Hello everyone!
Today, I will continue to explain underground optical cable installation. In this article, I will explain digging trenches.
The first task of underground cable installation is digging trenches. The trench should have a depth of 0.8 to 1.2 m. In case of extreme situations, rocks, or groundwater, the trenches may be of smaller depth. In a situation with hard rock conditions, the minimum trench depth is 0.3 m. Then concrete slabs are placed, which shall have a strength of 20 MPa.
Figure 1. Trenche
The width of the trench depends on the number of PVC pipes that are laid. Two or more pipes are recommended. To avoid digging in the future. There should always be a reserve for expansion - both for cables (more fibers) and for PVC pipes.
Figure 2. The width of the trenches
Some situations require crossing the river - so if there is no bridge, horizontal drilling is done. Special machines are used for this purpose - HDD (Horizontal Directional Drilling). They can drill up to 300 m. The minimum distance from the bottom of the river must be 3 m. If there is a bridge, it should be checked whether there are cable pipes or ducts provided for cables.
Extreme situations – hard rock conditions, and demolition using dynamite. In these situations, special permits are required.
As we can see in figure 1, every trench has five layers: bedding, padding, and three layers of backfills. Bedding and padding are usually fine sand. The first layer is bedding, the thickness of this layer is about 150 mm, after that, we can put PVC pipes and then goes the next layer padding. The thickness is the same, about 150 mm. After that, the next layer is backfill, which thickness is about 300 mm. Then, we put a warning tape (marker tape). And the last two layers are 300 mm second backfill and 200 mm final backfill.
After the last layer, the soil should be compacted. And finally, we return the grass, flowers, concrete slabs, asphalt, etc.
I will continue to explain this theme in the next article >> Underground optical cable installation (3).
Thank you!
