Double-sided drain liner

A landfill cap for covering a landfill, the landfill cap comprising:

• a gas-venting geotextile for facing the landfill;
• a double-sided drain liner having a flexible fluid impervious barrier sheet with a lower surface facing the gas-venting geotextile and an upper surface opposite the lower surface, lower truncated projections projecting from the lower surface of the barrier sheet and having blunt surfaces extending transverse to projecting directions of the lower truncated projections from the barrier sheet, the blunt surfaces being supported in nonpenetrating contact with the gas-venting geotextile so that the barrier layer is spaced from the gas-venting geotextile and so that gas venting passages are defined between the lower truncated projections, upper truncated projections projecting from the upper surface of the barrier sheet and having blunt surfaces extending transverse to projecting directions of the upper truncated projections from the barrier sheet;
• and
• a fluid permeable layer supported in nonpenetrating contact on the blunt surfaces of the upper truncated projections of the double-sided drain liner so that liquid drainage passages are defined between the upper truncated projections.

A method for controlling gas and liquid flows at a landfill, comprising:

• applying a gas-venting geotextile over the landfill;
• providing a double-sided drain liner having a flexible fluid impervious barrier sheet with opposite first and second surfaces, first truncated projections projecting from the first surface and second truncated projections projecting from the second surface, the first and second truncated projections having blunt surfaces extending transverse to projecting directions of the first and second truncated directions;
• applying the double-sided drain liner on the gas-venting geotextile so that the blunt surfaces of the first truncated projections are supported in nonpenetrating contact on the gas-venting geotextile with the barrier layer spaced from the gas-venting geotextile while forming gas venting passages between the first truncated projections, second truncated projections projecting from the second surface of the barrier sheet;
• and
• applying a fluid permeable layer on the double-sided drain liner so that the fluid permeable layer is supported in nonpenetrating contact on the blunt surfaces of the second truncated projections of the double-sided drain liner with liquid drainage passages being defined between the second truncated projections, wherein gas generated from the landfill flows through the gas venting passages between the first truncated projections to gas collection points and so that liquid precipitation flows through the liquid drainage passages between the second truncated projections to liquid collection points.