Behavior of waves in high density polyethylene geomembranes

In this dissertation, the behavior of waves of the type that are seen in field deployed high density polyethylene (HDPE) geomembranes was studied. The effect of four experimental variables on the behavior of the waves was evaluated. The variables were normal stress, original wave height, thickness of geomembrane and temperature. The resulting experimental design represented twenty-five separate tests each conducted for 1,000 hours. In addition, a single control test was maintained for 10,000 hours. Each of the tests utilized HDPE geomembranes with strain gages attached in a number of critical locations. The results of the strain measurements in the 1,000 hour tests were modeled and extrapolated to 10,000 hours using the Kelvin-Chain model. The applicability of the Kelvin-Chain model was justified on the basis of the results of the 10,000 hour test. The measured and extrapolated strains were then converted to stresses via the Maxwell-Weichert model and the stress relaxation master curves established using the results of the large scale stress relaxation experiments. With the completion of the experiments and their extrapolation into a near steady state condition, it was found that tensile strain up to 5% could be induced in the geomembranes, leaving residual stress equivalent to 22% of the yield stress remained in the geomembranes. It was also found that a contact between the geomembrane and the underlying subgrade soil is not likely to be achieved over time. The results of this dissertation show that if waves are to be avoided, the geomembrane must be essentially flat on the underlying subgrade before backfilling. Possible changes in the current practice of field deployment and seaming of geomembranes were provided.