Study On Coupling Between Sensing Optical Cable Sensitized With Anchors And Compression Deformation Of Sand

Distributed fiber optic sensing technology has been successfully applied in rock and soil deformation monitoring due to its advantages of distributed,long distance measurement and high sensitivity.When distributed optical fiber sensing technology is applied to soil deformation monitoring,the interface between optical fiber and soil is prone to slip and debonding,which reduces the reliability of monitoring data.Therefore,when using distributed optical fiber sensing technology to monitor soil deformation,it is necessary to first explore the coupling between optical cable and soil..In order to study the effect of anchorage point with enlarged diameter(referred to as anchor point)on the deformation coupling between sensing optical cable and soil,an evaluation model for the deformation coupling between sensing optical cable sensitized with anchors(referred to as anchored optical cable)and soil was established,and the deformation coupling test of sensing optical cable and sand under triaxial compression was carried out.The related work and research results are as follows:(1)This paper expounds the unique advantages of distributed fiber optic sensing technology compared with traditional sensing technology,and summarizes the research status of the coupling test,theoretical model,and enhancement methods of the coupling between sensing optical cable and soil at home and abroad.(2)In view of the existing problems in the current research,a new test scheme is proposed to study the deformation coupling between the anchored optical cable and sand under triaxial compression.Four different types of anchorage points are designed,and the fabrication method and test conditions of the anchored optical cable are introduced.Therefore,with the increase of confining pressure,the enhancement effect of anchor point on the coupling between sensing cable and soil decreases.(3)In this paper,the failure criterion of the interface between sensing optical cable and soil with four different anchoring forms are derived,and the relationship between the critical normal stress and the type of optical cable,the strain difference and the diameter of the anchoring point is analyzed under the condition of no sliding of the interface between the sensing optical cable and soil.The theoretical analysis of the strain transfer between the anchored optical cable and the soil is carried out,and the distribution of the strain transfer coefficient and the shear stress of the interface between the sensing optical cable and soil are summarized.(4)The coupling test of cable and sand under triaxial compression was carried out.The analysis results of the deformation coupling coefficient of soil and anchored optical cable and the maximum measurable average shear stress show that,the coupling between 2 mm diameter anchored optical cable and soil is better than that of the 0.9mm diameter anchored optical cable.The coupling between soil and anchored optical cable of unsaturated sand is better than that of saturated sand;The results show that the coupling between anchored optical cable and soil decreases with the increase of anchorage distance or the decrease of anchorage diameter,and increases with the decrease of sand particle size.The coupling between the wafer anchored cable and soil is the strongest.(5)When the confining pressure is 100 kPa,200 kPa,and 400 kPa,and the average deformation coupling coefficient is taken as the comparison basis,the highest improvement rate of the deformation coupling between optical cable and soil is 50.6%,32.5% and 34.5% respectively;When the maximum deformation coupling coefficient is used as the comparison basis,the highest improvement rate of the deformation coupling between optical cable and soil is 54.8%,32.4% and 34.5% respectively.With the increase of the axial deflection stress,the deformation coupling between anchored optical cable and soil tends to increase.Under the unloading condition,the anchor point effectively limits the rebound deformation of the optical cable and improves the coupling between sensing optical cable and soil compared with the non-anchored optical cable.In conclusion,the increase of anchor point can effectively improve the deformation coupling between optical cable and soil.The research results of this paper provide a new basis for monitoring soil compression deformation by anchored optical cable.