KRV54-vaihteiden monitorointi Alppilassa

The goal of this study is to monitor the condition and the stresses and
movements of four diamond crossings with double-slip V460-V463 located in
the Helsinki. The research period of this study was 07/2020 – 12/2020. These
double slips have been caused excessive amount of maintenance work before
the monitoring period, so the reasons for these problems had to be clarified.

Chapter 2 concentrates more closely to condition and the maintenance history
of these turnouts and also reveals the distinguished main problems. Several
obtuse crossing noses have been welded and totally replaced during recent
years. Despite these repeated maintenance actions, several surface defects
were noticed in the inspections on spring 2020 and finally two separate obtuse
crossings cracked.

Chapter 3 presents the recent results of Finnish track inspection car EMMA.
These results reveal that many class D rail errors have been measured in these
turnouts during recent years, especially in turnout V460, which has the worst
condition. Tamping process in spring 2020 has removed many of these class D
errors and deterioration of track geometry has been really slow after that.
Unfortunately, this tamping excluded the turnout V460, which is still in bad
geometrical condition.

Chapters 4 – 6 concentrates to the measurement arrangements along with
results and analysis from those measurements. The measurements showed
that the vertical reversible deflections of bearers are moderate, which means
that the tamping has been quite successful under these obtuse crossings. The
reversible deflection was 1-3 mm, which is little bit more than in normal main
line. Still, this kind of deflection cannot be the main reason for the cracked
crossings in the turnouts V461 and V463. Visual inspections also assured that
the surface defects haven’t been increased between the first inspection on
August and the second inspection on November.

The effect of the reversible deflection on the rail stresses was measured from
the obtuse crossing and results showed that the strain of crossing was close to
normal strains in the main line. This means that the actual loads in the crossing
are much bigger, because the structure of obtuse crossing is more rigid than in
main line. The final strain is highly dependent on the rail surface defects, which
increases the dynamic factor of train loads. Nevertheless, it was discovered that
the strain doesn’t increase with the train speed. During this inspection period,
the maximum operation speed in this area was decreased to 30 km/h – 60 km/h,
so it was not possible to study the relationship between strain and train speed
on the maximum obtuse crossing operation speed, which is 80 km/h in Finland.

Overall, the geometry of these monitored double slips has remained quite well
during this study. The main reason for that is the 60 km/h speed limitation set in May 2020. After this modification the rail wear is still detectable, but the
degradation of rails is dramatically slower. With these results it is
recommendable to keep this speed limitation valid also for the future. If there is
a necessary need to increase the operation speed back to normal 80 km/h
design level, this kind of monitoring should be done again to assure that the
relationship between rail strain and train speed remains controlled.