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Bolt

(1) Bolt suspension: bolt through the weak, loose, unstable rock and soil body, anchoring in the deep as stable rock and soil body, provide enough tension, overcome the weight of sliding rock and soil body and sliding force, prevent cave wall slip, collapse.

(2) Extrusion reinforcement effect: after the bolt is stressed, a compression zone is formed in a certain range around it. The bolts are arranged in an appropriate way so that the compression zones formed by adjacent bolts overlap each other to form compression zones. The loose strata in the compression zone are strengthened by bolt to enhance the integrity and bearing capacity.

(3) Composite beam (arch) effect: after the bolt is inserted into the stratum at a certain depth, the strata under the action of the anchoring force squeeze each other, the interlayer friction resistance increases, and the internal stress and deflection decrease greatly, which is equivalent to turning the simple composite beam (arch) into composite beam (arch). The flexural stiffness and strength of composite beams (arches) are greatly improved, thus enhancing the bearing capacity of the stratum. The greater the anchoring force provided by the bolt, the more obvious the effect.

(4) bolt length: the total length required when the bolt can effectively play its role in accordance with the design. When calculated according to suspension action, it is the sum of anchorage length, reinforcement length and exposed length. When calculated according to the combined beam (arch) function, it is 1.2 times the sum of the combined beam (arch) height and exposed length. In actual value, additional length increased due to uneven excavation contour should also be considered.

(5) Anchorage length: the length of anchor bolt in stable stratum can be selected according to experience or calculation. According to the experience of selection, consider the anchorage mode and bolt diameter. When selecting according to calculation, the bond between mortar and bolt and the bond between mortar and hole wall should be considered.

(6) Reinforcement length: according to the height of the surrounding rock suspended along the direction of the bolt, or the height of the surrounding rock load, can also be used to determine the thickness of the loose circle measured by acoustic wave and other testing technology.

(7) Bolt pull test: one of the methods of inspecting bolt construction quality and determining bolt pull force. Before the bolt is covered with shotcrete, the bolt tension gauge or torsional torque wrench is used to measure it directly. After clamping the bolt, pressure slowly and evenly until the pressure gauge reading reaches the value corresponding to the design value, or make the bolt loose, generally do not do destructive test. After the bolt is covered with shotcrete, it is proved by bolt detector and then measured by planing. The number of test bolts should be sampled as per 30-50 meters of tunnel length or 300 bolts in a group, and each group should not be less than 3 bolts, which should be evenly selected from a row of bolts in the same section at the checkpoint.

Anchor rod is the rod system structure of rock and soil reinforcement.

Through the longitudinal tension action of the bolt, the shortcoming that the tensile capacity of rock and soil is much lower than the compressive capacity can be overcome.

On the surface, it restricts the separation of rock and soil mass from the original.

Macroscopically, it increases the cohesiveness of rock and soil.

From the mechanical point of view, it is mainly to improve the cohesion C and internal friction Angle φ of surrounding rock mass.

In essence, the bolt is located in the rock and soil body and forms a new complex. The bolt in this complex solves the shortcoming of low tensile capacity of surrounding rock mass. Thus, the bearing capacity of rock mass itself is greatly strengthened.

Bolt is the most basic part of roadway support in contemporary underground mining, which binds the surrounding rock of the roadway together and makes the surrounding rock itself.

Support itself now bolt is not only used in mines, but also used in engineering technology, active reinforcement of slopes, tunnels, DAMS and so on.

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