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Old US 91 'slow-moving slide' will take millions to fix

Started by Kniwt, September 18, 2016, 01:33:10 PM

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Kniwt

St. George News reports (with lots of pics) about a slow-motion landslide that's consuming part of old US 91 between Washington and SR 9.
http://www.stgeorgeutah.com/news/archive/2016/09/18/mgk-city-settles-on-costly-solution-to-telegraph-sink-and-slide/

QuoteWithin the year prior to the discovery of the hillside cracks, the road had sunk at least 12 inches or more, Shaw said in February. During that time the city paved and patched the affected roadway to keep it usable.

That part of Telegraph Street hadn't given the city much grief until after a water line in the area broke, Washington Mayor Ken Neilson said. Following the break, that part of the hillside started to creep at a faster rate.

What was a noticeable yet seemingly smooth pavement-patch on the roadway accompanied by a slight drop on the surface in February has since transformed into a spiderweb of cracks and traffic cones. The four-lane road has been reduced to two lanes and a speed-limit of 20-25 mph has been imposed — at least for those motorists who bother to pay attention.

On the other side of the barricades that line the edge of the road are the visible cracks in the ground, including one that reaches from the roadway and cuts right next to the foundation of a leaning power pole.



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Interstates clinched: 4, 57, 275 (IN-KY-OH), 465 (IN), 640 (TN), 985
State Interstates clinched: I-26 (TN), I-75 (GA), I-75 (KY), I-75 (TN), I-81 (WV), I-95 (NH)

sdmichael

The slide may have been there before, judging by older aerial photography, just reactivated by the highway widening and the proper amount of water. If it were closer, I'd do my own geologic study to see what is going on.

Kniwt

Quote from: sdmichael on September 18, 2016, 08:16:24 PM
The slide may have been there before, judging by older aerial photography, just reactivated by the highway widening and the proper amount of water.

There's also some sentiment among locals that another cause might be the extensive building of hundreds of new homes atop the hill during the past few years, in developments on both sides of the highway.

sdmichael

Quote from: Kniwt on September 18, 2016, 08:43:23 PM
Quote from: sdmichael on September 18, 2016, 08:16:24 PM
The slide may have been there before, judging by older aerial photography, just reactivated by the highway widening and the proper amount of water.

There's also some sentiment among locals that another cause might be the extensive building of hundreds of new homes atop the hill during the past few years, in developments on both sides of the highway.

The construction itself may not be the issue, but the addition of water to a pre-existing slide plane, caused by the additional houses. Geologic reports have to be done before construction can take place, but they don't always take a larger picture beyond what regional geology exists. Without seeing a decent geological map of the area, I can't assess is that is contributing, though it more than likely is to an extent.

The Ghostbuster

Maybe the road should be abandoned altogether, or isn't that an option?

Kniwt

Quote from: The Ghostbuster on September 20, 2016, 06:26:34 PM
Maybe the road should be abandoned altogether, or isn't that an option?

Not really an option. The only other road through there is I-15; also, it would seriously reduce access to all of the new housing that's been built east of the hill. (And it would shut down the only practical bicycle access to that area, even though I-15 is technically bike-legal through there.)

sdmichael

Quote from: The Ghostbuster on September 20, 2016, 06:26:34 PM
Maybe the road should be abandoned altogether, or isn't that an option?

The geological problems there can be mitigated. Sometimes it is as simple as dewatering the slide mass. Water is at least partly the issue at this location.

Kniwt

#8
Oops! The road is now closed after the highway slipped 6 inches in 24 hours.
http://www.stgeorgeutah.com/news/archive/2016/09/27/mgk-traffic-advisory-telegraph-street-closed-in-both-directions/

QuoteCommuters who regularly use Telegraph Street will be stopped and turned around after Washington City was forced to close a section of the roadway due to movement in the hill slide that has already caused traffic delays and headaches.

Mike Shaw, public works director for Washington City, said Tuesday afternoon that Telegraph is now closed between Washington Parkway and Highland Parkway because of additional movement by the slide. The hillside moved at least six inches within the past 24 hours, he added.



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