Experimental Examination of Selected Limit States of Structural Liners at Locations of Ring Fracture

While designing rehabilitation solution for deteriorated pressurized potable water mains, presence discontinuities in the pipe's walls must be considered. This experimental work involves investigation of three limit states e.g. flexure, shear and axial that could cause liner instability as a result of internal water pressure and uneven ground movement at a broken location e.g. ring fracture - frequently found in small diameter cast iron pipes suffering from loss of beam support. It is reasonable to assume that natural settlement of the bedding materials has long been completed for pipes that have been buried for many years. Therefore, the differential ground movements induced by frost, moisture changes in `reactive' clays or a nearby excavation causes a transverse fracture on the brittle cast iron pipes. The liner product needs to be able to accommodate such movements, which tend to take the form of flexure, shear or axial displacement. Six testing specimens were prepared (each comprised of two 4 ft long sections of a 70-year old 6 in. ID cast iron pipe) by forming a simulated transverse ring break at their lengthwise middle point and then lining them with a fiber reinforced CIPP liner. For pressurized condition test, three specimens were capped and subjected to three-point flexural, pull, and shear loading using custom-built testing apparatus. In the non-pressurized condition similar steps were followed except the caps were hollow. The behavior of the pipe and the liner was monitored with increased deflection, and geometrical changes in the liners were noted. Strain and stress measurements in the axial and hoop directions within the liner structure at the location of the ring failure were also monitored. Conclusions were made regarding governing failure mechanisms for fiber-reinforced CIPP liners subjected to angular and axial displacement.