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The 3D morphology of the joint surface significantly influences the shear behavior of the jointrock. Constant normal load (CNL) direct shear tests with different shear displacement were conducted to understand the shear stress changing with joint roughness and damage degree during shear. The rough joint specimens were prepared using 3D scanning and printing techniques, and shear tests with different normal stresses and shear displacements were performed. Four different parameters and the damaged area quantitatively described by the image binarization and box dimension were calculated and compared to study the roughness evolution of joint surfaces. The experimental results demonstrated that the roughness parameter and shear stress decrease and approach constant values with increasing shear displacement. A JRC degradation model was presented based on regression analyses to evaluate the JRC values of rock joints under various displacements to replace it in the JRC–JCS model. Additionally, a new postshear behavior modeling was proposed for rock joints based on surface degradation characteristics under various initial joint roughness coefficients (JRC0) and normal stress. The stress–displacement curves resulting from the proposed modified model work well in predicting the postpeak stress–displacement curve, which can prove the effectiveness of the postpeak shear behavior modeling. [ABSTRACT FROM AUTHOR]

Freeze–thaw failure of frozen rock slope often occurs during engineering construction and mining in cold area, which poses a great threat to engineering construction and people's life safety. The properties of rock mass in cold region will change with the periodic change of temperature, which makes it difficult to accurately evaluate the stability of slope under the action of freeze–thaw cycle by conventional methods. Based on field investigation and literature review, this paper discusses the characteristics of frozen rock mass and the failure mechanism of frozen rock slope, and gives the types and failure modes of frozen rock slope. Then, the research status of frozen rock slope is analyzed. It is pointed out that the failure of frozen rock slope is the result of thermo-hydro-mechanical (THM) coupling. It is considered that freeze–thaw cycle, rainfall infiltration and fracture propagation have significant effects on the stability of frozen rock slope, and numerical simulation is used to demonstrate. The research shows that the safety factor of frozen rock slope changes dynamically with the surface temperature, and the safety factor of slope decreases year by year with the increase of freeze–thaw cycles, and the fracture expansion will significantly reduce the safety factor. Based on the above knowledge, a time-varying evaluation method of frozen rock slope stability based on THM coupling theory is proposed. This paper can deepen scholars' understanding of rock fracture slope in cold area and promote related research work. [ABSTRACT FROM AUTHOR]

In this paper, eight shear tests were carried out utilising a double shear with infilled shear interfaces after determining an appropriate experimental design and modified testing scheme. For this, two rock bolts, 20 and 30 tonnes, were tested with modified double shear testing apparatus at different pretension loads. The infilled test scheme was conducted with 5 mm thick sandy clay infilled shear interfaces. A 40 MPa small aggregate concrete was used for all samples to simulate the host rock. Based on the shear profiles, it was found that all samples followed a three-part failure profile consisting of elastic, strain softening, and failure regions. The results of double shear tests revealed that the 20 tonne rock bolt saw a significant overall decrease of approximately 30% in its failure displacement response as opposed to the 30 tonne samples, which saw a 6% increase. Also, it was concluded that the 30 tonne samples outperformed the 20 tonne rock bolts by up to 30%, irrespective of initial pretension settings. Comparing the physical failure characteristics of the samples found that both the 20 and 30 tonne samples exhibited the same response to increased pretension. As the pretension increased, the angle experienced at the hinge point also increased incrementally. [ABSTRACT FROM AUTHOR]

Taking the return-airway 4204 with roof cutting in Longquan Coal Mine as the engineering background, roof structure, key parameters, and deviatoric stress evolution were studied. Conclusion: The Key Stratum within a 4–8 times mining height is considered as Near Key Stratum. Cutting the roof makes it possible to form a cantilever structure of the Key Stratum on the solid coal side, which is more conducive to the stability of gob-side roadway. During cutting angle of 90–55°, the deviatoric stress increases linearly, and the increase rate is coal pillar > solid coal > roof > floor. While cutting length from 0 to 35 m, the deviatoric stress decreases linearly, and the decreasing range: coal pillar > solid coal > roof > floor. When coal pillar width is from 30 to 4 m, the deviatoric stress of left side and floor presents a "single peak" distribution. The deviatoric stress of coal pillar changes from an asymmetric "double peak" to a bell-shaped distribution, and the deviatoric stress of roof changes from a "single peak" to an asymmetric "double peak" distribution. Under same coal pillar width, the deviatoric stress of left, coal pillar and roof after roof cutting decreases most obviously, followed by the floor. Finally, the coal pillar width is 8 m, the cutting angle is 75°, the cutting length is 20 m, and the hole spacing is 1.0 m. The support scheme is bolt + metal mesh + steel belt + anchor cable combined support. The stable period of roadway is about 10 days. [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]

In recent years, high-strength bolts with friction-type joints have been lengthened to withstand increased traffic load. However, with increase in the joint length, the force able to be resisted by bolted joints has decreased owing to uneven distribution of the bolts within the joint. In addition, the proximity of secondary members to the joint has restricted the allowable size of the splice plates. It is therefore necessary to reduce the joint length while maintaining its design strength. In this study, interference fit bolts were assembled at both ends of a friction-type bolted joint to form a hybrid joint, and tensile tests were conducted to elucidate the load transmission mechanism, analyse the slip resistance, and verify whether the addition of the interference fit bolts improves the strength of the friction-type joint. It was concluded that despite a minor slip in the hybrid joint, the slip resistance was approximately 10% higher than that of the friction-type joint, and the overall load–deformation relationship maintained a quasi-linear behaviour up to 1.1 times the slip resistance of the friction-type joint. In addition, the hybrid joint had smaller data scattering than the friction-type joint, suggesting that the uneven load distribution and deformation in the joint was slightly improved by installing the interference fit bolts. The performance of hybrid joints is superior to that of the existing friction-type joints under the current slip limit specification. [ABSTRACT FROM AUTHOR]

Accurate analysis of the strength of steel-fiber-reinforced concrete (SFRC) is important for ensuring construction quality and safety. Cube compression and splitting tensile tests of steel fiber with different varieties, lengths, and dosages were performed, and the effects of different varieties, lengths, and dosages on the compressive and splitting properties of secondary concrete were obtained. It was determined that the compression and splitting strengths of concrete could be effectively improved by the addition of end-hooked and milled steel fibers. The compressive and splitting strengths of concrete can be enhanced by increasing the fiber length and content. However, concrete also exhibits obvious uncertainty owing to the comprehensive influence of steel fiber variety, fiber length, and fiber content. In order to solve this engineering uncertainty, the traditional RBF neural network is improved by using central value and weight learning strategy especially. On this basis, the RBF fuzzy neural network prediction model of the strength of secondary steel fiber-reinforced concrete was innovatively established with the type, length and content of steel fiber as input information and the compressive strength and splitting tensile strength as output information. In order to further verify the engineering reliability of the prediction model, the compressive strength and splitting tensile strength of steel fiber reinforced concrete with rock anchor beams are predicted by the prediction model. The results show that the convergence rate of the prediction model is increased by 15%, and the error between the predicted value and the measured value is less than 10%, which is more efficient and accurate than the traditional one. Additionally, the improved model algorithm is efficient and reasonable, providing technical support for the safe construction of large-volume steel fiber concrete projects, such as rock anchor beams. The fuzzy random method can also be applied to similar engineering fields. [ABSTRACT FROM AUTHOR]

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

• An effective mathematical model for bolted flange joints is proposed. • The proposed model is applicable for both bolt looseness and no-looseness conditions. • Experimental results validate the proposed model. • The soft nonlinearity characteristics of bolted flange joint multi-plate structure under base excitation are revealed. Bolted flange joints are widely used in various engineering structures to combine two or more substructures together. However, the understanding of mechanical mechanism of bolted flange joints is still insufficient due to the lack of efficient mathematical models. This paper proposes an effective mathematical model for bolted flange joints, which is then employed to conduct vibration analysis on bolted flange joint multiple-plate structures. During the modeling process, the flange is modeled by the Kirchhoff plate theory, and the bolted joints are modeled by the two-dimensional face constraint in bolted joint affected region (BJAR). The artificial spring technique is adopted to simulate the face constraint. The friction contact model and equivalent linearization technique are adopted to analyze the stick and slip states of bolted joints. By adopting the Chebyshev orthogonal polynomials as admissible functions, governing equations are derived. Then, the Rayleigh-Ritz method is applied to study the free vibration characteristics, and the Newmark-beta method is employed to study the vibration response under base excitation. The experimental studies are performed on the bolted flange joint two-plate structure (BFJTPS) to illustrate the effectiveness of the proposed theoretical model. The results indicate that the proposed mathematical model can well predict the vibration characteristics of multiple-plate structures under both bolt looseness and no-looseness conditions. The soft nonlinearity phenomenon under bolt looseness condition can be successfully revealed by the model. [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]

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]

With the continuous deepening that humans exploit underground space, tunnel engineering passing through sensitive strata, e.g., ultralarge buried depth, high water pressure, and active faults, has become more frequent. However, the current tunnel-supporting concept emphasizes the passive regulation effect of the primary support and the secondary lining on the surrounding rock deformation and ignores the principle of fully utilizing the self-bearing capacity of the surrounding rock in the New Austrian Tunneling method. Therefore, the current supporting system is not ideal for controlling the deformation under these sensitive strata, and it is imperative to propose an active supporting system that can mobilize the surrounding rock to be self-supporting. In this paper, through mathematically analyzing the deformation monitoring data of 203 tunnel sections, a deformation control benchmark under the active deformation control concept is proposed. The deformation control effect of the prestressed rock bolt is obtained based on field measurements and numerical calculations. Furthermore, the proposed virtual supporting force method is used to solve the range and parameters required for advanced support. Finally, the active supporting parameters satisfying the deformation control benchmark are obtained by using the elastic–plastic theory. The results show that the established deformation control benchmark can be used to evaluate the active supporting parameters. On this basis, the solving method for the active supporting system and its parameter are constructed. By adopting this method, the suitable forms and parameters of the prestressed rock bolt and the range and parameters of the advanced support in different geological environments are obtained. Finally, the composition forms and parameters of the active supporting systems with different lithologies and different buried depths are proposed. [ABSTRACT FROM AUTHOR]

An investigation of rock fracture characteristics subjected to the true triaxial intermediate principal stress is crucial for understanding the failure mechanism of surrounding rock in an actual underground engineering project and guiding the project's implementation. In this study, a series of different true triaxial stress path tests were conducted to investigate the distribution of macroscopic rock fractures and internal cracks under various stress paths using a true triaxial servo test system and combining it with CT scanning technology. The results indicated that, due to the intermediate principal stress with constant direction, the true triaxial stress path has obvious directionality compared to the regular triaxial rock macroscopic and internal fracture distribution law and the fracture planes are aligned along the σ2 direction. Once the direction of the intermediate principal stress changes, the corresponding crack propagation direction immediately reverses and expands along the new intermediate principal stress direction. The direction of rock fracture is strongly dependent on the state (direction) of the intermediate principal stress, i.e., the direction of σ2 plays a decisive role in the macroscopic rock fracture characteristics. Accordingly, the "effect of intermediate principal stress-induced rock fracture" was proposed in this study. Based on the results of the CT scans in which the fracture dip angle within the rock is approximately parallel to the σ2 direction under different true triaxial paths, the intermediate principal stress plays a vital role in rock rupture. Combined with experimental and theoretical analyses, the rationality of this effect was verified. In addition, a numerical calculation method for the true triaxial rupture evolution of rocks with random fractures was proposed using ABAQUS software (version 2020), and a numerical calculation model for typical roadway excavation was developed. The rupture growth of the roadway surrounding rock was characterized by stratified evolution along the σ2 direction corresponding to the actual engineering. In addition, the numerical analysis of a typical roadway excavation with two different intermediate principal stress orientations indicated that the fracture of the surrounding rock in both kinds of roadways is roughly along the σ2 direction, which further supports the rationality of the "effect of intermediate principal stress-induced rock fracture." [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]

Many designs of anchor cables are currently in use for rock support in civil and mining operations. Because of the exposed surface and weak shear performance of the cable bolt's free section (CBFS) in end-anchored structures, breaking failure frequently occurs. Numerical simulations and laboratory experiments were performed in this study to develop measures to improve CBFS resistance to shear failure. Analysis of shear characteristics of the CBFS showed that higher axial tension weakens the cable bolt's shear resistance, and that shear damage on the cable surface and uneven distribution of shear stress aggravate CBFS tensile–shear failure. A high-strength steel pipe is proposed to protect the shear cable bolt, and the preliminary design of a CBFS-strengthening device (CFSD) is presented. Numerical simulation revealed that the CFSD effectively improved CBFS shear resistance and provided protection from harmful shear damage. The optimal performance of a Q-type (slotted steel pipe) CFSD was confirmed. The mechanism of improvement of the cable's shear resistance to surrounding rock by employing the CFSD was analyzed. Double-shear tests were carried out on a bare cable bolt and a cable bolt with a Q-CFSD. The results revealed that the CFSD increased the peak shear force on the joint plane, cable peak axial force, and ultimate shear displacement by 31%, 18%, and 11%, respectively. The proposed device is effective in improving the shear performance of end-anchored cable bolts and enhancing surrounding rock stability. [ABSTRACT FROM AUTHOR]

The pre-tightening force loss (PTFL) of bolts is an important but underestimated cause of roadway instability. In mine anchorage systems, the actual pre-tightening force of bolts is only 50% to 80% of the design value. Through a case study at Xiahuo Coal Mine, it was found that the essential causes of PTFL are the increasing friction coefficient between supporting units controlled by factors such as pre-tightening torque levels, pre-tightening cycles, and surrounding rock roughness. This study investigates the behavioral characteristics of PTFL and its influence on surrounding rock failure in roadways. This research reveals a linear correlation between pre-tightening force and torque, with an average torque conversion coefficient of approximately 0.19. However, the PTFL increases with higher levels of pre-tightening torque, increasing pre-tightening cycles, and rougher surrounding rock conditions. For every 30 N·m increase in pre-tightening torque, the PTFL increases by approximately 1.67 kN. Reducing the PTFL can expedite the stress redistribution process and shorten the self-stabilizing period of the roadway by approximately 10 days, thereby enhancing the active supporting potential of bolts. [ABSTRACT FROM AUTHOR]

A study was conducted along the Jantho-Lamno road to identify and mitigate landslide risks by analyzing the relationship between seismic wave propagation velocity and rock resistivity. The research aimed to assess geological conditions and pinpoint areas prone to slope failure, employing both seismic and resistivity methods on three selected lines (L1, L2, L3). Seismic wave propagation velocity (Vp) and resistivity () values were analyzed using ZondST2D and Res2Dinv software. The results revealed a distinct weak zone characterized by contrasting layers: a soft first layer and a denser second layer. Within this zone, Vp ranged from 0.3 to 0.9 km/s, with resistivity measuring less than 10 Om, mainly comprising sandstone and clay. This weak zone acted as a slip plane, driven by a water-saturated layer's pushing force, making it susceptible to structural instability due to gravitational pressure. To mitigate land creep, the proposed strategy involved constructing retaining walls, piles, shotcrete, wire mesh, net rock bolting, and rock removal techniques, tailored to the geological conditions of L2 and L3 Jantho. Similar measures would be implemented at L1 Lamno. L1 Lamno was identified as an ideal location for studying slope stability mitigation measures. Landslides in Aceh Province result from factors such as active tectonic movements, intense rainfall, geological structures, weathering processes, and seismic activity. Implementing slope stabilization and protection methods effectively reduces landslide risks, benefiting the region's safety and infrastructure. [ABSTRACT FROM AUTHOR]

Summary: Composite shear wall (CSW) system, which consists of a steel boundary frame and a steel panel with a reinforced concrete (RC) panel attached to one side of it using bolts, is commonly used in mid‐ to high‐rise buildings. In a CSW system, RC panel functions as out‐of‐plane restraint to prevent overall buckling of steel panel, thereby enhancing system behavior. However, for a traditional CSW system, the RC panel is in direct contact with the steel boundary frame. The RC panel tends to crush under seismic loading, thereby leading to a weak constraint to steel panel buckling. The innovative CSW system, where a gap remained between steel boundary frame and RC panel, demonstrated better cyclic behavior than the traditional CSW system. Current studies aimed to investigate cyclic behavior, parameter effects, and determination of RC panel stiffness of CSW systems. In this paper, detailed FE models were developed for simulating cyclic behavior of both innovative and traditional CSW systems and validated by test results. FE models accurately predicted lateral load‐drift response and failure patterns of both innovative and traditional CSW systems. System failure patterns and load‐carrying mechanism of RC panels were discussed. The effects of major parameters, including steel panel thickness, RC panel thickness, ratio of bolt spacing to steel panel thickness, and gap between frame and RC panel, were examined using the validated models. Simulation results indicated that steel panel thickness contributed to increase the lateral strength and initial stiffness of both innovative and traditional CSW systems. Although RC panel thickness, ratio of bolt spacing to steel panel thickness, and gap between frame and RC panel had negligible effects on system strength and stiffness, they should also be carefully designed to ensure local stability of the steel panel and system ductility. Formulations were proposed for predicting the lateral strength of both innovative and traditional CSW systems. The average difference between calculated and test/simulated lateral strength was less than 3%. [ABSTRACT FROM AUTHOR]

In addition to analysing the mechanism of failure of the prestressed rock anchor anchor system and investigating the appropriate depth for fixing the rock anchors, theoretical equations were derived to calculate the rock anchors' axial force, ultimate capacity, and the interfacial shear force in the elastic phase. These equations are then used to analyse the pressure distribution within the rock bolt anchorage section and to investigate the effect of interfacial shear strength, shear stiffness, and anchorage length on interface failure. Drawing on the findings from both field-based rock bolt pull-out tests and numerical simulations, analyzed the failure mechanism of the anchor system, and proposed a reasonable anchor length design method for rock bolt. The results show that there is a strong dependence between ultimate load carrying capability of rock bolts and interfacial shear stress and shear rigidity, and that increasing the anchorage length and reducing the interface shear stiffness can avoid the stress concentration phenomenon. The primary factor leading to the anchor system failure is secondary interface failure. The evolution law of interface damage is that the damage occurs first at the initial position. As the interface damage location changes, the peak shearing stress moves towards the bottom of the anchored section. The engineering application results verified the feasibility of a reasonable anchorage length calculation method and rock bolt design process. The findings of this paper can be used as a basic reference for determining rock bolt anchorage support parameters during the design and construction of underground engineering projects. [ABSTRACT FROM AUTHOR]

Higher demand for the load‐bearing ability of supporting foundations is required if its upper wind turbine is substituted by a larger one. Presently, there is a lack of strengthening and retrofitting methods for existing wind turbine foundations. A combined‐connection retrofitting method by adding anchor bolts to the existing wind turbine foundation with embedded‐ring is prompted in this study. Furthermore, a strengthening measure by adding a stiffening beam, expanding the foundation plate, and adding rock bolts to increase the ability to resist basal bending moment is proposed. Finite element analysis is conducted to analyze the effectiveness of the proposed strengthening and retrofitting methods for a 2 MW wind turbine foundation. The result shows that the peak stress of embedded‐ring is decreased by 36% by using the internal combined‐connection, and the peak tensile stress of concrete is reduced by 4.0%. When the external combined‐connection is adopted, the peak stress of the embedded‐ring is reduced by 69.3%, and the peak tensile stress of the concrete is reduced by 26.0%. It illustrates that the external combined‐connection method is more effective to increase the load‐bearing capability of the connection than the internal combined‐connection method. Additionally, the proposed strengthening measure by adding a stiffening beam, expanding the foundation plate, and adding rock bolts is effective to decrease the responses of foundation. The maximum tensile stress of concrete, the maximum compressive stress of concrete, and the maximum stress of the embedded‐ring are reduced by 19.8%, 31.3%, and 22.2%, respectively. To summarize, the proposed strengthening and retrofitting methods are capable of ensuring the safety and stability of higher‐power wind turbine operation. [ABSTRACT FROM AUTHOR]

A combined support scheme was proposed to address the issue of large deformation in the deep soft rock roadway at the Tangkou coal mine in Shanxi Province, China. This support scheme includes high constant resistance, elongation, and prestressed negative Poisson's ratio (NPR) bolts as the core element, along with metal mesh, shotcrete, cable, and bottom angle grouting bolt. A numerical simulation test using Flac3D was conducted to verify the feasibility of the NPR bolt-anchored soft rock roadway. In addition, a constitutive model for a rock mass supported by NPR bolts was established. The model is based on a parallel model of a generalised Kelvin body and elastic–viscous sliding body, which was used to reveal the mechanical behaviour of an NPR bolt-anchored rock mass. The results showed that the stress–strain relationship of the NPR bolt-anchored rock mass was obtained as a piecewise function consisting of the initial, slipping, and sticking stages. The stress and strain of the NPR bolt-anchored rock mass exhibit distinct patterns under different stress conditions. Specifically, when the stress remains constant, the strain of the NPR bolt-anchored rock mass increases continuously while the stress decreases in a step-like manner. On the other hand, when the stress increases linearly with time, the strain of the anchored rock mass increases linearly, while the stress of the anchorage rock mass increases slowly in a sawtooth pattern. Furthermore, a field support test fully confirmed the effective control of the NPR bolt support on the large deformations of soft rock roadways. These findings can guide further theoretical research, engineering design, and field applications of NPR bolt-anchored rock masses. Highlights: A new combined support scheme is proposed using the NPR bolt as the core. The mechanical behaviour of an NPR bolt-anchored rock mass is revealed. Both numerical simulations and field tests demonstrated that the combined support scheme effectively controls the large deformations of soft rock roadways. [ABSTRACT FROM AUTHOR]

In order to effectively control the stability of surrounding rock in ultra-large span open-off cuts by employing the techniques of support strength theory calculations and analogical application methods, two sets of rational support schemes were proposed, and the optimal design of active support parameters in thick coal seams with ultra-large span open-off cuts was explored by using theoretical analysis, numerical simulation, and field experiments. The results demonstrated that the span is one of the key factors influencing the stability of the roadway roof, exhibiting an inverse quadratic relationship with the peak stress borne by the roadway roof. By utilizing the pre-stressing force of anchor cables and support strength formulas, two sets of active support schemes for controlling the surrounding rock in thick coal seams with ultra-large span open-off cuts were established, and an optimized support scheme was obtained through numerical simulation. These findings provide references and guidance for related mining engineering under actual conditions in mines. [ABSTRACT FROM AUTHOR]

Thorough and accurate assessment of rock mass units is important for development of engineering infrastructures and groundwater resources assessments. Rock mass units are widely evaluated by reliable geomechanical parameters namely rock quality designation (RQD) and rock core index (RCI). Conventionally, these parameters are acquired via an extensive number of geotechnical tests. Such tests, however, suffer efficiency for data coverage, cost, equipment and topographic constrictions, and hence cause ambiguity in geological models for a detailed evaluation of rock mass integrity. Conversely, geophysical surveys offer fast, more user-friendly, less invasive, more cost-effective and less time-consuming approach for geological investigations. The past research confirms a useful link between geophysical and geotechnical parameters. But, none of the past studies provides a suitable and generalized relation between these parameters which can reduce geotechnical model uncertainty mostly caused by inadequate data and subsurface heterogeneity. This paper proposes a meaningful and feasible method to obtain geomechanical parameters using a certain number of drillings and geophysical data of four different sites. Based on electrical resistivity obtained from electrical resistivity tomography (ERT) and controlled-source audio-frequency magneto telluric (CSAMT), this research provides the general and adaptable formulas for geotechnical parameter estimation and reduces geological model uncertainty for more detailed 2D/3D imaging of RQD and RCI covering the whole sites where even no drilling data exists. Thus, the investigated sites are assessed laterally and vertically along each geophysical profile via distinct value ranges of geological parameters for a thorough and reliable evaluation of rock mass units in highly heterogeneous setting. Our research reduces the ambiguity caused by structural heterogeneities and scarce data, fills the gap between inadequate well tests and the true geological models, and gives new insights into the rock mass units for proper engineering design and groundwater exploitation. [ABSTRACT FROM AUTHOR]

A new type of parallel operation unit for excavating and supporting anchors is proposed to address the issue of imbalanced excavation anchor ratio in coal mines. By equipping a straddle type anchoring drilling rig group, the synchronous parallel and fast operation mode for excavating and supporting anchors is achieved; Consider the problem of poor drilling stability of drill pipes in coal mines due to the coupling vibration between surrounding rock and anchoring equipment. Firstly, taking the multi drilling rig anchoring system as the research object, considering the influence of the equipment itself as an influencing factor on the vibration of the drill pipe, a dynamic model of the system is constructed using Lagrangian equations, and analytical solutions for the vibration displacement of each mass block are obtained; In order to more intuitively represent the vibration process of the drill pipe, Ansys is used to conduct modal analysis on the key components of the anchoring drilling rig system, and obtain the natural frequencies and vibration modes of each order of the key components; Using Adams to solve the rigid flexible coupling dynamic model of the anchoring drilling rig system, the vibration response laws of the drill pipe under different operating states were obtained. Secondly, Abaqus was used to simulate the drilling process of the drill pipe and obtain the vibration response law generated by the interaction between the drill pipe and the surrounding rock; The results indicate that the anchoring equipment has a greater impact on the vibration of the drill pipe, and the surrounding rock has a more stable impact on the vibration of the drill pipe. Due to the short body and large span structure of the anchoring system crossbeam expansion frame, the vibration response of the drill pipe is significantly greater than that of the retracted state of the drilling rig due to being in an unstable cantilever state when the drilling rig is extended. The theoretical reliability of the vibration response law of the drill pipe under different states has been further verified through drilling experiments of the anchoring system prototype. The relevant theories can provide a theoretical basis for the implementation of automatic anchoring technology in the anchoring system. [ABSTRACT FROM AUTHOR]

Conventional cross-laminated timber (CLT) shear walls often use commercial hold-downs and shear brackets with small-diameter fasteners that limit their lateral capacities. By using higher capacity hold-down connections with large diameter dowels, bolts, or mixed angle screws, a CLT shear wall's strength and stiffness can be significantly improved. This experimental study assessed the performance of CLT shear walls using high-capacity hold-down and shear key connections. A total of six full-scale, five-ply cantilever CLT shear walls were cyclically tested to evaluate their strength, stiffness, and hysteretic behavior. The specimens had three height-to-width aspect ratios (0.52, 1.3, and 3.3) and two hold-down fastener types (bolts and mixed angle screws). All six wall specimens exhibited significantly higher strength and initial stiffness when compared to previously tested conventional CLT shear walls. Four of the six specimens exhibited ductile behavior through yielding of their hold-down fasteners. However, the two long walls buckled prematurely, highlighting a possible failure mode for CLT shear walls with significant in-plane loading. A maximum system overstrength factor of 2.0 was observed for the walls with mixed angle screw hold-downs, and the overstrength values reduced with increasing aspect ratios. The three walls with bolted hold-downs were not tested to failure due to the longest wall buckling and the other two specimens reaching the test setup's maximum allowable drifts of 4.5% and 6.0% for the 2.6 m–tall and 6.6 m–tall walls, respectively. Although post peak behavior was not reached, high local ductility demands of 14 and 21 were observed in the bolted connections. Therefore, their ultimate overstrength factors were not found, but the test results indicate an overstrength of 2.7 or greater can occur due to significant "rope effect" of the bolts and their excellent local ductility capacity. [ABSTRACT FROM AUTHOR]

An inflatable rockbolt is a steel tube that has been rolled into an omega shape. During installation, water is injected into the tube, which expands the profile of the rockbolt, generating a radial force against the borehole wall. This reinforces the rock mass through the friction at the bolt–rock interface. This study aims to quantify the effects of borehole size, borehole roughness, and installation water pressure on the pull load capacity of the bolt. This was achieved through a series of pull tests under laboratory conditions. The test results showed that the load capacity was higher in boreholes that were either close to the initial profile diameter of the bolt or the fully unfolded diameter of the bolt, that were 26.8 mm and 38.7 mm, respectively, in the study. The load capacity and the radial stiffness of the bolt were lowest in the medium-sized boreholes (33 and 33.5 mm). In small boreholes, the shoulders of the bolt tongue are tightly compressed such that the outward elastic deformation of the bolt tube is locked in after installation. This deformation locking enhances the load capacity of the bolt. In addition, the load capacity was found to be higher in percussively drilled boreholes than in diamond-drilled boreholes. The additional friction angle of the percussive boreholes was back-calculated to be approximately 5.83°. The load capacity was also found to increase as the installation water pressure increases in the range of pressures tested. It was observed that the inflatable bolt was clamped against the borehole in three zones: on the two tongue shoulders and the side of the bolt opposite the tongue. Highlights: The pull load of an inflatable bolt is minimum as the borehole diameter is in the middle of the initial and fully unfolded diameters of the bolt. In small boreholes, the clamping of the shoulders of the tube tongue results in higher contact stress and consequently higher pull load capacities. Borehole roughness is vital in enhancing the pull load capacity of inflatable bolt. The roughness angle of a percussive borehole is around 5.83°. The pull load capacity of the inflatable bolts increased as the installation water pressure increased from 24 to 30 MPa. An installed inflatable bolt contacts the borehole at the two tongue shoulders and in a zone around the opposite of the tongue. [ABSTRACT FROM AUTHOR]

Brittleness is an intrinsic mechanical property of rock materials that has attracted significant attention to be properly quantified as it plays an important role in characterization of brittle fracturing. Endeavors have led to the establishment of many Brittleness Indices (BIs) for various rock types and widespread engineering applications. Among them, assessing burst proneness as a serious challenge in underground mining has received considerable attention. Parallel to BIs' development, various Bursting Liability Indices (BLIs) have been proposed to specifically assess coal bursting phenomenon. Despite having different names, both BI and BLI in principle have aimed at evaluating the burst–brittleness level of different rocks for different applications. In this study, the principles of burst and brittleness were discussed followed by the development of a novel so-called burst–brittleness ratio (BBR) to assess the relative burst–brittleness of rock types irrespective of their applications. To do so, the proposed BBR was governed by point load testing (PLT) which has significant advantages over the other rock testing methods used in BI estimation such as direct or indirect tensile testing. To examine the suitability of the proposed ratio, three different rock types from various geological origins including coal, granite and sandstone were selected and tested under uniaxial compressive, indirect tensile Brazilian and point loadings. The high-speed imaging technique and Acoustic Emission (AE) were utilized to characterize the cracking process (e.g., failure under shear or tension) and to monitor the real-time failure behavior of samples under different loading conditions. The resulting data revealed that the severity of strength loss in coal samples was significantly higher than that observed in other rock types particularly under uniaxial compression endorsing the validity of the proposed BBR. Highlights: Comparing Brittleness index with Bursting Liability Index along with their pros and cons Development of a new Burst–Brittleness Ratio (BBR) based on UCS and point load strength index Validation of the proposed ratio through point load and UCS tests on granite, coal, and sandstone using high-speed imaging and Acoustic Emission (AE) techniques [ABSTRACT FROM AUTHOR]

In this paper, after determining an appropriate experimental design and testing scheme to test the shear performance suitably, the impacts of pretension and shear interfaces on fibreglass rock bolts were investigated. For this purpose, at the first stage, the double shear testing apparatus was modified to address the issues and shortcomings of the established testing methodology. Then, 20-tonne and 30-tonne rock bolts were tested with pretension loads of 0 kN, 10 kN, 15 kN, and 20 kN for each test scheme. For this, a 40 MPa small aggregate concrete was used for all samples to simulate the host rock. The grout used to anchor the rock bolts was mixed to the product's recommended guidelines to ensure close resemblance to field mixtures. To maintain consistency, all samples were manufactured with the same concrete and grout recipes. The results of double shear tests revealed that increasing the pretension also increased the confining pressures at the shear interfaces for clean joints. This, in turn, reduced the damage propagating from the bolt at the shear interface and decreased the hinge point bending. The results can be applied for further analytical and numerical studies, which could utilise for a better understanding of the shear behaviour of fibreglass rock bolts. Highlights: Two types of fibreglass rock bolts, the 20-tonne and 30-tonne rock bolts, were tested utilising the modified double-shear apparatus. The double-shear testing apparatus was modified to address the issues and shortcomings of the established testing methodology. The double shear performance profiles of the bolts could be described by three regions categorised as the elastic, strain-softening, and failure regions. Increasing the pretension of each rock bolt type resulted in a reduction in the severity of the recorded shear force dip. The increased pretension yielded less physical damage to the rock bolt propagating away from the shear plane. [ABSTRACT FROM AUTHOR]

During the excavation and support construction process used in coal mine roadways, the stress path is the unloading of in situ stress and the compensation of support stress. The 150 mm × 150 mm × 150 mm coal mass samples were obtained in situ underground and prepared, the true triaxial loading–unloading–confining pressure restoring test method was used, and the mechanical response and deformation failure evolution characteristics of the coal seam during the excavation and support process of the shallow, medium depth, and deep coal roadways in the coal mine were simulated and studied. Based on the distribution law of the bolt and cable support stress field, the support compensation stress required for the stability of the surrounding rock after the excavation of the coal roadway with different burial depths was determined, and the corresponding roadways' surrounding rock control technologies were proposed. This study's results indicate that the compensation stress required for support in shallow coal roadways (with a burial depth of about 200 m) was much less than 0.1 MPa. A single rock bolt support can keep the surrounding rock of the roadway stable; the compensation stress required for support in the medium buried coal roadway (with a depth of about 600 m) is around 0.1 MPa, and the combined support of rock bolts and cables can meet the support requirements. Deep coal roadways under high stress (with a depth of about 1000 m) require support to provide compensation stress. Even if the compensation stress reaches 0.2 MPa, the surrounding rock of the roadway will experience varying degrees of creep. In this study, it was necessary to increase the support density and surface area of rock bolts and cables, the pre-tension forces of rock bolts and cables were improved, and in synergy with grouting modification, destressing and other technologies could control the large deformation of the surrounding rock of the roadway in 1000 m deep coal mines. This study's results provide a theoretical basis for the selection of control technologies for use in coal roadways at different depths. [ABSTRACT FROM AUTHOR]

Complex grid-like structures such as steel truss bridges and steel truss roofs commonly exist in civil engineering applications. Since these structures are usually subject to dynamic operational forces, faults like chemical corrosion, fatigue crack, and bolt loosening arise, and seriously affect structural health. To consider some issues in existing frequency domain fault evaluation methods like applicability for complex structures, requirement of baseline data, neglect of nonlinear boundaries, and localization of local faults, a novel method using nonlinear vibration features and Euclidean distance measurement is presented in this paper. Firstly, complex grid-like structures are decomposed into a series of simple T-type substructures according to structural characteristics and load paths. Secondly, related T-type multi-degree-of-freedom model is built by simulating potential faults and nonlinear boundaries as related nonlinear damper-spring connections. Thirdly, exciting the model and extracting output responses only, novel and local fault features, which are functions of structural properties, nonlinear fault-induced loads and transmissibility functions, are defined. Then, utilizing defined features from the local substructure to be evaluated only, a novel fault index is defined with Euclidean distance measurement. Finally, corresponding evaluation method is developed, and its effectiveness and applicability are demonstrated by comparative studies on a lab bolted grid-like structure. [ABSTRACT FROM AUTHOR]

Compared to traditional steel reinforcement, GFRP anchors demonstrate outstanding mechanical performance and corrosion resistance, and so they are an ideal substitute for steel reinforcement in anti-floating projects. Based on finite element software, a 3D axisymmetric calculation model of GFRP anti-floating anchors in medium-weathered granite was established in this paper. Combined with the in-situ ultimate pull-out tests, the bonding anchoring performance and bearing characteristics between the anchor body, anchoring mortar, and rock–soil mass were analyzed. The research findings indicated that the cohesive bonding elements exhibited a high degree of conformity in defining the interface contact relationship of the GFRP anti-floating anchor anchoring system. The axial force of the GFRP anti-floating anchor body is "attenuated" along the depth direction, and there was a critical value of anchoring length; under the same conditions, the reasonable anchoring length should be 3.5~5.0 m. All the anchors in the in-situ tests exhibited interfacial shear slip failure between the anchor body and the anchor mortar, with an average maximum load of 450 kN, which is consistent with the maximum failure load of the simulated anchors. Compared to a load of 50 kN, the maximum stress of the anchor mortar increased by 50% under a load of 450 kN. The displacement variation of the surrounding rock–soil mass showed a decreasing trend from the inside to the outside and from the top to the bottom. The research results provided valuable references for the optimization design of GFRP anti-floating anchors. [ABSTRACT FROM AUTHOR]

Introduction: The rock avalanches are a frequent and disruptive phenomenon in the Himalayas and other mountain chains. To minimize future losses, it is essential to investigate the engineering geological causative factors and mechanism of these mass wasting events. Study area: The present work is aimed at assessing the failure mechanism of the disastrous 2014 Jure rock avalanche along Araniko Highway, Northern Nepal. The event had blocked the Sunkoshi River and blocked an economically significant route to China. Geotechnical properties and analysis: Initially, rockmass characterization and intact strength attribute were determined for the site to classify the failure zone. The parameters measured and obtained from the field and laboratory were integrated into the analytical models to obtain a conclusive interpretation of the failure mechanism. Structural, kinematic, and key block theory analyses have been carried out for decipher the evolution of the failure zone. Results and discussion: Rock mass was found to be of fair quality, however, the structural instabilities and the presence of water has led to a progressive failure. Movement of the key block and subsequent sliding of wedges and foot failure appears to be a possible failure mechanism. Conclusion: The present research explores the contributory engineering geological aspects of the Jure rock avalanche. The investigation results can be used to tackle similar large scale rock avalanches in similar geological terrains and thus minimizing the losses. [ABSTRACT FROM AUTHOR]

Recent advances in roller coasters accelerate the creation of complex tracks to provide stimulation and excitement for humans. As the main load-bearing component, tracks are prone to damage such as loose connecting bolts, paint peeling, corroded sleeper welds, corroded butt welds, reduced track wall thickness and surface cracks under complex environments and long-term alternating loads. However, inspection of the roller coaster tracks, especially the high-altitude rolling tracks, is a crucial problem that traditional manual detection methods have difficulty solving. In addition, traditional inspection is labor-intensive, time-consuming, and provides only discrete information. Here, a concept of the multifunctional detection robot with a mechanical structure, electrical control system, camera, electromagnetic ultrasonic probes and an array of eddy current probes for detecting large roller coaster tracks is reported. By optimizing the design layout, integrating multiple systems and completing machine testing, the multifunctional roller coaster track detection robot exhibits outstanding performance in track appearance, thickness and crack detection. This study provides great potential for intelligent detection in amusement equipment, railcar, train and so on. [ABSTRACT FROM AUTHOR]

Taking the roadway peripheral rock anchoring unit as the research object, the rock compression test containing the anchor solid was carried out to analyze the influence of the degree of peripheral rock fragmentation and the anchor support method on the mechanical properties of the rock body. The test results showed that the smaller the size of the structural surface, the more a greater number of anchor rods were needed, which in turn provided better support. With the increase in the size of the structural surface, the uniaxial compressive strength and modulus of elasticity of the specimen showed a gradual decrease. Numerical tests of the uniaxial compression of rock containing cohesive units showed that the deformation of the specimen near the anchor bar was significantly reduced, while the main rupture surface was blocked, and an obvious reinforcement zone was formed near the anchor bar. Under the double-anchor condition, the anchor tension stress was more obvious, the reinforcement zone was wider, and the rock rupture surface was strongly blocked, all of which made its reinforcement effect the more obvious. This double-anchor condition showed that the anchoring effect of the anchor rods on the specimens was reflected in two aspects of reinforcement and crack stopping. The denser the anchor rods, the wider the reinforcement zone and hence the more likely that the superposition effect will occur, which allowed the anchor rods to play a greater supporting role in stabilizing the rock. The research results can provide a theoretical basis for the design of anchor support and early warning prediction of destabilization damage in the fractured surrounding rock of coal mine roadways. [ABSTRACT FROM AUTHOR]

Investigating the mechanism and measures of controlling rockburst in deeply buried underground caverns is a prerequisite for ensuring the safety of personnel, reducing the damage to construction equipment caused by the rockburst, and making the project economical and efficient. Efficient analysis methods for evaluating rockburst control in underground caverns are crucial for qualitatively selecting rockburst control methods and quantifying the effectiveness of rockburst measures. Based on the mechanism of energy accumulation in rock mass and the occurrence of rockburst as well as the active methods for controlling rockburst, we propose a mathematical model for simulating borehole stress relief using implicit borehole elements. In this modeling approach, we combine vector superposition in different borehole directions to analyze the effect of borehole stress relief on improving the external environment of the rock mass. Based on the interaction between the anchor support and the surrounding rock as well as the implementation of passive rockburst control measures, we propose a mathematical model that utilizes the implicit anchor column elements to simulate the reinforcement of the surrounding rock with anchors. By combining system anchors into arches and suspending anchors to reinforce the caverns, the overall stiffness of the surrounding rock can be improved and the stress accumulation can be alleviated. The coordinated deformation between the surrounding rock and the anchor provides support to prevent the rockburst. The effects of two rockburst control measures, borehole releasement and anchor reinforcement, are analyzed using both the strength theory and the energy theory. Engineering examples are provided to illustrate that the use of borehole elements to simulate local stress relief can effectively improve the external environment of the rock mass to control the occurrence of rockburst. Additionally, the mechanism of using anchor column elements in combination with the surrounding rock elements to enhance the overall stiffness of the rock mass and prevent rockburst is explored. [ABSTRACT FROM AUTHOR]

In wind turbine systems, bolted connections are frequently subjected to gravitational and centrifugal loads transmitted by the blades during operation. This can lead to the attenuation of bolt preloading, resulting in bolt loosening or uneven loading, which in turn affects the service life of the generator unit. Therefore, the study of bolt preloading variations is crucial. However, there are numerous factors influencing bolt preloading, and the existing techniques struggle to precisely assess bolt preloading. This paper proposed a bolt preloading evaluation technique based on the hammer modal method. Focusing on the 42CrMo4 bolted connection of a pitch bearing, a test platform for bolt preloading assessment is constructed. Hammer modal tests are conducted under various preloading forces. By combining finite element modal analysis, the correspondence between preloading changes and the bending frequencies and modes of the bolted connection is obtained. The research illustrated that with changes in bolt preloading, variations occur in coherence, phase, and natural frequencies of frequency response functions. The fundamental correlation between bolt preloading and the second-order bending frequency can be utilized to assess changes in preloading. Furthermore, the applicability of this method has been validated, offering a reference for evaluating bolt preloading. [ABSTRACT FROM AUTHOR]

This study aims to comprehensively investigate the reinforcement mechanism of the tunnel support structure and its supporting characteristics in layered and weak rock tunnels. Uniaxial compressive tests were carried out to study the mechanical and deformation characteristics of anchored rock with the system anchor bolt and the steel floral pipe. Besides, a three-point bending test of the steel–concrete composite beam was conducted to investigate the bending capacity of the grilles and I-beams. The experiment showed the following results: (1) The anchor bolt achieved the anchoring effect by improving the stress state and the strength of the surrounding rock. The improvement of the anchorage strength to the surrounding rock was reflected by the effect of the compression zone of preload, the healing effect of the anchorage agent on the surrounding rock, and the reinforcement effect of the anchor bolt on the density and strength of the anchor bolt. (2) By the CT scanning of the anchored samples after the experiment, it was found that the crack was blunted and arrested within the anchorage zone, and the crack-arresting effect was related to the range of the anchorage zone. The larger the anchorage zones, the better the crack-arresting effect. (3) The steel arch could effectively improve the ability of concrete antideformation. Compared with the lattice girder, the coordination ability of steel arch and concrete deformation was relatively weak. Its coordinate deformation stage was shorter than that of the lattice girder and earlier into the debonding stage. However, the stiffness of the steel arch and concrete was greater than that of the lattice girder after debonding and showed a strong bearing capacity. [ABSTRACT FROM AUTHOR]

This paper presents a reliability analysis of deep tunnels reinforced by fully grouted bolts using a homogenization approach. From the constitutive viewpoint, the anisotropic elastoplastic behavior of bolted rock mass is formulated in the context of the homogenization method. Reliability design analysis is undertaken considering the configurations of both radial and face bolts used separately or in association. The combination of rock bolting associated with classical shotcrete lining is also addressed. Restricting to deep tunnels and axisymmetry conditions, a simplified analytical approach followed by finite element numerical modeling are developed in the framework of the homogenization method. Reliability analyzes are performed using the Monte Carlo simulation (MCS) and the first‐order reliability method (FORM). The response surface method (RSM) provides analytical approximations to enable reliability analyses without time‐consuming computational models. The results show excellent correlation between the obtained reliability parameters, which emphasizes the relevancy of the adopted reliability methods. Structural failure probabilities below or close to 1.0% were obtained in all cases studied for the best structural tunnel conditions. [ABSTRACT FROM AUTHOR]

The second generation of Eurocode 7 includes both soil and rock. In addition to the current practice of ground engineering, this document aims at incorporating rock engineering, improving the ease of use, the harmonization of regulations and covering new developments. This paper provides an overview of some of the significant changes to Eurocode 7 in rock engineering design, taking into consideration limit state design, robustness, durability, and reliability. It focuses on the design of slopes, spread foundations, and retaining structures. The clauses focus on soil mechanics, but also include special rock mechanical issues such as the influence of discontinuities and strength anisotropy on the limit states. Many matters associated to verification of rock mechanical design are linked to the use of prescriptive rules and shall be given in National Annexes. For geotechnical structures in rock, it is mentioned that geotechnical mapping and documentation is important to verify the limit states. However, the basic issues with partial factor methods for verification of the ground‐structure interaction of reinforced slopes and retaining structures are not fully resolved. This has caused some difficulties in setting up partial factors and obtaining a sufficient overview of the application of partial factor method, especially in rock engineering. The design of slopes, spread foundations and retaining structures must likewise consider other clauses in the Eurocode. Rock support for slopes and retaining structures is described in Clause 13 "Rock Bolts and Surface Support". Groundwater‐related issues are described in clause 12 "Ground water control" which influence the design and limit states for the actual geotechnical structure. Dams and levees are featured in Clause 4 "Slopes, Cuttings and Embankments". [ABSTRACT FROM AUTHOR]

In 2025 the new generation of the Eurocode 7 will be introduced and set a framework for geotechnical design for the next 20 years. As Eurocode 7 is an essential design code, the changes will affect numerous practising geotechnical Engineers. The paper provides an overview of significant changes in rock engineering design introduced in the new EN 1997 part 3, considering limit state design, durability, reliability, testing and other crucial design aspects. It focuses on the anchor clause revision and first introduced design rules for rock bolts and soil‐nailed structures. The improvements described include distinguishing between different tension supporting elements that have often been confused. Furthermore, the provisions for groundwater control measures influencing the working condition and limit states for all other geotechnical systems that have not yet been comprehensively addressed in the current Eurocode 7 are also clarified. Finally, the design of the described geotechnical structure will also be strongly affected by changes in the overall philosophy of the Eurocodes, which is also explained. [ABSTRACT FROM AUTHOR]

Due to the substantial need to continuously ensure safe excavations and sustainable operation of deep engineering structures, structural health monitoring based on remote sensing techniques has become a prominent research topic in this field. Indeed, throughout their lifetime, deep tunnels are usually exposed to many complex situations which inevitably affect their structural health. Therefore, appropriate and effective monitoring systems are required to provide real-time information that can be used as a true basis for efficient and timely decision-making. Since sensors are at the heart of any monitoring system, their selection and conception for deep rock tunnels necessitates special attention. This work identifies and describes relevant structural health problems of deep rock tunnels and the applicability of sensors employed in monitoring systems, based on in-depth searches performed on pertinent research. The outcomes and challenges of monitoring are discussed as well. Results show that over time, deep rock tunnels suffer several typical structural diseases namely degradation of the excavation damaged areas, corrosion of rock bolts and cable bolts, cracks, fractures and strains in secondary lining, groundwater leaks in secondary lining, convergence deformation and damage provoked by the triggering of fires. Various types of remote sensors are deployed to monitor such diseases. For deep rock tunnels, it is suggested to adopt comprehensive monitoring systems with adaptive and robust sensors for their reliable and long-lasting performance. [ABSTRACT FROM AUTHOR]