Analytical model to characterise thermal loads and deformation of internal replacement pipe systems

Abstract

The internal replacement pipe (IRP) involves the rehabilitation of underground cast iron (CI), ductile iron (DI), and steel pipelines through reinforcement with a pipe or liner typically installed by trenchless construction methods inside the host pipeline. This paper focuses on a host pipeline with a circumferential crack in the body of the pipe or separation within a weak or deteriorated joint. New analytical solutions are presented for modelling thermal loads and displacements in IRP systems with linear and nonlinear material behaviour. In addition to including material nonlinearities, the mobilisation of soil friction force along the pipeline affected by temperature change is incorporated in the analytical solution. To include IRP debonding in the analytical solution, a set of experimental tests and mechanical finite element (FE) simulations were carried out to characterise the IRP debonded length. The effects of material and geometrical properties of the host pipeline and soil on the mobilisation of soil friction force are evaluated. Characteristics of the IRP, host pipeline, and soil as well as the discontinuity width and temperature change are systematically ranked in terms of their significance on the discontinuity opening. Results show that excluding soil friction and/or the nonlinear material behaviour of the IRP can lead to significant underestimation of the discontinuity opening, which may result in unsafe conditions. There is excellent agreement between the results of thermal FE analysis and the outcomes of the nonlinear analytical solution, which uses a tri-linear stress-strain curve for the IRP. Hence, the nonlinear analytical model presented in this paper can be reliably applied in the analysis and design of IRP systems.