The Pacific plate and the North American plate do meet each other under Blue Cut (about midway through this project). The surrounding hills are the result of millenia of crustal movement. Cajon Pass follows (as do most pass routes) the general alignment of surface runoff in the arroyos. This means the soil is very thick with accumulated sediment.
The bridge structures are designed for seismic “flexibility” and the rails have built in capability to withstand moderate movement of the ground.
Bottom line is that a seismic event of large enough magnitude to disrupt rail traffic in this vicinity would cause more damage to other infrastructure so as to gather more attention for recovery efforts.
It’s just the price one pays to live in earthquake country …
…Yes, I too wondered about that turn out on the right side of above mentioned photo…?? Realize the telephoto lens conpacts it’s length, but still it sure looks short.
Once again, really nice update photos from Warren. Again my thanks for sharing as it is interesting to see the build thru pretty rough territory for the third main…
Have a question: So many times I witness brand new track positioned right down on the bare graded {ground}, before ballast is in place. Not being an expert on such construction, why is the track put down before the ballast is in place…Just seems like the process is turned around but I’m sure there is a good reason for it…It just seems to me the rails would get bent all out of shape when the ballast has to be stuffed under them as the rails are lifted to do so, etc…
Quentin is right - the telephoto effect shortens the actual length of that siding. It is used when the helper DPU’s disconnect at Summit and switch themselves over. They can either connect to the rear of a westbound for additional dynamic braking, or run down to Devore by themselves.
As to laying the prefab sections of rail and crossties on the ground. I’ll pay closer attention next time a crew gang sets it up, but I think the equipment that grabs the rails, paddles the ballast and aligns itself to the forward sensor can do all that without damaging the track. I’m sure Mudchicken or some specialist workers can address this more clearly …
I am curious about your use of the term “prefab”. To me, that picture looks like concrete ties in place with CWR laid alongside, ready for positioning…the parallell lines on the ties I take to be the railholding/positioning plates…
ALso, a couple of years ago in a Trains article about double tracking the SF transcon across the panhandle of Texas, pictures and the article noted that the RR was paving the subbed before laying ties and ballest. Have you noted anything of that nature on this project?
You’re right - pre-positioned ties would be a more accurate description. The whole tracklaying process is a pretty impressive choreography.
As to paving the subballast - it’s a soils engineering call. Some soils will allow excess water to seep upward, and will require a “capping”. In Cajon Pass, groundwater tends to head downstream pretty quickly. In flatter terrain, paving would be appropriate.
Wow! That’s some rugged country. A couple of questions: A photo of a bridge being built shows pilings. Is the soil that bad? And,what are the pilings driven into or down to? A tunnel shown (#2?) says it’s going to be daylighted. It doesn’t seem that long, as you can see through it. Why was it a tunnel in the first place, and not just a cut?
The bridges all cross streams, which make the existing ground alluvial. The piles are driven to refusal. New support structure design here in California is calculated for seismic activity, with allowance for elasticity.
The two tunnels are each about 500’ long. In order to daylight them, and stay within the right-of-way, a 1/2:1 slope is required. This entails drilling soil nails - rebar and grout - to stabilize the woven wire fabric and concrete face. The original construction of a single line opted to bore and build essentially a culvert.
Not to downplay the importance of the work at Cajon, but the BNSF is doing lots of track work in the flatlands of SoCal too. When I ride Metrolink betwen Fullerton and LA I am moving through a constant landscape of stacks of ties and preassembled switches, ballast spread out in advance of tracks, new tracks already ballasted and waiting tp be finally aligned, and miles of rail waiting for attention. They have widened one bridge to take one more track and seem to be preparing the approaches to others. Regrading the ROW has been going on constantly at a couple of places. Concrete retaining walls are going up along one long cut.
Some of the work looks like another main line, some is onviously lengthening the sidings right up to any obstacles, switching them back into the main, and then starting up another siding just after the obstacle. It is clear that as soon as they need the capacity, they’ll widen the bridges and crossings, move the signal towers, and connect the sidings as a new main. All the new sidings look like they are built for heavy traffic. Concrete ties are everywhere there is new track, with wooden ones only for switch assemblies.
I rode Metrolink yesterday from Riverside thru Pomona to LA on the UP and they are doing a good amount of work but not as much as I see on BNSF. One station on that line has a shoo-fly built at platform to allow a new bridge to be built just west. The rails at the station have been covered with plastic sheeting so that asphalt could be laid right over the rails for a new temporary platform giving access to the trains on the shoo-fly.
Could be. The plans we are staking from state “work by others” - meaning BNSF MOW crews. I’ll see if I can find out, but it would be the usual source …
I asked one of the technicians in the van, who said that they are monitoring exhaust. They have a similar device over at the UP tracks. It’s all part of the air quality mandate in the L.A. basin. That’s why you’ll see newer motive power on these lines …
