Moisture Effects on Degraded Ballast Shear Strength Behavior

Ballast consisting of large sized aggregate particles with uniform size distribution is an essential component of the track substructure, to facilitate load distribution and drainage. As freight tonnage accumulates with traffic, ballast will accumulate an increasing percentage of fines due to either aggregate breakdown or outside contamination such as subgrade soil intrusion and coal dust collection. According to the classical text by Selig and Waters [1], ballast degradation from traffic involves up to 76% of all fouling cases; voids will be occupied by fines from the bottom of ballast layer gradually causing ballast clogging and losing its drainage ability. When moisture is trapped within ballast, especially fouled ballast, ballast layer stability is compromised. In the recent studies at the University of Illinois, the focus has been to evaluate behavior of fouled ballast due to aggregate degradation using large scale triaxial testing. To investigate the effects of moisture on degraded ballast, fouled ballast was generated in the laboratory through controlled Los Angeles (LA) abrasion tests intended to mimic aggregate abrasion and breakdown and generate fouled ballast at compositions similar to those observed in the field due to repeated train loadings. Triaxial shear strength tests were performed on the fouled ballast at different moisture contents. Important findings of this preliminary study on characterizing wet fouled ballast are presented in this paper. Moisture was found to have a significant effect on the fouled ballast strength behavior. Adding a small amount of 3% moisture (by weight of particles smaller than 3/8 in. size or smaller than 9.5 mm) caused test specimens to indicate approximately 50% decrease in shear strength of the dry fouled ballast. Wet fouled ballast samples peaked at significantly lower maximum deviator stress values at relatively smaller axial strains and remained at these low levels as the axial strain was increased.

Modeling Track Geometry Degradation Using Support Vector Machine Technique

Analyzing track geometry defects is of crucial importance for railway safety. Understanding when a defect will need to be repaired can help in both planning a preventive maintenance schedule and reducing the probability of track failures. This paper discusses the data cleaning and analysis processes for modeling track geometry degradation. An analytical data model named the Support Vector Machine (SVM) was developed to model the deterioration of track geometry defects. This paper mainly focuses on the following three defect types — surface, cross level and dip. The model accounts for traffic volume, defect amplitude, track class, speed and other potential factors. Results demonstrate that the proposed analytical data model can have a prediction accuracy above 70%.

On Railroad Tank Car Puncture Performance: Part II — Estimating Metrics

This paper is the second in a two-part series on the puncture performance of railroad tank cars carrying hazardous materials in the event of an accident. Various metrics are often mentioned in the open literature to characterize the structural performance of tank cars under accident loading conditions. One of the consequences in terms of structural damage to the tank during accidents is puncture. This two-part series of papers focuses on four metrics to quantify the performance of tank cars against the threat of puncture: (1) speed, (2) force, (3) energy, and (4) conditional probability of release. In Part I, generalized tank car impact scenarios were illustrated. Particular focus is given to the generalized shell impact scenario because performance-based requirements for shell puncture resistance are being considered by the regulatory agencies in United States and Canada. Definitions for the four performance metrics were given. Physical and mathematical relationships among these metrics were outlined. Strengths and limitations of these performance metrics were discussed. In this paper (Part II), the multi-disciplinary approach to develop engineering tools to estimate the performance metrics is described. The complementary connection between testing and modeling is emphasized. Puncture performance metrics, which were estimated from other sources, are compared for different tank car designs. These comparisons are presented to interpret the metrics from a probabilistic point of view. In addition, sensitivity of the metrics to the operational and design factors is examined qualitatively.

Rail-to-Earth Resistance Assessment for a Medium Capacity Transit System With Continuous Negative Rails by Potential Measurement

This paper presents the development of a qualitative and quantitative assessment of the resistance to ground for the electrically continuous negative rails of a medium capacity transit line of the Taipei Rapid Transit System. Using synchronous potential measurements at three stations we examine potential profiles to locate potential rail sections with low resistance to ground qualitatively. Also the voltage sag values are used to quantitatively calculate rail-to-ground resistance per unit length. The approach presented in this paper requires only voltage measurements with the traction current as the energization source. Thus, this approach can be performed as a routine maintenance procedure to obtain rail-to-ground resistance values from a system-wide point of view.

Comparison of Energy-Saving Driving Style Strategies

Due to the increasing scarcity of fossil fuels and the climate change, the importance of energy efficiency is increasing. This importance is major especially in areas where the energy consumption is high. Rail transport depicts such an area. The highest proportion of energy consumed in the railway is the so called traction energy. This energy is required for the train run. In the timetable, allowances leave a margin for the driving style of train run. By the selective use of strategies that change the driving style, it is possible to exploit these allowances and reduce the traction energy consumption. The first objective of this study deals with the development of algorithms for energy-saving driving style. First, the necessary input variables of the algorithms based on the literature research and the formulas of train dynamics were determined. Then the algorithms were developed to create different energy-saving driving styles, resulting choose the best result which should be shown as a driving recommendation. The developed algorithms were used in an application example in order to calculate the potential of energy-savings. The example should represent the influence of the input variables for a comparison of different situations. At last the acceptance of the determined driving strategies in practice was investigated. By implementing the design thinking method it was identified that driver advisory systems and training programs are necessary to facilitate energy-saving driving in practice.

Case Studies of PTC-Preventable Accidents

A 1969 collision of two Penn Central train resulted in four fatalities and forty-five injuries. This accident could have been prevented, had some type of train control system been in place. After this accident, the National Transportation Safety Board (NTSB) asked the Federal Railroad Administration (FRA) to study the feasibility of requiring railroads to install some type of automatic train control system that would prevent human-factor caused accidents. Over the next almost four decades, a number of additional accidents occurred, culminating in the January, 2005 Graniteville Norfolk-Southern accident and the September, 2008 Metrolink Chatsworth accident. A little more than one month after the Metrolink accident, Congress passed the Rail Safety Improvement Act, which requires Positive Train Control (PTC). To better explain the positive train control requirements, this paper traces each to a detailed case study. Four different accidents are studied, each being an example of one of the four, core positive train control requirements. Included in the case study is a discussion about how positive train control would have prevented the accident, had it been present. This provides positive train control implementers and other railroad professionals with a better understanding of the factors that have caused or contributed to the cause of the positive train control preventable accidents studied.

Estimating Deterioration in the Concrete Tie-Ballast Interface Based on Vertical Tie Deflection Profile: A Numerical Study

In ballasted concrete tie track, the tie-ballast interface can deteriorate resulting in concrete tie bottom abrasion, ballast pulverization and/or voids in tie-ballast interfaces. Tie-ballast voids toward tie ends can lead to unfavorable center binding support conditions that can result in premature concrete tie failure and possible train derailment. Direct detection of these conditions is difficult. There is a strong interest in assessing the concrete tie-ballast interface conditions indirectly using measured vertical deflections. This paper seeks to establish a link between the vertical deflection profile of a concrete tie top surface and the tie-ballast interface condition using the finite element analysis (FEA) method. The concrete tie is modeled as a concrete matrix embedded with prestressing steel strands or wires. The configurations of two commonly used concrete ties, one with 8 prestressing strands and the other with 20 prestressing wires, are employed in this study. All models are three-dimensional and symmetric about the tie center. A damaged plasticity model that can predict onset and propagation of tensile cracks is applied to the concrete material. The steel-concrete interface is homogenized and represented with a thin layer of cohesive elements sandwiched between steel and concrete elements. Strand- or wire-specific elasto-plastic bond models developed at the Volpe Center are applied to the cohesive elements to account for the interface bonding mechanisms. FE models are developed for both original and worn concrete ties, with the latter assuming hypothetical patterns of reduced cross sections resulting from abrasive interactions with the ballast. Static analyses of pretension release in these concrete ties are conducted, and vertical deflection gradients along tie lengths are calculated and shown to correspond well with the worn cross sectional patterns for a given reinforcement type. The ballast is further modeled with Extended Drucker-Prager plasticity, and hypothetical voids are applied toward the tie ends along the concrete tie-ballast interface to simulate center binding support conditions. The distance range over which the concrete tie is supported in the center is variable and yields different center binding severity. Static simulations are completed with vertical rail seat loads applied on the concrete tie-ballast assembly. The influences of various factors on the vertical deflection profile, including tie type, vertical load magnitude, center binding severity, cross sectional material loss and prestress loss, are examined based on the FEA results. The work presented in this paper demonstrates the potential of using the vertical deflection profile of concrete tie top surfaces to assess deteriorations in the tie-ballast interface. The simulation results further help to clarify minimum technical requirements on inspection technologies that measure concrete tie vertical deflection profiles.

Modeling of Diffraction Coupling in Radio Propagation Inside Tunnel Environments

The overall performance of a Communication-Based Train Control (CBTC) system largely depends on the performance of its Data Communication Subsystem (DCS). The DCS network in almost all CBTC commercial system products marketed in the last decade utilizes radio communications in the open ISM bands (2.4 GHz or 5.8 GHz) to establish the bi-directional data link between the central/wayside and onboard segments. To ensure a stable and sound radio communication, a key question is the number of the wayside Access Points (APs) and locations of their antennas. Radio propagation modeling aims to provide an optimal and reasonably reliable solution to the cited question. The diffraction impact of sharp corners and edges in tunnels on the radio propagation process, however, has not been accounted for in majority of models. The purpose of the present research is to incorporate the effect of diffraction coupling due to sharp edges in tunnel sections which include geometrical discontinuities such as cross-junctions and L-bends through ray-mode conversion. The proposed modeling approach offers sufficient versatility to assimilate a variety of discontinuous geometries involving sharp edges in a tunnel environment. Numerical and empirical results suggest that the model provides an accurate tool for analyzing diffraction effects of tunnel discontinuities with sharp edges on the process of radio propagation.

Rail Tank Car Total Containment Fire Testing: Results and Observations

The frequent incidences of Non-Accident Releases (NARs) of lading from tank cars have resulted in an increasing interest in transporting hazardous materials in total containment conditions (i.e., no pressure relief devices). However, the ability of tank cars to meet thermal protection requirements provided in the Code of Federal Regulations under conditions of total containment has not been established. The intent of this effort was to evaluate through a series of third-scale fire tests, the ability of tank cars to meet the thermal protection requirements under total containment conditions, with a particular focus on caustic ladings. A previous paper on this effort described the test design and planning effort associated with this research effort. A series of seven fire tests were conducted using third scale tanks. The test fires simulated fully engulfing, hydrocarbon fueled, pool fire conditions. The initial tests were conducted with water as a lading under jacketed and non-jacketed conditions and also with different fill levels (98% full or 50% full). Additionally, two tests were conducted with the caustic, Sodium Hydroxide as the lading, each test with a different fill level. In general, the tanks with water were allowed to fail or reach near-failure conditions, whereas, the tests with the caustic lading were not allowed to proceed near failure for safety reasons. This paper describes the results and observations from the fire tests, and discusses the various factors that affected the fire test performance of the test tanks. Review of results from the one-third scale tests, and subsequent scaling to full-scale suggest that a full-scale tank car filled with 50% NaOH solution is unlikely to meet the 100-minute survival requirement under conditions of total containment.

Tank Car Top Fittings Protection: Evaluation of Derailment Failure Risks — A Conceptual Study

Top fittings devices on tank cars are subject to damage and failure under derailment conditions, potentially leading to the release of hazardous lading. This paper describes the conceptual development of an objective methodology for evaluating the risk of fittings protection failure and the potential reduction in that risk when mitigating strategies such as improved fittings protective structure are deployed. The methodology captures several key elements that affect fittings survival, including: the speed of derailment initiation, the impact velocity/force spectrum experienced by the fittings protective structure during the event, the strength/structural capacity of the protective structure, and the rigidity of the ground surface. Detailed finite element modeling efforts were employed to capture derailment dynamics and corresponding impact velocity spectra, as well as the strength of multiple protective designs. Future work, including validation, is planned to extend the concept into a detailed methodology.