This dissertation details an attempt to experimentally evaluate the Giroud et al. (1995) concentration factors for geomembranes loaded in tension perpendicular to a seam by laboratory measurement. Field observations of the performance of geomembrane liner systems indicates that tears occur at average strains well below the yield criteria. These observations have been attributed, in part, to localized strain concentrations in the geomembrane loaded in tension in a direction perpendicular to the seam. Giroud et al. (1995) has presented theoretical strain concentration factors for geomembrane seams loaded in tension when the seam is perpendicular to the applied tensile strain. However, these factors have never been verified. This dissertation was prepared in fulfillment of the requirements for graduation from Barrett, the Honors College at Arizona State University. The work described herein was sponsored by the National Science Foundation as a part of a larger research project entitled "NEESR: Performance Based Design of Geomembrane Liner Systems Subject to Extreme Loading." The work is motivated by geomembrane tears observed at the Chiquita Canyon landfill following the 1994 Northridge earthquake. Numerical analysis of the strains in the Chiquita Canyon landfill liner induced by the earthquake indicated that the tensile strains, were well below the yield strain of the geomembrane material. In order to explain why the membrane did fail, strain concentration factors due to bending at seams perpendicular to the load in the model proposed by Giroud et al. (1995) had to be applied to the geomembrane (Arab, 2011). Due to the localized nature of seam strain concentrations, digital image correlation (DIC) was used. The high resolution attained with DIC had a sufficient resolution to capture the localized strain concentrations. High density polyethylene (HDPE) geomembrane samples prepared by a leading geomembrane manufacturer were used in the testing described herein. The samples included both extrusion fillet and dual hot wedge fusion seams. The samples were loaded in tension in a standard triaxial test apparatus. to the seams in the samples including both extrusion fillet and dual hot wedge seams. DIC was used to capture the deformation field and strain fields were subsequently created by computer analysis.

A series of experiments were conducted to support validation of a numerical model for the performance of geomembrane liners subject to waste settlement and seismic loading. These experiments included large scale centrifuge model testing of a geomembrane-lined landfill, small scale laboratory testing to get the relevant properties of the materials used in the large scale centrifuge model, and tensile tests on seamed geomembrane coupons. The landfill model in the large scale centrifuge test was built with a cemented sand base, a thin film NafionTM geomembrane liner, and a mixture of sand and peat for model waste. The centrifuge model was spun up to 60 g, allowed to settle, and then subjected to seismic loading at three different peak ground accelerations (PGA). Strain on the liner and settlement of the waste during model spin-up and subsequent seismic loading and accelerations throughout the model due to seismic loading were acquired from sensors within the model. Laboratory testing conducted to evaluate the properties of the materials used in the model included triaxial compression tests on the cemented sand base, wide-width tensile testing of the thin film geomembrane, interface shear testing between the thin film geomembrane and the waste material, and one dimensional compression and cyclic direct simple shear testing of the sand-peat mixture used to simulate the waste. The tensile tests on seamed high-density polyethylene (HDPE) coupons were conducted to evaluate strain concentration associated with seams oriented perpendicular to an applied tensile load. Digital image correlation (DIC) was employed to evaluate the strain field, and hence seam strain concentrations, in these tensile tests. One-dimensional compression tests were also conducted on composite sand and HDPE samples to evaluate the compressive modulus of HDPE. The large scale centrifuge model and small scale laboratory tests provide the necessary data for numerical model validation. The tensile tests on seamed HDPE specimens show that maximum tensile strain due to strain concentrations at a seam is greater than previously suggested, a finding with profound implications for landfill liner design and construction quality control/quality assurance (QC/QA) practices. The results of the one-dimensional compression tests on composite sand-HDPE specimens were inconclusive.

The effect of earthquake-induced liquefaction on the local void ratio distribution of cohesionless soil is evaluated using x-ray computed tomography (CT) and an advanced image processing software package. Intact, relatively undisturbed specimens of cohesionless soil were recovered before and after liquefaction by freezing and coring soil deposits created by pluviation and by sedimentation through water. Pluviated soil deposits were liquefied in the small geotechnical centrifuge at the University of California at Davis shared-use National Science Foundation (NSF)-supported Network for Earthquake Engineering Simulation (NEES) facility. A soil deposit created by sedimentation through water was liquefied on a small shake table in the Arizona State University geotechnical laboratory. Initial centrifuge tests employed Ottawa 20-30 sand but this material proved to be too coarse to liquefy in the centrifuge. Therefore, subsequent centrifuge tests employed Ottawa F60 sand. The shake table test employed Ottawa 20-30 sand. Recovered cores were stabilized by impregnation with optical grade epoxy and sent to the University of Texas at Austin NSF-supported facility at the University of Texas at Austin for high-resolution CT scanning of geologic media. The local void ratio distribution of a CT-scanned core of Ottawa 20-30 sand evaluated using Avizo® Fire, a commercially available advanced program for image analysis, was compared to the local void ratio distribution established on the same core by analysis of optical images to demonstrate that analysis of the CT scans gave similar results to optical methods. CT scans were subsequently conducted on liquefied and not-liquefied specimens of Ottawa 20-30 sand and Ottawa F60 sand. The resolution of F60 specimens was inadequate to establish the local void ratio distribution. Results of the analysis of the Ottawa 20-30 specimens recovered from the model built for the shake table test showed that liquefaction can substantially influence the variability in local void ratio, increasing the degree of non-homogeneity in the specimen.