Lipping is defined as the amount of overlap between two adjacent precast concrete pipes or culverts. Lipping is necessary to establish a secure connection between the two units by allowing one unit to fit into the other. This is achieved through the use of grooves, recesses or notches cut into the end of the pipe/culvert section.
Trenchlesspedia Explains Lipping
Lipping has widely replaced butt joints (joints with no integrated sockets) in concrete pipes. Lipping can commonly be found in precast joints during pipe jacking. Adjacent sections of pipe are inserted into each other via the lipped joints. As each pipe section is jacked forward a sufficient distance, the other section is fitted into the lip before repeating the jacking process.
In underground sewer pipes, watertightness is a concern for lipped joints. Therefore, special attention is given to the sealing and waterproofing of lipped joints.