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Coal people must know how much the role of bolt support components is! Bolt support is composed of bolt body, supporting plate and nut, anchoring 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 respectively.
01 function of anchor rod body for the anchor rod body itself, the size in the length direction of the rod body is much larger than that in the other two directions, so it belongs to the rod body in mechanics.
This member can provide two functions, the first is tensile, and the second is shear.
As for the bending capacity and compressive capacity of the rod body, it is very small and can be ignored.
(anchor rod body) for the common anchor rod body with diameter of 20mm, round steel (Q235), high-strength deformed steel (bhrb400) and ultra-high-strength deformed steel The tensile breaking loads of (bhrb600) are 119.4kn, 179.1kn and 251.3kn respectively, and the latter two are 1.5 and 2.1 times of the former respectively.
According to material mechanics, for plastic materials, the shear strength is generally 0.6 ~ 0.8 times of the tensile strength.
For anchor rod bodies with a common diameter of 20mm, round steel (Q235), high strength deformed steel (bhrb400) and ultra-high strength deformed steel The shear loads of (bhrb600) are 83.6kn, 125.3kn and 175.9kn respectively.
02 the role of anchor bolt support plate is an important component of anchor bolt, which has a great impact on the role of anchor bolt support.
The of support plate is in two aspects: one is to apply a certain torque to the nut to make the support plate press the roadway surface, provide preload to the anchor bolt, and spread the preload into the coal and rock mass around the anchor bolt, So as to improve the stress state of surrounding rock, restrain the separation of surrounding rock, the sliding of structural plane and the opening of joint fissure, and realize the active and timely support function of anchor bolt; Secondly, the surrounding rock deformation makes the load act on the supporting plate, and the load is transmitted to the anchor rod body through the supporting plate, so as to increase the working resistance of the anchor rod and give 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 in order to give full play to the supporting role of the anchor rod.
Insufficient strength of supporting plate, poor installation quality and large eccentric load will significantly reduce the effect of anchor rod.
For the end anchored anchor bolt, the supporting plate is the component that the tail of the anchor bolt contacts the surrounding rock.
The preload is applied to the anchor bolt through the supporting plate to transfer the surrounding rock load to the anchor rod body.
The supporting plate itself fails, and the surrounding rock below the supporting plate is loose and falls off, resulting in the non close contact between the supporting plate and the surface, which will make the anchor bolt lose its supporting function.
For the lengthened anchor bolt, the role of the supporting plate is also important.
The supporting plate compresses the roadway surface to apply the preload to the anchor bolt.
The preload has an impact on the working resistance and stress distribution of the anchor bolt, so as to improve the support effect.
The supporting plate has an obvious influence on the stress distribution of the full-length anchor bolt.
When there is no supporting plate, the axial force of 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 applied by the anchor rod and the force of the surrounding rock acting 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 maximum axial force of the anchor rod moves to the orifice, which is closer to the roadway surface.
(arch anchor bolt support plate) 03 role of anchoring agent the role of anchoring agent is to bond the rock of borehole wall with the rod body to make the anchor bolt play a supporting role.
At the same time, the anchoring agent also has certain shear and tensile capacity to strengthen the surrounding rock together with the anchor bolt.
(numerical anchoring agent) the tensile strength of resin anchoring agent in China is generally 11.5MPa.
If the hole with diameter of 28mm is not installed with anchor bolt and only resin anchoring agent is injected, the anchoring agent can provide 7.08kn tensile force.
If the rod with diameter of 20mm is installed in the hole with diameter of 28mm, the anchoring agent can provide 3.47kn tensile force.
It can be seen that the tensile force provided by the anchoring agent is far less than that of the anchor bolt.
Tree Generally, the tensile strength of grease anchoring agent can be 35MPa.
If no anchor bolt is installed in the borehole with diameter of 28mm and only resin anchoring agent is injected, the anchoring agent can provide shear resistance of 21.54kn.
If a 20mm diameter rod is installed in a 28mm diameter borehole, the anchoring agent can provide shear resistance of 10.55kn, They are round steel (Q235), high strength deformed steel (bhrb400) and ultra-high strength deformed steel The shear load of (bhrb600) is 12.4%, 8.4% and 5.9% of the shear load.
It can be seen that the anchoring agent can provide certain shear resistance.
04 steel belt 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 role of steel belt is mainly reflected in the following three aspects: 1) the diffusion of bolt preload and 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 bolt preload and working resistance, and make the load tend to be uniform.
2) Supporting roadway surface and improving surrounding rock stress state.
The steel belt provides support for the roadway surface, inhibits the separation and crack opening of shallow rock strata, maintains the integrity of surrounding rock, reduces the tensile damage caused by rock stratum bending, improves the stress state of rock strata, and prevents loose rock blocks between bolts from falling.
3) Balance the stress of anchor rod and improve the overall support effect.
The steel belt connects several anchor bolts together, which can balance the stress of anchor bolts, form a combined support system, and improve the overall support capacity.
The role of (steel belt) 05 mesh is generally considered that the mesh can be used to maintain the surrounding rock between anchor bolts and prevent loose small rock blocks from falling.
In fact, the role of mesh is far more than this, especially under the conditions of high ground stress and broken surrounding rock, the mesh is an indispensable and important component in the anchor bolt support system.
The role of (metal mesh) mesh is mainly reflected in the following three aspects: 1) maintain the surrounding rock between anchor bolts to prevent the collapse of broken rock blocks.
2) close to the roadway surface to provide a certain support force (the existing research results show that the diamond metal mesh currently used in China can provide 0.01Mpa support force under the condition of ensuring the construction quality), which can improve the stress condition of the rock stratum on the roadway surface to a certain extent.
At the same time, the load of the rock stratum between the anchor bolts is transmitted to the anchor bolts to form an overall support system.
3) the mesh can not only effectively control the deformation and damage of the shallow surrounding rock of the roadway, but also Deep surrounding rock also has good supporting effect.
In the case of network, although the surrounding rock on the roadway surface has been damaged, it is not loose and straddling.
It can be used as the force transmission medium to make the deep surrounding rock of the roadway still in the three-dimensional stress state, improve the residual life strength of the rock mass, significantly reduce the scope of the loose and broken area of the surrounding rock, and ensure the anchoring effect of the anchor bolt.
The laboratory test data show that when the specimens strengthened with anchor mesh are damaged under load, they crack into dense thin cylindrical rod system, the residual body is relatively complete, and the residual strength is about 1 / 4 of the ultimate compressive strength; The residual body of the specimen strengthened with non mesh bolt is incomplete and has no obvious residual strength.
If there is no metal mesh or the metal mesh fails, the surrounding rock damage will develop from the surface to the deep, gradually break, loosen and lose strength, resulting in the collapse of surrounding rock and the failure of anchor rod.
Disclaimer: 1, part of the official account..
