Telescopic device and telescopic annular tunnel steel arch

A telescopic device, comprising:

• a first U-shaped connector with a plurality sets of adjustment slots defined in two sides thereof and arranged along an adjustment direction;
• a second U-shaped connector defining first through holes in two sides thereof, the second U-shaped connector being inserted into the first U-shaped connector, an U-shaped opening of the first U-shaped connector and an U-shaped opening of the second U-shaped connector being opposite to each other, so as to define an accommodating space;
• a first spring being located in the accommodating space and abutting against the first U-shaped connector and the second U-shaped connector, respectively;
• an elastic pin with two ends thereof extending through the first through holes at the two sides and engaging into one of the plurality sets of adjustment slots, the elastic pin being adjustable unidirectionally among the plurality of sets of adjustment slots which are arranged along the adjustment direction under a pushing force of the first spring;
• and
• an initial fixing pin being detachably connected to the first U-shaped connector and the second U-shaped connector, wherein when the fixing pin connects the first and second U-shaped connectors, the first spring is in a compressed state;
• and when the fixing pin is disassembled, the first spring provides the pushing force and the elastic pin is adjusted unidirectionally to a balanced position among the plurality sets of adjustment slots which are arranged along the adjustment direction.