Abstract: Apparatus for forming a high shear strength clay liner comprising two synthetic geotextiles surrounding a semihydrated layer of swellable clay. The apparatus includes two parallel needle bars each carrying a row of needles reciprocating in opposed directions and cooperating with a reciprocating needle plate having a plurality of parallel fingers and a looper bar with a plurality of parallel looper plates rocking on an axis to form loops which can be melted to form protruding knots.

Abstract: A high shear strength clay liner comprising two synthetic geotextiles (1a, 1b) and a semihydrated layer (1c) of swellable clay therebetween with fastening means (5) arranged in such a pattern of connecting threads to form pockets (7) through the clay layer. The pattern comprises rows of independent fasteners arranged according two intersecting directions. The fasteners have knots (8) at their ends protruding from the surface of the liner. The invention also comprises a method and a machine for forming the independent fasteners by means of two parallel needle bars (104a, b) each carrying a row of needles (105) reciprocating in opposed directions and cooperating with a reciprocating needle plate (109) having a plurality of parallel fingers (110) and a looper bar (117) with a plurality of parallel looper plates (118) rocking on its axis to form loops (5a, 5b) which can be melted into protruding knots (8).