Pile Detection Technology And Its Application Research Based On Distributed Fiber Optical Sensing

With the sustainable development of the national economy as well as constructing or planning large infrastructural projects,the pile foundation has been increasing widely used.As the pile type becomes more complex,technical difficulty becomes higher,and pile foundation engineering accidents occur frequently.Research on pile-soil interaction can provides technical and safety support for large complex foundation engineering.Distributed fiber optical sensing(DFOS)technology amounts to enbeding nerves in the structures(rock or soil),so it is able to sense their physical and mechanical properties,that is why it is superior to other monitoring technologies,and has wide potential applicabity.In this thesis,the DFOS technology is applied to the research of pile detection,leading to the following results and innovations:1.The research methods for pile-soil interaction were reviewed,introducing the principles,current developments and the application of DFOS technology based on Rayleigh scattering,Brillouin scattering,Raman scattering and fiber Bragg grating.The technological advantages of DFOS technology in the study of pile detection were summarized.2.In order to handle varying standards and parameters of different optical fiber(cable)products,a selection process suitable for the distributed optical fiber sensor was proposed.An installation method of DFOS sensor of pile foundation was designed.3.In consideration of the great spatial resolution of BOTDR DFOS technology,field experiments were conducted.By testing DFOS temperature measurement tubes of different diameters,materials,in varying stress conditions and temperature shifts,a suitable high spatial resolution temperature sensor for temperature field monitoring was developed and a patent applcaition was applied.4.In the research of pile detecton data processing system using the DFOS technology,the filting methods based on signal processing theory were proposed and applied in data analysis.Using the pile-soil interaction transmission theory,the relationship between stress,strain,displacement and deflection of constant corss-section piles under vertical and horizontal load was derived.The stress deformation characteristics of variable cross-section piles were discussed.The safety diagnosis of strain field theory was applied to the pile detection.Numerical computations and inversion analysis were combined to study the pile-soil interaction rules.5.To study the characteristics of stress deformation of anti-slide pile and soil,the distributed optical fiber sensors were implanted into piles with varying stiffness and shape in indoor model tests.The physical indicators such as strain,deflection,displacement and deformation of anti-slide pile in the soil under loading were obtained,and the feasibility of BOTDA technology in the analysis of pile detection was verified.6.To study the characteristics of deformation of tubular pile during piling,FBG quasi-distributed optical fiber sensors and BOTDA fully-distributed optical fiber sensors were installed.Via simulation,the characteristics of deformation of tubular pile under the dynamic load stress and in static state were obtained.And a detection process of FBG-BOTDA sensing of pipe driving was proposed,with which a parent applction was filed.7.The application of DFOS technology on bored pile,pre-stressed concrete pipe,up-liftr pile,super-long pile,self-balanced loading test pile,squeezed branch pile were proposed.Combined with the above results,the deformation characteristics of different piles under different stress statuses were analyzed,verifying the feasibility of the research ideas.