Railway

RAILWAY

 

1. INTRODUCTION

Railways form the most important mode of transport in India. Railways have brought about many political, social and economic changes in the life of Indian people. The network of Indian Railways is divided into nine zonal divisions for administrative purposes.

TABLE 1 ZONAL DIVISIONS OF INDIAN RAILWAYS

 

TABLE 2 COMPARISON BETWEEN ROADWAYS AND RAILWAYS

Advantages of Railways

Railways have the following advantages over other modes of transport:

• Migration of people on a mass scale

• Mobilising troops during war periods

• Large scale movement of commodities

• Encourages commercial unity

• Stabilisation of the prices of commodities

• Ensures safe and comfortable journey

• Easy access to major places of tourist attraction

• Development of a nation

 

2. RAILWAY TRACK (PERMANENT WAY)

he combination of rails, fitted on sleepers and resting on ballast and formation is called the railway track or permanent way. Sometimes temporary tracks are also laid for conveyance of earth and materials for construction work. The name permanent way is given to distinguish the final layout from these temporary tracks.

Requirements of a Permanent Way

In order to achieve higher speed and better ride qualities with less maintenance in future, the following requirements of a permanent way are to be met:

1. Gauge should be correct and uniform.

2. Rails should be in proper level.

3. Alignment should be correct, i.e. it should be free from kinks or irregularities.

4. Gradient should be uniform and any change of gradient should be followed by a smooth vertical curve.

5. Track should be resilient, i.e., there must be a certain amount of elasticity in the track.

6. Radii and super elevation on curves should be properly designed and maintained.

7. Joints, the weakest points in the railway track should be properly designed and maintained.

8. Drainage system should be perfect.

 

3.  COMPONENTS OF A RAILWAY TRACK

1. Rails

The rails on the track can be considered as beams carrying loads. They are made of high carbon steel to withstand wear and tear.

Functions of Rails

a) To provide a hard, smooth and unchanging surface for the passage of heavy moving loads with minimum friction between the steel rails and steel wheels.

b) To bear the stresses developed due to heavy vertical loads, lateral and braking forces as well as thermal stresses.

c) To transmit the load to sleepers and consequently reduce pressure on ballast and formation.

Types of Rail Section

The types of rail section are Double headed rails (D.H. rails), Bull headed rails (B.H. rails) and Flat footed rails (F.F. rails) as given in Fig. 2.

Rail track is subjected to bending stress when a train moves over it. Bending stress is higher at the top and bottom sides of the cross-section than at the mid-portion of the section as explained in Section 4 of Chapter 1. Hence, I-section is preferred for rails and in construction since the section has more material where bending stress is higher. Thus, the I-section is more economical since it reduces the weight of rail or beam.

In India, flat footed rails are most commonly used because they have more strength and stiffness, both vertically and laterally than B.H. rails. Fitting of rails with sleepers is simpler and as such they can be easily laid and re-laid.

Gauge

Rail gauge is the distance from the inside of one rail on a railroad track to the inside of the other. The widths of different gauges of rails are given in Table 3.

TABLE 3 WIDTHS OF DIFFERENT GAUGES

2.  Rail Joints

The weakest point of track is the joint between two rails. An ideal or perfect rail point is one which provides the same strength and stiffness as the other sections of the track.

TABLE 4 FEATURES OF DIFFERENT TYPES OF SLEEPERS

3. Sleepers

Sleepers are laid transverse to the rails. Rails are supported and fixed on them. They are laid to transfer the load from rails to the ballast and subgrade as shown in fig. 1.

Functions

i) To hold the rails to a proper gauge

ii) To hold the rails at proper level

iii) To interpose an elastic medium in between the ballast and rails

iv) To distribute the load from the rails to the underlying ballast

Classification

According to the materials used in their construction, sleepers can be classified into the following three classes:

i) Wooden sleepers

ii) Metal sleepers

a. Cast iron sleepers

b. Steel sleepers

iii) Concrete sleepers

a. Reinforced cement concrete sleepers

b. Prestressed concrete sleepers

Sleeper Density

Sleeper density is the number of sleepers per rail length and it is specified as (n+x). The number of sleepers per rail varies in India from ‘n+3' to 'n+6' for main tracks, where, 'n' is the length of rail in meters.

4. Track Fittings

Rail fixtures and fastenings are used to keep the rails in a proper position and to set the points and crossings properly. The major rail fittings are as follows:

1. Fish Plate

Fish plate is used in rail joint to maintain the continuity of the rails as shown in Fig. 3.

The requirements of fish plate are:

1. To support the underside of the rail and top of the foot

2. To allow for free movement of rails for expansions and contractions

3. To hold the ends of the rail both laterally in line and vertically in level.

4. To withstand the stresses due to bending moments without getting distorted

5. To absorb shocks caused by the jumping of the wheel over the expansion gap.

2. Spikes

Spikes are used for holding the rails to the wooden sleepers. The characteristics of a good spike are:

1. It should be strong enough to hold the rail in position

2. It should be as deep as possible.

3. It should be easy to fix and remove from the sleepers

4. It should properly maintain the gauge.

3. Bolts

Bolts are used for fastening various components of railway tracks. For example, fish bolts are used to connect fish plates with the rail. Four bolts are used at each joint.

4. Chairs

In case of double headed and bull-headed rails, chairs are required to hold them in position. They help in distributing the load from the rails to the sleepers.

5. Keys

Keys are small tapered pieces of timber or steel to fix rails to chairs on metal sleepers.

6. Bearing

Plates Bearing plates are rectangular plates made of M.S or C.1. They are used below flat-footed rails to distribute the load on a larger area of timber sleepers.

 

5. Ballast

Ballast is the granular material usually comprising broken stone or brick, shingle or kankar, gravel or sand placed and packed below and around the sleepers (Fig. 1). The functions of ballast are given below:

1. It is used to transmit load from sleepers to formation and allow drainage of the track.

2. It provides a suitable foundation for the sleepers.  

3. It holds the sleepers in their correct position by preventing their displacement by lateral or longitudinal thrusts.

4. Lateral stability of a track depends on the ballast.

Size and Quantity of Ballast

The size of stone ballast varies from 19 mm to 51 mm with a reasonable proportion of intermediate sizes. The depth of the ballast is defined as the distance between the bottom of sleeper and top of subgrade.

Subgrade: It is the naturally occurring soil, prepared to hold the ballast, sleepers and rails for constructing the railway track. This prepared surface is also called formation. Formation could be in embankment level or cutting, depending upon the ground condition.

Embankment: It is a raised bank of earth or other materials constructed above the natural ground. It is constructed when railways have to be carried in lower grounds or valleys.

Cutting: It is raised ground or hill, cut or excavated, for constructing the railway line at the required level below ground level.

Formation: The prepared surface which is ready to receive ballast is called formation. The stability of the track depends upon the quality of the formation under it.

The formation for a track is obtained by either constructing an embankment or cutting. Formation performs the following functions:

1. It bears the load transmitted to it through the ballast in a uniform manner.

2. It prevents the ballast from punctuating into it.

3. It drains off the water entering from its top

4. It provides a smooth regular and graded surface on which the ballast and the track may be safely rested.

5. It does not change its volume due to variation in moisture. Otherwise, it would induce stresses on the track and disrupt the track.