Mechanical Characteristics And Experimental Study Of Drainage Concrete Pipes And Liner Structure Cured With CIPP Technology

Reinforced concrete drainage pipes are widely used in urban municipal drainage projects by virtue of their simple manufacturing process,low cost and smooth structural walls.However,in the past two decades,accidents caused by cracking,corrosion,leakage and even collapse of reinforced concrete drainage pipes in operation have occurred frequently,and the maintenance and renewal of reinforced concrete drainage networks have become a hot topic of concern for the industry.Safe,reliable,economical,environmentally friendly and durable,Cured-In-Place Pipe repair technology has been attempted as a composite material to work with old structures with a view to providing a lasting enhancement to deteriorated reinforced concrete pipes.Current CIPP lining design methods ignore the effects of host pipe deterioration when analyzing structural stability,stiffness and strength,and fail to explore the issues of load sharing and joint loading of old and new structures,resulting in lining structural designs that do not match the actual situation,limiting the application of the technology.This thesis attempts to use a combination of case induction,probabilistic analysis,model testing,numerical simulation and theoretical analysis to explore the classification and quantification of the defect condition of deteriorated reinforced concrete pipes,the calculation method of critical buckling external pressure of liners under two working conditions,the calculation method of load-bearing performance of deteriorated pipe-CIPP liners under concentrated load,the variation law of soil-pressure static load and traffic load,and the law of load sharing between pipe-liners and the evaluation method.The main findings of the full thesis are as follows:（1）Study on the causes and classification model of reinforced concrete drainage pipe distress.Through the analysis of the classification and causes of diseases that occur during the operation of municipal drainage pipes,the failure mechanisms of drainage pipe corrosion,damage collapse and pipe joints are discussed.Through a comparative study of existing drainage pipe disease assessment methods such as the WRc assessment model,the PACP pipeline condition assessment procedure,the NRC assessment model and the CJJ 181 urban drainage pipe inspection and assessment procedure,the limitations of various models are analyzed and a defect condition classification model based on drainage pipe operation time is further proposed.The results show that the model can effectively reflect the deterioration of the pipeline over time,with the higher the attenuation resistance factor,the later in the service life of the pipeline the defects（or further deterioration of the defects）arise.The grading model can accurately predict the time point of deterioration of pipeline defects and provide specific rehabilitation solutions based on this.（2）Boundary condition-based stability study of CIPP liners under external pressure.A method is proposed for calculating the buckling of CIPP liners with host pipes under two boundary conditions:the presence of gap and tight bond.The buckling process and post-buckling mechanics of CIPP specimens with free boundaries were clarified by two sets of full-scale tests.Based on the material mechanical properties tests of the CIPP liner,tensile and bending modulus were obtained,from which a three-dimensional finite element model of the rehabilitated pipe was developed to investigate the influence of the liner DR value and annular gap on the buckling behavior of the liner under interface free conditions and the influence of the liner DR value and ellipticity（host pipe deterioration state）on the buckling behavior of the liner under interface bonded conditions respectively.The results show that the interface-free CIPP liner undergoes three processes of liner elliptization,arching and stepwise buckling under external pressure,while the interface-bonded CIPP liner undergoes local pressure concentration buckling due to the failure of the interface bonding.The theoretical analysis method agrees well with the experimental and numerical simulation results and effectively predicts the critical buckling pressure of CIPP-lined pipes under different boundary conditions.（3）Study of the load-bearing performance of CIPP liner-deteriorated pipe composite structures.A total of 48 deteriorated pipe-liner load-bearing performance tests were carried out.The DIC technique was used to obtain the displacement and strain fields at the end face of the deteriorated pipe-repair lining structure and to obtain the relative displacement-time test curve of the interface during plate loading.Based on the phenomena and patterns presented by multiple sets of test results,a model for calculating the stiffness and strength of the rehabilitated structure considering the deterioration state of the host pipeline was developed.A method for discounting and quantifying the intrinsic parameters of the degraded pipe CDP based on a concentrated load model test of the pipe section is proposed,combining the digital image correlation method with the finite element technique.Further,extended finite element simulations were carried out for 54 sets of deteriorated structures and 108 sets of repaired structures.The results of the study show that under the action of the plate load,the pipe lining structure reaches its ultimate bearing state when the lining is subjected to the concentrated load of the plastic hinge of the rigid pipe at the crown and invert of the pipe,and the extrusion of the outer pipe at the springlines of the lining.The theoretical calculation method for structural stiffness and strength,which measures the range of action of the two load models in terms ofαandβ,established in this thesis can be effectively matched with experiments and numerical simulations.（4）Mechanical response analysis of buried pipe-liner structures under external loading.A three-dimensional finite element model of a buried rehabilitation pipeline structure under the action of soil was developed by introducing a CDP model of plastic damage to reinforced concrete and an interfacial Cohesive cohesion model.The influence of the depth of burial,the type of soil compacted around the pipe,the diameter of the pipe and the deterioration state of the host pipe on the model of pipe soil interaction and the sharing of bending moments of the pipe-lining structure under static load and traffic load is analyzed.The evolutionary polynomial regression（EPR）technique was used to develop prediction models for the bedding coefficients B_FEand B_FLLunder static and traffic loads.The results show that the combined bedding coefficients of the rehabilitated structure show significant variability and no regularity with the bedding coefficients of the new pipeline（given by the AASHTO standard）.By stripping the bedding coefficients for static and traffic loading effects,B_FEand B_FLLcalculation paradigms that take into account the pipe diameter,wall thickness,burial depth,initial pipe deterioration level and initial backfill type are obtained,using which more economical and robust drainage pipe CIPP rehabilitation designs can be achieved.（5）Analysis of CIPP repairing calculation example of deteriorated drainage pipeline.Combined with the research results from Chapter 3 to Chapter 5,the CIPP repair design process of deteriorated drainage RCPs is proposed.From the lateral comparison of structural stiffness and strength,lining stiffness should be the main design factor when CIPP material is used to reinforce the deteriorated pipeline.The design equation given by ASTM F1216 only reflects the influence of the material modulus E and the lining wall thickness DR value of the repaired structure,so a more radical result is obtained.Considering the mechanical influence of the host pipe on the repaired liner,the stiffness design result of the model proposed in this thesis is lower than that of the liner alone.