E21D—SHAFTS; TUNNELS; GALLERIES; LARGE UNDERGROUND CHAMBERS
E21D15/00—Props; Chocks, e.g. made of flexible containers filled with backfilling material
E21D15/14—Telescopic props
E21D15/28—Telescopic props with parts held relatively to each other by friction or gripping
E21D15/30—Telescopic props with parts held relatively to each other by friction or gripping by means expanded or contracted by pressure applied through the medium of a fluid or quasi- fluid, e.g. rubber
E21D15/306—Telescopic props with parts held relatively to each other by friction or gripping by means expanded or contracted by pressure applied through the medium of a fluid or quasi- fluid, e.g. rubber by means of a liquid