5. Track irregularity estimation system based on looseness detection during for constructing a crossing structure under railway tracks

To eliminate level crossings and to widen rivers, tunnel construction projects for roads and other purposes that cross under railway tracks are being carried out in various locations.
When constructing such tunnels, square steel pipes are inserted ahead of the main tunnel body to excavate the interior and construct a temporary tunnel. If the loosening of the ground caused by the insertion of these square steel pipes is transmitted to the ground surface due to repeated train loads, it appears as track settlement after excavation. While such settlements are difficult to detect in advance, they affect train running safety and require urgent track maintenance when they occur.

In response to this, we developed a system to estimate the amount of track settlement by detecting ground loosening, which is a sign of potential track settlement. The system consists of a handheld ground survey device and software for calculating the amount of track settlement (Figure 1).
In general, when the ground loosens, the elastic wave velocity traveling through the ground decreases. Therefore, the ground survey device measures the difference in arrival time of elastic waves before and after excavation to determine the rate of decrease in elastic wave velocity. The track settlement calculation software uses the relationship between the progress of ground loosening and the rate of decrease in the elastic wave velocity propagating through the ground to estimate the amount of track settlement according to the degree of ground loosening (Figure 2).
Through construction tests using real steel pipes and measurements at an actual construction site, we have confirmed that this system can estimate the amount of track settlement on the safe side within a range of about 1 mm (Figure 3).

This system enables early detection of signs of track settlement and reviewing of the digging length to prevent track settlement and improve safety. In addition, cost savings can be expected by reducing the number of days required to secure track maintenance systems.