Discrete element numerical simulation of cable-soil deformation compatibility in borehole distributed optical fiber monitoring

Land subsidence has been one of the main geological disasters with great harm. Full section monitoring of land subsidence borehole using distributed fiber optic sensing (DFOS) techniques has been proved to be an effective method. The deformation compatibility between cable and soil is a key factor which matters the land subsidence monitoring effectiveness. Using the discrete element numerical simulation software MatDEM, a 2D discrete element cable pull-out test model was established to explore the deformation compatibility between cable and the surrounding soil during pull out under different confining pressures. The results show that the 2D discrete element cable pull out tests model can accurately reflect the distribution of axial strain along cable and the displacement of soil element during the pull out. The curves of pull-out force versus pull out displacement and the distribution of axial strain along cable under different confining pressures show a progressive failure mode. Based on the slip depth of cable obtained by the discrete element method, the coefficient of cable-soil deformation compatibility is corrected. Moreover, the monitoring data of land subsidence in Shengze, Suzhou, was taken as an example to analyze the cable-soil deformation compatibility under different confining pressures and pull out displacement conditions. The critical confining pressure is about 0.19 MPa and the critical depth is about 17 m in this region. The results verify the feasibility of the discrete element numerical simulation method in exploring the cable-soil deformation compatibility, and further demonstrate the reliability of DFOS in land subsidence monitoring.