Distributed Strain Sensing to Study a Composite Liner for Cast Iron Water Pipe Rehabilitation

Abstract

Abstract The use of cured-in-place pipe lining systems for the rehabilitation of cast iron water pressure pipe has grown significantly in the past 20 years. With limited information on the performance of these lining systems in service, strain measurements are needed to evaluate theoretical findings about three-dimensional strength limits. The application of distributed optical fiber sensing to study the properties of a polymer composite liner was investigated in this research. Polyimide optical fibers were installed into flat liner coupons fabricated in the laboratory, and the specimens were subsequently tested in uniaxial tension and four-point bending. Using optical frequency domain reflectometry, Rayleigh backscatter was monitored from preinstalled optical fiber sensors and strains of up to 4,000 με were obtained. Comparisons between experimental optical fiber measurements and results obtained from conventional strain measurement techniques (i.e., extensometer and crosshead displacement) showed a strong correlation with an average difference of 3 % in four-point bending and 6 % in tension. However, the orientation and diameter of the composite fiber reinforcements were observed to affect distributed sensing performance.