What Does Full Bench Mean?
A full bench in the context of manholes refers to a bench formed with a full-depth channel. It provides better hydraulics than in a half bench installation.
Instead of having only part of the channel benched, the entire area has the sand concrete mix infill between the manhole walls and the inflow pipe. Since manholes are access points for sewage repair and rehabilitation, the design of the bench is an important aspect.
Benching is installed at a pitch and uses a sand and cement mixture to be completed. It is essential that the bench is raised for the channel to drain appropriately. There are two styles of benching: the half bench and the full bench.
Trenchlesspedia Explains Full Bench
Having a bench over the full depth of the channel is optimal in areas willing to build one despite the cost. This design provides higher hydraulic flow and the heightened flow helps to ensure that the sewage lines connected through the manholes attain their self-cleaning flow velocity at least once during the day so that debris keeps moving.
However; constructing a full-bench design is costlier than the half bench method. Also, the slope between the channel and the walls are higher to cover the full depth of the circuit. This makes it a little more difficult to reach into the channel to clear debris if needed.
As there needs to be an adequate slope to provide drainage, it may be too steep for workers to stand safely while maintaining the system.