Theoretical Study on Design of Composite Lining Structure with Rigid–Flexible Combination for Trenchless Pipeline Rehabilitation

Trenchless rehabilitation lining can be divided into flexible solid wall lining structures, rigid lining structures and rigid–flexible composite lining structures. This paper reviews the research status of the design theory of trenchless rehabilitation lining pipes, analyzes the theory of rigid–flexible composite lining structures, and points out that the value of the factor determined from non-grouting angle K1 is not clear in the design formula of the rigid–flexible composite lining structure mentioned in the ASTM ‘Standard Practice for Installation of Machine Spiral Wound Poly (Vinyl Chloride) (PVC) Liner Pipe for Rehabilitation of Existing Sewers and Conduits (ASTM F 1741)’. The value of K1 was obtained by the numerical analysis method with MATLAB software. Through the analysis of the variation trend of the K1 value, it is concluded that the design formula in the ASTM standard is only applicable to the case of incomplete grouting filling between the original pipe and the lining pipe, and is not applicable to the composite lining pipe with complete grouting filling. Finally, the explicit formula of the non-grouting angle is obtained by fitting, which is more convenient to use.