A Field Scale Evaluation of Wrinkles in Exposed HDPE Geomembranes
Chappel, Melissa Jill
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Intact geomembranes are barriers to advective aqueous flow and are often a key component in the design of composite bottom liner and cover systems. During installation, the combination of solar heating, a high coefficient of expansion, and the stiffness of high density polyethylene (HDPE) causes the geomembrane to expand and buckle, forming wrinkles (waves). Up to 20 – 30% of the area of the geomembrane may be below hydraulically connected wrinkles, which could substantially increase leakage through the composite liner if there is a hole on or near a wrinkle in the connected network. To quantify wrinkles at the field scale, a technique for low altitude aerial photography and photogrammetric correction was developed. Wrinkles were quantified for nine field cases involving a variety of installation (area, geomembrane thickness and texture, orientation, subgrade) and weather conditions. The technique was used to quantify the geometry of individual wrinkles (length, width and area) and, more importantly, the length of the longest hydraulically connected wrinkle at each time. Hand measurements of height and width were conducted at five of the cases. Air temperature, solar radiation, and geomembrane surface temperature was recorded as permitted by site conditions and instrumentation. The longest measured connected wrinkle was 5330 m on a 0.61 ha slope. For a 1.5-mm-thick geomembrane, the average wrinkle width over a GCL was 0.20-0.23 m and 0.24 – 0.32 m over a CCL. The average hand-measured wrinkle height was 0.06 m, and the tallest wrinkle measured was 0.18 m. The longest connected wrinkle length was <200 m when the sum of the wrinkle lengths was < 580 m (<8% of the area of the geomembrane was wrinkles). The reported connected wrinkle lengths are significantly longer than previously reported values. When used as input into an existing theoretical leakage solution, these very long wrinkles can explain previous large field measurements of leakage. The results also suggest that simply limiting the time of day when cover soil is placed and/or reducing the area in which wrinkles can form may greatly reduce the length of connected wrinkles after covering.