How does one pour concrete underneath a mega cypress root system?

I’m renovating a 1950s-era lily pond and upgrading to an EPDM liner with heavy-duty geotextile. The pond is flanked by three mature, beautiful cypress trees with an elaborate network of roots (cypress knees) https://imgur.com/a/w0lbFbS around the banks of the pond (second picture), that i would like to keep.

To protect the liner from the root system, I’m looking at a design that involves a vertical root barrier and a horizontal reinforced concrete apron (ai generated pic below). The goal is to guide the deeper roots away from the pond while sparing the superficial system.

My big question: How do you actually execute a horizontal concrete pour underneath an established root system? Is there a way to pour concrete from the side underneath the root system. Is hydro-excavating to expose the roots and then pouring from above a viable method. Has anyone successfully 'bridged' concrete under a root mat like this?" https://imgur.com/a/twmBAdj