When laying optical cables or cables in the same trench, they should be pulled and laid separately at the same time. It is strictly forbidden to mix gravel, bricks, hard soil blocks, etc. 01 This best practices procedure provides general information for the installation of fiber optic cables in direct buried applications. The methods described are intended for guideline use only, as it is impossible to cover all the various conditions that may arise during an installation. Note that Recommendation ITU-T L.