A device to give better support in underground mining operations. It can be anchored more firmly than conventional bolts because the principle of explosive forming enables the anchor to grip the sides of the borehole along its entire length, if necessary. The key to the design is a seamless steel anchoring tube, welded to the threaded end of the bolt. Exploding a small charge inside the tube makes it expand to fit tightly in the borehole. Water, wax, or a similar buffer surrounds the charge to distribute the force of the explosion evenly and prevent it from rupturing the tube. Its use may permit mining of mineral deposits formerly considered uneconomic because of the hazards encountered in loose rock formations.