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.