Hanalan liikennepaikan geometriavirheiden selvitystyö

The main goal of this study was to find out, why the track junction in Hanala has major geometrical errors, which causes train delays even though there are continuous maintenance efforts. After those reasons for errors has been clarified, the aim is to give recommendations how to fix those problems, so that the stability of track would be better in future.

In this study the track inspection history and the development of errors has been
examined. During the study, geometrical measurements were done with the help of GEDO track survey trolley, reversible deflection of track was measured as well as cross section profiles of crossings. Also the condition of ballast and substructure was inspected with the help of soil samples from every turnout area. One of the track inspection measurement was done only two days after tamping the whole area and the results of inspection showed that this tamping couldn’t remove all the short wavelength elevation errors, which has developed around crossing nose. Also cant and twist errors remained throughout the tamping.

The current tamping methods in Finland are not the ideal ways to remove short wavelength errors. The main reason for that is too short chord system. The measurement chords are created in this area only once in 10 meters and none of these points were actually in the crossing nose area. That is the reason why the lift of the crossing area was insufficient during tamping. Another critical reason for the immediate errors could be that the plotter oftamping machine doesn’t printthe elevation at all. This could mean that tamping machine actually doesn’t even try to correct the short wavelength errors in reference rail. The cant errors are at least corrected automatically, which can be seen at the results where lift values of another rail change often than reference rail.

The long turnout bearers are often little bit convex. This leads to situation where there is always some kind of cant values either on straight route or diverging route. This feature is probably not commonly known among the tamping crew. During the tamping process the straight route is commonly tamped first and the attempt is to remove all the cant in this route. After that the diverging route is tamped and the aim is same, which turns the straight route and leaves crossing nose higher that straight route reference rail. So when the bearers are convex, the tamping of the diverging route could easily weaken the tamping results of straight route. These problems are even increased if there are adjustment plates underneath the crossing as in Hanala. These adjustment plates also increase the stresses in the overall structure leading to straightening of these convex bearers through bending or creeping in long term.

The soil samples reveal that the structural layers of track are appropriate, even thought the thickness and properties of different layers varied a little bit. The granularity of ballast was almost as new and the middle layer was good and frost insulation was done by frost insulation plates. Underneath the frost insulation plates there are old crushed ballast or middle layer material approximately 0,3 m. Underneath these materials are insulating sand, which is little bit finer than instructed. All the materials were actually little it finer than instructed. The overall thickness of structure is approximately 1,4–1,6 meters, which can be said to be adequate to the loads in Hanala. Soil samples from the middle layer above the frost insulation plate and the old crushed ballast underneath the plate was completely wet. It seems like the frost insulation plate is disturbing the
drainage of above layer and old ballast contains so much fines that it binds water.