The Role of Cementitious Liners on the Structural Preservation of Overburdened Buried Concrete Pipes

Abstract

Reinforced and unreinforced concrete sewers are essential means of conveying stormwater and sewage. Many such structures together with concrete culverts are approaching the end of their service lives and may need to be rehabilitated or strengthened. In rigid pipes, circumferential bending moments are regarded as the critical load mechanism, and this paper presents a new design model to select the thickness of liners installed within reinforced or unreinforced concrete pipes. Firstly, the design addresses the bending moments that result from earth loads applied to buried rigid pipe. Next, two potential failure conditions are examined—cracking at the inner surface of the liner at the crown or invert and cracking of the concrete pipe under the liner at those locations (because cracking of the concrete could precede cracking of the liner and induce a stress concentration that then causes the liner to crack). Example calculations are presented for a sprayed cementitious liner and for a cement mortar liner. For the sprayed cementitious liner, design is expected to be controlled by concrete cracking, while the cement mortar liner is expected to crack before the concrete. Comparisons have been made between strain distributions calculated using the design model and finite element analyses, and these demonstrated that the design model produced safe effective estimates compared to the more complex and time-consuming finite element solutions.