Construction of New Railway Lines

Construction of New Railway Lines

The main work involved in the construction of a new line is the following.

(a)  Land acquisition

(b) Earthwork and bridges

(c)  Station building, staff quarters, and other allied facilities, including platforms and sheds

(d) Plate laying, including ballasting of track

(e)  Opening of section for traffic

1 Land Acquisition

The work of land acquisition should start well in advance so that all legal and financial formalities are completed on time and possession of the land can be taken for starting construction work. Land acquisition is done with the help of the member state government as per the procedure laid down in the land acquisition act. Normally Sections 4 and 6 of the Land Acquisition Act are applied for acquisition of land in India. Land is generally acquired after giving a notice and paying compensation to the previous occupants. In the case of an emergency, land can also be acquired urgently by operating the Special Sections 9 and 17 of the Land Acquisition Act in India.

The land to be acquired should be adequate for the formation, berm, and borrow pits. It should also have adequate provision for future expansion. Even when a single line is to be constructed, the land available should be sufficient for the construct of a double line for future expansion. Normally a strip of 25 to 35 m of land is acquired for the construction of a railway line. For station yards, an extra width of land is acquired. For small stations, the width normally adopted is 150 × 1000 m.

The minimum land to be arranged should conform to the following.

Width of formation: The land should be adequate to accommodate the width of formation.

(ii)  Side slope: The side slope depends on the nature of the soil and is normally taken as 2:1 (horizontal:vertical).

(iii) Width of berms: The usual width of the berm is kept at 3 m.

(iv) Borrow pits: If the land is not very costly, adequate land should be made available for borrow pits also. Borrow pits may be on one side of the track for low banks and on both sides for medium and high banks. When the land is costly, borrow pits need not be provided for and earth can be borrowed from adjoining areas. Extra land is, however, required for station yards, level crossings, and bridge approaches.

2 Earthwork for Formation

The formation may be in an embankment or a cutting depending upon the rail level and general contour of the area. A formation in an embankment is normally preferred from the point of view of good drainage. The height of the embankment also depends on the high flood level of the area and a reasonable free board is provided above this level. The standard width of formation is given in Table 4.1.

Table 4.1   Standard width of formation

Some points worth noting with regard to the specifications for earthwork are as follows.

(a)  Earthwork is normally done in 30-cm-deep layers so that the soil is well compacted.

(b) Mechanical compaction is normally done after each layer with the help of a 'sheep foot roller' to obtain 90% of the maximum dry density at optimum moisture content.

(c)  A shrinkage allowance of 5% is made from the final cross section for consolidation in the case of mechanical compaction. For other types of compaction the shrinkage allowance is 10%.

(d) When the soil is not good, a 30-cm-thick blanket is provided at the top of the embankment.

(e)  In areas where there are both cuttings and embankments, the earth from the cuttings should be used for the embankments up to an economical lead. The economical lead of moving earth in the longitudinal direction is determined by the mass-haul curve .

For the early execution of earthwork, the section is normally divided into different convenient zones, each zone having earthwork requirement costing approximately Rs 1.5 to 3 million. Tenders are invited for each zone separately so that work can progress simultaneously in all zones.

3 Bridges

Bridges should be designed for the heaviest locomotive likely to pass that section. Depending upon the topography of the country and the type of stream to be crossed, hume pipe culverts, reinforced cement (RCC) slab bridges, plate girders or prestressed concrete (PRC) girder bridges or steel bridges, are designed. Bridges, being important structures, are normally made for double-line tracks, even in single-line sections, with a view to plan for future expansion.

For the construction of important bridges, separate tenders are called, with design and construction details included in the tender documents. Minor bridges and culverts are normally included in the earthwork zones mentioned above.

4 Service Buildings and Staff Quarters

Service buildings include the station master's office, telegraph office, etc., which are basically required for providing services for running the trains. Apart from this, staff quarters and other passenger amenity works such as platforms, foot over bridges, waiting halls, and retiring rooms are also provided at stations. Many other ancillary facilities such as water supply, drainage, telephone lines, and electricity are also made available.

All these constructions are simultaneously taken up by civil engineers, electrical engineers, and signal engineers so that they can progress together.

5 Plate Laying or Track Linking

Once the formation is ready, plate laying or track linking is required. It consists of laying rails, sleepers, and fastenings. The following methodology is adopted for plate laying.

Tram Line Method

In this method, a temporary line known as the 'tram line' is laid by the side of the proposed track for taking track materials to the site. This method is useful in flat terrain, where laying the tram line on natural ground may be comparatively easier. This method is, however, seldom used in practice.

A modification of the above method is the side method. This method is used where track and bridge material is carried to the site on trucks on a service road parallel to the track. The material is then unloaded near the work site. This method is used only in cases where comparatively flat gradients are available.

American Method

In the American method, rails and sleepers are first assembled in the base depot and pre-assembled track panels are then taken to the site along with the necessary cranes, etc. The track panels are unloaded at the work site either manually or with the help of cranes and are then laid in the final position. This procedure is used in many developed countries, particularly those where concrete sleepers are laid, since these sleepers are quite heavy and it is not easy to handle them manually.

Telescopic Method

This method is widely used on Indian Railways. In this method, the rails, sleepers, and other fittings are taken to the base depot and unloaded. The track material is then taken to the rail head and the track is linked and packed. The rail head is then advanced up to the extent of laid track. The track material is then taken up to the advanced rail head with the help of a dip lorry and the track is again linked and packed. In this way, the rail head goes on advancing till the full track is linked. The main operations involved are as follows.

Unloading of materials The track material is taken to the base depot and unloaded with the help of material gangs. The first base depot is the junction of the existing line and the new line to be constructed. All track material is taken from the base depot with the help of a dip lorry (a special type of trolley) to the rail head. The rail head goes on advancing till the track is sufficiently linked. After that, a subsidiary depot is established at a distance of about 5 km where the track material is taken with the help of a material train. Alternatively, the track material is moved from the base depot with the help of dip lorry only up to a distance of about 2 km and by material train beyond this distance. In the base depot, advance arrangements such as adzing and boring of the sleeper and arrangement of matching materials are made so that the track is linked as soon as possible to the site.

Track linking Once the track material is unloaded, the track is linked with the help of linking gangs. The following procedure is normally adopted.

1.  A string is first stretched along the centre line of the alignment and sleepers are laid with their centres on the string. The sleepers are laid roughly at the desired spacing, keeping the total number of sleepers per rail intact.

2.  The rails are carried by rail tongs and kept on the cess of the bank almost in the final position. As carrying rails is a very strenuous job (each rail weighs above 600 kg and about 12-15 gangmen are required to carry one rail), a special type of rail carrier known as the Anderson rail carrier can be used for carrying rails with lesser strain.

3.  The sleepers are spread out on the formation. The rails have markings where the final position of the sleepers should come.

4.  Small fittings such as fish plates and bolts are placed near the joints, other fittings required for each sleeper are placed near the end of the sleeper.

5.  The rails are then placed on the sleeper and fixed with the help of fittings depending upon the type of sleeper. For example, in the case of wooden sleepers, rail screws are used for fixing the rails to the wooden sleepers. In the case of steel sleepers, rails are fixed with the help of a key. Bearing plates are also provided wherever required, as per the prescribed track standards.

6.  The rails are joined to each other keeping a proper gap. Now-a-days, normally three rail panels are initially used for laying the track. In the case of single-rail panels as well as three-rail panels, adequate expansion gaps should be left. The recommended expansion gaps are provided with the help of steel liners or shims of correct thickness (1-4 mm), which are fixed between the two rail ends.

Track packing The track is then thoroughly packed with the help of beaters by 'packing-in-gangs'. The following aspects should be checked.

(a)  The track should have a proper gradient.

(b) The track should have proper curvature, if it is on a curve

(c)  The cross levels should be even. If superelevation is to be provided, the outer rail should be raised so as to have the recommended superelevation.

(d) The track should be thoroughly packed and no spaces should be left.

Ballasting of track The ballast is normally spread on the railway lines after the embankment has settled well and at least two monsoons have passed over it. Ballasting is generally done with the help of ballast trains, which have special hoppers through which the ballast can be automatically unloaded onto the track. Alternatively, the ballast is carried on the cess and then laid on the track manually. Using either method, the ballast is thoroughly packed and inserted under the track.