Underfloor heating pipe as protective pipe / empty conduit in the ground?

Hello,
During modernization work in an old building, among other things, underfloor heating is to be installed in the basement. The old floor was completely excavated up to a depth of 30 cm below the future finished level.
In the soil, under the screed, in the capillary-breaking layer of gravel, various cables (NYY-J) are to be laid. Are no longer used underfloor heating pipes, e.g., 20x2 mm, made of PE-RT or PE-Xa or PE-Xc suitable as empty or protective conduits?

Best regards

Layman's opinion: I think no. If the aforementioned pipe experiences too tight bending radii, it kinks and sharp-edged indentations form on the inside! which can lead to high point pressure on the cable. NYY-J also doesn’t have much bending space in a 20/2 underfloor heating pipe. 5x 2.5mm² has about a 15mm outer diameter, so it’s not going to be fun pulling it through the internally existing 16mm anyway. Even 5x1.5mm² doesn’t slide through easily there. Additionally, there might be the thermal insulation properties of the composite pipe which in this case could be counterproductive (heat increases the internal resistance of the cable). Even good cable protection pipe costs so little, I wouldn’t take any risks...

In the soil, under the screed, in the capillary-breaking layer of gravel, various cables (NYY-J) are to be laid.

If you already want to use underground cables, just lay them on/in the ground. That's what they are for.