drill rods for trenchless guided and directional drilling are often subjected to bending forces while being subjected to greater tensile and torsion forces. When the drill rods passes through the curved section, the drill rods is forced to bend, the inner side of the arc is subjected to compressive stress, and the outer side of the arc is subjected to tensile stress. When the drill rods rotates in the curved section, the rod body is subjected to the tension and compression alternating stress, and the smaller the drilling radius of curvature, the greater the alternating stress.

Studies have shown that after this alternating stress reaches a certain value, it is extremely easy to cause fatigue cracks in the drill rods. Fatigue cracks at the beginning of drill rods Fatigue cracks are very small and difficult to find with the naked eye, but fatigue cracks develop extremely fast, and finally appear as sudden brittle fractures. Tests have proved that fatigue fracture of drill rods subjected to alternating stress is the main reason for the failure of trenchless drill rods. A lot of drill rods fracture accidents during the construction of pilot holes confirm this conclusion.

At present, many of our country’s trenchless construction teams are experienced and highly qualified professional companies, but most of them are improvised teams without any construction experience and technology. They often have not even heard of the radius of curvature of the drill rods. , Letting them direct the trenchless construction is the main reason for the man-made aspect of drill rods fracture.