Bolt support is widely used in underground engineering, and its usage is increasing year by year. Whether prestressed structure can be formed is the standard to judge the rationality of bolt support. The thickness and bearing capacity of prestressed structure is the key to control the deformation of surrounding rock, which depends on the arrangement of components and the magnitude of pre-tension. The pre-tightening force of domestic metal anchor under the torque of 300k.m is generally 10-30kn. Due to the influence of blasting, the fastener is loose, resulting in repeated loosening of surrounding rock and poor supporting effect. At present, there are three kinds of similar metal anchors in China. One is the expansion shell type quick installation anchor described in patent No.2000200 1 for mining roadway. 9922 1864.0. The rod body is made of round steel, and the outer end is threaded, which is fastened with a tray and a nut. The rod end is machined into a frustum shape, and a cylindrical expansion shell with a groove is put on when it is installed. Its disadvantages are: 1, the rod end is a frustum, and the diameter of the big end of the frustum is almost equal to the diameter of the drilling hole, so it is impossible to use a resin cartridge for lengthening anchorage; 2. The expansion shell is cylindrical, and the friction with the shaft wall is low, so the anchor rod is easy to loosen and lose the function of prestress. The second type is a common steel bar anchor, the outer end of which is fastened with a tray and a nut matched with the steel bar screw, and the tail is anchored with a resin cartridge. Its disadvantages are: 1, the thread at the outer end depends on the thread of the rod body, the pitch is large, and the prestress is small when fastening; 2. The tail is anchored by resin cartridge, and the installation speed of the cartridge is slow after curing. The third is the inverted wedge anchor. The anchor tail is fastened with matching small wedges, which is limited by its structure. Its disadvantage is that the prestress is small. Therefore, the mechanical anchoring device of fully prestressed metal anchor rod was invented to overcome the above problems.
Two. Technical characteristics (or advantages) and application fields
Under the action of 300n.m torque, the pre-tightening force of the technical device can be completely increased by 2-8 times, reaching 20- 100 kN, and the high pre-tightening force can be achieved by simple manual operation. Moreover, the rod body in the hole has pre-tightening force in the whole length except the anchor core connection section, which effectively controls the deformation of surrounding rock. After the rod body of the anchor rod is rotated in the opposite direction, the rod body is retracted and the expansion force is eliminated, the anchor rod can be recycled and reused.