Cost based determination of rail corrugation maintenance period for ballastless superstructures

Parallel to the increased demand for railway transportation, operating speeds and freight loads are also increasing. As a consequence of increased number of passengers and freight traffic, the annual tonnage over the rail tracks increases, which might lead to increased deterioration in the railway superstructure, running rails, and sometimes railway infrastructure. Repairment of these deteriorations requires extensive maintenance needs. The corrugation of rails occurs on railways depending on the geometry of the track, the wheel-rail contact surfaces and the quality of infrastructure and superstructure. The corrugations can be generally defined as surface irregularities that periodically occur on top of rail head in short wave or long wave forms. In the first chapter, ballastless track system and preventive - corrective maintenance works in such superstructures are described. In preventive maintenance section; visual inspections, track measurements and service-based maintenance activities are described. In corrective maintenance section, all interventions against track failures and track geometry deteriorations are detailed. In the second, third and fourth chapters, the corrugations which are the main topic of the thesis were have been examined in detail. The definition and types of the corrugations are categorized according to their wave length and effects. The literature survey has been given on how the corrugations occur. The damages caused by the corrugation are classified as environmental problems, damage in components of infrastructure and superstructure, and damage to vehicle sub-systems, and explained. The mitigation measures to prevent the corrugation occurrence have been proposed from three different points of view; during design phase, operation phase and on rolling stock. Types of corrugation measurement equipment are described and evaluation of corrugation measurements on a sample track is explained. When dealing with the corrugation, the track, rolling stock and wheel-rail contact should be treated with the same importance level. Even the precautions are taken during the design phase and on the rolling stocks, the corrugations cannot be completely eliminated and it will be necessary to make interventions during operation. The most common method for reducing corrugations during operation is to periodically apply rail grinding. Wave depth, grinding method and grinding period are most important subjects to be determined in rail grinding. In this study, rail grinding on sample track and number of grinding passes is determined with the assumption of using the same grinding machine in all time. As the wave depth increases, the required number of grinding passes also increases, therefore it is more economical to grind before the wave depth increases too much. Moreover, it is necessary to take into account that the big wave depths can lead to damages in the superstructure that cannot be rectified. Usually, periodical measurement of the corrugations and grinding rails on time provides advantages to track maintenance. In the remaining Chapters, the maintenance activities towards corrugation and the cost of these activities are discussed. The cost of these maintenance activities for a sample ballastless track section has been examined. The costs of maintenance necessitated from corrugation, the other necessary maintenance activities were separately examined, and the percentage of the corrugation-related maintenance cost in all maintenance activities is calculated. In the last Chapter, the economical analysis of the corrugations on the sample track was performed and the benefit/cost analyses were carried out by calculating the cost of corrugation maintenance and the economic benefits brought by corrugation maintenance. During the benefit/cost analyses; the costs for rail grinding, corrugation measurements, local rail grinding operations (especially in the turn-outs), the on-board lubrication system and its maintenance, the replacement of rail fasteners, noise measurements were taken into account. The benefits are derived from; extending life cycle of rails and fasteners, prolonged intervals of wheel lathing, train suspension system, lesser deterioration of track superstructure and sub-structure, reduction of energy consumption. Benefit/cost analyses were calculated for short wave length corrugations with wave depths of 0.01, 0.05, 0.1, 0.15 and 0.2 mm and this study on the sample track has been generalized in tables, so as to be applied to the ballastless track. With these tables that is applicable for all ballastless track, it is necessary to input data that varies according to the characteristic of the track, the machine-equipment used, maintenance periods, failure frequency, operation conditions, materials and labor costs. By inputting data to these tables, the wave depth with the highest level of benefit/cost ratio is calculated which suggests the optimum grinding timing. The duration of reaching the wave depth with the highest benefit/cost ratio varies depending on the operating conditions for each track. Intervention limit for maximum total tonnage and intervention limit based on time can be derived from the duration of reaching intervention limit of peak depth of corrugation. Each railway authority determines the rail-grinding period according to its own conditions. Corrugation failures vary depending on operating conditions, quality of maintenance, superstructure, infrastructure and used materials. Therefore, depending on the occurrence of the corrugations each railway authority can determine the rail-grinding period in terms of the load that is passed over the track by inputting data to the table obtained from this study. In the case of a single type of traffic such as metro lines, the treatment of the corrugation and the cost for it are important. Nowadays, as urban rail systems spread quickly, cost-based maintenance will contribute to the operator company and country economy. In the study, the corrugation maintenance cost of the sample metro track has been optimized and the excel tables have been created to be applied to other metro slab tracks. If the characteristics of the rolling stock, operation and superstructure are correctly entered in the data parts of the tables, the B/C analysis, intervention limit of corrugation based on wave depth, maximum tonnage limit for rail grinding for optimized track are calculated. This study in the thesis can also be applied to other metro lines with these features.