We described ploughing in an earlier post. See it here. In this article we will summarize trenching. Trenching may be chosen to bury fiber optic cable in urban and suburban areas where the high number of obstacles (sidewalk and street crossings) makes ploughing impractical.
The choice of location for trenching in fiber optic cable follows the same set of rules as for ploughing. Buried cable should be located where there is the least possibility of it being disturbed. Along roads, the cable should be located so that future surfacing and widening operations will not extend over it.
Care should be taken that the route selected will not interfere with the natural drainage of the area and so that the natural drainage does not result in the depth of cable coverage being affected.
Trenching is normally conducted by using machinery. In some areas however, it may be necessary to hand-dig the trench. For maximum speed, hand digging should be held to a minimum. For maximum trenching speed, never dig a deeper or wider trench than required.
However, it is recommended that a 4” wide trench be considered the minimum practical width.
The backfilling material must conform to local regulations. Clean backfill should be placed from 9” to 12” from the bottom of the trench to provide protection for the cable. On private right-of-way (ROW), the earth should be mounded over the trench to compensate for future settling.
The backfilled trench may, in some cases, be satisfactorily packed down by running the tractor or wheel of a truck along the trench line on top of the backfill. When possible the top should be filled with top soil. Rocks and debris should never be left in the bottom of the trench. Surface compression could cause cable damage in the future.
All permanent pavement and sidewalks must be restored to the satisfaction of proper authorities. When shrubs or other local vegetation must be disturbed it should be set aside and replaced when possible. Where lawn has been removed, it should be replaced or re-seeded.
In general, the most desirable and economical method of cable placement in open or rural areas is ploughing. Here there will be fewer obstacles to impede the progress of the ploughing equipment.
Advantages of Ploughing
- Speed of installation in open areas
- Less ground disturbance than may be caused by trenching
Disadvantages of Ploughing
- Large size and high cost of equipment
- Requires skilled equipment operators, quality supervision, and equipment in good condition
- Can not be used for all soil and terrain conditions
- Possibility of damaging cables or underground utilities
In urban or suburban areas where there can be many obstacles such as underground utilities, sidewalk and paved road crossings, trenching has advantages.
Advantages of Trenching
- Lower cost of equipment
- Digging operation is separate from cable placement
- Better depth control
- Less risk of damaging underground utilities
- Provides the opportunity to place conduit at the same time
Disadvantages of Trenching
- Slower rate of cable placement than with plow
- Not suitable for all soil and terrain conditions
