Anchor Cable Research Articles

Experimental study on double cuneiform reamed anchorages for cable bolt boreholes in soft rock

This paper deals with the problems of the low bonding force between hardened resin and soft surrounding rock, and the rapid attenuation of anchoring forces when conventional anchoring methods are used for cable bolts. The main goal of paper is to develop methods that will take full advantage of the potentially great supporting force that can be provided by high-strength cable bolts installed in soft rock. The study described in this paper discusses cuneiform reamed anchors for cable bolt boreholes. It is proposed that increasing the number of cuneiform cavities in the boreholes (with each cavity having appropriate geometric dimensions) is an effective way to prevent cable bolt anchorage failure. The results of a comparative analysis of single cuneiform reamed anchors (SCRAs) and double cuneiform reamed anchors (DCRAs) using numerical simulations are described. The simulations show that after being deformed by tensional forces of up to 200 kN, the maximum displacement of hardened resin in a DCRA borehole and the maximum plastic strain in the rock surrounding a DCRA borehole are, respectively, 50% and 46% smaller that they are for an SCRA borehole. The DCRA provides more stability and is an effective way to access the great supporting forces that a high-strength cable bolt is potentially capable of providing. The simulations were also able to determine the appropriate reaming angles for rocks of different strength. Using the simulation data, a double cuneiform reaming tool (DCRT) was developed. A field test has verified that this tool can ream two cuneiform cavities in a borehole to enlarge a section of the borehole when the tool is rotated by the drill rod. The DCRAs guarantee that cable bolts installed in soft rock will provide high supporting forces and that the cable bolts will not suffer anchoring force attenuation under severe ground pressure. • The synergistic mechanism of DCRAs was revealed, and the optimal reaming angle for different surrounding rock strengths was determined. • The DCRT was developed, boreholes reamed with the DCRT can prevent the resin encasing the cable bolt from separating from surrounding rock. • DCRAs allow high-strength cable bolts to take full advantage of their supporting force and minimize supporting force attenuation.

Shear Test of Pre-stressed Anchor Block and Fracture Mechanism Analysis of Anchor Cable

Shear Test of Pre-stressed Anchor Block and Fracture Mechanism Analysis of Anchor Cable

Reasonable stopping method and retracement channel support at fully mechanized top coal caving working face of 15 m extra‐thick coal seam: A case study

AbstractExtra‐thick coal seams are widely distributed in the Datong mine area in China. The rapid stopping of mining and the support withdrawal technology for extra‐thick coal seams need to be developed urgently. The reasonable stopping top coal caving distance, main roof's fracture line position, and large section roadway during the stopping period (LSRSP) support method of the header face of 15 m extra‐thick coal seam are systematically studied by using field measurement, experiment, numerical simulation, and similar material simulation methods. With the increase in stopping coal caving distance, the range of the medium and low displacement zone of the LSRSP overburden gradually expands. In contrast, the depth of the plastic zone decreases. The scope and intensity of the high‐stress area of the overlying rock in front gradually decrease and shift from deep to the outside, while the peak stress area shifts from the top coal area to the coal rib of the retracement channel. Comparing the stopping of medium‐thick and thick coal seam working face, the interaction between “main roof−unmined top coal−supports” is analyzed. The unique characteristics of the extra‐thick coal seam working face are derived: when the stopping coal caving distance is shorter than the length of the key block, the dropped coal body cannot effectively restrict the movement of key blocks. Mutual compression and subsidence occur between key blocks, making the broken coal rock block squeeze into the supports. By the simulation study of each index, the stopping coal caving distance of the extra‐thick coal seam is optimal when it is slightly larger than the length of the key block (i.e., the periodic weighting step), simultaneously, the main roof fracture line behind the supports is most favorable for stopping mining. After ensuring the stability of the LSRSP's overburden structure, the differentiated support scheme of “controlled zoning−strength grading” was proposed, and the scheme was modified and verified by simulating the support prestress field. After field practice, the roof of the retracement channel is better controlled in deformation under the joint horizontal and vertical support, the robust control effect of the combined anchor cable is noticeable, the integrity of the polyurethane network is more substantial, and the working face supports have successfully achieved a safe and rapid evacuation.

Development of the Large-Tonnage Pressure-Type Prestressed Anchor Cable with BFRP for Geotechnical Engineering and Its Mechanical Properties

Prestressed anchor cable is widely used in geotechnical engineering to control the displacement or landslide of an unstable slope. However, the traditional cable anchor is made of steel material, which is easy to get rust in a corrosive environment. Basalt fiber-reinforced plastics (BFRP) are a kind of emerging compound material, with a good performance of high strength, low weight, and anticorrosion. Herein, an innovative large-tonnage pressure-type prestressed anchor is made with BFRP. This large-tonnage BFRP anchor cable has seven bunch structures of the “BFRP-connector-strand.” In each bunch of the “BFRP-connector-strand,” three BFRP tendons and one steel strand are connected inside a steel sleeve connector using the epoxy resin adhesive. The ultimate load-bearing capacity of this BFRP cable anchor can reach 202.38 tonnages. At the ultimate tensioning force condition, the strain of BFRP tendons for this large-tonnage BFRP anchor cable ranges from 1.51% to 1.76%. In the tensioning operation, there is a linear growth relationship between the tensioning force and the strain for this BFRP cable anchor. Once the tensioning force reaches the ultimate strength of this BFRP anchor cable, this cable will present system failure. This situation primarily results from the failure of the “BFRP-connector-strand.” The failure modes of this BFRP anchor cable can be classified into three types: the steel strand rupture, the steel connector rupture, and the BFRP tendon rupture. During the tensioning operation, due to the length difference of the BFRP tendons, this large-tonnage BFRP cable anchor presents an end-off-axis effect. It makes the load bearing of the BFRP tendons 5.00~6.60 times larger than that of the no end-off-axis effect. Nevertheless, due to the plastic deformation of the end steel anchor sleeve, the influence of the end-off-axis effect decreases with the increase of applied tensioning force. The load-bearing capacity of this large-tonnage BFRP cable anchor reaches 87.70~91.50% of its theoretical value.

Superimposed Stress Calculation of Soil Underlying Anchor Beam considering Anisotropy and Strength Nonhomogeneity

Prestress anchor beams are an important reinforcement method for underground engineering and rock slopes, and they are crucial for maintaining the stability of civil engineering structures. In this study, the computational formula of superimposed stress of soil underlying an anchor beam was proposed in this paper, based on the assumption that the anchor beam is completely rigid and the prestress of the anchor cable is acting on soil in the form of a strip uniform load. By considering the anisotropy and strength nonhomogeneity of the saturated soft clay, the failure envelopes of the soil and the maximum effective depth underlying the anchor beam were obtained by the D-P yield criterion suitable for soft clay analysis. Furthermore, the experimental comparisons with the previous findings were used to validate the proposed approach. The proposed method was valid to assess the maximum effective depth. Considering the influence of the factors on the failure envelopes of soil, a parametric study was carried out to optimize the design of the prestressed anchor cable. The findings of this study provide a theoretical basis for designing prestressed anchor cables; these can also be used to predict the response of prestressed anchor cables as well as to optimize the design of the cables, such as the anchorage length of cable and grouting radius.

Research on Deformation and Failure Control Technology of a Gob-Side Roadway in Close Extra-Thick Coal Seams

Close extra-thick coal seams are subject to the broken overburden of mined coal seams, and the deformation and damage of the roadways is serious, which affects the safe operation of the mine. To reduce the deformation and damage of the roadways, this paper studied the deformation and damage law of the gob-side roadway in close extra-thick coal seams through numerical simulation and field monitoring, compared and analyzed the deformation and damage characteristics of the roadway under different reinforcement support methods, determined the optimal reinforcement support method, and carried out field verification. The obtained results indicated that the deformation and damage of the gob-side roadway showed asymmetric characteristics. The large deformation of the coal body in the deep part of the roadway wall is an important reason for the continuous occurrence of roadway wall heave in the coal pillar. Under the action of unbalanced support pressure, the floor is subject to the coupling effect of horizontal extrusion pressure and vertical stress that cause extrusion mobility floor heave. The horizontal and vertical displacement of the coal pillar side of the roadway under different support methods is much larger than that of the solid coal side. Increasing the anchor cable length and fan-shaped arrangement can improve the support effect. Grouting at the coal pillar side can significantly improve the bearing capacity and stability of the coal pillar. The effect of floor grouting is much better than the anchor cable in controlling the floor heave. The integrated reinforcement method of anchor cable + coal pillar side grouting + floor grouting has the best effect with the least horizontal and vertical deformation. The research results are of great significance for ensuring the stability of similarly endowed roadways.

Support characteristics of flexible negative Poisson’s ratio anchor cable response to blasting impacts

With the gradual decrease and exhaustion of shallow mineral resources, underground mining has progressed to greater depths. Here, the geological environment is significantly more complex and nonlinear, and large deformations of rock masses have great potential to occur. Many geotechnical engineering disasters have occurred even while using Poisson’s ratio (PR) anchor cable supports. To efficiently deal with these issues, a new support material called negative Poisson’s ratio (NPR) anchor cable is proposed; this material can withstand large deformations and provide high constant resistance. In this study, the support characteristics of macro-NPR anchor cable under blasting impact were mainly studied. The support effects of PR anchor cable and macro-NPR anchor cable were compared and analyzed with the help of field experiments and numerical simulations. The results indicate that field experiments and discontinuous deformation analysis accurately reflect the failure state of the selected roadway, as well as the tension and deformation of the anchor cables. The roadway supported by PR anchor cables cannot resist rock bursts under ordinary circumstances. However, the NPR anchor cable-supported roadway resisted a rock burst caused by the impact equivalent to a mine earthquake magnitude above 3; it meets the requirements of roadway stability.

Pseudo-dynamic analysis of reinforced slope with anchor cables

The anchor cable is an excellent reinforcement device for enhancing slope performance subjected to earthquakes. Thus, this work combines the minimum potential energy principle with the pseudo-dynamic method and develops a novel approach to determining a reinforced slope safety factor (SF). Specifically, the mobilized shear stress on the slip surface is solved utilizing the moment equilibrium equation of the sliding mass. Moreover, the proposed scheme introduces the elastic foundation coefficient characterizing the soil’s compressibility. Subsequently, the potential energy equation is derived. Finally, the SF is calculated as the ratio of the anti-sliding moment to the sliding moment for evaluating the slope stability. The developed method is evaluated on four examples, with the results highlighting that our method is efficient and accurate. Meanwhile, we examine the influence of the variation of the axis forces on the SF when the foundation coefficient is smaller, revealing that the depth of the sliding mass is negatively correlated with the SF, while the landslide area and length of the sliding mass are positively correlated with the SF. Furthermore, this work also studies the influences of amplification factor, earthquake acceleration factor, anchored force, cohesion, and internal friction angle on the SF. Overall, this work provides suggestions for the design and construction management of reinforced slopes with anchor cables.

Study on Anchorage Performance of New High-Strength Fast Anchorage Agent

To achieve the efficient, rapid construction of prestressed anchor cables, in this study, through an indoor pull-out test and field basic test, we investigated the mechanical behavior, expansion, drawing performance and bond properties of a new type of high-strength, fast anchorage agent. We analyzed the influence of the water material ratio and curing time on its performance and determined the corresponding construction. It was found that the new anchoring agent could be effectively applied in field construction and achieved a compressive strength of 30 MPa within 30 h. Moreover, during the solidification process, the hydration reaction node could be reached within 5–6 h when the material expansion was and the feedback to the water–material ratio were the strongest. In addition, in the drawing process, the anchorage agent exhibited a strong bond with the reinforcement and the rock layer, and the bonding of the anchorage agent to the rock layer was greater than that of the steel bar. Therefore, in order to provide anchorage, it is necessary to increase the contact area between the steel strand and the anchorage agent.

Study on Stability of Anchored Slope under Static Load with Weak Interlayer

To study the stability characteristics of a rock slope with a weak interlayer, a test of the anchor frame slope was designed in this paper. The analysis model was established with FLAC3D, and the development law of safety factor, deformation, axial anchor force, soil pressure and maximum shear strain increment of the slope, and the supporting effect of frame anchor cable were obtained by grading loading. The research showed that the supporting effect of frame anchor cable support on the slope was remarkable, and the influence of slope vertical load on the slope safety factor was evident. The lateral deformation mode of the slope surface was large up and down, and minor in the middle. The weak intercalated layer blocked the internal diffusion of the settlement. The failure trend of slope was sliding along the weak interlayer and collapse occurred below the loading zone, and the final failure mode is wedge failure. The peak value of maximum shear strain increment was developed along the weak interlayer, and a shear strain mutation zone was formed inside the slope. It could be considered that the weak interlayer was the potential sliding surface of the slope.

Research on the safety control technology of gob-side entry in inclined thick coal seam

To study the safety control technology of the gob-side entry in an inclined thick coal seam, the asymmetric deformation characteristics and control mechanism of the gob-side entry in an inclined thick coal seam were analysed by combining theoretical analyses, numerical simulations and field monitoring with the prototype of a gob-side entry in a deep inclined thick coal seam in a high gas mine in Xinjiang. The research results showed that the deformation of the solid coal gang and top plate is more intense than that of the narrow coal pillar gang and bottom plate. Combined with the asymmetry of deformation surrounding rock, the gob-side entry safety control technology based on a high prestressing high-strength anchor support and a reinforced support by inclined anchor cables in key areas (a zero-displacement area within the narrow coal pillar and an intense deformation area of the solid coal gang angle) is proposed. Reasonable the gob-side entry support parameters were further determined via numerical simulation experiments, and a reasonable anchor length, row spacing and spacing to maintain the stability of the gob-side entry were obtained as 2200 mm, 800 mm and 800 mm, respectively. Engineering practice showed that the adoption of the new support technology can effectively control the asymmetric large deformation of the solid coal gang and top plate, which can maintain the stability of the gob-side entry for a long period of time and ensure the safe and efficient production of coal resources in the mine.

Large Deformation Mechanism of Foliated Rock and NPR Anchor Cable Support Technology in the Changning Tunnel: A Case Study

Large Deformation Mechanism of Foliated Rock and NPR Anchor Cable Support Technology in the Changning Tunnel: A Case Study

A novel plastic failure model of prestressed anchor cables for upper bound stability analyses of rotational reinforced slopes

In the existing upper bound limit analyses (UBLA) of rotational slopes reinforced with prestressed anchor cables, the mobilized axial forces of all cables are assumed to be equal to the ultimate pullout force. However, such an assumption overestimates the mechanical contribution of prestressed anchor cables, resulting in excessively high safety factors. In this technical note, we aim to tackle this issue by proposing a pseudo-plastic design concept, in which soil masses and prestressed cables are treated as plastic and elastic-plastic, respectively, when slopes collapse. A pseudo-plastic failure model of prestressed anchor cables is proposed, where the variation of tension forces and movement of anchor heads are accounted for. Several interesting conclusions are drawn as follows: (1) Contrary to the conventional plastic failure mode of cables, upper bound solutions obtained by the proposed model are much closer to the exact solutions. (2) Variation of factors of safety (FSs) against the accumulated rotational displacement can be explained by the force-displacement curve obtained in the pullout test of prestressed anchor cables. (3) The sliding slope reinforced with cables may turn out to be stable after a slight rotational movement, which can be utilized in the economical design.

Transfer matrix method for analyzing dynamic response of multi-span elastically supported SFT under moving load

This paper proposed a new theoretical model for analyzing the submerged floating tunnel(SFT) under moving load, whose boundary at two ends was regarded as elastic constraint, and the anchor cable was simplified as the discrete spring support. Besides, the tunnel joint was simulated as a flexural spring to connect two adjacent tube segments. The modes and natural frequencies of the model were solved by transfer matrix method, and the dynamic response of the SFT under moving load was investigated by the modal superposition method, which was verified by comparing with the results obtained by the general FEM software. The influence of boundary conditions, dissimilarity of cable stiffness and joint flexural stiffness on the dynamic response of the SFT was analyzed. The difference of the response between the beam on elastic supports (BOES) and the beam on elastic foundation (BOEF) was compared. The results showed that the boundary conditions had little influence on the vibration response of SFT's intermediate spans, but had great influence on the displacement and bending moment of the side span. Besides, even in the case when the frequency differentials of the BOES and the BOEF were small (1.84%), the displacements of the two models also had significant difference. The disparity of the cable stiffness and joint flexural stiffness had great influence on the distribution of displacement and bending moment of SFT.

Experimental Study on the Shear Mechanical Properties of Anchor Cable with C-Shaped Tube

Faced with serious tensile–shear fracturing of anchor bolts and cables in deep roadways, it is of great significance to investigate Anchor Cable with C-shaped tube (ACC), a combined structure of a C-shaped tube and an anchor cable with high strength and shear resistance. The shear mechanical properties of the anchor cable and ACC are systematically investigated using the technical means of theoretical analysis and double-shear tests. The improved equipment for a double-shear test not only considers the initial normal stress but also ensures the continuity of the anchor cable’s axial force transmission while considering the influence of the inclination angle on the shear performance of supporting components. The research indicates that the C-shaped tube inhibits the occurrence of stress concentration near the joint surface and improves the stress state of the anchor cable, transforming its failure mode from tensile–shear failure to tensile failure. Compared with the anchor cable, ACC has a higher shear capacity, greater shear stiffness and better ductility in the shear direction. The shear capacity of ACC is higher when it is perpendicular to the joint plane than when inclined to 80°, and the shear capacity of the joint plane is linear with the initial normal stress. Two methods were proposed to contrast the shear capacity between the anchor cable and ACC, including the shear capacity of supporting components and the shear capacity of the joint surface. The former is to evaluate the shear capability of the anchor cable and ACC, while the latter is to evaluate the ability of the anchor cable and ACC to control the shear deformation of the joint surface. The tests results show that the average shear capacity of ACC is 279 kN higher than the anchor cable, with an average increase of 34.9%. The average shear capacity of the joint surface anchored by ACC is 306 kN higher than the anchor cable, with an average increase of 25.2%. ACC can effectively improve the shear capacity of the anchor cable in the free section and has wide application prospects.

Feasibility Analysis on the Support of Rock Slopes Against Flexural Toppling Failure Using the DDA Method-A Case Study

As a typical and complex failure type of rock slopes, flexural toppling failure has increasingly received attention, mainly focused on its failure mechanism and introducing a proper numerical method to reproduce the failure phenomena. However, there are few studies related to the supporting mechanism against flexural toppling failure. This study attempted to make a preliminary analysis on the research gap. For this purpose, an anti-dip layered rock slope supported with anchor cables that failed owning to flexural toppling was taken as an example, and the numerical method discontinuous deformation analysis (DDA) was taken as the major analytical tool. Firstly, the rationality of DDA was verified by correctly simulating the failure state of the anti-layered rock slope and the underlying failure mechanism was studied. The results indicated that the lack of the support from slope toe is the crucial factor inducing the flexural toppling failure, which posed a great obstacle to the further excavation of the open-pit mine. Secondly, by introducing the anchor cable support to the slope toe in the DDA model, the interaction mechanism between the anchor cables and the rock slope was investigated. the results indicated that the supporting system of the ordinary anchor cables is very sensitive to the inhomogeneous flexural toppling deformation. The tension values of the anchor cables are very inhomogeneous, and once some of anchor cables beyond their tension limit, the anchor cables failed, which will greatly threaten the safety of the adjacent anchor cables and even the stability of the whole slope. Meanwhile, a novel anchor cable called constant-resistance-large-deformation (CRLD) anchor cable was introduced for a comparative study using DDA. just replacing the anchor cables of the original slope with the CRLD anchor cables, the slope can reach stable state eventually even without the slope toe being enhanced. In addition, the CRLD anchor cables were able to support the slope well against the inhomogeneous deformation, because they can provide high constant resistances and withstand large deformations. This study can provide a deeper insight into the support mechanism for the snit-layered rock slope against flexural toppling failure and introduce a novel supporting method for such slopes.

Negative Poisson’s ratio and peripheral strain of an NPR anchor cable

Negative Poisson’s ratio and peripheral strain of an NPR anchor cable

Research on influence of anchor cable failure on slope dynamic response

Anchor cables are an important branch of geotechnical engineering and are widely used in slope reinforcement. The Wenchuan earthquake showed that the anchor cable fracture can cause the instability of the slope. The anchor cables in the numerical software obey the ideal elastic-plastic law and cannot simulate fracture and failure. To achieve the fracture effect, the anchor cable model is modified. Based on stepped slopes, the dynamic response characteristics are analyzed, and the effect of pre-tension is discussed. The results show that: 1) The influence of anchor cable failure on slope safety cannot be ignored. After the failure conditions are met, the free segment no longer transmits tension, and the anchored segment degenerates into soil nails. 2) When the slope is unstable, the anchor cable will show a continuous fracture phenomenon. The fracture first occurred in the dangerous parts such as the slope toe, and then turned to the top. 3) The fracture of the anchor cable will lead to the release of the soil stress, accompanied by the change of the acceleration amplitude and frequency, and finally manifested as a larger residual displacement. Slope reinforcement not only needs to consider the anchoring force, but also the coordination relationship.

Stability analysis and control technology of gob-side entry retaining with double roadways by filling with high-water material in gently inclined coal seam

To ameliorate the defects of insufficient support resistance of traditional roadside filling bodies for gob-side entry retaining (GER), overcome the inability to adapt to the deformation of surrounding rock, and isolate the goaf effectively, a new type of high-water material as a roadside filling body for GER technology with double roadways was proposed. The instability analysis and control technology of GER with double roadways by filling high-water material into a gently inclined coal seam were studied. The basic mechanical properties of the new high-water material were investigated through laboratory experiments, and their main advantages were identified. The reasonable width of the roadside filling wall of a high-water material was obtained by combining ground pressure observation and theoretical calculations. The distribution characteristics of the stress and plastic zone of surrounding rock of GER after being stabilized by the disturbance of the working face were studied using numerical simulations, and the failure range of GER by filling with high-water material was revealed. Based on this, a coupling control technology of anchor cables and bolts + single props + metal mesh + anchor bolts is proposed. Through the coupling methods of arranging borehole peeping and observing the convergences of surrounding rock, the results demonstrate that GER with double roadways by filling with a 1.8-m-wide high-water material has a good control effect. The above research will play an active role in promoting the application of high-water materials in GER roadside filling.

Study on Failure Mechanism and Control Technology of Roadway Surrounding Rock under Complex Occurrence Coal Seam

Aiming at the characteristics of large deformation and long deformation time under the mining influence of the 2254 east floor roadway surrounding rock, which under the condition of complex coal occurrence in Jiahe Mine. Through the actual measurement, it is found that the mineral composition of the roadway surrounding rock is mainly siderite, and it also contains 9.52% of kaolinite minerals, and the surrounding rock is relatively weak. Through drilling and peeping, it is found that the roadway surrounding rock is mainly thin-layered, and a large number of fissures are developed in the surrounding rock near the surface of the roadway. Through the in situ stress test, it is concluded that the in situ stress field of Jiahe Mine is dominated by horizontal stress, the minimum principal stress is vertical principal stress, and the lateral pressure coefficient exceeds 2, causing serious damage to the two sides of the roadway. Using the gas drainage drilling data of the 2254 east floor roadway and using SketchUp and Rhino software, the complex geological occurrence model of the coal seam above the roadway was constructed, and on this basis, the FLAC3D numerical calculation model was constructed. The analysis results show that the plastic zone of the roadway surrounding rock is large, the bolt anchoring section is within the plastic zone, and the control effect on the deformation of the roadway surrounding rock is poor. Therefore, a comprehensive support method of “reserved deformation, anchor rod, metal mesh, shotcrete, grouting anchor cable, and full-section grouting” is proposed. The monitoring results of the surrounding rock deformation of the roadway 12 months after construction show that the support scheme can effectively control the deformation of the roadway surrounding rock. The research results provide a reference for the stability control of similar roadways.