Centrifuge modelling of the effects of soil loading on flexible sewer liners

This paper presents an experimental study of the effects of soil loading on large-diameter, close-fitting, non-bonded, flexible sewer liners as typified by ‘cured-in-place pipes’ (CIPP). CIPP is the process whereby a polymeric pipe lining is cast directly against the wall of a deteriorating sewer pipe. The transfer of soil loading to CIPP liners is strongly influenced by the interaction between the existing host pipe and the surrounding soil. In adjusting to deterioration events of the host pipe and possible void formation in the soil, the existing pipe-soil structure deforms and interacts with the liner inside it. By monitoring deformations of the liner and host structure the magnitude of load transfer can be inferred. The paper describes 1/30th scale physical models tested in dry sand under 30g of centrifugal acceleration. The models included: (a) a host pipe with two simulated modes of deterioration; (b) an instrumented close-fitting, non-bonded, flexible liner; (c) voids in the soil; and (d) moving, heavy traffic loading. The tests showed that, even under extreme loading conditions, the deformations of the liner are relatively small (2–3% of diameter), implying that the presence of a thin, flexible non-bonded and close-fitting liner has an important stiffening effect on the response of the deteriorating host pipe. The important influence of void position in the surrounding soil was also demonstrated.