Interpretation of the provisions of the Rules for Repair of Conventional Railway Lines

Article 3.3.2

The top surface of the ballast at the bottom of the rail should be 20 to 30 mm lower than the top surface of the sleeper. The middle part of the ballast of type I concrete sleepers should be hollowed out, and its top surface should not be less than 20 mm below the bottom of the sleeper, and the length should be 200 to 400 mm; the middle part of the ballast of type II and type III concrete sleepers should be filled and not higher than the top surface of the sleeper.
(1) In order to maintain the stability of the track structure and improve the longitudinal and lateral resistance of the ballast, the ballast in the sleeper box and at the end of the sleeper should be kept full. The top surface of the ballast at the bottom of the rail is lower than the top surface of the sleeper. First, to avoid the impact of ballast splashing under the influence of wind at high speed, second, to prevent moisture on the surface of the ballast during rainfall from rusting the rails and fasteners, and third, to avoid affecting the normal operation of the track circuit. Through verification, the top surface of the ballast in the conventional speed section should be 20 to 30 mm lower than the top surface of the sleeper. Regardless of whether there is an iron pad on the wooden sleeper or a slope on the concrete sleeper rail groove, the sleeper surface at the center line of the rail bottom shall prevail.

(2) In order to avoid excessive negative bending moment caused by the middle support under the sleeper and the generation of transverse cracks on the upper surface of the middle part of the sleeper, this rule requires that the middle part of the roadbed under the type I concrete sleeper be hollowed out, and the hollowing length should be kept at 200-400 mm. Type II and Type III concrete sleepers increase the strength of the middle part to resist negative bending moment, so it is stipulated that the middle part of the roadbed under the sleeper shall not be hollowed out, and it is required to be kept full, the middle part is filled, and not higher than the top surface of the sleeper.

Article 3.5.2 In the section where new type II concrete sleepers or wooden sleepers are laid on the main line that meets one of the following conditions, the number of sleepers should be increased during the overhaul of the line equipment:
1. Curved sections with a radius of 800 m or less (including the transition curves at both ends).
2. Sections with a slope greater than 12‰.
When the above conditions overlap, the number of sleepers laid is increased only once; the number of sleepers added per kilometer in the section where sleepers are strengthened and the maximum number of sleepers laid are as follows:
The number of sleepers added per kilometer for new type II concrete sleepers is 80, and the maximum number of sleepers laid is 1840; the number of sleepers added per kilometer for wooden sleepers is 160, and the maximum number of sleepers laid is 1920.
The working conditions of the track in the curved and steep slope sections are worse than those on the straight line, and the external forces it bears are also more complicated. The track maintenance conditions in the tunnel are poor, so the track should be strengthened in the curved and steep slope sections and in the tunnel. Increasing the number of sleepers can increase the longitudinal and transverse resistance of the track, reduce the stress of the rails and the roadbed, and help maintain the stability of the track and improve the track strength.
① When the train passes through the curve, the stress of the rail will increase due to the eccentricity of the vertical and horizontal forces on the rails, and the increase is inversely proportional to the radius of the curve. According to actual measurements, when the curve radius decreases from 800m to 300m, the transverse horizontal force coefficient increases by 42%, and when the curve radius is greater than 800m, the transverse horizontal force coefficient is close to the straight line. Therefore, from the relationship between the transverse horizontal force and the curve radius and many years of practice, it is appropriate to increase the number of sleepers in the curve section with a radius of 800m and below.
② Frequent braking is required in downhill sections with a slope greater than 12‰, which will increase the longitudinal force acting on the rails and cause track creeping. The greater the slope and when multiple machines are used for traction, the more serious the track creeping. Therefore, it is required to increase the number of sleepers in downhill braking sections with a slope greater than 12‰ to enhance the anti-creeping ability of the track.
③ When increasing the number of sleepers to improve the track strength and stability, it cannot be increased without principle. From the perspective of economy and maintenance, the number of sleepers cannot be too many, and should meet the requirements for the clear distance between sleepers required for large, medium and maintenance tamping operations. For this reason, this rule stipulates that the maximum number of sleepers per kilometer is: 1840 for Type II concrete sleepers and 1920 for wooden sleepers.

Article 3.5.3

The following sections should not be laid with concrete sleepers:

1. 5 sleepers at each end of an ordinary turnout with wooden turnout sleepers.

2. No less than 15 sleepers within the ballast wall of an open bridge deck and a ballasted bridge with wooden sleepers and at both ends (when there is a guardrail, it should be extended to no less than 5 sleepers outside the shuttle head).

(1) In order to make the transition between the two ends of the turnout and the track rigidity smooth and uniform, there should be a certain amount of concrete sleeper transition at both ends of the turnout with wooden turnout sleepers.

(2) Concrete sleepers should not be laid. The main consideration is the requirement for smooth elastic transition between concrete sleepers, wooden sleepers and open bridge deck sections.

Article 3.5.5

The sleepers of seamless lines should be arranged evenly: the sleeper spacing is shown in Table 3.5.5-1; the sleeper spacing of ordinary lines is shown in Table 3.5.5-2.
(1) Considering the large-scale laying of seamless lines and the promotion and use of large-scale road maintenance machinery, in order to facilitate the tamping operation of large-scale machinery, this rule stipulates that the sleeper spacing of seamless lines should be arranged evenly.

(2) The relationship between the sleeper spacing is a>b>c. The sleeper spacing is reduced at the joint to improve the joint strength. The same sleeper spacing is used in the middle section to ensure uniform force on the track.

(2) For sections with non-standard length rails, the standard number of sleepers used must be the same as that of the standard rail sections in the section. Due to the length of the rails, the practical spacing cannot be consistent with the standard spacing. In order to maintain the strength of the track in a section, the difference between the two spacings should not be too large, so it is stipulated that the a value shall not be 20 mm larger than the standard.

The following regulations should be observed when using wooden sleepers (including wooden split sleepers):

1. When the wide side of the wooden sleeper is at the bottom and the top and bottom are the same width, the heartwood side should be facing downward.

2. Wooden sleepers of good quality should be used at the joints.

3. Wooden sleepers should be tied before laying.

4. When using new wooden sleepers, holes should be drilled in advance with a hole diameter of 12.5 mm. The hole depth should be 110 mm when there is an iron pad and 130 mm when there is no iron pad. When using threaded spikes, they should be handled in the same way as ordinary spikes.

5. The specifications of the spike hole wood pieces used for diversion should be 110 mm long, 15 mm wide, and 5-10 mm thick, and should be treated with anti-corrosion.

(1) When laying wooden sleepers, the wide side of the wooden sleeper should be at the bottom to increase displacement resistance and maintain good stability. When the width of the upper and lower sides is the same, or the width difference between the two sides is not large, the heartwood side should be facing downward to delay the decay of the wooden sleeper.

(2) Since the rail joint structure is relatively weak and bears a large impact force, good quality wooden sleepers should be used at the joint to strengthen the rail joint. If one wooden sleeper fails at the rail joint, the two wooden sleepers at the joint should be replaced together to make the joint support balanced. The replaced available wooden sleepers should be moved outside the joint.

(3) New wooden sleepers that are split should be repaired by nailing boards and bundling before laying to avoid aggravating the splitting after laying.

(4) Drilling spike holes can increase the pull-out resistance by 25% to 30% and the squeeze resistance by 20% compared to not drilling spike holes. It can also prevent accelerated decay due to damage to wood fibers, which is beneficial to extending the service life of wooden sleepers. Generally, when replacing wooden sleepers, you should first drill the nail holes on one end and drive the spikes, and then measure the track gauge on the other end before drilling holes and driving nails.

(5) The wood chips for the nail holes are small and simple, but they play an important role and can affect the service life of the wooden sleepers. Therefore, they must be processed according to standards and should be treated with anti-corrosion. When using them, they must be selected carefully and be properly inserted into the nail holes.