Abstract: A liner adapted to be installed against an earth surface bordering a cavity such as a cave or a hole in the ground to prevent flow of fluid into and from the surrounding earth. The liner is a flexible, inextensible, fluid impervious material which is a wall of a closed hollow member adapted to be inflated after installation in the cavity to expand it with a fluid under pressure until its wall presses against the earth wall about the cavity. A non-woven fabric layer between the earth and flexible inextensible wall facilitates sliding of the wall over the earth surface. The clamps have spaced elongated cylindrical members such as tubes disposed along the cavity wall and secured to the earth wall with base members having one end embedded in the earth and an opposite end fixed to the tube. An arcuate shaped clamping member is associated with the tube to form a jaw for clamping the liner between the tube and arcuate shaped member.

Abstract: A flexible collapsible dam for a watercourse is provided with one or more conduits for carrying water from upstream to downstream of the dam and thereby regulate the depth of water flowing over the dam to reduce vibrations of the dam caused by the water flowing over it. The water which is conveyed around the dam is discharged immediately downstream of the dam to prevent the deposit of objects on the bottom or banks of the watercourse where the collapsed dam contacts said bottom and banks.

Abstract: A collapsible dam comprising a flexible substantially rectangular substantially water repellant web stretched across the width of a waterway with one edge fixed to the bottom of the waterway and the opposite edge supported by a rigid rod adjacent to the water surface. The rigid rod is hinged with respect to the bottom of the waterway and connected at one end to a pressure actuated piston-cylinder assembly which moves the opposite end of the rod and attached web upwardly while the fixed edge remains submerged against the bottom of the waterway.

Abstract: A cavity in the earth such as a reservoir, tunnel or the like is lined with a flexible, fluid impervious sheet such as a rubberized fabric supported by a grid-like skeleton structure having distorted elongated resilient structural members which are under tension and press the liner against the walls of the cavity. The members of the skeleton structure are made of a material which resists permanent distortion. The liner is disposed between the skeleton structures and the wall of the cavity and is fastened at spaced points to the wall of the cavity.

Abstract: An artificial dam or barrage which is adapted to be moved vertically from e bottom of the waterway in which it is installed is provided with a sheet of flexible material fixed to the bottom of the waterway and suspended with flexible cables above the bottom of the waterway.

Abstract: A non-woven fabric having a fibrous surface similar to that of leather and high mechanical characteristics so that it is adapted for use as a substitute for leather in industrial applications is prepared by saturating a matt of fibers with an elastomeric polyurethane which can be cross-linked with moisture. The so obtained composite laminar structure, having a thickness of from 0.1 to 10 mm, has a density of about 0.85 to 1.4 g/cm.sup.3, a hardness of 85 to 95 Shore A and a tensile strength of about 1.5 to 2.5 kg/mm.sup.2, and possesses a water-vapor permeability in the range of about 30 to 100 g/m.sup.2 /24 hours according to DIN 53 333.