Solution

Use adhesive material to anchor one end in the formation, and fix the outer end (anchor head) to the tension rod on the engineering structure. Rock anchor rods are anchored to engineering structures through anchor heads. The tensile force borne by the steel tie rod is first transmitted to the bonding material through the surrounding grip force of the tie rod, and then transmitted to the stable formation in the anchorage zone through the frictional resistance of the surrounding strata of the anchorage section. Rock and soil anchor rods have the advantages of fully utilizing the strength and self stabilization ability of the formation, simplifying the foundation structure and support structure, reducing the self weight of the structure, reasonable stress, occupying less space, shortening the construction period, and reducing project costs.

The types of anchor rods are classified according to their manufacturing methods, including simple anchor rods and prestressed anchor rods. Divided by their service life, there are temporary anchor rods (with a service life of less than 2 years) and permanent anchor rods (with a service life of more than 2 years). According to the shape of the anchor body, there are cylindrical, end enlarged head, and continuous spherical anchor rods. According to the force transmission method of the anchor body, there are tension type, pressure type, and shear type anchor rods.

The anchor rod structure is simple. The anchor rod consists of an anchor rod and a rod body. The prestressed anchor rod consists of an anchor head, a free section of the rod body, and an anchored section of the rod body (Figure 1). The anchor head consists of a threaded end rod, a nut, and a cushion plate, and its function is to fix the anchor rod to the engineering structure; The free section of the rod is the section where the rod is not bonded to the formation, and its function is to apply prestress to the rod; The anchoring section of the anchor rod is a section that uses bonding materials to bond the rod to the formation, and its function is to transfer the force borne by the anchor rod to the formation.

The main design contents of anchor rod include: determining the bearing capacity of anchor rod design, anchor rod layout, anchor rod parameters, and overall stability verification of anchor rod and engineering structure.

The ultimate bearing capacity of the designed anchor rod should be determined through on-site testing, and can be determined using calculation methods when there are no testing conditions. In relatively intact hard rock layers, the ultimate bearing capacity Tu of anchor rods can be calculated according to the formula Tu=π dLeu; In weathered rocks and soil layers, the ultimate bearing capacity Tu of anchor rods can be calculated according to the formula Tu=π DLe τ; In the formula, d is the diameter of the steel tie rod, D is the diameter of the anchor bolt drilling hole, Le is the effective anchorage length, u is the average grip force of cement mortar on the steel tie rod, and τ is the shear strength of the soil layer around the anchorage section. The ultimate bearing capacity Tu is divided by the safety factor K to obtain the design bearing capacity.