Research On The Mechanism And Distributed Fiber Optic Monitoring Method Of Ground Deformation Caused By Leakage Of Water Transmission Pipelines In Loess Regions

In recent years,in order to meet the needs of urban industrial and domestic water use,a number of long-distance,large flow,and high lift pipeline water transmission projects have been constructed in the loess area.However,due to the instability of loess properties,the damage and leakage of water pipelines can easily lead to ground collapse accidents,seriously affecting the performance of engineering benefits,and even endangering the safety of local residents’ lives and property.Therefore,it is urgent to conduct in-depth research on the ground collapse disaster caused by water pipeline leakage,among which monitoring and grasping the deformation process of collapsed soil is crucial for monitoring and predicting ground collapse accidents.This article first studied the finite element analysis method of ground subsidence caused by water pipeline leakage,explored the general law of ground deformation caused by underlying cavities caused by water pipeline leakage,and analyzed the feasibility of using distributed optical fiber monitoring for ground deformation;Then,based on the results of indoor fiber soil pull-out test and continuous discontinuous coupling numerical simulation,the coupling performance of fiber soil under different influence factors is studied;On this basis,a physical model experiment was conducted to study the distributed optical fiber monitoring of ground deformation caused by water pipeline leakage.The spatiotemporal distribution law of soil settlement under different burial depths of cavities was studied,and the influence of different strain sensing optical fiber anchoring methods on the monitoring results of optical fibers was explored;Finally,a strain displacement transformation method based on the Sequence to Sequence(Seq2Seq)model was proposed and validated using indoor model test data.The main research results and conclusions obtained in the paper are as follows:(1)By studying the finite element analysis and calculation method of ground deformation caused by the development of cavities,the process of cavity failure was simulated from two aspects:the depth of cavity burial and its size.The numerical simulation results indicate that as the span of the cavity increases and the burial depth decreases,the stability of the road surface decreases,the settlement rate of the road surface accelerates,and sudden settlement is prone to occur.The decrease in soil strength is one of the reasons for the collapse and damage of the road surface;By using a modified Gaussian curve model to fit the settlement curve,the results show that the surface settlement caused by water pipeline leakage follows the modified Gaussian distribution law;After analyzing indicators such as ground settlement value,settlement area,and soil strain measurement,this study shows that distributed fiber optic monitoring technology can effectively monitor the deformation of the soil at the maximum settlement position during the formation and development of ground collapse;The voids generated by leakage do not cause significant damage to the pipeline,but the secondary damage caused by the collapse of the surrounding soil around the voids is the main potential threat to the safe operation of the pipeline.(2)The strain distribution during the detachment process between the sensing fiber and the soil was obtained through indoor experiments on the coupling characteristics of the fiber optic loess soil interface.The test results show that the increase of anchor pieces and the appropriate increase of the moisture content of loess can help to enhance the coupling between optical fiber and soil.With the increase of soil compactness and anchor diameter,the shear stress also increases.In addition,as the soil moisture content approaches the optimal moisture content,the shear stress will gradually increase;Based on indoor experiments and using continuous discontinuous numerical simulation methods,the numerical pull-out test results show that the overlying pressure and anchor plate diameter can affect the contact coupling effect and resistance between the optical fiber and the surrounding soil,thereby affecting the numerical value and range of the movement of surrounding soil particles when the optical fiber moves.Through the evaluation of coupling deformation coefficient,it is found that the addition of anchor pieces on the strain sensing optical fiber can effectively improve the coupling between the optical fiber and the soil,with a significant increase.(3)Based on the study of fiber optic loess soil interface coupling,a distributed fiber optic monitoring model experimental study on ground subsidence caused by water pipeline leakage was conducted.The experimental results indicate that the fiber optic monitoring results can accurately predict and monitor the location,settlement,and strain distribution of ground subsidence,and reveal its deformation evolution law;The surface settlement displacement curve of the experimental soil exhibits a parabolic distribution,which is consistent with the spatial distribution of the ground settlement displacement curve calculated by the finite element model in Chapter 2;At the same time,the fiber optic strain test curve presents a "saddle" shape,revealing the stress state of the surrounding soil around the collapse and the process of collapse developing from the bottom to the upper layer.A strain displacement conversion method based on Sequence to Sequence(Seq2Seq)model is proposed for the problem of strain displacement conversion in fiber optic measurement,and it is validated through indoor model experiments.The experimental results indicate that the Seq2Seq model in this paper has high accuracy in predicting strain and ground settlement displacement in fiber optic monitoring of ground subsidence.