Telecom Duct Under Sidewalks 1

[tfarren]

Hello all!

We are quite used to burying 3-4" duct under 4-5' of gravel, clean fill and pavement, usually under a standard street in Quebec, Canada. Our frost line is usually 4' under normal conditions, and we always cover those ducts/conduits with 3" of un-renforced concrete on each side, for strength, and excavation strike protection. They usually house fiber optics.

We have been asked recently to put a couple of kilometers of 3" conduit under the sidewalk as opposed to the street, which would be buried between 12-24" under the sidewalk. The config would be the same, buried with clean fill, concrete 3" all around the conduit, then the sidewalk.

I was wondering if anyone had any suggestions on how to do this without any shearing or breaking of the concrete and conduit. I should mention that the underlayment of all of this will be clean fill and quite fresh. The pull vaults will have no bottom and have 3-4' of 3/4" gravel under to allow water to drain away, instead of flooding the vaults or conduits.

The duct will be ipex super-duct:

http://www.ipexinc.com/Content/en_ca/2_0_Products/2_2_electrical_systems/2_2_4_Super_Duct.asp

I would really appreciate any input on this...

Thanks!

 

[CarlB]

Do the sidewalks typically experience a lot of movement? I would thing the gravel subbase under sidwalk would be similar to under the street, enough to keep frost movement to a small amount. Conduits within this fill should likewise not move much. In other words, if sufficient gravel depth is provided to contain frost within primarily NFS soils, doesn't matter what depth the conduit are (as far as movement goes).

 

[tfarren]

That makes good sense, I would think that the gravel they will use, which I will confirm of course , should be 3/4" gravel, which doesnt move all that much, but doesn't compact and heave like 0-3/4" gravel which becomes essentially solid with a little water and compaction....

Any disadvantages to using loose gravel like that?