Iinstalled several miles of concrete encased ductbank using this method. While it is easier to fabricate and install the primary problem is the plastic sheet causes a bond break in the concrete and will drastically reduce the strength of the rebar and also introduce water into the concrete causing the rebar to rust. Id you aren’t encasing the ductbank and are using sand backfill around the conduits then you will have better results.

How are they glueing the pipe together?

Very interesting idea. I'd need a guide spec to give the Contractor though. Plus, your web link is dead/changed.

I tried to go to www.delucchielectric.com/underground-duct-bank, and the site still undergoing maintenance. Anyway, if there is power and C&I cables in the duct bank, is there any minimum distance so there is no interference between power and C&I cables?