Physical Response of Geomembrane Wrinkles Overlying Compacted Clay

The short-term physical response of a 1.5-mm-thick, high-density polyethylene geomembrane with an artificially formed wrinkle and overlying three different subgrade materials (sand and compacted clay at two initial water contents) are reported. The influence of the subgrade, protection layer, backfill, and applied pressure on the fate of the gap beneath the wrinkle, wrinkle deformations, and local geomembrane indentations is investigated. The gap beneath the geomembrane wrinkle was observed to remain with sand above and below the geomembrane, even at applied pressures of $\mathrm{1,100}\mathrm{kPa}$ . The gap was eliminated with compacted clay as the subgrade, depending on the applied pressure and the clay water content. When the clay was compacted at a water content equal to the standard Proctor optimum $\left({\omega }_{\mathrm{opt}}\right)+4\%$ , the gap was eliminated at pressures greater than $100\mathrm{kPa}$ , whereas the gap remained at $250\mathrm{kPa}$ and was eliminated at $500\mathrm{kPa}$ and larger when compacted at ${\omega }_{\mathrm{opt}}+1\%$ . It was found that the presence of a wrinkle increases the maximum geomembrane strain due to local gravel indentations by 10% as compared to a flat geomembrane. The protection layers tested did not significantly influence the change in height and width of the wrinkle, but did influence the local geomembrane strain. The maximum strain in the geomembrane (at $250\mathrm{kPa}$ with $50\mathrm{mm}$ gravel backfill and the softer clay subgrade) was 42% without protection; 15 and 11% with nonwoven needle-punched geotextiles with mass per unit area of 390 and $\mathrm{1,200}\mathrm{g}∕{\mathrm{m}}^2$ , respectively; and 2% with a 150-mm-thick sand protection layer.