PURPOSE: To surely protect lock bolts from rust.

CONSTITUTION: A lock bolt main body 3 is inserted into a drilled hole 12 into which a hardening agent is injected by excavating a soil and the surrounding parts of the lock bolt main body is covered with a corrosion proof sheet 4 before the hardening agent is hardened. Artificial resin or stainless steel can be adopted for the material of the corrosion proof sheet 4. As for their shapes, various shapes can be adopted as well. For example, flat-shaped straight sheets on the peripheral surfaces or projected and recessed spiral sheath on their peripheral surfaces. A desired extended portion L1 from the ground surface of the lock bolt main body 3 and a desired projected portion L2 are covered with the sheath 4. It is suitable that the L1 exceeds 1m while the L2 exceeds 10cm. The outer and inner surfaces of the sheath 4 are filled with a hardening agent, such as cement paste and hardened. The corrosion proof sheath 4 is laid out around the lock bolt main body 3 preliminarily. It is also possible to inject a hardening agent into drilled holes by way of the corrosion sheath 4.