a geomembrane comprising a unitary structure fabricated by co - extrusion including a center core , a thermoplastic adhesive layer secured on one side of the center core , and a textured layer secured on the opposite side of the center core . the geomembrane is utilized in the manufacture of a liner for earthen constructions by employing the thermoplastic layer of the geomembrane to secure the geomembrane to a geosynthetic clay liner .