Asphalt road wash out - how much is too much

[Barney4671]

Western NC mountains. Helena storm water runoff caused a loss of 15ft long, 10ft down, and approx 8ft wide road shoulder dirt at the location of a 8-inch road surface water discharge drain. It appears that prior to washing out the drain and discharge piping cracked and sent a water jet back towards the center of the road resulting in a 3ft "cave" under the asphalt (which has subsequently collapsed). The uphill side lane appears fine and still intact and in use. Last couple days dump trucks of boulders have been delivered for a different wash out.

Question is how far from back of the wash out "cave" should cars pass. Is there a rule of thumb as to how much dirt is needed to support the road - like a 45-degree stress cone - how close to wash out can a car drive without causing more damage?

How urgent is a fix needed - couple of months, years?

This is really outside my wheelhouse, so any help would be appreciated.

PIC attached[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1728426083/tips/Wash_Out_l2phu0.pdf[/url]

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[1503-44]

A rule of thumb for an embankment, given no site inspection report and soil data, could be a slope of 1 rise in 2 run. What might be safe distance for a car would not be safe for a loaded truck, so establishing a load limit might also be appropriate. If the cracks in the pavement are the result of the washout, conditions below are not good. Best to close the entire lane until it can be repaired. Frequent inspection, certainly after any rainfall, is needed to ensure conditions do not worsen. How long? Depends on those soil conditions not deterorating further, traffic load and danger to traffic that a lane closure would entail. Warning signs, concrete barriers and lights should be set out immediately.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[TerryScan]

How far back should cars pass? I would not make guesses or internet estimates about a life safety issue such as this. I would not drive my car through that section. There may be more to the issue than you can readily observe.

How urgent is the fix needed? This depends on many factors starting with how essential the road is (are there alternate routes?) and where it is prioritized amongst many roads with issues right now.