Towards Fully Automated Tunnel Inspection: A Survey and Future Trends C. Balaguer, R. Montero, J. G. Victores, S. Martínez, A. Jardón RoboticsLab, University Carlos III of Madrid, Spain E-mail: balaguer@ing.uc3m.es, romonter@pa.uc3m.es, jcgvicto@ing.uc3m.es, scasa@ing.uc3m.es, ajardon@ing.uc3m.es Abstract – Tunnels environments are characterized by dust, humidity, and absence of natural light. Artificial and natural impacts, change in load criteria, or the simple effect of ageing, make tunnels require inspection and maintenance. These operations are commonly performed by human workers taking time and expertise without guarantee quality control. Robotic tunnel inspection and maintenance (RTIM) introduces high productivity, quality and repetitiveness. This paper describes the current trends in the subject, and introduces new technologies such as scenario modeling, robotic platforms, image and ultrasound sensors, control algorithms and decision making strategies. Additionally, the result of several recent and ongoing projects will be presented. Keywords - Robotics, Automation, Inspection, Maintenance, Tunnels, IAARC 1 Introduction One of the greatest challenges engineers face is the inspection, assessment, maintenance and safe operation of the existing civil infrastructure. This includes large- scale constructs such as tunnels, bridges, roads and pipelines. In the case of tunnels (water supply, metro, railway, road, etc.), they have increased in both total length and number, and will continue to do so. Furthermore, some tunnels still in service were completed over 50 years ago, with the existing construction and materials technology. Only in Japan in 2006, the number of active tunnels was up to 9000 [1], with tunnels such as the Seikan Tunnel which is 54 km long and partially below the seabed [2]. Figure 1 shows the evolution of Japanese tunnels in terms of number and length until 2006. Tunnels progressively deteriorate due to ageing, environmental factors, increased loading, change in use, damages caused by human/natural factors, inadequate or poor maintenance, and deferred repairs. Unfortunately, several incidents related to the structural condition of tunnels have taken place, such as the Big Dig ceiling collapse in 2006 in Boston [3], or the Sasago Tunnel collapse in 2012 in Tokyo [4]. Figure 1. Changes in the number and total length of road tunnels in Japan (2006) [1] These examples highlight the need of automated, cost-effective and exhaustive inspection of tunnels that prevents such disasters. In this work, we present current tendencies and future trends within this area. 1.1 Tunnel Defects The first aspect of inspection that must be defined is the related to the types of defects that may affect tunnels. Identifying these defects is crucial for performing a successful inspection, verifying the state of a tunnel, and performing maintenance if required. The 31st International Symposium on Automation and Robotics in Construction and Mining (ISARC 2014)