Technical Guide on Derailments - In-Depth Notes

PREFACE

  • Continuous challenges faced by Indian Railways regarding derailments.
  • Various causes leading to derailments and the discovery of remedial measures.
  • The objective is to help staff understand the rail-wheel interaction mechanisms.
  • Importance of thorough analysis and new ideas for preventing derailments.
  • Recognition of contributions from experts involved in the preparation of the guide.

DERAILMENT DEFINITION

  • Definition of Derailment:
    • Occurs when a wheel or set of wheels leave their due position on the rail.
    • Can range from minor incidents, like an empty wagon derailing without affecting traffic, to major incidents involving multiple loaded wagons that can obstruct traffic or lead to collisions.

CAUSES OF DERAILMENTS

  • Main Causes of Derailments:
    • Failure of railway staff in examining equipment properly.
    • Inadequate maintenance of locomotives and rolling stock.
    • Operational irregularities, including wrong marshalling or improper train operation by the driver.
    • Sudden shifts in load, excessive speed, and obstruction on track.

DERAILMENT MECHANISM

Categories of Derailment:
  1. **Sudden Derailments: **
    • Caused by high forces that lead to the immediate jumping of wheels from the rail without prior flange mounting marks.
  2. Gradual Derailments:
    • Occur as wheel flanges climb the rail due to lateral forces slowly overcoming the vertical load on the wheels.
Wheel Flange Climbing Mechanism:
  • Factors Influencing Flange Climbing:
    • Ratio of lateral force (Y) to vertical load (Q).
    • If the ratio exceeds a critical limit (ideally shouldn't exceed 1.4, but Indian Railways sets a lower limit of 1.0), the chances of a derailment increase.
  • Key Formulas:
    Y <= Q an eta + rac{eta imes an eta}{ ext{Coefficient of Friction}}

VEHICLE OSCILLATIONS AND RAIL-WHEEL INTERACTIONS

  • Oscillations occur due to uneven loading and vertical irregularities in the track.
  • Lateral movements caused by vehicle responses to these conditions can lead to off-loading of wheels, increasing derailment risks.

TRACK MAINTENANCE ISSUES

Key Factors Affecting Track Stability:
  • Formation:
    • Needs to distribute weight effectively and prevent sinking, especially during heavy rains.
  • Ballast:
    • Adequate depth and quality essential for stabilizing track and absorbing vibrations.
  • Sleepers and Fastenings:
    • Should maintain rail alignment and strength.
Standards for Gauge and Twist Levels:
  • Irregularities in gauge cause excessive oscillations leading to derailment.
  • Measurement of cross levels and twist critical to ensure safety and stability of tracks.

DERAILMENTS ON CURVES

  • Curved tracks are particularly prone to derailments due to continuous flange contact with the outer rail.
  • Effects of Cant or Superelevation:
    • Used to counteract centrifugal forces, but excess or inadequate cant can lead to increased derailment risk.
  • Importance of maintaining proper cant levels based on curve radius and maximum speed.

POINTS AND CROSSINGS

  • Derailments often occur at switches and crossings due to operational errors, poorly maintained equipment, or sudden movements of trains.
  • Check rail clearances and switch alignments are critical to ensuring smooth train movement.

APPENDICES

  • Proforma for Reporting Derailments:
    • To record details and causes of accidents including initial investigation steps.
  • Standard Dimension of Permanent Way:
    • Details rail gauge measurements and permissible variations.
  • Calculation of Gauge Slackness:
    • Allows evaluation of how slackness could contribute to derailments, emphasizing the need for vigilant measurements.

GLOSSARY

  • Definitions for key terms such as:
    • Creep, Cant, Gauge, Flange force, etc. to better understand the context of derailments and track mechanics.