Field-Scale Monitoring and Laboratory Simulation of Geosynthetic Liners During Construction and After Placement of Waste
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Two physical issues of geomembrane wrinkle deformations and downslope shear deformations – that need to be considered to obtain good long-term geomembrane liner performance – are examined. First, field-scale monitoring of geomembrane wrinkles in a 1.5-mm-thick, black high-density polyethylene geomembrane during placement of cover soil is reported from three field investigations with an emphasis on the effects of cover soil placement techniques, construction equipment and geomembrane temperature on the fate of geomembrane wrinkles. In many cases, wrinkles were found to exist after placement of cover soil and were smaller in size than previously reported dimensions for uncovered geomembrane wrinkles. Post-backfill wrinkle heights between 10 to 50 mm and widths between 70 to 120 mm were measured for wrinkles that did not experience construction equipment loading, while post-backfill wrinkle heights between 10 to 60 mm and widths between 50 to 80 mm were measured for wrinkles that experienced equipment loading Second, post-backfill wrinkle geometries attained from field measurements were used in short-term physical experiments to examine the fate of geomembrane wrinkles when subjected to additional overburden pressures. The influence of the field cover soil placement technique, applied pressure, and subgrade material on wrinkle deformations and the fate of the gap beneath the wrinkle were examined. Increasing the applied vertical pressure produced relatively small wrinkle deformations, even at pressures of 3000 kPa due to the high degree of stiffness sustained in the small and narrow wrinkles tested. The gap beneath a 10-mm-high and 55-mm-wide wrinkle was eliminated from downward wrinkle deflection and upward foundation displacement for a hydrated geosynthetic clay liner beneath the wrinkle. Displacements along a 66-m-long, 3H:1V geosynthetic lined landfill side slope are reported during installation of a gravel drainage layer and subsequent waste placement. During construction of the gravel drainage layer, large downslope displacements were detected in the gravel, geogrid, and geotextile (up to 420 mm), with only minor movements in the geomembrane (less than 35 mm). Placement of waste (to-date 2/3rd up slope) has generated only small (1-2 mm) relative displacements between the gravel and geomembrane and the maximum geomembrane tensile strain was measured to be under 0.2% after 1.6 years of monitoring.