Förutsättningar för ökad metervikt och axellast på Malmbanan

Sammanfattning: LKAB intends to increase the production of iron ore in the upcoming years. To prevent problems with the capacity along Malmbanan (The Iron Ore Line) an increase in the maximum permissible axle load is required. The first step is an increase from 30 ton to 32.5 ton. The vision is to increase the axle load in 4 steps of 32.5 - 35 - 37.5 – 40 ton, where an axle load of 40 ton is the final goal. The report deals with the influence of an increased axle load for each track component. This is in order to present the deterioration of the track quality when the axle load is increased. Different methods of track maintenance and reinforcements will also be discussed. The work is focused on the southern circuit of Malmbanan. Track conditions on individual track sections will not be considered. The work only includes the track structure i.e. signaling systems and power supply systems will not be considered. Economical calculations of reinforcement and maintenance activities is left for future investigations. The working process has included a literature study, field study, computational study and an interview study. This has led to an assessment of to what extent each track component is affected by an increase in maximum permissible axle load. The rail will be exposed to a higher amount of wear, an increased risk for rail defects and plastic deformation of the rail head. Rail damage is most easily prevented by rail grinding and rail lubrication in sharp curves. More extensive measures are to replace the rail with a stronger rail steel or replace with a larger rail profile. The rail fastenings will be affected by higher track forces and are particularly exposed in sharp curves. The rail fastening systems has to be replaced gradually when increasing the permissible axle load. The only fastening device, in use today, that will be approved for 40 ton axle load is the Fastclip and the strongest e-clips with plastic rail pads. The lifetime of the sleepers will be shortened with an increased axle load. A critical factor is the bending moment at the position of the rail and in the middle of the sleeper. According to the performed calculations all sleeper models eventually have to be replaced, except sleeper model A22. However, there is a lack of knowledge about the sleeper strength for some models. Strength tests for each specific sleeper model should therefore be carried out. It is recommended that a research study is performed to gain knowledge about the track position and model for all the fastening systems and sleepers along the track. This in order to ease future track upgrades. A higher axle load leads to an accelerated deterioration of the ballast. Ballast cleaning is recommended in the near future to reduce the rate of ballast contamination. The ballast thickness should not be less than 50 cm, according to performed calculations. An increased axle load will cause an increased need for maintenance of the track substructure. Reinforcements have to be carried out on several bridges and culverts. This also applies to the geotechnics, which is mainly reinforced by pressure banks at track sections with poor subgrade. A complete investigation of the bearing capacity of the track subgrade should be performed. This in order to find track sections with insufficient bearing capacity. An investigation of the load carrying capacity for all bridges along the southern circuit of Malmbanan should also be performed.