EXTENSIBLE-RETRACTABLE DEVICE AND ANNULARLY EXTENSIBLE-RETRACTABLE TUNNEL STEEL ARCH

Disclosed in the present invention are an extensible-retractable device and an annularly extensible-retractable tunnel steel arch. The extensible-retractable device comprises: a first U-shaped connecting member, both sides of which are provided with a plurality of sets of adjusting slots arranged in an adjustment direction; a second U-shaped connecting member, both sides of which are provided with first through holes, the second U-shaped connecting member being inserted into the first U-shaped connecting member, and U-shaped openings of said connecting members facing each other so as to form an accommodating space; first springs, which abut against both the first U-shaped connecting member and the second U-shaped connecting member, and are located in the accommodating space; an elastic pin, both ends of which pass through the first through holes in the two sides and then inserted into one set of the adjusting slots; and an initial fixing bolt which is detachably connected to the first U-shaped connecting memb