I am installing a culvert pipe to get across a subdivision drainage ditch. The subdivision has specified the culvert pipe diameter as 500mm. What type and how much cover should I put over this pipe? It was suggested to me to use a granualar A type gravel, and then compact it after. Does this sound right. TIA
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suitable cover for culvert pipe
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note that backfill, compaction and depth of cover will differ based on the type of pipe you choose such as concrete, steel, polyethylene etc. Reinforcement and pipe class for concrete will also dictate the method of installation. Normally, however I wouldn't use a gravel over the top of the pipe. Depending on the native soil, you may want to use that for backfill instead. Depending upon the depth to the roadway subgrade, you might want to use road base material over the top.
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Did they do the hydrology? Is it common practice for a developer to designate the size of pipe, or are you determining how many barrels there will be? You can flow fill for lateral support - it's really hard to compact under the haunches, particularly of metal or plastic. Then again, if a contractor isn't very experienced he may float the pipe with a flowable fill.
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Engineering Folks.......
I'm a homeowner with a question on a driveway. Can you help, please??
Is "flowable fill" suitable to put under a 12" diameter non-concrete culvert pipe? The culvert pipe is near the road-end of the driveway to carry drainage water. The driveway guy originally put a 15" pipe because the Town told him to, but it was too large and caused our brand new driveway to start lifting within 6 months.
The driveway guy agreed to re-do it, with a 12" culvert pipe (Town ok'd), and will put "flowable fill" as the base if we want it. Neither the Town nor the driveway guy have any experienece with it. We heard it is a good product which will help prevent the lifting caused by freezing and thawing.
Can anybody tell me if this is recommended??
Thanks so much for the help, really...
Debbie
I'm a homeowner with a question on a driveway. Can you help, please??
Is "flowable fill" suitable to put under a 12" diameter non-concrete culvert pipe? The culvert pipe is near the road-end of the driveway to carry drainage water. The driveway guy originally put a 15" pipe because the Town told him to, but it was too large and caused our brand new driveway to start lifting within 6 months.
The driveway guy agreed to re-do it, with a 12" culvert pipe (Town ok'd), and will put "flowable fill" as the base if we want it. Neither the Town nor the driveway guy have any experienece with it. We heard it is a good product which will help prevent the lifting caused by freezing and thawing.
Can anybody tell me if this is recommended??
Thanks so much for the help, really...
Debbie
you have frost susceptible soils and bedding your pipe on native material will allow frost heave. you need to replace the bedding with either an impermeable material such as concrete or with a gravel which will promote good drainage. The bedding depth should extend to the approximate frost depth. If you use a gravel, you may also need a filter fabric around it.
CVG,
Thanks so much for responding but, as I said, I'm a homeowner and I have no idea what your recommendation is! I'm sorry.
Because this culvert pipe is sitting underneath our driveway to carry the draining water, the depth of the pipe is restricted by the height of a culvert 20 feet away. If we bury our pipe too low, it will be lower than the pipe 20 feet away which, of course, will not allow for good flow. I'm just wondering if this "flowable fill" stuff is a good medium to use instead of gravel or anything else.
Thanks a million to whomever answers...
debbie
Thanks so much for responding but, as I said, I'm a homeowner and I have no idea what your recommendation is! I'm sorry.
Because this culvert pipe is sitting underneath our driveway to carry the draining water, the depth of the pipe is restricted by the height of a culvert 20 feet away. If we bury our pipe too low, it will be lower than the pipe 20 feet away which, of course, will not allow for good flow. I'm just wondering if this "flowable fill" stuff is a good medium to use instead of gravel or anything else.
Thanks a million to whomever answers...
debbie
Flowable fill is a type of low strength concrete. It could solve your problem if done right. However, it is difficult to advise you without know a lot more details. It doesn't sound like your contractor is very knowledgeable or he would have installed the culvert properly the first time. You should contact a contractor or an engineer locally who can assist you. You might talk with the town engineer and ask for his (free) advise.
Hi Guys:
This is interesting. C1323 apparently is in frost heave country.
What is odd about this is I have seen lots of frost action (in northern states) and most of the time the land on either side of the pipe raises with frost action, but the culvert stays there. The larger the culvert, usually the greater this difference. In winter the roads have a dip at the culvert.
I'd think reducing the culvert would tend to make the culvert act along with adjacent soil and everything then raises and lowers together.
I have my suspicions that frost is what caused the "lifting", unless it was water from the ditch line that fed the frost lenses, a most unusual situation. You get the least frost heave (depth of freezing) where there is plenty of water (take a lake for instance) Maybe it was just settlement of the backfill alongside the culvert making it look like it raised up.
If the action is not positively frost action, I'd wait a year or so before I do anything to be sure.
Sometimes we have dug out natural soil at sites where some significant differential frost heaving takes place with tapered up edges of the cut on each end. Then backfill the whole area with non-frost susceptible material, such as sand with no more than 5 percent passing the Number 200 sieve. Concrete fine aggregate will meet this. In this case dig down at least 2 feet at the culvert, bed it at the ditch flow line. The most fancy job would be an excavation to 4 feet at the culvert area, which usually is OK in most northern states.
Not knowing the site, I'd start at the nearby road with the end of a taper and end up about 10 feet beyond the culvert with the other end of taper.
I see no need for fancy work like flowable fill here for a job this small. This treatment (undercut and sand fill) then creates a gradual transition of normal frost heave at the ends of the underut, to little or no frost heave at the culvert (making a dip). It will be necessary to go below the culvert some with the undercut to minimize the frost heave there (due to the cold air in the culvert)
This is interesting. C1323 apparently is in frost heave country.
What is odd about this is I have seen lots of frost action (in northern states) and most of the time the land on either side of the pipe raises with frost action, but the culvert stays there. The larger the culvert, usually the greater this difference. In winter the roads have a dip at the culvert.
I'd think reducing the culvert would tend to make the culvert act along with adjacent soil and everything then raises and lowers together.
I have my suspicions that frost is what caused the "lifting", unless it was water from the ditch line that fed the frost lenses, a most unusual situation. You get the least frost heave (depth of freezing) where there is plenty of water (take a lake for instance) Maybe it was just settlement of the backfill alongside the culvert making it look like it raised up.
If the action is not positively frost action, I'd wait a year or so before I do anything to be sure.
Sometimes we have dug out natural soil at sites where some significant differential frost heaving takes place with tapered up edges of the cut on each end. Then backfill the whole area with non-frost susceptible material, such as sand with no more than 5 percent passing the Number 200 sieve. Concrete fine aggregate will meet this. In this case dig down at least 2 feet at the culvert, bed it at the ditch flow line. The most fancy job would be an excavation to 4 feet at the culvert area, which usually is OK in most northern states.
Not knowing the site, I'd start at the nearby road with the end of a taper and end up about 10 feet beyond the culvert with the other end of taper.
I see no need for fancy work like flowable fill here for a job this small. This treatment (undercut and sand fill) then creates a gradual transition of normal frost heave at the ends of the underut, to little or no frost heave at the culvert (making a dip). It will be necessary to go below the culvert some with the undercut to minimize the frost heave there (due to the cold air in the culvert)
Thanks for the comments, guys!
The culvert pipe is currently black plastic, 15" in diameter, installed under a newly paved driveway. This culvert carries rainwater drainage from the street. It is not a large quantity of water, just an average amount, carrying only water run-off from the road.
Before the driveway was paved and it was just gravel, the culvert pipe that had been in there for many years was 12" concrete. When the driveway guy was preparing it for paving, he dug up the concrete pipe in hopes of burying it a little deeper. We discovered that the concrete was really two separate pieces, at one time connected, which had come apart. We replaced it with 12" plastic. It looked great, and it was buried deep enough so that we thought there would be no "frost heaving" issue.
Well, at the last minute, the Town comes and tells us to dig it up and replace it with a 15" culvert because "that's the rule." The problem with a 15" pipe is that we cannot bury it deep enough since this culvert drains to another culvert about 20' away which is HIGHER in grade. It was late in the season, the weather was going to turn on us, the Town said it was required, and so the driveway guy re-did it at his own expense. (The Town insisted that the driveway guy should have known the rules because the Town sends the rules to all the local driveway installers, so they say.) Anyway, the installer rushed, slapped it together, and between his haste and losing 3" in depth (going from the 12" pipe to the 15"), it was buried too close to the surface of the asphalt. Within 6 months it had cracked.
Come to find out, it is NOT a Town requirement to have a 15" pipe, and we could have used the 12", as originally done. So now it is being replaced again with the 12" black plastic pipe, and the best way to bury it is in question.
We heard about "flowable fill" and because there isn't as much depth as we'd like, we thought this product might help keep the pipe from lifting in the frost.
The driveway guy said he'd do whatever we want; He's been cooperative.
The pipe was originally buried at least 3-4" from the surface, as deep as possible with the 15" pipe. It was placed on gravel with stone under it....a generally accepted practice from a driveway installer with a GOOD reputation. Our problem seemed to be the last minute change to an unnecessary 15" pipe.
But now we're leaning toward using flowable fill rather than gravel, thinking it might help stop some of the lifting associated with frost in this part of the country (New England.)
So, if this clarifies the situation any better, are there any other opinions about using flowable fill in this application??
Comments are very much appreciated from you fine folk...
Thanks to all!
Debbie
The culvert pipe is currently black plastic, 15" in diameter, installed under a newly paved driveway. This culvert carries rainwater drainage from the street. It is not a large quantity of water, just an average amount, carrying only water run-off from the road.
Before the driveway was paved and it was just gravel, the culvert pipe that had been in there for many years was 12" concrete. When the driveway guy was preparing it for paving, he dug up the concrete pipe in hopes of burying it a little deeper. We discovered that the concrete was really two separate pieces, at one time connected, which had come apart. We replaced it with 12" plastic. It looked great, and it was buried deep enough so that we thought there would be no "frost heaving" issue.
Well, at the last minute, the Town comes and tells us to dig it up and replace it with a 15" culvert because "that's the rule." The problem with a 15" pipe is that we cannot bury it deep enough since this culvert drains to another culvert about 20' away which is HIGHER in grade. It was late in the season, the weather was going to turn on us, the Town said it was required, and so the driveway guy re-did it at his own expense. (The Town insisted that the driveway guy should have known the rules because the Town sends the rules to all the local driveway installers, so they say.) Anyway, the installer rushed, slapped it together, and between his haste and losing 3" in depth (going from the 12" pipe to the 15"), it was buried too close to the surface of the asphalt. Within 6 months it had cracked.
Come to find out, it is NOT a Town requirement to have a 15" pipe, and we could have used the 12", as originally done. So now it is being replaced again with the 12" black plastic pipe, and the best way to bury it is in question.
We heard about "flowable fill" and because there isn't as much depth as we'd like, we thought this product might help keep the pipe from lifting in the frost.
The driveway guy said he'd do whatever we want; He's been cooperative.
The pipe was originally buried at least 3-4" from the surface, as deep as possible with the 15" pipe. It was placed on gravel with stone under it....a generally accepted practice from a driveway installer with a GOOD reputation. Our problem seemed to be the last minute change to an unnecessary 15" pipe.
But now we're leaning toward using flowable fill rather than gravel, thinking it might help stop some of the lifting associated with frost in this part of the country (New England.)
So, if this clarifies the situation any better, are there any other opinions about using flowable fill in this application??
Comments are very much appreciated from you fine folk...
Thanks to all!
Debbie
It sounds like you will have 6 - 7 inches of cover over your new 12" pipe when you reinstall it. Typical requirement is 24". This helps to explain why your first concrete pipe was broken. It was crushed by repeated traffic loads. The plastic pipe is flexible and won't crack. However, it may flatten over time, so I wouldn't assume it will last longer than the last one. You didn't mention whether you had used a reinforced concrete pipe. A well reinforced concrete pipe (maybe Class V) might have been a better choice. With the plastic pipe, it is very difficult to get the soil compacted tightly underneath the haunches. Then, with the shallow depth of cover and poor compaction, you can expect it to fail quickly. A flowable concrete backfill might be a better choice for either type of pipe in this circumstance as it will provide additional support which helps to prevent pipe cracking or flattening.
Dear CVG,
Is the "flowable concrete backfill" you mentioned the same thing as "flowable fill?" (So that I can construe this to mean you believe the flowable fill would be better than regular old gravel/sand stuff?)
I sure do wish we had 24" to bury the pipe, but we are going down as far as we can in order to keep the water flowing without incident. I will ask about the new 12" plastic pipe "crushing" in the future. But isn't it better to have plastic with some "give" than concrete which would crack??
Thanks for your prompt response,
Debbie
Is the "flowable concrete backfill" you mentioned the same thing as "flowable fill?" (So that I can construe this to mean you believe the flowable fill would be better than regular old gravel/sand stuff?)
I sure do wish we had 24" to bury the pipe, but we are going down as far as we can in order to keep the water flowing without incident. I will ask about the new 12" plastic pipe "crushing" in the future. But isn't it better to have plastic with some "give" than concrete which would crack??
Thanks for your prompt response,
Debbie
The flowable fill that I am referring to is a lean concrete mixture. It is concrete which consists of about 1 sack portland cement per cubic yard of concrete. It should have a "slump" of about 7 or 8 inches which means it is very thin and will flow around the pipe and fill all the voids. If you decide to use it, be aware that it can cause the pipe to float when you pour in the flowable fill. You will need to anchor the pipe down to prevent that from happening.
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