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Anchorage failure occurs mostly at the anchorage interface, and the mechanical mechanism of the anchorage interface is the key point and difficulty in the analysis and research of anchorage. In order to study the mechanics and failure mechanism of the anchorage interface, the shear failure characteristics of the anchorage interface and the deformation rule of the anchored rock under different rib spacings were analyzed through the indoor plane anchorage pull‐out test. Reasonable rib spacing can significantly improve the shear strength of the anchored solid. Finite element software ABAQUS was used to create an axisymmetric plane model of rock bolt pull‐out under different rib conditions to simulate the whole process of rock bolt pull‐out and anchorage interface failure. The results show that during the pull‐out process of anchorage rock mass, stress concentration zones occur at rib corners, and peak shear stress moves to the depths of the anchorage section. As the load increases, cracks emerge from the top of the rib and the edge of the rib angle of the rock bolt and propagate to the deep anchorage along the edge of the costal angle, resulting in damage at the rock mass interface. Load–displacement curves of different transverse rib shapes, heights, widths, and spacings indicate that rib changes affect the anchor‐bearing limit. The anchoring failure mode changes from rib wear and spreading slip, rib shear convex body propagation to interfacial crack propagation, and rib causes varying degrees of damage to the surrounding rock mass. Therefore, reasonable rib parameter improvements can enhance anchoring force performance. [ABSTRACT FROM AUTHOR]

Layered composite roofs are characterized by developed bedding fissures, resulting in severe deformation and damage of rock bolts at the top of the roadway, as well as a poor roadway support effect. Increasing pretension force is an effective way to enhance the stiffness of the rock bolt support system. To clarify the influence and mechanism of the pretension force on the support effect of rock bolts in the layered roof, a roadway model of the layered roof was established using the interface unit of FLAC3D, and the simulation rock bolts were constructed using the pile unit, which can simulate the mechanical behaviors of rock bolts, such as tension, shear, bending, fracture, and anchor failure, and the pretension force was applied. On this basis, the deformation and failure characteristics and influencing factors of rock bolts in the layered roadway roof under different surrounding rock conditions were simulated and analyzed. The research shows the following: ① Field measurements showed minor shear deformation in the rock bolts at the center of the roadway roof, with lateral displacements of 5.7 cm and 5.3 cm. Significant shear deformation occurred in the rock bolts at the roof corners, with lateral displacements of 18.2 cm and 17.6 cm. ② Simulations of rock bolt deformation characteristics matched the field measurements closely, confirming the reliability of the simulation method, parameter selection, and calculation sequence. ③ The primary factors affecting rock bolt deformation are the structural plane strength and surrounding rock strength. Rock bolts are most susceptible to lateral displacement when the structural plane strength is low, the strength difference between rock layers is large, and the weaker layer is below the structural plane. The presented research can provide a reference for the instability mechanism and support treatment of the layered composite roof roadway. [ABSTRACT FROM AUTHOR]

The effect of bedding cohesion and loading conditions on the bolting behavioral characteristics of a bedded rock mass was investigated using a self-developed artificial material and loading system. First, physical samples with dimensions of 15 cm × 15 cm × 8 cm containing both the grout and gypsum layers were prepared. The ratio of the thickness of the grout layer to the gypsum layer was 0/100, 25/75, 50/50, 75/25, and 100/0. One grouted bolt was situated in the middle of the sample. Two types of filling materials were chosen as a filling segment around the rock bolt, i.e., gypsum and grout. The tensile strengths of gypsum and grout were 1.4 and 2.4 MPa, respectively. The length and diameter of the bolt were 12 and 2 cm, respectively. The grout dimension was 5 cm × 5 cm × 8 cm. These samples were tested under two different axial loading conditions. A total of 20 distinct tests were conducted concurrently with laboratory experiments utilizing Particle Flow Code in Two Dimensions. The loading rate was 0.05 mm/s. The findings revealed a strong correlation between breakage patterns and loading conditions. Moreover, it was observed that the grout filling significantly impacts the ultimate axial load compared to gypsum filling. When loading the interface between the rock bolt and the filling segment, the final axial load remained consistently similar across all filling types. Notably, the grout filling resulted in a notably higher final axial force. The variation in grout and gypsum bedding layer thicknesses did not demonstrate any discernible effect on the final axial load. Conversely, when loading the interface between the filling and bedding layers, an increase in grout layer thickness led to an augmented final axial load. The grout filling segment also contributed to a heightened final axial force. The results of the numerical simulations exhibited a commendable agreement with the experimental outputs. This research effectively addresses two critical aspects: stability control and support design for the bedded rock mass. Practical Applications: This study used a unique artificial material and loading system to investigate how bedding cohesion and loading conditions affect bolting behavior in rock mass. The findings showed a significant difference in ultimate axial load when grout was used compared to gypsum filling around the rock bolt, emphasizing the importance of this factor in stability control. The research revealed a strong connection between breakage patterns and the specific loading conditions applied, providing valuable insights into support design in a bedded rock mass. The study also demonstrated a high level of agreement between experimental and numerical simulations, strengthening the credibility of the findings and their relevance to real-world stability control measures. [ABSTRACT FROM AUTHOR]

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

Rock bolts play a critical role in ground support in mining, tunneling and construction. Being able to obtain timely information on rock bolt load condition and deformation could help immensely in safeguarding workers' safety, optimization of ground support system, and ensuring stability and longevity of underground structures. The objective of this work was to develop a practical ultrasonic rock bolt sensing technology for monitoring axial load and deformation of a full-bodied rock bolt in both elastic and plastic deformation regimes. To this end, empirical mathematical models involving simultaneous use of times of flight of longitudinal and shear ultrasonic waves propagating along the axial direction of the rock bolt were developed, sensors were designed and fabricated, and laboratory studies were conducted. The results showed that the technology was able to measure load change, provide early detection of yield, and measure both plastic and total elongations of the rock bolt undergoing a pull test. Additionally, sectional load and elongation information could be obtained by applying the technology to rock bolts divided into sections by drilled holes along their shanks, therefore, providing the capability to assess the condition of grouted bolts at different depths within a rock mass. This work has laid the groundwork for the deployment of the technology in the field. Highlights: Empirical models based on simultaneous use of times of flight of longitudinal and shear ultrasonic waves were proposed for condition monitoring of full-bodied rock bolts Methods for instrumenting full-bodied rock bolts were developed Calibration methods for determining values of parameters used in the empirical models were established Pull testing showed that the technology could measure load changes within and beyond the elastic limit, detect yield, and measure plastic and total elongations of the rock bolt Sectional load and elongation information could be obtained by applying the technology to rock bolts divided into sections by drilled holes along their shanks [ABSTRACT FROM AUTHOR]

This study aims to evaluate the sensing performance of glass fiber-reinforced polymer (GFRP) rock bolt sensors instrumented with strain gauges for monitoring rockslides. Experimental studies are conducted with four different types of GFRP rock bolt sensors and concrete blocks having central holes and two shear joints. Two GFRP rock bolt sensors are inserted into holes and then fixed in concrete blocks with cement grout and soil, respectively. The other two are coated with heat-shrink tubes to protect strain gauges and wires, which are then fixed in concrete blocks with cement grout and soil, respectively. Double shear tests are performed to produce shear deformations of GFRP rock bolt sensors, and then strain change with shear displacement is monitored. The results manifest that the variation in strain with shear displacement is more sensitive in the GFRP rock bolt sensor fixed with soil than with cement grout. Also, strain gauge wires in the GFRP rock bolt sensor fixed with cement grout are broken earlier than with soil. Furthermore, it is confirmed that the heat-shrink tube effectively protects strain gauges and wires, so that GFRP rock bolt sensors coated with heat-shrink tubes work for a longer time than the uncoated sensors. The present study shows that the GFRP rock bolt sensor can be useful for monitoring rock slope failure. [ABSTRACT FROM AUTHOR]

Periodic loads cause periodic deformation of rock, resulting in the gradual accumulation of energy of rock bolts and eventually damage. Thus, it is vital to propose novel resistant rock bolts that adapt to large deformation and absorb and release energy in time. In this study, a new resistant rock bolt was developed and its large deformation performance was analyzed by theoretical analysis and pull-out tests. The structure of the new bolt consists of rebar with multi gears, a cannula, and steel balls. The working principle is that the resistance fluctuation is caused by the plastic deformation of steel-ball cutting multi-gears, and then achieves the periodic absorption and release of energy. The mathematical model of the working resistance was calculated considering the diameters and number of steel balls, the thickness, and the slope of gears, based on the metal cutting mechanics. The new rock bolts made of 20# steel had working resistance of 100 ~ 110 kN, which belongs to the medium category but has a higher energy-absorbing-releasing capacity. The slope angle only changed the velocity of working resistance, but had no obvious effect on the high resistance. Theoretical analysis and experimental results verified that the parameters of steel balls were positively correlated with the working resistance of the new rock bolt, and the available maximum resistance of the similarity model is 4.5 kN when the number and diameter of steel balls are 5 and 6.0 mm. Finally, two numerical models of tunneling with ordinary and new rock bolts were constructed. The results found that after two dynamic loads, new rock bolts still proved the high performance but the ordinary bolt system failed. Therefore, the new rock bolt obviously increased the long-term stability of the rock mass. [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 longwall system is an extraction system commonly used in coal mining in many countries, including Poland. One of the methods for reducing extraction costs is the dual use of the gateroad. In the first instance, the gateroad serves as the tailgate, and during the exploitation of the second coal panel, it functions as the headgate. Such a situation requires maintenance of the roadway behind the longwall face, which is typically challenging, due to significant stress-related loads on the support and its substantial deformation. The support design for this kind of roadway should take into consideration the dual impact of exploitation pressure and the caved zone influence behind the longwall face. This article presents the results of in-situ research conducted on two roadways behind the longwall face. In both roadways, the effectiveness of specially designed steel arch frames and rock bolt patterns were examined to minimize roadway deformations and maintain their functionality. The research project was comprised of several stages. Initially, mining and laboratory studies were conducted to determine the geomechanical parameters of the rocks. Subsequently, excavation stability and functionality forecasts were performed based on the authors' empirical indicators. Then, numerical analyses were carried out to design support schemes (steel arches and rock bolt) in both roadways. A fully automated monitoring system with programmed data loggers was designed to check the behaviour of a specific rock mass and the support elements. The load on the steel arch support was measured with the help of load cells, while the load on the rock bolt support was carried out with the help of measurement bolts. Behind the longwall face, the loads on the wooden cribs set from the goaf side were also monitored. Additionally, the measurement station was equipped with extensometers to monitor the movement of roof layers and stress meters to determine changes in rock mass stress. Laser scanning or traditional surveying methods were also used to verify the support schemes through roadway convergence measurements. The obtained results allowed us to draw conclusions regarding the optimization of support schemes and to give recommendations for the practical application of specific reinforcements in excavations maintained behind the longwall face. [ABSTRACT FROM AUTHOR]

Featured Application: This research highlights the implementation of a novel sensing approach allowing for geomechanics insights in rock bolt performance and behaviour; recent advancements in the technique are also presented. An often-utilized solution in terms of providing support to underground excavation, the fully grouted rebar rock bolt system presents optimization potential due to existing technological limitations in capturing and understanding its composite system response. In order to address these limitations, the development and application of Distributed Optic Fiber Sensing (DOS) allows for continuous strain monitoring (at a spatial resolution of 0.65 mm utilizing the technique defined herein) across a full spectrum of loading. A robust laboratory investigation was conducted featuring 24 rock bolt specimens. This examined the effects of two selected independent variables: rib spacing (from 13 mm to 68 mm) and grout annulus (from 7.7 mm to 22.8 mm). This body of research provides valuable insight into the performance of grouted rebar rock bolts and the effects of the selected parameters (rib spacing and size of the grout annulus), while also highlighting an advanced monitoring technique. Results indicated that rib spacing was a negative predictor of bond performance. No definite conclusions were drawn in terms of the effect of the size of grout annulus; however, findings provide limited support for an optimal sizing in relation to rib height. The results were also compared to analytic and numerical models. These insights can aid in calibrating and validating numerical models, and improve monitoring and rock bolt design within the overall goal of improving and optimizing ground support design arrangements. [ABSTRACT FROM AUTHOR]

Purpose is to study the influence of mining and geological conditions on the time-dependent stability of the collective refuge chamber for mine workers with the adjacent mine workings and develop support schemes for different conditions of construction of such mine workings. Methods. Numerical modelling methods of the connected processes of elastoplastic deformation of gas-bearing rocks and gas filtration within the area disturbed during mining operations were used to study stability of mine workings with a compound cross-section, i.e. the collective refuge chambers and its adjacent extraction gallery. The model was based on fundamental principles of solid mechanics and filtration theory. The problem was solved using a finite element method. Findings. A classification of the conditions for locating collective refuge chambers for mine workers according to the relative strength of the enclosing rocks was developed. Support schemes for the chamber and its adjacent mine working were elaborated. The schemes include basic support and provide for its strengthening with rock bolts located in the roof of the mine working and chamber, or in their walls. The compliance of these support schemes with the developed classification of location conditions was determined. A numerical study of the time-dependent stability of the chamber and its adjacent mine working, while applying the recommended support scheme, was performed. It is shown that the strengthening of rock bolting schemes reduces the multicomponent stress field and the area of the zone of inelastic deformations, forms a rock-bolt overlap in the roof of the mine workings and chambers, which helps increase their stability under the complicated mining and geological conditions. Originality. Dependence of the changes within the area of a zone of inelastic deformations around the chamber with its adjacent mine working on the relative strength of the enclosing rocks was identified; time-dependent changes within the area of the zone of inelastic deformations, when using different support types, were specified. Practical implications. Support schemes for collective rescue chambers for mine workers in terms of different construction conditions were developed along with the procedure of their selection for specific mining and geological conditions. The results of the study provide theoretical substantiation and scientific guidelines for the selection of supports for collective refuge chambers adjacent to the mine working. [ABSTRACT FROM AUTHOR]

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

Rock bolt is widely used to stabilize suspended rock blocks at an excavation section, reinforce rock mass, and reduce displacement along rock joints. To simulate the rock bolt behavior in discrete element method (DEM), this study proposed a rock bolt model based on discrete element method software Particle Flow Code (PFC), which simulates the interfaces between the rock bolt and surrounding rock mass using the particulate interface model with high strength and stiffness. On the basis of the proposed model, the DEM simulation can effectively install a series of rock bolts at particular positions to form a support system. The proposed model was verified using laboratory pull-out and shear tests. A series of tunnel cases were further simulated to compare the difference among the displacement distributions of the tunnel under different rock bolt configurations. The simulation results showed that the proposed model can simulate rock bolt functions on tunnel excavation. Furthermore, the results showed that increasing the length and number of rock bolts increases the reinforced effect; however, as the length and number of rock bolts increased to an upper bound value, a limited increment was observed in the reinforced effect. The proposed model provides a useful tool to simulate the rock bolt system for tunnel engineering. [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]

Determining the rock bolt response under the typical in situ loading conditions of tension, shear and bending is an important part of the support design process. Calibrated numerical modelling can be an important tool for simulating the rock bolt response under in situ loads. However, currently available structural support models do not accurately model the rock bolt behaviour under shear loads. These models need to be modified to simulate the actual rock bolt response as determined under laboratory testing. Results from double shear laboratory tests by Kostecki (2019) have been used to calibrate the numerical models in ANSYS (ANSYS® Academic Research Mechanical 2019). The calibrated numerical models were used to study the state of stress along the rock bolt under different concrete strength. These numerical models are compared with the analytical model proposed by Pellet and Egger (1996). The results show that the rock reaction and consequently the shear load on rock bolt in the analytical model is underestimated (by up to 50% in case of high strength concrete). In high strength concrete, the yield and failure behaviour is determined by the shear stress rather than the bending and tensile stress as predicted by the analytical models. The analytical model is modified to better predict the shear forces in high strength concrete. The pile structural element available in FLAC3D (FLAC3D — Fast Lagrangian Analysis of Continua in Three-Dimensions 2017) finite difference method neglects the transverse shear strain in the element. In this paper, the pile structural element is modified to simulate the correct response of rock bolt under shear. The FLAC3D code is also modified to simulate the bolt yielding and failure under combined axial, bending and shear load. The modified model is validated with laboratory results from Mchugh and Signer (McHugh and Signer 1999) and is shown to be better at simulating the shear response and failure of rock bolt under shear compared to the original pile model. [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]

Anchor plate is a necessary component of the prestressed rock bolt, which plays a decisive role in actively resisting the rock mass deformation and improving the self-bearing capacity of the surrounding rock. In this paper, in order to investigate the effect of anchor plate on the mechanical behavior of prestressed rock bolt used in squeezing large deformation tunnel, a series of numerical, field and laboratory tests were performed. The mechanical characteristics of anchor plate with different shapes and sizes were systematically analyzed. Based on the Muzhailing Tunnel in Gansu Province, China, which is a typical deep-buried soft rock tunnel and suffered from serious squeezing large deformation disaster, the field verification was carried out. Meanwhile, the influences of spherical washer on the mechanical behavior of bolt shaft and anchor plate were also investigated. The result shows that the bowl-shaped plate has much better performance than the flat one, while the rounded bowl plate performs slightly better than the squared bowl plate. With the increase of plate thickness or plane size, the anchor plate has the better bearing capacity, while the stress transfer effect will be worse. Furthermore, the non-uniform deformation will gradually increase with the decrease of plate thickness or increase of plane size. Therefore, it is advised to increase the plate thickness rather than the plane size under the condition of better bearing capacity. The bending-induced stress of the anchor plate increases rapidly with the increase of the inclination angle between bolt shaft and anchor plate. Whereas the installation angle is unavoidable in practice, the spherical washer which has great effects on reducing the bending-induced stress could be a necessary component of the prestressed rock bolt system. [ABSTRACT FROM AUTHOR]

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Estimating the axial force of rock bolts is vital for the stability and safety of underground excavations. Current methods suffer from being labor-intensive, time-consuming, and prone to inaccuracies. This paper presents a novel method for estimating the axial force of a rock bolt, a critical element in underground engineering, by analyzing the deformation field of the bearing plate. This innovative approach combines 3D laser scanning for data acquisition with a developed convolutional neural network (CNN) model for data processing, resulting in an efficient and non-destructive external monitoring technique. The proposed method was verified with 27 laboratory experiments. The results showed an accurate estimation of the axial forces of rock bolts with an average error of ± 5 kN, underlining the method's potential for in-situ application in underground engineering. This research not only contributes to the development of intelligent systems in rock mechanics and engineering but also has significant implications for industries, such as mining, tunneling, and underground engineering. Highlights: The study introduces a novel method that utilizes 3D laser scanning and a developed CNN model to accurately estimate the axial force of rock bolts. The proposed method achieves accurate estimations of rock bolts' axial forces with an average error of ± 5 kN. Future work includes the integration of object detection algorithms for large-scale 3D laser scanning and the creation of a database of various bearing plates to enhance the method's robustness. [ABSTRACT FROM AUTHOR]

Rock bolts have been widely applied with roadway excavation in underground coal mines to prevent roadway collapse and improve the stability of roadway surrounding rocks. Overloading and failures of rock bolts could result in accidents or casualties in coal mine roadways. Consequently, monitoring axial forces and work conditions of rock bolts plays an increasingly important role in ensuring safe operations of underground coal mines. Conventional mechanical or electronic rock bolt monitoring systems are typically affected by electromagnetic interference, corrosive groundwater, and dusty circumstance in underground working sites. This work proposed a FBG-based instrumented rock bolt. Quasi-distributed FBG sensors were installed on a slotted rock bolt and encapsulated by epoxy resin that was used to fix FBG sensors on the rock bolt and protect FBG sensors from damage. The FBG sensors were calibrated before the in situ application. Monitoring results indicated that the axial forces of rock bolts installed on the roof of the roadway were higher than that of others, and the maximum axial forces of each rock bolt were typically detected near the middle portion of rock bolts. A real-time and accurate rock bolt monitoring system was established by integrating instrumented rock bolts to the existing monitoring system of the coal mine. [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]

A D bolt, an energy-absorbing rock bolt, is a smooth steel bar with a number of anchors along its length. The anchors, which can be spaced evenly or unevenly along its length, are firmly fixed within a borehole using either cement grout or resin, while the smooth sections of the bolt between the anchors may freely deform in response to rock dilation. A series of numerical simulations have been conducted using the finite difference method to investigate the effects of D bolt on the displacement increase of rock mass around a roadway in comparison with normal fully encapsulated rebar. As a result, the displacement of 49 mm at the top of roadway roof in the D bolts supported model is much larger than 30.08 mm in the fully encapsulated rebar bolts supported model so that the former is capable of absorbing potential deformation energy of rock mass around a roadway to tolerate the large deformation of rock. Plans of spacing arrangement of D bolt's anchor have a significant effect on stress redistribution of the bolt. The numerical simulation result shows that for the D bolt with its whole length of 2.4 m, the length of its exposed section of 0.1 m, and the 4 anchors with the length of 0.1 m, the maximum tensile stress of 3.25 GPa generated in the D bolt with the ratio of the spacing between anchors (RSA) of 30 : 40 : 50 : 70 is lower about 1.13–1.31 times than the other D bolts with different ratio of spacing, and the changing range of stress is also the smallest, where the ratio of 30 : 40 : 50 : 70 indicates a ratio of lengths of deformable sections which is determined by turns from the innermost section of rock mass around roadway to the outermost section of roadway space. This study demonstrates that it is reasonable to employ the RSA of D bolt which makes it bring out its energy-absorbing capability to the full. [ABSTRACT FROM AUTHOR]

In this study, the mechanical behavior of novel fully grouted cable rock bolts made of basalt fiber–reinforced polymer (BFRP) was investigated, which included pullout and double-shear joint behavior. Three BFRP cables were prepared: (1) single-tendon; (2) untwisted multiple-tendon; and (3) twisted multiple-tendon. In the pullout tests, the effects of cable type, borehole diameter, and encapsulated length were studied. However, the influence of the pretension load level was focused on in the double-shear joint tests. The results suggested that an overly thick grout annulus significantly reduced the pullout strength and stiffness. For the BFRP cable with multiple tendons, the initial pullout stiffness was enhanced compared with the BFRP cable with a single tendon due to better interfacial bonding with the grout. In the double-shear joint tests, the pretension of the cable significantly improved the shear capacity and stiffness. With an enhancement in the confinement from pretension, the partial failure of the grout at an early stage could be prevented. The parallel and twisted-tendon BFRP cable rock bolts had larger failure displacements than the single-tendon cable. This analytical study found that a pullout analytical model available in the literature was accurate when back-calculating the stress conditions along the rock bolt. The predicted shear capacity of the rock joint showed good agreement with the experimental values. A parametric study indicated that the joint shear capacity was sensitive to the tensile and shear strengths of the cable but was irrelevant to the cable moduli. Considering the effectiveness of pretension and creep safety for BFRP, a suitable range for the pretension load was suggested. Practical Applications: This study attempts to promote the use of novel, fully grouted cable rock bolts made of basalt fiber–reinforced polymer (BFRP) materials in geotechnical engineering applications. Different types of cable rock bolts are produced, which include single-tendon, untwisted multiple-tendon, and twisted multiple-tendon cables. In the pullout tests, the untwisted multiple-tendon cable exhibited the highest pullout capacity, because of its better interfacial bonding with the grout. From the double-shear joint tests, the pretension of the cable could significantly improve the shear capacity and stiffness. In general, the BFRP cable rock bolts could have a competitive mechanical behavior compared with the steel rock bolts. The respective analytical models for pullout and double-shear joint specimens have proved to be accurate for predicting the mechanical responses of the cable rock bolts. These concise but reliable analytical models could allow researchers and designers to better utilize these novel cable rock bolts in potential applications. [ABSTRACT FROM AUTHOR]

Anchoring mechanism and failure characteristics of composite soft rock with weak interface usually exhibit remarkable difference from those in single rock mass. In order to fully understand the reinforcement mechanism of composite soft roof in western mining area of China, a mechanical model of composite soft rock with weak interface and rock bolt which considering the transverse shear sliding between different rock layers was established firstly. The anchoring effect was quantified by a factor defined as anchoring effect coefficient and its evolution equation was further deduced based on the deformation relationship and homogenized distribution assumption of stress acting on composite structure. Meanwhile, the numerical simulation model of composite soft rock with shear joint was prompted by finite element method. Then detailed analysis were carried out for the deformation features, stress distribution and failure behavior of rock mass and rock bolt near the joint under transverse load. The theoretical result indicates that the anchoring effect of rock-bolt through weak joint changes with the working status of rock mass and closely relates with the physical and geometric parameters of rock mass and rock bolt. From the numerical results, the bending deformation of rock bolt accurately characterized by Doseresp model is mainly concentrated between two plastic hinges near the shear joint. The maximum tensile and compression stresses distribute in the plastic hinge. However, the maximum shear stress appears at the positions of joint surface. The failure zones of composite rock are produced firstly at the joint surface due to the reaction of rock bolt. The above results laid a theoretical and computational foundation for further study of anchorage failure in composite soft rock. [ABSTRACT FROM AUTHOR]

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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]

Rock bolt and lining are very common and effective support ways, and they are often used together in many projects because their bearing and reinforcement effects. However, the mechanism of the two support methods in the surrounding rock is not clear, especially the theoretical analysis. Therefore, a model is put forward to analyze the mechanical behavior of a deeply buried circular hydraulic tunnel jointly supported by double-linings and point anchored rock bolts, in which rock mass, double linings and bolts maintain elastic state and are in full contact with each other. And point anchored rock bolts are creatively replaced by pairs of concentrated forces of equal magnitude and opposite direction. By using the complex function method, the linear equations for solving the axial force of the bolts and the relevant analytical function coefficients can be established, based on the stress condition of the inner boundary of the secondary lining, continuity condition between the primary lining and the surrounding rock, and continuity condition between the primary lining and the secondary lining, as well as the compatibility condition of the displacement between the bolts and the surrounding rock. Then, using the analytical functions, the stress and displacement of any point in the double linings and surrounding rock can be calculated. Besides, the influence of inner hydrostatic pressure and exchange of Young's modulus of double linings are discussed, in which the support laws and mode of load transmission are analyzed. The results are in line with actual laws and can provide guiding suggestions for the design and construction of support works. [ABSTRACT FROM AUTHOR]

The force-measuring rock bolt instrumented with bare fiber Bragg grating (FBG) sensors are generally factory-fabricated. To enable users to fabricate a force-measuring rock bolt by themselves, the microclamped FBG sensor is proposed to replace the encapsulated bare FBG sensor. A theoretical formula of strain sensitivity is also established. The strain sensibility measured by indoor calibration is consistent with the theoretical one, indicating that the microclamped FBG sensor can measure strain accurately. Besides, the measured strain sensibility coefficient (wavelength difference/strain) matches the theoretical values, making the installed microclamped sensor free from the need for recalibration and proving the installation method to be reliable. Also, the test sensitivity can be adjusted as needed. The instrumented rock bolt with microclamped FBG sensors shows great mechanical performance in the field test, awaiting further usage in applications. [ABSTRACT FROM AUTHOR]

Copyright of Mining of Mineral Deposits is the property of Dnipro University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

High stress in surrounding rock mass could cause serious stability problems such as larger squeezing deformation in soft rock and rock burst in hard rock. The support system applied in high in situ stress conditions should be able to carry high load and accommodate large deformation of rock mass. This paper presented a new yielding rock bolt, called tension and compression-coupled yielding rock bolt, which is promising to provide support for both squeezing and burst-prone rock mass encountered in mining or tunneling at depth. The new bolt mainly consists of a steel rod and two additional anchors. The steel rod is a round shape bar with varying surface conditions. The inner segment is processed into rough surface, while the middle segment of the rod has smooth surface. Two additional anchors were arranged on both ends of smooth segment. The bolt is fully encapsulated in a borehole with either cement or resin grout. The rough segment and the inner anchor are firmly fixed in the bottom of the borehole, while the smooth segment has no or very weak bonding to the grout, which can stretch to accommodate rock dilatation. First, direct quasi-static pull tests were performed to examine the load capacity of tension and compression-coupled anchor. The results showed that the coupling action of tension to the rough rod and compression on the inner additional anchor by grout in different positions can increase the ultimate bearing capacity of inner anchoring segment significantly. Second, the performance of the new bolt and the fully encapsulated rebar bolt was tested under fracture opening condition. Results showed that the load and strain concentration could result in premature failure of fully encapsulated rebar bolt. However, the smooth segment of TCC Yielding rock bolt can detach from the grout under pull loading and provide a larger deformation to accommodate rock dilations. Third, shear tests were performed to examine the deformation mechanism of the new rock bolt under fracture sliding condition. Results showed that the smooth section of the new bolt specimen can deform freely to accommodate the sliding of fracture. The maximum shear displacement of the new bolt specimen is much larger than the fully encapsulated rebar bolt specimen, which is promising a better ability to accommodate the large displacement sliding of fracture in engineering practice. [ABSTRACT FROM AUTHOR]

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]

The article highlights the research pertaining to the problem of reinforcement of underground excavations with bolting system, using chemical method based on resin cartridges, which currently is a global trend in mines. Theoretical model of rock bolt installed in a rockmass was discussed and described with proper formulas for explanation the role of single discontinuity and its mechanism affecting stress-strain characteristics of the reinforcement system, based on an adhesive method. The presented model has been verified with results of numerical modelling of stress-strain and deformation composition of the "rock bolt/resin cartridge/rock block" system, depending on the bond coefficient of the mixture which fixes the rock bolt. The analysis of the modelling results showed that for the stress-strain conditions of the rock bolt, too high a bond between the bolt and the rock is dangerous (critical), as it leads to high local tensile and deformation stresses. [ABSTRACT FROM AUTHOR]

To investigate the mechanical behavior for rock bolt embedded in composite rock mass, a modified nonlinear bond-slip model considering the residual strength is established, and then a numerical model of composite rock mass is proposed. The modified nonlinear bond-slip model and the numerical model are verified by comparing with pullout test data, which show excellent performance in explaining and predicting the pullout response of rock bolt embedded in composite rock mass. The results show that the bearing capacity of anchoring interface in hard rock stratum is obviously better than that in soft rock stratum under the same anchoring length. The axial force and interfacial shear stress distribution curves have an obvious inflection point and mutation point at the rock strata interface. The axial force decays faster in hard rock stratum than that in soft rock stratum. The modified nonlinear bond-slip model and the numerical model improves the understanding of the mechanical mechanism for rock bolts embedded in composite rock mass. [ABSTRACT FROM AUTHOR]

In response to the unreasonable support plan for the water-rich and fractured area of the mining excavation roadway, which has caused problems such as roof fall and fragmentation, the optimization of tunnel support parameters was studied based on the engineering background of the marble fractured area m the front of the 1 660 m level YM-II roadway. In order to reasonably and effectively support the roadway and reduce support costs, a roadway model was established based on onsite practice. The support plan was designed through orthogonal experiments, and FLAC3D numerical simulation software was used to simulate and calculate. The stability of the surrounding rock n the roadway was compared and analyzed through simulation result. The analysis results indicate that the length of anchor rods mainly affects the deformation of the surrounding rock of the tunnel, and the spacing between anchor rods mainly affects the damage of the surrounding rock of the tunnel; The optimal support plan is for anchor rods with a diameter of 40 mm, a length of 1. 8 m, and a spacing of 0. 9 m between rows X 0. 9 m can reduce the displacement of tunnel surrounding rock by 70.77%, plastic zone volume by 63.91%, and vertical stress by 12.96%, effectively controlling the stability of tunnel surrounding rock and providing assurance for mine safety production. The research results may provide reference for the support design and ground pressure control of surrounding rock tunnels in water-rich and fractured areas. [ABSTRACT FROM AUTHOR]

Computer modeling can be used to explore and gain new insights into the impacts of rock bolt intersecting joints in rock masses, and to estimate the effectiveness of the rock reinforcement system. In order to achieve this goal, we couple a rock bolt element into the two-dimensional discontinuous deformation analysis (DDA) program. The coupling algorithm is based on the analytically-derived interface behavior between a rock bolt and the rock material for grouted rock bolts. The shear force generated by slippage along the interface is assumed to have a linear relationship with respect to the relative slipping distance between the rock bolt and the rock. The linear elastic criterion is applied to determine the material behavior of rock bolts before the axial stress reaches the yield value. The pullout tests are simulated to verify the coupling algorithm and the effects of the proposed rock bolt elements. Parametrical studies are also carried out to analyze the effectiveness of the rock bolts under various end conditions, joint locations and bond stiffness. In addition, the performance of the rock bolt during the interface debonding is analyzed using two types of constitutive laws, i.e., the friction law and the reduction law. The simulation results show that the proposed rock bolt models can predict the shear forces and axial loading along the rock bolts. [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]

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]

This study analyzes the phenomenon of performance deterioration in fully grouted rock bolts in tunnels with a dry, hot environment and high geothermal activity with a focus on temperature effects on interfacial bond performance. Three groups of fully grouted rock bolt specimens were designed based on similar mechanical principles. They were produced and maintained at 20 °C, 35 °C, and 50 °C. Through the indoor gradual loading tensile test of specimens, variations of axial force and shear stress between the rock bolt and mortar adhesive interface were obtained under different environmental temperatures. Distribution of the axial force and shear stress on the anchorage section were found under different tensile forces. Results showed that, with an increase in specimen environmental temperature, maximum shear stress of the rock bolt section became smaller, while shear stress distribution along the rock bolt segment became more uniform. In addition, the axial force value at the same position along the pull end was greater, while axial stress along the anchorage's length decayed faster. With an increase in tensile force under different temperatures, the axial force and maximum shear stress of rock bolt specimens along the anchorage section has a corresponding increase. [ABSTRACT FROM AUTHOR]

Copyright of Science Technology & Engineering is the property of Chinese Society of Technology Economics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Rock bolts are one of the most effective and conventional support techniques widely used in underground mining and tunneling operations to stabilize excavations and jointed rock masses. External factors such as corrosion, overloading, and improper installation can weaken rock bolts, which could result in ground failure causing injury or loss of life and production. Monitoring the health condition of rock bolts will reduce the risk of accidents providing a safer environment for workers and equipment. This paper reviews monitoring methods currently used to assess the condition of installed rock bolts. Furthermore, we classify the surveyed techniques depending on the type of problems they attempt to solve. Presented are methods such as ultrasonics, fiber optics, piezoelectric, electromagnetics, impact echo, acoustic emission, and numerical algorithms. Each method is based on a unique physical principle that aids in evaluating corrosion and strain levels in the rock bolt. However, recent research to detect corrosion has primarily focused on rebar type of rock bolts used in concrete structures. Consequently, more research is needed to monitor the condition of the other types of rock bolts used in the industry such as cable bolts and split set bolts. In conclusion, the paper highlights various methods of studying rock bolt failure initiated by strain, corrosion, and improper installation of the grouts. It also explores the research advancement made for the study of rock bolt failure. This investigation is specifically beneficial to the mining and tunneling industry for better understanding and prediction of rock bolt failure. [ABSTRACT FROM AUTHOR]

Conventional tunnelling methods (i.e., the drill and blast tunnelling method or the new Austrian tunnelling method) have been frequently applied for the construction of tunnels/caverns under a high overburden and with a large cross section. Under such adverse conditions, tunnel support materials may yield because of ground pressure and tunnel deformation. As a result, a tunnel may lose its stability due to a reduced effectiveness of the tunnel supports. Rock bolts have been widely used as an essential component of tunnel support, and many studies have been conducted on the performance of rock bolts in strengthening the jointed rock mass. However, there is a lack of understanding on the interface behaviour between the rock bolt and the bond material, especially the crack initiation and propagation inside the bond material. This study aims to investigate the interface behaviour between rock bolts and bond materials using laboratory tests (shear tests) and numerical simulations (Discontinuous deformation analysis). By assessing the impact of the key parameters in the rock bolting system, such as the ribs, rib angle, strength of the bond material and the confining pressure, we are able to better understand the supporting mechanism and the effects of rock bolting. [ABSTRACT FROM AUTHOR]

This paper presents results of 71 in situ nondestructive rock bolt and tendon pull tests conducted in the Powerhouse Complex of the Uma Oya Multipurpose Development Project, located in Sri Lanka. The pull tests are performed on 6 and 8 m Double Corrosion Protected fully and partially grouted rock bolts (high strength threadbar) as well as 4 m normal fully grouted rock bolts and 26 m pre-stressed tendons, which are installed in different types of Gneiss. Based on the recorded load–displacement curve of the rock bolt head in each test, stiffness of fully and partially grouted rock bolt is measured in the bonded section. Effect of some parameters on the stiffness such as rock mass types and characteristics, bond length as well as rock bolt diameter and steel type are investigated. Primarily, the pull tests are done to approve the working load capacity of rock bolts and tendons and quality control of the installation process. Besides, the stiffness of bonded rock bolt is also calculated. The results show that the stiffness declines by decreasing the rock mass mechanical characteristics, rock bolt bond length, and rock bolt diameter as well as steel bar grade. [ABSTRACT FROM AUTHOR]

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