Recliner <recliner.usenet@gmail.com> wrote:
> Roland Perry <roland@perry.co.uk> wrote:
>> In message <svg8gp$3r1$1@dont-email.me>, at 16:22:49 on Sun, 27 Feb
>> 2022, Recliner <recliner.usenet@gmail.com> remarked:
>>> ColinR <rail@greystane.shetland.co.uk> wrote:
>>>> On 26/02/2022 17:21, Roland Perry wrote:
>>>>> In message <svdjpv$e1j$1@dont-email.me>, at 16:17:03 on Sat, 26 Feb
>>>>> 2022, Sam Wilson <ukr@dummy.wislons.fastmail.co.uk> remarked:
>>>>>
>>>>>>> I'm glad it's all sorted now, and that the most strident notions about
>>>>>>> the track sliding down some sort of slope under its own weight, have
>>>>>>> been well and truly debunked.
>>>>>>
>>>>>> Yes, it turns out we were all wrong.  Your most strident assertion, that
>>>>>> the track must have remained straight because it was under tension, has
>>>>>> also been completely debunked in a different subthread because the
>>>>>> jointed
>>>>>> track was not under tension.  A little humility would make life here much
>>>>>> more pleasant.
>>>>>
>>>>> You are misdirecting yourself. While I agree that whoever implied it was
>>>>> continuously-welded rail under tension (an assertion upon which much
>>>>> later speculation was based) was mistaken, even classic jointed rail has
>>>>> very limited "stretch" built into it.
>>>>>
>>>>> But even *that* turns out to be a red herring because the track didn't
>>>>> slide sideways "down a slope", because the driver is now known to have
>>>>> just seen a dip.
>>>>>
>>>>> And all the photos purporting to show otherwise are now known to be
>>>>> hours later *after* the ground had eroded even more.
>>>>>
>>>>> The prior zig-zag is a hoax, and that's all I was trying to say.
>>>>
>>>> And that folks, is called "humility".....
>>>
>>> Indeed. As Roland has never been wrong about anything, ever, he has nothing
>>> to be humble about.
>>
>> That playbook comes out again.
>>
>> Yes, there are several things I've not got right, but this episode with
>> the sideways sliding track isn't one of them. Modulo I was probably
>> wrong to assume the person who originally mentioned continuous welded
>> rail tension at that site was correct.
>>
>> Oh, that was you! (I wasn't going to mention it, but you've forced my
>> hand).
>
> You were delighted to assume, just as I did, that it was CWR when you
> thought it supported your theory (which turned out to be no more correct
> than any others that were proposed):
>
> Roland Perry <roland@perry.co.uk> wrote:
>> In message <stoe9d$fkg$1@dont-email.me>, at 12:17:49 on Sun, 6 Feb 2022,
>> Recliner <recliner.usenet@gmail.com> remarked:
>>> Roland Perry <roland@perry.co.uk> wrote:
>>>> In message <sto9hd$g9t$1@dont-email.me>, at 10:56:45 on Sun, 6 Feb 2022,
>>>> Recliner <recliner.usenet@gmail.com> remarked:
>>>>> Roland Perry <roland@perry.co.uk> wrote:
>>>>>> In message <sto7bj$5cb$2@dont-email.me>, at 10:19:31 on Sun, 6 Feb 2022,
>>>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>>>>>>> Roland Perry <roland@perry.co.uk> wrote:
>>>>>>>> In message <sth7uq$f0i$1@dont-email.me>, at 18:46:50 on Thu, 3 Feb 2022,
>>>>>>>> Tweed <usenet.tweed@gmail.com> remarked:
>>>>>>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> wrote:
>>>>>>>>>> Roland Perry <roland@perry.co.uk> wrote:
>>>>>>>>>>> In message <stgal4$t5h$1@dont-email.me>, at 10:26:45 on Thu, 3
>>>>>>>>>>> Feb 2022,
>>>>>>>>>>> Anna Noyd-Dryver <anna@noyd-dryver.com> remarked:
>>>>>>>>>>>
>>>>>>>>>>>>>> If you watch a stream of water cutting a channel, it’s
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> upstream end of the channel that gets the most energetic erosion.
>>>>>>>>>>>>>
>>>>>>>>>>>>> Yes, but why does that cause lateral slewing (upstream), rather than
>>>>>>>>>>>>> more droop?
>>>>>>>>>>>>
>>>>>>>>>>>> Because the upstream side of the track gets eroded-under first,
>>>>>>>>>>>> before the other side of the track. So the track is unsupported
>>>>>>>>>>>> under one side only; has non-zero weight and is not a rigid
>>>>>>>>>>>> structure. Why do you think it *wouldn't* slew to one side?
>>>>>>>>>>>> It's not Hornby "long straight" rigid track which can be used
>>>>>>>>>>>> as a bridge without any further support!
>>>>>>>>>>>
>>>>>>>>>>> Slewing requires a horizontal force perpendicular to the
>>>>>>>>>>> track, and what
>>>>>>>>>>> is providing that force. Drooping requires gravity acting
>>>>>>>>>>> downwards, and
>>>>>>>>>>> that's in plentiful supply.
>>>>>>>>>>
>>>>>>>>>> The imbalance of force is provided by the erosion being initially
>>>>>>>>>> predominantly under one side only of the track.
>>>>>>>>>
>>>>>>>>> If you put a marble on a slope the only force according to
>>>>>>>>> Roland is just downwards gravity. Yet as the marble rolls down
>>>>>>>>> the hill it moves both vertically and horizontally.
>>>>>>>>>
>>>>>>>>> The eroded track length is effectively rolling down hill (well
>>>>>>>>> not rolling but you know what I mean).
>>>>>>>>
>>>>>>>> If the ground under the track has eroded by more than about six inches,
>>>>>>>> there isn't a slope for the track to slide down. It's just hanging in
>>>>>>>> mid air.
>>>>>>>
>>>>>>> But at that point it had only eroded under *one side of the track*.
>>>>>>
>>>>>> Sure about that?
>>>>>>
>>>>>> <https://i.dailymail.co.uk/1s/2022/01/30/18/53556263-10457643-image-m-
>>>>>> 23_1643568862268.jpg>
>>>>>
>>>>> That was taken later.
>>>>
>>>> What we need (and there won't be one, unless GA released some cab
>>>> footage) is a picture of the tracks before the train arrived.
>>>>
>>>> The one linked above doesn't show anything like as much of a kink as
>>>> <https://twitter.com/ianhardie9018/status/1487783395660869633?s=21>
>>>> which suggests it was moving left and right quite a bit.
>>>>
>>>> I still think the ianhardie kink is a result of the track buckling from
>>>> the braking force of the train, not sliding sideways downhill.
>>>
>>> Why would braking cause a track to buckle sideways? CWR is under tension.
>>
>> If it's under tension [and yes, I agree it is, and underpins my own
>> theory], how can it do a crazy zig-zag buckle in the way that's being
>> claimed, when the only force on it is gravity downwards - and what that
>> would cause is just a small droop.
>
>
>
From the RAIB report

As the train approached the section of track concerned, the driver of the
train noticed what appeared to be standing water on the line ahead and
started braking. The train, which was formed of three passenger vehicles
and a power car, stopped with its front carriage above the flowing water.
Over the next twenty minutes the flowing water caused all support for the
track to be lost and the track sank significantly, causing the front
carriage to tilt forwards and sideways. The driver attempted to move the
train back clear of the damaged section of track, but this proved
impossible because of the angle of the front carriage.

Note the use of the word sideways. Roland’s original assertion that there
was only a downwards force and this could not cause a lateral motion.
Clearly there was a slope and the weight of the train provided the force
that was converted to some extent into a sideways force. Had the ballast
been completely washed out, ie under both rails, the weight of the train
would only cause a vertical dip.