Measurement of Railway Tunnel Cross-section with Laser Range Finder

Abstract

Nowadays, State Railway of Thailand (SRT) provides the structure gauge along theirs own railway countrywide. Loading gauge is necessary limited and controlled to pass through the structure gauge. Tunnel is also one of the structure gauge needed to be concerned. Distance between the tunnel’s wall and rail cars may varied due to the wall movement itself, new locomotive, new passenger car, new container car and due to the rehabilitation of permanent way. All mentioned scenarios may cause the collision of tunnel wall and rail cars. From a report of a SRT working group responsible for inspecting railway supporting structure, there were unknown collisions between the mock up car and tunnel’s wall at Chongkhao tunnel, Nakhon Si Thammarat province. Therefore, for safety railway operation, precise inspection should be carried out and determines the exact locations of collision in the target tunnel. This paper shows two typical laser range finders were applied to develop basic measuring tools, accessories and a simple method to measure the target tunnel’s cross section. There were two prototypes with and without angle graduated discs. The measured data of distances from center of rail alignment to the tunnel’s wall at different angles were recorded and used to model proportionally the tunnel’s wall in a computer. The results showed that the prototypes were in function as expected to determine a specific collision location in the target tunnel. In conclusion, with the tools and measuring method in this paper, some scenario, e.g., abnormal of tunnel’s wall movements, unexpected lifting of rail and permanent structure, as well as enlargement of new loading gauges, will be effectively verified by the SRT local officers who are capable of using a user friendly and simple tool with low cost operation and maintenance.