A new design method for non-circular sewer linings: Fid-Bau Portal

A new design method for non-circular sewer linings

Thepot, O.

This article presents a new design method for non-circular sewer linings, which has been developed within the framework of the French National Project of research and experimentation named RERAU (Rehabilitation of Urban Network Sewers). The method examines the effect of external long-term hydrostatic pressure but does not extend to the short-term effect of filling injections (for linings with annular space). It takes into consideration the exact geometry of the lining (curve radii) and the beneficial interaction with the existing host that may be attenuated by an annular void. The method puts linings into two categories: critical linings that are liable to buckle but whose deflection lobe remains localized and sub-critical linings that do not buckle but whose deflection lobe may extend to the entire lining. If the lining is critical, the method gives formulas for the buckling pressure, the bending moment and the axial force. The method gives safety factors with respect to buckling and material breakdown. If the lining is sub-critical, non-linear finite element analysis with appropriate formulation of the boundary condition may be used. Calculation examples are given together with comparisons with the WRc structural design of type II linings.