Six-Dimensional Strain Sensor Based on Fiber Bragg Gratings for Frozen Soil

Industrial equipment, such as wind turbine foundations and oil and gas pipelines in cold regions, may undergo extrusion/expansion deformation during the freezing and thawing of frozen soil, which affects their power response and safe operation. Measuring the internal deformation of frozen soil can immediately reflect the strain situation of industrial equipment to reduce the risk of equipment operation. We designed a 6-dimensional strain sensor (6-S Sensor) based on fiber Bragg gratings (FBGs) to obtain the spatial principal strain distribution. The strain range, linearity, and average error of the sensor were -4000 to 8000 mu epsilon, 0.997, and 2.94%, respectively. The sensor accurately measured the frozen and thermal expansion of frozen soil at different temperatures in the laboratory. The maximum frozen expansion was 6471.38 mu epsilon, which occurred in the X-direction. The accuracy of spatial principal strain monitoring for the sensor was evaluated through uniaxial compression. The stability of the sensor was verified by the monitoring experiment under natural temperature for half a month. This study provided a pioneering method for monitoring the internal spatial principal strain of frozen soil.