trench for conduit – asphalt parking lot
I am planning a project that will require having 1″ PVC conduit installed underneath an existing asphalt parking lot. The run will be approximately 100 feet. This will be in the St. Louis, MO area. The conduit run will be parallel to one edge of the parking lot, about 2 feet away from an 8′ high chain link fence.
What’s the best method to trench this?
How deep does the conduit need to be buried?
I am assuming that material from the trench (asphalt & gravel) can be used to then backfill, ultimately topping off the top few inches with asphalt patch.
*** And, yes, I will call to have any buried utilities marked prior to the contractor trenching this area.
Thanks in advance for any advice!
“Preach the Gospel at all times; if necessary, use words.” – St. Francis of Assisi
Replies
I thought maybe ditchwitch might have an attachment, but a local rental company said we would need a boring machine?
"Preach the Gospel at all times; if necessary, use words." - St. Francis of Assisi
A boring service would be faster and less traumatic to the asphalt.
The TOP of the conduit needs to be at least 24" below grade, In practice, this means starting with a 30" deep trench.
You will need to lay a sand bed for the pipe, then cover the pipe with a few inches of compacted sand as well. Then you can backfill with what you took out - after removing large or sharp rocks.
St. Louis has a fair amount of rock, so the use of an excavator - in the hands of a SKILLED operator - is worth considering. Otherwise, to reduce the chance of damage to other buried lines (the "call before you dig" folks won't find them all), it's a job for a lot of guys with picks and shovels.
No matter how meticulous your asphalt cuts, you will need to cart off the top layer to the dump, and pave anew. Don't skimp on the compacting!
That's the problem with a "ditch witch" ... the trench isn't wide enough for a compactor. Driving over it a few times with your truck doesn't count.
PVC pipe is fine, in general. You will be better served, however, if you use steel elbows ("sweeps) at the bends. Your pulling rope can cut a slot in the PVC at turns ... which can catch the wire. Wrap the steel pipe with 'pipe wrap tape' and you'll be fine.
For a similar reason - protection from physical damage - the pipe ought to be wrapped steel where it exits the pavement.
If your pipe terminates in a concrete box ("Christy box"), you will need to make sure you get the all steel 'traffic rated' cover.
Because of these issues, I recommend against running your pipe straight into the base of a light pole. There simply isn't room for proper wire pulling, etc. Rather, set a box next to the pole, and make a splice there. Have a separate pipe lead into the pole itself.
I find it well worthwhile to "over engineer" a job like this. After all, you don't EVER want to have to dig it up again. Oversize your pipe, pull individual conductors (not UF cable), use primer on your connections, as well as PVC cement, be meticulous in your backfill and compaction.
It seems that nearly every underground pipe run problem is the result of taking 'short cuts.' The pipe gets crushed (sometimes by the compactor!), joints come apart, rocks pierce the pipe over time.
There are problems with underground connections. Like wire taping [irresistable & rare pun].
During rainy weather, the box will fill up with rainwater for some reason and you will see little bubbles rising from the wirenuts. I don't know if these are steam or hydrogen.
So, if you splice, use something like ScotchGuard. Or pull enough extra and push the wire straight through without a splice.
~Peter
Agreed ... there is no substitute for proper wire connections. As you mentioned, there are specific products made for such wet locations.
I know not the reason the OP want to make this run. However, one possiblity was to feed a light pole ... and I wanted him to avoid the errors caused by making a direct run into the pole .... because, sooer or later, that pole is going to get knocked down.