Effects of Spray-On Lining Rehabilitation on Behavior of Buried Corroded Metal Pipes Subjected to Surface Loading

Corrugated metal pipes (CMPs) buried in the ground for decades may get corroded and lose their structural capacities supporting surface loading, leading to the end of their service life. Three maintenance options are commonly adopted in the practice for these corroded CMPs: repair, rehabilitate, and replace. The maintenance option of replacement of CMPs buried under roadways through excavation often disrupts traffic and requires considerable time and budget. Therefore, trenchless rehabilitation methods, such as cement mortar (spray-on) lining, sliplining, cured-in-place pipe, fold-and-reformed pipe, spot repair, and spiral wound, have been increasingly used to rehabilitate corroded CMPs under roadways. Nevertheless, limited studies have been conducted to assess the behavior of the rehabilitated CMPs using the spray-on lining method. In this study, a numerical analysis using the FLAC3D software was conducted to evaluate the behavior of buried corroded CMPs rehabilitated with the spray-on lining method. The numerical model was first verified using the available field test results of a corroded CMP. Then a parametric study was carried out to examine the effects of the CMP diameter, embedment depth, compressive strength and thickness of spray-on lining, and type of the pavement on the changes of the horizontal and vertical diameter, and the pavement surface settlement under five cycles of truck loading. The numerical results show that an increase of the lining thickness in the rehabilitated CMPs by 50% and 100% (i.e., from 20 to 30 and 40 mm) reduced the vertical and horizontal diameter changes by 41% and 65%, respectively. When the unconfined compressive strength of cement lining decreased to half, the vertical and horizontal diameter changes increased by approximately 16%.