Site Investigation PDF

CAMTECH/M/3 27 CHAPTER 2 SITE INVESTIGATION Unless reasons for derailment are obvious from the initial inspection at site, comprehensive investigation in a logical sequence is needed to ascertain t...

CAMTECH/M/3 27 CHAPTER 2 SITE INVESTIGATION Unless reasons for derailment are obvious from the initial inspection at site, comprehensive investigation in a logical sequence is needed to ascertain the actual cause of derailment. The site investigation is primarily concerned with identification of evidence and related data before restoring the track and vehicles. The main purposes are to : 1. Locate the initial point of derailment 2. To identify the first derailed vehicle and wheel 3. To obtain sufficient evidence to determine the course of events up to the time derailed train came to a halt and 4. To explain why the vehicle derailed initially at that particular point on the track. The site investigation should be carried out in the following sequence : 1. First considerations 2. Site sketch 3. Flange marks 4. Operational Defects/Failures 5. Track survey and examination 6. Vehicle examination A TECHNICAL GUIDE ON DERAILMENTS April ‘98 CAMTECH/M/3 28 2.1 FIRST CONSIDERATIONS The sequence of events to be recorded i.e. how derailment occurred prima facie, from the beginning to the time the train came to a halt. The position of vehicles after derailment must be recorded. The wheel marks at the initial point of derailment are to be examined in order to establish the category of derailment i.e. sudden or gradual. It is important for the investigators to make rapid observations and record the position of vehicles. It is also important that such a survey must be completed before the restoration work commences on the track especially in the rear of point of derailment. 2.2 SITE SKETCH A sketch of the whole site showing the position of derailed vehicles relative to both rails as well as other evidences if any together with the track damages must be prepared. If this is not done, serious difficulties will be encountered later when this evidence is required for correlating the events relating to vehicle and track interaction. 2.3 FLANGE MARKS ON THE RAIL The most important thing in investigating the derailments is to locate and examine the wheel mounting marks or the marks at the initial point of derailment in order to determine whether the derailment was sudden or gradual. A TECHNICAL GUIDE ON DERAILMENTS April ‘98 CAMTECH/M/3 29 Fig. 2.1 Flange Mounting Marks A careful analysis is required to be done on wheel mounting marks found on the rail table (Fig. 2.1). If it is difficult to ascertain the first vehicle which derailed, it is necessary to detail the damage sleeper by sleeper. The details of mounting marks must be recorded including the following details : A. Length B. Profile or path followed after mounting C. Whether marks are strong or faint D. Whether continuous or broken E. Single/multiple marks A TECHNICAL GUIDE ON DERAILMENTS April ‘98 CAMTECH/M/3 30 Preferably, photographs should be taken not only of mounting marks found on the rail but also those found on the sleeper fastenings and ballast. These marks must be carefully noted and measured. Often many vehicles derail before the train comes to halt. This creates multiplicity of wheel mounting marks. Thus it becomes necessary to identify the particular wheel set which derailed first. This can only be achieved by matching the length and nature of various trail marks left by wheels against the position and orientation of derailed vehicles, analysis of marks on the wheel tread and flanges, damage to vehicles and wheel sets etc. 2.4 OPERATIONAL DEFECTS/FAILURES The following are the major operational features which are significant in a derailment: 2.4.1 Speed The speed of train plays a vital role in derailments. If speed is in excess of permissible speed, lateral forces on the flange increase and the formation may not be able to resist this increased force thereby resulting in either flange mounting or jumping off from the rail table. Under dynamic conditions, the speed of train plays a vital part in derailment of a vehicle. Higher the speed, smaller will be the range of permissible imperfections on the track and A TECHNICAL GUIDE ON DERAILMENTS April ‘98 CAMTECH/M/3 31 rolling stock. The rolling stock by virtue of its spring and suspension system responds to the disturbances and is free to perform inherent oscillations. As the rolling stock moves over the track, exciting oscillations are produced and the exciting frequency directly depends upon the speed. Conditions of - resonance may occur if the exciting frequency approaches the natural frequency. The oscillations become more pronounced while the train is coasting i.e. when the drawbar pull is absent. The amplitude of these oscillations increase with increase in speed especially if the causative factors amplifying the oscillations are present. It will therefore be seen that the wheel load changes due to oscillations on run. The degree of track imperfections, state of maintenance on rolling stock, its suspension characteristics, disposition of load on wheels and speed are the main items of attention in the investigation of a derailment. 2.4.2 Loading Irregular or excess loading may lead to derailment of a vehicle as the wheel may float due to off-loading.. 2.4.3 Wrong Marshalling Empty stock marshalled in between two loaded wagons forces the empty stock, specially the four wheeler units, to jump off under the impact of draw bar forces and derail. A TECHNICAL GUIDE ON DERAILMENTS April ‘98 CAMTECH/M/3 32 2.4.4 Mismanipulation of Point Due to mismanipulation of a point under movement, derailment occurs. In such cases the leading wheel or trolley will travel on one side of the track and the trailing trolley will travel on the other track. This happens on points in facing direction only. In such cases, the important points to be checked are : A. Length of tongue rail B. Rigid wheel base of the stock C. Gap between toe of switch and stock rail By examination of the above factors, one can ascertain whether the point was operated under movement. Another aspect which is not pertaining to operational failures but must be checked is whether the point was working freely and correctly. 2.4.5 Operating Staff Failure Following problems may also result in a derailment : Points not being properly set and locked during shunting operation at the station. Operation of point under wheel movement. Undetected obstruction between toe of switch and stock rail Loose couplings A TECHNICAL GUIDE ON DERAILMENTS April ‘98 CAMTECH/M/3 33 2.4.6 Improper Train Operation by the Driver Sudden application of brakes cause bunching and off loading of light loaded wheels. This may also result in derailments. 2.5 ROLLING STOCK EXAMINATION The details are given in Chapter 3. 2.6 TRACK SURVEY AND EXAMINATION The details are given in Chapter 4 and 5. A TECHNICAL GUIDE ON DERAILMENTS April ‘98