New measurement technology to prevent ground heaving in tunnels

- Installed under the roadbed for highly accurate monitoring -

Abstract

This article is the summary of the published paper (Kinashi et al., 2020) which won the technology award from Japan Society of Rock Mechanics (JSRM). In railway and road tunnels in service, incidents of ground swelling have sometimes occurred, causing difficulties in maintenance. To avoid these kinds of problems during the construction of a tunnel, it is critical to watch and identify a potential heaving of the roadbed and to confirm that the displacement inducing such heaving has completely converged. Since during tunnel construction, there is a continual traffic of heavy construction machines and dump trucks, it is difficult to provide reference marks on the roadbed to measure the amounts of heaving. To resolve this problem, we have developed “Invert-Displacement Gauge” able to automatically measure ground swelling with high precision, which when used, is embedded into the roadbed to prevent the effect of operating vehicles. The water pressure gauge set in the roadbed and a water reservoir serving as a reference are directly connected through a water-filled PVC pipe enabling measurement of the amount of ground swelling by keeping the water level in the reservoir constant. To date, this system has been applied to 22 sites (113 locations) with various geological conditions and has been successful in preventing roadbed heaving after they are put into service.