Experimental Study On Pipe-Soil Interaction Mechanism Under Ground Subsidence Conditions

Intelligent sensing and real-time monitoring of the health status of buried pipelines in engineering ground subsidence areas,on the basis of which reveals the mechanism of pipeline deformation damage,which is of great significance to the construction and operation of urban pipeline network.Based on DFOS technology,a refined monitoring scheme for analyzing the mechanism of pipe-soil interaction under ground subsidence conditions is designed,as well as the corresponding method of laboratory experiment.In this paper,the internal force distribution of the pipeline,longitudinal and hoop deformation of the pipeline,soil settlement,earth pressure around the pipe and pipesoil interaction were studied.The main achievements were as follows:(1)Summarize the research background of buried pipelines and research progress at home and abroad.It is found that ground subsidence is an important cause of deformation damage of buried pipelines.Point out the shortcomings of traditional monitoring technology,meanwhile,the advanced distributed fiber-optic sensing(DFOS)technology is introduced.(2)From the perspective of pipe-soil interaction,the current theory of elastic foundation beam and contact surface theory are summarized.Then,based on the improved conjugate beam method(ICBM)and the classical double integration method(DIM),a detailed derivation of the pipeline settlement formula is carried out.At last,the deflection curve differential equation of the ring is introduced,and the hoop deformation formula of the pipe is briefly derived.(3)Using water bladder array drainage to simulate two-dimensional Gaussian subsidence,the monitoring experiment of buried pipeline deformation based on fiber Bragg grating(FBG)technology was carried out.The material preparation and specific setup of the experiment were introduced in detail.A refined monitoring scheme for buried pipelines based on FBG technology was proposed,to study the longitudinal and hoop strain and deformation distribution of pipelines and their development trend with subsidence under different soil thickness and subsidence conditions.Moreover,a preliminary explanation was given from the perspective of pipe-soil interaction.(4)The experimental study on pipe-soil interaction under ground subsidence conditions based on optical frequency domain reflectometry(OFDR)technology was carried out.Specific analysis and discussion were carried out from the aspects of pipeline,soil and pipe-oil interaction.Firstly,based on the one-dimensional strain measured by the optical cable,the internal forces in the longitudinal and hoop of the buried pipeline are obtained,including the distribution and variation characteristics of axial force,shear force,rotation angle and bending moment.Then,the pipeline settlement is calculated by the ICBM and DIM respectively,and the calculation errors of the two methods are compared and analyzed.At the same time,the ovality formula was derived to quantify the hoop deformation of the pipeline.The experiment also obtained the distribution and variation of the settlement and volume transfer rate of surface soil and the same layer soil on the pipe side,as well as the variation of earth pressure around the pipe and the soil arching coefficient with the settlement development on the typical cross section of the pipeline.At last,the mechanism of pipesoil interaction under ground subsidence conditions is quantitatively analyzed from the perspectives of relative displacement of pipe-soil,coordinated deformation coefficient of pipe-soil,interface shear stress of pipe-soil and relative stiffness of pipe-soil.