Tunnel-support systems made of steel are roughly of five types: continuous rib; rib and post; rib and wallplate; rib, wallplate, and post; and full circle rib. (1) A continuous rib system is usually made in two pieces for maximum speed of erection, lowest first cost, and lowest erection cost. Sometimes used in three or four pieces to meet special conditions and the following methods of attack: full face, side drift, and multiple drift. (2) A rib and post system is employed with the following methods of attack: full face in tunnels whose roof arch makes an angle with the sidewall; multiple drift and side drift in tunnels of such large size that two-piece continuous ribs cannot be shipped and/or handled; and heading and bench and top heading for support in the drift (with truss panels) for early support to roof. (3) In a rib and wallplate system, the rib is also usually made in two pieces for maximum speed of erection, lowest first cost, and lowest erection cost. It is sometimes used in three or more pieces to meet special conditions and with the following methods of attack: heading and bench, top heading, and full face. This type is esp. applicable to circular and high-sided tunnel sections where only a light roof support is needed. (4) In a rib, wallplate, and post system, these elements of support are used with the following methods of attack: heading and bench and top heading--for quick support to a roof; side drift--in large tunnels with bad rock conditions requiring quick support; and full face--for favorable rock where support is not needed tight to the face, for a tunnel whose roof makes an angle with the sidewall, and where post and rib spacing differ; and (5) A full circle rib--this method is used with the following attack: full face-- in tunnels in squeezing, swelling and crushed rock, or any rock that imposes considerable side pressure, also where bottom conditions make it impossible to carry roof loads on foot blocks, and in earth tunnel conditions sometimes encountered in rock tunnels; and heading and bench--under earth tunnel conditions with joints at spring line. The inverted strut is used where mild side pressures are encountered and also to prevent the bottom from heaving. A full circle with ribs closely spaced is heavily lagged for heavy loads associated with squeezing conditions.