What commonly available transmission line can be buried directly in the ground for some distance without adverse effects?

Coaxial cable consists of a center conductor surrounded by a dielectric insulator, a tubular shield, and an outer waterproof jacket. Because the electromagnetic field is confined entirely within the outer shield, the surrounding environment (like soil, moisture, or metal) does not affect its electrical properties. In contrast, parallel-conductor lines like 600-ohm open-wire line, 300-ohm window line, or 75-ohm twin-lead rely on the space and air around them to maintain their characteristic impedance. Burying them in the ground would alter their dielectric environment, causing severe impedance mismatches and high signal loss. Therefore, coaxial cable is the only practical option among the choices for direct burial, provided its outer jacket is intact and preferably rated for direct burial.