This retention (relief) tank for the mixed sewerage system is a completely separate structure from the "flyover" or bypass being built. They are approximately 2 km apart. Nevertheless, the two structures are linked. Until the retention basin is completed, it will not even be possible to approve the bypass. The northern part of the bypass will be drained into the sewer on which the reservoir is being built. This is being built exclusively for the bypass, but there will be other development projects that will connect to the sewer.
The main importance of the retention basin is during periods of heavy rainfall when there would be a risk of overloading the old sewers. When the flow rate increases, the retention basin will begin to accumulate wastewater and when the situation calms down, the basin will slowly drain again. The total volume is 6000 cubic meters.
Probably the most challenging from the surveyor's point of view was the primary elevation settlement of the entire structure. The structure is connected on both sides (inflow and outflow) to an approximately 60-year-old sewer, which is about 10 meters deep. So the exact elevation of the sewer, which was in full operation, was not easy. It was also tricky to move the point field for accurate delineation to the walls of the backwaters so that we were able to delineate at the bottom of the trench while also monitoring whether the retaining walls were positionally failing.
The most interesting part was watching the progress of the structure as a whole. The body of the tank is designed to be underground, so after the large excavations and the rather large and massive reinforced concrete structure, everything was backfilled with dirt and the terrain followed the original condition.
The construction is nearing completion and the surface roads and park landscaping (sand paths, trees, etc.) are already being laid out. Want to know more? Look at the articles that have been published on the website city of Pilsen.
Radek Burián
