Theoretical And Experimental Study On In Suit Spraying Repair Technology For Damaged Concrete Pipe

The drainage pipeline is the lifeline of a city,which bears the heavy responsibility of urban sewage discharge and collection and transportation.Whether it can normally play its design function will directly affect the safety of the town and the sustainable development of society,economy and environment.At present,most of the early drainage pipelines in China have reached the design service life,and large-scale damage and failure have occurred,which need to be updated and repaired urgently.As a new technology for buried pipeline,trenchless repairing technology can realize the repair or replacement of buried pipelines without excavation or partial excavation,and has been widely used in China and other countries.The in situ spraying mortar repair method is a new trenchless repairing technology.This technology mainly uses centrifugal pouring or manual spraying to spray the mortar material evenly onto the surface of the pipeline to form a mortar lining.It has the advantages of fast construction speed,tight bonding between the lining pipe and the existing pipeline,and continuous seamlessness of the whole pipe section.It is suitable for dealing with various types of concrete pipeline diseases.At present,this technology has been applied to repair concrete pipelines,but there are some deficiencies in highperformance mortar materials,residual bearing capacity of damaged pipelines,structural stress model of repaired pipelines,and bearing capacity calculation of in situ spraying mortar repair method.It is urgent to carry out relevant theoretical and experimental research.In this thesis,the following researches are carried out through theoretical analysis,analytical calculation,full-scale experiment and numerical simulation.The main research work and results are as follows:1.Study on residual bearing capacity of damaged concrete pipe.Based on the plastic hinge model in pipe mechanics and the analysis of double-bar rectangular bending section,the calculation method of the maximum bearing capacity of reinforced concrete pipe is proposed,and the calculation model of residual bearing capacity of corroded and thinned reinforced concrete pipe is given.2.Theoretical study on in situ spraying mortar repair of concrete pipe.Relying on concrete pipe repair loading experiment,the stress model of composite curved beam is studied.The influence of relevant calculation parameters on the interface stress is analyzed.It is found that the diameter of the existing pipeline,the ratio of the lining thickness to the wall thickness of the existing pipeline,and the elastic modulus ratio of the material are the main factors affecting the interface shear stress.According to the relevant influencing factors,the calculation formula of the interface shear stress is optimized.Based on the stress theory of composite curved beams,the calculation models for the bearing capacity of damaged concrete pipelines after repair were proposed.3.Study on high performance in situ spraying mortar materials.According to the construction characteristics and environment of the in situ spraying mortar repair method,the scheme of in-situ spraying mortar is developed by orthogonal experiment.High efficiency water reducing agent 0.3%;fly ash 15%;accelerator 0.3%;water cement ratio 0.26;silica fume 4%;1.3% PVA fiber;1.3% latex powder;quartz sand(sand cement ratio)0.8.Durability experiment of in-situ spraying mortar was carried out.The experimental results show that the mass loss rate of the repair mortar is 51.7%lower than that of the ordinary mortar.The compressive strength of the repair mortar is74.6% higher than that of the ordinary mortar at 30 d and 108.17% higher than that of the ordinary mortar at 90 d.The repair mortar has good corrosion resistance and is suitable for the use environment of drainage pipelines.4.Experimental study on bearing performance of plain concrete pipe repaired by in situ spraying.The calculation model of bearing capacity was verified by loading experiment of repaired pipeline.It is found that the ultimate bearing capacity of corroded thinned plain concrete pipe repaired by in situ spraying is positively correlated with the thickness of spraying and the reinforcement ratio of mortar lining.Under the same reinforcement ratio and spraying thickness,the ultimate load of the experimental pipe section of the interface planting nail group is higher than that of the natural spraying experimental pipe,which indicates that the bearing capacity of the repaired pipe can be improved more effectively by the interface planting nail transformation.5.Full-scale experimental study on in situ spraying repair of reinforced concrete pipes.The experimental results show that when the deformation of the cracked reinforced concrete pipeline is too large,the repair effect cannot be achieved only by using mortar.The load-displacement curve of the repaired pipeline did not show a significant decline,the convergence deformation was too large,and the ductility of the overall structure was improved.The top and bottom of the pipe are the most severely damaged parts of the original pipe.They are also the first place where interface peeling occurs in the repaired pipe.The experimental value of the cracking load of the repaired pipeline is obviously smaller than the theoretical calculation value.This phenomenon is due to the fact that the local lining interface of the pipeline has cracked before the “pipelined” structure cracks,and the laminated structure is transformed into a composite structure.When the reinforced concrete pipeline is repaired,the shear strength of the interface can be increased by planting bars at the interface to ensure that the mortar lining layer and the original pipeline are in a superimposed stress state,thereby improving the bearing capacity of the pipeline after repair.6.Numerical simulation research on in-situ spray repair of concrete pipe.A tensile damage failure model based on stiffness reduction is proposed,which can effectively simulate the damage of concrete pipelines under different initial deformation states.Taking No.2 pipeline in full scale experiment as the research object,the following results are obtained through simulation analysis: When the initial deformation degree of the pipe is less than 2.7 %,the strength of the pipe can be improved by using 50 mm thick mortar.When the deformation degree is greater than 2.7 %,the strength of the repaired pipeline will still be lower than that of the original pipeline,and the structural strength cannot be enhanced,which will only slow down the pipeline damage.The increased thickness of the mortar lining can improve the stiffness and load-bearing capacity of the pipe structure.The influence of reinforcement on the mechanical properties of the repaired pipe structure is determined by the reinforcement position and reinforcement ratio.The ultimate bearing capacity of the repaired structure is positively related to the distance between the reinforcement and the inner wall of the mortar layer and the reinforcement ratio.There is a high linear relationship between the ultimate load of the repaired structure and the reinforcement ratio of the mortar layer.