Experimental Studies of Soil Load Transfer to Flexible Sewer Liners: Latest Results and Implications for Design

Abstract

The authors' paper in the Proceedings of the ASCE Pipelines 2003 Conference described use of the Cambridge University geotechnical centrifuge to simulate the loading sequence and possible deterioration mechanisms of a sewer and its soil surround, both before and after renovation by lining with cured-in-place pipe (CIPP) or 'close-fit' thermoplastics pipe. The preliminary results reported referred to tests using a sand surround placed at the same initial density, and a single model liner/host pipe assembly with a consistent initial lack of fit, in which the main variable was the sequence of application of a series of extreme deterioration events in the soil (formation and collapse of large voids) and the host pipe (complete loss of both flexural and compressive ring stiffnesses). The effects of traffic loading on both deep and shallow buried lined pipes were also examined. This follow-up paper describes the outcome of further centrifuge tests in which both the initial density of the soil surround and the initial annular gap between liner and host pipe were substantially reduced in order to simulate, in conjunction with the extreme soil and host pipe deterioration events previously applied, the worst practically conceivable case for transfer of soil and traffic loads to a close-fitting, flexible sewer liner. Some basic principles and the implications of the test results for liner design practice are also considered.