Check rails (Fig. 13.22) are provided parallel to the inner rail on sharp curves to reduce the lateral wear on the outer rail. They also prevent the outer wheel flange from mounting the outer rail and thus decrease the chances of derailment of vehicles. Check rails wear out quite fast but since, normally, these are worn out rails, further wear is not considered objectionable.
According to the stipulations presently laid down by Indian Railways, check rails are provided on the gauge face side of the inner rails on curves sharper than 8° on BG, 10° on MG, and 14° on NG routes. The minimum clearance prescribed for check rails is 44 mm for BG and MG routes and 41 mm for NG routes.
The design of the horizontal and vertical curves is extremely important for railway tracks. Both the speed and safety of the vehicles greatly depend on the design of the horizontal curves. Important stipulations laid down by Indian Railways with resepct to the design of horizontal curves are highlighted in this chapter. The methods of calculating superelevation, lengths of transition curves, and extra clearance on horizontal curves are also discussed.
1. What is superelevation? Why is it necessary to provide superelevation on the curves of a railway track?
2. A 8° curve track diverges from a main curve of 5° in the opposite direction. In the layout of a BG yard, calculate the superelevation and the speed on the branch line when the maximum speed permitted on the main line is 45 km/h.
3. Explain the objective of providing transition curves on either side of a circular curve.
4. Why is the widening of gauge required on sharp curves? Determine the extent of gauge widening required for a board gauge track on a 5° curve, given the following data: B = 6 m is the rigid wheel base, D = 1.5 m is the diameter of wheel, and h = 3.2 m is the depth of flange below rail top.
5. For a main line and a branch line on 5° curves, calculate the superelevation and the speed on the branch line if the maximum speed permitted on the main line is 48 km/h.
6. Define the terms equilibrium cant and cant deficiency on a railway track. Calculate cant deficiency for a 4° curve on a BG track.
7. A 5° curve diverges from a 3° main curve in the reverse direction in the layout of a broad gauge yard. If the speed on the branch line is restricted to 35 km/h, determine the restricted speed on the main line.
8. Calculate the maximum permissible speed on a curve on a Rajdhani route with a maximum sanctioned speed of 130 km/h. The superelevation provided is 50 mm and the transition length is 60 m. Also, the transition length of the curve cannot be increased due to proximity of the yard.
9. Calculate the superelevation to be provided for a 1.5 in. transitioned curve on a high-speed route. The maximum sanctioned speed in the section is 120 km/ h. The speed for calculating the superelevation is set at 88 km/h. What is the length of the transition to be provided?
10. Explain the following terms and state the circumstances under which they occur:
(a) Negative superelevation
(b) Grade compensation on curves
(c) Realignment of curves
11. Clearly explain the string lining method to realign the original curve.
12. Explain 'degree of a simple rail track curve' and derive a simple expression for the radius of a curve in terms of its degree.
13. A transition curve is to be laid to join the ends of a 3° circular curve with straight track. The length of the transition curve is 10 m. Work out the shift and the offset at every 20-m interval for setting the transition curve. Describe how the transition curve can be set.
14. Define equilibrium speed and cant deficiency. A 1 in 8.5 BG turnout takes off from the outside of a 2° curve. Allowing for a speed of 20 km/h (32 km/h) on the turnout and 3 in. (7.5 cm) cant deficiency, both for the line and the turnout, find the maximum permissible speed for the main line.
15. Work out the complete data needed for setting out both the circular and transition portions of a 3° curve for a BG track. The deflection angle is 20°-30°. Cant gradient should be taken as 1 in 720. Maximum speed is 100 km/h. Describe the process of laying out the curve on ground with the data that have been worked out.
16. What would be the equilibrium cant on a curved MG track with a 7° curve for an average speed of 50 km/h? Also calculate the maximum permissible speed after allowing a maximum cant deficiency of 5 cm. The formula given by the Railway Board is
V = 4.35y/R - 67
17. The design speed on a BG track for a circular curve with transitions is 96 km/h. Determine the length of transition. Assume suitable values for the other data required to solve the problem.
18. What are the elements to be considered for the geometric design of a railway track? A BG branch line tracks off as a contrary flexure through a 1 in 12 turnout from the main line of a 2° curve. The maximum permissible speed on the branch line is 40 km/h. Calculate the negative superelevation to be provided on the branch line and the maximum permissible speed on the main line track.
19. Why are vertical curves provided? Calculate the length of vertical curve between two gradients, one rising at a rate of 1 in 200 and the other falling at a rate of 1 in 400.
20. What are the extra clearances provided on a curved track? Describe the extra clearances provided between two adjacent curved tracks.
21. Establish a relationship between the radius and versine of a curve. How is the degree of a curve determined in the field?
22. Enumerate the various methods of setting out a circular curve. Describe the tangential offset method for laying a circular curve.
23. What do you understand by equilibrium superelevation? Describe the thumb rules for calculating superelevation in the field.