Creek Culvert Project

TNhobbyfarmer · Apr 13, 2007

Keith:

Since this is what you do for a living, I'm going to lean on you a little for advice here. Do you think that BTDT's advice is a solution that will work for the long run, or do you think that I need to just start all over again? Thank you for the help.

KeithInSpace · Apr 13, 2007

I guess it's a pretty good start. If you were pressed for time or if the project was difficult to complete for some reason leading you to want to try an alternative solution, that would be an OK place to start. It would be nice for you to pass the full capacity you originally intended.

In the end, you'll always be somewhat at risk unless you bury the invert of the pipe. You will never get the compaction around the lower portion of the pipe you'll need to remove all risk.

If you simply pull the center pipe, I have some suggestions. Go ahead and pull material away as much as you can and compact it as you go up in "lifts" of not more than 4" or 6". And if you can, rent a "vibrator" or "jumping jack" to mechanically consolidate the material around the pipe. The back of a backhoe bucket MAY work, but I'd use a dynamic machine. The back of your FEL bucket will NOT get you the compaction you need.

The part you're going to really care about is the lower portion of the pipe up to what is called the "spring line" halfway up the pipe...or 1' of fill on your 24" pipes. Personally, I would carefully consolidate to a solid 3/4 of the way up.

Then when you get to the "crown" of the pipe (the top), place and compact the material with your bucket. I would put at least 2 feet of fill over the pipe.

If you can, I would certainly armor both sides with good rip-rap...I'm talking 20# angular stones a couple feet thick on the face.. That will help with your material being carried away.

em14 · Apr 13, 2007

Keith has given you some very sound advice. If you do as he advises I think you will be in great shape for many years to come.
Leo

dqdave1 · Apr 13, 2007

If I see the pipes correctly; the center pipe is double walled and will hold weight well. The two outer pipes are single wall and will not hold much weight.
It would not take much time to backdrag off top fill; pull pipes; back drag remaining fill and start over.

KeithInSpace · Apr 14, 2007

Based on Mr. Dqdave's observations, I looked at the pipes again. It appears in the pictures that the center pipe has a smooth interior surface and the other two pipes have the raw corrogations.

Allow me to clarify the nature of HDPE pipes. On their own, they are non-weight bearing. Think of them as "cells" that hold open a space in the soil. HDPE storm piping relies almost entirely on the backfill and compacted earth around them for their strength. As an example, drive your 6,000# tractor over one of the pipes...guess what's going to happen. Squish.

These pipes are very different in nature than concrete pipes, for example, which posess their own structural integrity. And they weigh a huge amount more. Backfill doesn't matter nearly as much on concrete pipes and we wouldn't be having the same conversation about careful compaction, sufficient cover, and certainly about them floating down the stream.

All this said, there is a minimal difference between a smooth interior wall (Type S) HDPE pipe and a "raw" corrogated interior wall HDPE pipe. Nearly all the pipe's strength is in the "spiral" of HDPE that creates the pipe itself. The primary purpose for the smooth interior is to provide better hydraulic characteristics so when I provide detailed calculations on a comprehensive storm drain system's HGL (Hydraulic Grade Line), I have a very smooth pipe to work with that can carry more flow instead of a very rough pipe that is more resistant to flow. The interior wall is quite thin and of minimal benefit structurally.

That's the detailed, long, boring answer to the concern. Given the nature of your project, I don't think you're all that concerned about the Mannings Coefficient of Friction of the corrogated vs. non-corrogated pipe. You just would like something that will, well, stay there.

95% of the strength of the pipe in this situation will come directly from proper backfill and compaction around the pipe. Very careful compation to 3/4 up the pipe will really set you straight. And I'm not overly concerned about what you do directly over the crown...you're better off just rolling dirt in there and distributing the load since this is by far the weakest point in the pipe. Beating down on the crown of HDPE pipe in a backfill operation will certainly deform it.

KentT · Apr 14, 2007

One final thought that may be worth considering. You may want to see if you can get some good clay to put in there, rather than the sandy, rocky loam that it appears you're using. It will compact much better and will hold the culvert much better -- and it has no "market value" in comparison to topsoil. People will often give it away to get rid of it.

When I was putting in a culvert last year in East Tennessee, we found a guy a couple miles down the road who gave us all the clay I wanted for free. I just had to pay for loading and hauling. We hauled 12 drop-axle tandem loads to set my single culvert, then covered this fill with a 4" - 6" layer of topsoil so I could grow grass on the banks to control erosion. It turned out pretty nice, and is holding up well, as shown in the last pic.

TNhobbyfarmer · Apr 14, 2007

As has been well documented in this thread, this WILL fail. As I see it, I can approach this dilemma from a couple of different directions. Option Number 1: Let it fail, retrieve the pipes and do it right now that I know how to do it right. Option Number 2: Tear everthing out now and redo the job.

As I mentioned earlier in this thread this crossing is not critical. It is at a place that isn't used on a regular basis, in other words, it is a want not a need. My inclination is to go with option number 1. That option requires less work. Basically I am letting water do the tear down for me.

Is choosing option number 1 going to cause problems I am not recognizing or considering? Again, thanks for all the help. Your expertise and opinions are definitely appreciated.

KeithInSpace · Apr 14, 2007

Your stream looks fairly dry, so I'm not sure of the environmental implications...in my area, the Tree Hugger Police would be reviewing satellite images and trying to bust people for puting in crossing such as yours without a permit from the Army Corps of Engineers.

In any case, to be a good steward of the environment (as well as your dirt), I would probably go ahead and fix it at some time in the next month or two...not simply decide to let it lie until everything gets washed downstream.

Remember there is a fair possibility of a catastrophic pipe failure while driving your tractor over the pipes. It may be fine a time or two, or even 142, but when the pipes heat up in the summer heat, they WILL begin to "egg" (settle in to a non-circular, elliptical shape) and be more dimensionally un-stable than even now.

It is more for this reason than the washout concern that I would be inclined to NOT pursue Option Number 1. But if you are the only user, and you understand/navigate the risks, you can put off Option Number 2 until there is a gap in the NASCAR schedule.

Mr. Kent T's project looks like the real deal. Nice work.

EddieWalker · Apr 14, 2007

I've tried to imagine what will happen when it fails and what some of the problems are that you might encounter. Moving water always does something unexpected, so it's likely that what happens will be a suprise. I don't think the pipes will be damaged, but I wonder how much effort it will be to retrieve them? How far down stream can they travel? What degree of a headache will be be to get them out if they are tangled or forced under some other debri, trees or ????

If you have the time, pull the end ones out one at a time and leave the middle one alone. Space them out far enough to allow you to get good compaction between each pipel. Two feet is plenty.

I don't see too much of a problem using the gravel fill that you have, but after you get it in, I'd build up a wall at the front of the pipes. I'm thinkng sacks of concrete with rebar through them to defelect the water away from the fill material and into the culverts. 40 pound sacks are easy to work with, affordable and pretty much bullet proof.

Eddie