Theoretical and numerical analyses of the structural stability of the pipe-grout-liner system with a crown void subjected to external pressure

The thin-walled polymer liner is widely used to rehabilitate the deteriorated underground pipe. Although the liner is installed close-fitting in the lining procedure, an annular shrinkage gap is inevitable between the liner and the pipe. The grouting technique is commonly employed to eliminate the small gap and often results in a small crown void between the liner and the pipe. Therefore, a pipe-grout-liner system generates. This paper focuses on the structural stability of the pipe-grout-liner system with a crown void subjected to external pressure. It is found that the radially-inward out-of-roundness imperfection results in a single-lobe deformation and the radially-outward out-of-roundness imperfection results in a double-lobe deformation, respectively. The critical buckling pressure is derived and obtained theoretically, and then verified by developing a two-dimensional finite element model. The numerical result shows very close agreement with the analytical solution and other closed form expressions for both single-lobe and double-lobe cases, respectively. Finally, the effect of the crown void is examined. It is found that the system with a small crown void can sustain the same buckling pressure as the perfectly-confined liner without void. However, a significant reduction of the critical buckling pressure was observed when the crown void is larger than the small size level.