by Every person who pays attention to learning pays close attention to the role of the bolt support components of the “coal mine safety knowledge learning platform”, which is put on the top of the “coal mine safety knowledge learning platform”.
Coal miners must know! Bolt support is composed of bolt body, supporting plate and nut, anchor agent, steel belt and metal mesh.
The role of bolt support is completed by these components.
Therefore, it is necessary to analyze the role of bolt support components separately.
01 The role of the anchor rod body for the anchor rod body itself, because the size of the length direction of the rod body is much larger than the size of the other two directions, it belongs to the rod body in mechanics.
This kind of member can provide two functions, the first is tension, and the second is shear.
The bending resistance and compression resistance of the rod body are very small and can be ignored.
(Bolt body) For the bolt body with a common diameter of 20mm, the breaking load of round steel (Q235), high-strength deformed steel (BHRB400) and ultra-high-strength deformed steel (BHRB600) are 119.4KN, 179.1KN and 251.3KN respectively, and the latter two are 1.5 and 2.1 times of the former.
According to material mechanics, for plastic materials, the shear strength is generally 0.6~0.8 times of the tensile strength.
For the bolt body with a diameter of 20mm, the shear load of round steel (Q235), high-strength deformed steel (BHRB400) and ultra-high-strength deformed steel (BHRB600) is 83.6KN, 125.3KN and 175.9KN respectively.
02 The role of the anchor plate The anchor plate is an important component of the anchor rod, which has a great impact on the role of the anchor rod support.
The supporting plate has two aspects: one is to apply a certain torque to the nut to make the supporting plate press the roadway surface, provide the pre-tightening force for the bolt, and spread the pre-tightening force to the coal and rock mass around the bolt, so as to improve the stress state of the surrounding rock, inhibit the separation of the surrounding rock, the sliding of the structural plane and the opening of the joint fissure, and realize the active and timely support function of the bolt; The second is that the surrounding rock deformation causes the load to act on the supporting plate, which transfers the load to the anchor rod body, increases the working resistance of the anchor rod, and gives full play to the role of the anchor rod in controlling the surrounding rock deformation.
The mechanical properties of the supporting plate should match the properties of the anchor rod body to fully play the supporting role of the anchor rod.
Insufficient strength of the supporting plate, poor installation quality and large eccentric load will significantly reduce the effect of the anchor rod.
For end-anchored anchor bolts, the supporting plate is the component that the rear of the anchor rod contacts with the surrounding rock.
The anchor rod is applied with preload through the supporting plate, and the surrounding rock load is transferred to the anchor rod body.
The supporting plate itself fails, and the surrounding rock under the supporting plate is loose and falls off, which causes the supporting plate not close to the surface, which will cause the anchor rod to lose its support function.
For the lengthened anchor bolt, the role of the supporting plate is also important.
The pre-tightening force is applied to the anchor bolt by pressing the roadway surface with the supporting plate.
The pre-tightening force has an impact on the working resistance and stress distribution of the anchor bolt and improves the support effect.
The supporting plate has obvious influence on the stress distribution of the full-length anchor bolt.
When there is no supporting plate, the axial force of the bolt is zero at the roadway surface, reaches the maximum at a certain depth, and the shear force is zero at the maximum axial force; When there is a supporting plate, due to the preload exerted by the anchor rod and the force exerted by the surrounding rock on the anchor rod body through the supporting plate, the axial force of the anchor rod reaches a certain value at the roadway surface, and the position with the largest axial force of the anchor rod moves towards the orifice, closer to the roadway surface.
(Arched anchor bolt supporting plate) 03 The role of anchor agent is to bond the rock on the borehole wall with the rod body, so that the anchor rod can play a supporting role.
At the same time, the anchoring agent also has certain shear and tensile strength, and it can reinforce the surrounding rock together with the anchor rod.
(Numerical anchoring agent) The tensile strength of resin anchoring agent in China is generally 11.5MPa.
If the anchor rod is not installed in the hole with diameter of 28mm and only resin anchoring agent is injected, the anchoring agent can provide 7.08KN tensile resistance.
If the rod body with a diameter of 20 mm is installed in a hole with a diameter of 28 mm, the anchoring agent can provide 3.47KN tensile resistance.
It can be seen that the tensile resistance provided by the anchoring agent is far less than that of the anchor rod.
The tensile strength of resin anchoring agent is generally 35MPa.
If the bolt is not installed in the hole with diameter of 28mm and only resin anchoring agent is injected, the anchoring agent can provide 21.54KN shear resistance.
If the rod body with a diameter of 20 mm is installed in a hole with a diameter of 28 mm, the anchoring agent can provide 10.55 KN of shear resistance, which is 12.4%, 8.4% and 5.9% of the shear load of round steel (Q235), high-strength deformed steel (BHRB400) and ultra-high-strength deformed steel (BHRB600).
It can be seen that the anchoring agent can provide certain shear resistance.
The steel band is an important component in the bolt support system, and plays a key role in improving the overall support effect of bolt support and maintaining the integrity of surrounding rock.
The function of steel belt is mainly shown in the following three aspects: 1) The pre-tightening force of anchor bolt and the diffusion effect of working resistance.
The action of a single bolt on the roadway surface can be approximately regarded as a point load.
The steel belt can expand the action range of the bolt, realize the diffusion of the bolt preload and working resistance, and make the load tend to be uniform.
2) Support the roadway surface and improve the stress state of surrounding rock.
The steel belt provides support for the roadway surface, inhibits the separation of shallow strata and the opening of cracks, maintains the integrity of surrounding rock, reduces the tensile damage caused by the bending of rock strata, improves the stress state of rock strata, and prevents loose rock blocks from falling off between bolts.
3) Balance the stress of anchor bolts and improve the overall support function.
The steel belt connects several bolts together, which can balance the stress of the bolts, form a combined support system, and improve the overall support capacity.
(Steel band) 05 net is generally considered to be used to maintain the surrounding rock between the anchor bolts and prevent loose small rock from falling.
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