Definition - What does Half Bench mean?
A half bench in the context of a manhole is a design in which only the lower half of the pipe extends through the manhole.
A half bench is designed such that an area of the channel remains open should there be an issue for which maintaining the channel is necessary. This makes it easier for workers to access and address the issues. The slopes in half bench are not as steep as those in the full bench designs, making it easier for workers to keep their footing and place their tools.
Trenchlesspedia explains Half Bench
The horizontal benches extend from the semi-circular channel and into the manhole interior wall. 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. The cost of preparing a half-bench is less than that of the full bench design.
However; half benching gives a lower hydraulic result so that the system does not reach its peak flow velocity for the sewer to reach the self-cleaning flow velocity needed. Without self-cleaning velocity through the pipes, deposits build up to obstruct the sewage lines.