This is real life issue I am having currently and I am puzzled as to why it happened. I have lived over the subway lines (two actually each going in the opposite direction, two sets of tracks) for two years. The noise has always been a soft background hum, with an occasional louder train (that usually needs maintenance), hardly noticeable. One early morning near the end of January I was jolted out of bed by a loud noise. Turns out it is the subway. It is as if someone turned the volume up from 3 to 8 all of a sudden. Noise much louder (both tracks), last longer and there is shaking indoors too. Some small variances in the loudness of each train, but all much louder. The quietest train now is much loudest then the loudest one was before. I know that no changes were made to the tracks, trains, schedules or my building. What else could have caused it - noise from subway became much louder overnight?
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$\begingroup$ Why not state the city, subway operator and track section? $\endgroup$– TransistorApr 20, 2018 at 23:52
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$\begingroup$ How would that help? $\endgroup$– VanessApr 21, 2018 at 0:04
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$\begingroup$ Because someone who knows the subway might have some knowledge of engineering changes that have recently taken place, of course! $\endgroup$– TransistorApr 21, 2018 at 0:09
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$\begingroup$ No changes - have been talking to a relevant person within the transit authority (who even visited), have had an inspection done of the tracks underneath (twice). No changes what so ever. And again, it happened over night. One Friday night I fell asleep to be woken up by the noise at 6.30. Unlikely major changes happened Friday night....But if it helps thee city is Toronto, Toronto subway $\endgroup$– VanessApr 21, 2018 at 0:16
2 Answers
It is possible that because of percolation, the moisture content of the layer of dirt between you and subway has changed to near optimal compaction, which is in the range of 12 to 24 % in siltyclay, assuming your strata is CL, ML, SC. These are sensitive to moisture ratio and at optimal compaction transmit sound better.
Some change in moisture is seasonal, therefor it could go back to initial condition. But if a main sewer or water line has cracked, there is room for concern.
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$\begingroup$ Not sure what type the soil is below. You think the moisture level could stay the same over a period of 2 1/2 months? $\endgroup$– VanessApr 22, 2018 at 2:10
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$\begingroup$ Sorry that was meant to say Do you think.... $\endgroup$– VanessApr 22, 2018 at 13:03
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$\begingroup$ The only way to arrive at a meaningful estimate is to test. There are fast tests, such as a calcium carbide reagent type. Regardless of method one needs to have the help of a geotechnical engineer or at least a lab and an hourly technician. Your local building department may have useful information and public domain searchable geology reports. $\endgroup$– kamranApr 23, 2018 at 3:21
If you were to stand next to a long train going by at speed, you would likely notice that some cars are incredibly noisy while others are relatively quiet. the most likely answer to your question is that the railroad cars now in service on that portion of track are different from those previously used.
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$\begingroup$ Appreciate the answer but no. Subway train fleet running on full capacity no exchanges or new trains or cars planned until 2020 - info from the transit authority and their wiki page. . When it does happen it will be with pomp and politicians like it was on another line they did recently and not overnight and without telling the public.. Occassionally a train is removed for wheel maitenance overnight and returned in a day or two $\endgroup$– VanessApr 20, 2018 at 22:02
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1$\begingroup$ Wow! the main source of noise is in the wheels and rail surfaces. I wonder what happened! $\endgroup$ Apr 20, 2018 at 23:00
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$\begingroup$ Could the 'path' of the sound between me and the train have changed significantly (i.e. the ground between) in which case is the building unstable,.. $\endgroup$– VanessApr 21, 2018 at 0:03
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2$\begingroup$ if the ground froze between the tracks and your house, it would make the noise much, much worse! $\endgroup$ Apr 21, 2018 at 0:37
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1$\begingroup$ Well the frozen ground possibility is one reason that stating your location was helpful. That wouldn't have been a problem in Athens, for example. $\endgroup$ Apr 22, 2018 at 9:00