Theoretical Research On Spraying Repair Of Sewer Pipe Strength

Underground drainage pipeline spraying repairing technology refers to using compressed air to spray a certain proportion of sprayed mixed materials on the inner wall of the pipeline without the need to excavate the road surface.After the material is hardened,a complete inner liner layer is formed.Pipeline anti-corrosion,plugging and structural reinforcement required pipeline repair technology.In this paper,the strength of composite pipeline repaired by spraying method is divided into three parts: the study of remaining strength of old pipeline,the strength of sprayed lining layer and the composite strength of new pipe after repair.Works carried out in this paper and results achieved mainly include:(1)Methods for evaluating the residual strength of steel and concrete drainage pipes was summarized and compared.For steel pipelines,remaining strength evaluation theory of pipeline is discussed from semi-empirical formula method,standard method,and numerical simulation method.The influence of flow stress and expansion coefficient on calculation results is obtained.The adaptability of evaluation method to the steel grade.For concrete pipes,effects of penetration cracks on pipe in axial and circumferential directions are considered.Corresponding calculation models and comparison results are given.Listed four types of evaluation theory:semi-empirical formula method,standard method,elastoplastic mechanics method,and fracture mechanics theory,and combined calculation examples to analyze and compare calculation models in various methods.(2)Design theory of inner liner wall thickness is summarized and its applicability is analyzed.Under the same conditions,the wall thickness of inner liner is greater than wall thickness of inner liner when structural repair is performed,and there is a section loss.However,due to the small resistance coefficient of sprayed liner material,overcurrent capability does not decrease.(3)The formulae for calculating strength of different material types inner liners are combed and derived.Design methods for wall thicknesses of existing circular and square pipe linings are summarized.They are respectively described in terms ofsemi-structural and structural restorations.(4)Two methods,test and numerical simulation,were used to study the bonding strength of interface between old pipe and inner liner.Through a single-variable control experiment,influence of the contact surface wetness degree,interface agent properties,and curing time on the bond strength was obtained.Through numerical simulation method,influence of liner wall thickness on internal shear stress of material was obtained.The safest and most economical spray thickness advice is given.(5)Based on the theory of combined thick-walled circles management,calculation method for strength of sprayed composite pipes was deduced.The sum of individual strengths of old pipe and inner liner is taken as the strength of the composite pipe after spray repair.