Abstract: Disaster monitoring and prediction play significant roles in the fields of geology and geotechnical engineering. Distributed fiber optic sensing technology plays a significant role in long-distance, long-cycle, highly hidden, strong sudden disaster monitoring by virtue of its continuous, real-time, anti-interference, good stability and other advantages. However, effectively evaluating and addressing the coordination deformation issue between the sensing fiber optic cable and the measured rock and soil mass is crucial for different engineering problems. This coordination is essential for accurately analyzing deformation distribution and understanding the evolutionary patterns of rock and soil masses. In this paper, the development of a three-dimensional active deformation controllable confining pressure fiber-sand coupling test device is presented. The device aims to investigate the coordination between the metal base cable sensing fiber and the compression deformation of coarse sand medium under a confining pressure range of 0 to 4.0 MPa. Experimental results show that the metal base cable exhibits inadequate coordination with sand compression deformation at low confining pressures, displaying nonlinear deformation characteristics. However, as the confining pressure increases, the coupling effect between the sensor cable and the sand intensifies, resulting in linear deformation changes. Notably, when the confining pressure reaches 1.6 MPa, there is a significant enhancement in coordinated deformation, transitioning the deformation from nonlinear to linear behavior. Based on the aforementioned deformation characteristics, we propose a numerical model of confining surface projection. To predict the actual displacement of non-test data, we employ the spline interpolation algorithm with non-kink boundary conditions. The results demonstrate the reliability of the model. Furthermore, the experimental study highlights the higher accuracy of the metal base cable for sand deformation testing under high confining pressure conditions. The findings of this study serve as a scientific reference for the application of distributed optical fiber sensing technology in deep stratum deformation monitoring.

Key words: distributed optical fiber, geotechnical deformation, strain transfer, coordinated deformation, numerical model