Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE credits
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
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.