Sym P. le said:
Unless I misunderstood, the reports were that the initiation was more recent (as in the past few years) and that the progression was accelerating. Obviously the underlying issues were misunderstood and authorities failed to appreciate the significance of the acceleration, even in the week prior to the failure.
I'm right there with you. WYDOT should have done more to investigate what was going on, and luckily, the mudslide closed the pass, avoiding a true tragedy.
GreenLama said:
MTNClimber, you compared the Million Dollar Highway to this situation. Do you think that's fair? The MDH was carved out of fairly stable rock, and once carried mining trains. At least that is my recollection. Here we have a large man made embankment comprised entirely of fill.
Also, your reference about boulders falling from above and coming to rest in the roadway is interesting. We've all seen them. I'm not trying to be snarky, but it's kind of unrelated to this situation.
I do think it's fair to compare man-made highway mountain passes with each other, especially when talking about the required maintenance involved. These are relatively active geologic areas. Debris flow, slope instabilities, avalanches, and rockfalls are just the start of the issues they contend with. It costs a lot to construct them and maintain them. I've driven them enough to realize there is a limit of what a DOT can do. At some point, they adopt a mentality that resolves them to, "We can't do more with what we currently have". I'm not saying it's right, I'm just saying that's what it appears to be based on my experiences.
MDH and I-70 through the Rockies are not stable in all areas and require constant maintenance and mitigation efforts by CDOT.
It also relates to the situation in that people here are saying, "I can't believe they ever thought that the slope was stable." Well, it was for a very long time, which is better than some mountain passes. I would also invite those to drive the mountain passes that I've driven, and they will be filled with examples of "I can't believe they think this will work long term." After years of living in the mountains, I learned that they don't. It's just the best they could do at the time with what they had. Drive it at your own risk. Not saying that it's right. It's just what it is.
GreenLama said:
Do you think any special measures will be taken to drain water from the embankment? Or will they just rely on grading and surface runoff as was done in the past? In the last Casey video he may have mentioned WYDOT plans for a culvert, but I could be mistaken.
I hope so! To avoid this issue again, they should make sure that the foundation soils for the embankment are strong and well drained. I'm not sure if a culvert is the answer or if putting in horizontal drains would work. It's tough to tell with the limited information we have. Ground improvement could also consist of aggregate piers which would help reduce the chance of porewater pressure building up in the clay layer, if that exists. I don't have the borings and Casey sounded like that was an assumption on his part.