Research FBG Sensor In The Secondary Highway Tunnel Lining And Rock Pressure Monitoring

The construction of Highway tunnel is a long-term project, and to ensure the quality of the project is the basic requirement of the owner. With the increase in the number of highway tunnel projects and the accelerated pace of construction, large section, flat shape, requires high characteristics of ventilation and waterproof. Currently, most of the domestic stabling road tunnels have various degrees of quality problems, such as tunneling leakage, lining cracking and gauge limited. Therefore, timely and effectively monitor the safety information of highway tunnel, timely and accurately forecast the quality problems of highway tunnel probably happened. To guarantee the safe operation of the tunnel and to save the cost of the tunnel disease is beneficial to economic and social.Fiber Bragg grating sensor has such characteristics as anti-electromagnetic interference, wide measurement range, small transmission loss, high degree of accuracy, and strong real-time. It is especially suitable for large-scale construction that required real-time monitoring of the multi-parameter (strain, temperature, vibration), such as dams, tunnels, bridges, highways. Traditional detection techniques can be proven highway tunnel’s distribution status of surrounding rock pressure and the quality of secondary lining, but it is difficult to achieve the monitoring and disease forecast about the performance degradation process of surrounding rock and secondary lining, and at the same time monitoring process interferes with traffic significantly. Therefore, optical fiber Bragg grating sensor was embedded between the surrounding rock and support, within the secondary lining concrete. Not only can obtain detailed structural of the stress field, but also can get the process of performance change which about surrounding rock pressure and secondary lining, and to predict the future situation, to ensure long-term stability of the monitoring system.This paper is based on the background of the project which is about the quality monitoring of easy Mindanao high secondary road in tunnel. And it carry out a study of the application of fiber Bragg grating sensing technology in the Tin Sum tunnel secondary lining and surrounding rock pressure monitoring. It mainly includes the following aspects of work:1. This paper analyzes and studies the sensing structure, the sensing model and the sensing principle of the FBG temperature sensor, the embedded FBG strain sensors and the FBG earth pressure sensor. Using the characteristics of FBG sensors that is easy to make up the sensing network, these several FBG sensors form the network, to achieve long-term monitoring of the operation of the highway tunnel construction, and predict and alarm the disease may appear.2. This paper analyzes and studies the scene disease situation of Tin Sum tunnel. Using the method of finite element analysis, this paper analyses and studies the distribution of Tin Sum tunnel initial surrounding rock pressure and secondary lining stress. The study shows that in each section of vault, spandrel, hence and the location of sidewall strain sensors are installed, between each section of spandrel and hence earth pressure sensors are installed, to achieve the long-term process of monitoring of the highway tunnel surrounding rock pressure distribution and the situation of secondary lining performance changed, and ensure the stability of the construction and operation of the tunnel. At the same time, this paper analyses the characteristics of the tunnel environmental temperature changed. To reduce the influence of temperature on detection accuracy of FBG sensors, temperature sensors are installed in each section of the arch foot.3. For the mass dates that the scene gauged, relevant mathematical models are used to transform wave length values that the FBG sensor feeds back to test parameter values, such as strain, pressure, etc. And then intuitive graphs are used to demonstrate changes of measured parameters, providing the basis for judging running situation.4. Using method of non-linear regression analysis to carry on the fitting analysis of the monitoring data. First, the optical fiber monitoring data is fitted by the logarithmic function, the exponential function and hyperbolic function separately. Through the analysis and comparison, the fitting effect of hyperbolic function is best, which can reflect its development trend very well and provide the basis for judging the stability of tunnel structure. Each cross section of tunnel is fitted by the hyperbolic function model. Practice has shown that this method can judge the structural change trend of tunnel and forecast the disease may happen.