In the composite pipe construction method defined in the Japan Sewage Works Association's Design and Construction Guidelines for Sewer Pipe Rehabilitation, a liner pipe is constructed inside an existing sewer and the annular space behind the liner is filled with cementitious grout under pressure to form a highly integrated structure. The Guidelines for sewer renovation in Japan define a composite pipe as a composite structure that requires complete integration between liner materials and an existing pipe. However, in general, owing to the refinement of the small and enclosed working space inside sewers and the significant extension of the pipe to be renovated, mechanical shear connectors are not used to rigidly connect a renovation layer with an existing pipe. To fully explore the advantages of the composite pipe method in sewer renovation while maintaining safe design, a semi-composite structure has been applied in the renovation design of aging sewers using nonlinear FEM analysis for more than 50 sewers (over a total length of 300 km), primarily in big cities in Japan. This paper focuses on the mechanics of the structure.
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