Railway sleepers

Sleepers

The members which are laid transverse to the rails on which the rails are Supported and fixed to transfer the loads from rails to the ballast and sub grade below.

Functions

1)      To hold the rails to correct gauge.

2)      To hold the rails in proper level.

3)      To act an elastic medium in between ballast and rails.

4)      To distribute the load from rails to index area of ballast underlying it.

5)      To support the rails at a proper level in straight tracks and proper super elevation on curves.

6)      It also gives lateral and longitudinal stability of the permanent track.

7)      To rectify the track geometry during service life.

Requirement

       i.          They should be economical i.e. should be minimum initial and maintenance cost.

      ii.          Fittings of sleepers should be so adjusted during maintenance operations.

     iii.          The weight of sleepers should have moderate weighty, for easy handling.

     iv.          Design of sleepers should be such that the gauge, alignment of track and levels of rails can be easily adjusted and maintained.

      v.          Bearing area of sleepers below the rail seat and over the ballast should be enough.

     vi.          Sleeper design and spacing should be such that to facilitate easy removal and replacement of ballast.

   vii.          Sleepers should be capable of resisting shocks and vibrations.

  viii.          Sleepers should not damage during packing processes.

     ix.          Insulation of rails should be possible for track circuiting.

      x.          Sleepers should not easily pushed out due to moving trains.

Types of sleepers

They are classified in the following categories

(1) Wooden sleepers

(2) Metal sleepers

       (a) cast iron sleepers

       (b) steel sleepers

(3) Concrete sleepers

       (a) Reinforced concrete sleepers

       (b) Pre-stressed concrete sleepers

(1) Wooden or timber sleepers

As they fulfill all requirements of ideal sleeper, wooden sleepers are regarded as best. The life of timber sleepers depends upon their ability to resist (i) wear (ii) decay (iii) attack by vermin.

 Advantages

1.      It is easily available in India.

2.      Fitting of wooden sleepers is simple in design.

3.      They ale able to resist the shocks and vibration.

4.      They are very easy to lay, relay, pack, lift and maintain.

5.      They are suitable for all types of ballast.

6.      They are best for track circuited operation.

7.      They are overall economical.

Disadvantages

1.      They are subjected to wear, decay, attack by white ants, spike killing, warping, cracking, end splitting, rail cutting etc.

2.      Difficult to maintain the gauge in case of wooden sleepers.

3.      Easily disturbed i.e. alignment maintenance is difficult.

4.      It has minimum service life as compared to other sleepers.

5.      Maintenance cost of wooden sleepers is highest as compare to other sleeper.

(2) Metal sleepers

Metal sleepers are either of steel or cast iron. Metal sleepers should satisfy

       i.          They should provide sufficient area for rails.

      ii.          Metal sleepers should be all over economical as compared to wooden sleepers.

     iii.          They should bear the tensile and compressive stresses.

     iv.          For track circuiting, insulation should be possible.

      v.          Tampling and packing of ballast should not disturb the sleeper.

Advantages

       i.          Sleepers are uniform in strength and durability.

      ii.          Lesser creep occurs because performance of fittings is better.

     iii.          As life is longer, metal sleepers are economical.

     iv.          Gauge can be easily adjusted and maintained.

      v.          Frequent renewal is not required.

     vi.          Good scrap value, easy in manufacturing.

Disadvantages

       i.          More ballast is required.

      ii.          Fittings required are greater in number, difficult to maintained.

     iii.           CI or steel are liable to rusting/corrosion.

     iv.           Metal being good conductor of electricity interferes with track circuiting.

      v.          It is unsuitable for bridges, level crossings and crossings.

     vi.          It is only suitable for stone ballast.

(3) Concrete sleepers

Experiment proves that concrete sleepers is ideal because they are made of a strong homogenous material, impervious to effect of moisture, unaffected by chemical attack of atmospheric gases. It can be moulded easily to size and shape.

Advantages

       i.          They are free from natural decay and attacks by vermin, insects etc.

      ii.          Maximum life compared to other sleepers.

     iii.          Not affected by moisture chemical action of ballast, cinder

     iv.          No difficulty in tract circuiting

      v.          High weight of sleepers helps minimizing joint maintenance by providing longer welded lengths

     vi.          Higher elastic modules, can withstand stresses induced by fast and heavy traffic.

Disadvantages

       i.          Weight of this sleeper is as high as 2.5 to 3 times of wooden sleeper, requiring mechanical appliances for handling.

      ii.          Requires pads and plugs for spikes.

     iii.          Damage the bottom edge during packing.

     iv.          Scrape value is nil.

      v.          Damages to the concrete sleeper is very heavy in derailment.

Sleeper density

It is the number of sleepers per rail length and it is specified as (M+x or N+x), where M is the length of rail in meters; N is the length of rail in yards and x is a number, varying according to the following factors and is fixed by the Railway Board for various axle loads. The factors are (a) Axle load and speed (b) Type and section of rails (c) Type Of ballast and ballast cushion (d) Type and strength of sleeper (e) Nature of foundation.