"FULLY DETERIORATED" DESIGN IN RIGID PIPE REHABILITATION WITH FLEXIBLE LINERS

An ASCE/PLD 2001 Conference paper by the author (McAlpine 2001) discussed available test data, research findings and technical discussions by various groups on the subject of “Fully Deteriorated Design” for rigid pipe rehabilitation by flexible liners. The paper concluded that there is no experimental or theoretical support for the current design method as it would apply to flexible liners of buried rigid pipes. The design equation, appropriated from the design practice for direct burial of fiberglass pipe, is based on a phenomenological model of the soil- pipe-liner structure that is inappropriate for rehabilitation liners in rigid pipes. This paper further argues that, under most realistic field conditions, there will be no earth load transferred to the liner. In addition, in the most unusual and unlikely cases that could produce load transfer (non existent or unstable soil support), the load will produce pure bending stresses and buckling will not be the failure state (as assumed in the current practice). A deflection control design method is proposed for “weak” soils and host pipes that have lost their rigidity.