There is an urgent need of new strategy for the monitoring of ground movement ahead of mountain tunnel face to improve the safety management. A new sensor is under development for the monitoring based on the concept of "On Site Visualization". This method is different from the conventional field measurement techniques in that deformation is measured on site and visualized by different colors of light in real-time. Since this method makes use of optical fibers as the light propagation medium, it could keep on visualizing the displacement of measuring points even if its front part is cut as needed during excavation. The paper presents some laboratory experiments to demonstrate the applicability of this scheme. By doing this, it is found possible to monitor the ground deformation by the proposed sensor. Finally, some work in future is discussed briefly.

1 Introduction

In the field of mountain tunneling, the frequency of accidents remains a considerable level due to the collapse or water inflow at the tunneling face during construction, though many efforts have been made to ensure the stability of tunneling face. Monitoring is thought to take an important part in tunneling and other disaster risk reduction project. However, because of the problem of cost and operability of exiting approaches, the monitoring measures cannot be taken to cover all the places of risk.

Recently, a new concept called "On Site Visualization" (S. Akutagawa et al. 2011b) has been proposed originally in Japan to provide a new scheme of monitoring for structures on site. It is capable of monitoring the displacement or force, and visually outputting the measurement results in real-time for workers and all concerned. It uses the color of light as a key technology to demonstrate the risk condition of construction directly. Based on this concept, a series of sensors with low cost and power consumption are developed or under development for monitoring and visualization on site, some of which have already been employed in practice. Since the new sensors could provide not only the basic monitoring but also the function of visualization of result at low cost, it makes possible to carry out monitoring in wider areas to improve the risk management practices.

In this paper, a new sensor for monitoring ground deformation ahead of mountain tunneling face is introduced. The sensor consists of plastic optical fiber, color filter film, sliding stopper and so on, using LED as the light source. Laboratory experiments were conducted to verify the applicability of the measurement scheme. By doing the primary experiments, it is found possible to monitor and visually present the ground movement by this sensor.

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