Expansive Soils

[Mike01]

What is the best way to install conduit underground where you have expansive soils? We have a project where structurally they are installing ?Void Boxes? that will deteriorate after the concrete is poured creating a void under the slab and it would be supported from the associated drilled piers. I was instructed to install the conduit prior to the ?Void Boxes? being installed but what happens when the boxes are gone and the slab is suspended 12? above grade how do you install the underground conduit? When the soil expands I do not want it to affect the feeders and conduit in witch they are installed. I tried searching the net but could not find anything regarding this with electrical conduit installation has anyone ever encontured it and if so how did your handle it ?

 

[BAHTAH]

Conduits in slab

Conduits in slab

I have to admit I have never been exposed to this type of construction. From your description I would ask, is the suspended slab thick enough to support the conduits being installed in the slab sturcture? I would assume the slab would be thicker than what I normally see since it is not supported by the earth directly beneith.

 

[nakulak]

pretend that the dirt isn't there, hang the conduit from the slab with embedded hangars (all thread) per code. when the support from the void disappears the conduit will be hung from slab per code. (even if the rats will be the only ones to see it)

 

[Mike01]

How?

How?

Curious how would you install it suspended from a slab that does not exist yet? once the concrete is poured ther is no access to the void space left. The structural engineer will not allow any conduits installed within a supported slab. Probally will not even let me use anchors into it either if I could find a way to install them.

 

[nakulak]

you put the pipe in the dirt, the hangars on the pipe, the allthread on the hangars and into the slab to be poured.