A telescopic device includes 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 with U-shaped openings thereof opposite to each other to define an accommodating space; a first spring located in the accommodating space and abutting against the first and second U-shaped connectors, respectively; an elastic pin with two ends thereof extending through the first through holes and engaging into one of the plurality sets of adjustment slots; and an initial fixing pin being detachably connected to the first and second U-shaped connectors. A telescopic annular tunnel steel arch includes an upper arch, two lower arches and two telescopic devices connecting two ends of the upper arch to the two lower arches, respectively.

A device for connecting the structural elements, in particular elements of ribs used to support and to consolidate an excavation, reticular structures and similar, comprises at least a first housing (4; 44; 403; 411) having a cavity (14; 414; 144) and capable of being associated with a first structural element (2; 20; 200; 121), at least one connection body (5; 56; 511) having at least one insertion portion (119; 58; 591) for insertion in the said cavity (14; 414; 144) of the said first housing (4; 44; 403; 411) and capable of being associated with a second structural element (3; 30; 131), and locking means (11, 12, 13, 15, 17; 60, 61, 62, 63, 47; 621, 623, 653) for locking the said insertion portion (119; 58; 591) of the said connection body (5; 56; 511) inside the said cavity (14; 414; 144). The housing may be arranged in a cup-shaped element and may be linked in a revolving/hinging manner with the connection body.