUREMENTS AND EVALUATION OF TRACK DEFECTS .......................................................... 593.1.1 Superstructure ...................................................... ........................................................... ............................... 593.1.2. Substructure......................................................... ........................................................... ............................... 66

3.2 MEASUREMENTS AND EVALUATION OF DEFECTS IN TRACK GEOMETRY .................................. 683.3 THE "MEASUREMENT TRAIN"CONCEPT ..................................................................................... 71

3.3.1 The "unattended measurement" concept ........................................................... ........................................ 72

4 DATA SYSTEM.......................................................................................................................75

4.1 INTRODUCTION ............................................................................................................................. 754.2 SENSOR DATA ANALYSIS............................................................................................................... 764.3 DATA MEASUREMENT TRANSMISSION. ........................................................................................ 764.4 DATA MEASUREMENT ANALYSIS AND THRESHOLD EVALUATION. ............................................ 774.5 MAINTENANCE EVALUATION ....................................................................................................... 784.6 MAINTENANCE PLANNING AND SCHEDULING ............................................................................. 794.7 ALGORITHMS AND TOOLS ............................................................................................................ 79

5 RAILWAY INSPECTION TECHNIQUES ..........................................................................83

5.1 INTRODUCTION ............................................................................................................................. 835.2 NON-DESTRUCTIVE EVALUATION METHODS FOR RAILWAY COMPONENTS .............................. 83

5.2.1 Ultrasonic inspection .......................................................... ........................................................... ........... 835.2.2 Acoustic Inspection Techniques ................................................... ........................................................... . 865.2.3 Electromagnetic Inspection.......................................................................................................................875.2.4 Thermographic inspection ............................................................ ........................................................... . 895.2.5 Radiographic inspection............................................................................................................................905.2.6 Inspection using visual cameras................................................................................................................905.2.7 Distributed Optical Fibres.........................................................................................................................92

5.3 ARTIFICIAL INTELLIGENCE TECHNIQUES FOR RAILWAY INSPECTION ..................................... 93


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5.3.1 Neural networks........................................................................................................................................945.3.2 Machine vision..........................................................................................................................................945.3.3 Fuzzy logic................................................................................................................................................955.3.4 Case base reasoning..................................................................................................................................95

5.3.5 Expert systems .......................................................... ........................................................... ..................... 955.3.6 Data mining...............................................................................................................................................96

6 A REVIEW OF INFRASTRUCTURE MAINTENANCE PLANNING MODELS..........97

6.1 INTRODUCTION ............................................................................................................................. 976.2 GENERAL MODELLING CONCEPTS ............................................................................................... 996.3 MAINTENANCE OPTIMIZATION MODELS ................................................................................... 100

6.3.1 Strategic level ........................................................... ........................................................... ................... 1006.3.2 Tactical level...........................................................................................................................................1006.3.3 Operational level.....................................................................................................................................101

6.4 TRACK MAINTENANCE COST MODELS ....................................................................................... 1026.5 MAINTENANCE PLANNING AND OPTIMIZATION TOOLS............................................................ 1056.6

LITERATURE SUMMARY ............................................................................................................. 109

7 RECENT R&D EFFORTS IN THE WORLD....................................................................111

7.1 EUROPEAN PROJECTS................................................................................................................. 1117.2 INTERNATIONAL PROJECTS ....................................................................................................... 120

ANNEX A GLOSSARY OF NON-DESTRUCTIVE TESTING TECHNIQUES................123

ANNEX B ACRONYMS............................................................................................................127

REFERENCES AND BIBLIOGRAPHY.....................................................................................129


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List of Figures

Figure 1: Superstructure and subgrade..............................................................................................23

Figure 2: Rail profiles UIC 50 (50 E1), UIC 54 (54 E1), UIC 60 (60 E1) and UIC 71 (71 E1). .....24Figure 3: Twin-block sleepers............................................................................................................26Figure 4: Monoblock sleepers............................................................................................................27Figure 5: Elastic fastenings................................................................................................................28Figure 6: Resilient pads......................................................................................................................29Figure 7: Crossings ............................................................................................................................30Figure 8: Codification of rail defects .................................................................................................36Figure 9: Rail defect UIC 211 (tache oval) ........................................................................................37Figure 10: Rail defect UIC 221..........................................................................................................37Figure 11: Rail defects UIC 2201 (on the left) and UIC 2202 (on the right).....................................38Figure 12: Rail defect UIC 2221........................................................................................................39

Figure 13: Rail defect UIC 2222........................................................................................................39Figure 14: Head checks......................................................................................................................40Figure 15: Rail defect UIC 301..........................................................................................................40Figure 16: Rail defect UIC 302..........................................................................................................40Figure 17: Rail head with plastic deformation in initial state ............................................................41Figure 18: Rail head with plastic deformation in advance state ........................................................42Figure 19: Measurement points in a tunnel cross section. .................................................................47Figure 20: Embankment building ......................................................................................................48Figure 21: Manual weld recharge in a head of turnout .....................................................................49Figure 22: Welding in union of rail, and last grinding in the same union with manual grindingmachine ..............................................................................................................................................49

Figure 23: Surface of contact in rail head before grinding, with small defect and after grinding,where roughness can be seen on the grinding surface. ......................................................................50Figure 24: Large grinding machine for massive grinding in track line, and medium grindingmachine for grinding medium distance of the rail. ............................................................................51Figure 25: Video image of wrong fastening. .....................................................................................52Figure 26: Ballast profile machines ...................................................................................................53Figure 27: tramping machine: the first arm fixes the rail and the second ones remove the ballast...54Figure 28: Formation layer rehabilitation machine...........................................................................55Figure 29: Formation rehabilitation machine scheme.......................................................................55Figure 30: Damaged embankment, the bad drainage move the soil just under the ballast................57Figure 31: Artificial defect in rail head used for calibration and system testing ...............................60Figure 32: Star crack around of bolt hole. ......................................................................................60Figure 33: Rail profile and gauge measurement instrument..............................................................62Figure 34: Typical result of a rail profile processing according to UIC 519 norm............................63Figure 35: System for switches measurements ..................................................................................65Figure 36: ballast curb........................................................................................................................65Figure 37: Principle of tunnel geometry measurement by a rotating range finder. ...........................66Figure 38: Tunnel measurement equipment.......................................................................................67Figure 39: Tunnel image of measurement equipment .......................................................................67Figure 40: Transfer functions for the different track geometry measurements. ................................69Figure 41: Typical result of a track geometry measurement. ............................................................70

Figure 42: System for gauge track measuremet.................................................................................70Figure 43: Block diagram of a measurement train.............................................................................71Figure 44: Possible extension of a measurement train within ACEM Rail. ......................................72


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Figure 45: Sketch of data processing .................................................................................................77Figure 46: Underfloor Testing Unit at Deutsche Bahn (UFPE, German acronym)...........................84Figure 47: AURA Testing Assembly at Deutsche Bahn for wheel set and solid axle testing ...........84Figure 48: Ultrasonic Railway Wheel Inspection System .................................................................85Figure 49: Test train of the Deutsche Bahn for non-destructive testing of railway tracks ................85Figure 50: Hollow-shaft integrated wireless multi-sensor system for evaluation of the rail-wheelcontact ................................................................................................................................................87Figure 51: Simulation of wave propagation from the rail/wheel contact to the sensor (left hand side)and typical averaged signal from the noisy raw data (right hand side, measured). ...........................87Figure 52: Schematical lay-out (left) and photograph (right) of early test set-up of the sensorsystem.................................................................................................................................................88Figure 53: Thermal image: part of a rail with defects at the upper , Image field: 8 cm x 8 cm ........90Figure 54: Positions of the visual cameras........................................................................................91Figure 55: Example of an assembled camera image..........................................................................91

Figure 56: Black and white image for detection of rail surface defects ............................................92Figure 57: Maintenance planning scheme .........................................................................................98Figure 58: Track renewal and maintenance activities distinguished by Esveld (2001)...................103Figure 59: Ramsys main input/output capabilities (Source: Mermec, 2011). .................................107


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List of Tables

Table 1. List of EU-funded Projects. ...............................................................................................111Table 2: Research projects carried out in the European Research Area. .........................................112Table 3: Research works at international level. ...............................................................................121


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1. Introduction

In the last fifty years, maintenance of technical systems has become increasingly important in mostindustrial and service sectors. Failures of these systems may cause expensive production losses andcan have negative effects on the people and environment.

The termMaintenancealso broadly stands forRepair, Operationsand Overhaul (MRO).It involvesfixing any sort of mechanical or electrical device should it become out of order or broken (known asrepair, unscheduled or casualty maintenance). It also includes performing routine actions whichkeep the device in working order (known as scheduled maintenance) or prevent trouble from arising(preventive maintenance). MRO may be defined as, "All actions which have the objective ofretaining or restoring an item in or to a state in which it can perform its required function. The

actions include the combination of all technical and corresponding administrative, managerial, andsupervision actions" (EFNMS). By maintenance operations, such as repairs and replacements, thefailed components can be restored to the operational state.

1.1 Basic concepts and definitions

Maintenance includes all actions necessary for retaining a system or an item in, or restoring it to, astate in which it can perform its required function (British Standard, 1984).

Other definitions of the concept ofMaintenanceis given (ITS, 2007) as:

1. Any activity such as tests, measurements, replacements, adjustments and repairs intended to retain or restore a functional unit in or to a specified state in which the unit canperform its required functions.

2. For material all action taken to retain material in a serviceable condition or to restore itto serviceability. It includes inspection, testing, servicing, classification as to serviceability,repair, rebuilding, and reclamation.

3. For material all supply and repair action taken to keep a force in condition to carry outits mission.

4. For material the routine recurring work required to keep a facility (plant, building,

structure, ground facility, utility system, or other real property) in such condition that it maybe continuously used, at its original or designed capacity and efficiency for its intendedpurpose.

The concept of maintenance actions has been subjected to substantive changes during the lastdecades (Kobbacy and Murthy, 2007), trespassing the original focus on repairing-replacing actionsto preventing activities.

The pressure to have the technical systems working under the highest quality standards give way toan increase of maintenance actions, which derives in the increases of maintenance costs.


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1.2 Maintenance classification

Maintenance activities are grouped into tasks. These tasks can be classified into three maincategories (Budai-Balke, 2009):

breakdown maintenance corrective maintenance, preventive maintenance, predictive maintenance.

Breakdown maintenance (BM). They are the tasks where equipment is run down to its breakingdown point, and maintenance is carried out afterward. Its purpose is to enhance the useful life of aparticular equipment/system. These tasks aim to intentionally run the equipment to failure foranalyzing purposes.

Corrective maintenance (CM). The maintenance tasks are carried out after break down. It aims toget back a failed or malfunctioned item, equipment or system to run operationally at earliest. It canbe defined as the tasks required when an item has failed or worn out, to bring it back to workingorder. This maintenance is triggered by an unscheduled event, such as failure of an item. The costsof this type of maintenance are usually high due to several reasons: a) the urgency to have thesystem repaired, b) the failure of an item might concatenate others, c) external costs may be derivedas a consequential of the original failure, such as lost of production, personal and environmentalsafety and integrity.

Preventive maintenance (PM).This maintenance is carried out before break down occurs. Its aim isto reduce the probability of occurrence of failure. This type of maintenance has many different

variations and includes preplanned actions as adjustments, replacements, renewals, inspections. Thetasks corresponding to this type of maintenance take place under a deterministic schedule inopposite to the unpredicted case of the corrective maintenance which follows a random failurepatterns. This type of maintenance is carried out to prevent breakdown during operational time bymaintaining it in off time. Therefore, it can be planned ahead and performed when it is convenient.The main purpose of this type of maintenance is to avoid failures. It follows a scheme of actionsand inspection intervals. There is not guarantee that the equipment will continue to work even if it ismaintained it according to the maintenance plan, though the probability of failure decreases. Thistype of maintenance can be subclassified into:

Systematic preventive maintenance (SPM), it includes operations preplanned in advance.Operations prescribed by the technical specifications of equipments, apparatus and systemsare included in this set; it also includes all major operations to be carried on the main assesof railway infrastructure (i.e.: ballast, tamping, geometry).

Detected preventive maintenance(DPM), are the defects and malfunctioning detected in situduring another maintenance work or inspection which can be carried out immediately. Incase the operations have to be postponed, due to lack of resources (material, personal, time-window), the operations are reported either preventive or corrective according to its severityand duly scheduled.

Predictive maintenance (PdM). Also known as Conditional-based maintenance. They are thetechniques and tasks that help determine the conditions of in-service equipment for predictingpossible degradations in order to predict when maintenance is needed and should be performed.


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They try to predict when failure will occur and to plan the preventive maintenance. The techniquesused are based on statistical analysis and control to determine at what state preventive/correctivemaintenance will take place.

1.3 Maintenance costs

Railway transport has risen up impulsed by the increase of demand in the last decade. Moreover,several European States prioritize policies tending to transfer road transport (passengers and freight)to rail in order to reduce road congestion, and taking into account the inability to build new roadsdue to lack of land and space.

Longer operating time, higher number of services and trains increase the annual traffic load andaccelerate the infrastructure deterioration; this results into an increase of the number, severity andfrequency of renewal work and maintenance operations and, on the other hand, it has decreased the

available time for maintenance as railway services posses the infrastructure and rolling stock mostof the 24 hours of the day. The need for more maintenance and the increase of infrastructurepossession time (right-of-way, RoW) to carry it out, is in conflict with the increment of theinfrastructure use by train services to satisfy the demand.

In addition to the above issues, the European directive regarding infrastructure charges and capacityallocation (EU OJ, 2001) defines an organizational and regulatory framework tending to anoptimization of the railway infrastructure.

All this factors have make maintenance costs scale severely and the infrastructure administrator andrailway operator to balance these factors by management systems that provide a reasonable solution

to users regarding many aspects of the service (quality, safety, cost).

The interest of all railway administrations and operators to keep costs bounded have fostered, in thelast years, to invest efforts in R&D programmes to easy a practical solution to this problem.

Orders of magnitude of maintenance costs in some sectors are presented in Cross (1988) as apercentage of the total operating costs.

These costs are affected by factors such as: increases of maintenance actions due to higher quality standards, increases of manpower costs of maintenance personnel, increases of management costs.

Preventing maintenance is an increasing area of importance due to the economic interest to reducemaintenance costs. Corrective maintenance tasks will be never avoided because of unexpectedfailures. These failures provoke disruption of the production/service and cause not only additionalcosts for production losses but additional malfunctions/damages to other related components andequipments.

Predictive maintenance is a step forward intended to minimize corrective maintenance. This is oneof the most active area of research in maintenance, as it is most founded in inferring models thatpredicts the risk of failure and residual life of components, to integrate these single componentmodels into the system model composed of its components, and finally to merge them into theequipment predictive model. The difficulties encountered in this bottom-up modelling process may


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end up with conservative prediction scheduling actions that might increase the maintenance actionssubjected to the equipment over those strictly needed. This conservative behaviour gives lieu to anincrement in the maintenance costs, due to earlier part replacement with still substantial residuallife.

The four maintenance types can be coordinated under a scheduling scheme, by combining activities,in order to minimize the period of time the equipment is idle. This approach helps saving costs. Thisway of proceeding has also consequences. The replanning of the maintenance scheduling should becarefully optimized in order to avoid non-attention to previous maintenance scheduled tasks, whichmight additional increase costs.

Railway infrastructure maintenance costs

Regarding railway infrastructure maintenance, a survey conducted among maintenance agencies(Daniels, 2008) revealed that most maintenance activities are concentrated in:

rail maintenance, track geometry maintenance, tie and fastener, ballast maintenance, track inspection, and emergency services (i.e.: derailment, weather repairs).

All above activities affect the track system mainly. The primary maintenance costs follows fromwear and fatigue rather that secondary sources such as corrosion, derailment, human error andvandalism. These two main causes affect severely to track geometry and switches, reporting a 50 %

of total maintenance costs (Zoeteman, 2007).

Additional to this revealed fact, track maintenance costs and planning are heavily influenced bytrack possession and site access windows. An average work window of 4 hours is most common, ofwhich 50 % is expended for displacements to the work site. This means that a planning regardingaccess, to coordinate maintenance crews and resources, is required in order to keep costs bounded.

There is a second additional factor that cannot be neglected and influences the overall maintenancebudget, it comes from the need of replacement of components due to their inappropriateperformance or design during the project deployment.

Finally, the third most influence factor is deferred track maintenance. When this case occurs,corrective maintenance has to be carried out as a matter of urgency, and costs rise up.

These findings are almost repeated for all type of railway infrastructures.

The state of the art reports that maintenance costs are influenced by the following factors:

Infrastructure maintenance activities. The costs associated can vary with systemconfiguration and the technology associated to the infrastructure. Maintenance activities arecharacterised by the Maintenance Demand defined as the level of resources (effort,materials, equipment, organizational and administrative) to provide and acceptable assetcondition level.

Resources (labour, material, equipments, organizational and administrative) costs.


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Work-window costs. It stands for the cost associated to the time-window created to conductmaintenance activities when the infrastructure possession is detracted from railway service.

Inspection and maintenance technologies costs. They are affected by the inspection

technology used and the maintenance techniques utilised to carry out the operations. Inspection and maintenance policies costs. They are affected by the level of maintenanceenforced, the frequency of inspections.

Operating costs. They stand for the costs associated to operational optimisation ofmaintenance operations.

Indirect cost. They represent the costs not directly involved in the maintenance tasks such aspreparing crews and materials for a task, mid-level supervision, stocktaking of inventory,purchasing activities, equipment procurement and maintenance, training and organisationoverheads).

It is worth mentioning that maintenance costs vary dramatically over time. In some cases decreasing

(i.e.: some materials) in other intensifying (i.e.: labour). There is a huge number of documents in theliterature reporting unit prices of components by different railway administrations and constructorsover time. Higher difficulty is encountered in pointing out unitary costs for maintenance operationsperformed by the administrations. Though these figure are of primary interest for a costoptimisation planning programme, there is no point to import them from other railway infrastructureadministrations but for the sake of comparative purpose (Daniels, 2008).

There are numerous cost-estimating approaches, ranging from statistical and data mining techniquesto degradation models (Kumar, 2008). Some methodologies associate the dependent variables (cost,degradation level) with influence parameters (traffic characteristics, component age) to derivepredicting models. For the case of degradation models a further correlating model between cost and

degradation levels has to be inferred. For particular assets, i.e. track, predictive degradation modelsallow a quantitative relationship between influence factors, degradation and maintenance costs(Larsson, 2004). This defines a two-process approach, the first one predicts the rate of degradationof the system/equipment/component through quantifiable modeling, the second stage estimatesmaintenance demand and the management of this degradation through maintenance cost models; inthis last case modelling efforts relay in historical maintenance and expenditure records, and a well-maintain database should be available.

Several studies have reported a weak relationship between maintenance costs and pre-definedexplicative independent variables. In the particular case of track maintenance, railway traffic seemsto be not statistically significant regarding costs (Daniels, 2008). In other cases (Anderson, 2006)significant interaction is found between switch maintenance costs, assets age and rail weight.

1.4 Maintenance techniques

The techniques and approaches for maintenance vary with respect to the type of maintenanceaccording to its classification.

General techniques for Predictive maintenance (PdM).The main pile where predictive maintenanceis founded is performing either periodic or continuous monitoring of the equipment condition. Thedata captured in these monitoring inspections are used under an analysis scheme to derive predictive

patterns. Most PdM inspections take place while equipment is in service. This is the reason of thismaintenance type is known as condition-based maintenance. The analysis schemes are based onstatistics, fuzzy logic, artificial intelligence, etcetera.


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To evaluate equipment condition, predictive maintenance utilizes nondestructive testingtechnologies such as infrared, acoustic vibration analysis and other specific online tests. Mixed

methods such as Collaborative Process Automation Systems (CPAS) utilize measurements on theactual equipment in combination with measurement of process performance, measured by otherdevices, to trigger maintenance conditions. A brief and general description of most used andpromising techniques in railways is attached in Annex A.

1.5 Maintenance planning and scheduling

The scope of maintenance planning and scheduling is to perform all maintenance activities in such away that cost, generalized cost, is minimized. Planning involves ordering of tasks and resources;scheduling takes care of sequencing the tasks regarding time.

From a chronological point of view maintenance activities can be grouped into two classes:

Stationary or tactical, which are planned on the long term. The maintenance scheduling canbe modeled in an infinite planning horizon, defining static rules which do not change withtime. This type of activities allows to group them into related-activity sets with the interestof programming them under an optimum scheme.

Dynamic or operational, carried out on the short term. The activities take place due tounexpected tasks to carry out corrective operations and other non-corrective operationsmaking use of unexpected opportunities. The maintenance scheduling is modeled in a finite

planning horizon, which changes continuously. The activities are also able to be groupedinto sets under dynamic optimization overhead management. Dynamic maintenancemanagement models pursuit the optimum scheduling of maintenance operations under a costobjective function subjected to constraints (technological, service, time-window, amongothers). These models group preplanned operations with unexpected ones in order torationalize all maintenance activities. When unplanned operations appear unexpectedly dueto deterioration of components for instance, the maintenance belongs to the corrective type;in this case the maintenance operation is known for certain and a deterministic maintenancescheduling can be settled. On the other hand when unplanned operations are envisaged fromPdMmodels, under a probabilistic environment, the prospective maintenance operations areexpected with an appearance probability, and a stochastic maintenance scheduling should

take the lead. These two last cases to classify the maintenance management into eitherdeterministicor stochasticmodels.

The objective of the stochasticPredictive Maintenance(SPdM) is to give an answer of themost probable maintenance operations, onwards these will be as deterministic PMoperations.


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2. Railway Infrastructure Maintenance

2.1 General maintenance aspects

The primary tasks of rail infrastructure are:

first of all, to ensure safe operations of rolling stocks at the scheduled speed,

to afford conditions for the highest quality and reliability of transport,

to contribute to a sustainable development.

The management of infrastructure should respond to the following objectives:

to maintain and increase high level of safety,

to reduce costs, without however decreasing safety standards,

to improve organization, materials, equipment and staffs qualification in order to respondmore efficiently to requirements of operation.

Appropriate maintenance of infrastructure is vital to achieve the aforementioned goals.

Railway infrastructure maintenance works need possession of the infrastructure. The termpossessionof the infrastructureindicates the use of the infrastructure by some activities. When the

infrastructure is used by trains the possession for servicetakes place, possession for maintenanceindicated the use of the infrastructure by maintenance operations. Thepossession for maintenancecan be either partial, when maintenance and trains share the infrastructure, or privative when themaintenance takes full possession of it. The first category implies safety risk conditions to beproperly assessed and may be precluded by some/many Administrations. In that follows the term

possession for maintenance stands for full possession of the infrastructure by maintenanceoperations. As train services is the most usual activity supported by the railway infrastructure,single termpossessionis customary identified with maintenance operations, and is a synonymous of

possessionfor maintenance.Possession can be divided into several categories (Office of the Rail Regulator, 2001; Budai-Balke,2009), ordered according to the severity of the inconveniences carried out by the disruption of thetrain services:

Overnight possession takes place in the free-of-service periods (time-window). Thepossession for maintenance depends on the extension of the available time-windows definedby the service of last train on a day and the first train of next day.

Weekend possessionmakes use of the fact that train services are reduced (may be reduced,re-scheduled or re-routed) respect to labor-day services, therefore larger and more frequenttime-windows might be available.

Daytime possession, the shortage of available time-windows makes this possession to befocused on operations that cannot be postponed for latter, such as corrective works.


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Maintenance is critical for ensuring safety, train punctuality, overall capacity utilization and lower costs formodern railways. Maintenance productivity is directly related to the available time-windows of trainservices. Due to the fact that time-windows are more scarce regarding the experienced increment inrail transport demand, advance managerial techniques and procedures get into action as a tool tocombine the objective pursuit by both need, train service and the maintenance.

2.2 Organization of the Railway sector

Small private companies led the initial development of Railway, in 19th century and in the early20th. Later on, due to the strategic importance of the railway sector, most governments initiated aprocess for the nationalization of their railways during the period 1935-1960. Between 1960 and1980 most railways were under State control.

In the 1980s and 1990, the deregulation and gradual liberalization of transport market forced therailway sector to show more flexibility, reduce cost, adapt to new technologies and modernize. Inthis period some countries like Japan and Great Britain privatized their railways.

Since 1990s, important changes occurred in the organization/management of railway around theworld in order to proof the financial efficiency and competitiveness of the rail transport comparedto other means like roads or airplanes. To achieve that goal, most countries are performing changesin the organization/management of infrastructure and in the operation of exploitation of railservices. Railway is evolving to a more open market performance allowing the possibility of otheroperators, different than national ones, to run services.

Following worldwide trends, in the last 20 years, the European Commission has been very active inrestructuring the European rail transport market and strengthening the position of railways withrespect to other transport modes. Commission efforts have concentrated on three major areas whichare all crucial for developing a strong, transparent and competitive rail transport industry: (i)opening of the rail transport to market competition, (ii) improving the interoperability and safety ofnational networks and (iii) developing rail transport infrastructure.

The liberalization of the railway sector, as in other strategic fields like electricity, gas or telephone,requires the distinction between the infrastructure owners and managers who run the network andthe railways companies that use it for transporting passenger and goods. The former (infrastructureownership/management) is a natural monopoly while the latter (operation of the transport service)

should be competitive in an open market. Different organisational entities must be set up fortransport operation, on the one hand, and infrastructure management, on the other. Essentialfunctions such as allocation of rail capacity (train paths), infrastructure charging and licensinghave to be defined. All these operation must be performed in a neutral fashion to give new railoperators fair access to the market.

On the other hand, improving the interoperability and safety of national networks is essential inorder to promote a single European Rail Market. Some technical barriers still need to be overcomefor the sake of interoperability.


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2.2.1.The liberalization of the Railway sector in the European Union

European Union Directive 1991/440/EU was the first step towards the definition of infrastructuremanager and service operator as different agents. Most relevant EU legislation on this issue is listedbelow:

Separation of the management of infrastructure from the operation of rail services: Directives1991/440/EU, 2001/12/EU, 2004/14/EU and 2004/51/EU: The infrastructure manager and the

Operators must have separate balance sheets.

Separation of passenger and freight transport and avoid cross of subsidies among them.

Determination of minimum conditions to be met for a rail operator to run infrastructure: Directives1995/187EU and 2001/13/EU).

Methodology of calculation of infrastructure charges: Directives 1995/19/EU and 14/2001/14/EU.This methodology helps outsiders to enter into the railway sector or to perform its activities in

another country under equal conditions than already-running operators.

Definition of the infrastructure manager duties in order to avoid discriminations: Directive2001/12/EU.

Definition of rules to ensure transparency in finances including measures to avoid state subsidies forfreight transport and possibly subsidies form infrastructure manager: Directive 2001/12/EU.

Definition of the figure of a Regulator agent to control the infrastructure manager: Directive

2001/14/EU.

The full liberalization of the railway freight transport in 2007 and of the passenger transport in 2012were other of the EU legislation objectives as it is described in the European Commission web page.

Finally, the European Union legislation can not impose any rules about ownership of transport(article 222 of the Treaty of Rome), leaving each country the decision whether privatizing or not

parts of the railway.

2.2.2.Models for the organization of the rail sector

To accomplish with the separation of infrastructure management and rail operation (Directives1991/440/EU and 12/2001/12/EU), countries in the EU has chosen different models.

Below different models for the organization of the railway business in different countries aredescribed. The main goal is to allow new rail operators to enter into the market. Nevertheless, sofar, in most cases, the new rail operator is the one and only operator. Not only EU models areexplained but also those in Japan and USA.

2.2.2.1.The semi integrated model (France)From the Second World War and until the 1990s, the public company SNCF (Socit Nationale desChemins de Fer) managed both the infrastructure and the operations of railway, it were a public

company. When the directive 1991/440/EU forced to separate the infrastructure managing from theoperation, the government created a new organization RFF (Rseau Ferr de France) to manage theinfrastructure. Little resources (personnel and technical equipment) were given to the new entity so


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that it had to subcontract all the maintenance operations. Furthermore, RFF demanded a uniquesubcontractor for the whole French railway network. As a consequence, the only company with therequired resources for such task was SNCF.

Therefore, since then RFF is the public authority on railways and the infrastructure manager.Responsibilities, objectives, strategies and financial issues concerning the management of theinfrastructure are carried by RFF, but the maintenance is still subcontracted to SNCF. Therefore,although changes in the organization of the rail sector has been accomplish to meet EU regulation,the public authority (RFF) and the public company (SNCF) work together leaving little room forcompetitors.

2.2.2.2.The separated model (Germany, Italy, Greece, Spain)This model led a legal separation of business responsibilities and different train operators andinfrastructure managers. The infrastructure manager and the rail services operation company can be

overruled by a Holding Company (Germany, Greece) but both have total independence.2.2.2.3.The separated model with privatization (UK)

In the UK the separation of the railway manager and the train operator was performed inconjunction with the partition of the train operator in 25 small operators called TOCs Both theTOCs and the infrastructure manager (Railtrack) had been privatized in the 1980. In the 1990s thegovernment partially renationalized Railtrack because it had serious financial problems.

2.2.2.4.USAThe most relevant characteristic of the American rail market is that rail operators can own the trackthey are running on. As competition is the basis rule in the American economy, legislation tries to

assure rights of rail operators so that they can run on infrastructure owned by another (and oftencompetitor) company.

Both passenger and freight services were operated by private companies until 1970 when theNational Passenger Railroad Corporation (AMTRAK), a federal owned corporation subsidized bythe federal government was established. AMTRAK owns and operate part of the country railinfrastructure. It also has the right to operate all other tracks under negotiated access agreements,subject to adjudication in the event of dispute with the infrastructure owner).

Regulation of the transport sector in US is assured by the Surface transportation board, whosejurisdiction covers all railways operating within the United States and has duties to:

Ensure that rail carriers have trackage rights to operate on another carrier's infrastructure,reduce tariffs, particularly when complaints for market dominance and power have been addressed,

address quality, control exit, under specific circumstances, from the market, approve or decline

mergers in the rail industry or impose conditions (i.e. trackage rights) on the merger, to promote

competition.

2.2.2.5.JapanStrong densities of population in Japan (with 1,500 people living per km2 of habitable area, against160 in France, 260 in the United Kingdom and 50 in the USA), favour rail passenger traffic. On thecontrary, freight has a rather marginal share.

Japanese National Railways (JNR) started facing serious fiscal problem in the mid-1960s, whichwerent overcome after two decades, in spite of four restructuring plans. The whole rail network


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was split in 1987 in 6 regional private passenger companies (each one owing its own infrastructure).Another company, Japan Freight Railways, which pays fees to the 6 rail passenger companies forusing their tracks and other facilities, took freight traffic.

After almost 25 years, the deregulation and privatization has reach its objective. There is a strongcompetition in the rail market in Japan with more than 130 rail passenger companies and 30 railfreight operators.

2.2.3.Interoperability and safety in the EU

As mentioned above, one of the main goals of the European Commission is the promotion anddevelopment of a single European rail market. Such achievement requires to overcome sometechnical barriers to allow for an improve interoperability (or technical compatibility) ofinfrastructure, rolling stock, signalling and other rail systems, as well as less complex procedures

for approving rolling stock for use across the European rail network.Over the years, national rail networks have developed different technical specifications forinfrastructure. Different gauge widths, electrification standards and safety and signalling systemsmake more difficult and more costly to run a train from one country to another. Specific EUlegislation has been set to promote interoperability and overcome such differences but there is still alot of technical trouble to be solved.

The European Commission issued several directives aimed at removing technical barriers to thesupply of equipment and the running of trains between Member States. They were adopted by theEuropean Council and the Parliament between 1996 and 2004. After that date, other directives and

amendments have been published

There are three main groups of Directives:

i)High-Speed directives: (1994/48/EC, 1996/48/EC, 2008/57/EC).ii)Conventional directive (2001/16/EC)iii)Amendment Directive (2004/50/EC) which made changes to the High-Speed and Conventional

directives.

The purposes of the above directives are:

To allow common technical standards, called Technical Specifications for Interoperability(TSIs) to be applied across Europes railways. These specifications lay down the fundamentalelements of each subsystem and identify the constituents that are critical from the perspective ofinteroperability. They are drafted by working groups overseen by the European Rail Agency(ERA), an agency set up in 2006 with the purpose of reinforcing rail safety, harmonisingtechnical standards and promoting interoperability, a process in which cooperation between EUMember States and rail stakeholders is essential.To establish a common European verification and authorisation process for placing new,upgraded or renewed infrastructure or rolling stock into service.To provide a process for putting certain rail components known as interoperability constituentsonto the rail market.

The set of interoperability directive is the cornerstone of a three-tiered structure:


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The Directives itself, containing essential requirements to be met by the system. Theyprovide specific details regarding the proper implementation of the interoperabilityrequirements including the authorisation of placing in service, the EC checking procedureand the EC declaration of conformity with the essential requirements and the TSIs, as wellas the definition of the role of the notified bodies and cooperation between them.

The technical specifications for interoperability, which have to be adopted in accordancewith the procedures laid down by the Directive;

All the other European specifications, including European standards from the Europeanstandards bodies: CEN, Cenelec and ETSI. They are not compulsory but confer apresumption of conformity with the essential requirements of the Directives.

The main points of the interoperability system are:

o The signalling systemo

The railway gauge width2.2.3.1.Interoperability and gauge width

The gauge width was fixed by standards since the 19 thcentury. All the EU countries have the samegauge width except for Spain. Since 1990 Spain is building its new high speed lines with Europeangauge. Therefore the European high speed gauge width is unique.

2.2.3.2.Interoperability and Signalling systemThe signalling system is one of the first items of the interoperability system. Europe has more thantwenty different signalling and speed control systems for rail transport. Although expensive, on-

board systems in locomotives fitted with transducers, which react to signals transmitted from thetrack, are necessary for both safety and traffic management. Nevertheless, the coexistence ofvarious systems is a barrier to the development of international rail traffic, as locomotives have tobe able to 'read' the signals from different networks when crossing borders. The Thalys train forexample, which links Paris and Brussels in particular, has seven on-board systems. This results inincreased costs and breakdown risk, as well as being a headache for drivers, who have to be able to

juggle several interfaces. In addition, this segmentation represents an obstacle to the integration ofrail transport on a European scale, while road transport benefits from the absence of such barriers.The twenty different systems coexisting in Europe are currently developed on a national level. Theyare very different in terms of performance and safety. Several fatal accidents, including those inBologna in 2005, Albacete in 2003 and London in 1999, show that a more effective signalling

system with automatic train speed control could improve the safety of the railways.

Locomotives operating internationally also have to be equipped with a variety of on-board systemsable to process the information transmitted by track-side systems. As adding on-board systems isexpensive, and sometimes even impossible, some trains have to stop at borders in order to changelocomotive. As a result, for the Thalys train the numerous signalling systems to be integrated pushup the cost of manufacturing each trainset by 60%. Such obstacles make the connection andintegration of the different European networks problematic.

The Commission therefore calls for the gradual transition to a system that is common to the variousMember States: the European Rail Traffic Management System (ERTMS). This has two

components:


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GSM-R, a radio communication system based on standard GSM (used by mobiletelephones), but using various frequencies specific to rail;

ETCS (European Train Control System), which not only allows permitted speed informationto be transmitted to the driver, but also monitors the driver's compliance with theseinstructions.

While the deployment of GSM-R, based on successful public GSM place quickly, ETCS has beendeveloped specifically for the rail sector and is advancing slower. It requires the installation of aspecific module on board the train and the use of the same ETCS format for the transducers laidalong the track.

Given the long service life of rail equipment (more than 20 years), it is impossible to renovate theentire network at once. The Commission therefore estimates that it is inevitable that there will oftenbe at least one system coexisting with ETCS on board and/or on the track.

The Commission is planning a rapid migration strategy, with the aim of quickly reaching a criticalmass of ETCS equipment. It therefore hopes that a sufficient number of traction units will beequipped over a period of ten to twelve years, while at the same time large interoperableinternational corridors are created.

2.3 Inspection and maintenance operators

The railway infrastructure manager can perform inspection and maintenance tasks:- Using its own resources- Subcontracting all or part of it (inspection, track, catenary or communications) to different

subcontractors- Subcontracting everything to only one subcontractor (as it is the case in France)

Usually large railway administrators prefer to subcontract maintenance tasks, that require a lot ofemployees and to perform inspection ones themselves. On the contrary small railway administratorscannot afford to have (expensive) inspection trains but can perform maintenance activities withtheir own resources.

In general, the administrators are not technologic developers and must buy different instruments andsoftware from different suppliers, which are in different systems and data format. In fact the bigtramping and ballast cleaning machines are designed by a few companies (Plasser, Robel, Speno)

which usually operate it themselves, but the measurements instruments involves a lot of companieswhich must be coordinated.

Summarising, railway maintenance involves many different companies:

- The infrastructure manager, who, in some cases (but not usually), may perform all tasksitself, but in most occasions subcontracts at least parts of the work.

- Inspection companies that owns inspection vehicles or install measurement instrumentationinto other company vehicles.

- Specialised track maintenance companies that own tramping and ballast cleaning machines.- Communications and electric companies who that perform maintenance activities on the

electrical and communications systems.- Building companies that take care of subgrade maintenance.


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2.4 Railway infrastructure. The track

The term railway infrastructure covers all assets used for train operations, except rolling stocks. Adefinition of railway infrastructure is given by European Community Regulation 2598/1970 and

comprises routes, tracks and field installations necessary for the safe circulation of trains.

Railway infrastructure consists on the following items:

i. Track: including rails, sleepers, fastenings, switches and crossings, ballast and platform. Itcan be structured into superstructure and subgrade.

ii. Bridges and viaducts: including pillars, decks, foundationsiii. Tunnelsiv. Electric system: including catenary and support third rail, substations and control

equipment,v. Safety, signaling and communication systems including fixed signals, track circuits, train

control equipment, signal cables or wires, signal boxes and, for high speed lines, cabsignaling systems.

vi. Lightning installations for traffic safety purposes.vii. Level crossings including appliances to ensure the safety of road traffic.

viii. Passenger and goods platform and access ways

Maintenance of infrastructure can refer to the following components:

maintenance of track, maintenance of electrification equipment, maintenance of signalling equipment, maintenance of rail traffic.

The maintenance of all these subsystems is a complex issue which makes it difficult to plan andexecute the maintenance task. Factors such as geographical and geological features, topography orclimatic conditions need to be considered when planning for maintenance. Furthermore, theavailability of the track for maintenance (on possession for maintenance, defined in Section 2.1)without disrupting train services is also an important issue to be considered when planning themaintenance tasks to be executed. Maintenance is critical for ensuring safety, train punctuality,overall capacity utilization and lower costs for modern railways.

The ACEM-Rail project focuses exclusively on the maintenance of the track itself together with

some engineering structures like bridges or tunnels. The track can be structured into: The track and track bed, also called superstructure, which supports and distributes train

loads and is subject to periodical and maintenance and replacement. It consists of:o The rails, which support and guide the train wheels.o The sleepers (also called ties, mainly in North America) with their fastenings, which

distribute the loads applied to the rails and keep them at a constant spacing.o The ballast, usually consisting of crushed stone and only in exceptional cases of

gravel. The ballast should ensure the damping of most of the train vibrations,adequate load distribution and fast drainage of rainwater.

o The sub-ballast, consisting of gravel and sand. It protects the upper layer of thesubgrade from the penetration of ballast stones, while at the same time contributes to

further distributing external loads and ensuring the quick drainage of rainwater.


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The subgrade, on which the train loads, after adequate distribution in the superstructure, aretransferred and which in principle should not be subjected to interventions during periodicalmaintenance of the railway track. It consists of:

o The base, which in the case of the track laid along a cut consists of onsite soil, whilein the case of an embankment is composed of soil transported to the site.

o The formation layer, used whenever the base soil material is not of appropriatequality.

Figure 1: Superstructure and subgrade

The track usually lies on ballast which provides a flexible support. It is referred as ballasted track.However, it is possible, that the track is supported by a concrete slab, instead of ballast. In this case,the support is inflexible and it is called slab track. Although a slab track is used in certain railways(e.g. the Japanese and the German, among others), it is most effective when used in tunnels,because it allows a smaller cross-section and facilitates maintenance. In most of the tracksworldwide, a ballasted track is still the case, as it ensures flexibility (an important factor in the eventof differential settlements) and much lower construction cost, while at the same time offering a verysatisfactory transverse resistance, even at high speeds. The problem of noise, which is much greaterwith the track on concrete slab than with the track on ballast, should not be disregarded. When aslab track is applied (e.g. in the case of a tunnel), the sudden variation in track stiffness (felt bypassengers as a jolt) is lessened by placing rubber pads of a suitable thickness along the tunnelentrance and exit.

The choice between ballasted and non-ballasted track should consider construction cost (much

greater for non-ballasted track), maintenance cost (much greater for ballasted track), together withtechnical requirements. Both solutions have pros and cons.

2.4.1.Superstructure

The elements to be considered in the superstructure are:- Track

o Railo Sleeperso Fasteningso Switches and crossing

- Track bedo Ballasto Sub-ballast


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2.4.1.1.TrackThe track is composed of several elements: rail, sleepers and fastenings. Others elements that can befound at certain points in the track layout are switches and crossings.

Rails

Rails support and guide the wheels of the train vehicles. Rail profile has been the object ofcontinuous improvement since the beginning of railways.

The cross-sections of gauge rails have been standardized by the UIC.

Figure 2: Rail profiles UIC 50 (50 E1), UIC 54 (54 E1), UIC 60 (60 E1) and UIC 71 (71 E1).

Sleepers

Sleepers are the track components used to transmit stress from rail to ballast.

The railway lines have sleepers of different types and materials. The selection of the materialsdepends on the following factors:

- Sleepers construction cost.- Purchase cost of fastening and other indispensable sleepers accessories.- Sleeper lifetime- Maintenance cost- Probable waste values of sleepers at the end of its lifetime- Weight of sleepers (it affect to transverse resistance)- Distributions of train loads.- Electrical insulating contributions

Sleepers can be made of steel, timber or concrete.

a. Steel sleepers


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The steel sleeper is an industrial product of simple construction. It consists of a profile in the formof U. Its ends are forged to provide anchoring in the ballast, so as to ensure transverse trackstability.

Steel sleepers are easily manufactured, installed and maintained. They keep the track gaugeadequately constant for a long time. As steel sleepers are out of production today, no recent costdata are available. Their lifetime is relatively long and after replacement they have still a certainvalue as crap iron.

However, steel sleepers have many disadvantages. They have a low transverse resistance, a factprohibiting increased speeds on tracks with steel sleepers. Their form makes longitudinal andtransverse track positioning difficult. Steel sleepers are noisy, they require special insulating devicesfor signalling, and their maintenance is difficult. Furthermore, steel sleepers are sensitive tochemical attacks and particularly vulnerable in lines close to industrial and coastal areas. All the

above disadvantages have led to the economic devaluation and to the gradual withdrawal of steelsleepers, particularly in Europe.

b. Timber sleepersTimber sleepers distribute loads better than other sleeper types. They are accordingly recommendedfor tracks laid on fair or poor quality subgrade, where concrete sleepers would require acomparatively greater thickness for the ballast layer. Because of their higher cost and shorterlifetime, their use in Europe is presently limited to instances where concrete sleepers are not used.However, they are still extensively used in North America.

The kinds of wood presently used for timber sleepers include beech and oak from European trees,

and azobe from tropical ones. Pine tree timber has also been used in the past. Timber sleepers in useby the various railways today are mostly of azobe tropical timber, which is stronger and moredurable. In underground tunnels, Australian jarrah hardwood sleepers have been used extensively.

The principal advantage of timber sleepers is flexibility and better load distribution. Timber sleepersare accordingly recommended in the case of poor quality subgrades. Moreover, timber sleepersprovide good insulation which is important with special devices for signalling and electric traction.Finally, compared to concrete sleepers, timber sleepers are shorter in height.

The disadvantages of timber sleepers include their relatively short lifetime, their comparativelyhigher cost (in Europe, though the situation is inverse in other parts of the world) and their low

transverse resistance (a result of their low weight), thus precluding high speeds on their tracks.

c. Concrete sleepersConcrete presents two weaknesses for its use in sleepers: brittle fracture and little fatigue resistance.To overcome such disadvantages, it is required to place an absorbing material between sleepers andrail and to use reinforcing bars inside the sleepers.

There are two types of reinforced-concrete sleepers.

Twin-block reinforced-concrete sleeper

The sleepers have two block of concrete in the extreme, in that block be installed the rail,while in the central part the concrete was replaced by a connecting bar.


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Figure 3:Twin-block sleepers

Due to its large weight, the twin-block sleeper provides very good transverse trackresistance and allows high speeds. It keeps track gauge within satisfactory tolerances andhas a long lifetime.

Twin-block sleeper behaviour is less satisfactory when the ballast does not have the suitablethickness and mechanical characteristics. Load distribution and flexibility are less

satisfactory with twin-block than with timber or monoblock concrete sleepers. In addition,twin-block sleepers require elastic fastenings and because of their great weight, handling isdifficult. The twin-block sleeper (in contrast to the timber sleeper) requires specialaccessories, so as to ensure the necessary insulation for signalling and electric traction.Special attention should be given to the behaviour of the connecting bar. If the latter is notappropriately placed and anchored, it may produce a maintenance hazard to staff working onthe track.

Monoblock prestressed-concrete sleepers

The monoblock sleeper has the following characteristics:- It withstands alternating stresses better, since the stress on the concrete is always

compressive.- It offers a reduced sleeper height at the central part, since the steel bars do not have

to be located, as in reinforced-concrete, as far away from the neutral axis as possible- It allows a reduction of the steel used, in comparison to the twin-block sleeper- It is generally lighter, compared to the twin-block sleeper; this fact, however,

reduces transverse resistance.


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Figure 4: Monoblock sleepers

Monoblock sleepers present a similar behaviour to that of the twin-blocks. They maintainthe track gauge in a satisfactory manner and have a long lifetime. They require elasticfastenings and special accessories for signalling. However, monoblock sleepers distributeloads better than twin-blocks, but not as well as timber sleepers. Their transverse resistanceis lower than that of twin-blocks, but higher compared to timber sleepers; monoblocksleepers provide also a good surface for the maintenance inspection staff.

Fastenings

The word fastening refers to all elements to ensure the rail-sleeper connection. Fastening shouldprovide the following properties:

- Keep track gauge and transverse rail inclination on the sleeper constant,

- Transfer loads from the rail to the sleeper- Attenuate and dampen vibrations caused by train traffic- Easy installation and maintenance- Electrical insulation- Resilience and adequate deflection- Avoidance of abrasion between components and of over-stressing- Adequate corrosion resistance- Reasonable cost and lifetime compatible to that of sleeper- Resistance to vandalism

Fastenings are classified into rigid or elastic ones.

a. Rigid fasteningsRigid fastenings are used only with timber or steel sleepers. In rigid fastenings the rail is connectedto the sleeper with bolts or nails. During train passage the rail compresses the sleeper and part of thestrain is plastic (i.e. it does not disappear when the load disappears), resulting in the creation of agap between nail head and rail. With successive train passages the gaps grow, causing a gradualslackening of the fastening, which affects safety and may be the origin of a derailment. In additionto plastic strain, high frequency vibrations caused by rolling stock traffic also contribute to thewidening of the gaps and the slackening of the fastening.

Rigid fastenings may be installed either without or with a seating plate, the latter being thepreferable solution.


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b. Elastic fasteningsThe use of elastic fastenings is mandatory with concrete sleepers and optional with timber and steelsleepers. Two types of elastic fastenings may be distinguished:

- Screw-type elastic fastenings. They have the advantage of great fastening strength and easymaintenance and replacement. They have the disadvantage that correct installation is affectedby local conditions. The common elements are:o A threaded element (a), which is used to apply a force to a spring steel

element, this threaded element being removable from the sleeper,o The spring steel element (b), which can be a bar or a plate,o A pad (c) between rail and sleeper to absorb vibrations, to provide a

suitable layer between rail and sleeper and also electric insulation,o Insulating elements (d) to isolate electrically the rail from any metallic path into the

sleeper.

Figure 5:Elastic fastenings

- Spring-type elastic fastenings. They are less adaptable than screw-type fastenings, but lessaffected by installation conditions, and any error is easily located visually. The commonelements in spring-type fastenings (which should not require any subsequent maintenance)are:o Some form of anchorage (a) fixed in the sleeper, generally at the time the sleeper is

manufactured,o A spring steel element (b) to generate clamping forces on the rail foot,o A rail pad (c) between rail and sleeper to attenuate forces and stresses and to provideelectrical insulation, which is necessary for the signalling system,o Insulators or a layer of insulating materials (d), to provide electrical insulation between


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the rail and any metallic path, such as via (a) and (b), to the sleeper.

Figure 6:Resilient pads

An important element of the fastening is the resilient pad. Resilient pads are used between rail and

sleeper or between rail and concrete slab. When a baseplate is used (both in ballasted and non-ballasted tracks), then pads are used between baseplate and sleeper or between baseplate andconcrete slab. They are called baseplate pads.

Pads must fulfil a number of functions and properties:- Load distribution.- Vibration attenuation- Resilience- Resistance to creep- Electrical insulation- Durability

Switches and crossing

A fundamental characteristic of railway is the one degree of freedom of the movement of the railvehicle on the track. However, trains must have the possibility to change course from one track toanother. This is realized by so-called switching devices, defined as the equipment and parts thoughtwhich the direction of movement of a rail vehicle can be change without interrupting its course.

Switches and crossing are a track fundamental part with different geometrical characteristic to thelinear track but the same components too (rail, sleepers and fastening), with different geometricalcharacteristic. Switches and crossings are subject to more intense stresses that linear tracks.Therefore, although the types of defects and required maintenance tasks are similar to those in

linear tracks, the behaviour and evolution of switches and crossings defects are different than thosein linear tracks, because of the harder stresses.


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Switching devices take a great variety of forms. In spite of their apparent complexity, they can bedistinguished into two basic forms, and a third combining the first two:

- Simple, or multiple turnouts, allowing a track to be split in two (sometimes in three) andthe moving rail vehicle to change course.

- Crossing, where two tracks meet at grade witch no change of course.- Turnout crossing, combining the functions of turnouts and crossing.

Thus, the functions of switches and crossing are: (i) to enable rail routes to branch from or to joinup with one another; (ii) to provide flexibility within a route so that trains may move from onetrack; and finally (iii) to enable vehicles to be sorted out, in order to respond efficiently to theserequirements. Switching and crossing must fulfil certain requirements, which include the following:

- Impose the fewest possible speed restrictions,- Be sited exactly where operational exigencies demand,- Provide maximum operational flexibility,

- Support axle weight required to be carried,- Be cheap to manufacture, simply to lay, easily worked, robust and easy to replace,- Resist wear, corrosion and decay, and require minimum maintenance,- Be compatible with signalling requirements.

Figure 7:Crossings

2.4.1.2.Track bed

Ballast

The term ballast denotes the layer of crushed stone (and only in exceptional cases of gravel) onwhich the sleepers rest. Furthermore, the ballast fills the space between sleepers as well as at somedistance (called ballast shoulder) beyond the sleeper ends.

The railway ballast performs several functions:- Further distributing stresses transmitted by the sleepers.- Attenuating the greatest part of train vibrations.- Resisting track shifting (transverse and longitudinal).- Facilitating rainwater drainage.- Allowing track geometry to be restored and correcting track defects.

The above functions are clearly contradictory in some aspects, thus the ballast cannot completelyfulfil all of them. It could be argued that for good load bearing characteristics and added track


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stability, the ballast needs to be well graded and compact which, in turn, however, makes dispersalof water more difficult, together with associated maintenance. A balance, therefore, among thevarious functions that ballast is required to perform is aimed at.

Subballast

Under the ballast layer, the gavel subballast is laid and has the following functions- Protection of the upper surface of the subgrade from the intrusion of ballast stones,- Further distributing stresses,- Further facilitating rainwater runoff,- Imparting a transverse slope (commonly 3-5%) to the upper surface of the subgrade for

proper runoff.

The usual thickness of the gravel subballast layer is 15 cm. However, some railways do not use asubballast layer and they simply use a greater thickness of the formation layer, which is placed on

top of the subgrade.

2.4.2.Substructure

The term substructure will be used to denote the subgrade together with structures like bridges,tunnels, cuttings & embankments and drainages.

2.4.2.1.SubgradeSubgrade is the layer below the subballast. It supports the stresses transmitted by the track to thesoil. The subgrade is the first layer of the soil in railway infrastructure. It has to be designedaccording to the stresses that it will have to support.

Railway subgrade is particularly important in ensuring that track quality reaches the standardnecessary for the safe and comfortable operation of trains. Railway networks make serious efforts toimprove passenger comfort. These efforts, however, mainly concentrate on the railway track andoften disregard the fact that many problems appearing at track level are traceable to the subgrade,rather than to the track.

Before the construction of the track, an analytical geotechnical study has to be performed. Thisstudy will be required to define the design of the subgrade along the track line These studiesdetermine the soil characteristics such as soil type, hydrogeological conditions, and mechanicalstrengths.

The design of the subgrade will take into account track loading (load per axle and track tonnage),sleeper type and ballast thickness together with soil parameters: soil type, hydrogeologicalconditions, and mechanical strengths.

In existing layouts built decades ago, it may be required to adapt the subgrade characteristics tothose required by higher speed and higher load per axle trains, which increase subgrade stresses. Inthese cases, often the lower surface of the subballast and the upper surface of the subgrade haveformed a compact zone, which should be disturbed as little as possible. Therefore any interventionin the subgrade should be limited to areas where particular problems have arisen and should bescheduled, as much as possible, to be performed during periodical track maintenance. The decision

between improving the subgrade and increasing the ballast layer thickness should be the subject of atechnical and economic study.


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The railway subgrade should fulfill the following functions:- Enable passenger and freight trains to run safety at the specified speed.- Support the heavy axle loads of freight trains.- Minimize future track maintenance costs.

These functions can be achieved by:- Limiting settlements of the original ground and of the embankment filling.- Providing stable mechanical behaviour under the train loads and the weight of the

earthworks.- Ensuring that the condition of the subgrade does not deteriorate during its working life.

2.4.2.2.StructuresStructures include bridges and retaining walls. Their mission is to support the track.The most common bridges are stone and masonry ones (19thcentury), steel ones (19thand early 20th

centuries) composite ones (20

th

-21

st

centuries) and concrete ones (20

th

-21

st

centuries). There are alsospecial structures for big spans (over 40 m) like arcs and suspended bridges.

The typology of retaining walls includes:- Concrete Walls- Rubble Walls- Reinforced soil

Railway structure includes the structural design, structural analysis, structural construction andmaintenance of bridges and walls. This involves identifying the loads which act upon a structureand the forces and stresses which arise within that structure due to those loads, and then designing

the structure to successfully support and resist those loads. The loads can be self weight of thestructures, other dead load, live loads, moving (wheel) load, wind load, earthquake load, load fromtemperature change etc. The structural engineer must design structures to be safe for their users andto successfully fulfil the function they are designed for. Due to the nature of some loadingconditions, sub-disciplines within structural engineering have emerged, including wind engineeringand earthquake engineering.

Design considerations will include strength, stiffness, and stability of the structure when subjectedto loads which may be static, such as furniture or self-weight, or dynamic, such as wind, seismic,crowd or vehicle loads, or transitory, such as temporary construction loads or impact. Otherconsiderations include cost, constructability, safety, aesthetics and sustainable.

Reinforced soil is a flexible technique which can, in many instances, replace retaining walls orstructures. Reinforced soil is an assembly consisting of:

- The embankment edge.- Good quality soil material.- Metal bars or polyethylene bars.- Concrete cover.

2.4.2.3.TunnelsTunnels are a special type of structure in the railway infrastructure.A tunnel is an undergroundpassageway, completely enclosed except for openings for egress, commonly at each end.


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The construction of a tunnel must start with a comprehensive investigation of ground conditions bycollecting samples from boreholes and by other geophysical techniques. A reported choice can thenbe made of machinery and methods for excavation and ground support, which will reduce the riskof encountering unforeseen ground conditions. In planning the route, the horizontal and verticalalignments will make use of the best ground and water conditions.

In some cases conventional desk and site studies yield insufficient information to assess suchfactors as the blocky nature of rocks, the exact location of fault zones, or the stand-up times ofsofter ground. This may be of particular concern in large diameter tunnels. To gathe

acem-rail d1.1 state of practice r0

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