Design guidance for protection of geomembrane liners in landfill applications

A new method of evaluating strains and predicting required protection layers that are placed over geomembranes is developed based on the combined effects of the clay strength and stiffness and the cushioning effect of a nonwoven protection layer. Plots giving the required geotextile protection for different maximum strains are presented for expected landfill pressures under 300 kPa for angular, 38 mm gravel placed above a geomembrane liner for both drained and undrained loading conditions of the clay. A similar plot is also given for tire-derived aggregate placed above the liner for pressures under 500 kPa for undrained loading conditions. All tests were conducted at room temperature. For all cases, nonwoven geosynthetic protection layers with mass per unit area (MUA) exceeding at least 1200 g/m2 were required to limit long-term strains below current threshold levels. The MUA of the protection layer, for the particular aggregates and geomembranes tested, is dependent on the loading rate, water content relative to optimum, the silt content, and the activity of the clay below.