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Methane explosions are the main cause of coal mine disasters. Considering the scale effect involved in the process of methane explosion, small-scale methane explosion experiments can only obtain a qualitative trend of explosion parameters. It is necessary to study methane explosions in a full-size complex pipe network. In this study, the No. 501 experiment at the Lynn Lake Experimental Mine in the United States was used as the background case. GASFLOW-MPI was used to study the oscillation, attenuation, and dynamic pressure evolution laws of the explosion shockwaves in a full-size complex pipe network with consideration of the heat loss. The results showed that the numerical simulation results considering heat loss were more accurate than the adiabatic simulation results, and the average error of the peak pressure was only 4.25%. The pressure – time history curve of methane explosion shockwaves in a complex pipe network differed from that in a single pipe. The pressure peak was a bimodal curve near the explosion source, the dynamic pressure changes significantly, and both forward and reverse wind reaching 200 m/s occurred. The pressure curve far from the explosion source was a unimodal peak curve, and only the forward wind occurred. This reasonably explains the bidirectional deformation of rock bolted plates found in the US UBB accident. The results are expected to provide theoretical support for emergency mine rescue operations and mitigating the effects of methane explosions. [ABSTRACT FROM AUTHOR]

Rocking structures are recognized as an effective seismic response modification technique due to their peculiar dynamic characteristics. Meanwhile, in bridge structures, strong ground motions have frequently caused a rocking motion of pin bearings around their two toes, resulting in the pulling‐out of anchor bolts. This study, motivated by the promising features of rocking behaviors, seeks to develop a rocking isolation bearing system (RIBS) to control excessive response in bridges. An example bridge featuring such a RIBS, consisting of the pin bearings removing anchor bolts to release the rocking motion, the girder type superstructure, and an array of bridge piers, is characterized by a simplified model. Two coefficients of restitution (COR) models are used to investigate the effects of energy dissipation during impact: the Housner model, and a model which simultaneously modifies the velocities of the superstructure and substructures. The dynamic characteristics of RIBS and its control effectiveness on the bridge structure are discussed through a series of dynamic analyses, under both observed ground motions and the design ground motions specified in the Japan Road Association (JRA) design specifications for highway bridges. The simulation results demonstrate that the seismic performance of the bridge structure can be substantially improved, with decreased pier displacement at an allowable bearing rotation level. [ABSTRACT FROM AUTHOR]

This paper presents a unified elasto‐plastic analysis of rock mass supported with fully ground bolts for deep tunnels. In the analysis, depending on whether the relative movement at the grout–bolt interface is considered, two finite‐difference algorithms are discussed. For each algorithm, two conditions, one when the rock bolt is inserted into the elastic area and one when it is included within the plastic area, are comprehensively investigated. In the algorithms, the initial and final states for the rock–bolt interaction are presented, and for each state, the surrounding rock mass consisting of the bolt or the plastic area is divided into a finite number of annuli through a constant radius increment. Based on this, the stress and displacement for the rock mass and the rock bolt are obtained step by step. The results of the two algorithms are verified by the analytical method and the field test data, respectively. Parametric studies were conducted to compare bolt force, rock displacement and stress components that are solved by the algorithms with and without considering relative movement. The proposed algorithms can be written into the software for guiding the rock bolt design in practical engineering. [ABSTRACT FROM AUTHOR]

Summary: Bolted connection functions to fasten and secure parts together for engineering structures. Newly developed percussion‐based approaches have been proven as a fast and effective tool for bolt looseness identification; however, most of the existing studies use machine learning assisted approaches to classify percussion sounds and predict looseness conditions without investigating the relationship between percussion sounds and bolt vibrations. This paper presents a conceptual research to utilize bolt vibration signal to reconstruct percussion sounds, which significantly improves the validity and accuracy of bolt looseness identification. In the experimental study, a laser Doppler vibrometry was used to capture vibrational information of the test bolt; meanwhile, percussion sounds were collected by microphones. The relationship between sound and vibration signals was investigated using wavelet packet decomposition and correlation analysis. A new set of sounds were reconstructed by combination of the sound packets which showed the strongest correlation with the vibration signal. The reconstructed sound database was then transformed into spectrograms and trained by a two‐dimensional convolution neural network to identify bolt looseness conditions. [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]

The stability of longwall coal mines has been a challenging concern for geotechnical and mining engineers. Rock-bolting is the commonly used support system preventing roof and wall convergence and floor heave. This study attempts to suggest an optimized new rock-bolting pattern to effectively prevent the convergence of transportation and ventilation tunnels in Tabas coal longwall mine at panels 2 and 3. Three-dimensional numerical analysis was performed on the support system using FLAC3d code. Investigating the rock bolts axial force applied to the ventilation tunnels roofs shows that, the safety factor of the new support system compared to the old one can be reduced by the ratio of 1.2 to 2, while the amount of the roof displacements are still within the allowable limit. Moreover, rock bolts installed in the transportation tunnels walls have yielded about 10 m from the working face, which became stable in the redesigned rock-bolting pattern. In order to decrease the floor heave, a support system with inclined bolts was proposed, in which the amount of floor heave in the transportation and ventilation tunnels decreased about 40% and 33%, respectively. [ABSTRACT FROM AUTHOR]

The distribution and magnitude of the shear stress at the interface between the grout of a compression anchor rod and rock are strongly affected by the Poisson effect. A new analytical equation of the influence coefficient of the Poisson effect is proposed to quantitatively evaluate the influence of the Poisson effect on the interfacial shear stress. When the Poisson effect is considered, the interfacial shear stress from the neutral point to the bearing plate increases, and the distribution curve becomes steep. However, the interfacial shear stress far from the neutral point is low, and the distribution curve becomes smooth. Overall, the Poisson effect leads to a more nonuniform distribution of the shear stress at the interface of the compression anchor rod. A larger Poisson's ratio, smaller elastic modulus, and smaller diameter of the grout lead to a greater influence of the Poisson effect. Furthermore, a larger elastic modulus of rock leads to a greater influence of the Poisson effect. The Poisson's ratio of rock and that of grout both affect the Poisson effect greatly, but the influence of the variation in the Poisson's ratio of rock on the Poisson effect is negligible. A larger interface friction angle leads to a greater influence of the Poisson effect. [ABSTRACT FROM AUTHOR]

The joint planes in fractured rock mass will reduce the tensile strength and shear strength of rock mass, which has a decisive influence on the deformation and failure mode of engineering rock mass. Furthermore, infill also exists between the joint surfaces, which will also affect the shear characteristics of the joint. A method of importing standard joint profile into PFC2D was proposed, and a series of numerical simulation tests were carried out to study the effect of joint roughness and infill thickness on the shear characteristics of joints. The numerical results revealed that rock bolts profoundly improved the shear strength of the infilled rock joints, enhanced the toughness of the joint surface, increased the number of micro-cracks, and made the dilatation more obvious. The shear stress and the normal displacement of unbolted or bolted infilled rock joints increased with increasing the joint roughness and decreasing the infill thickness. The maximum horizontal compression stress in the middle of the bolt gradually increased with the increase of joint roughness coefficient. Different roughness has different effects on the number of micro-cracks in the sample. The number of total cracks and tensile cracks of the bolted and unbolted specimens increased with the increase of joint roughness coefficient, while the shear cracks remained almost the same. Through the study of the coupling effect of joint roughness and infill thickness on peak shear stress, results can be obtained as follows. The unbolted samples are highly sensitive to JRC changes. The greater the infill thickness, the greater the sensitivity of unbolted samples to JRC changes. The reinforcement effect of the bolt will strengthen the meshing strength between the joint surface and the filling material; that is, the meshing strength is positively correlated with joint roughness and negatively correlated with filling thickness. [ABSTRACT FROM AUTHOR]

At present, the development of bolt support technology is in the ascendant period, which is of great significance to promote the development of geotechnical engineering. The numerical simulation software RFPA (Rock Failure Process Analysis) has been used to analyze the reinforcement effect of bolt on deep surrounding rock under dynamic load and conduct a comprehensive research on the force state of bolt. The characteristics of stress and displacement change in rock mass and bolt caused by stress wave are compared when the surrounding rock of underground chamber is supported with bolt or not. Numerical experimental results show that, under the action of dynamic load, the high stress area in surrounding rock can be transferred to the interior of rock mass by adding bolt to the surrounding rock of a high ground stress underground chamber, and the displacement value of each segment of bolt is basically the same. Moreover, the acoustic emission (AE) energy and AE count released by surrounding rock have been able to be reduced, and the force pattern of surrounding rock has been changed. [ABSTRACT FROM AUTHOR]

On fatigue strength of large‐size bolt‐assemblies in steel constructions under consideration of manufacturing and surface condition related impacts – part 2: evaluation of fatigue tests Manufacturing related impact factor significantly affect the fatigue strength of bolt assemblies used in steel constructions. The effects are taken into account very inconsistently in the design bases, depending on the normative reference used. Especially for bolt assemblies with large diameters, as they are commonly applied in large numbers at towers for wind energy plants, only a very limited experimental background for assessment of relevant impact factors has been available in the past. This paper presents and evaluates results from 20 different fatigue test series, most of them conducted in the recent past on three different high‐strength bolt assembly systems with varying manufacturing conditions. The data base covers a diameter range between M12 and M64 and focuses on test series with high mean stress in a representative order of magnitude for practical application of the bolts. Based on the knowledge given in the relevant literature, the test results are evaluated regarding the impact of different manufacturing related effects. Furthermore, the results are compared to the specifications of the relevant international normative guidelines. In addition to the results of fatigue tests, supplementary metallographic examinations of the fracture surface shape and surface‐layer condition behavior are taken into account. On this basis, the paper derives recommendations for future design considerations and gives an outlook on further expedient investigations. [ABSTRACT FROM AUTHOR]

Applied loads in bolted geometries of safety critical components can vary with time and operating conditions. Structural integrity and remaining life assessments of such components in aging industrial plants must consider the resultant changes in damage accumulation rates and acceptable defect sizes. Two case studies are presented that demonstrate the effect of bolt pre-load on creep and fatigue lives as well as on the acceptability assessments of defects. In the first case the sensitivity of creep damage accumulation and crack propagation rates to bolt pre-load in high temperature flanged connections are considered. Predicted results were found to compare well with actual damage quantified on a high pressure turbine loop pipe flange connection. It was shown that decreased pre-loads, in this case, leads to an increase the allowable safe defect size during assembly at room temperature. In contrast to this the second case study of corrosion fatigue cracking in a boiler water circulating pump illustrates that an increase in bolt pre-load leads to an increase in fatigue initiation life, a decrease in fatigue crack propagation rate and an increase in the acceptable defect size. Strain gauge measurements of bolt and casing strain, which correlated well with finite element calculations, indicated the necessity for close control of bolt pre-load during assembly to ensure specified levels are attained. In both cases metallurgical analysis and structural integrity assessments of cracked and excavated geometries were conducted which enabled limited continued operation of the components after which repairs and/or replacements will be implemented. [ABSTRACT FROM AUTHOR]

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

In 2017, the Central Mining Institute (GIG), Jastrzębska Spółka Węglowa SA (JSW SA), the largest producer of coking coal in Europe, and JOY KOMATSU, the producer of mining machinery, signed a consortium. The project's main goal was to reduce the costs of driving mine workings by reintroducing the rock bolt support. The works began in November 2019, and for the first time in the history of Polish coal mining, a Bolter Miner machine was used for the purpose. The paper presents the results of measuring the axial forces in rock bolts at the measurement base and their analysis with numerical modelling. [ABSTRACT FROM AUTHOR]

The Stockholm bypass (E4 Förbifart Stockholm) is being built by the Swedish Transport Administration (Trafikverket) – the office responsible for transport infrastructure in Sweden. The project aims to improve connections between the regional town centres and reduce congestion on the main urban roads. The route, which runs mainly underground, employs numerous contractors and has a planned construction period of 14 years, preceded by a 10‐year planning phase. This article looks at three projects: the FSE 61 Akalla Interchange, the FSE 309 Lovön Interchange and in particular, the FSE 613 Akalla Tunnel. The Akalla Tunnel is driven as a conventional full‐face excavation with pre‐grouting and supported with rock bolts and steel‐fibre‐reinforced shotcrete. The tunnel excavation is followed by the interior work comprising precast concrete walls, a suspended membrane reinforced with shotcrete, ceiling foundations and the carriageway structure. [ABSTRACT FROM AUTHOR]

In the present experimental study, 12 specimens were tested to assess and quantify the effects of bolt tightness on the overall behavior of a bolt-ball joint under uniaxial loading. A three-dimensional (3D) nonlinear finite-element (NFE) model with all geometrical complexities, including the threads, was developed to examine the significance of bolt tightness on overall behavior. Three types of parameters were studied, namely, tightness torque, material properties, and friction coefficients. The tests showed that the tightness torque moments had a significant effect on the axial stiffness of the specimens under compressive loading. Observations during the tests indicated that the bolt and sleeve had important roles in the load transferring mechanism. Based on the results of the current experimental study, the finite-element model (FEM) was verified against the test specimens. An acceptable qualitative agreement was observed between the FE models and the experiments for the axial behavior of the joint. It was found that the material properties had a significant role in changing the failure mode and load-bearing capacity. Based on experimental tests and NFE analyses, the present study provides a nonlinear model for determining the relationship between the torque and the preload using gene expression programming. It was concluded that the simplified formulation proposed in this study can calculate the relationship between the torque and the initial load against the bolt tightness database with good accuracy. [ABSTRACT FROM AUTHOR]

This study investigated the behavior of end-plate connections for column splices with construction tolerance. To adjust misalignment between upper and lower columns, oversize holes were drilled on the end plate and plate washers were then placed to bridge over the oversize holes under the head or nut. Six columns with the misaligned connection in the plastic hinge region were tested under cyclic loads. Test variables considered were misalignments, end-plate details (i.e., thickness and stiffener), and the flexural capacity of columns. The test results showed that although plastic deformations occurred significantly near the connection with misalignment, the connection performance of the columns was good: prying action and plate deformation at the connection were minimized although the connection strength of the end plate was only 60% of the required strength because the plate washers provided additional resistance. In addition, slip deformation on the faying surface was negligible due to the preloads of fully tightened bolts. The stiffened end plate was effective in reducing the required thickness of end plate, whereas the shim plate between the top and bottom end plates slightly degraded the slip resistance. The force-transfer mechanism at the end-plate connection under axial compression was investigated and verified through finite-element analysis. [ABSTRACT FROM AUTHOR]

In order to reveal the mechanism of surrounding rock deformation and instability of soft rock roadway in 12# working face of Puhe coal mine, and synthetical analysis of the surrounding rock, deformation and failure of the roadway shows that the original support scheme is difficult to maintain the stability of roadway. Thus the basic concept of roadway surrounding rock control: Single anchor bolt form a compression zone to control the failure and expansion of surrounding rock, and a comparable number of anchor bolts form a homogeneous compression zone to inhibit the development of surrounding rock plastic zone. The "anchor blot + anchor cable net + concrete shotcrete support plan (arrangement of anchor cables four to five)" is proposed. Furthermore, and FLAC3d numerical simulation software was used to verify the rationality and reliability of the supporting scheme of "bolt + anchor cable net + concrete shotcrete support scheme (four to five anchor cables)" support scheme. The on-site monitoring results show that the soft rock roadway in Puhe Coal Mine 12# working face return airway passes through the "bolt + anchor cable net + concrete shotcrete support scheme (anchor cable four to five arrangement)" to reduce the surrounding rock deformation and become stable. The sinking amount of the roof and floor in the roadway is 251.2 mm, the convergence amount of the two sides in the roadway is 231 mm, supporting system and surrounding rock form the stable compression zone, the soft rock roadway can be effectively controlled by the support scheme, which can provide reference value for other similar engineering. [ABSTRACT FROM AUTHOR]

Soft and hard rock assemblages and anchor solids have important effects on rock mechanics properties under different inclinations and assemblages, so it is of great significance to study their damage and acoustic emission. Numerical simulation software RFPA2D was used to analyze the damage and acoustic emission characteristics of soft and hard rocks under different inclinations and combinations under uniaxial compression. The results show that :(1) with the increase of contact dip Angle, the rock mass strength and peak strain decrease first and then increase; (2) The mechanical properties of the composite rock mass are affected by the contact dip Angle. With the increase of the strength of the upper hard rock, the strength and peak strain tend to decrease and then increase, and the critical contact dip Angle is 75°. (3) When the contact Angle of the composite rock mass is 0~60°, the greater the contact Angle of the composite rock mass is, the more obvious the effect of the bolt on improving the mechanical properties of the rock mass is. The research results have certain reference significance to the damage and prevention of the soft and hard combined anchor solid. [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]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department 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.)

The delayed fracture of high-strength bolts occurs frequently in the bolt connections of long-span steel bridges. This phenomenon can threaten the safety of structures and even lead to serious accidents in certain cases. However, the manual inspection commonly used in engineering to detect the fractured bolts is time-consuming and inconvenient. Therefore, a computer vision-based inspection approach is proposed in this paper to rapidly and automatically detect the fractured bolts. The proposed approach is realized by a convolutional neural network- (CNN-) based deep learning algorithm, the third version of You Only Look Once (YOLOv3). A challenge for the detector training using YOLOv3 is that only limited amounts of images of the fractured bolts are available in practice. To address this challenge, five data augmentation methods are introduced to produce more labeled images, including brightness transformation, Gaussian blur, flipping, perspective transformation, and scaling. Six YOLOv3 neural networks are trained using six different augmented training sets, and then, the performance of each detector is tested on the same testing set to compare the effectiveness of different augmentation methods. The highest average precision (AP) of the trained detectors is 89.14% when the intersection over union (IOU) threshold is set to 0.5. The practicality and robustness of the proposed method are further demonstrated on images that were never used in the training and testing of the detector. The results demonstrate that the proposed method can quickly and automatically detect the delayed fracture of high-strength bolts. [ABSTRACT FROM AUTHOR]

In situ pull-out tests were performed in claystones at the Andra Underground Research Laboratory of Meuse/Haute-Marne on fully grouted bolts. The bolts were instrumented with strain gauges along their entire length and axial strains were measured from the head to the far end of the bolts, from bolts installation until the end of the pull-out tests. After bolts setting up, one or several neutral points were identified on most of the bolts. The axial strains increased from the head to the far end of the bolts during the pull-out tests. Tests interpretation required numerical modelling to overcome the shortcomings of analytical models, unable to explain the measured axial strain profiles. Numerical modelling was based on a cohesive zone model. The model qualitatively reproduced measured strain distributions and indicated that the bonding between the bolt and the grout is better in the far end of the bolt than at its head. This result is attributed to a more pronounced fracturing during the development of the induced fractured zone at the wall of the gallery, which is typical of these claystones and caused a debonding of the interface at the head of the bolt. [ABSTRACT FROM AUTHOR]

For road tunnels in most Nordic countries, temporary rock support installed during tunnel excavation usually becomes a part of the permanent rock support. Rock bolts are the most common rock support measure in road tunnels excavated in hard rock, and their conditions over the period of tunnel operation play a significant role in the safety of these tunnels. The rock bolt types and aggressive environmental conditions considered in this research are focused on those used and observed in Norwegian and Swedish road tunnels. Findings elsewhere in similar environments are included to highlight the different kinetics of degradation. Based on the collected data, the corrosion levels in these road tunnels are comparable to those in the most polluted industrial areas. Aggressive groundwater conditions for rock bolts include a groundwater pH below four (which can be caused by sulfuric acid formation due to the oxidation of the mineral pyrite in the rock), marine groundwater, and flowing groundwater with a high concentration of dissolved oxygen. Furthermore, chloride-bearing deicing salts commonly used on roads located in cold climate regions during winter can promote corrosion in rock bolts from the tunnel room. For these environments, this research proposes a lognormal probability function to quantify the expected steel corrosion level for 25, 50, and 100 years of exposure time. The corrosion protection given by cement grouting, hot-dip galvanizing and epoxy coating are also addressed to explore their contributions to the lifespan extension of rock bolts in acidic and chloride-rich environments. [ABSTRACT FROM AUTHOR]

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office 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.)

During the blasting excavation of deep underground caverns, the effects of the structural surface on crack propagation are usually considered in addition to the clamping effects of high in situ stress. Based on the notched borehole and timing sequence control (TSC) fracture blasting method, this paper studies the effects of different borehole shapes on the degree of damage of the surrounding rock and profile flatness of the rock anchor beams and the effects of different filled joint characteristics on the blasting crack propagation rules. The results show that the damage depth of the surrounding rocks by round hole smooth blasting is approximately twice that by notched hole smooth blasting, by which the profile formed is flatter. The notched primary borehole (PBH) remains a strong guidance for crack propagation in a rock mass with filled joints, while the stress concentration effects of the round target borehole (TBH) cannot fully guide the cracks until they fall within a certain distance between the PBH and TBH. It is favourable for cracks to propagate along the lines between boreholes with larger filled joint strengths and larger angles between boreholes. [ABSTRACT FROM AUTHOR]

In roadways with high ground stress or burial depths, the joints distributed within rock formations are subject to complex stresses and interlayer misalignments frequently. Rock bolts and cable bolts anchored in the rock formations are subject to tensile and shear forces. Most of the bolts used in roadway engineering are local anchored, resulting in insufficient shear strength at the bolt free end close to roadway surface and increasing bolts breaking. The anchor cable and C-shaped tube (ACC) is a highly prestressed cable bolt that can withstand high shear force in its free end. This paper examines the effect of the relationship between C-shaped tube length and joint location on the shear resistance of ACC by double shear tests. To fully exploit the ACC's shear resistance, the C-shaped tube ends should be at least 30 cm beyond the joint. The effect of preload and concrete spray thicknesses on roadway deformation and plastic zone is investigated by numerical simulation. Results show that ACC and concrete spraying layer can form a stable extruded arch structure, so that the broken and soft rock within the loosen zone is in three-dimensional-stress state, effectively improving surrounding rock properties and controlling its deformation size. Based on these results, the ACC support design method is proposed. [ABSTRACT FROM AUTHOR]

• Displacements of the rock joint are categorised into opening and shear displacement. • Analytical solutions are developed for bolts subject to opening displacements of joints. • A numerical approach is presented for bolts under shear loads of joint. • A method of predicting failure modes of bolts under joint deformation is proposed. Since the failure modes of fully grouted bolts subject to displacements of rock joints are difficult to predict, the joint displacements in this study are categorised into two types: opening displacement and shear displacement. At first, a closed-form solution incorporating the nonlinear constitutive model of interfaces between bolts and grout is developed, which is able to formulate the full-range behaviour of bolts subject to the opening displacements of rock joints. Then, a novel numerical approach considering the nonlinear rock reaction force is proposed, which can analyse stress and displacement conditions on each point along a bolt. The results of the proposed numerical approach are validated by existing test results. Combining the proposed numerical approach with the improved closed-form solution, a comprehensive model for predicting yield and failure patterns of rock bolts is proposed. In this way, decoupling between the bolt and grout, the yield and failure patterns of two potential points along the bolt are also highlighted and discussed. Further discussions about the influences of bolt inclined angles to the discontinuity and the dilatancy effect of the joint face are carried out at last. This work provides a useful tool to evaluate the behaviours and estimate the load-bearing capacity of fully grouted bolts in jointed rock masses. [ABSTRACT FROM AUTHOR]

The A26 not only relieves the central part of the road network in Linz but also allows the river Danube to be crossed by means of a 300 m long bridge, anchored in the rock slopes which form the banks of the Danube. The elements of the 1st phase are the Danube bridge and two underground motorway junctions, Danube North and South, with excavation cross‐sections of up to 375 m2 and the tight radii of the motorway on‐ramps. In addition to the elevated location of the main portals, the river Danube, the infrastructure facilities and the built‐up area take space in the valley cause unfavourable conditions. Besides these conditions, urban planning requirements have an effect on the realization of the construction project. The excavated material from the tunnel is transported off‐site by ship. The project conditions such as the high number of portals, the noise‐reflecting effect of the "Danube gorge" and the low overburden require substantial measures to limit and monitor the immissions. [ABSTRACT FROM AUTHOR]

This paper presents the results of experimental research on the fire response of steel beams and their end-plate connections in column-tree moment-resisting frames (CMRFs). Using subframe assembly, full-scale steel beams with different stub-to-link end-plate connections were tested under a standard fire curve. The failure modes as well as the structural and thermal responses of the beam and the end-plate connections were studied. The influence of critical factors, including bolt grade and flange plate's size, were investigated. The findings of the experimental studies indicate that the beam flexural failure occurs at the temperature of 720°C when deflections surpass the limiting value specified in a relevant British Standard Institution standard. The end-plate connections fail when the temperature exceeds 760°C, while the beam experiences deflections larger than span/20. The results also show that the plate bending, the bolt tensile fracture, and thread stripping control the failure of the end-plate connection in fire conditions. The end-plate connection detail has a considerable effect on the fire performance of the beam, e.g., using Grade 8.8 bolts and thicker plates in the end-plate connection can enhance the fire resistance and rating of the beams and their connections in steel CMRFs. [ABSTRACT FROM AUTHOR]

The deformation of a deep foundation pit in Ulanqab city was analyzed by in situ monitoring and numerical simulation data. First, a limit equilibrium method was used to evaluate the stability of foundation pit under non-supporting and ribbed plate anchored retaining wall support. The results show that the ribbed plate anchored retaining wall support could control the soil deformation effectively in deep foundation pit. Additionally, a three-dimensional finite difference model of excavation zone and reinforcement structure was established using FLAC3D software to simulate the excavation of deep foundation pit. The simulation results were verified by monitoring field data. The simulation results show that all the bolts are in the tension state, and the maximum axial force is located at the end of the bolt, with a value of 46.4 kN. Foundation pit excavation is a continuous stress release process, making the rock and soil of side wall of foundation pit slide towards the free surface. The largest deformation is 4.0 mm, near the side wall of foundation pit, consistent with the deformation monitoring results. [ABSTRACT FROM AUTHOR]

Kizilkaya ignimbrite, characterized by a blocky structure in the Ihlara Valley (Cappadocia, Turkey), poses many hazards to visitors and the human-made churches and dwellings carved in the valley slopes. The instability mechanism in the valley should be carefully investigated to determine and implement a suitable prevention method. For this purpose, the finite element method (FEM) models were developed in RS2 software to illustrate the problem of progressive failure in the valley's cliffs. A simple geometry represented the rock strata and its surroundings. The effect of columnar structure on the cliff stability was mimicked as a jointed medium in two-dimensional numerical models. The results of FEM models revealed that as the stage of failure progresses in the slope, the strength reduction factor decreased subsequently from 2.05 to 0.45. These models correctly captured the prevailing failure mechanisms observed in the valley slopes. Depending on the size of the rock blocks described in the FEM analysis, an effective support system was proposed to remedy the slope failure. It was found that fully bonded rock bolts with a length of at least 2.5 times the width of a typical block should be implemented with a certain grid pattern. The study clearly showed that it was promising to realize a numerical solution to secondary toppling failure in a jointed rock mass using the FEM. [ABSTRACT FROM AUTHOR]

The maintaining needed for underground mining operations is satisfied by installing a support system or leaving an ore pillars. These pillars need to have enough stability to bearing the overburden loading. Designing a pillar with optimum dimensions is the most significant issues in room and pillars underground mining method. The purpose of this paper is to determine the optimum dimensions of rock pillars in Faryab mine and reducing their dimensions using grouting technology based on a numerical simulation. The modeling results, before grouting operation, show that in the area where the pillars height is 12 m, the pillars with a width of 8 m are stable and the pillars with a width of 7 m are unstable and are on the verge of destruction. So a pillar with a width of 7 m is considered in order to stabilization. 2D and 3D numerical modeling results show that using bolt grouting in jointed rocks, improved the strength properties and as a result increase the strength of pillars and make it completely stable. Accordingly, in the rock masses that can be injected, the grouting operation can reduce the pillars width and increase the extraction recovery. [ABSTRACT FROM AUTHOR]

The vibration characteristics of bolted structures are crucially affected by the pre-tightening torque. An approach for identifying the pre-tightening torque dependent stiffness parameters of bolted joints is proposed in this paper. Firstly, the interface of the bolted joint is characterized by the thin layer element with the isotropic material property, and the parameter value of the property is assigned relative to the distance from the center of the bolt; the influence of the bolt is ignored. Secondly, the model updating method is adopted to identify the parameters of thin layer elements using experimental data, and modal data under different values of pre-tightening torque in the range of 2 N·m~22 N·m are obtained; the torque wrench is used to determine the pre-tightening torque in the modal test. Finally, after identifying the material parameters using partial experimental data on pre-tightening torque range, the empirical equation of the interface parameters with the pre-tightening torque parameter is obtained by curve fitting and the rest of the experimental data are used to verify the accuracy of the fitted empirical equations. It is concluded that this method can obtain all the parameters of the equivalent thin layer elements within a certain range of pre-tightening torque, which can provide a reference for the empirical modeling of bolted structures, improve modeling efficiency and reflect the characteristic performance of real structural dynamics. [ABSTRACT FROM AUTHOR]

This study investigates the load-carrying mechanism and proposes precise strength prediction methods for hole threads in Thread-fixed One-side Bolts bolted curved T-stubs to circular steel tube connections. A series of parametric analysis was performed with an advanced 3D finite element model considering critical parameters including tube wall thickness, bolt angle and bolt size. The axial load distribution along the hole threads and the shear stress distribution at the thread root were analyzed in detail. It was found that there were three typical load distribution patterns along hole threads, which were (1) linear pattern; (2) concave parabola pattern; and (3) convex parabola pattern, and the ratio of bolt stiffness to tube wall stiffness was identified as the pivotal factor affecting the axial load distribution. Meanwhile, the analysis results indicated that the bending moment on the TOBs did not affect the load distribution along hole threads, but led to a non-uniform stress distribution along the thread in the same turn. In the end, the prediction formulas for the carrying capacity of hole threads are presented by modifying Yamamoto's equation based on the analysis findings. The formulas are validated against the finite element analysis results and previous test results. The prediction can reach the highest accuracy when adopting the proposed failure criterion 2, with average errors of − 0.001 and − 0.002, respectively, demonstrating the accuracy and reliability. • An advanced 3D finite element model for bolted connections was developed. • The load distribution along hole threads were analyzed in detail. • Three typical load distribution patterns along hole threads were found. • Proposing methods to predict the load-carrying capacity of hole threads. [ABSTRACT FROM AUTHOR]

• The ratio of the shear deformation segment length to the anchor rod diameter in soft rock typically ranges from 0.7 to 1.5. • In soft rock, as Δ increases, the contribution rate of the anchor rod to shear resistance gradually increases. • As Δ increases,the microscopic structure of the joints evolve from a loose, porous state to fragmented granular morphology. • Established a mechanical model for anchoring resistance in soft rock filled joints. The calculation model of anchorage resistance is the core issue in the study of anchorage theory in jointed rock masses. Due to the complex geological environment of deep rock masses, the anchorage mechanism of soft rock filled in joints is even more complicated and has not yet been clearly defined. Based on the theory of structural mechanics, considering the restraining stress in the plastic extrusion deformation zone of the bolt as a rectangular distribution pattern is more in line with the interaction state between the bolt and the surrounding medium when the rod is at its limit load. Taking into account the influence of the joint filling part, the value of restraining stress is revised to include a formula expression that factors in the strength of the filling material(σ cj ) and the degree of filling(Δ).Develop a mechanical model of anchorage resistance for filled joint soft rock considering large deformation conditions due to turning angles. Further, conduct shear tests on anchored filled joint rock bodies under various σ cj − Δ combination patterns with constant normal stiffness (CNS) boundary conditions to validate and analyze the model. The research results indicate that under the influence of deep rock mass mechanical boundaries, the ratio of the shear deformation section length to the bolt diameter differs from existing research results, with specimens l / D under different σ cj − Δ combinations typically ranging between 0.7 and 1.5 times.The displacement of the bolt at turning angle θ increases with the increase of Δ and decreases with the decrease of σ cj , where Δ is the main factor affecting the degree of tensile-bending deformation of the bolt. As Δ increases, the calculated contribution rates of bolt shear resistance under three different σ cj conditions increase from 9.8% to 34.8%, 40.3%, and 39.4%, respectively. This indicates that an increase in Δ can reduce the increment of normal stress, further decrease the overall stress and compressive deformation zone's normal constraint stress in the rock mass, leading to a gradual increase in the degree of tensile-bending deformation of the bolt and an increase in resistance contribution.For the specimens with three different values of σ cj , the ratio of shear force to axial force providing resistance on the joint surface decreased from a maximum of 2.83 to 0.72, 1.04, and 2.01, respectively. This indicates that when σ cj is relatively large, tensile-bending deformation is more likely to occur, mobilizing the axial force of the bolt to provide the main resistance. Further systematic analysis was conducted on the length of the shear deformation section of the bolt and the distribution characteristics of the anchor resistance under condition β = 30 ° ∼ 90 °. The reasonableness of the model was verified through the comparison of model calculation results with experimental data. Finally, a series of recommendations were proposed for preventing failure of the anchored system in filled jointed rock masses in actual engineering projects. [ABSTRACT FROM AUTHOR]

Friction is an important source of energy dissipation in structural damping. The effect of friction on the damping ratio, however, has not been fully investigated. This paper presents an experimental study of the nonlinear damping ratio induced by friction at bolted joints of a bridge model in the laboratory. The decay responses of the bridge were tested under various bolt configurations and pre-torques. The nonlinear characteristics of the damping ratio were analyzed, and the experimental results were interpreted through numerical simulations. The relationship between damping ratio and amplitude of the Iwan model was derived. The results show that friction induces a nonlinear damping ratio. The damping ratio exhibits two opposite nonlinear characteristics under the influence of bolt joints. The damping ratio may either decrease with decreasing amplitude or may increase, and both of these nonlinear patterns can be elucidated by the Iwan model. Numerical simulations successfully replicate these two nonlinear damping ratios. A case study of an actual steel truss bridge is used to discuss the possible effects of bolt joints on the damping ratio. The results of this paper reveal the nonlinear damping patterns induced by bolt joints and provide an optional model for such structures. • There are two opposite nonlinear patterns of bridge damping ratio under the influence of bolt joints. • The configuration and pre-torque of bolts induce the damping ratio to vary in the range of approximately 0.25% to 1.20%. • High pre-torque may result in lower damping ratio. • The Iwan model can explain the two nonlinear patterns of the damping ratio. [ABSTRACT FROM AUTHOR]

Non-destructive testing (NDT) of rock bolt anchoring quality is an important part of engineering quality and safety control, electromagnetic ultrasonic NDT is one of the promising detection methods, and improving the efficiency of ultrasonic transducer by optimizing the bias magnetic field is an important factor to obtain effective information. In this paper, several factors affecting the bias magnetic field are studied, and the work is divided into simulation and demonstration: COMSOL was used to simulate the electromagnetic ultrasonic transducer(EMAT) in order to analyze the influence of the number of magnetic circuit, the thickness of magnet and the thickness of yoke iron on the bias magnetic field. Then, an experimental platform was built, the magnetic circuit structure of the transducer was set with reference to the simulation results, and several important parameters of the bias magnetic field were determined by analyzing the collected signals. The results show that with the increase of the bias magnetic field magnetic circuit structure from independent to ring form, the magnetic field strength of the rock bolt increases, the magnetic field uniformity becomes better, and the efficiency of the transducer is also improved accordingly. In addition, under the same magnetic circuit condition, increasing the thickness of permanent magnet and yoke iron does not increase the magnetic flux density of the rock bolt axis proportionally, and has a limited effect on the efficiency of the transducer. In practical application, the corresponding structure is selected according to the needs, and the better bias magnetic field structure is selected while meeting the efficiency of the transducer. [Display omitted] • Several factors affecting the efficiency of the transducer were simulated by COMSOL. • An experimental platform was set up. • The parameters of magnetic circuit number, permanent magnet and yoke iron thickness were analyzed. [ABSTRACT FROM AUTHOR]

The study presented in this paper aims to advance the current understanding of Rock Anchor (RA) performance under axial loading through large deformation numerical analyses. Simulations are conducted using the Geotechnical Particle Finite Element Method within a coupled hydro-mechanical framework. Experimental data from the literature is used to calibrate a strain hardening plasticity constitutive model for rocks. The calibrated model is then used to investigate rate effects on the axial response of a novel rock anchor design. The axial pullout induces rock dilatation at the bottom edge of the anchor with the consequent formation of a zone of negative water pressure change and a bulb of positive pore water pressure change above it. Depending on the pullout rate, distinct drained, partially drained, and undrained hydraulic regimes are identified. These, along with the variable damage distributions, are shown to influence the rock anchor axial capacity considerably. The geometrical and elastic properties of the rock anchor modelled as a deformable body, along with the interface friction angle between the anchor and the rock are also explored. Results such as load capacity curves, stress path evolutions, and stress distributions on the rock-rock anchor interface are analysed emphasizing their impact on rock anchor design. [ABSTRACT FROM AUTHOR]

• The deformation instability process and critical load of jointed surrounding rock are analyzed. • The interaction mechanism between prestressed rock bolt and jointed surrounding rock is studied. • The feasibility of prestressed rock bolt controlling the deformation of jointed surrounding rock is verified. The existence of jointed rock masses in tunnels is a key problem that leads to the deformation and instability of the surrounding rock. Based on the engineering background of the Qingdao Metro, a physical model and a numerical model are constructed to analyze the mechanism of deformation and instability of the surrounding rock of a jointed tunnel using model blocks that conform to the characteristics of joint distribution. The results show that during the whole test process, the cracks between the blocks in the tunnel arch are in the "development − stability − closure − penetration" state. Finally, the block falls in the left area of the tunnel, and the corresponding anchor axial force transits from the linear growth stage to the steady growth stage. After the axial force of the rock bolt suddenly decreases in the loading stage, the bolt enters the stability stage, and finally, S-shaped failure occurs when the surrounding rock is unstable. Under the action of a prestressed rock bolt, the normal stress and radial stress of the rock mass increase, and the difference between the major and minor principal stresses decreases significantly. The radial stress on the surrounding rock surface of the arch is approximately 8 % greater than that in the traditional rock bolt scheme, which improves the strength reserve of the rock mass. In the field test, the prestressed rock bolt can control the deformation of the surrounding rock in the arch within 2 ∼ 5 mm, which provides a reference for the control of the surrounding rock in jointed tunnels. [ABSTRACT FROM AUTHOR]

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

Engineering rock mass classifications are used to describe rock masses and to assist in the design of rock support in hard rock tunneling. In most of the encountered geological- and rock mechanical conditions, from hard and competent rock to poor and fractured rock masses, the application of classification systems has normally resulted in successful and economic designs. However, complex ground conditions as these derived from tunneling in low rock overburden pose several challenges to rock mass classification and support design. In the present study, an analysis of the ground behavior and tunnel stability in a portion with very low rock overburden during the construction of the Hestnes railway tunnel (Norway) was conducted to investigate the performance of the current classification practice for tunnel rock support design. The results have revealed several challenges, which are related to conservative rock mass and rock support assessments due to the lack of consideration of the important stabilizing effect that rock arching has on tunnel stability. It was also found that with the application of an integrated methodology able to combine classification methods with numerical simulations and detailed information of the ground properties and behavior, more optimal designs in the form of rock reinforcement with bolts and shotcrete can be achieved when rock mass quality Q < 1. On this basis, a set of design recommendations was developed for the integration of classification systems with more elaborated engineering design analyses to provide guidance in design optimization for hard rock tunnels subject to low overburden. [ABSTRACT FROM AUTHOR]

Ribs of reinforced sprayed concrete (RRS) is a rock support measure used in weak rock mass and other challenging rock mass conditions where support that exceeds bolts and shotcrete is needed. RRS is typically constructed using four to ten rebars in one or two layers mounted on rock bolts along the tunnel profile and covered with sprayed concrete. In Norway, the tradition of using RRS started in the 1980s by experience based, on-site dimensioning as a support measure to avoid cast concrete constructions. Since then, RRS has completely replaced the use of cast concrete as a support measure in Norway. In 2002, the Q-system had its second update, where RRS dimensioning was incorporated into the Q-system support chart. This update introduced the arched load-bearing RRS, rather than the unarched rock reinforcing structure following the uneven tunnel profile that had been the common design up to then. This article reviews the technical basis for the calculations in the update, including the Q-system’s ability to be a technical assumption for the dimensioning of load-bearing support, and concludes that a further revision of the Q-system is needed. Measurements and parameter analysis performed in later years have suggested that RRS is over-dimensioned in most cases. In addition, a few RRS collapses suggest that RRS has weaknesses in its actual supportive design and may, in some cases, be under-dimensioned. A discussion on these matters is important both from a technical point of view and in terms of an economical/environmental aspect, as steel and concrete volumes can be reduced using leaner rock reinforcement than arched RRS. [ABSTRACT FROM AUTHOR]

In natural rock mass, the existence of joints or fissures makes the strength of surrounding rock significantly reduced. In this paper, the influence of deformation and failure law of jointed rock mass on the stability of surrounding rock is studied by prefabricating five kinds of single fracture rock samples with different angles. Firstly, the failure and deformation of the unanchored and anchored specimens under different loading conditions (uniaxial compression and cyclic loading) were studied in laboratory tests, respectively. Secondly, the microscopic fracture characteristics and deformation damage modes of the specimens were simulated by using PFC numerical simulation software. The results show that the peak strength and elastic modulus of the sample increase with the increase in the inclination angle. After the sample is anchored, the peak strength of the sample is effectively improved, and the number of cracks is significantly reduced. In practical engineering applications, bolts can change the crack propagation mode and limit the initiation of cracks in the surrounding rock. By studying the crack propagation law and failure characteristics of fractured anchored rock samples, we can deepen the understanding of rock fracture behavior and better reveal the failure and deformation mechanism of surrounding rock instability in tunnel construction. [ABSTRACT FROM AUTHOR]

In seismic-prone regions, due to the presence of link beams as energy dissipating elements, eccentrically braced frames have always been of interest to designers and are a significant part of resilient seismic-resistant systems. On the other hand, numerous studies have shown that in addition to appropriate energy dissipation during the earthquake event, reducing residual responses of the system, such as relative inter-story drifts at the end of the earthquake event, is also very important. Therefore, in this study, a new hybrid system is presented by combining eccentrically braced frame with rotational friction damper for achieving energy dissipation and shape memory alloyed bolts for achieving flag-shape hysteretic behavior. To thoroughly examine the efficiency of the proposed system, two types of hybrid eccentrically braced frames are produced and their experimental results are compared with those of conventional corresponding frames. The results indicate that the proposed system exhibits appropriate self-centered behavior, and also, due to the incorporation of a rotational friction damper, the required energy dissipation is achieved. Comparing the energy dissipation among the frames, the highest amount of dissipation is related to the equipped symmetric frame due to more rotation of friction damper in comparison with unsymmetrical frame. In the following, in order to check the effectiveness of the proposed idea, models of 5, 10, and 15 floor symmetrical and asymmetrical frames were developed in OpenSEES software, and cyclic and dynamic analyses of time history were performed and observed on the models, equipping the frames with rotational friction dampers as well as shape memory alloyed bolts will reduce the floor displacement response and also the permanent displacement of the floors. • A new hybrid system is presented by combining eccentrically braced frame with rotational friction damper and SMA bolts. • Hybrid eccentrically braced frames are produced and their experimental results are compared with conventional frames. • Proposed system exhibits appropriate self-centered behavior, and also energy dissipation. • Equipping the frames with rotational friction dampers and SMA bolts will reduce the floor response. [ABSTRACT FROM AUTHOR]

In this paper, the anchorage mechanism and bearing capacity of the special type of pawl bolt anchored in concrete under uplift load were studied. Static tests were carried out on two typical pawl bolts, namely 135° and 180° pawl bolts, and the effects of anchorage depth and pawl type on their failure modes were studied. The experimental results show that the uplift bearing capacity of pawl bolt is improved more effectively than that of smooth bolt. The two typical failure modes of pawl bolts under uplift load are concrete breakout failure and bolt yield failure. The concrete breakout failure exclusively occurs with anchorage depth of 5 d , while the failure mode could change from concrete breakout failure to bolt yield failure with the increase of anchorage depth. The finite element model was established to elucidate the failure mechanism of anchorage bolt and concrete. The crack propagation and diffusion angle distribution of anchorage concrete can be directly judged by concrete tensile damage and stress vector in simulation analysis. Additionally, a calculation method to accurately predict the uplift bearing capacity of pawl bolt was proposed, which considered the effect of diffusion angle θ i on the uplift bearing capacity and further discusses the change law of cone diffusion angle θ i and concrete crack propagation. The calculated results exhibited a concordance with the experimental and numerical results, which shows that the formula presented in this paper can be considered reliable and can guide the practical engineering design. ● Studied design params' impact on pawl bolts force transfer mechanism and concrete cone diffusion angle. ● Examined concrete crack behavior under uplift load for pawl bolts. ● Proposed spatial angle-variation elliptic concrete cone calculation model for pawl bolts based on cone diffusion angle. [ABSTRACT FROM AUTHOR]