Abstract: To strengthen the roof of an underground passage such as an adit, drift or gallery of a mine, bores drilled from below into the roof are stuffed with frangible packages of interreacting components of a bonding agent which are subsequently pierced by the tips of anchor bolts introduced into these bores. Each anchor bolt terminates at its lower end in screw threads engaged by a nut which supports a washer, the threads being provided with a discontinuity preventing the detachment of the nut. During emplacement of each bolt, the nut is gripped by a rotating socket wrench which is turned under upward pressure first in a reverse or unscrewing direction, causing the nut to engage the discontinuity and to entrain the inserted bolt to pierce the packages and to stir their contents until the adhesive begins to set, and then in a forward or screw-tightening directing until the washer comes to rest against the roof surface under a pressure which tensions the sealed-in bolt against the surrounding roof structure.