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Rock bolts are extensively utilized in underground engineering as a means of offering support and stability to rock masses in tunnels, mines, and other underground structures. In environments of high ground stress, faults or weak zones can frequently arise in rock formations, presenting a significant challenge for engineering and potentially leading to underground engineering collapse. Rock bolts serve as a crucial structural element for the transmission of tensile stress and are capable of withstanding shear loads to prevent sliding of weak zones within rock mass. Therefore, a complete understanding of the behavior of rock bolts subjected to shear loads is essential. This paper presents a state-of-the-art review of the research progress of rock bolts subjected to shear load in three categories: experiment, numerical simulation, and analytical model. The review focuses on the research studies and developments in this area since the 1970s, providing a comprehensive overview of numerous factors that influence the anchorage performance of rock bolts. These factors include the diameter and angle of the rock bolt installation, rock strength, grouting material, bolt material, borehole diameter, rock bolt preload, normal stress, joint surface roughness and joint expansion angle. The paper reviews the improvement of mechanical parameter setting in numerical simulation of rock bolt shear. Furthermore, it delves into the optimization of the analytical model concerning rock bolt shear theory, approached from the perspectives of both Elastic foundation beam theory coupled with Elastoplasticity theory and Structural mechanic methods. The significance of this review lies in its ability to provide insights into the mechanical behavior of rock bolts. The paper also highlights the limitations of current research and guidelines for further research of rock bolts. [ABSTRACT FROM AUTHOR]

The mechanical and deformation properties of bolted joints are important research issues in rock mechanics and rock engineering. Quite a few tests have been performed to study the performance of rock bolts in resisting shear loading. The effect of cyclic shear loadings on the bolts in the joints under different joint roughness was studied through a series of shear tests. The results illustrate that the peak shear strength was substantially equal to the residual strength with the increase in the number of cycles, and the slope of the normal displacement curve gradually decreased. When the number of shears is greater than three, the shear stress curve and the slope of the normal displacement curve tend to be stable gradually, which means it has completed the asperity degradation. The cyclic shear loading affects the rock bolt and reduces its bearing capacity. For specimens with larger JRC, the peak shear stress in both the direct shear and the first cycle was significantly elevated compared with small JRC, and so was the normal displacement. An evaluation index of shear energy loss ratio (SELR) was introduced to evaluate the shear performance of the rock bolts and rock joints under a cyclic shear loading condition. When the JRC is large enough, the asperities are difficult to degrade, and the jointed rock still has a more remarkable ability to resist shear deformation. This shows that JRC significantly affects the performance of joint plane and rock bolts under cyclic shear loading. Highlights: The effect of cyclic shear loading on the bolted rock joints under different JRC conditions were investigated. The cyclic shear load affects the rock bolt and reduce its supporting capacity. An evaluation index of shear energy loss ratio (SELR) was introduced to evaluate the shear performance of the rock bolts and rock joints under a cyclic shear loading condition. [ABSTRACT FROM AUTHOR]

Because of its simplicity, cost-effectiveness, and high efficiency, bolt-anchoring technology has been widely used in various fields such as tunnel and slope engineering. In this study, the mechanical behavior and damage pattern of bolted joints are investigated by a direct shear test of bolted joints, considering different bolt numbers, anchoring angles, and arrangements. The results showed that there are five distinct stages in the shear stress–displacement curve of the bolted joint, namely, the compaction deformation stage, the elastic deformation stage, the separation and drop stage, the yield damage stage, and the residual deformation stage. An increase in the bolt number increased the elastic modulus and shear strength of the bolted joint, although the yield deformation of the bolted mass first increased and then decreased. An increase in the anchoring angle caused the shear strength of the bolted joint to first increase and then decrease. The optimal anchoring angle was approximately 45°, and the safety factor was higher under large anchoring angles than under small anchoring angles. In particular, multiple rows of widely spaced bolts arranged perpendicular to the shear direction had significantly higher shear strength than a single row of narrowly spaced bolts placed parallel to the shear direction. These findings offer a guideline for the design of bolted rock mass in engineering projects. [ABSTRACT FROM AUTHOR]

• Simulation of geological laminated strata by 3D concrete printing technology. • Failure mechanism of rock bolt reinforcement 3D printed concrete laminated strata. • Effect of printing and loading directions on bonding failure of 3D printed layers. 3D concrete printing has the potential to simulate physical models for engineering investigations. However, it has not been fully exploited and validated. In this study, 3D concrete printing was used to construct laminated strata, including bolting, to mimic an underground excavation environment. Loading tests were conducted using various experimental techniques, such as digital image correlation (DIC) and acoustic emissions (AE). Monotonic and cyclic loading were applied to investigate the laminate failure in an engineering scenario. Attention was focused on the bonding effect between the 3D printing layers and the orientation between printing and loading directions. This study has three main contributions. Firstly, it exploits 3D printing to accurately mimic laminated strata in a geological scenario. Secondly, it integrates rock bolts with 3D printing models to replicate the interlocking mechanism between rock bolts and strata. Finally, it highlights the benefits of using 3D concrete printing to mimic geological strata, which can be adapted to accurately simulate various engineering failure patterns. The results suggest that 3D concrete printing has the potential to decrease manual labor, enhance precision, and more effectively tackle engineering challenges in comparison to traditional physical models. [ABSTRACT FROM AUTHOR]

Due to the effects of discontinuous deformation in fractured rock masses and complex shearing between the rock bolt and the grout, the strain of rock bolt in fractured zone can hardly be measured accurately. A fully-grouted rock bolt was prepared by using 3D printing, and strain gauges were installed inside and outside the bolt respectively. The evolution law of tensile strain in the fully-grouted rock bolt during the fracture propagation process was obtained by uniaxial compression test. It was found that the outer strain gauges were greatly affected by the shear deformation of the grout, and the measurement results are easy to be distorted when the plastic deformation capacity of the grout is high. However, the internal strain gauges could accurately obtain the complete strain of bolt. Finally, the failure process of rock bolt in fractured zone was numerically simulated by FLAC software, the influence of strain gauge location on the measurement results was verified, which further proved the reliability of measurement by strain gauges inside the rock bolt. [ABSTRACT FROM AUTHOR]

An extensive parametric analysis of 729 typical cases was developed with a calculation procedure allowing to simulate in detail the behavior of the passive bolts and their interaction with the surrounding rock. The parametric analysis allowed to evaluate the effectiveness of the bolts, on the basis of the extent of the stabilization forces produced, in relation to the geometric and mechanical characteristics of the binder used in the realization of the bolts. Different bolt diameters and lengths, binder thickness and elastic moduli and block displacement values with respect to the horizontal plane have been considered. It has been possible to detect how such parameters have a great influence on the mechanical behavior of the bolt and on the extent of the stabilizing forces which are applied to the potentially unstable rock block. For this reason, therefore, the definition of the characteristics of the binder (and in particular the thickness of the binder around the steel bar and the elastic modulus of the binder itself) cannot be assessed only in relation to application aspects, but it must be able to consider the effects on the efficiency of the bolt and in particular on the stabilization forces on the potentially unstable rock block. [ABSTRACT FROM AUTHOR]

This article presents the methodology and results of single shear tests of bolt rods under dynamic impact loading generated by means of a drop hammer. Comparative analysis was also performed for bolt rod load capacity, stress and shear work under static and dynamic (impact) loading. The developed method of single shear testing of bolt rods under impact loading makes it possible to obtain repeatable test results concerning maximum bolt rod shearing force, shear stress and shear work values. Comparative shear tests of four types of bolt rods under static and impact loading showed that the APB-type bolt rods made of AP770 steel, which was characterised by having the highest strength, exhibited the greatest shear work. AM22-type bolt rods exhibited a very similar work value. Though the AM22-type bolt rods made of A500sh steel demonstrated lower strength than the APB-type bolts, as well as a smaller diameter and cross section, they dissipated the impact energy better thanks to their higher plasticity. This could indicate the direction of optimisation for bolt rods in order to increase their impact strength. Mathematical relationships were also formulated for selected tests, describing the real single shear courses F d =f(t) of bolts under impact loading. The obtained relationships could be applied in the load assessment process of bolt rods intended for use under roof caving, tremor and rock burst conditions. [ABSTRACT FROM AUTHOR]

Rock bolts are widely used in the main structure of the DC transit system and play the role of the main body reinforcement and support. Because of the extensive stray current in the subway system, the corrosion risk of rock bolts is greatly increased. Therefore, the rock bolt was experimentally studied by simulating the input stray current and monitoring the polarization potential in this paper. After the stray current corrosion (SCC) process was finished, a tensile and breaking experiment of the corroded specimens was conducted for the mechanical properties. As an important parameter to indirectly characterize the corrosion strength of the stray current, the polarization potential was analyzed. Two types of rock bolts were compared for their mechanical properties and corrosion parameters. The result shows that the rock bolt with stranded steel wire as the rod has better corrosion resistance than the HRB500 rebar. Hence, the bonded stranded steel wire is more resistant to the stray current corrosion than the HRB500 rebar, which is adaptive for rock bolts in the direct current (DC) transit system. [ABSTRACT FROM AUTHOR]

Shear behavior of the bolt–grout interface basically depends on site-specific boundary conditions, i.e., initial normal stress and normal stiffness of the borehole wall. Few studies have been conducted to investigate the shear behaviors between the bolt and grout material under different boundary conditions. To better understand the effect of boundary conditions on the shear behaviors of the bolt–grout interface, simplified two-dimensional (2D) bolt–grout interface specimens are prepared and tested using direct shear tests at various initial normal stresses and normal stiffnesses in this context. The testing results showed that both initial normal stress and normal stiffness significantly influence the bolt–grout interface shearing behaviors. Increasing the normal stiffness or initial normal stress would increase the peak and residual shear strength. However, the degree of the brittleness after the peak, normal displacement, and peak friction coefficient was reduced. It is noted that the peak and residual shear strength points under the constant normal stiffness conditions located near the peak and residual strength envelopes for the constant normal load tests, respectively. Besides, the shear failure process of the bolt–grout interface was captured by PAC acoustic emission (AE) monitoring and digital camera technology, a good correlation between the evolution of AE parameters and the shear stress curves was obtained. [ABSTRACT FROM AUTHOR]

The jointed rock mass is a multi-crack body, which is cut by discontinuities such as joints and faults. These joints and faults destroy the integrity and continuity of rock mass and reduce the mechanical behavior of rock mass. The rock bolting is a suitable way to reinforce the jointed rock mass. By transferring tension and shear force, the rock bolting can make best use of the strength and stability of rock mass and restrict the deformation of rock mass. In this study, the specimens containing pre-set non-persistent joints were made with granite as prototype. A series of uniaxial compression tests of the reinforced jointed specimens were conducted by rock bolts with various inclinations. The relationships among the stress-strain, anchoring force, bolt strain, bolt inclination were studied, and the change rules of the parameters of the specimens and bolt with crack evolution during compression were analyzed. Results show that the peak strength and the equivalent elastic modulus of the anchored specimens with multiple non-persistent joints first increase and then decrease with the bolt inclination increasing. The optimal anchorage angle is about 65°. The anchoring force is relatively large when the angle between the rock bolt and the minimum principal stress surface is small. There is a strong internal correlation among the stress, anchoring force, bolt strain and crack evolution of the jointed specimens. The obtained conclusions in this study can provide a reference to the similar engineering practice. [ABSTRACT FROM AUTHOR]

The shear performance of bolted rock joints under cyclic loading condition was studied through laboratory shear tests. The tests were performed on a cyclic shear testing apparatus. The fully encapsulated rock bolts were inserted in the rock joints. The upper block was fixed in the horizontal direction, and the cyclic shear load was applied laterally on the lower block. A total of 16 shear tests were conducted for two types of rough joints. The results showed that the failure mode of rock bolts in cyclic shear test was different with the case of direct shear test. When the cyclic displacement was small, the rock bolt played a very small role in the second-to-fifth cycles, the rock bolt remained unbroken during cyclic shearing. The shear resistance of the rock bolt would gradually recover after the shear displacement has exceeded the cyclic displacement in the termination cyclic after five cycles. When the cyclic displacement was large, the rock bolt broke during cyclic shearing, and the shear resistance could not be recovered in the termination cyclic. It is indicated that the rock bolt had completely lost its supporting role after cyclic shear loading. The shear strength reduction of bolted joints under the cyclic loading condition was much significant compared to the un-bolted joints. Therefore, the influence of cyclic loading on the shear resistance of the rock bolt was much larger than its counterpart of the rock joint itself. These results showed that the shear performance of a rock bolt inserted in a rock joint was strongly influenced by cyclic shear loading. [ABSTRACT FROM AUTHOR]

The reinforcement for jointed rock mass using rock bolts has always been one of the most effective and economical geo-structural reinforcing technologies widely used in practical civil engineer projects for a long time. In the field of rock mass engineering, the reinforcement effect of the rock bolt(s) on rock mass is much more obvious due to a large number of natural fractures in rock masses. In this paper, an optimized method using Discontinuous Deformation Analysis for Rock Failure (DDARF) is presented to perform numerical investigations on mechanical property and reinforcement effect of bolted jointed rock mass. In order to verify the effectiveness of the proposed optimized DDARF, laboratory experiments using analog material have also been performed. Experimental results are very favorable with those obtained by the optimized DDARF. Moreover, this numerical method has also been employed to study mechanical property and reinforcement effect of rock specimen with single joint and single rock bolt when the joint and rock bolt have different locations in the specimens. The optimal reinforced location for the rock bolt in the specimen has been obtained through the comparative analysis of reinforcement effects under different conditions. The single jointed rock specimens with two rock bolts have also been numerically simulated and the optimal reinforcing location for the rock bolts has also been obtained. It is concluded that this optimized DDARF would provide an alternative effective tool to investigate the mechanical property and reinforcement effect for bolted jointed rock mass. [ABSTRACT FROM AUTHOR]

The existence of the weak interlayer in the roadway surrounding rock mass presents a huge threat to the stability of the underground structure and the safety of mining engineering. By the characteristics of strong adaptability, superior anchoring effect and high efficiency of construction, rock bolt has been widely applied in mine reinforcement. However, the influence of the weak interlayer on the compressive performance of the bolted rock mass is still poorly understood due to the challenges in constructing an efficient experimental platform and complex testing processes. Here, we used the self-developed test system to investigate the influence of the thickness, uniaxial compressive strength, and dip angle of the weak interlayer on the compressive behavior of the bolted rock mass with a single free surface. The results show that the weak interlayer has a great weakening effect on the peak strength and elastic modulus of the specimens due to its low mechanical properties, as well as influencing the crack distribution and failure mode of the samples. As the strength of the weak interlayer is lower than 1.27 MPa, the thickness exceeds 20 mm, and the dip angle exceeds 15°, the synergistic bearing effect will be significantly reduced and affect the mechanical performance of the specimens. The evolution of the bolt force and bending moment are greatly impacted by the deformation process which could be divided into distinct stages of destruction, thereby providing an excellent detection method for judging the stability of the surrounding rock of the mine. The discovery of this research promote a better understanding of the impact of the weak interlayer on mining engineering and guide the mine reinforcement in the future. [ABSTRACT FROM AUTHOR]

• A new energy-absorbing rock bolt was proposed, called the CEF bolt. • A theoretical model was developed to predict the constant resistance of the CEF bolt. • The effects of main parameters on the CEF bolt were investigated. • The applicability and accuracy of the current theoretical model were verified. To provide an effective support device for dealing with the instability problems in geotechnical engineering, this paper proposes a new energy-absorbing rock bolt based on the existing energy-absorbing devices, called compression-expansion-friction bolt (abbreviated as the CEF bolt). The CEF bolt mainly consists of two parts, a variable-diameter tube and a hollow cone attached at the distal end of the bar. Controllable constant resistance and large displacement are the characteristics of the CEF bolt. The constant resistance was generated by the expansion of the tube under the compression of the cone, as well as the friction between the tube and cone. And the large displacement was provided by the sliding of the cone relative to the tube. A theoretical model was developed to predict the constant resistance by taking into account the effect of material strain-hardening. Based on the energy conservation law, the effect of shear deformation was also considered. Further, the current model was formulated as three forms to consider different conditions. The predictions of the current theoretical model were in good agreement with existing experimental data. An experimentally validated finite element model was established to study the effects of main parameters on the constant resistance of the CEF bolt, such as cone angle, tube wall thickness, friction coefficient, expansion ratio and the strain-hardening property of the tube. The results of numerical simulation and theoretical analysis show that the constant resistance was directly proportional to the tube wall thickness, friction coefficient, expansion ratio and the strain-hardening modulus of the tube. But the constant resistance increased first and then decreased with respect to the cone angle, with an inflection point existed between 5° and 10°. The shear stress distribution and the deformation of the tube were investigated as well. According to the shear stress distribution, the zone under expasion of the tube can be divided into three characteristic areas: stress concentration area, smooth transition area, and stress re-concentration area. In addition, compared with the large number of experimentally validated numerical results, the wide applicability and sufficient accuracy of the current theoretical model were verified. By taking the derivative of the current theoretical model, the location of the inflection point can be obtained. These results can provide theoretical basis for the design and field application of the CEF bolt, as well as the similar structure. [ABSTRACT FROM AUTHOR]

This paper introduces a simplified smooth rock reinforcement modeling approach based on the 2D combined finite discrete element method (FDEM). The goal is to facilitate modeling the end grouting process and the full grouting process of rock bolts reinforcement, and to improve further understanding of the interaction between bolt, grouting, and host rock based on material mechanical behavior. The study analyzed the mechanical model and fracture mode extracted from experimental results using the rebar bolt specimen. This facilitated the study of the bond strength component of the rib. Then, the bond force-slip relationship was explored using physical modeling with different combinations of bolt and cover constraints, with different types of grouts and rocks. Corroboration of the laboratory axial pullout test was then conducted. A power law for the stress-displacement of the radial component of bond force was generated, to elaborate simplified modeling method and the data range of parameters in the diverse combination of constraining forces. Then, the action law was implemented into the material rock reinforcement model in FDEM. The verification process, done by comparing the bond force-slip curve with the physical modeling, shows the model can effectively reflect the action rule of rebar bolts. The model simplifies rebar bolt modeling and adds a new ability to model rock reinforcement features into FDEM, making the FDEM technology extend fundamentally. [ABSTRACT FROM AUTHOR]

Rock bolts have been widely used to reinforce the jointed rock mass. Modelling the mechanical shear behaviors of the bolted rock joints are difficult due to the complex interactions between bolts and rock joints. The applied pretension forces combined with the axial loads developed in the bolt act as the normal forces which are applied to the rock joints. However, these combined normal forces are not considered in the existing analytical models. An analytical model is proposed in this study to predict the shear behavior of the bolted rock joints, by taking into account the pretension forces, the axial forces developed in the bolt, the interfacial bond stress between the bolt and grout, and dowel shear loads acting transversely to the bolt axis. The proposed analytical model is able to provide complete curves of the dowel shear loads, axial loads, and the global shear loads as a function of the joint shear displacement. The analytically predicted axial load vs shear displacement curves and the global shear load vs shear displacement curves are verified by available experimental tests. The validation shows that the proposed model has the capacity to predict the global shear load evolution as well as the axial load evolution. The factors such as the pretension forces, the bolt inclination angles, the concrete strength and the rock joint friction are successfully accounted for in the analytical model. [ABSTRACT FROM AUTHOR]