Anchorage Body Research Articles

Study on Stress Distribution Law of Anchorage Body

In order to reveal the stress distribution law of the anchorage body during the drawing process, through the analysis and research on the anchoring mechanism of the anchor rod, it is found that the bonding mechanism of the interface between the anchor rod and the anchoring material is mainly determined by three factors : bonding force, mechanical interlocking and friction force. The bonding mechanism of the anchorage material-surrounding rock interface is mainly determined by two factors : bonding force and friction force. Then, the mechanical model of anchorage body is established, and the distribution equations of axial force and interfacial shear stress of anchorage body are obtained by theoretical analysis. The axial force and shear stress curves are obtained by substituting the relevant parameters. It is found that the axial force and interfacial shear stress curves are exponentially decreasing. The axial force of the bolt is approximately equal to the load applied on the bolt, and at the end of the anchorage, the axial force approaches zero.

Interfacial bonding properties of the reef limestone anchorage body at different curing ages under the impact of dynamic disturbance

The interfacial bonding strength (IBS) of a reef limestone anchorage body at different curing ages was investigated based on pull-out and push-out experiments. By combining the experiments with dynamic impact disturbance, the damage evolution of the IBS for the reef limestone anchorage body was determined. The IBSs of the bolt-mortar (B-M) interface and reef limestone-mortar (R-M) interface increase logarithmically with curing age: IBSs are positively correlated with curing age. Under the effect of impact disturbance, the IBSs of two types of anchorage body both show a descending tendency; while as the curing age increases, the impact-resistant capabilities of the anchorage body are enhanced, accompanied by the gradual decrease of interfacial damage. Hence, engineering activities characterized by strong dynamic disturbance should be avoided as much as possible at early curing ages of the limestone anchorage body in engineering practice. In the meanwhile, the calculations using wave velocities to denote rock damage deviate significantly from the real damage strength of anchorage body interfaces. Therefore, one should be cautious in adopting damage thresholds for an anchorage body calculated using wave velocities.

Study on bonding performance and load transfer model between polyurethane anchor bolts and silty soil

The bonding performance between the anchor anchorage body and soil is an important index to evaluate the anchoring performance of anchor bolts. In this work, the vertical polyurethane grouting anchor bolt is taken as the research object, and the bonding performance between polyurethane anchorage body and silty soil was studied by 13 sets of field pull-out tests, and the distribution law of the axial force and the bonding stress of the polyurethane anchor bolts along the anchoring depth, as well as the influence of the diameter (D = 60 mm, 75 mm, 90 mm, 100 mm, 120 mm), density (ρ = 0.2 g/cm3, 0.3 g/cm3, 0.4 g/cm3, 0.5 g/cm3, 0.6 g/cm3) and length (L = 2.0 m, 2.5 m, 3.0 m, 4.0 m, 5.0 m) of the polyurethane anchorage body on the bonding strength between the polyurethane anchorage body and silty soil were analyzed in detail, and finally the load transfer equation of polyurethane anchorage body under vertical pull-out load was obtained by theoretical derivation. The results show that the error between the calculated results of the load transfer equation and the experimental results is less than 12%, which further indicates that the load transfer equation derived in this paper can reasonably describe the distribution of axial force and bonding stress along the anchorage depth of the polyurethane anchor bolts. The axial force of polyurethane anchor bolt is the largest at the top of the bolt body, and decreases along the anchoring depth, and the axial force at the bottom is far less than that at the top. Polyurethane anchor bolt has significant bonding stress concentration phenomenon, with the increase of load the peak bonding stress and bonding stress distribution area increases, and shifts to the bottom of the anchorage body. The borehole diameter, anchorage body density, and anchorage body length all have important effects on the bonding strength: the bonding strength increases with the increase of anchorage body density, and the increase is more obvious in the case of small density, and the increase of bonding strength becomes smaller after the density exceeds 0.4 g/cm3, the bonding strength decreases with the increase of anchorage body length and borehole diameter.

Upper-Bound Limit Analysis of Ultimate Pullout Capacity of Expanded Anchor Cable

Expanded anchor cables have been widely used in the rapid development of underground engineering. However, there are still some deficiencies in the computation of the ultimate bearing capacity of expanded anchor cables. Based on the upper-bound theorem of limit analysis, the upper-bound solution of the ultimate bearing capacity of an expanded anchor cable was derived. For this calculation, the instability mechanism of the soil at the front surface of the anchorage segment of the expanded anchor cable was assumed to satisfy the logarithmic spiral failure model, its 3D velocity discontinuity surface was generated using the spatial discretization technique, and the optimal solution was determined through the particle swarm optimization (PSO) algorithm. The breakage mechanism of the anchorage side surface was assumed to appear at the interface between the anchorage body and the soil, and its velocity field satisfied the requirements of the associated flow rule. The accuracy of the proposed analytical solution was well-verified through a comparison with three-dimensional numerical simulations, and its superiority was also well-demonstrated in comparison to the existing theoretical calculation method. Subsequently, the influence of the key parameters of the anchor cable on the ultimate lateral resistance, end resistance, and total pullout capacity was discussed. The results showed that: the anchorage segment diameter, anchorage segment length, and buried depth of the expanded anchor cable had a great influence on the ultimate lateral resistance, ultimate end resistance, and total ultimate pullout capacity; however, the anchorage segment length had little influence on the ultimate end resistance, and the inclination angle of the anchor cable had relatively little influence on the resistance.

Numerical investigation on the debonding of cement anchorage in clay rocks based on a hybrid FEM/DEM model

In this study, the failure process of the cement mortar-clay rock (C–C) binary was analyzed using a composite hybrid FEM/DEM model. First, an improved pressure-related cohesive element was used to simulate the mechanical properties of the binary interface. Then, a numerical model of the cement anchorage body in clay rocks was constructed based on the new interfacial cohesive element and FDEM model of clay rock. Finally, the debonding and slip failure process of the anchorage was analyzed by the numerical model and a corresponding physical model test. The results show that: except for the debonding of the interface, the fracture of weaker side material (clay rock) is also a potential failure mode of the C–C binary. The clay rocks have a larger internal friction angle but smaller cohesion, so the failure mode changes from the shear failure of clay rock to the debonding of the interface when the normal pressure is up to 200 kPa. The failure of the anchor may also cause by the generation of the shear failure zone in soft rock instead of the interface debonding. Therefore, the shear strength of the rock should also be considered in the calculation of anchorage resistance.

Field-Scale Experiment on Deformation Characteristics and Bearing Capacity of Tunnel-Type Anchorage of Suspension Bridge

The suspension pipe bridge has become the main span type due to its large span, light structure, and other characteristics, playing an important role in the construction of the oil and gas backbone network and energy layout. Tunnel-type anchorage (TTA) is a special underground structure that provides anchorage tension for the suspension bridge. Since its form and bearing mechanism are complex, there is no general design method for tunnel-type anchorage so far, and the theoretical and normative research is not mature. In this paper, a field-scale experiment was carried out to study the north side tunnel of Wujiagang Bridge in Yichang, China. According to the similarity principle, the 1:12 tunnel anchor scale model was established. The tunnel anchor scale model is selected in the area adjacent to the actual project site to ensure the similarity of stratigraphic conditions. Through the use of a displacement meter, inclinometer hole, strain gauge, micrometers, and other comprehensive monitoring methods, the design load test, overload test, overload rheological test, and ultimate bearing capacity failure test were carried out. Through the structural deformation observation and stress observation of the anchorage body and surrounding rock, the stress deformation characteristics and rheological characteristics of the anchorage body and surrounding rock in the field-scale experiment were analyzed. The deformation failure mechanism, deformation failure process, potential failure mode, and overload capacity of solid tunnel anchor were studied. The control indexes such as deformation and stress values of key parts of the solid tunnel anchor at different stages are predicted. Based on the limit equilibrium analysis results of the model, the safety and rationality of the tunnel anchorage structure design of the actual suspension bridge were evaluated.

Analytic Study on the Force Transfer of Full Encapsulating Rock Bolts Subjected to Tensile Force

Full encapsulating rock bolts are widely used in mining and civil engineering to keep the stability of underground excavations. Nevertheless, decoupling at the interface between the bolt and grout (first interface) still occurs. To disclose the loading mechanism of the bolting system and preventing decoupling at the first interface, experimental and analytic studies were conducted in this paper. First, a nonlinear shearing-slipping law is used to describe the coupling and decoupling behavior of the first interface. Then, this shearing-slipping law is merged into the anchorage body. Following this, the whole loading process is divided into two components: elastic period and elastic-plastic period. Consequently, the analytic force-deformation relation of bolts is obtained. To confirm the rationality of this solution, experimental tensile tests on bolts were performed. It shows that there was a good match between analytic results and experimental tests. With the confirmed analytic solution, a parameter study is performed to investigate the impact of shearing-slipping parameters on the bolting performance. It indicates that increasing the shearing strength of the first interface and the shearing slipping have a positive impact in improving the bearing capacity of bolts. Inversely, the softening coefficient for the post-failure stage has a negative impact on determining the bearing capacity of bolts. Overall, the shearing strength of the first interface has a major impact in determining the loading performance of bolts.

Numerical Study on the Bearing Properties of Multi-airbag Inflatable Bolt in Soft Soil

In response to the limited execution space underground in soft soil area, and the disadvantages of weak bearing capacity, overlength anchorage body, non-recyclability, and low economic benefits of the conventional bolt, the related numerical simulation research was carried out on the multi-airbag inflatable bolt in this paper. Primarily, the research history of the multi-airbag inflatable bolt was briefly introduced, and the problems of this bolt existing in the current engineering application were analyzed. Subsequently, based on the numerical software MIDAS/GTS, the pull-out tests of the multi-airbag inflatable bolt in soft soil were simulated. By means of successively changing the airbag diameter, airbag length, airbag interval, airbag burial depth and airbag number, the corresponding bearing properties of the bolt were obtained, and the bearing capacity and ultimate displacement of bolt with different airbag parameters combinations were determined, which provides certain guidance for further field tests and verifies its applicability and social value in underground project in soft soil area.

Anchoring effect and energy-absorbing support mechanism of large deformation bolt

To research the anchoring effect of large deformation bolt, tensile and drawing models are established. Then, the evolution laws of drawing force, bolt axial force and interfacial shear stress are analyzed. Additionally, the influence of structure element position on the anchoring effect of large deformation bolt is discussed. At last, the energy-absorbing support mechanism is discussed. Results show that during the drawing process of normal bolt, drawing force, bolt axial force and interfacial shear stress all gradually increase as increasing the drawing displacement, but when the large deformation bolt enters the structural deformation stage, these three values will keep stable; when the structure element of large deformation bolt approaches the drawing end, the fluctuation range of drawing force decreases, the distributions of bolt axial force and interfacial shear stress of anchorage section are steady and the increasing rate of interfacial shear stress decreases, which are advantageous for keeping the stress stability of the anchorage body. During the working process of large deformation bolt, the strain of bolt body is small, the working resistance is stable and the distributions of bolt axial force and interfacial shear stress are steady. When a rock burst event occurs, the bolt and bonding interface cannot easily break, which weakens the dynamic disaster degree.

Combined support mechanism of rock bolts and anchor cables for adjacent roadways in the external staggered split-level panel layout

Using the spatial structure of the external staggered split-level panel layout, a combined support technology for adjacent roadways was developed and analyzed for a rock bolt and anchor cable mechanism. The influence of the side rock bolt and anchor cable parameters on the mechanical properties of the anchorage body and the support stress distribution of the lateral coal body were revealed using the FLAC3D software. The optimal support parameters of the side rock bolts and anchor cables were subsequently determined, and the support effect of gob-side entry in a mining scenario was verified. The results show that the support of the side rock bolts and anchor cables improves the mechanical properties and stress state of the anchorage body, producing a good protective effect on the coal body of the air-intake entry roof and side wall. This is beneficial to the stability of the side wall and the realization of the suspension effect for roof rock bolts and anchor cables, which in turn makes the surrounding rock maintenance of the gob-side entry to a thick coal seam more favorable.

A Study of the Anchorage Body Fracture Evolution and the Energy Dissipation Rule: Comparison between Tensioned Rock Bolts and Torqued Rock Bolts

Rock bolt support is an effective technique for controlling surrounding rock of deep roadway. The stability of the anchorage body composed of rock bolts and surrounding rock mass is the core in keeping the stability of roadways. In this paper, the UDEC Trigon model was used in simulating uniaxial compressive test on the anchorage body under different pretension loads. The energy equilibrium criterion of the anchorage body under the uniaxial compressive state was proposed. Furthermore, the fracture evolution and the energy dissipation during the failure process of the anchorage body were analyzed. Results showed that before the peak strength, the external work was stored in the anchorage body in the form of the elastic strain energy (Ue). After the peak, energy dissipated through three ways, including the fracture developing friction (Wf), plastic deformation (Wp), and acoustic emission (Ur). Based on the simulation results, the high pretensioned rock bolts can eliminate the continuous tensile fractures in the anchorage body, decreasing the damaging extent of the anchorage body and the energy that was consumed by the following two main approaches: fracture developing friction (Wf) and plastic deformation (Wp). Moreover, the surplus of the elastic strain energy (Ue) and the strength of the anchorage body can be improved. The pretension load had a positive relationship with elastic strain energy and a negative relationship with the anchorage body damage degree. Based on the above research, the transport roadway of the working face 6208 in the Wangzhuang Coal Mine selected tensile rock bolts to establish the high‐performance anchorage body. The monitoring data showed that this reinforcement method effectively managed the serious deformation issue of the roadway surrounding the rock masses.

Evaluation of failure mode of tunnel-type anchorage for a suspension bridge via scaled model tests and image processing

In this study, the pull-out behavior of a tunnel-type anchorage for suspension bridges was investigated using experimental tests and image processing analyses. The study focused on evaluating the initial failure behavior and failure mode of the tunnel-type anchorage. In order to evaluate the failure mode of tunnel-type anchorage, a series of scaled model tests were conducted based on the prototype anchorage of the Ulsan Grand Bridge. In the model tests, the anchorage body and surrounding rocks were fabricated using a gypsum mixture. The pull-out behavior was investigated under plane strain conditions. The results of the model tests demonstrate that the tunnel-type anchorage underwent a wedge-shaped failure. In addition, the failure mode changed according to the differences in the physical properties of the surrounding rock and the anchorage body and the size of the anchor plate. The size of the anchor plate was found to be an important parameter that determines the failure mode. However, the difference in physical properties between the surrounding rock and the anchorage body did not affect its size. In addition, this study analyzed the initial failure behavior of the tunnel-type anchorage through image analysis and confirmed that the failure was sequentially transferred from the inside of the tunnel to the surrounding rock according to the image analysis. The reasonable failure mode for the design of the tunnel-type anchorage should be wedge-type rather than pull-out type.

The analysis of rheological damage of anchorage body based on visco-elasto-plastic model

In order to study the rheological damage of anchorage body, rheological damage model of anchorage body is established in this paper, and it is based on visco-elasto plastic model that is often used to simulate rock rheological characteristics. The expressions of creep constitutive equation and elastic modulus of anchorage body are obtained through the analysis of rheological damage model of anchorage body, and by the fitting calculation results, finding that the theoretical creep curve is matched with the experimental creep curve under certain conditions. The research conclusions have critical significance to the bolting support and design.

Modeling and Simulation of Deformation Mechanism of Soft Rock Roadway considering the Mine Water

The existence of coal mine water has an important influence on the instability of soft rock roadway in mining engineering. Considering the effect of mine water, a case study on the fracture mechanism and control technology of soft rock roadway was performed in this paper. The results showed that with the increase of moisture content, the uniaxial compressive strength of mudstone nonlinearly decreased, while the tensile strength, Young’s modulus, cohesion, and friction angle tended to a linear decrease approximately. Meanwhile, with the increase of the weakening coefficient, the axial force of the anchorage body increased gradually, while the maximum shear stress decreased gradually. With the increase of moisture content, the failure zone was further propagated into the deep surrounding rock, resulting in a larger stress relaxation around the roadway, especially in the roof and floor. Finally, the supporting technology of the roadway was proposed, and then its support principle, design process, and parameters were also analyzed in detail. The field monitoring data showed that the support technology can control the surrounding rock deformation effectively and maintain the long-term stability of the roadway.

Stress Transfer Properties and Displacement Difference of GFRP Antifloating Anchor

Glass fiber reinforced polymer (GFRP) antifloating anchors are widely used in reinforcing underground structures. Despite the outstanding application advances of GFRP anchors in the antifloating field, research on the mechanical transmission and deformation properties of the anchor rod and anchorage body is still scarce. This paper introduces pull‐out experiments of GFRP antifloating anchors based on the FBG sensor strings technology. The experimental data demonstrates that the distribution curve of the axial stress shows a reversed‐S shape, and the shear stress distribution presents the law of increasing first and then decreasing from the position of peak shear stress. The rod‐anchorage body displacement difference curves of the anchors with an anchorage length that is closer to the critical anchorage length are smoother than those of the anchors with a larger length difference from the critical anchorage length. Finally, a simplified distribution model of the shear stress is applied for predicting the rod‐anchorage body displacement difference, and the experimental data of the anchors with a rod slip failure is more applicable for this model than that of the anchors with a rod rupture failure.

Mechanical Characteristics of Fully Grouted and Antiseismic Bolts considering Transverse Deformation in Underground Caverns

The load transfer control equations under bolt-surrounding rock interaction are established on the basis of classical beam theory and the trilinear shear slip model. The axial stress and transverse shear force distributions of the anchorage body are obtained by solving the equations. The equivalent forces obtained by the transverse force and axial shear stress of the bolts are applied to rock mass elements to simulate the support effect. A new dynamic algorithm for bolts is proposed in considering of the axial and transverse deformation of the anchorage body. The rationality of the algorithm is verified by comparing with laboratory pullout and shear tests of bolts. A dynamic time-history case study of underground caverns is conducted using this algorithm. Results indicate that (1) the algorithm may reflect the stress and deformation characteristics of bolts during an earthquake; (2) for the antiseismic support effect of the surrounding rock at fault, the bolt algorithm in this study is more valid than the algorithm that considered only the axial deformation of bolts; (3) in the support force of the bolt to the surrounding rock, transverse force is the key to limit fault dislocation and reduce the dynamic damage of the rock at fault.

Investigation on the interaction mechanism and failure behavior between bolt and rock-like mass

The matching relationship between bolt diameter and borehole diameter determines the bolt supporting effect in the mining roadway. In this paper, the failure modes of the anchorage body under different diameter matching were studied by the pullout test. When the anchorage agent was pulled out completely with bolt, the anchoring effect was ideal. Whereas, when the bolt was pulled out smoothly with only a thin layer of anchorage agent, the anchoring effect was relatively worse. Through multiple pullout tests, the suitable diameter matching difference can be defined with a range of 6–11 mm. Based on the interface sliding failure mode between anchorage agent and rock-like mass, a mechanical model of diameter matching was established. Both equations of tensile force and interfacial shear stress along with the anchorage direction in perfectly elastic state were derived. FLAC 3D was applied to analyze the distribution of interfacial shear stress and axial stress under different diameter matching between the bolt and the borehole. As a result, a 4–11 mm diameter difference shows the best anchoring effect. According to both experimental and simulation results, the optimal diameter matching difference is 6–11 mm.

Study and engineering application on the bolt-grouting reinforcement effect in underground engineering with fractured surrounding rock

Bolt-grouting support is an effective means for addressing the difficulty of fractured surrounding rock control in underground engineering. In this paper, to determine the improvement in the anchorage body interface strength resulting from grouting, theoretical equations for calculating the anchorage body interface shear strength before and after grouting were derived, and the influence law of various mechanical parameters (elastic modulus, cohesion, internal friction angle, and dilation angle) of the surrounding rock on the anchorage body interface strength were obtained. Based on the aforementioned theoretical analysis, a systematic field bolt-grouting test was performed on surrounding rock with the same lithology and different fragmentation degrees. The variation trend of the grout diffusion performance under the different grouting bolt length was analyzed. Furthermore, the effects law of various bolt-grouting parameters on the surrounding rock and support system were also revealed. The following results were obtained: (1) The pullout forces of the common bolts increased significantly after grouting. In addition, the grout diffusion basically stabilized 7 days after grouting. (2) The increasing rate of pullout force on the common bolt around the grouting bolt presented the rule of “Below > Side > Above”. (3) With the length of grouting bolt increasing, its effective reinforcement range gradually expanded. (4) The variation in the grouting bolt length had a relatively insignificant impact on pullout forces of the common bolts in its immediate vicinity. Based on the above theory and experimental study, relevant engineering proposal were recommended and adopted in the design of site bolt-grouting support schemes. The research results can provide methods and basis for selecting and evaluating of grouting bolt parameters in underground engineering with fractured surrounding rock.

A numeral simulation of anchored interface shear stress for bolt in rock mass slope under earthquake

In order to extract the distribution regularities of shear stress on both slope’s anchored interfaces under earthquake at the same time, and reveal the mechanism of the shear interaction on anchored interfaces. Based on finite difference software FLAC3D, we build an anchored rock slope numerical model, simulated shear interaction on cable-grout interface and grout-rock interface by interface element, to study the distribution regularities of wholly grouted anchor bar anchored interface shear stress in anchored slope under simple harmonic vibration of seismic waves. The results of the study include the following: the shear stress on grout-rock interface reaches ultimate bond strength first, and debonding, the peak value of shear stress on grout-rock interface develop from failure surface to bolt end; at the same time, the shear stress on bolt-grout interface doesn’t reach ultimate bond strength, but the peak value of shear stress on bolt-grout interface move accordingly with that on grout-rock interface; after grout-rock interface debonding, the distribution of axial force along bolt is herringbone curve with both convex outer side, there is a one-to-one correspondence between curve inflection point of axial force and peak value point of shear stress on interface. The anchorage body in debonding region subjected uniform tension, the axial force in this region distributed relatively uniform. The study can provide references for study of model test, field monitoring, design and construction on relevant aspect.

Control Mechanism and Support Technology of Soft Coal Roadway in the Fully Mechanized Mining Work Face

Aiming at characteristics of the soft coal roadway engineering geology and deformation, the exposure research of the soft coal seam, theoretical analysis, numerical calculation and program design were carried out. First of all, according to the disclosure, soft coal seam engineering characteristics and geological conditions in Xinxing coal mine were expounded. Meanwhile, the soft coal roadway bolt supporting axial effect, the bolt supporting transverse effect, the anchorage body mechanics strengthening mechanism and problems such as supporting strength have been analyzed. The paper pointed out that the soft coal with very small cohesive force can form a composite anchorage body under the combined action of the anchor cable group, the W-type steel band and the metal net. The soft coal body in the plastic damage area formed anchorage balance arch with a certain bearing capacity and adapted to the rock deformation, and which played an effective support role in the roof outside the balance arch of the roadway. Therefore, the full-cable support technology was proposed. And then, numerical calculation and comparative analysis were conducted on three schemes of the roadway with non-support, with combined support of “anchor bolt and cable” and the full-cable support. The results show that when the roof is supported by anchor cable, it not only controls the continued increase of the subsidence value of the roof, but also effectively suppresses the convergence amount of the floor heave value and the amount on the sidewalls of the roadway. Whether it is from the stress distribution situation, or the viewpoint of plastic zone scope, the combined support of full-cable is more reasonable than that with non-support and that with the combined support of “anchor bolt and cable”. Finally, based on the features of soft coal seam in No.2265 work face of Xinxing coal mine, the relevant support schemes were put forward, and its specific support parameters and cross-section designs were drawn as well.