Complex sentence: It is in place from the usally short time from when the tunnel is excavated until it can be lined with a permanent support structure made up of (depending on the period) bricks, concrete, cast iron, or steel.
Split into simpler sentences: It is in place for the usally short time from when the tunnel is excavated until it can be lined with a permanent support structure. The permanent structure may be made up of, depending on the period, bricks, concrete, cast iron, or steel.