Alignment of railway tracks
- 1. TOPIC: Alignment of Railway Tracks HIGHWAY AND RAILWAY ENGINEERING 15C504 By: Gowtham G, BE Civil Engineering, PSG College of Technology, Coimbatore
- 2. CONTENTS Need for a new railway line Track Alignment 1. Importance of a good alignment 2. Basic Requirements 3. Selection of good alignment 4. Mountain Railways and Rack railways ConclusionIntroduction
- 3. INTRODUCTION • Transportation is regarded as an index of economic, social and commercial progress of the country. • Where, in various modes of transportation, railways are cheap, fast, reliable and safe. • To make the above advantages of railways to be true, it is needed to align the railway track with due consideration. • The proper alignment of the tracks for the above advantages are discussed here.
- 4. TRACK ALIGNMENT • Giving direction and position to the centre line of the proposed railway track on ground. • Horizontal Alignment – straight path, its width, deviations in width and horizontal curves. • Vertical Alignment – changes in gradients and vertical curves
- 5. NEED FOR A NEW RAILWAY LINE • Strategic Reasons: for quick and easy movement of defence forces in times of war threat. • Political Reasons: for political needs • Development of backward areas: to develop and foster development of under developed and developing areas
- 6. Need for a new railway line (Contd.,) • To connect new trade centres: connecting new trade centres helps in transfer of goods quicker and facilitate their development. • To shorten existing rail link: Short route is economical, faster movement of goods and passengers. • To meet traffic requirements: doubling the existing routes to meet heavy traffic (few cases) • Conversion of Gauge: Recently all Meter Gauges (MG) are converted to Broad Gauges (BG), which may require new railway lines.
- 7. BASIC REQUIREMENTS OF GOOD ALIGNMENT An ideal alignment should fulfil the following requirements: Purpose of the track: In general railway serves for the following purposes: 1. Transportation: to carry passenger and goods traffic 2. Political and Strategic: for defence purpose and political reasons
- 8. 3. Linking of centres: linking two important stations or trade centres 4. To open new tracks: new tracks for the land whose resources are not yet tapped 5. Shortening of existing track: Short route is economical, faster movement of goods and passengers.
- 9. Feasibility: Proposed track should meet all the technical requirements and general planning of the country. Economy: Economy of the track can be achieved by considering the factors like shortest possible route, minimum initial construction cost, minimum maintenance cost and minimum operating cost. Safety: Accidents should be minimum. This can be achieved by having due considerations on curves, gradients, stability of natural slopes and embankments. Aesthetic aspects: travel should be comfortable and pleasant.
- 10. FACTORS IN SELECTION OF A GOOD ALIGNMENT • The direct route is the shortest route which is also the most economical route. But practically it will be impossible to connect two points by direct route. • It may be due to intermediate obstructions, steep gradients, etc., • An alignment may be economical in initial cost, but maintenance and operational cost may increase. • Hence the requirements cannot be satisfied simultaneously.
- 11. For satisfying the requirements the following factors are to be considered in selection of good track alignment. Obligatory points Position, amount and type of traffic Gauge selection Geometric standards Topography of the country Economic considerations Other considerations FACTORS IN SELECTION OF A GOOD ALIGNMENT (Contd.,)
- 12. I. Obligatory Points • They can be classified in to two categories: points through which the track should pass and points through which the track should not pass. Points through which the track should pass: Important cities and towns Major bridges and River Crossings Hill passes (or) saddles Site for tunnels
- 13. Points through which the track should not pass: Acquisition of costly land – results in heavy compensation Religious places – they are protected by law Areas liable to flooding – water logged areas, marshy areas, cutting in snow fall, etc. With the following figure these can be explained.
- 15. II. Traffic – its position, nature and amount • Position of traffic sources gives control points for general alignment • Nature of traffic and potential volume of traffic (passenger and goods), govern the type of construction. General considerations are: • Traffic varies as square of population • Freight earnings are more than passenger earnings • For a new alignment – influence area up to width of 15km on either side and increased to 25km after few years.
- 16. III. Gauge Selection What is Gauge? Gauge of a railway track is defined as the clear distance between the inner or running faces of the two track rails.
- 17. The following are the types of gauges used in India: Types of Gauge Gauge Width Standard Gauge/ Broad Gauge (BG) 1.67m Meter Gauge (MG) 1.00m Narrow Gauge (NG) 0.762m Feeder Track Gauge/ Light Gauge (LG) 0.610m
- 18. How to select a gauge? – Factors governing Gauge selection: 1. Cost of construction 2. Volume and nature of traffic 3. Development of the areas 4. Physical features of the country 5. Speed of movement
- 19. DISADVANTAGES OF MULTI GAUGE SYSTEM: Inconvenience to passengers Difficulty in trans-shipment of goods Inefficient use of rolling stock Hindrance to fast movement of goods and passenger traffic Additional facilities at station yards Difficulties in balanced economic growth Difficulties in future gauge conversion projects “The above difficulties can be overcome by adopting a uniform gauging system”
- 20. IV. Geometric Standards The following geometric elements are to be considered which would give economical combination of construction and operating costs. Gradients, speed, loading and method of traction used Ruling gradient and minimum permissible radius of curve Curve should have maximum possible radii – economical Reverse curves – long length of straight portion to be provided (min. 36m) At stations and bridges – curves to be avoided Use of steep gradients – high operating costs
- 21. V. Topography of the country If the topography of the country is such a way that, if steeper gradients are unavoidable, then special ways to reduce the rate and cost of high gradients are need to be adopted. For alignment, topography can be classified as: Valley alignment Cross country alignment Mountain alignment
- 22. VALLEY ALIGNMENT • Has no problems • If two control points lie in the same valley, the engineer should choose a straight line between the terminal points with a uniform rate of gradient. • The ends having steeper gradients can be further negotiated by some other development.
- 23. CROSS COUNTRY ALIGNMENT • This alignment crosses two or more streams/ water sheds of different sizes. • Uniform gradient is not possible, because the rail levels are so high that there are no appreciable sags or summits between the bridges. • Hence the routes in this alignment have sags in succession. • Lowest saddles or tunnels form the obligatory points
- 24. MOUNTAIN ALIGNMENT It is best when accompanied by tunnelling. The length of the alignment is first increased between the two extreme ends of elevation so as to limit the gradient maximum up to the ruling gradient. This can be accomplished by the following special ways: Zigzag development Switch Back development Spirals or complete loops development
- 27. BRIDGE SPIRALS
- 28. TUNNEL SPIRAL
- 29. Mountain Alignment (Contd.,) • If the gradients are less than 3%, then no problems will arise and normal railways can be provided. • But, if the gradients are more than 3%, special care must be taken as said above. • If the gradients are more than 6%, a central rack rail has to be provided in between the two conventional parallel rails.
- 30. Mountain Alignment (Contd.,) RACK RAILS • In case of very steep gradients, it becomes difficult for the locomotive to pull the train load and hence the train may slide down or slip back along the downward gradient. • The rack railway system consists of three rails, i.e. two conventional rails and one extra toothed rail in middle. • There are various systems existing in the Indian Railways like: Fell System, Riggenbach system and Abt System.
- 31. THE FELL SYSTEM: The Fell System was developed in 1860’s. It uses a central raised toothed rail, in addition to the two parallel rails. These rails are braked by shoes pressing horizontally on to the central rail, as well as by means of normal running wheels. For traction the locomotives are provided with auxiliary engines powering the wheels that clamp onto the third rail. Brazil, France and New Zealand are the only countries that have lines with the Fell System.
- 32. THE REIGGENBACH RACK SYSTEM: • Invented by Niklaus Reiggenbach. • It was given French patent in 1863. • In this the gear teeth where in the form of rollers arranged in the form of rungs of a ladder between two L – shaped wrought iron rails. • Fixed ladder rack was more complex and difficult to build.
- 33. THE ABT SYSTEM: • The Abt System was devised by Roman Abt, a Swiss Locomotive Engineer in early 1880’s. • It overcame the limitations of The Reiggenbach system. • Designed using solid bars having vertical teeth machined to them. • Two or three bars were placed in the middle of the rails. They ensure that the pinions in the locomotive driving wheels are constantly engaged with the track. • First used in Harzbahn in Germany, opened in 1885. • In India, a distance of about 20km from the ghat at Kallar to Coonoor on Nigiri Railway, is constructed at a uniform slope of 1 in 12 ½ and is being operated on the Abt System
- 34. THE ABT SYSTEM
- 37. VI. Economic Considerations • Along with above factors, the alignment should be economical also. • The best alignment is the one which gives the maximum annual return (r) which is given by the formula: r = i.e. r = (R – E)/ l This shows that for r to be maximum, proper selection of route and increasing the annual returns by sound track construction is to be considered.
- 38. VII. Other Considerations 1) Geological considerations Alignment should be on good soil, free of slips or slides, not on rocky soil. 2) Effect of flood and climate Avoiding water logged areas. Stations should be located on outside of the city or town and on a level surface. If possible track should pass through proximity of quarries – source for ballasts are nearer. If possible track should pass nearer to a village for cheap labours.
- 39. CONCLUSION • Giving direction and position to the centre line of the proposed railway track on ground, is called as track alignment. • The need for new track may be due to strategic, political reasons, to develop backward areas, to connect new trade centres and to shorten existing railway track. • The factors affecting a good alignment are obligatory points; amount, type and nature of traffic; topography of the country; geometric; economic and other considerations.
- 40. REFERENCES 1. Saxena, S.C and Arora, S.P. “A Text Book of Railway Engineering”, Dhanpat Rai Publications, New Delhi, 8th edition, 2015. 2. Chandra, Satish and Agarwal, M. M. “Railway Engineering”, Oxford University Press, New Delhi, 2nd edition, 2013. 3. Images from Google Images