(1) Suspension function: the anchor rod suspends the weak rock stratum on the solid and stable rock stratum above to prevent it from falling off. The direct roof of coal seam roadway is generally weak and thin, which is easy to fall off, while the old roof above it is relatively strong. The anchor rod can pass through the direct roof to reach the old roof and anchor the direct roof to the old roof.

(2) The function of composite beam: A series of anchor rods are anchored in the roadway roof of layered rock, and the thin rock within the anchor rod length is anchored into a rock composite beam, thus improving its bearing capacity. Under the same load, the deflection and internal stress of composite beams are much smaller than those of non-composite beams.

(3) Surrounding rock reinforcement: the rock in the deep surrounding rock of the roadway is in triaxial compression state, while the rock near the roadway is in biaxial stress state, and its strength is less than the former, so it is easy to be destroyed and lose its stability. After the surrounding rock of the roadway is anchored by the anchor rod, the surface rock partially restores the triaxial stress state, which increases its own strength. In addition, the anchor can also increase the shear capacity of the weak surface of the rock stratum, so that the surrounding rock of the roadway is not easy to be destroyed and unstable, which is called surrounding rock reinforcement.

(4) Extrusion connection: the anchor rod extrudes the surrounding rock of the roadway, and pre-stresses the rock to prevent the crack from expanding. In addition, it can also play a role in squeezing and strengthening loose rocks. A simple and interesting experiment was done abroad: a rectangular wooden box was filled with small gravel, and they anchored it with simulated anchor rods. After the bolt was tightened, the wooden box was turned over, but the filled small gravel could not be poured out. Through the prestress of the anchor, a kind of lateral extrusion friction resistance can be generated between the gravel, and there is no cohesive force, which is enough to support the weight of the gravel without falling off, as if the gravel is connected with each other.

(5) The function of squeezing to strengthen the arch of foot: Continue the above experiment. Small broken stones tied with anchor bolts can not only be squeezed together to support their own weight, but also be used as load-bearing structures to support additional loads. Through the loading test, it is found that the tensile stress zone will be generated between the anchor pads of the anchor macadam members after loading, which will make the small macadam loose and fall off to form a dome. When the load increases, the dome will expand and lead to the collapse and disintegration of the load-bearing structure. In order to prevent this situation, fine wire mesh is hung under the anchor pad, which greatly improves the supporting ability of the anchor. When the load increases to a considerable daily inch (repeated load), the failure begins when the barbed wire is cut off. The above tests show that the loose gravel forms a cylindrical compression zone or compression stress zone with cones at both ends around each anchor under the prestress, and these compression zones form a uniform compression strengthening zone with a considerable width in the systematically arranged anchor groups, which is equivalent to a load-bearing structure and supports a considerable load. After installing group and radial anchor rods around the roadway, an arch compression zone or compression strengthening arch is formed in the surrounding rock of a certain thickness range, which makes the surrounding rock of the roadway change from "load" to "load-bearing" structure in support. The thickness of arch compression zone is related to the length and spacing of anchor rods.

Question 2: What is the principle of bolt support? 30 minutes 1, in layered rock, the anchor rod suspends the lower unstable rock from the upper stable rock. The tension of the anchor comes from the suspended rock stratum. 2. In the thin rock stratum without stable rock stratum, the clamping force of the anchor rod will increase the friction between layers, which can prevent the rock from sliding along the layer, thus locking several thin rock strata in a thick rock stratum through the anchor rod. The maximum bending stress and strain in this thick rock beam are inversely proportional to the square of the beam thickness. The thicker the whole rock beam, the smaller the maximum bending stress and strain. At the same time, the strength of the anchor itself also increases the overall shear capacity of the beam. 3. According to the principle of arch-anchor combination, when prestressed anchor is installed in the fractured zone of surrounding rock of donor roadway, conical compressive stress will be formed at both ends of the rod body. If the anchor groups are arranged along the roof, the compressive stress cones formed by each anchor will be staggered and overlapped, forming a bearing arch to prevent the diffusion of the broken zone and bear the radial load exerted by the broken rock on its upper part. The pre-tightening force along the axial direction of the anchor produces circumferential stress in the composite arch, which obviously improves the stress state of the bearing arch and changes the surrounding rock state from uniaxial and biaxial to triaxial compression. In this way, a continuous and uniformly compressed bearing zone is formed in the surrounding rock, thus greatly improving the bearing capacity of the composite arch.

Question 3: There are several principles of bolt support: ① The tensile strength is higher than that of rock and soil; ② One end of the rod can be in close contact with the rock and soil to form a friction (or bonding) resistance anchor.

(3) The other end of the rod * * * outside the rock and soil can form a radial resistance anchor rod for the rock and soil, which can be used as a tensile member deep underground. One end of the pole is connected with the engineering structure, and the other end goes deep into the ground. The whole bolt is divided into free section and anchoring section. Free section refers to the transmission of the tension at the anchor head to the anchorage zone, and its function is to prestress the anchor rod; Anchorage section refers to the area where prestressed tendons are bonded to soil layer through cement slurry, and its function is to increase the bonding friction between anchor body and soil layer, improve the bearing capacity of anchor body, and transfer the tension of free section to the depth of soil layer.

Anchor rod is a bar system structure reinforced by rock and soil. Through the longitudinal tension of the anchor rod, the shortcoming that the tensile capacity of rock and soil is much lower than the compressive capacity is overcome. On the surface, the separation between rock and soil and the original body is limited. Macroscopically, the cohesiveness of rock and soil is increased. From the mechanical point of view, it is mainly to improve the cohesion c and internal friction angle φ of surrounding rock. In essence, the anchor rod is located in the rock and soil, forming a new complex with the rock and soil. The anchor rod in the complex solves the defect of low tensile capacity of surrounding rock. Thereby greatly improving the bearing capacity of rock and soil itself. Bolt is the most basic part of roadway support in contemporary underground mines. It bonds the surrounding rocks of the roadway together and makes the surrounding rocks support themselves. At present, anchor rods are not only used in mines, but also in engineering technology to actively strengthen slopes, tunnels and dams.

Question 4: What is the mechanism of bolt support? By using bolts (from Wuhu or other countries) and pallets, tail pallets, etc. It hits the rock stratum, plays the role of composite beam, combined arch and suspended beam, and increases the strength of the organization!

Achieve structural stability,

Question 5: What are the four principles of bolt support? Bolt is the most basic part of roadway support in contemporary coal mines. It bonds the surrounding rocks of the roadway together and makes the surrounding rocks support themselves.

At present, anchor rods are not only used in mines, but also in engineering technology to actively strengthen slopes, tunnels and dams.

As a tensile member that goes deep into the stratum, the anchor rod has one end connected with the engineering structure and the other end goes deep into the stratum. The whole bolt is divided into free section and anchoring section. Free section refers to the transmission of the tension at the anchor head to the anchor body area, and its function is to prestress the anchor rod. Anchorage section refers to the area where cement paste bonds prestressed tendons with soil layer, and its function is to increase the bonding friction between anchor body and soil layer, improve the bearing capacity of anchor body, and transfer the tension of free section to the depth of soil layer.

According to the materials used, anchors can be divided into: wood anchors, steel anchors, FRP anchors, etc.

According to the anchorage mode, it can be divided into terminal anchorage, extended anchorage and full-length anchorage.

The following are several names of anchor rods.

(1) wooden anchor. There are two kinds of wooden anchors used in China, ordinary wooden anchors and compressed wooden anchors. ?

(2) steel bar or steel wire rope mortar anchor. Cement mortar is used as an adhesive between anchor and surrounding rock. ?

(3) Inverted wedge-shaped metal anchor. This kind of anchor was once one of the most widely used anchor forms. Because of its simple processing, convenient installation and certain anchoring force, this kind of anchor rod is still in use in a certain range. ?

(4) Joint bolts. This is a full-length friction anchor bolt. This kind of anchor rod has the characteristics of simple installation, reliable anchorage, large initial anchorage force and long-term anchorage force increasing with the movement of surrounding rock. ?

(5) Resin anchor. It is expensive to use resin as a binder for anchor rods. ?

(6) Fast hardening expansive cement anchor. It is made of ordinary portland cement or slag portland cement with additives and has the characteristics of quick setting, early strength, water reduction and expansion?

(7) Double quick cement anchor. It is made of finished early strength cement and double quick cement according to a certain proportion. It has the characteristics of quick hardening, quick setting and early strength. ?

Question 6: What are the design methods of bolt support? In the design and construction of tunnel, flexible support can be realized by bolt support, shotcrete support and shotcrete (net) composite support. Flexible support is a kind of support measure that can cling to or penetrate into the surrounding rock, give full play to the self-supporting ability of the surrounding rock, allow the surrounding rock to be deformed without damage, and ensure considerable support resistance even when it moves with the reinforced rock mass as a whole. Tunnel design and construction can adopt flexible support methods such as bolt support, shotcrete support and shotcrete (net) composite support. The tunnel adopts composite lining with flexible support system structure, except the entrance, that is, rigid arch, anchor rod and shotcrete are used as primary support, molded concrete is used as secondary lining, and EVA waterproof board and geotextile are laid between the two linings. In the current tunnel construction project, the application of NATM is more and more extensive. The essence of NATM is the application of flexible support (shotcrete and bolt support). Shotcrete and anchor support is a commonly used surrounding rock support method at present. Shotcrete-anchor support can give full play to the supporting ability of surrounding rock, effectively use the clearance in tunnel, improve the safety and efficiency of operation, and adapt to tunnel excavation in soft and expansive stratum. It can also be used to control landslide and crack damage of tunnel lining. Including bolt support, shotcrete support, shotcrete bolt combined support, shotcrete steel mesh combined support, shotcrete bolt steel mesh combined support and so on.

Question 7: What auxiliary parts are there in the bolt support system? What are the auxiliary effects? Traditional bolt support theory includes: suspension theory, composite beam theory, composite arch theory and so on. These theories are based on certain assumptions and put forward for different surrounding rock conditions. Because the theory is concise and easy to understand, the design and calculation are simple, it has been widely used in production practice and played a positive role. However, these theories have certain one-sidedness and limitations and cannot be applied to all kinds of road conditions. At present, the concept of "three highs and one low" bolt support is mainly adopted, that is, high strength, high stiffness, high reliability and low support density. The mechanism of bolt support mainly includes the following points:

(1) The main function of bolt support is to control the expansion, deformation and damage of surrounding rock in the anchorage zone, such as delamination, sliding, crack opening and the generation of new cracks, so as to keep the surrounding rock in a compressed state, inhibit the occurrence of bending, deformation, tension and shear damage of surrounding rock, maintain the integrity of surrounding rock in the anchorage zone to the maximum extent, reduce the reduction of surrounding rock strength in the anchorage zone, and make surrounding rock become the main body of bearing. A prestressed load-bearing structure with greater rigidity is formed in the anchorage zone, which can prevent the strata from delaminating outside the anchorage zone and improve the stress distribution of deep surrounding rock. Bolt support has no obvious control effect on the elastic deformation and plastic deformation of rock before reaching the peak strength, so it is required that the support system should have a certain elongation to release the elastic deformation of surrounding rock and the plastic deformation before obvious expansion deformation.

(2) The rigidity of the bolt support system is very important, and the prestress of the bolt and its propagation play a decisive role. It is the key of support design to determine reasonable prestress according to roadway conditions and make prestress spread effectively. The application range of single anchor prestress is very limited, so the anchor prestress must be dispersed to the surrounding rock farther away from the anchor through the components such as supporting plate, steel belt and metal mesh. Especially for the roadway surface, even if a small supporting force is applied, the deformation and damage of surrounding rock will be obviously suppressed and the roof will be kept intact. Surface protection components play an extremely important role in prestressed support system.

(3) There is critical support stiffness in the bolt support system, even if the anchorage zone does not produce obvious delamination and the stiffness required by the support system in the tensile stress zone. The stiffness of the support system is less than the critical support stiffness, and the surrounding rock will be in a state of deformation and instability for a long time; On the contrary, the stiffness of the support system reaches or exceeds the critical support stiffness, the deformation of surrounding rock is effectively suppressed, and the roadway is in a long-term stable state. The key factor of supporting stiffness is the prestress of anchor, so there is a critical prestress value of anchor. When the prestress of anchor reaches a certain value, the deformation and delamination of surrounding rock are effectively controlled, and the stress of anchor rod changes little.

(4) The function of anchor cable mainly has two aspects: one is to connect the prestressed bearing structure formed by anchor bolt support with the deep surrounding rock to improve the stability of the prestressed bearing structure, and at the same time fully mobilize the bearing capacity of the deep surrounding rock, so that the rock mass in a wider range can bear the same load; Secondly, the anchor cable exerts a large pre-tightening force to provide compressive stress to the surrounding rock, which combines with the compressive stress zone formed by the anchor bolt to form a skeleton network structure, actively supporting the surrounding rock and maintaining its integrity.

(5) The most effective way to improve the effect of roadway support is to improve the prestress of bolt and anchor cable, so as to make them spread effectively. For the complicated and difficult roadway, the combined support with high prestress and strong anchor should be adopted, and the deformation and failure of surrounding rock should be effectively controlled by one-time support as much as possible to avoid secondary support and roadway maintenance.

Question 8: The combined action of bolt support defines a suspension action.

When the direct roof is thin and the main roof is firm, the hanging effect of bolt support is outstanding. The anchor rod suspends the lower unstable rock stratum on the last stable rock stratum, and the anchor rod bears the weight of soft rock or dangerous rock, thus achieving the goal of roadway stability. Practice has proved that even if there is no stable rock stratum above the roadway, the bolt can also play a supporting role. For example, in the all-coal roadway, the bolt can achieve the purpose of support even if it is anchored in the coal seam.

Function of double anchor composite beam

In order to solve the limitation of suspension cable theory, the theory of composite beams in layered strata is put forward. The theory of composite beam is applicable to the roadway whose roof is composed of multiple layers of continuous strata with small thickness. Its principle is that in the thin rock stratum without stable rock stratum to provide suspension fulcrum, the layered rock stratum can be combined by the tension of anchor rod to form a composite beam structure for support. With the help of the anchor itself to provide a certain shear capacity, to prevent interlayer dislocation is to prevent delamination from bending and deformation under pressure, showing a combined state, thus improving the bending stiffness and strength of the roof. The main factors that determine the stability of composite beams are the pre-tightening force of bolts, the strength of members and the properties of rock strata.

Span reduction effect of three kinds of anchors

If the unstable roof strata is regarded as a composite beam supported on both sides, since the anchor hanging on the old roof can be regarded as a fulcrum, installing the anchor is equivalent to increasing the fulcrum, thus reducing the span of the roof, reducing the bending stress and deflection of the roof strata and maintaining the stability of the roof. This is the span reduction function of anchor, and this theory actually comes from the suspension function of anchor.

Fourth, strengthen the role of arch.

For the blocky or fractured surrounding rock cut by crisscross weak faces, if the anchor rod is used to reinforce it in time, the shear strength of the weak faces of the rock mass structure can be improved, and a reinforced arch can be formed around the surrounding rock within a certain thickness range, which can not only maintain its own stability, but also prevent the upper surrounding rock from loosening and deforming, thus maintaining the stability of the roadway.

Question 9: What is the principle of soil anchor? It's a lever.