Types of isolation:-
(1)Derailing Switch (2) Sand Hump (3) Catch Siding (4) Slip Siding
(5)Long and Short Sidings (6) Snag Dead End Crossing
It is provided at one end of the line to isolate the train movement on adjoining line. It consists of one tongue rail and one stock rail with necessary fittings connected with the nearest point in such a way to inter lock the connected points to permit one train movement at a time on any turnout and thus to avoid the possibility of any accident due to rolling down of vehicle from adjoining line. It is normally kept in open condition, whenever it is required to admit the train on derailing switch the point is set and locked before train is allowed to enter.
This is provided at far end of receiving loop line and protected by a stop signal. The signal is kept in ON position thus no train is allowed to admit in sand hump. The overall length of sand hump is kept 78 meters starting from ANC. The sand hump is actually constructed at a distance of 18meter from ANC. The first 10 meter is open at top, walled track. Further 20meter is sanded walled track. The top level of wall is kept 65mm above the rail top table. Further 30meter is completely filled with earth. The top width of sand hump is 4m and the walls are 300mm apart for sand fill. The sanded 20m length is having a rising gradient of 1 in 40.
Catch siding is provided to protect the station ahead due to continuous falling gradient of 1 in 80 or steeper within 45meter beyond the outer most point. The signal ahead is kept in ‘ON’ position and point is normally set towards catch siding. The train approaching to catch siding is stopped at the signal for 2 minutes for testing the brake power of train. After the train stop the point is set towards mainline, the signal is taken ‘OFF’ and the train allowed to go ahead. If the train does not stop at the signal the train is allowed to enter the catch siding. Normally the length of catch siding is equal to the maximum length of a goods train plying in the section. The catch siding prevents the possibility of any accident in station ahead. Train detention has been reduced by providing two glued joints and relay systems one at 1 km ahead and another at a 2 minute distance from first glued joint. The train is allowed to move with a SR of 20 kmph if the train follows above SR strictly. The point is set towards mainline and signal is taken ‘OFF’ to allow the train to block section.
Slip siding is provided to protect the block section in rear due to continuous falling gradient of 1 in 100 or steeper from trailing point within 45meter beyond the outer most point.. It is normally set towards the slip siding. The vehicle escaped from station and yard is trapped in slip siding. The slip siding is protected by a signal is rear.
The length of slip siding is generally kept to accommodate 4 to 6 wagons it prevents the possibility of accident in rear block section.
Slip siding is also provided where there is a gradient of 1 in 260 or steeper in station and yards.
Long Siding and Short Siding:-
These sidings are connected to running lines, normally provided to isolate the adjoining lines. These sidings are the part of special yards where dead ends are provided.
When length of siding is more than 180m it is called Long siding and when length of siding is less than 180 m is called Short siding.
Snag Dead End Crossing:-
This is a special type of crossing normally provided where there is directional movement of traffic in crossing portion and no train is allowed on the second part of the crossing which is a sand hump pr dead end. The length of snag dead end is kept 180m. The RH wing rail is raised from 420mm away from ATS to 1260mm about 38mm.
LH wing rail is ordinary rail. While RH wing rail is gradually raised to lift the flange o wheel to jump in case of accidental entry of vehicle towards sand hump or dead end. The mild steel plates are attached in gauge face of wing rail and Vee railand gradual lifting of wheel flange of vehicle and similarly gradual drop of wheel. The life of snag dead end crossing is 20-25 years.
Ghat section :- section with more than 30% section is with gradient steeper than 1 in 80 or more than 50 % section is laid on gradient steeper than 1 in 100 is called Ghat section.