Study On The Design And Performance Of Full Stress Fiber Optic Sensor In Soil

In some large-scale projects and major infrastructure projects,it is an indispensable project to conduct health monitoring and diagnosis of the interior soil in real time during the construction process in the field of geotechnical engineering.Currently,earth pressure sensors for monitoring are used in most of the engineering.In the current research,the full stress sensor that can test normal stress and shear stress at one point is not yet mature.In this paper,a fiber-optic sensor capable of testing a full stress state in soil at one point is developed.The feasibility and reliability of the sensor are verified by ANSYS numerical analysis and mechanical tests.The research is of great significance to geotechnical monitoring technology.The research content is as follows.Firstly,the sensor sensing principle is designed according to the sensor test requirements.The sensor tests a total of 6 stress values for 3 normal stress values and 3 shear stress values.At the same time,the sensor should consider the temperature and strain cross-sensitive problem.The stress caused by temperature is removed,so the sensor is set to a hollow,square-shaped structure where a stress-free fiber is placed.According to the sensing principle,the ANSYS finite element numerical analysis software is used to design and optimize the model size.After the model is established,the fiber layout direction planning,the strain transfer law between the packaging material and the optical fiber,and the strain transfer law of the simulation of the one-dimensional sensor under the force state are studied.According to the plan,the sensor strain test points should be no less than 7 and the layout direction is different.The one-dimensional sensor is verified and the relevant theories are correct.Based on one-dimensional sensor research,studying the internal deformation law of the full stress sensor.It is found that the embedding of the optical fiber has little effect on the resin matrix,and the optical fibers have no influence on each other.At 30°C,the fiber itself has a small strain value and the resin matrix strain value is relatively large.Therefore,the operating temperature of the sensor should not be too high,and the temperature range of the use environment should not be too large.In this experiment,the ratio of the additional earth pressure acting on the sensor to the true earth pressure was 1.347.Secondly,researching on sensor encapsulation technology was carried out.Selecting encapsulation materials according to encapsulation design criteria.After a series of mechanical properties tests and standardized testing of inspection institutions,and bringing its parameter results into numerical simulation analysis,finding material parameters accord with the fabrication requirements of the sensor.K-9761 was finally determined as the encapsulation material for the optical fiber.Finally,fabricating one-dimensional and full-stress fiber optic sensors.According to the fabrication and calibration of one-dimensional,directing the fabrication and calibration of fullstress fiber optic sensors.By testing the one-dimensional sensor in oil pressure and sand medium,founding that the sensor is sensitive to changes in pressure and the linear correlation is over 99%.By testing the full-stress fiber optic sensor in oil pressure,founding that there are too many fiber bending points.After be improved,the measured strain values are sensitive to pressure changes and the linear correlation is over 99%.In summary,the principle of the full stress sensor is correct,the design method is reasonable,and the manufacturing process is practicable.After continuous improvement,this kind of sensor has important application prospects in the field of monitoring earth pressure in geotechnical engineering.