Fill around culverts?

[Innovate1]

Putting a small culvert under my driveway and have read up on what to use for fill around the culvert. It makes a big difference as to the load it can support. Have read that 3/4 clean rock will flow so is better to support the pipe. But recently read that the soil around the gravel can ooze into the spaces between the gravel and loose some support of the pipe so crushed rock with fines is better (Called CA6 or grade 8 around here). It does pack well but doesn't flow as well so would be more difficult to get packed in without voids and loose spots.

 

[ch612T]

Recently had a 25' length of 15" HDPE pipe installed in the driveway. Contractor used "modified" around it. Modified in this area is #2 stone with dust, packs in great.

 

[walrus]

Fabric would stop the mud from filling in the voids. Pea stone will go into the ditch and be 95% compact. You can chink under the pipe with a shovel handle but if its a small culvert I think you are over thinking it on that regard

 

[Crawlin]

How much cover will it have? What size and is it HDPE?

 

[stevied916]

Generally around here, bedding sand is specified for fill within the pipe zone (generally 4" below to 8-12" above) and class 2 aggregate base above that. You don't want just crushed aggregate without fines, especially if the pipe is shallow since you can't compact crushed aggregate. The other issue you run into with crushed agg or pea gravel is you create a french drain which defeats the purpose of trying to convey the water in the culvert.

 

[Innovate1]

I put in an 8" HDPE double wall culvert about 6 months ago. Top is 12" down. I used 3/4 clean gravel as I had read that was best - maybe I misunderstood. It flows and compacts very little with tamping but there are voids between the pieces. The inlet is a catch basin with dirt around it and there is dirt around the exit so there isn't any issue with water flow through the gravel rather than through the culvert.

Now I am putting in a 6" pipe with catch basin for a small area. The depth may be a bit shallower but I should be able to get 10" of cover. I had some trouble finding HDPE so am planning to use PVC SDR35. It's also a little smaller OD so can use a trencher with just a bit of widening.

 

[Crawlin]

Obviously varies depending on region. I have bedded plenty of pipe/culverts with 3/4" clean stone. Usually to about half way up the pipe. Then use your ABC or base stone above that so it will pack. Clean stone wont require any compaction around the pipe. Its a non issue that it can flow water through the stone, unless its a pond overflow pipe lol.