The Performance of HDPE Geomembrane Fusion and Bituminous Geomembrane Seams

Abstract

The properties of geomembrane (GMB) sheet material and seams are critical factors controlling the design life of a constructed barrier system. In particular, the resistance to stress cracking and retention of antioxidants in the GMB are critical factors to both the short and long-term performance. Thus, stress crack resistance (SCR) and standard oxidative induction time (Std-OIT) test were performed on both the sheet and fusion seams. SCR experiments on high density polyethylene (HDPE) GMB seams found that the exclusion of a predetermined defect (i.e., a notch) allowed the GMB seam to fail preferentially where it would in the field, in addition to providing failure times that included the seam heat-affected zone (HAZ) within the crack initiation region of the test specimen. Seam squeeze-out geometry and the presence of discontinuities within the squeeze-out bead were found to influence unaged seam SCR, with discontinuities running parallel to the direction of the seam creating lower seam SCR values on average. Seam squeezeout is shown to be susceptible to Std-OIT loss, with some seams showing near complete antioxidant depletion for specific welding parameter combinations. Seam thickness reduction was found to correlate with the degree of antioxidant depletion within a seams squeeze-out bead, with thickness reductions greater than 0.6mm for a 1.5mm HDPE geomembrane generally coinciding with significant antioxidant depletion. Adherence of seam squeeze-out to the GMB seam’s HAZ resulted in faster time to nominal failure (tNF) compared to the unnotched sheet material, with three seams exhibiting squeeze-out adherence having a tNF ~21-35% faster than that of the sheet material, while seams without adhered squeeze-out beads showed a tNF similar to that of the unnotched sheet following immersion tests at 85°C in a synthetic leachate solution. The short-term tensile shear strength and constant tensile load failure times of bituminous geomembrane (BGM) seams are also examined. Tensile shear specimens experienced failure in the sheet material when seams strength was >0.8 times that of the sheet, while all constant tensile load specimens experienced failure within the seam. The presence of geotextile engagement is hypothesized to significantly increase a BGM seams performance when subject to constant tensile loads.