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Rock bolts of steel are the most frequently used components in systems for rock reinforcement. Special types are used as energy absorbing elements in systems exposed to dynamic loads and these must yield plastically under high loading velocities. A new type of energy absorbing rock bolt of soft steel has been suggested and tested. To investigate the strain rate effects on the yield stress and ultimate strength of the steel were bars dynamically loaded in a high speed testing machine. The observed tensile forces can be divided into one part from impact and another from quasi-static straining. The tests showed that there was a considerable strain rate effect on the yield stress of the steel. It is recommended that higher dynamic yield stresses are utilized in the dynamic design which has to incorporate the risk of high peak forces from impact loading.

A research programme into both the static and dynamic performance of ground anchorage systems, with an emphasis on resin bonded rock bolts, started at the University of Aberdeen in the early 1980s. The work involved measurements on active construction sites which was underpinned by laboratory and computer modelling and led to the development of a new method for the non-destructive testing of anchorages. Part of the research programme was focused on assessing how changes in the load influence the dynamic responses of an anchorage. This in turn produced a new testing method able to determine the variation in frequency response of the anchorage with changes in load. The development of a lumped parameter model able to simulate the response of anchorages to changes in static load and an applied impulse load was a further step forward in the research programme. The achievements of the lumped parameter model revealed the head of the anchorage to be the most influential component of the anchorage system in determining dynamic response. The results obtained from the numerical model when laboratory anchorages were simulated are shown to be in agreement with the results obtained from the actual laboratory tests. Based on the successful results obtained to date regarding laboratory rock bolt anchorages, a further step was made in order to employ the numerical model for the first time to observe the influence of load on the frequency response of rock bolt anchorages installed in the field. This paper describes the application of the model to such field anchorages and highlights some of the detailed modelling aspects required to replicate real anchorage behaviour.

Combined with the 3D FEM, end-anchored anchorage bolts were simulated by implicit anchorage bolt element. Implicit anchorage bolt elements hide in the elements of rock mass and extremely simplify the element subdivision. The calculated value of anchorage bolt stress is larger than the measured one for the most time. we further analyzed the reciprocity of anchorage bolt and rock mass, and then deduced the analytical equations of anchorage bolt stress and rock mass deformation under elasto-plastic state. The results indicate that it is essential to revise the anchorage bolts stress by using the formulas deduced when rock mass is softened or significantly deformed. Finally, a case study indicates that the calculated results agree with those measured. Some helpful methods are offerd for more accurate simulation of the support effect and anchorage bolts real stress state.

This paper represents the result of a project conducted with developing a safe, practical and economical support system for engineering workings. In rock engineering, untensioned, fully cement-grouted rock bolts have been used for many years. However, there is only limited information about the action and the pull-out load capacity of rock bolts, and the relationship between bolt-grout or grout-rock and the influence of the grout properties on the pull-out load capacity of a rock bolt. The effect of grout properties on the ultimate bolt load capacity in a pull-out test has been investigated in order to evaluate the support effect of rock bolts. Approximately 80 laboratory rock bolt pull-out tests in basalt blocks have been carried out in order to explain and develop the relations between the grouting materials and untensioned, fully grouted rock bolts. The effects of the mechanical properties of grouting materials on the pull-out load capacity of a fully grouted bolt have been qualified and a number of empirical formulae have been developed for the calculating of the pull-out load capacity of the fully cement-grouted bolts on the basis of the shear strength, the uniaxial compressive strength of the grouting material, the bolt length, the bolt diameter, the bonding area and the curing time of the grouting material. © 2002 Elsevier Science Ltd. All rights reserved. The authors would like to thank the Research Fund of Cukurova University for supporting this research. No. FBE.2000.YL.50.

鋼管膨張型ロックボルトは湧水のある地山や掘削による初期変位のあるトンネル工事で使用される。湧水中での耐久性を評価するために，溶融Zn-6％Al-3％Mg合金めっき製ボルトおよびめっきなしボルトを東海北陸自動車道飛騨トンネルの湧水地山に試験設置した。1，2，3年経過後にオーバーコアリング法によりボルトを地山から回収し，腐食挙動を調査した。めっきなしボルトの場合，腐食（板厚減少）速度は直線近似でき，溶存酸素拡散支配型の腐食と判断された。一方，合金めっき製ボルトの場合，灰色外観を呈しほとんど腐食の認められない領域とめっき層が局部的に腐食した黒変色領域とが混在していたが，黒変色領域における腐食の進行も2年経過以降はほぼ停止していると見なされた。3年経過後の灰色領域，黒変色領域および溶射補修した溶接部のいずれの部位も最表層はZn-Si-O系の均一な皮膜で覆われており，試験設置場所で採取した湧水の分析結果などからケイ酸亜鉛皮膜と推定された。このケイ酸亜鉛皮膜の腐食抑制効果により，それ以上の腐食の進行がほぼ停止した状態になっていると考えられる。

Doolayi Tunnel, located in Toyserkan, is one of the strategic tunnels that connect Hamedan to the western provinces of Iran. This tunnel was excavated in proximity to the Sannandaj-Sirjan active fault and is exposed to landslide hornfels stone and groundwater. It means that, due to the occurrence of possible destructive earthquakes in this region. tunnel demolition - as a result of undesirable geology conditions - is definite. In this article, dynamic behavior of a tunnel is studied by FLAC 3D V3.00 software. Moreover, an optimum arrangement of rock bolt and reinforced Shotcrete is proposed to be able to have the most stability against accompanied effects of quake and groundwater. The results of this study indicate that the use of a composite system - in addition to making dynamic stability of the tunnel - significantly decreases displacement, swelling, settlement, stress and shear stress.

The main goal of the paper is to describe a reinforcement consisting of fully grouted bolts, which is applied to stabilizing underground openings and tunnels. After a variational formulation is given, the existence and uniqueness is proved. Some asymptotic results that make it possible to replace the real system with a continuous one more suitable for discretization are presented. Some other types of reinforcements and properties are studied.

Rock bolt dynamometer is the important safety equipment which measures the rock bolt stress and is powered by battery which the most capacity is limited to 2500mAh. Replacing battery is forbidden in coal mine according to requirement of mine safety. Therefore to reduce power consumption and improve battery life is the key technology of the design of rock bolt dynamometer. Choosing a low-power microcontroller with high density of integration which controls the operation mode of power supply of each circuit unit and the electric level of microcontroller interfaces through software mode, we successfully reduced the power consumption of the entire system and extended battery life. The experimental results show that the standby current is low to 36μA and the working time of rock bolt dynamometer is from half or one year to six years. This design has the advantages of no battery replacement within working life of the whole system, which brings convenience to the coal mine and reduces the maintenance costs.

Tunnels are crucial infrastructures used for passage of humans, cars, trains or utility lines. Among this, tunnels used for road or rail purpose needs a great attention. The tunnel to serve its intended function, rock bolt and concrete lining are provided based on the ground condition. These two support systems are worthy and need great consideration as their impact remain on tunnel cost and convergence. Thus the optimum uses of these support systems are a challenge which demands the best design solution. Consequently, the study on tunnel rock bolt and concrete lining combination optimization which need study and improving, worth researching a lot. In this paper which is a case study, based on the design of data for optimization, the most influential support elements are selected. For different parameter combinations, the finite element methods have been performed followed by forming displacement parameter correlation. Likewise, the cost is represented by using polynomial model. Considering displacement and cost functions, the optimum combination of rock bolt and concrete lining has been found. The result show that the optimum combination is found if the number of rock bolt is 15 and concrete lining thickness 25 cm with in the constraint bolts [7,23] and lining thickness [10cm,40cm]. The optimized combination is modeled using numerical model and analysis along with the verification. The finite element analysis result gives total displacement of 6.34cm. But the observed total displacement inside the tunnel is about 60mm which is less than the predicted displacement of optimum combination using numerical analysis. The induced shear on concrete lining is 96.85 KN/m which is lower than the shear capacity of concrete lining. The total cost of rock bolt & concrete lining accounted for the optimum combination is $30,700 per 34 m2 tunnel rock bolt and concrete lining construction. Parametric study performed on pre stress rock bolt shows that increasing number of rock bolt would slightly increase stress and strain. Conversely, the convergence of tunnel is reduced. Similarly the plastic points are greatly reduced because of the pre stress rock bolt.

A ground convergence-support reaction analysis is extended to the case of an opening excavated in horizontally layered strata. Simplifying assumptions include linear elastic behaviour and classical beam theory. The method is used to demonstrate the influence on bolt loads of a number of factors including the timing of support installation, failure of the roof, number, thicknesses and flexibilities of the rock layers, type of rock bolt, bolt spacings, bolt lengths, roof span, and roof beam thickness.

In order to improve the design of rock bolts, it is necessary to have a good understanding of the behavior of rock bolts in rock masses. Several analytical models of describing the interaction among of the rock bolts, the grout medium and the rock mass have been proposed in literatures. In this paper, a numerical simulation procedure was developed for a rock bolt subjected to a concentrated load in pullout tests. The study was concentrated on the failure at the interface between the bolt and the grout. The commercial code FLAC3D was used to analyze the coupling and decoupling phenomenon at the bolt-grout interface. The interface provided by FLAC3D which is characterized by Coulomb sliding and/or tensile separation is proved the premise for simulating the problem. On the basis of a numerical parametric study, the effects of dilation angle and confining pressure on the behavior of the inter-face were clarified and the failure mechanism on the interface was identified.

Nowadays, the New Austrian Tunneling Method (NATM) is most popular in Japan. Shotcrete and a steel rock bolt are used as the main supports of this method. However, when a tunnel is constructed in a corrosive environment as a hot spring, a steel rock bolt may be corroded within a long term and lose their supporting effect. Moreover, a long steel rock bolt is heavy and difficult for handling in a narrow space like as a tunnel. Recently, since fiber reinforced polymer (FRP) is light in weight, moreover it has a high strength and an excellent durability, it has been applied in the civil engineering field. Especially, it is used as reinforcement or prestressing tendon for concrete members. In the field of NATM, a glass fiber reinforced polymer (GFRP) rock bolt has sometimes been applied. However, the bearing capacity of the head was only a quarter or one fifth of the tensile capacity of the rod. It was only effective as a temporary support but not as a permanent one. Therefore, the authors have developed a new GFRP composite rock bolt. It had a special type of GFRP head, the rod was composed of GFRP and lauan wood, and the bearing capacity of the head was greater than the tensile capacity of the rod. In order to clarify the difference of the supporting effect between the GFRP composite rock bolt and a conventional steel rock bolt, three kinds of test were carried out, namely the tension test in a laboratory, the pull-out test and the long-term measurement in some tunnels.

Bolt is widely used in slope engineering, tunnel and cavern supporting, and restoration of engineering structure. It can improve the strength and stability of ground, rock mass, and other structures. Traditional steel bolt has some disadvantages, such as easy corrosion, heavy weight. Glass Fiber Reinforced Polymer (GFRP) is impervious to chloride ion and low pH chemical attack, and its tensile strength is much greater than steel while with lighter weight. 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 determined. This paper presented the research on bonding behavior of anchor bolt made from GFRP bar and concrete block used to model rock in laboratory. The modified pullout tests were conducted on selected GFRP bars that were grouted with mortar in concrete blocks. According to the results of laboratory, bond characteristics of mortar grouted GFRP rock bolts were evaluated.

2.4m立方の模型地山に60cmのトンネルを設け, ロックボルトパターンを種々変えて載荷試験を行い, ボルトのトンネル補強効果と最適パターンの研究を行った. 載荷は側圧係数1.0と0.5の二通りで行った. 模型地山には一軸強度1.0MPa, 内部摩擦角30の砂質低強度モルタルを用いた. ボルトは長さ40～10cm, 本数は8cm間隔の1断面に12～48本とした. この実験の範囲では, 短いボルトを数多く用いることの有効性が明らかとなった.

The three dimensional elasto-viscoplastic composite element method is formulated in this paper for rock masses reinforced by a fully-grouted bolt. If a bolt segment penetrates a finite element representing the rock mass, then a composite element is formed including five sub-elements corresponding to the rock material, the grout material, the bolt material, the rock-grout interface and the bolt-grout interface. The displacements in each sub-element are interpolated from the corresponding nodal displacements of the composite element. By the virtual work principle the governing equation for the solution of the nodal displacements can be formulated. The elasto-viscoplastic characteristics of the materials are considered in the formulation. The new model can be incorporated into the conventional finite element analysis grid, in which several composite elements have fully grouted bolts embedded. In this way the mesh generation of large scale bolted rock structures becomes convenient and feasible. The model has been implemented in a FEM program, and a comparative study between the numerical analysis and a pull out field test has been carried out, from which the validity and the robustness of the new model are justified.

Yielding rock bolt support systems have been developed to accommodate ground movement in shifting ground such as in coal operations; in creeping ground such as salt, trona, and potash; and in swelling ground associated with some clays. These systems, designed to remain intact despite ground movement, should enhance mine safety and help contain costs in areas where revolting of rigid non-yielding systems is typically required. Four such systems were tested in straight tensile pulls in the laboratory. They include the Slip Nut System from Dywidag Systems International USA, Inc., Ischebeck`s bolt mounted Titan Load Indicator, Rocky Mountain Bolt Company`s Yielding Cable Bolt, and a rock bolt installed variation of the yielding steel post developed by RE/SPEC Inc. The first two systems are currently marketed products and the latter two are prototype systems. Each system responds to load and displacement by yielding in a unique manner. All are designed to yield at predetermined loads. A description of each system and its yield function is provided. Each system was tested over its prescribed yield range in a test machine. At least five tests were performed on each system. Each system yielded and continued to provide support according to its design. Each showsmore » promise for ground control use in shifting or creeping rock. This work helps to illustrate the comparative differences in performance between these specialized systems and the applications where they may be most useful.« less

The passivation behavior of Yucca Mountain Repository rock bolt carbon steel in deaerated 3.5% NaCl solution containing SiO{sub 3}{sup 2} and HCO{sub 3} ions was investigated by potentiodynamic polarization, electrochemical impedance spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopic methods. Polarization results indicate that combinations of silicate and bicarbonate anions decrease the passive current density and raise the pitting potential. XPS results indicate the enrichment of silica at passive potentials and the formation of mixed FeCO{sub 3} and silica film at lower potentials. This change in film composition was responsible for the changes in corrosion rate at lower and higher potentials. XPS results also support the thermodynamic data with regard to the occurrence of second oxidation peak observed in the polarization curves to be due to the oxidation of FeCO{sub 3} to Fe{sub 2}O{sub 3}.

An integrated hypermedia training tool on underground rock bolting was evaluated using qualitative and quantitative methodologies to compare it with the traditional method of training underground rock bolters. Usability experiments performed underscore the need to evaluate a new product to ensure that it meets the requirements of users. Statistical results from comparative experiment indicate that a task must be sufficiently complex in order to render a traditional paper-based method less effective than a computer-based method. Additionally, participants in the computer-based group (n = 25) rated the training effectiveness more positively than those in the paper-based group (n = 25).

Rock bolts play a crucial role in reinforcement support systems for tunnels and rock slopes. In this study documented herein, guided ultrasonic waves are used to evaluate the integrity of rock bolts. The dispersion characteristics of the guided waves are identified by numerical simulations. Experimental studies using the transmission of guided waves are carried out with different defect ratios for grouted nonembedded rock bolts, and for rock bolts embedded into a concrete block and rock mass. Analytical solutions are suggested to estimate the equivalent velocity for both the grouted and the embedment portions. Numerical simulations reveal that the optimal frequency range of guided waves is 20∼70 kHz in the first longitudinal mode. Field and laboratory experimental studies and associated analyses show the velocity of guided waves increases as the defect ratio increases. The velocity for the grouted portion in the nonembedded rock bolts is essentially constant. However, the velocity in the embedment portion decreases with increasing embedment length due to the increase in the size of the influence zone. Results suggest that the integrity of rock bolts can be easily evaluated by the transmission method using guided waves.

A new model is introduced for rock bolt support of a single block. The model assumes that the bolt supports the block in much the same way that another block would. It therefore includes approximations to the geometric as well as the force constraints imposed by the bolt. Depending on its mode of support, the bolt either is represented as in the traditional model or else acts like a keystone to make the block geometrically stable. The latter analogy provides a useful computational test of the bolt's orientation, entailing only the addition of the appropriate fictitious fixed face into a stability analysis of the block. An associated procedure enables either the tension in the bolt or the factor of safety to be determined if the other has been specified. In some circumstances the lower values of these two quantities violate the block's equilibrium and are therefore physically unattainable, although they would be valid in the traditional model. But all other tensions and factors of safety are identical in both models. The paper also reviews a number of the block types in the existing Warburton and Goodman-Shi methods of analysis and points out the correspondence between them. This review leads to a reassessment of the roles of some types in supporting other blocks in an assemblage. In particular, the key blocks identified in Goodman and Shi's sample calculations could also be identified by Warburton's method, but support of all such blocks in an assemblage could not in practice be relied on to stabilize the excavation. Although blocks that could fill the role intended for key blocks undoubtedly do exist, there would generally not be enough information to identify them. Goodman and Shi's method can identify removable blocks as an intermediate type, but Warburton's method is more direct when the resultant driving forces (or even their directions) are known. However, other features of the two methods make Goodman and Shi's best suited to design and Warburton's to construction.

An investigation of effect of variability of strength and orientation on stability of tetrahedral wedges with two free surfaces is presented. Study was limited to potential sliding along the line of intersection of the two joint planes. Minimum rock bolt force and minimum static acceleration were considered as output stability parameters in this study. An analytical procedure which combines a deterministic analytical method and Monte-Carlo simulation technique was used to perform this study. Variability of orientations of the joint planes was modeled by the hemispherical normal distribution. Shear strength of the joint planes was modeled by the Mohr Coulomb criterion. Variability of shear strength parameters of the joint planes was modeled by the bivariate normal distributions. Effect of variability of orientation was found to be more pronounced than the effect of variability of strength on both output parameters. Variability of the magnitudes of the output parameters increased with decreasing co...

A system of twelve equations have been developed for the elastic-plastic analysis of split-set roof bolts and these equations have been programmed for solution on the IBM 370/168 computer. Typical solutions have been presented in graphical form for comparison with experemental data. The results compare favorably for most of the split-sets providing the system parameters are properly specified. It appears that this analytical solution will be valuable to mining engineers since the solutions have been put in graphical form. Plots of the effects of the various parameters (material strength, material strain-hardening, friction, thickness, radius, angle of contact) on the holding capacity of split-sets have been constructed and are presented in this paper.

Two approaches to finite element analysis of the effects of rock joints and fractures on underground unlined, lined, or reinforced tunnel openings are considered. First, a three-dimensional ubiquitous joint analysis is described and applied to tunnel design. Although this approach allows an estimate of the weakening effect of closely spaced joint sets, it is based on the assumption that the existence of a joint does not alter the stress distribution significantly. Since this may not always be a satisfactory assumption and because it may sometimes be desirable to model the action of individual joints occurring in determined locations, a new rock joint representation is developed and a joint stiffness analysis applied to a series of basic problems. The different types of rock joints and their relative significance are discussed and a classification system based on shear strength of the joint, stiffness perpendicular to the joint and tangential stiffness of the joint is suggested. Using a finite element axisymmetric program, states of stress in the rock due to single and multiple rock bolt installation are examined and iso-stress maps of the triaxial compression zones are shown. States of stress in the vicinity of the rock bolt anchor and bearing plate are investigated. The effectiveness of a single rock bolt installation to strengthen rock joints of various orientations is investigated. In a very preliminary study, the theory of a layered orthographic shell was coded using a finite element plane strain representation. An evaluation of the load resisting capability of various tunnel linings incorporating different types of stiffeners was made. Further analytical work is recommended.

Despite their frequent natural occurrence and engineering encounter, heterogeneous rock joints (rock joints with different lithological characters on both sides of the joint surface) have been studied much less systematically. To study the shear behavior and failure mechanism of bolted heterogeneous rock joints, laboratory tests were performed on the heterogeneous rock joints having different joint roughness coefficients (JRC) under different anchorage conditions. The results indicate that shear strength increases with the increase of JRC, showing exponential growth. Under the same roughness, the shear strengths of rock joints from large to small are fully grouted, end anchorage, and without anchorage. The mechanical characteristics of the bolt and joint are poorly matched under the end anchorage condition, which is easy to cause these two to be broken one by one. Under fully grouted, the extrusion force caused by the rock bolt will diffuse around the anchorage agent and will not cause partial continuous damage. The surface damage of heterogeneous rock joints increases with the increase of JRC and presents obvious heterogeneous characteristics. The shear dislocation between the blocks under shear load results in the interaction between the bolt and surrounding media. Under the action of shear force, the bolt body produced both axial and transverse deformation, which leads to breakage of anchorage agent and rock mass. Rock bolt has a significant impact on the shear behavior of the anchorage system, and the damage of the rock bolt to rock mass should be considered in rock engineering reinforcement design.

Fully grouted rock bolts are one of the main forms of rock reinforcement used in underground mines, especially in coal mines. Analytical models describing the deformation behaviour of rock bolts under various loading conditions are used in numerical models for designing appropriate rock reinforcement. A reliable analytical model capable of accurately predicting rock bolts’ responses under different loading conditions is, therefore, important for more realistic numerical models and effective reinforcement design. In this paper, a new analytical model for shear behaviour of rock bolts is proposed which can better predict rock bolt behaviour under large shear deformations. A method to consider the effect of post-elastic strain hardening on bending stiffness of rock bolt is presented. The analytical model is validated with results from laboratory shear tests and found to be consistent with the laboratory results. To analyse the effect of post-elastic strain hardening on shear behaviour of a rock bolt, results from the proposed analytical model is compared with analytical model without strain-hardening effect. Without strain hardening, the analytical models overestimate the ultimate shear displacement by up to 35% in the examples shown in the paper.

Rock bolts have been widely used in slopes as a reinforcement measure. Modelling the shear mechanical behaviours of bolted rock joints is very complicated due to the complex factors that affect the axial force and shear force on the bolts. Rock bolts under shear action exhibit the guide rail effect; that is, the rock mass slides along the rock bolt as if the rock bolt is a rail. The normal stress can inhibit the guide rail effect and reduce the axial force on bolts. However, this factor is not considered by the existing analysis models. Shear tests of bolted joints under different normal stresses were carried out in the laboratory. During the test, the axial force on each point monitored on the bolt was recorded by a strain gauge, and the attenuation trend of the strain was studied. An analytical model that considers the inhibition of the bolt rail effect due to an increase in the normal stress was proposed to predict the shear mechanical behaviour of rock bolted joints. The new model accommodates the bolt shear behaviours in the elastic stage and plastic stage, and the estimated values agree well with the results of the direct shear tests in the laboratory. The validation shows that the proposed model can effectively describe the deformation characteristics of the bolts in the shear tests.

SYNOPSIS According to the information of measurement in situ at the Dayaoshan tunnel, this paper shows rationality of the adopted parameters of initial support of rock-bolts and shotcrete and the deformation rule of soft and fractured surrounding rocks. It develops that in such rocks the displacement speed should be used as the index of unstability and support design should be mainly based on the control of displacements around the excavation.

SYNOPSIS This paper discusses requirements of the basic characteristics of rock anchor for the deformation control of the soft surrounding rock, mechanics of friction rock bolts (split set bolts) and the interaction between the rock anchor and the surrounding rock. The application of friction rock bolts to the headings and stopes of coal, manganese and iron ore mines is presented, focusing on the favorable results from the control of soft host rock deformation.

Rock bolting technique is an important reinforcement measure in the geotechnical engineering practice. New rock bolts have been continuously emerging through the development of rock supporting technology. Complex conditions, such as high crustal stress, extremely soft rock, and strong mining disturbance often occur in the deep mining, resulting in large deformation of the surrounding rock masses. Since the deformation of traditional rock bolts is generally below 200 mm, failure often occurs to the rock bolts because of insufficient deformability. To effectively control the large deformation of surrounding rock masses caused by complex conditions, it is necessary to develop large deformation rock bolts with high constant resistance, also called energy-absorbing bolts. This paper systematically reviews the development of large deformation rock bolts and the structure, energy absorption mechanism, anchorage performance, and mechanical properties of several typical large deformation rock bolts. The advantages and disadvantages of existing large deformation rock bolts are compared and the concept of constant resistance large deformation support is introduced.

Numerical simulation is a useful tool in investigating the loading performance of rock bolts. The cable structural elements (cableSELs) in FLAC3D are commonly adopted to simulate rock bolts to solve geotechnical issues. In this study, the bonding performance of the interface between the rock bolt and the grout material was simulated with a two-stage shearing coupling model. Furthermore, the FISH language was used to incorporate this two-stage shear coupling model into FLAC3D to modify the current cableSELs. Comparison was performed between numerical and experimental results to confirm that the numerical approach can properly simulate the loading performance of rock bolts. Based on the modified cableSELs, the influence of the bolt diameter on the performance of rock bolts and the shear stress propagation along the interface between the bolt and the grout were studied. The simulation results indicated that the load transfer capacity of rock bolts rose with the rock bolt diameter apparently. With the bolt diameter increasing, the performance of the rock bolting system was likely to change from the ductile behaviour to the brittle behaviour. Moreover, after the rock bolt was loaded, the position where the maximum shear stress occurred was variable. Specifically, with the continuous loading, it shifted from the rock bolt loaded end to the other end.

Medium carbon steel (AISI 1040) was one of the candidate materials for rock bolts to reinforce the borehole liners and emplacement drifts of the high-level nuclear waste repository in Yucca Mountain. The corrosion performance of this structural steel was investigated by techniques such as linear polarization, electrochemical impedance spectroscopy (EIS), and laboratory immersion tests in simulated ground waters. The corrosion rates of the steel were measured for the temperatures in the range from 25 °C to 85 °C, for the ionic concentrations of 1 time (1×), 10 times (10×), and a hundred times (100×) ground water concentration. The steel corroded uniformly at penetration rates of 35 to 200 µm/year in the deaerated waters, and at 200 to 1000 µm/year in the aerated waters. Increasing temperatures in the deaerated waters increased the corrosion rate of the steel. However, increasing ionic concentrations influenced the corrosion rate only slightly. In the aerated 1×and 10×waters, increasing temperatures increased the rates of the steel significantly. In the aerated 100×waters, the corrosion rate increased from 25 °C to 45 °C and decreased at higher temperatures (65 °C and up) due to the formation of oxide/hydroxide films and salt scales on the surface of the steel specimen. The steel suffered pitting corrosion in the both deaerated and aerated hot ground water environments after anodic polarization.

Understanding the performance and failure mechanisms of surface support in mine roadways is paramount to the success of mine productivity. A sophisticated facility has been developed to evaluate the mechanical behavior of surface support under quasi-static loading. Three different types of mesh, welded wire mesh, chain-link mesh, and geogrid mesh are tested in conjunction with different surface components including rock bolt plate, steel strap and W-strap. It is found that the welded wire mesh has the higher stiffness and load-bearing capacity than the diamond mesh and the geogrid mesh. For each mesh, the incorporation of steel strap or W-strap helps the load to distribute more uniformly to more wires than just adopting bearing plate alone, leading to a substantial improvement in both the stiffness and the load-bearing capacity. The welded wire mesh can still withstand large deformation after peak load. In contrast, the diamond mesh and the geogrid mesh lose its capacity quickly after peak load.

Attacking underground caverns with earth-penetrating bombs usually involves multiple explosions in succession. To assess the dynamic responses and cumulative damage of underground caverns under multiple explosions, based on a reduced-scale physical model test, the modified Riedel–Hiermaier–Thoma (RHT) model in the finite-element software LS-DYNA is used to build an underground cavern model that encounters four explosions above the vault. The characteristics of the stress wave attenuation and the evolution laws for the cumulative damage of the surrounding rock in the process of the four explosions are presented. Also, the displacement of the vault, the strain of the cavern wall, and the damage of a rock bolt-supported cavern and an unanchored cavern are compared. The results indicate that the peak pressure is attenuated increasingly in the latter three explosions. The circumferential strain of the cavern wall changes from tensile to compressive from the vault to the corner. The damage of the surrounding rock on the left and right sides of the explosion source is attenuated with increasing distance from the explosion source, and the attenuation curve has a reverse “S” shape. Moreover, the attenuation rate of the curve decreases with each explosion. Multiple explosions do not affect the size of the crushed zone, but they do increase the range of the fracture zone. With each explosion, the cumulative damage of the surrounding rock increases irreversibly, but the damage increment decreases. The cumulative damage of the surrounding rock exhibits a highly nonlinear relationship with successive explosions, and the effect of the rock bolt reinforcement becomes more obvious with successive explosions. Accordingly, the present research results offer a reference for antiexplosion design and support the optimization of underground engineering.

Rock bolts are highly important underground to prevent falls of ground and thus, ensure safety. In situ, the ground reinforcement is subjected to a combination of loads, such as shear, tensile, and/or bending loads. Studies have been conducted to evaluate the effect of either shear, tensile, or bending loads on the ground support. However, only a few studies have been done to evaluate the effect of combined load on the rock bolt performance. In situ, the order of loads acting on the bar cannot be predicted, and more than one load can act on the bar at the same time. Thus, a hybrid failure criterion was developed that covered all combined loading conditions. Fifty-eight un-grouted laboratory rock bolt tests were conducted in total under two load conditions: applying shear displacement to the rock bolt and then tensile load to failure, and applying tensile displacement to the rock bolt and then shear load to failure. From the test results, the failure criterion was developed based on regression analysis. A nonlinear relationship was determined for the loading condition variations. The failure criterion presented in this paper can be used as a guide in the rock bolt capacity design under all loading conditions.