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I have a concrete culvert under my driveway. The first pipe section on the input side has dropped about 2 inches causing water to back up into my yard.

Digging up the pipe section would be expensive.

Considering pouring a soupy concrete mix into the pipe to effectively level the dropped pipe section. The pipe diameter is too small to access the total area needing leveling which is why using a watery concrete mix could fill the place I can't reach. Will this work? Other ideas?

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    I'm confused how a lowered pipe causes a backup. Wouldn't that allow more drainage? – isherwood Apr 29 '16 at 13:48
  • The first pipe section settled 2 inches making the next pipe section 2 inches higher than the first pipe section. Water backs from the point between the first and second pipes into the yard. My idea is to pump out the backed up water and replace it with a watered down concrete mix that would essentially take the place of the water backup. Now the first and second pipe are at the same level allowing the water to flow through without backing up. – Walter Apr 30 '16 at 10:43
  • Yeah, that's not making sense. The second pipe will remain at the same level, and so will the water. Maybe a photo would clear things up. – isherwood Apr 30 '16 at 17:02
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As I mentioned in a comment, a lowered pipe shouldn't cause a backup. The high point in the system is where the water level stabilizes.

That said, I see no reason why a concrete enhancement would cause problems on the intake side, assuming adequate flow volume remains. You wouldn't want to reduce volume on the outflow side as this could result in foreign object obstructions.

Also, you'd use a standard concrete mix, and not an overwatered mix, which would be weaker and more prone to disintegration. It's not difficult to level concrete with a little agitation.

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If I understand correctly, the pipe settled, but the surrounding area did not. Therefore the inlet/outlet arrangement determines what flow the culvert can accommodate. You will basically have reduced the cross sectional area of the pipe. You will want to avoid stagnant water in the pipe, so your idea of filling it with concrete makes sense.

From a concreting point of view, you will have a very long piece of concrete which is in the form of a lens. Tensile forces in the concrete caused during the hydration process of the cement will result in shrinkage cracks of the concrete (across the length of the pipe). Additionally, the lens shape will result in tensile cracks at the corners. In essence, your concrete will break up into smaller pieces. If you have fast running water through the culvert, your concrete might erode away, starting at the edges.

To mitigate this, you might want to look at concrete products or admixtures which are purpose made for this. Speak to your local ABE or Sika agent, they should be able to advise you.

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