How much tamping required for a culvert?

[Fallon]

Borrowed a friend's backhoe for a couple projects 2 weeks ago & dug a trench across the driveway just before it had to go home. Trench us to deep (kind of by design). I finally picked up the required 25' of culvert yesterday. 12" double wall corrugated outside smooth inside stuff.

How well do I have to worry about tamping under & around the culvert? It's going to be snowy & muddy for the next week or 2, so good tamping really won't be possible. And the trench is slowly starting to cave in, especially with the moisture. 3' trench, 1' of culvert & generally you need 1' over the culvert, so I need to backfill a foot or so.

Not to worried about settling causing a dip as I have a box blade & maintain the driveway regularly. Not to mention needing to dump more gravel on it this summer or fall.

I'm mostly worried about the culvert crushing before stuff settles or it getting really out of kilter.

Can I skimp on tamping because of the mud? Should I wait for it to dry out a bit in a few weeks & manually re-excivate the trench as needed & tamp by hand? We can drive around for now, but it's tearing up the grass a bit.

I do need to re-grade the exit side of the trench smoother & a bit deeper a but should be able to do that with the box blade after the culver is in & leveled just past plumb so water will flow.

 

[Cord]

It being a gravel drive will be much more forgiving than if the surface was paved. Cheat the compaction if you'd like and just recognize that you'll have to fill in with some gravel a few years down the road.

Looks like your culvert is set a bit deep, unless you have plans to do a lot of digging at either end.

 

[ovrszd]

I've installed hundreds of culverts. No tamping required. Lay the culvert against one side of the trench and fill with the smallest clods you can until you get above the culvert. Tamp with the backhoe tires. Then come back when things have settled down a bit and do some finish work. Leave excess material on sight so you have stuff to refill after settling.

 

[Fallon]

Thanks. Ya, the trench is to deep, need to back fill a bit & clear out & taper the inlet & outlet a bit. Need to re-grade the driveway up the shop (hidden behind the hoe) too. It currently tilts away from the culvert a bit.

 

[Egon]

There are articles that will explain how to properly install a culvert so it doesn't collapse or wash out.

 

[/pine]

FWIW...

The capacity of any culvert to
carry loads depends on proper
backfilling, especially in the area
under the haunches (lower third).
The soil surrounding the culvert
provides critical support to it. For
maximum strength, and to pre-
vent wash outs and settling, the
backfill must be properly placed
and carefully compacted. Dry
trench conditions make the
process more efficient.
The National Corrugated Steel
Pipe Association culvert instal-
lation manual tells us too much
emphasis cannot be placed on
the necessity of adequate com-
paction of backfill. Faulty com-
paction has led to more trouble
with pipe installations, flexible
and rigid, than all other factors
combined! There is no way to
say it better.
There are two important
things to consider in backfilling:
use no more than 6 lifts at a
time and compact it evenly and
well, particularly under the
haunch of the pipe. Backfill
material should be free of rocks
larger than 3 in diameter. The
material must be dumped care-
fully and evenly along both sides
of the pipe. Avoid dumping large
quantities at once against or on
top of the pipe. The material should also have enough moisture to compact well, but
not too much so as to become unstable. This can be dif-
ficult to achieve, but produces excellent results. Watch
the weather closely during installation, particularly the
chance of heavy rain.
Hand tamping is adequate and is often the best
method to compact and seal the backfill against the
lower half of the pipe. If you use mechanical com-
paction, work parallel to the pipe, not against it. If large
equipment is used for compaction, don稚 over-compact
so that the pipe begins to lift or is pushed laterally out of
alignment. This is particularly important for flexible pipe
arches. Continue filling in even lifts until the installation
is finished. It is best to have at least 24 of fill over a
pipe, even on low-volume rural roads.
The most common problem with backfilling opera-
tions is that the filling crew works too fast and the
tamping crew never has a chance to adequately compact
the first material before more is placed in the trench.
To
prevent this, instruct filling crews to wait until a layer
is fully compacted before adding another layer.

 

[Egon]

Good Show /Pine.:thumbsup::thumbsup::thumbsup:

Government road contracts are usually kinda fussy about culvert backfill methods and materials.

 

[ovrszd]

Good Show /Pine.:thumbsup::thumbsup::thumbsup:

Government road contracts are usually kinda fussy about culvert backfill methods and materials.

Missouri DOT uses a hydraulic tamper. Then for the next 5 or 6 years they attempt to repair the area. Their mistake is digging the trench exactly the width of the culvert. No room for compaction so wasting their time.

 

[Egon]

Missouri DOT uses a hydraulic tamper. Then for the next 5 or 6 years they attempt to repair the area. Their mistake is digging the trench exactly the width of the culvert. No room for compaction so wasting their time.

Soo, your saying improper compaction don't work?

 

[ovrszd]

Soo, your saying improper compaction don't work?

I'm saying improper installation doesn't work, regardless of how much you compact.

OP is going to fill the bottom of his trench to elevate the culvert, which is great. Gives the culvert a "loose" bed to lay on. Then start filling with small material, finishing with the larger clumps. Pack with backhoe front tires and let Mother Nature do the rest.

I have never, ever installed a culvert that didn't settle, compacted or not. So just expect to do maintenance on it for a couple years depending on soil type.