Application Research Of An FBG Based Sensor Designed For Uneven Settlement Monitoring Of The Subgrade

The area of the seasonally frozen region of our country is larger than half of the national territorial area. However, the uneven settlement of the subgrade is prone to happen in the frozen region due to the cycle of freezing and thawing. The uneven settlement generates the additional stress in the pavement structure and even damages the pavement structure. So, the study about the law of the frost heave and thaw settlement is very significant. In order to do the research about the proposed law, the vertical shape change of the subgrade need to be effectively monitored. However, the traditional methods and sensors used in civil engineering have many defects in practical application. Hence, a new measurement mean is needed in order to measure the vertical deformation of the subgrade effectively.The optical fiber based sensor have many advantages comparing to the traditional sensors, such as small volume, high accuracy, low cost and so on. Hence, the utilization of the optical based sensor in the structural health monitoring is very appropriate. Considering the advantages of the optical fiber based sensor, a sort of fiber bragg grating(FBG) based sensor is used to measure the vertical deformation in this paper.The proposed sensor can overcome the disadvantages of the traditional sensor. It can provide large-scale shape monitoring for the subgrade using only one FBG, so it has a low cost. The data directly acquired by the sensor is discrete. In order to draw the deformation curve of the subgrade, a data processing method is designed in this paper. Considering the temperature effect in the field test, a noise reduction algorithm is introduced in this paper. It can separate the temperature effect from the acquired data effectively. The feasibility of the sensor has been tested in lab. The proposed sensor has been applied to monitor the subgrade deformation in a field test carried out in He-Da highway. Ten sets of the sensors with individual length of 15m were installed on the surface of the subgrade in He-da highway. The deformation curve of the subgrade is constructed after the processing of the acquired data. The result of the field test shows the potential of the proposed sensor for future application.