Research On Fiber Grating Fault Coulomb Force Sensor And Calculation Method

The change of the Coulomb force on the fault plane caused by the seismic activity can affect the temporal and spatial distribution of subsequent earthquakes.By calculating the change of the Coulomb stress of the fault,the monitoring of the earthquake precursors on the fault plane and the regional fault risk analysis can be carried out.The traditional strain measurement is spatially discrete and has many influencing factors.It is difficult to match the needs of the study of Coulomb stress changes on the fault plane in terms of spatiotemporal resolution and continuity.Aiming at the problem of lack of detection methods for Coulomb stress change on fault plane,a method to measure Coulomb force and determine the direction of fault movement is proposed.An anchor stress sensor based on fiber grating is designed.The possible variation range of Coulomb stress can be calculated by establishing a Coulomb force model and combining with numerical simulation.For the sensor structure,a morphological algorithm is proposed to analyze the direction of fault movement.The thesis launched the research of fiber grating stress sensor,the main contents are as follows:1.Researched the method of measuring ground stress,analyzed the principle of fiber grating strain,and introduced the concept of Coulomb force.The two-dimensional fault plane Coulomb force calculation model and the three-dimensional fault plane Coulomb force calculation model are analyzed,which provides a theoretical basis for the experiment.2.A fiber grating anchor stress sensor is designed,and the structure placement is determined through structural simulation.Polyimide fiber gratings with higher tensile strength were obtained through micro-nano processing,the manufacturing process of fiber grating stress sensors was studied,and tensile experiments were conducted.The strain range of the sensor is-2000??-2000??,the axial strain sensitivity is 168 pm / KN,and the linearity is 0.9956.3.Complete the fault test on the triaxial test machine,complete the calculation of Coulomb stress,and comparatively analyze the experimental data.Through the use of small-scale numerical simulation for analysis,the calculation results are consistent with the experimental results,verify the feasibility of this method,and provide a theoretical basis for practical application.4.A sensor shape resolution algorithm is proposed,and the bending angle and bending radius of the sensor are calculated according to the special structure of the sensor and experimental data,in order to analyze the deformation direction of the sensor due to fault sliding in the fault,and then determine the moving direction of the fault.Based on this algorithm and the data of the fault experiment,the trend of the fault is judged,and the result is consistent with the experimental process.