| Over-exploitation of groundwater can cause ground subsidence,which can lead to a series of disasters.The development process of land subsidence is extremely slow and difficult to detect,which makes it more difficult to control and treatment.Therefore,the fine monitoring of the deformation of the underground soil layer in the ground subsidence area is an effective means to reduce the degree of disaster.Distributed Fiber Optic Sensing(DFOS)technology can break through the limitations of traditional point-based monitoring(bedrock standard layered standard system)and achieve finegrained monitoring of full-section soil deformation,and prediction and evaluation of ground subsidence.It has important practical significance.However,the deformation law of the soil is complex and susceptible to external factors,resulting in a relatively complicated interaction between the fiber and the soil.The structure,modulus and size of the sensing optical cable are different,and the sensing performance is also different;the nature of the backfill material and the quality of the backfill are different,and the impact on the optical fiber monitoring data is also different.The coupling problem of fiber-soil deformation has always been a key problem in the popularization and application of the full-section monitoring technology for ground settlement drilling.This paper takes distributed fiber monitoring ground subsidence as a research background.In view of the fiber-soil deformation coupling problem,it has carried out more in-depth research from the three aspects of test method,improvement measures,theory and evaluation,and achieved the following results:(1)The fiber-soil deformation coupling test device with controllable confining pressure is used,and the optical frequency domain reflection technology(full name,OFDR)is used to obtain the strain distribution along the axial direction of the sensor cable during the drawing process with a high spatial resolution of 1mm,Reveals the interaction mechanism between fiber and soil in the confining pressure range of 0 ?1.0MPa,and discusses the effect of confining pressure on fiber-soil deformation coupling.(2)A simplified model is introduced to describe the progressive failure process of the cable-soil interface,and the pull test data under 0 ? 1.0Mpa is simulated,indicating that the ideal elastic-plastic pull model can better fit the pull Pulling force-pulling displacement curve,and verify the reliability of the test results.The distribution of shear stress at the sensing fiber-soil interface is calculated,and the progressive failure process of the interface between the two is presented,which supports the processing analysis of distributed optical fiber monitoring data and the popularization and application of distributed optical fiber monitoring technology.(3)In order to solve the problem of poor fiber-soil coupling without confining pressure,a micro anchor point sensing optical cable is developed.The influence of different backfill materials on the fiber-soil coupling and the influence of anchor point diameter and spacing on the fiber-soil deformation coupling are explored.The test results show that the larger the anchor point diameter is,the smaller the spacing is,the better the reinforcement effect is,but the best anchorage is straight The diameter and spacing shall be determined according to the confining pressure and drilling diameter.(4)Under different confining pressures,the spacing and diameter of different anchoring pieces are required to achieve strong fiber-soil coupling.The results show that the increasing of confining pressure can increase the spacing of anchoring pieces appropriately.No anchoring is required to enhance fiber-soil coupling. |
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