A feasibility study of the measuring accuracy and capability of wireless sensor networks in tunnel monitoring

Fire disasters and the deterioration of tunnel structures are major concerns for tunnel operation and maintenance.Traditional wired monitoring systems have many drawbacks in terms of installation time,overall cost,and flexibility in tunnel environments.In recent years,there has been growing interest in the use of wireless sensor networks(WSNs)for the monitoring of various structural monitoring applications.This paper evaluated the feasibility of applying a WSN in the monitoring of tunnels.The monitoring requirements of tunnels under explosion and combustion fire scenarios are analyzed using numerical simulation,and the maximum possible distance for temperature sensors is derived.The displacement monitoring of tunnels using an inclinometer is investigated.It is recommended that the inclinometer should be installed in the 1/4 span of the tunnel structure.The maximum wireless transmission distances in both outdoor and tunnel environments were examined.The influences of surface materials and sensor node locations on the data transmission distance in tunnel environments were also investigated.The experimental results show that the data loss in tunnel environments is approximately three times that in outdoor environments.Surface material has a considerable influence on the transmission distance of radio signals.The distance is 25~28 m for a raw concrete surface,20 m for a brick surface,and 36 m for a terrazzo surface.The transmission distances along the middle of quarter points are approximately 0.9D(D is the transmission distance in the center of the tunnel),and the relative error is less than±3%.The transmission distances at different locations along the bottom exhibit significant differences,decreasing from the middle to the comer point,with distances of approximately 0.8D at the quarter points and minimum distances of approximately 0.55D at the comer points.