Sinkhole Update: The hole has been fixed!

A few weeks ago, I wrote about a sinkhole that appeared along my daily commuting route, exploring what may have caused it and the condition of the pavement above it before it collapsed. Last Wednesday, about two months after the hole appeared, it was suddenly fixed!

The post I wrote explored a host of possibilities for what may have caused the sinkhole and what would be required for repairing it. Since the hole was next to a drywell, it seemed that ground water had likely been entering the sides of the well, and had washed some of the surrounding soil in over time. Seeing the finished work, I think for a few reasons that this guess was probably accurate.

The sinkhole after the area had been excavated and refilled last Wednesday.
The sinkhole after the area had been excavated and refilled last Wednesday.

First, the repair seemed to consist of digging out around the manhole and refilling the area. Drywells are typically surrounded by a “filter layer” that is designed to gradually transition from bigger, coarser gravel near the manhole structure to the native soil at the edge of the excavation. This is supposed to keep dirt from moving along with the water, preventing the kind of failure that happened here. Had the problem been a leak in a connecting pipe – another common cause of sinkholes – a much larger area would have been affected by the repair work.

The repair was also completed fairly quickly. On Tuesday the sinkhole was still there; on Wednesday the pavement had been cut and the hole excavated and backfilled; and on Thursday the area had been repaved. I have seen issues like this where the City has also needed to replace the manhole. These repairs require equipment to remove the old manhole and set the new and there is usually some sign – a staged backhoe or a manhole waiting to be installed the day before – that a more involved repair took place. This work included none of these. One day there was a hole, the next there wasn’t.

The hole before repair.
The hole before repair.

So the sinkhole is fixed! Now drivers (and cyclists) can use the full street width and we don’t have to worry about this particular instance of the problem growing. This has been a learning experience for me. Based on what I saw over time, I suspect that there is a way to use the condition of the overlying pavement to identify some holes before collapse. I have even found a few spots that I think are undergoing this same process. You can look forward to these being the subject of a future post!

To stay up to date with future Civil PDX sinkhole content, subscribe to this blog by entering your email address at the top of this page. New blog posts will automatically be delivered to your inbox.

If you found this post interesting, you might also like the following past posts from Civil PDX.
And then there was a sinkhole…
Passive vs. Proactive Design
Three Raindrops


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