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In this study, different plate fixing designs were tested in order to improve rock bolting performances. Instead of commonly used steel nuts, different plate fixing designs were investigated by both laboratory and site studies. In addition, the usability of nuts and energy absorbers made of the polyamide type engineering polymer was investigated to assess whether they are advantageous for the aim of supplying high-energy absorbing features. In this experimental study, deformation-controlled load tests were carried out to evaluate the bearing and energy absorption capacities of totally eight different groups of specimens. According to the findings from this study, use of the polyamide material with steel nuts as an energy absorber material, rather than using instead of steel nuts supplies good results. As another outcome, it has been determined that use of proper washers between steel nuts and polyamide absorbers can significantly improve the energy absorption performances. It has been evaluated that the energy absorption capacity of the bolt plates can be economically increased up to 10 times by using suitable polyamide energy absorbers placed between the plate and steel nut parts. It was concluded that the polyamides can be used to remarkably improve the rock bolting performances especially in the rock masses where the high energy absorption capacity property is needed, like those with rock bursting, squeezing and swelling problems. [ABSTRACT FROM AUTHOR]

Roof falls are currently one of the most dangerous threats associated with underground mining at great depth. Every occurrence of such an event poses a significant risk to the mining crew and disturbs the continuity of the mining process, which clearly affects the economy of the exploitation process. The development of a reliable monitoring system may significantly reduce the impact of eventual roof failure and will have a positive effect on the sustainability of the extraction process. Within this research study, a prototype of an instrumented rock bolt developed for continuous stress measurement is presented. The procedure of a 4-groove multilevel instrumented rock bolt is described and the calibration process is shown. Then, preliminary results of long-term in situ monitoring are presented. Based on the continuous monitoring of stress distribution within immediate roof strata, it was concluded that the developed instrumented rock bolt provides reliable results and is a very useful device, ensuring the possibility of early warning for miners about increasing roof fall risk. [ABSTRACT FROM AUTHOR]

The longitudinal wave velocity (v L) in a rock bolt is a useful parameter for evaluating the conditions of the rock bolt and the surrounding rock mass. This study investigated the influence of rock properties on the prediction of v L in a rock bolt using numerical and machine learning approaches. Through numerical simulations, we obtained a dataset of the variations in v L according to rock properties, compressional wave velocity (v p), shear wave velocity (v s), density (ρ), Poisson's ratio (μ), porosity (η), uniaxial compressive strength (UCS), and slake durability index (I SD). This dataset was used to design a deep neural network, and the predicted v L was correlated with rock properties. Notably, v L is strongly correlated with v p , v s , ρ , η , UCS , and I SD. Principal component analysis was employed to characterize the relationship between the rock properties, and the retaining rock properties for random forest (RF) were determined. In the RF, the variable importance (VI) of rock properties was assessed. In particular, v s emerged as the most significant predictor of v L. However, relying on v s to predict v L is not sufficient because it accounts for approximately 60–70 % of the VI. For a more reliable prediction of v L , it is essential to incorporate both v s and v p , which collectively account for approximately 80 % of VI. Notably, the VI of physical properties (v p , v s , ρ , and η) accounts for more than 90 %, implying that these properties can be effectively used to predict v L even in the absence of data concerning mechanical properties. [ABSTRACT FROM AUTHOR]

The construction of the deep-buried tunnels of the Sichuan-Tibet railway is facing severe rockburst disasters. Pressure relief boreholes and rock bolt support are effective methods for mitigating rockburst in hard rock. However, the mechanisms and differences in control effectiveness of these methods for different types of rockburst have yet to be revealed. This paper presents the results of two true triaxial unloading rockburst tests: Static-driven rockburst (static tests) due to excavation disturbance and dynamic-triggered rockburst (dynamic tests) due to adjacent tunnel excavation. The rockburst samples include intact granite, granite with a borehole (hole-granite), and granite with a negative Poisson's ratio bolt (bolt-granite). The mitigation mechanisms of the borehole and bolt were investigated in terms of rockburst intensity, failure patterns, and acoustic emission precursors. The results show that borehole and bolt inhibit the formation of a shear fracture plane during rockburst, with the bolt's inhibition effect being more pronounced. For static tests, borehole and bolt significantly reduce rockburst intensity, with the reduction being more significant for bolt-granite. The bolt mainly inhibits the propagation and penetration of shear microcracks. In contrast, the borehole promotes the propagation of shear microcracks. However, for dynamic tests, the rockburst intensity of bolt-granite is equivalent to that of intact granite, while the borehole enhances the rockburst intensity. The bolt inhibits the final buckling crack penetration in dynamic tests, while the borehole promotes slabbing. For static and dynamic tests, the borehole has little influence on precursor indicators, while the bolt increases the difficulty of precursor capture. Generally, the pressure relief borehole is more effective in controlling static tests, while bolt-reinforced support has advantages in dynamic test control. • Rockburst mitigation mechanisms using stress relief borehole and rock bolt support were revealed. • Static and dynamic rockburst tests were conducted on intact granite, hole-granite, and bolt-granite. • Pressure relief borehole is more effective in controlling static tests. • Boreholes and NPR bolts inhibit the formation of shear fracture during rockburst. • The borehole does not influence the optimal AE precursor, but the bolt increases the difficulty of capturing it. [ABSTRACT FROM AUTHOR]

In grouted rock bolt systems, bond defects often occur, which seriously affects the safety of rock mass structures. Therefore, in this study, based on the existence of bond defects, laboratory tests were conducted to detect the location and length of bond defects and study the guided wave propagation in grouted rock bolt systems under different pullout loads. The guided wave signal was analysed in the time domain and frequency domain. In addition to the laboratory test, a numerical simulation of the effect of different bond defect locations on ultrasonic guided wave propagation in rock bolts was conducted using a damage-based model. The influence mechanism of bond defects on guided wave propagation under different pullout loads was explored. The study confirmed that there existed a stress platform in the rock bolt at the bond defect under a pullout load. The location and length of the bond defect could be detected by the stress platform and guided wave. The debonding length increased exponentially with the amplitude ratio (Q) of low frequency to high frequency, and the Q value could be used as the quantitative index of debonding length. As the pullout load increased, the impedance mismatch between the rock bolt and cement mortar (defect) increased, and the guided wave propagation in grouted rock bolt systems was irregular. The pullout load weakened the guided wave propagation law. The larger the pullout load is, the greater the weakening effect is. [ABSTRACT FROM AUTHOR]

The mechanical equation on the mechanical characteristics of rock bolt in rock mass with bedding separation is established, based on the bond slip relationship of anchoring interface by the load transfer method. The validity of the numerical simulation is verified by the analytical solution of mechanical equation, when the bond slip relationship is linear. Further, the nonlinear bond slip relationship of anchoring interface is input into Flac3D by FISH. The mechanical characteristics of rock bolt are studied with the single and multiple bedding separation by numerical simulation. The results show that the axial force and the interfacial shear stress distribution curves on both sides are symmetrically distributed with the single bedding separation in rock mass, when the bedding separation is located in the center of the anchoring segment. When the bedding separation positions are not located in the center of the anchoring segment, the bedding separation value at different positions versus the axial force curves shows a single peak distribution. The axial force of rock bolt is mainly controlled by the side with the shorter anchoring length. Compared with the single bedding separation in rock mass, the additional stress of rock bolt occurred by the multiple bedding separation will superimpose each other. This paper leads to a better understanding for the load transfer mechanism for grouted rock bolt systems in rock mass with bedding separation and provides a reference for scientific support design and evaluation method. [ABSTRACT FROM AUTHOR]

This study presents a novel analytical model to simulate the axial strain and stress distribution along the full embedment length of the grouted rock bolt under axial loading. The model is derived based on the force equilibrium equation at one infinitesimal section of the rock bolt to grout interface and solved using second order partial differential equation method. Such a model is advanced in a way that all the input parameters can be pre-determined by rock bolt geometry information and direct shear testing of the grout without the need to conduct any pull-out test. In addition, this model is the first one in literature addressing the influence of the confining pressure applied to the grouted rock bolt on the axial strain and stress distribution in the rock bolt. Such a model also corrects the correlation between the axial load and axial stress at the loading end of the rock bolt as many past research underestimate the stress level. The features of the proposed model enable its engineering application to be user-friendly and universal. The close agreement between the simulation results of the proposed model and the experimental data in the literature validates the model's capability for successfully and accurately mapping out the axial strain and stress distribution along the grouted rock bolt under axial loading. [ABSTRACT FROM AUTHOR]

Usually, in a fully grouted rock bolt pullout test the load-displacement curve of the rock bolt head is recorded. This paper presents an analytical method to use this curve for determining the bond (bolt-grout and grout-rock interface) shear strength parameters. For this purpose, the fully grouted rock bolt interaction with grout and surrounding rock in the pullout test is investigated and the loaddisplacement curve of the bolt head (beginning of the bonded section) is obtained analytically. For modeling the bolt-grout interface behavior a distribution of the shear stress along the fully grouted rock bolt by consideration of bolt shank failure is used. In this regard, different stages including complete bonding, partial decoupling, decoupling with the residual shear strength and complete decoupling are considered. With increasing the applied load, two possible cases involving the rock bolt complete pullout and bolt shank yielding are taken into account. Based on the presented analytical method, the obtained bolt head load-displacement curve can be compared with the one recorded in the pullout test. With this, the relevance of selected shear strength parameters compared to real parameters can be assessed. A flowchart for determining the bolt bond shear strength parameters is presented using the trial and error method (coded in Matlab). The proposed solution is used to determine two experimental pullout shear strength parameters. The results show good agreement between predicted and calculated load-displacement curves. [ABSTRACT FROM AUTHOR]

A good bolt support structure effectively enhances the strength of the surrounding rock. Bolt support monitoring provides a basis for modifying and improving the design of this structure and enables safety hazards to be identified so that safe production can continue. A bolt fiber Bragg grating (FBG) stress sensor is developed based on FBG sensor technology, providing a data-driven analysis tool for monitoring the bolt stress in the working face. Continuous dynamic monitoring of the internal force distribution in a high-precision roadway bolt support structure is achieved through strict laboratory calibration, thus enabling comprehensive safety monitoring. Furthermore, the anchor FBG stress sensor is used to analyze the real-time stress variations in a bolt support structure during excavation. The results reveal the security evolution characteristics of bolts buried in shallow bedrocks and show that the security state varies with location (i.e., the roof, roadside, apex between roof and roadside, and apex between roadside and floor) and depth. [ABSTRACT FROM AUTHOR]

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. The masses and dimensions of machines and devices transported via monorail have increased considerably in recent times. This particularly concerns the transport of longwall system elements. In Poland, the maximum speed of suspended monorail travel is 2 m/s. Due to the fact that preparations are currently underway to increase the maximum speed above 2 m/s, it is necessary to inspect what influence it will have on work safety and mining support stability. Current operational experience and tests have shown that dynamic loads induced by the suspended monorail transportation have a significant influence on the roadway support stability, working protection durability and on the monorail operators. This is particularly true during the emergency braking of a suspended monorail by means of a braking trolley, where the overloads reach 3g. Bench tests of the selected steel arch and rock bolt support elements utilised in the Polish hard coal mines were conducted in order to determine the resistance of steel arch and rock bolt supports to static and dynamic loads. The article presents the results of the tests conducted on a steel arch support in the form of the sliding joints of an ŁP/V29 yielding roadway support, which is commonly employed in the Polish hard coal mines. Tests of elements of the threaded bolts with trapezoidal threads over the entire rod length were conducted as well. The conducted strength tests of steel arch and rock bolt support elements under static and dynamic loading have shown that dynamic loading has decisive influence on the support's retaining of its stability. Support element stability decreases along with the increase of the impact velocity. This concerns both the steel arch support and the rock bolt support. [ABSTRACT FROM AUTHOR]

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. The masses and dimensions of machines and devices transported via monorail have increased considerably in recent times. This particularly concerns the transport of longwall system elements. In Poland, the maximum speed of suspended monorail travel is 2 m/s. Due to the fact that preparations are currently underway to increase the maximum speed above 2 m/s, it is necessary to inspect what influence it will have on work safety and mining support stability. Current operational experience and tests have shown that dynamic loads induced by the suspended monorail transportation have a significant influence on the roadway support stability, working protection durability and on the monorail operators. This is particularly true during the emergency braking of a suspended monorail by means of a braking trolley, where the overloads reach 3g. Bench tests of the selected steel arch and rock bolt support elements utilised in the Polish hard coal mines were conducted in order to determine the resistance of steel arch and rock bolt supports to static and dynamic loads. The article presents the results of the tests conducted on a steel arch support in the form of the sliding joints of an ŁP/V29 yielding roadway support, which is commonly employed in the Polish hard coal mines. Tests of elements of the threaded bolts with trapezoidal threads over the entire rod length were conducted as well. The conducted strength tests of steel arch and rock bolt support elements under static and dynamic loading have shown that dynamic loading has decisive influence on the support's retaining of its stability. Support element stability decreases along with the increase of the impact velocity. This concerns both the steel arch support and the rock bolt support. [ABSTRACT FROM AUTHOR]

Abstract Rock joints will undergo a sequence of cyclic shearing loadings during a seismic event. However, the effect of cyclic shear loading on the energy-absorbing rock bolts has never been studied before. Laboratory shear experiments were carried out to study the shear behaviour of rock joints reinforced by the energy-absorbing rock bolts under cyclic loading condition. The results illustrated that the support effect of the energy-absorbing rock bolts was very small after the first cycles in the cyclic shear experiments. In the case of small cyclic distances, the shear resistance of the energy-absorbing rock bolts will gradually recover after the shear displacement has exceeded the cyclic distance in the subsequent shear experiment after 5 cycles. In the case of large cyclic distances, no recovery of shear resistance was found in the subsequent shear experiment, indicating that the energy-absorbing rock bolts had completely lost its supporting role after cyclic shear loading. A new index of shear energy loss ratio (SELR) was proposed to evaluate the shear behaviour of energy-absorbing rock bolt and rock joint under cyclic shear loading condition. The results showed that the SELR of rock joints was commonly less than 20%. However, the SELR of rock bolts could reach nearly 100% when the cyclic distance was larger than 8 mm. When the cyclic distance was 4 mm or 6 mm, the SELR of the fully encapsulated rock bolts almost reached 100%. However, the SELR of the energy-absorbing rock bolts were located in the range of 50–80% for the same condition. The results indicated that the shear behaviour of a rock bolt inserted in a rock joint was strongly influenced by cyclic shear loading. The shear performance of the energy-absorbing rock bolts was better than the fully encapsulated rock bolts under cyclic shear loading conditions. [ABSTRACT FROM AUTHOR]

• The bearing plate capacity can be enhanced by changing the shape of the curved surface of the plate. • A novel design of the pyramidal plate and its 3D prototypes with varying design parameters were developed. • The proposed analytical models provided higher load resistance and energy absorption of a pyramidal than a dome plate. • The bearing capacity of pyramidal plates was found superior to the dome plate in the experimental study. • Numerical analysis demonstrated that the bearing capacity improved by the novel pyramidal plate. Ground failures in underground mines are continuing to occur despite using rock bolt support with higher anchorage. The reason may be attributed to the mismatch between bolt anchorage and bearing plate capacity. Currently, the dome-bearing plates are widely used in the reinforcement of ground which often fails at loads below the bolt anchorage capacity. To address this problem, a novel pyramidal design of a bearing plate is proposed keeping the same size and material properties as the conventional dome plate. To evaluate the performance of pyramidal design, analytical formulations of load resistance, load efficiency, and energy absorption are formulated. In the experimental study, the prototypes of pyramidal design are developed and subjected to compression tests along with the conventional dome plate. The calibrated model of tested bearing plates is simulated using 3-dimensional finite element analysis. The pyramidal plate outperforms the dome plate in performance evaluation in terms of load resistance, load efficiency, and energy absorption. The experimental and numerical results also indicated that the capacity of the pyramidal plate is superior to that of a conventional dome plate. Thus, the proposed pyramidal plate can be used with rock bolt support in underground openings for improved ground control and stability. [ABSTRACT FROM AUTHOR]

Rock bolts, as a type of reinforcing element, are widely adopted in underground excavations and civil engineering structures. Given the importance of rock bolts, the research outlined in this paper attempts to develop a portable non-destructive evaluation method for assessing the length of installed rock bolts for inspection purposes. Traditionally, piezoelectric elements or hammer impacts were used to perform non-destructive evaluation of rock bolts. However, such methods suffered from many major issues, such as the weak energy generated and the requirement for permanent installation for piezoelectric elements, and the inconsistency of wave generation for hammer impact. In this paper, we proposed a portable device for the non-destructive evaluation of rock bolt conditions based on a giant magnetostrictive (GMS) actuator. The GMS actuator generates enough energy to ensure multiple reflections of the stress waves along the rock bolt and a lead zirconate titantate (PZT) sensor is used to detect the reflected waves. A new integrated procedure that involves correlation analysis, wavelet denoising, and Hilbert transform was proposed to process the multiple reflection signals to determine the length of an installed rock bolt. The experimental results from a lab test and field tests showed that, by analyzing the instant phase of the periodic reflections of the stress wave generated by the GMS transducer, the length of an embedded rock bolt can be accurately determined. [ABSTRACT FROM AUTHOR]

Abstract The role of rock bolts has become more important for a tunnel/cavern construction because of the wide use of conventional tunnelling methods under severe conditions. However, there is a lack of understanding on the interface behaviour between a rock bolt and bond material, especially on the crack initiation and propagation. The purpose of this paper is to investigate the effect of bolt configurations on the bolt-grout interface behaviour by discontinuous deformation analysis. By assessing the impact of key parameters, we can better understand the recommended parameter values and their impacts on the failure mechanism. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The present study focuses on the load transmission law along the rock bolt and the efficacy for different anchored conditions. Shear displacement along the joint face is considered on the basis of traditional rock bolt stress calculation method with regard to joint open displacement. Combining the elastic foundation beam model and the rock bolt pull-out model, an analytical solution for the stress distribution along the rock bolt through a single joint face is derived. The performance of the proposed analytical solution is compared with an experimental result and a previous study. In addition, joint displacement, joint location, and dip angle of the joint face are set as variables to further explore the corresponding anchored effect. The results indicate that larger joint displacement along the joint face tend to cause a distinct increase of the shear and compressive stress along the rock bolt. When the joint face moves inward, the interaction force between the rock bolt and the surrounding rock mass decreases, suggesting that the strength of the rock bolt is not taken full use. Moreover, for a certain joint displacement and joint location, larger anchored angle between the rock bolt and the joint face contributes to better reinforcement effect. [ABSTRACT FROM AUTHOR]

Rock bolts ensure structural stability for tunnels and many other underground structures. The pre-load on a rock bolt plays an important role in the structural reinforcement and it is vital to monitor the pre-load status of rock bolts. In this paper, a rock bolt pre-load monitoring method based on the piezoceramic enabled time reversal method is proposed. A lead zirconate titanate (PZT) patch transducer, which works as an actuator to generate stress waves, is bonded onto the anchor plate of the rock bolt. A smart washer, which is fabricated by sandwiching a PZT patch between two metal rings, is installed between the hex nut and the anchor plate along the rock bolt. The smart washer functions as a sensor to detect the stress wave. With the increase of the pre-load values on the rock bolt, the effective contact surface area between the smart washer and the anchor plate, benefiting the stress wave propagation crossing the contact surface. With the help of time reversal technique, experimental results reveal that the magnitude of focused signal clearly increases with the increase of the pre-load on a rock bolt before the saturation which happens beyond a relatively high value of the pre-load. The proposed method provides an innovative and real time means to monitor the pre-load level of a rock bolt. By employing this method, the pre-load degradation process on a rock bolt can be clearly monitored. Please note that, currently, the proposed method applies to only new rock bolts, on which it is possible to install the PZT smart washer. [ABSTRACT FROM AUTHOR]

Most of the surrounding rocks of offshore liquefied petroleum gas (LPG) reservoirs occur in jointed rock mass. This paper is aimed at the reinforcement of the layered composite rock masses. First, the structural mechanical model of the elastic deformation and completely plastic deformation for the bolt was constructed. Then, the equations of axial force, shear force, and bending moment in the cross section of the bolt were obtained by the force‐method canonical equation. The shear‐slip resistance effect of the bolt was decomposed into the friction effect and the dowel effect. In addition, the quantitative relationship between shear resistance and the characteristic angles (anchoring angle, friction angle, dilatancy angle, and deflection angle) and the geometrical and physical parameters of the bolt were derived. Finally, the influence of each characteristic angle on the mechanical properties of the bolt was analyzed in details and the model was verified. The analysis results showed that the laterally constrained load of the rock stratum on the bolt can be characterized by a power function, but the optimal power should be no less than 10. The dominant position of either the friction effect or the dowel effect was changed with the matching of different characteristic angles. The increase of the friction angle and dilatancy angle of the joint surface of the rock is beneficial to improve the lateral shear resistance of the bolt. The effect of the deflection angle on the lateral shear resistance of the bolt was affected by the anchoring angle. The optimal anchoring angle of the bolt should be in the range of 50°‐60°. The results in this study have important theoretical significance to guide the offshore anchoring engineering of layered composite rock masses. [ABSTRACT FROM AUTHOR]

Rock mass classification has played a crucial role in underground construction and mining projects in the past fifty years, especially the Rock Mass Rating (RMR) and Rock Tunneling Quality Index (Q) systems, which have been applied in many cases. The parameters of discontinuity conditions in the RMR system, along with the related ratings, were used to develop a new equation in order to introduce an intrinsic quality of a given rock mass, namely, rock bolt supporting factor (RSF). The RSF was used to develop a mathematical theory of the rock bolt supporting mechanism as a new principle in explaining rock bolting effects. Finally, using the parameters of the discontinuities in the Q-system, the QRSF is defined to present the capability of a given rock mass to be reinforced by rock bolting. The RSF leads to more reliable judgment of rock bolting capability of a given rock mass than the QRSF since it uses five parameters of discontinuity conditions while the QRSF uses only two parameters. [ABSTRACT FROM AUTHOR]

An innovative design of a twisted yieldable rock bolt has been developed using the system analysis of conventional rock bolt technology, a thermodynamic approach, and a theory of technical creativity. This bolt consists of one single piece of a metal cylindrical rod having longitudinal feathers that provided its maximal reliability and minimized the cost. The bolt can be driven into a hole with a pneumatic hammer and creates a set of dissipative structures during rock mass deformation that facilitates and intensifies the dissipation of ground pressure energy causing stress relief around an underground opening. A 30 cm section of the bolt was successfully tested in special laboratory equipment, one 1.8 m bolt in a mechanic workshop, and fifty-five 1.8 m bolts in an underground entry of a coal mine. The behavior of this bolt was simulated on the FLA3D model to verify its basic parameters and to understand deeper abilities to yield and resist rock mass deformation. This bolt is fastened to the hole's wall for its entire length, thus the resistance and the energy dissipation indicators of this bolt are extensive parameters, hence the 2-m-length bolt can exceed the performance of the best modern prototypes. This bolt is relevant to provide stability to underground openings in hard squeezing conditions. • Approach 'absorbing energy' has been changed to 'dissipating energy'. • Dissipative function has been transformed from the bolt to surrounding rock mass. • New yield bolt consists of a cylindrical rod having two spiral feathers along its rod. • Dissipative structures spontaneously disperse the ground pressure energy. • Innovative yield bolt may outperform the best modern yield rock bolts. [ABSTRACT FROM AUTHOR]

Abstract: This paper aims to investigate the effect of rock bolt corrosion on time-dependent system reliability of anchored rock slopes. First, a corrosion degradation model for reinforcing steel bars in concrete is selected to model the uniform corrosion of rock bolts. Second, two typical failure modes of rock bolts due to corrosion and the resultant slope failure modes are identified. Subsequently, a Monte Carlo simulation-based reliability approach is proposed to perform system reliability analysis of anchored rock slopes. Finally, an example of an anchored rock slope is worked out to investigate the effect of rock bolt corrosion on the time-dependent reliability of the anchored rock slope. The results indicate that the probability of slope failure upon yield failure of rock bolts at the free length only increases slightly with time. On the contrary, the probability of slope failure upon bond failure at the bolt–grout interface increases dramatically with time. The system probability of failure of the anchored rock slope decreases with increasing thickness of bolt cover and increases with increasing water–cement ratio of the grout. During the design and construction of pre-stressed rock bolts, a certain thickness of bolt cover should be guaranteed and the water–cement ratio of the grout should be strictly controlled to enhance the long-term stabilization effect of rock bolts. [Copyright &y& Elsevier]

Rock bolts have been widely used as rock reinforcing members in underground coal mine roadways and tunnels. Failures of rock bolts occur as a result of overloading, corrosion, seismic burst and bad grouting, leading to catastrophic economic and personnel losses. Monitoring the health condition of the rock bolts plays an important role in ensuring the safe operation of underground mines. This work presents a brief introduction on the types of rock bolts followed by a comprehensive review of rock bolt monitoring using smart sensors. Smart sensors that are used to assess rock bolt integrity are reviewed to provide a firm perception of the application of smart sensors for enhanced performance and reliability of rock bolts. The most widely used smart sensors for rock bolt monitoring are the piezoelectric sensors and the fiber optic sensors. The methodologies and principles of these smart sensors are reviewed from the point of view of rock bolt integrity monitoring. The applications of smart sensors in monitoring the critical status of rock bolts, such as the axial force, corrosion occurrence, grout quality and resin delamination, are highlighted. In addition, several prototypes or commercially available smart rock bolt devices are also introduced. [ABSTRACT FROM AUTHOR]

Physico-mechanical rock properties are typically investigated via laboratory tests using core samples. However, sample coring is time consuming and expensive. The longitudinal wave velocity in rock bolts embedded in a rock mass depends on the surrounding rock properties. Hence, the longitudinal wave velocity in rock bolts can be utilized to predict rock properties. This study presents the relationship between granite rock properties and longitudinal wave velocity (v L) in rock bolts to predict rock properties using the longitudinal wave velocity in a rock bolt. Chemical (saline solution) and mechanical (slake durability test) weathering processes are employed to diversify the properties of the rock specimens. Laboratory tests are conducted on rock specimens to measure the physico-mechanical rock properties, including the velocities (v p and v s) associated with constrained and shear moduli, density (ρ), Young's modulus (E), Poisson's ratio (μ), and porosity (η), compressive strength (f c), and slake durability index (SDI). The measured rock properties are used in the rock mass model, and variations in v L in the rock bolt with different properties are investigated via numerical simulations. Results show that v p , v s , ρ , E , and f c are correlated significantly with v L (R 2 > 0.9), whereas η and SDI are moderately correlated with v L (R 2 > 0.7). However, a meaningful correlation between μ and v L is not obtained. The root mean square and mean absolute percentage errors are estimated to validate the correlation equations, and errors are not considered. Results of the t -test show that the calculated t -value is higher than the critical t -value, and the p -value is smaller than the significance level of 0.05, indicating that the correlation coefficient is significant. This study shows that the velocity of longitudinal waves in a rock bolt can be a useful indicator for predicting in-situ rock properties. [ABSTRACT FROM AUTHOR]

Abstract: This paper considers our recent research on rock bolt stress corrosion cracking (SCC) which studied the influence of metallurgy using a range of (1) existing rock bolt steels and (2) commercial steels. The chemical composition, mechanical properties and microstructures of these steels varied considerably. The aim is to understand this failure mechanism and in particular to apply the knowledge gained from the study of SCC and hydrogen embrittlement (HE) of steels. The resistance of 1008, X65, X70 and 4145H to SCC/HE was similar, an effect which could be hardly expected as these steels have different strengths, microstructures and H-trap distributions. Different steel microstructures (pearlitic–ferritic and tempered martensite) had similar resistance to SCC and HE in the most aggressive conditions (pH2.1 and −1500mVSCE) and had the same dimple rupture fracture surface. [Copyright &y& Elsevier]

In order to study the dynamic mechanical properties of rock bolt under impact load，the mechanical properties of five different material rock bolts were tested. Lateral impact resistance test on the rock bolts was carried out using a free-fall hammer impact test device to evaluate the dynamic response of the rock bolts. The lateral impact test was performed with five different impact heights to obtain the dynamic impact response curve，the bolt axial strain-time curve，and the force-displacement-time curve at the impact point. The study found that under the condition of the same impact energy，the higher the impact absorbed energy of rock bolt，the smaller the impact peak load. Impact reaction time increases as the impact height decreases. The higher the impact absorbed energy of the rock bolt，the greater the peak strain and residual strain. The distinct differences in the impact peak load and the maximum displacement were observed among the different rock bolts. The larger the peak strength and the maximum displacement，the higher the breaking energy. It was also found that controlling the material content of beneficial and harmful elements can improve the impact resistance of the rock bolts. In addition，the microstructure and organization of the rock bolt fracture profiles were analyzed and it was found that the greater the impact absorbed energy of the rock bolt，the higher the grain size level. [ABSTRACT FROM AUTHOR]

Given the increase in mining depth and intensity, tunnel failure as a result of rock burst has become an important issue in the field of mining engineering in China. Based on the Composite Rock-Bolt Bearing Structure, which is formed due to the interaction of the bolts driven into the surrounding rock, this paper analyzes a rock burst prevention mechanism, establishes a mechanical model in burst-prone ground, deduces the strength calculation formula of the Composite Rock-Bolt Bearing Structure in burst-prone ground, and confirms the rock burst prevention criterion of the Composite Rock-Bolt Bearing Structure. According to the rock burst prevention criterion, the amount of the influence on rock burst prevention ability from the surrounding rock parameters and bolt support parameters is discussed. [ABSTRACT FROM AUTHOR]

Abstract: Analysis of mechanical behaviour of rock mass reinforced by fully grouted rock bolt is introduced based on the enriched finite element method (EFEM). A solid element intersected by a rock bolt along any arbitrary direction is defined as ‘enriched’ element and it has additional degrees of freedom at each node for estimating displacements and stresses in bolt rod. Numerical procedures of EFEM are developed to form enriched stiffness matrix using constitutive relations of rock mass, properties of bolt rod and grout material and orientation of the bolt. Decoupling of rock bolt and elasto-plastic behaviour of rock mass has been incorporated into the EFEM procedures. Released displacement of rock mass prior to bolt installation has also been considered in the procedures to provide realistic solution. The results of this method are verified with an analytical pull-out test model. In addition, a numerical example of a bolted tunnel is provided to demonstrate the efficacy of the proposed method for practical applications. [Copyright &y& Elsevier]

The article presents methods of making the rock bolt support more yieldable, especially for a stratified roof. Alongside the increasing depth of exploitation of raw material deposits, rock bolt support units are more often designed taking into account more intensive deformations and displacements of underground excavations. In the article, a room and pillar method with mined roof bending and roof reinforcement with bolt patterns of 1 m × 1 m, 1.5 m × 1.5 m and 2 m × 2 m is presented. Moreover, the laboratory tests included 1.8 m long bolts, which were embedded segmentally on the lengths of 100 mm, 150 mm and 200 mm were tested. Based on the load–displacement characteristics, the deformation energy for flat and profiled dome bearing plates was calculated. Making the segmentally embedded resin rock bolt support yieldable enabled it to perform additional work. Furthermore, it was found that rock bolt support with a dome bearing plate took over 2.5 times more energy compared to a rock bolt support equipped with a flat bearing plate. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: In order to understand the metallurgical influences on rock bolt stress corrosion cracking (SCC), an evaluation has been carried out of a range of steels subjected to the conditions previously identified as producing laboratory SCC similar to that observed for rock bolts in service. The approach has been to use the linearly increasing stress test for samples exposed to a dilute pH 2.1-sulphate solution, as per our prior studies. SCC was evaluated from the decrease in tensile strength, ductility and fractography as revealed by scanning electron microscopy observation. A range of SCC susceptibilities was observed. [Copyright &y& Elsevier]

The passivation behavior of Yucca Mountain Repository rock bolt carbon steel in deaerated 3.5% NaCl solution containing SiO32- and HCO3- 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 FeCO3 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 FeCO3 to Fe2O3. [Copyright &y& Elsevier]

An analytical model for rock bolts has been developed based on an improved Shear–Lag Model. The development of the model is based on the description of the interaction behavior of the rock bolt, the grout medium and the rock mass. On the basis of the model, the coupling and decoupling behavior of the rock bolt in pullout tests, uniform deformation the rock mass and intersecting joints are analyzed. The pullout test characteristic is described by the proposed model, and a back analysis method is proposed to calculate the shear strength of the interface media. For the rock bolts in a deformed rock mass, the influence of the installation time of the rock bolt has been taken into account, and the theoretical prediction is verified by the measured data. According to the proposed model, the position of the neutral point is not only related to the length of the rock bolt and the radius of a tunnel, but also is strongly influenced by the mechanical properties of the rock mass. Analysis of the joints intersecting the rock bolt shows that there may be more than one neutral point on the rock bolt, and the prediction of the simplified model is consistent with the pullout model. By using this model, a method is proposed to analyze the interaction behavior of the rock bolt and the surrounding rock mass, with a way of evaluating the supporting performance quantitatively. [Copyright &y& Elsevier]

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. [Copyright &y& Elsevier]

Rased on the analysis on damage modes of rock bolting components and factors resulting in the failure, their mechanical performances, including rebar, thread, plate, domed washer and anti-friction washer, were studied. The stress distribution features of rebar and thread on varying loading states were analyzed through theoretical calculation and numerical simulation. The effects of rebar profile and geometric parameters on die anchorage force and installation resistance were tested in laboratory, the compressive performance of plates and the compatibility between the components on bolt end were also tested. The mechanical performances of resin capsules and their affecting factors were studied. Research results point out:bolt rods are acted by tension, bending, torsion, shear and their combination, bolt yielding is in normal state, and generally fracture at four points in coal mine roadways. Thread teeth sharply change the stress distribution on its surface and adjacent zone, and stress concentration occurs in the valley of thread teeth. The compressive deformation of domed plates can be divided intofive stages, and the arch height of plates should be more than a fixed value to guarantee their bearing capacity. The profiles, parameters and mechanical performances of the components on bolt end should be compatible to guarantee rock bolts laying in good stress state. Resin capsules should be compatible with the rebar and borehole to guarantee a better cohesive performance between the interfaces of boltresin and resin-rock. The research achievements have been applied in many complicated roadways, the fractures of bolting components have been greatly reduced, and bolting performances obviously improved. [ABSTRACT FROM AUTHOR]

Steel tube is used to simulate rock mass in laboratory impact tests of rock bolts. The steel tube must be equivalent to the borehole in the rock mass in radial stiffness in order to obtain valid test results. The stiffness of the steel tube is directly associated with the thickness of the steel tube. The importance of the tube thickness has not been paid enough attention in the laboratory tests of rock bolts at present. This technical note derives a formula for calculating the required thickness of the steel tube used for laboratory tests of rock bolts. It also provides a formula for calculating the stiffness of the steel tube under plane stress which is the realistic loading condition of rock bolts in the field. The analysis reveals that the grout in the tube hole does not play a role in the calculation of the thickness of the steel tube. The required thickness of the steel tube is solely dependent on the Young's moduli and Poisson's ratios of the tube steel and the rock mass to be simulated. [ABSTRACT FROM AUTHOR]

Abstract: A continuous dynamic model for the axial vibration of a rock bolt system is presented. The model comprises three sections: the fixed length, bonded into the rock, the free length, which is not coupled to the rock, and the protruding length, which extends beyond the rock. The head assembly is modelled as a discrete mass and a spring, and a further discrete mass is included, representing a testing device that can be attached to the protruding end. Each section is modelled as a continuous elastic rod governed by the wave equation, with suitable compatibility conditions applied between the sections and boundary conditions, which also account for the effect of the discrete components, applied at the ends. Solutions in non-dimensional form are substituted into the boundary conditions to allow the natural frequencies to be calculated, and it is shown that two possible solutions for the mode shapes can be used for the fixed length—an exponential solution or the classical sinusoidal solution—depending on the stiffness of the grout relative to that of the bar. The conditions for which the two solutions are valid are developed, and changes in the frequency ratio with changes in length ratio, and the stiffness ratios of the grout and the anchor head relative to the stiffness of the fixed length of the anchorage are examined. Generally, the state of a bolt after installation is unknown and this does not provide proper assurance of the safety of the structure for which the bolts are used. The model provides a viable tool for helping to assess the condition of the bolt by using the natural frequencies associated with areas of the bolt of particular interest, e.g. the free length. The results show how the changes in the stiffness and/or length ratios affect the dynamics associated with fixed length of the bolt and the quality of the bonding installation. A case study is presented showing how the model can be used effectively to interpret real data. [Copyright &y& Elsevier]

To analyze rock-bolt dynamic mechanics, one theoretical model has been put forward based on several assumptions. At the interface of the bolt and surrounding rock-soil body, the coupling of a linear spring and a damper is used for the bolt system. The coefficient k of the spring and the damper coefficient η are key parameters between the rock-soil body and bolt. The elastic and viscoelastic kinematic equations are established, and the displacement control equations are binary second-order partial-differential equations that can be simulated by numerical methods. One example shows the displacement curves with input waves; the displacement decays with different distributions. The curves of different times were simulated, and it was found that as the ratio value of the coefficient k of the spring and elastic modulus E increases, the displacement-decay-ratio speed increases per unit length. The same is true for the ratio values of the damper coefficient η and elastic modulus E. The theoretical model can also be used to solve the impact-force problems. [ABSTRACT FROM AUTHOR]

The article presents the impact of geological and mining factors on the stability of room excavations in the Legnica-Głogów Copper District (LGOM) in Poland. In underground mining, the primary task of bolting of mining excavations is to ensure their stability as an essential condition of work safety. Appreciating the role and importance of the rock bolting in Polish ore mining; rock bolt load sensors were designed, manufactured and tested under laboratory conditions. The purpose of the research was to characterize the sensors and determine the elastic range of the bearing plate, which are an integral part of the sensor. The sensors have been verified in industrial conditions. The tests were carried out in the underground copper ore mine in Poland. Three rooms in the exploitation field were selected for testing, where exploitation was carried out at a depth of 809–820 m below the ground surface with the application of room and pillar with roof deflection and maintaining the central part of the field. The exploitation field included 60 rooms and pillars. The effectiveness of the mechanical load sensor of the expansion rock bolt support has been experimentally confirmed. Based on mine research, it was found that the largest increases in the load of the rock bolting, vertical stress and convergence occur in the middle of the mining field. [ABSTRACT FROM AUTHOR]

A high spatial resolution distributed optical fiber strain sensing technology is demonstrated to advance the assessment of support element behaviour during in-situ pull tests. A technique to instrument typical tendon support elements with a fiber optic sensor is discussed and was trialed at an underground salt mine through a series of pull tests on instrumented rebar elements. It is shown that a continuous strain profile can be measured along the length of a support element under pull test load, which, in turn, allows the interfacial shear stress distribution and deformation of the support element to be resolved. In comparison to load and displacement measurements solely at the support element head, which is what is traditionally reported for in-situ pull tests, the optical fiber strain sensor is found to provide significantly more insight into the mechanistic behaviour of the support element by readily measuring highly variable strain distributions and by quantifying the load development length of the support element. The sensor arrangement allowed the conventional handling and installation procedures to be followed without any implication to the integrity of the sensor. Accordingly, an instrumented reinforcement element can be installed with minimal interruption to on-going mining/construction procedures at the given project. • Distributed optical fiber strain sensing is used to augment the in-situ pull test. • A fiber optic sensor instrumenting procedure is discussed. • Instrumented support elements are installed and pull tested in an underground mine. • Coaxial strain distributions are measured along rebar rock bolts in-situ. • Support element bond behaviour is quantified and compared using various sensors. [ABSTRACT FROM AUTHOR]

In this article, a model of ore deposit in form of a lense carried out in the MineScape program, is presented. The lense had a thickness of 30 m, length along the strike 200 m, and the depth buried was for 80 m to 110 m below the surface. In the first layer, counting from the lowest level, a room and pillar method with variable geometry was designed. The width and length dimensions for rooms and pillars were: 4 m, 5 m and 6 m, respectively. For the selected part of the deposit, three variants of the system with variable geometry of rooms and pillars were designed, for which the deposit utilization coefficient was determined. The next stage of the research was to determine the influence of the geometry of the pillars and rooms on the range of the rock destruction zone around room excavations. For this purpose, numerical calculations using the three-dimensional Examine 3D program, based on the boundary element method, were made. The results of numerical tests were used to calculate the load of the rock bolt support, which is currently used in the zinc and lead underground mine "Olkusz-Pomorzany" in Poland. Currently in the mine, the bolt spacing is 1 m × 1 m, and the technology for fixing the bolt rod is based on resin cartridges that completely fill the bolt hole. In order to spread the spacing of the rock bolt support and to apply segmental fixing of the bolt rod, in the laboratory tests, rock bolt supports with increased strength were tested. Based on the results obtained, it was found that the rock bolt can be installed segmentally, using a cement grout, and its spacing can be increased to 2 m. [ABSTRACT FROM AUTHOR]

Hollow grouted rock bolts are widely used in deep soft rock roadways. The density of grout has a significant influence on the anchorage quality. However, there is still a lack of effective methods to detect the grouting quality fast, accurately, and extensively. Based on the wave velocity and the law of stress wave transmission and reflection in the impedance mismatch, non-destructive experiment focused on the defect in the anchorage was conducted. The wavelet transform was used to analyze the test signals. The test results show that the free length of hollow grouted rock bolt could be accurately detected through the analysis of the stress wave signal by using the low-pass filter in the wavelet toolbox. The grouted length, defect length, and specific position of the anchorage section can be accurately detected through the analysis of the stress wave signal by using the high-pass filter in the wavelet toolbox. The research can provide experiment foundation for further study of grouting quality based on the non-destructive methods. [ABSTRACT FROM AUTHOR]

This article presents the application of a self-excited acoustic SAS system for non-destructive testing (NDT) for roof-bolt housings in laboratory and real mine conditions. The proposed system with a filtering mechanism was applied to the J64-27 composite anchors. The conducted tests allowed successful confirmation of the usefulness of the system in the detection of rod defects, damage of the mechanism coupling the anchor to the rock mass and testing of the stress state of the anchor itself. The proposed filtering system allowed eliminating the effect of jump change of frequency in the limit cycle of self-excited system. The proposed method is a novel solution for safety diagnostics of bolt housings in mining applications. [ABSTRACT FROM AUTHOR]

Grouted rock bolts represent one of the most used elements for rock mass stabilization and reinforcement and the grouting quality has a crucial role in the load transfer mechanism. At the same time, the grouting quality as well as the grouting procedures are the least controlled in practice. This paper deals with the non-destructive investigation of grouting percentage through an analysis of the rock bolt's natural frequencies after applying an artificial longitudinal impulse to its head by using a soft-steel hammer as a generator. A series of laboratory models, with different positions and percentages of the grouted section, simulating grouting defects, were tested. A comprehensive statistical analysis was conducted and a high correlation between the grouting percentage and the first three natural frequencies of rock bolt models has been established. After validation of FEM numerical models based on experimentally obtained values, a further analysis includes consideration of grout stiffness variation and its impact on natural frequencies of rock bolt. [ABSTRACT FROM AUTHOR]

The loading states, stress distribution, deformation and supporting effects of bolt plates were studied by the combination method of laboratory tests, numerical modeling and field monitoring. The gauged plates were designed and manufactured in the laboratory, the relation between deformation, stresses of domed plates and loads under different supporting states were measured, and the loads, at which the plates start to yield, were obtained. By means of finite element method, the stress distribution features of domed plates under the supporting states of face contact, four sides, four points and three points were analyzed. The numerical model with single bolt anchored in the center of surrounding rock, which can simulate the stress field caused by bolt pretension, was built. The affects of plates to the stress field caused by bolt pretension, stress distribution in the plates, and the supporting effects of the plates to surrounding rock were discussed. The gauged plates were applied, and the stresses in the plates were monitored in underground extraction entries in the Tunliu Coal Mine, the Lu' an coal mining district. The stress distribution features and variation laws in the plates in the stages of bolt pretension, driving affect and stabilization were preliminarily analyzed. [ABSTRACT FROM AUTHOR]

We have proposed a theoretical model for the analysis of bolt anchorage effects through cross-section uniformity and elastic theory. When the surrounding rock and soil are fixed, then the slip resistance forces directly proportional to the displacement of the bolt. An equilibrium differential equation for the wholly bolt has been established. The axis stress expression has been presented from the combined boundary conditions. It is a monotonic function which consists of negative index and minus index function of the distance, away from the force. The effects of friction proportional coefficient and radius have been analyzed as well. For local stripping bolt, a different model having separate parts has also been analyzed. We have also deduced the axis stress distribution function. Moreover, the curves of different separate conditions were compared which conclude that there is a terrace for the separate part. The longer the separate part, the quicker the axis stress decreased. Finally, an experiment has been performed which show the distribution of axis stress has the same trend with the strain gauge record. The theory solution of axis stress is also proved to be reasonable. [ABSTRACT FROM AUTHOR]

Fiber Bragg grating (FBG) sensors, which can accurately measure strain, can be integrated with rock bolts with small fingerprints. In this paper, according to the force mechanism of prestressed anchor and non-prestressed anchor, different loading modes were designed, named active loading mode and passive loading mode. Then, FBG technology was used to monitor the axial force variation of prestressed anchor and non-prestressed anchor in different loading modes. Based on the test results, it is found that when the anchoring force is relatively small (<35 kN), prestressed anchors need to be tested by active loading mode, and non-prestressed anchors need to be tested by passive loading mode. For the prestressed anchor, the force condition of the bolt-shaft was similar to that of the two-force bar, and the axial force of the bolt-shaft was nearly the same along its entire length. Taking the applied load as the reference, the change rate of the axial force of the bolt-shaft was less than 10%. For non-prestressed anchor, due to the plate, there is a certain area surrounding the plate where the axial force of the bolt-shaft was greatly influenced. With applied loads of less than 15 kN, the change rate of the axial force on FBG1 was greater than 10%. With applied loads of greater than 20 kN, this was less than 10%. In this area, influenced by the plate, the axial force of the bolt-shaft increases, and as the applied load of the pullout test increases, the influence decreases. [ABSTRACT FROM AUTHOR]