old stevens pass route and original Cascade Tunnel

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New Member
old cascade tunnel and switchbacks

To save time I have provided a link to a world wide zig zag railway listing


In south America in one instance The Callao, Lima & Oroya Railway is the second highest railway in the world with many switchbacks/zig zags, sixty tunnels and bridges.

In 1923? a spur was opened to the Volcan region to a mine being developed and was operated until 1953. the spur and branch have been closed to traffic(I believe the mine was closed due to the ore running out)
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New Member
1929 Cascade Tunnel and ventilation of the tunnel bore

Well, it seems your hind sight is as it always is for us, 20-20. I pretty much disagree on every point you make concerning the factors leading to the Wellington slide, but that's actually a side issue. Again, given what the Board knew in 1925, given the history of the line from 1893-1925, I still say they made the right choice. As for making current updates to the tunnel, again, have you actually witnessed its operation, the door, the variable speed of the fans, the venting louvers behind the door structure..etc? How would you change the current useage of the fans' variable speed capabilities or the use of the door, for instance?

You have the knowlegde, what is the average length and tonnage of trains operating over switchbacks in Europe and these steep grades you talk about? How do they compare to the unit coal and grain trains operated here? I'm assuming they are of equal tonnage and length, correct?

Martin Burwash
Good morning Mr. Burwash,

About the air door for the exisiting Cascade tunnel the problem is two fold;

1. the existing leaks within the escape addits and any ventilation air escaping through the
Pioneer Tunnel to the exterior of the old workings.

2. Ventilation in mine tunnels and escapeways is controlled by active air lock doors, hand built
fire resistant walls walls and brattice cloth stoppings in the case of active mine workings which
are mined at right angles to the main air tunnels.

The active mining units, panels or yards as they are referred to in some circles have an
exhaust escape way which allows egress from the mining unit in the event of a fire on
the fresh air side of the mining panel.

The brattice wall curtain is erected for the entire length of the mining panel and the brattice line
may be left in place if fines (as was the case in the mine I retired from) disposal is to occur in the
inactive mining panel at some point in the future as the mining panel being back filled must have
an escape way exit the area.

The mine access doors may be a swing type door for vehicles to transit and also will include a
passive pressure man door to allow persons to move between airlocks separating fresh air doors
and access roads within the mine to separate separate the incoming fresh air from the exhaust
tunnels which are separated by erected permanent walls with overhead or swing doors for vehicle
access to the exhaust side of the mine which will have the mines conveyors.

The sliding door that is used to control the air flow into the tunnel is a barrier to prevent a great majority
of the air from escaping the bore and forces it to travel to the opposite portal.

Pressure losses from a fan set will effect every aspect of tunnel ventilation the turbulence created at the
fan blade tips and the ducting will simply bounce around within the fan area and then travel to the bore
and out the opposite portal.

Along the way the ventilation air will escape wherever posssible as air like water and electricity is lazy
and will take the easiest way to escape.

If there air leaks they can be found using smoke generator tests to fill the tunnel bore with smoke that
will allow them to find the air leaks which may oir may not exist in the New Cascade Tunnel.

In order to test the tunnel bore for leakage the west portal would have to be sealed off with a reinforced
brattice cloth wall to determine how effective the fresh air flushing is of the tunnel bore using a vent tube
in the erected brattice wall to provide back pressure against the air stream generated by the forced draft
fans used to flush the tunnel.

A smoke generator would have to be ignited a distance away from the east portal to eliminate or reduce the
loss of smoke near the doors if at all possible.

But as the line is moving 33 transits per day I do not think that BNSF would want to hold up operations in the
New Cascade Tunnel unless roof repairs were required to occur.

IF induced draft fans were installed that equaled the forced draft fans volume in cubic feet per minute and the
fans were activated at the same time the bore would be flushed much sooner but there would have to be a
second passive air lock door on the west side of the tunnel portal to aid in clearing the bore of exhaust smoke.

Many tunnels employ high speed fans in the crown of the tunnel using tube ducting to push the exhaust fumes
through the tunnel bore at all times and this has been done for years with good results. The problem of course
is clearances with double stack trains.

If the floor elevation was lowered the use of high speed ventilation fans and ventilation tubing supported by wire
rope cable would increase the air volume through the bore.

Ventilation tubing is constructed of brattice cloth or fiberglass and requires that the tubing be supported by a wire
rope cable anchored to the roof line or a long a tunnels floor id the tunnel is wide enough to allow it to occupy this
space along the tunnel wall.

If the New Cascade tunnels floor elevation was lowered the ventilation tubing could be extended directly outside
the west tunnel portal to exhaust the diesel fumes at a faster rate per minute as a series of fans and ventilation
tube sets would pull fresh air in and push exhaust air through the bore as the consist enters and exit the tunnel
this would also reduce the required flushing time and increase the amount of fresh air entering tunnel and aid in
exhausting the diesel fumes.

Individual mine ventilation fans are capable of moving tens of thousands of cubic feet per minute of fresh air
ventilation in a tunnel bore quickly and easily using 480-600-1000 volt fans as a common practice the key
would be employing the ducting at the correct length within the bore if space allows as the exhaust air
travels in one direction and the westportal could have several ducts or permanent fans using solid ducting
exiting the crown of the tunnel pulling the exhaust air from thousands of feet within the bore to aid in
clearing the exhaust gas.

The flush times permit the full airflow of the fans to be used to push the exhaust gasses out of the tunnel
where if fans in the tunnel crown and ventilation duct were employed at intervals the exhaust would be
removed sooner allowing more fresh air to enter the bore simply by exhange.

Dillution of the diesel exhaust is the main goal permiting more fresh air to enter at all times and flush out the fumes.

In essence the waiting time during your tunnel flushing is equal to the time required for explosive fumes to disipate
in an underground mining panel operation as the air will only move so fast.

The added benefit would be that the engines would not overheat as quickly or at all if enough air is moved within the
tunnel to increase the amount of active air exchange as the air volume in the tunnel is moving very slowly.
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Ed Sand

General Idiot
While the historic analysis is very interesting, if you're talking about current day operations the existing Cascade Tunnel isn't a major constraint on operating capacity.

If you could daylight and double track it, it still wouldn't gain BNSF much more than a train or two a day in overall line capacity.

The factors that matter for line capacity are: siding length and distance apart, track speed (itself a function of grade and curvature), and signalling. The whole line is the bottleneck, not the tunnel.

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