I am in the process of replacing a culvert. It had a 42 inch rusted out one and am putting a 48 inch plastic. The ground is really and i have concerns about egging the culvert. It will have 5 feet fill when done. What can I do to prevent it from bulging or how much is acceptable?
The ground is really.... what? Soft? Hard? Sandy? My guess is the answer to your question is gravel!
All the plastic culvert I've seen is pretty thick and corrugated. I think as long as the trench for it is smooth lay the culvert in and back fill it with multiple layers making sure the sides get filled and compacted. If the ground is soft may need a gravel base or put material in and pack it. 5' of compacted cover you shouldn't have a problem with it egging.
@Welder Dave is that 5 feet' or 5 inches"?
he spelled out feet in the OP
5' is 5 feet. 5" is 5 inches.
If it's double wall 48 inch pipe, from my experience is pretty strong. As long as you get good compaction you should be fine. You said 5 feet of fill...... Does that mean you will have 1 foot of fill over the pipe or 5 feet over the pipe?
Make sure that there is plenty of compaction for the haunches of the pipe! Don't use garbage material because the pipe needs to shed the weight to the surrounding soil to be able to keep its shape! If the ground at the bottom of the excavation is shaky, you may need to over excavate and put in a "foundation" to get some more weight bearing capability! Also, you may want to do that anyways on the upstream and downstream inverts to keep the culvert from eroding! Are you putting headwalls on this at all?
@Welder Dave Yes, I missed OPs 5' of fill. For whatever reason, though it's not really, 5 foot underground seemed like a lot in my mind.
One more thing to note, most culverts have a minimum cover requirement to that most people fail to mention as well. Typically 1.5' to 2' is acceptable depending on the pipe specs. The manufacturer can give you guidance based on the anticipated traffic loads though if you are less than their minimum spec.
Slurry to springline to fill the haunches is the best bet if it’s in the budget. That’s what we’re doin for Caltrans anyways.
As others have mentioned, try to get yourself a decent base to set the pipe on. As you backfill make sure that you are using good quality material that you can get compaction on. Bring up lifts on each side evenly and compact as you go. You're already into this project for the excavation and pipe, don't cheap out and ruin the outcome by not backfilling with good material. This means hauling it in if the material on site isn't very good. I don't know how much water you're dealing with, but if the existing material around the culvert is soft and wet then you should try to remove any mud and replace with good fill. I'm not sure what you mean with your 5' number, but if you're saying you have 5' cover on top of the pipe just make sure you compact as you go up to eliminate settling issues. If you only have 1' cover on top of the culvert, I'm not sure what the manufacturer recommends for a minimum coverage. You may have to add some fill on top to gain more coverage.
Here is the ADS pipe spec book on installation and backfill. https://www.ads-pipe.com/sites/default/files/Drainage_Handbook_ADH5_Installation_(11-16).pdf As others have stated the backfill material is the most important component with corrugated plastic pipe. If you trench floor is soft cut it out and come back up with stone. You need crushed stone backfill to at least 6" above the pipe. We use #57 crushed limestone for the trench floor and backfill 6" above pipe. We've installed 1000's of feet of plastic pipe in all sorts of commercial applications with no failures. #57 crushed limestone is a 1/2- 3/4" sized crushed stone that is washed with no fines. You could use an 8910 crushed stone which is 1/4" size crushed stone down to dust for the pipe backfill but you really need to use a 1/2 - 1" sized crushed stone for the trench floor. Also brought up were headwalls. If you are not installing precast then you will either need to pour the headwalls in place which or not that hard to do or rip-rap both ends well. We have even grouted rip-rap in place before for headwalls that worked out nicely. Basically place wet concrete and rip-rap starting at the bottom and work your way around the pipe to a couple of feet above the pipe depending on the ditch line. Good luck!
The only problem with clean stone is if using for a road crossing with both ends of pipe open water will follow stone and may wash out trench. You can use compacted dirt or concrete over both ends of pipe to act as dams to stop water flow.
That's why you either need a pre-cast headwall, CIP headwall, SP headwall or rip-rap preferably grouted.
Job done i got used hesco barriers and am filling them as head wall. I got a 590 hoe a trackhoe would be better. The 5 foot is over pipe.
Pictures or it didn't happen.....