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Rock bolts play a critical role In underground mining. Reinforcing jointed rock masses supports safer, more reliable and productive developments and, with mines installing thousands (if not millions) of units [...]

Full-length grouted bolts play a crucial role in geotechnical engineering thanks to their excellent stability. However, few studies have been concerned with the degrading performance of grouted rock bolts caused by extensive and continuous heat conduction from surrounding rocks in high-geothermal tunnels buried more than 100 m (temperature from 28 °C to 100 °C). To investigate the damage mechanism, we examined the time-varying behaviors of grouted rock bolts in both constant and variable temperature curing environments and their damage due to the coupling effects of high temperature and humidity through mechanical and micro-feature tests, including uniaxial compression test, pull-out test, computed tomography (CT) scans, X-ray diffraction (XRD) test, thermogravimetric analysis (TGA), etc., and further analyzed the relationship between grout properties and anchorage capability. In order to facilitate a rapid assessment and control of the anchorage performance of anchors in different conditions, results of the interface bond degradation tests were correlated to environment parameters based on the damage model of interfacial bond stress proposed. Accordingly, a thermal hazard classification criterion for anchorage design in high-geothermal tunnels was suggested. Based on the reported results, although high temperature accelerated the early-stage hydration reaction of grouting materials, it affected the distribution and quantity of hydration products by inhibiting hydration degree, thus causing mechanical damage to the anchorage system. There was a significant positive correlation between the strength of the grouting material and the anchoring force. Influenced by the changes in grout properties, three failure patterns of rock bolts typically existed. Applying a hot-wet curing regime results in less reduction in anchorage force compared to the hot-dry curing conditions. The findings of this study would contribute to the design and investigations of grouted rock bolts in high-geothermal tunnels.

ABSTRACT The corrosion of rock bolts buried in rock and soil layer is obviously different from that of general ground structure. The main corrosion sources of the latter come from [...]

ABSTRACT This paper aims to propose new numerical procedures for elasto-plastic analysis of the interactions between fully-grouted bolt and rock with slip and non-slip cases at a potential-failure interface. In [...]

Previous studies rarely involved the mechanical properties of anchorage system under the condition of internal absolute displacement of surrounding rock and the solution of important parameters of anchorage system. In this paper, the absolute displacement law of rock mass under the anchorage system is analyzed by the fiber grating (FBG) multi-point displacement meter and multidirectional displacement conversion formula. Based on the coordinated deformation principle for rock bolt and rock mass, the mechanical analysis model for rock bolt-rock mass system is established, and the influence rules of rock bolt length, rock bolt diameter and rock bolt preload on the internal force distribution of rock bolt is studied based on the stress analysis of full-length rock bolt in a tunnel engineering. The results show that: (1) with the increase of rock bolt length, the anchoring effect gradually enhances, but the improvement degree decreases gradually; (2) with the increase of rock bolt diameter, the anchoring effect is enhanced; at the same time, however, the shear stress of rock bolt is larger, and the possibility of rock bolt sliding also increases; and (3) with the increase of preload, the increase of “anchor length” makes the anti-sliding ability of rock bolt increase correspondingly, and the supporting effect of rock bolt increases gradually. Then the full-process analysis for the mechanical mechanism of rock bolt sliding failure and the iterative calculation method for rock bolt displacement are studied. At last, the numerical simulation for pull-out test is carried out through the finite element analysis to verify the calculation results of mechanical model, and according to the iterative operation, the two important parameters such as the interface shear stiffness Kand the interface peak shear strength τPare solved. The analysis show that the numerical simulation results are in good agreement with the mechanical model calculation. This study can provide a theoretical basis for rock bolt support technology and support structure design.

After the excavation of a tunnel, generally, rock bolts are used as primary support. Installation of rock bolts considerably reduces the further deformation in the rock mass around the tunnel boundary. Bolts provide additional support to mass and therefore mass becomes stiffer, rigid, and stronger. The theory of rock bolts–rock mass interaction is quite complex and contains numerous factors. The complex interaction between mass and bolts leads to complex theoretical analysis, and sometimes, it is very difficult to find out the solutions. Hence, to rectify this, the continuum model of numerical analysis is used which is simple and convenient. Rock mass and rock bolts are two distinct materials, and their mechanical properties are much different from each other. In continuum analysis, generally, they are modelled separately, i.e. different mechanical properties are assigned to rock mass and rock bolt. As the whole mass is treated as equivalent continua, separate modelling of the bolt and the rock mass may give misleading results. Proper interaction between mass and bolts may not develop due to the non-existence of joints in the continuum model. Hence, if, in the continuum model, rock and bolt to be modelled together with equivalent mechanical properties, the result would be different. The present research work deals with continuum analysis of a rock bolt-reinforced tunnel in which equivalent mechanical properties of bolt and rock are used. Equivalent mechanical properties were worked out from the laboratory investigations conducted on the specimens of natural jointed rock and rock bolt. The equivalent continuum model of a rock bolt-reinforced tunnel was developed, analyzed, and compared with the conventional continuum model. The result suggested that if rock bolts are taken as an integral part of the rock mass and modelled as an equivalent continua, the result would be more rational and reliable.

Bearing plates made from plastic composites can be used as an alternative to their steel counterparts in rock bolt or soil nail applications. To achieve this goal, an existing recycled high-density polyethylene bearing plate was investigated and later modified to improve its engineering properties. Laboratory studies were conducted to determine the failure load of the existing and modified plates, and a numerical model was developed for complementary analysis. The results of both efforts clearly showed that the existing bearing plate was not adequate in terms of strength and creep properties, as it quickly yielded with large displacements at relatively low loads. In order to enhance the strength of the plate, both geometric and material modifications are made by our research group to obtain a more efficient plate. Numerical models were used to determine the frame layout, and a series of analyses were performed to evaluate the effects of frame thickness, number and arrangement. Once the design was optimized and finalized, a mold was created to match the new geometry for manufacturing new plates through injection molding. A test setup was also established in the laboratory and numerous compression tests were performed on the manufactured new plates. The measured load-displacement behavior of plates made of polyethylene and polyamide with a variety of additives were discussed separately. It was determined that the new plastic plates reinforced with polyamide through various additives have the potential to reach a strength up to 200–240 kN, which is at least two times higher than the existing one, with distinct economic advantages.

This study aims to inspect grout defects in rock bolts using electromagnetic (EM) waves. The experiments are conducted using one intact rock bolt and eight defective rock bolts with defect ratios (DR) of 10–50%. A two-conductor transmission line is configured using a pair of rock bolts to transmit EM waves. The EM waves are generated and detected using a time-domain reflectometer. Consequently, the velocity of the EM waves increases with increasing DR. Additionally, almost identical velocities are observed at the same DR, regardless of the defect locations. Moreover, the EM wave reflections are observed at these defects. The defect locations are estimated using the velocity and reflection time of the defects. The estimated location is in good agreement with the actual location. This study demonstrates that EM waves can be an effective tool for evaluating grout defects in rock bolts.

In coal mining roadway support design, the working resistance of the rock bolt is the key factor affecting its maximum support load. Effective improvement of the working resistance is of great significance to roadway support. Based on the rock bolt’s tensile characteristics and the mining roadway surrounding rock deformation, a mechanical model for calculating the working resistance of the rock bolt was established and solved. Taking the mining roadway of the 17102 (3) working face at the Panji No. 3 Coal Mine of China as a research site, with a quadrilateral section roadway, the influence of pretension and anchorage length on the working resistance of high-strength and ordinary rock bolts in the middle and corner of the roadway is studied. The results show that when the bolt is in the elastic stage, increasing the pretension and anchorage length can effectively improve the working resistance. When the bolt is in the yield and strain-strengthening stages, increasing the pretension and anchorage length cannot effectively improve the working resistance. The influence of pretension and anchorage length on the ordinary and high-strength bolts is similar. The ordinary bolt’s working resistance is approximately 25 kN less than that of the high-strength bolt. When pretension and anchorage length are considered separately, the best pretensions of the high-strength bolt in the middle of the roadway side and the roadway corner are 41.55 and 104.26 kN, respectively, and the best anchorage lengths are 1.54 and 2.12 m, respectively. The best anchorage length of the ordinary bolt is the same as that of the high-strength bolt, and the best pretension for the ordinary bolt in the middle of the roadway side and at the roadway corner is 33.51 and 85.12 kN, respectively. The research results can provide a theoretical basis for supporting the design of quadrilateral mining roadways.

Rock bolts are components of tunnel support structures and their efficacy in reinforcement requires the appropriate estimation of the bolt pre-tension. However, cases of ineffective rock bolt application due to loosening are common which leads to the potential failure of the support structures, thus negatively affecting the tunnel stability. The effective employment of pre-tensioned bolt within support structures requires an appropriate installation tension as a result of sufficient bolt head/nut pre-load. Henceforth, this paper presents a load indicator washer (LIW) capable of withstanding assigned static loading as well as provides an appropriate pre-tension. The different LIW breadths are numerically analysed in the finite element code (ABAQUS) to estimate deformation when a designated 60-kN pre-load is applied. The numerical simulation employs a bi-linear isotropic hardening constitutive law governed by the von Mises yield criterion. The simulation also considers the nominal temperature of the nut-LIW-rock bolt connection. Therefore, a long-term relaxation effect on bolt pre-tension as a result of stress relaxation is neglected. The compressive force required to achieve the LIW-predetermined deformation is the bolt pre-tension. It is drawn from the simulation results that the 1.5-, 2.0-, 3.0-, 3.5-, and 4.0-mm-thick LIWs are completely flattened when subjected to 28-, 42.5-, 65-, 76-, and 88-kN pre-load respectively.

The problem of proper assessment of the technical functionality of rock bolt support systems is still valid. Many research centers have undertaken efforts to diagnose and monitor the technical state of such a support system used in mines and tunneling. With that aim the method of quality assessment of grouted rock bolts was invented and a relevant apparatus was constructed. The method concerns non-destructive identification of discontinuity of a resin layer (grout) surrounding rock bolts. The method is based on an impact excitation of a rock bolt and uses modal analysis procedures. Assuming that the installed rock bolt acts as an oscillator, different lengths and positions of grouting discontinuity alter its modal parameters. The extraction of these modal parameters, of which a resonant frequency is seen as the most valued, enable the relevant identification of grout discontinuity. After constructing a prototype version and validating the results for known cases of resin discontinuity in an experimental coal mine, the apparatus fulfilling ATEX requirements was developed. Subsequently that version was also verified both in laboratory conditions and in an experimental coal mine. As necessary for proper identification of discontinuity length, the reference data base was developed and elaborated consisting of a very large number of finite element models (FE models), namely discontinuity cases. The models encountered different rock bolt lengths and diameters, different rock strata parameters and different positions and lengths of resin layers. Then the method was used in a working coal mine to monitor a technical state of rock bolt support system mounted to reinforce long underground openings. The data base was utilized as reference for investigated rock bolts.

A parametric study was conducted to determine the influence of different bolt parameters (bolt length and diameter) on the maximum induced boundary displacements in jointed rockmass, using a numerical method based on finite element code. Three different types of jointed systems (Type A, Type B, and Type C) were considered and analyzed. Type A displays normal joint closure, Type B demonstrates a combination of normal and shear joint closure, and in Type C, the majority of the joint is loaded in shear condition. The ground surface settlement profiles for these three joint systems, under unsupported conditions, are presented in this work. For the same rockmass properties, the cases in Type A and Type B exhibit the maximum and minimum settlement, respectively. For each joint type, the effect of variable bolt parameters on the tunnel boundary is studied in terms of the total displacement. The simulation results confirm that an increase in the bolt length does not significantly reduce the boundary displacement, whereas an increase in the bolt diameter substantially reduces the tunnel boundary displacement.

AbstractThe position determination for rock bolt support design based on rock stress distribution is important in ensuring full mobilization of rock bolt tensions during excavation process. The monitoring of the progressive rock stress variation in magnitude and orientation can play an important role in optimal installation of rock bolt. The aim of this paper is to determine the optimal positions for rock bolt installation by computing the progressive directional variation of rock stresses and plot the stress distribution in a two-dimensional stereographic projection to capture the stress transformation during excavation process. Finally, an algorithm based on stress transformation determination for optimal rock bolt installation is proposed.

2017 NOV 11 (NewsRx) -- By a News Reporter-Staff News Editor at Obesity, Fitness & Wellness Week -- A patent application by the inventors Krekula, Hakan (Kiruna, SE); Eriksson, Leif [...]

A new method was developed to apply pull-and-shear loads to the bolt specimen in order to evaluate the anchorage performance of the rebar bolt and the D-Bolt. In the tests, five displacing angles (0°, 20°, 40°, 60°, and 90°), two joint gaps (0 mm and 30 mm), and three kinds of host rock materials (weak concrete, strong concrete, and concrete-granite) were considered, and stress–strain measurements were conducted. Results show that the ultimate loads of both the D-Bolt and the rebar bolt remained constant with any displacing angles. The ultimate displacement of the D-Bolt changed from 140 mm at the 0° displacing angle (pure pull) to approximately 70 mm at a displacing angle greater than 40°. The displacement capacity of the D-Bolt is approximately 3.5 times that of the rebar bolt under pure pull and 50% higher than that of the rebar bolt under pure shear. The compressive stress exists at 50 mm from the bolt head, and the maximum bending moment value rises with the increasing displacing angle. The rebar bolt mobilises greater applied load than the D-Bolt when subjected to the maximum bending. The yielding length (at 0°) of the D-Bolt is longer than that of the rebar bolt. The displacement capacity of the bolts increased with the joint gap. The bolt subjected to joint gap effect yields more quickly with greater bending moment and smaller applied load. The displacement capacities of the D-Bolt and the rebar bolt are greater in the weak host rock than that in the hard host rock. In pure shear condition, the ultimate load of the bolts slightly decreases in the hard rock. The yielding speed in the hard rock is higher than that in the weak rock.

Anchoring technology is widely used in slope, tunnels and underground engineering. However, the rock bolt quality is still a hot problem which is difficult to solve. Considering the shortcoming of pull-out testing, defect identification in a non-destructive way is necessary. In this paper, the signal decomposition is obtained by rock bolt quality detector and wavelet packet transform and energy feature is extracted; the normalised energy eigenvector is converted as input of probabilistic neural network (PNN); the smoothing factor in PNN is optimised based on particle swarm optimisation algorithm and the defect identification rate of PNN is improved. With a higher accuracy than radial basis functions (RBF) neural network and PNN, the improved PNN can provide a reference for defect identification of rock bolt in engineering without destruction.

In this study, usability of Polyamide-6 type engineering polymer as a new rock bolt material was investigated carrying out a series of laboratory and field scale experiments. The Polyamide-6 type polymer tested as a grouted rock bolt material was assessed to have a good body strength, large elastic deformation limit and high energy absorbing capacity. The load bearing capacity of Polyamide-6 rock bolts was found to dominantly depend on the mechanical anchorage in front of the shank as a result of having low adhesion to the cement grout values. In this study, polyamide rock bolts have been designed with different mechanical anchors. It was suggested to start the systematical use of polyamide rock bolts having ideal support reactions under both static and dynamic load conditions in rock engineering. Especially, Polyamide-6 rock bolts were assessed to be economically usable in rock masses with squeezing, swelling or bursting problem, which need for non-decreasing support pressure while being higly deformed and good energy absorption capacity.

Expandable rock bolts are widely used in hard rock mines as an efficient ground control product. However, capacity and service life can be significantly reduced if the metallic body is subjected to corrosion. In some hard rock mines in the U.S., highly corrosive ground conditions exist, and it has been reported that inflatable rock bolts have corroded within a few months after installation. To provide mining industry a cost-effective inflatable bolt and combat the corrosion issues, Jennmar Corporation, Inc., and its subsidiary Keystone Mining Services, LLC (KMS), analyzed corroded bolt samples, identified root causes, evaluated properties of various coating materials, and developed a new inflatable rock bolt, Python M3™, that is protected with an innovative PyFlexU2™ coating. The new generation Python M3™ features improved steel chemistry for reliable performance, modified profile for better inflation, and surface preparation and coating application. The PyFlexU2™ is impervious to liquid and air, durable, and UV resistant. With a flexible, adhesive, and highly corrosion-resistant undercoating, and a very hard sacrificial surface coating, the PyFlexU2™ coating system provides the Python M3™ superior protection against chemical corrosion and physical scratch damage. The under-coating has exceptional flexibility and adhesion to prevent coating micro-cracks or fractures after bolt inflation and possesses excellent corrosion resistance to acids (pH < 3), alkalis (pH > 11), fuels, and salt solvents. The corrosion and scratch resistant PyFlexU2™ coating offers very effective bolt protection for extra longevity in highly corrosive environments. The Python M3™ coated with PyFlexU2™ has been tested in the most challenging conditions, including laboratory corrosion tests in extreme acidic and basic solvents, rock slurry, and borehole scratch insertion tests. With demonstrated corrosion and scratch resistance, the product has been greatly welcomed by hard rock mines in the West and is currently installed in large scale. This paper identifies the root causes of the bolt corrosion, discusses the analysis process, and details laboratory and underground tests carried out on the Python M3™ coated with PyFlexU2™. The Python M3™ and PyFlexU2™ are subjects covered by pending U.S. Patent Applications assigned to FCI Holdings Delaware, LLC.

The length of the rock bolt is an important factor to evaluate the quality of anchor. According to the fact that the calculated value of anchor length is far different from the actual situation due to a lot of noises, a de-noising method based on Empirical Mode Decomposition (EMD) and Spectral Kurtosis (SK) is proposed in this paper, to filter noise, and improve accuracy of calculating anchor length. The fundamental idea is that calculating spectral kurtosis for each component after EMD, the larger spectral kurtosis are used to reconstruct signal to improve signal to noise ratio. The analysis results demonstrate that the method can improve spectral kurtosis of the reconstructed signal and decrease the error of anchor length. In addition, D-S evidence is introduced to realise high precision computation for anchor length by data fusion of wavelet threshold de-noising and spectral kurtosis filter.

At present, the suspended monorail systems constitute a very common means of transportation in the Polish hard coal mines. The main advantages of the suspended monorail include the independence of the route from the working floor surface irregularities and the possibility to transport cargo of significant mass and size.

Rock bolts are commonly used on transportation projects to stabilize cut slopes, reinforce undermined or unsupported blocks, and reduce potential for large rock slides. Installing bolts can be challenging. Locations where bolts are useful may not be easily accessible for personnel or large equipment, and targeted blocks generally are marginally stable. In addition, jointed rock with openings and voids, which are typical conditions, complicate hole advancement and full grout encapsulation. These issues can lead to construction delays, claims, reduced corrosion protection, or shorter design life. This paper describes research conducted to address two rock bolting challenges in open-jointed rock: i) advancement of drill holes to design depth, and ii) successful completion of grouting through the application of injected polyurethane foam (PUF). Testing utilized double-stacked concrete blocks aligned in rows to simulate a rock mass with vertical fractures. Steel spacers were placed between the stacks to simulate 2-, 4-, 6-, and 8-inch apertures. A standard rock drill advanced holes using a 3-inch bit. Research showed PUF could: bridge simulated aperture sizes up to 8 inches, survive drilling action during secondary reaming, resist drilling air and grouting pressures, and reduce grout consumption.

In the underground mines of the Legnica–Głogów Copper District (LGOM) the main way to protect the room excavation is the use of a rock bolt support. For many years, it has proven to be an efficient security measure in excavations which met all safety standards and requirements. The article presents the consumption of the rock bolt support in the Mining Department “Polkowice–Sieroszowice” in the years 2010–2015 as well as the number of bolt supports that were used to secure the excavations. In addition, it shows the percentage of bolt supports that were used to conduct rebuilding work and cover the surface of exposed roofs. One of the factors contributing to the loss of the functionality of bolt supports is corrosion whose occurrence may lead directly to a reduction in the diameter of rock bolt support parts, in particular rods, bearing plates and nuts. The phenomenon of the corrosion of the bolt support and its elements in underground mining is an extremely common phenomenon due to the favorable conditions for its development in mines, namely high temperature and humidity, as well as the presence of highly aggressive water. This involves primarily a decrease in the capacity of bolt support construction, which entails the need for its strengthening, and often the need to perform the reconstruction of the excavation.

The basic type of rock mass reinforcement method for both preparatory and operational workings in underground metal ore mines, both in Poland and in different countries across the world, is the expansion shell or adhesive-bonded rock bolt. The article discusses results of static loading test of the expansion shell rock bolts equipped with originally developed deformable component. This component consists of two profiled rock bolt washers, two disk springs, and three guide bars. The disk spring and disk washer material differs in stiffness. The construction materials ensure that at first the springs under loading are partially compressed, and then the rock bolt washer is plastically deformed. The rock bolts tested were installed in blocks simulating a rock mass with rock compressive strength of 80 MPa. The rock bolt was loaded statically until its ultimate loading capacity was exceeded. The study presents the results obtained under laboratory conditions in the test rig allowing testing of the rock bolts at their natural size, as used in underground metal ore mines. The stress-strain/displacement characteristics of the expansion shell rock bolt with the deformable component were determined experimentally. The relationships between the geometric parameters and specific strains or displacements of the bolt rod were described, and the percentage contribution of those values in total displacements, resulting from the deformation of rock bolt support components (washer, thread) and the expansion shell head displacements, were estimated. The stiffness of the yielded and stiff bolts was empirically determined, including stiffness parameters of every individual part (deformable component, steel rod). There were two phases of displacement observed during the static tension of the rock bolt which differed in their intensity.

The interaction mechanism between coal and rock masses with supporting materials is significant in roadway control, especially in deep underground mining situations where dynamic hazards frequently happened due to high geo-stress and strong disturbed effects. This paper is to investigate the strain energy evolution in the interaction between coal and rock masses with self-designed energy-absorbing props and rock bolts by numerical modeling with the finite difference method. The interaction between rock and rock bolt/prop is accomplished by the cables element and the interface between the inner and outer prop. Roadway excavation and coal extraction conditions in deep mining are numerically employed to investigate deformation, plastic zone ranges, strain energy input, accumulation, dissipation, and release. The effect on strain energy input, accumulation, dissipation, and release with rock deformation, and the plastic zone is addressed. A ratio of strain energy accumulation, dissipation, and release with energy input α, β, γis to assess the dynamic hazards. The effects on roadway excavation and coal extraction steps of α, β, γare discussed. The results show that: (1) In deep high geo-stress roadways, the energy-absorbing support system plays a dual role in resisting deformation and reducing the scope of plastic zones in surrounding rock, as well as absorbing energy release in the surrounding rock, especially in the coal extraction state to mitigate disturbed effects. (2) The strain energy input, accumulation is dependent on roadway deformation, the strain energy dissipation is relied on plastic zone area and disturbed effects, and strain energy release density are the difference among the three. The function of energy-absorbing rock bolts and props play a key role to mitigate strain energy release density and amount, especially in coal extraction condition, with a peak density value from 4×104to 1×104J/m3, and amount value from 3.57×108to 1.90×106J. (3) When mining is advanced in small steps, the strain energy accumulation is dominated. While in a large step, the released energy is dominant, thus a more dynamic hazards proneness. The energy-absorbing rock bolt and prop can reduce three times strain energy release amount, thus reducing the dynamic hazards. The results suggest that energy-absorbing props and rock bolts can effectively reduce the strain energy in the coal and rock masses, and prevent rock bursts and other hazards. The numerical model developed in this study can also be used to optimize the design of energy-absorbing props and rock bolts for specific mining conditions.

Grouted rock bolts subject to axial loading in the field exhibit various failure modes, among which the most predominant one is the bolt-grout interface failure. Thus, mechanical characterization of the grout is essential for understanding its performance in ground support. To date, few studies have been conducted to characterize the mechanical behaviour of fiber-reinforced grout (FRG) in rock bolt reinforcement. Here we experimentally studied the mechanical behaviour of FRG under uniaxial compression, indirect tension, and direct shear loading conditions. We also conducted a series of pullout tests of rebar bolt encapsulated with different grouts including conventional cementitious grout and FRG. FRG was developed using 15% silica fume (SF) replacement of cement (by weight) and steel fiber to achieve high-strength and crack-resistance to overcome drawbacks of the conventional grout. Two types of steel fibers including straight and wavy steel fibers were further added to enhance the grout quality. The effect of fiber shape and fiber volume proportion on the grout mechanical properties were examined. Our experimental results showed that the addition of SF and steel fiber by 1.5% fiber volume proportion could lead to the highest compressive, tensile, and shear strengths of the grout. The minimum volume of fiber that could improve the mechanical properties of grout was found at 0.5%. The scanning electron microscopy (SEM) analysis demonstrated that steel fibers act as an excellent bridge to prevent the cracks from propagating at the interfacial region and hence to aid in maintaining the integrity of the cementitious grout. Our laboratory pullout tests further confirmed that FRG could prevent the cylindrical grout annulus from radial crack and hence improve the rebar's load carrying capacity. Therefore, FRG has a potential to be utilized in civil and mining applications where high-strength and crack-resistance support is required.

The purpose of this paper is to establish confidence in anticipated minimum bond strength for inflatable rock bolts by comparing the bond strength to variable geotechnical conditions using the rock mass rating (RMR) system. To investigate a correlation between these parameters, the minimum bond strength of pull-out tested inflatable rock bolts was compared to the RMR of the rock in which these bolts were placed. Bond strength vs. RMR plots indicate that expected minimum bond strength is positively correlated with RMR; however, the correlation is not strong. Cumulative percent graphs indicate that 97% of pull-out tests result in a minimum bond strength of 3.3 and 1.7ton/m in RMR⩾45 and <45, respectively. Although lower bond strengths are more commonly encountered in low RMR ground, high bond strengths are possible as well, yielding higher variability in bond strengths in low RMR ground. Bond strength of friction bolts relies on contact between the rock bolt and drill hole. Experience in Nevada indicates that RMR is known to affect both the quality and consistency of drill holes which likely affects bond strength. Drilling and bolting in low RMR ground is more sensitive to drilling and bolting practices, and strategies for maximizing bond strength in these conditions are discussed.

Rock bolts are used as permanent and temporary support systems in tunneling and mining operations. A dynamic-expansion rock bolt system that can be installed rapidly in a drilled hole is introduced in this article. The dynamic-expansion rock bolt system consists of a star-shaped steel tube and an ignition system with a dynamic expansion agent in the steel tube of the rock bolt. After the ignition of the dynamic agent in the tube, the star-shaped steel tube expands dynamically as a result of gas production by the dynamic agent. This expansion leads to frictional mounting of the tube in a drilled hole. Laboratory-scale pull-out tests of the rock bolt, installed in a thick steel tube, were performed to investigate the friction behavior between the steel tube and the smooth wall of a drilled hole. These tests revealed that the ultimate pull-out load reached approximately 6 kN and that a long displacement subsequently occurred. Field-scale tests for two prototype rock bolts were performed to evaluate the pull-out load-bearing capacity of the rock bolt. The welded areas of the two tube bolts were broken when the pull-out loads reached approximately 114 and 91 kN.

A series of laboratory tests were performed to study the mechanical behaviours of newly developed high strength rock bolt components, including rebar, thread, plate, and domed washer. The characteristics of deformation and damage of each component were presented. The stress distribution of plate and domed washer was investigated through finite element modelling. The numerical results show that the yield and tensile strengths of the developed high strength rebar are 33.6%–58.3% and 17.2%–28.7% greater than those of the conventional rebar, respectively. The increase in yield strength was higher than that in tensile strength, suggesting an increase in yield to tensile strength ratio and a decrease in elongation. It is well-known that the thread processing may not be of high precision and accuracy as expected, which is characterised as rough thread surface, non-identical tooth height, toe stripping, and cracks in the surface. Hardening during thread processing tends to increase the thread yield and tensile strengths. In this paper, the typical deformation process of arch-shaped plate is classified into five stages. The tested plates exhibited distinct deformation characteristics and bearing capacities due to variations in shape, size, material and presence of washer. It was observed that uneven bottom surface, low bearing arch and large radius of the transitional arc connecting bearing arch and bottom surface were the major reasons accounting for low load-bearing capacity of plates. The performance of domed washer has a close relation with the shape, size, strength, and deformation compatibility with plate. Stress concentration was observed on the periphery of the contact surface between domed washer and plate, which is significantly influenced by the strength of domed washer and is considered to be 20%–30% higher than that of plate. Finally, a case study in the Datong coal mining district was presented, and the support pattern and effect of the developed rock bolt were described.

Current developments in numerical modelling techniques are presented to investigate the load transfer between the steel bolt surface and grout. Underground measurements of steel bolt performance indicate that amongst many parameters bolt profile configuration play an important role in load transfer capacity between the bolt and grout. This study proposes a new numerical solution to predict displacement, shear stress and shear strain of a fully grouted rock bolt intersected by single rock joint. The main characteristics of the numerical solution, consider the bolt profile and joint movement under pull test condition. In this paper, five types of rock bolts are used with different profiles. The rock bolts are modelled by ANSYS software. Profile rock bolt T3and T4with load capacity 180 kN and 195 kN in the jointed rocks, were choices as the optimum profiles. The results showed that there is a promising agreement between numerical and experimental methods.

—Abstract: The use of high-strength rock bolt in the underground often occured brittle fracture in the threaded section, this is closely related to bolt material impact toughness. Tested the impact absorbed energy of four manufacturers of the yield strength of 500MPa rock bolt and the impact absorbed energy value ranging from 19J to 165J. Tested bending test of the bolt rod and threaded section that has a different impact absorbed energy, the results showed that: the impact toughness affects the cold bending of the rock bolt thread segment, when the impact absorbed energy value is less than 30J rock bolt thread segment cold bending poor; impact toughness has no obvious affect on the cold bending of rod.

Pretension is a key factor affecting the performance of rock bolt. It is usually applied on the bolt by tightening the nut. The efficiency of the torque-to-pretension conversion is significantly influenced by the thread rolling accuracy. In this study, the influence of the thread rolling accuracy upon the pretension is investigated. Factors influencing the thread rolling efficiency, i.e., rock bolt material quality, rolling technic and equipments, are examined. To study the relationship between torque and pretension, a laboratory table was specially designed and a series of tests were carried out on the rock bolts with different thread accuracy. The result indicates that the higher the thread rolling accuracy, the higher the coefficient of torque-to-pretension conversion. And the coefficient can be improved by daubing lubrication oil on the thread. In China, the rock bolt thread encounters the issue of low rolling accuracy which results in coarse thread surface. As a result, the efficiency of the torque-to-pretension conversion is greatly reduced. In addition, the rock bolt is susceptible to break at the thread end. Essential approach to resolve these issues is to significantly improve the thread rolling accuracy by adopting advanced equipment.

A new method of rock bolt safety testing for use in mining and civil engineering is being developed by the University of Queensland's Julius Kruttschnitt Mineral Research Centre. The JKRockBoltTester [...]

The artificial neural network has been widely used in various field of science and engineering. The artificial neural network has marvelous ability to gain knowledge. In this paper, according to principle of artificial neural network , Model of artificial neural network of rock bolt support of roadway of coal mine has been constructed,Learning system of BP artificial neural network has been trained,it is shown by engineering application that artificial neural network can handle imperfect or incomplete data and it can capture nonlinear and complex relationships among variables of a system. the artificial neural network is emerging as a powerful tool for modeling with the complex system. Method and parameters of rock bolt support of roadway of coal mine can be predicated accurately using artificial neural network, that is of significance and valuable to those subjects of investigation and design of mining engineering

The rock bolt has been widely used as an effective reinforcement in civil and mining engineering for a long time. However, the anchored mechanism of it is not well understood. This paper obtained the expression of the shear stress and axial force of stretched fully grouted rock bolt base on previous working, and detailed analysis the influence parameters of stress distribution. It is considered the anchored effect is influenced by some factors. Augmenting diameter of rock bolt, increasing the pre-stress magnitude and improving the strength of grout may all improve the anchored effect of rock bolt. As the rock character and the grout property are similar, the rock bolt anchored effect is optimal. There is a stress concentrated phenomena at the front of rock bolt. It is shown that the distribution of shear stress and axial force are not even distribution and exponentially attenuated along a fully grouted bolt.

The bolt’s load transfer differential equation has established according the stress equilibrium in a small section of a bolt and load transfer mechanics. And according the rock mass deformation before and after bolt assembling, the rock bolt’s load transfer equation has gained. In this paper, from later researching achievement, the radial displacement function of brittle wall rock for tunnel is gotten. And combining the radial deformation of tunnel wall rock mass, the axial force and friction resistance of rock bolt have gotten in brittle wall rock mass. Through analyzing the stress distribution feature and stress distribution tendency and affection factors, the affection factors to anchoring results is the dilatancy angle. And through the studying, it is show that the axial force and shear stress of rock bolt are bigger with the dilatancy angle increase

It is important for evaluating the condition of rock bolts to theoretically investigate the propagation of elastic waves in Rock bolt .In this paper, ultrasonic guided wave propagation and the interaction law with the artificial corrosion ring defect in the solid cylinder were studied through the rock bolt was modeled as a cylindrical. A large number of numerical simulation experiments were carried out using finite element method based on ABAQUS, The longitudinal mode of the propagation characteristics and law were analyzed in the solid cylinder, and the best excitation model and frequency were selected for the signal dispersion by combining curve with wave structures knowledge. The outcome of this research indicated that L(0,1) reflection coefficient is increased as well as during the depth incremental change when given a particular axial length; With the increment of the axial, L(0,1) and F(1,1) of the reflection coefficient maintain the similar trend when the ring defect depth coefficient 10%.

Experiments were conducted to study the attenuation properties of ultrasonic guided wave propagating in anchored rock bolts. Results show that concrete as anchored material at different curing time can represent different bonding quality, and attenuation coefficient value of ultrasonic guided wave in anchored bolt increases as the increasing of curing time. At the mean time, the attenuation coefficient value becomes larger when the anchored length of rock bolt increases. So attenuation coefficient value is an efficient tool to evaluate the bonding quality of anchored rock bolt.

The anchorage length of the bolt in rock bolt crane girder is obtained by means of rigid limit equilibrium method and the critical the anchorage length of bolt is calculated by analytical solution. Combined with the calculation results, the analysis on the mechanical characteristics is carried on by building the finite element model of rock bolt crane girder with different anchorage length of bolt. The analysis results indicate that the bearing characteristics of rock bolt crane girder are not improved significantly with the increase of anchorage length when the anchorage length of bolt exceeds the engineering critical anchorage length. The existence of critical anchorage length of blot is proved further, and the rationality of analytical solution for critical anchorage length is validated.

In this paper, according to the reality that there is no mature Chinese national design criterion but partial enterprise standard for rock bolt crane girder in the underground powerhouse of large hydropower station up to now. Based on the geological conditions, the rock bolt crane girder was designed by using method of rigid body equilibrium. The reinforced anchoring measures for rock bolt crane girder in undesirable geology were studied subsequently by the experience of analogous projects. The stability of rock bolt crane girder in underground powerhouse was analyzed and evaluated by Finite Element Method (FEM). Then the bearing capacity of crane beam was researched by means of bearing testing. The results show FEM is practicable to evaluate the stability of the rock bolt crane girder and to guide the rock bolt crane girder designing. The results also show the reinforced anchoring measures are appropriate to displace the undesirable surrounding rock section by using concrete. The results of bearing testing show that the design of rock bolt crane girder and its anchoring measures are rational, and crane girder can meet to the requirement of safe operation.

Rock bolt crane girder is a structure form which is widely used in the underground powerhouse of hydropower station. It makes reinforced concrete anchored in the underground powerhouse rock using anchor rod, and makes the reinforced concrete, anchor rod and surrounding rock work together to resist the load. Stability has been a common problem in the realm of engineered construction. This article will analysis the stability of the rock bolt crane girder in a underground powerhouse of hydropower station by using the traditional rigid body limit equilibrium method and the finite element method, and give several destroying forms. The results show that the rigid body limit equilibrium method is flawed, need to be corrected; In overload cases, the contact surface of girder and rock crack, it turns the damage to the bottom O point at the end; When it is simulated by the strength storage method, the crane girder's shear yield slips the damage along the base.

Abstract: Based on guided wave theory and considering the grouted rock bolt as waveguide medium, we have constructed a three-dimensional model of grouted rock bolt with the dynamics of finite difference numerical simulation software FLAC3D4.0, and simulated the propagation behavior of the guided wave in the full grouted rock bolt. The simulated waveform and wave velocity matched well with the experimental results. We have made a more in-depth and comprehensive study of the wave velocity, wave component and attenuation characteristics of the guided wave propagating in rock bolt, and found some new characteristics and phenomena. In addition, some phenomena that haven’t been explained in the previous researches have also been discussed in this paper. The result showed that when guided wave propagates in grouted rock bolt, after the body wave decays, there is still the interface wave-Stoneley wave that does not decay in the axial direction of the bolt. The findings can provide some reference for rock bolt testing and the selection of the optimal excitation wave of testing.

Work recently was completed to reduce the risk of potential rock slides as part of a road relocation project at Pinkham's Grant in northern New Hampshire. Alvin J. Coleman & [...]

Bolts are widely used in slope engineering, tunnel and large cave supporting structures, as well as restoration of engineering structures. They can improve the strength and stability of ground, rock mass, and other structures. The traditional steel bolt has some disadvantages, such as easy corrosion, heavy weight, and difficult operation. Glass Fiber Reinforced Polymer (GFRP) is more resistant to chloride, stronger and lighter than steel. Those advantages make it a better alternative in some fields of engineering. To utilize GFRP bars as rock bolt, some aspects of its behavior, such as bond strength in mortar, bearing capacity, and bond stress distributing along its interface, have to be examined. This paper presents a research on bond behavior of GFRP rock bolts. A concrete block is used to represent rock mass in laboratory. Modified pull out tests were conducted on selected GFRP bars and compared with steel ones that were grouted with mortar in concrete blocks. Bond characteristics of mortar grouted GFRP rock bolts with diameter 16mm were mainly evaluated and other specs of bolts were also discussed.

The purpose of this study was to investigate the effect of bolt profile on load transfer mechanism of fully grouted bolts in jointed rocks using analytical and numerical methods. Based on the analytical method with development of methods, a new model is presented. To validate the analytical model, five different profiles modeled by ANSYS software. The profile of rock bolts T3and T4with load transfer capacity, respectively 180 and 195kN in the jointed rocks was selected as the optimum profiles. Finally, the selected profiles were examined in Tabas Coal Mine. FLAC analysis indicates that patterns 6+7 with 2NO flexi bolt 4m better than other patterns within the faulted zone.

The effect of long term exposure of full size bolts to corrosive environments is presented. A special test rig was used to test four bolts under different loading conditions. Four X-grade identical profile bolts, each 21·7 mm core diameter (23·7 mm full diameter) were subjected to prolonged corrosion testing using acid sulphate water. The pH value of the circulated water varied between 3·4 and 4·3. The corrosion exposure test period lasted 3·5 years. Two bolts were axially loaded to 10 t and 20 t force respectively, the third bolt was subjected to a 360 Nm torsion load and the fourth bolt was left unstressed to act as a reference bolt. After the test period ended, the bolts were stripped of their corroded coatings and weighted for weight loss. The diameter of each bolt was subsequently measured, and the loaded bolt samples were first tested non-destructively for tensile cracks and then tested for tensile failure. No cracks were found on post-corrosion bolts tested non-destructively. The failure strength reduction on all four post-corroded bolts was significant, varying between 21 and 39%. The onset of corrosion was not confined to the water targeted mid-section length of the bolt, however, the most severe corrosion occurred at the anchored ends of the bolts, possibly attributed to the combination of several types of corrosion which may have been also compounded with increased surface area of the threading at the bolt ends and excessive aeration corrosion due to increase in air movement.

With development of coal mining technology and equipment, the coal roadway section size increases gradually, making roadway more difficult to support. In the paper, the supporting of large cross-section roadway in Hedong mine is studied and roadway excavation supporting process is simulated by FLAC3D. Coal roadway deformation and the problem of original supporting scheme are analyzed including displacement field, stress filed and plastic zone. Several supporting optimizations are proposed combined with site investigation and simulation analysis. And the optimizations are simulated and calculated. By comprehensive comparison, the optimal supporting scheme is obtained and some supporting law in large cross-section roadway is concluded. These are helpful for supporting design in future.

In this paper, the mechanical behaviors of pipe roof and bolt of shallow and unsymmetrical tunnel in soft rock are analyzed. Through the finite element software Phase2.0, combined with the geological conditions that construction site often appear, the mechanical behaviors of pipe roof and bolt and surrounding rock in the process of horseshoe highway tunnel construction in the condition that surface is soft rock and underground for the bedrock are analyzed. Research results show that: after tunnel excavation in soft rock, surrounding rock near the tunnel is easy to suffer soft-rock large deformation even failure, which needs to timely support；Due to the impact of the unsymmetrical tunnel, the mechanical behaviors of surrounding rock are unsymmetrical, such as the maximum displacement of tunnel around 0.4 m distant from apex of arch ring, the stress is asymmetrical on both sides of the tunnel arch ring etc; In addition, pipe roof can effectively prevent from the displacement of soft rock strata, improve tunnel strength factor, reduce the plastic zone of surrounding rock. This paper provides theoretical basis for the design of pipe roof and bolt.