The Application Of Wireless Sensor Network Technology In Underground Engineering Monitoring

Wireless sensor network technology has been developed in recent years. It is a new technology which is based on the wireless sensor nodes to monitor the physical characteristics of the object. Underground engineering monitoring application based on wireless sensor network technology combines the advantages of wireless sensor network technology such as formidable early warning ability, lardge monitoring scope and high monitoring density, high efficiency of monitoring data transfer and low cost, which make it have good application prospect in the monitoring of underground engineering.This paper presents the study of the application of wireless monitoring in the foundation pit engineering and the shield tunnel project based on wireless sensor network. An underground engineering monitoring method based on the wireless inclinometer is proposed. According to the monitoring requirement of underground engineering, the hardware and software design of wireless inclinometer monitoring system is analyzed and the precision calibration test of the wireless inclinometer is analyzed. Targeted on the special conditions of underground engineering, the environmental adaptability of wireless inclinometer is studied and analyzed. The signal transmission test and the channel interference test are carried out, and the self-supply energy scheme of the wireless inclinometer in the metro tunnel is presented. According to the structural characteristics of underground engineering, layout scheme of underground engineering wireless monitoring are optimized combined with the finite element numerical simulation method. Finally, this paper selects the Southeast University Jiulonghu Civil & Transportation building foundation pit engineering and Nanjing Metro No.4 line shield tunnel field interval between Dongliu station and Qinglong station as test sites of wireless inclinometer sensor monitoring system. The main research results are as follows:(1) Based on the monitoring principle of wireless inclinometer, the monitoring method and data processing formula of the horizontal displacement monitoring of foundation retaining and deformation monitoring of shield tunnel are presented.(2) The system composition and performance parameters of the wireless inclinometer and modified wireless inclinometer are presented, and the working process of the data acquisition terminal of the wireless monitoring system is established.(3) According to the monitoring characteristics of underground engineering, four kinds of wireless communication protocols such as Bluetooth, UWB, Wi-Fi and ZigBee have been compared, and ZigBee wireless communication technology is proposed to be applied to the wireless monitoring in underground engineering.(4) Results from the wireless sensor signal transmission range test, networking capability test and channel interference test show that:The monitoring site type has a significant impact on the transmission distance of the wireless sensor. The signal shielding in the field can affect the transmission distance of the wireless signal, and the tunnel is helpful to the signal transmission. The minimum limit transmission distance of the measured wireless inclinometer in the tunnel environment is 127.8m. The packet loss rate of the wireless monitoring data increases with the signal transmission distance. Based on the analysis of the relationship between the packet loss rate and the signal transmission distance, the best signal transmission distance of wireless inclinometer is selected as 50 m. In the 2.4GHz frequency band, the same channel inclinometer has less influence on the intensity of the wireless signal.(5) According to the energy supply of wireless sensor in tunnel environment, a new energy self-supply method based on the piezoelectric effect is proposed.(6) The change tendancy of angle of the foundation pit support structure and the structure of shield tunnel segment is analyzed using finite element simulation. Combined with wireless inclination sensors foundation pit retaining structure horizontal displacement monitoring principle and the structure of shield tunnel lining deformation monitoring principle, the optimized monitoring layout of the wireless inclinometer sensor for underground engineering is proposed.(7) The results from the field monitoring in the Southeast University Jiulonghu Civil & Transportation building foundation pit engineering and Nanjing Metro No.4 line shield tunnel field interval between Dongliu station and Qinglong station show that in wireless inclinometer sensor engineering field monitoring, the monitoring data are continuous and the data loss rate is very low, which meet the reqirements of the underground engineering structure deformation monitoring.