The Internet has a lot of photos from real facilities where cable lines are laid, and such photos are interesting to study. There were several photos where a pipe was laid along the trench, from which flexible tubes connected to numerous vertical rods extend. There was no doubt that we had a water pumping system in front of us, but which way is the water flowing and why? I had to go through options 1️⃣ and 2️⃣ before understanding why such a system might be needed.

Idea 1️⃣ – pipes with water are needed to moisten sand/soil at the bottom of the trench before laying the cable, and thereby ensure its compactisation and the absence of possible cable movements. There was also an idea that some kind of special liquid could be supplied to the soil, which is necessary to stabilize its thermal resistance in the subsequent operation of the cable line. All these thoughts turned out to be wrong, that is, this system is not at all for “watering of the trench” ❌

Idea 2️⃣ – the water in the pipes is the water that has been pumped out, providing a dry trench, which is important for the proper and safe installation of cables and cable joints. This idea turned out to be correct, that is, the system is needed for “dewatering of the trench” ✅

The system shown in the photo may be called the “Wellpoint dewatering system”, and vertical tubes are “needle filters”, which are temporarily installed during cable laying.

What tasks can such a system solve:
👉 lower the groundwater level along the trench;
👉 drain the sandy base so that the cable fits into a dry and dense soil;
👉 prevent erosion of trench walls and quicksand;
👉 allow sand to be normally compactified around the cable.

How the system works:
👉 thin vertical tubes (“needle filters”) are embedded in the ground;
👉 they are connected to the collector and pumping station through hoses;
👉 the pump continuously pumps water out of the ground.

After the cable is laid and the trench is filled in, these tubes are dismantled – that is they do not relate to the operation of the cable line. You can discuss this system in LinkedIn public group “High Voltage Cable Lines”, by the link to the post.