A practical, engineering-focused guide to planning and installing underground fiber optic cables with the right cable structure, trench design and protection level for long-life, low-risk networks. Match trench method with the correct underground fiber structure (GYTS, GYTA53, GYTY53, micro-duct). 02 Placement methods for direct buried fiber optic cable are essentially the same as. Installing fiber underground is one of the most durable ways to protect a network's backbone — when it's done right. But because the cable sits in soil exposed to. Underground cables are pulled in conduit that is buried underground, usually 1-1. 2 meters (3-4 feet) deep to reduce the likelihood of accidentally being dug up.