基于离散元法的松散泥沙与埋置光缆力学耦合特性研究

Insight into the mechanical coupling behavior of loose sediment and embedded fiber-optic cable using discrete element method

Abstract: Distributed fiber optic sensing (DFOS) has recently emerged as a novel sensing technology for obtaining spatially continuous deformation of loose sediment. During the measurement, the mechanical coupling between the sediment and embedded fiber optic cable determines the accuracy of the results. However, it remains a major challenge to properly assess such coupling behavior in both laboratory and in-situ tests. To investigate the pullout characteristics of a fiber-optic cable embedded in loose sediment, we established a two-dimensional model consisting of 205,909 active elements using high-performance discrete element numerical simulation software (MatDEM). We found that the simulations using the discrete element method well reproduced the pullout behaviors of fiber-optic cable embedded in soil, and this was verified by the experiment. In particular, the simulations obtained the interfacial shear stress distributions along the cable-sediment interface and the energy conversion processes, which were both determined by the confining pressures. The results revealed that the slip depth (Ls) can better indicate the cable-soil coupling capability than the strain propagation length (Lε). Accordingly, we suggested two evaluation methods for the mechanical coupling of cable and sediment, one employing Ls obtained by the simulations and the other employing the effective critical strain (εcr) obtained from the actual measurements. The discrete element method filled the gaps in understanding the mechanical coupling of the sediment and the embedded fiber-optic cable and it can be a useful tool for evaluating the cable-sediment coupling behaviors.

FIGURE 9  Variation of axial strain of cable with time and the change of criterion for evaluating the coupling between soil and cable with the increasing PD.