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The strength of filled bolt holes of composites is an important parameter in developing the bearing bypass envelope curves for bolted joint structures in engineering design. This paper presents the procedures of tensile failure strengths and damage for a laminate with a filled bolt hole. Tests of two different cases, open‐hole tension (OHT) and filled‐hole tension (FHT), were performed and repeated seven times, respectively. A new type of virtual testing based on the LaRC05 criteria coupling with XFEM crack technique was developed to predict and analyze the crack initiation and early propagation around the bolt hole in the laminates. Two analytical methods were also adopted to predict the residual strength for a laminate after drilling. The results show that the thinner sample would present a higher strength with the same material system. It is also shown that the virtual test can well capture the failure modes, revealing that the 0° fiber has a natural function of crack arrest, the 90° layers that are the fracture pioneers with matrix tensile failure trigger the fiber breakage of 0° layers, and the failure of 45° layers occurs at the last. Additionally, an interesting phenomenon is observed that the initial failure around the filled hole edge does not affect the structural stiffness. Finally, a good agreement is achieved among the experimental, analytical and numerical results. It suggests that the results could provide a valuable guidance for the design of multi‐bolted joint structure. [ABSTRACT FROM AUTHOR]

For tunnel-support engineering, the bed separation of surrounding rock has a great influence on the support performance of bolts. In order to reveal the mechanical properties of the full-grouted prestressed bolt under the influence of bed separation, three typical working conditions of single-separation, multi-separation and different separation positions were set up, and theoretical models and numerical models were established. Furthermore, the characteristics of bolt axial force and anchorage–interface shear stress were analyzed by numerical method, and the sensitivity based on an orthogonal test was studied by means of range analysis and variance analysis. The results showed that: (1) under the single-separation condition, the separation value has a significant effect on the mechanical properties of the bolt, and with the increase in the separation value, the sliding failure unit of the bolt increases; (2) for multi-separation conditions, if the total separation value is the same, the increase in the number of separation interfaces is beneficial to the force of the bolt; (3) for the case where the separation layer is located at different positions, the separation layer on the right side is more likely to cause the overall slip failure of the bolt; and (4) for the above three influencing factors, the separation value has the greatest influence on the mechanical properties of the bolt, and the separation position has the least influence. [ABSTRACT FROM AUTHOR]

In this study, two caverns viz. Powerhouse Cavern (PHC) and Transformer Cavern (TC) forming major part of hydro-electric project in eastern Himalayas are considered for analysing convergence of cavern components and efficiency of support system with different pillar widths. Detailed comparative analysis of stability of caverns was carried out for unsupported, supported caverns with pillar widths of 30 m and 40 m between PHC and TC. Trend of cavern convergence, maximum principal stress together with deformations, axial, shear forces, bending moment in cavern support components like rock bolts, cable anchors, liner are examined. Pattern of distribution and location of points of concern enable identifying critical locations to resist collapse of cavern system. Evaluation of adequacy of support components were carried out to check the adequacy. Analysis revealed a strength factor greater than 1 for locations along periphery of both caverns and supports provided to the cavern system were adequate. Results establish site applicability of the support systems as well as adequacy of pillar width of 40 m to ensure stability of the entire system. The study concludes that a pillar width of 40 m ensured more stable conditions with minimal shear strain and no overlap of plastic zone between caverns. [ABSTRACT FROM AUTHOR]

Copyright of Railway Construction Technology is the property of Railway Construction Technology 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.)

Copyright of SDU Journal of Engineering Sciences & Design / Mühendislik Bilimleri ve Tasarım Dergisi is the property of Journal of Engineering Sciences & Design 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.)

Due to the construction technology, material characteristics, long-term coupling of environment and load, and other factors, quality defects produced in rock bolts, posed a potential threat to the safety of public infrastructure. Non-destructive testing for rock bolt structure in-service is an important part of anchoring quality evaluation and reinforcement. The stress wave method has strong adaptability and rapid development, which is the main method for non-destructive testing technology of bolt anchorage quality. The research state-of-the-art of non-destructive testing from the aspects of the theory of anchoring bolt quality detection based on stress wave, model test, stress wave excitation and reception, signal processing and analysis, and numerical simulation were systematically reviewed. The results show that the research on non-destructive testing technology of bolt anchorage quality in China is relatively late, but developed rapidly. The existing non-destructive testing technology for bolt anchorage quality is relatively mature, which can realize the detection of the length and grouting compactness of grouted bolts. However, it still has shortcomings, which limit the detection accuracy and detection length of the bolt. The non-destructive testing method for the service state of old bolts has yet rarely been reported, and further research is still needed. Finally, the future potential development direction has been prospected combined with the future development trend. In the follow-up study, the existing theory should be further improved and perfected, and the non-destructive testing technology and equipment should be developed and upgraded to expand the application scope of non-destructive testing technology for bolt anchorage quality. At the same time, the intelligent evaluation system for the bolt service state based on non-destructive testing technology should be constructed and the remaining service life prediction method needs to be proposed. [ABSTRACT FROM AUTHOR]

The seismic dynamic responses of rock slopes are a hot topic for geotechnical engineering studies. Based on the interaction between rock slope and anchor bolts, a dynamic numerical model of a layered rock slope was developed using the finite difference software FLAC3D. The dynamic response patterns of anchored and natural slopes under seismic loads were analysed to obtain the supporting effect of anchor bolts during seismic activity. The results indicate that under seismic loads, tensile cracks at the intersection of the top and joint surface develop into a drawing open surface of the back edge, and a shear slip occurs at the base of the slope, both of which result in the formation of tensile-shear slip failure. Permanent slope displacement accumulates only when seismic acceleration exceeds the critical acceleration. The slope deformation has been constrained, and the performance of the slope during the seismic activity has been strengthened by anchor bolt supports, which significantly increase the ductility of the rock slope under seismic loads. Moreover, during an earthquake, the axial forces of anchor bolts in the middle slope rise more than at any other position. After the earthquake, anchor bolts in the middle have been shown to exhibit maximum axial force. As a complex problem, stability analysis of seismic slopes is important. The analysis of seismic slope failure and the mechanism of slope anchoring are particularly complicated. The present study will help to improve future research on the seismic design and dynamic analysis of slopes supported by anchor bolts. [ABSTRACT FROM AUTHOR]

Rock bolting is one of the most effective and economical methods for jointed rock mass reinforcement. Therefore, the elastic constitutive relationship in an anchored rock mass, which could well reflect the rules of strength and deformation, should be studied. An orthotropic elastic model, which considered varying anchorage angles (α) and the corresponding mechanical parameters, was investigated based on the theory of mechanics of composite materials. To verify the suitability of the model and the mechanical parameters, a WAW-3,000 kN servo universal hydraulic testing machine was used to undertake a series of uniaxial compression tests on the anchored layered rock specimens. The mechanical parameters of composite specimens, such as elastic modulus (E), Poisson's ratio (ν), peak strength, and its variation with α were obtained. The results showed that the anchored effect of a bolt on the layered rock mass was very significant and anisotropic, for instance, increments in the elastic parameters in three orthogonal directions were quite different with the increase in α from 0° to 90°, which mainly depended on the relative volume content of the component materials in a certain direction. Comparing the calculated E with the experimental values, the variation rules for the mechanical parameters maintained good consistency, and this proved that the calculated equations in this work were reasonable and had acceptable precision. The spillway slope of a reservoir was simplified and simulated and the optimal α was obtained, which further demonstrated the reasonability and applicability of the proposed model from the viewpoint of engineering practice. [ABSTRACT FROM AUTHOR]

The magnetic anchoring system (MAS) for reef limestone reinforcement is proposed in this paper. The mix proportion of the artificial reef limestone was designed, and the parameters of the MAS were determined through orthogonal tests. The effect of the magnetic field on the anchoring materials was analyzed using XRD and the nitrogen adsorption method. The results indicate that the designed artificial reef limestone can be used in place of in situ rock samples for laboratory tests. In air, the bond samples of the anchoring material and reef limestone experienced cohesion failure of the artificial reef limestone. However, in seawater, it was cohesion failure of the reef limestone and interface adhesion failure. During the pull-out test, the reef limestone specimen reinforced by MAS showed interface failure between the anchoring material and the rock mass. The Fe3O4 powder present in the anchoring material has the ability to migrate towards the anchor, thereby enhancing the density of the anchoring material. This, in turn, helps to eliminate the free water present in the anchor hole, and consequently, improves the bonding effect of the interface. The reinforcement effect of MAS is particularly advantageous for rock reinforcement under complex working conditions. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study mainly investigated the nonlinear vibration performance of a rotor-casing coupling system containing a bolted flange connection. The dynamic equations of the coupling system were developed while considering the radial stiffness of the bolted flange structure, which contained a spigot, squirrel cage with ball bearing, and rotor-casing coupling vibration. To study the influence of the disk casing fixed-point rubbing fault on the coupling system's nonlinear dynamic performance, an analytical model of the nonlinear impact forces was established, which considered the contact and vibration responses of the rotor and casing. The frictional force was obtained based on the Coulomb friction law. The iterative analysis of motion equations was performed utilizing the Newmark method. Then, the nonlinear dynamic behaviors of the coupled systems were examined using data, including a bifurcation diagram, spectrum plot, greatest Lyapunov exponents, etc. The effects of rubbing fault on the dynamic properties of system were investigated in detail, indicating that there were various motion states, which were described as periodic, multi-periodic, and quasi-periodic motions. Comparing the simulation results, it was found that rubbing fault seriously affected the motion stability of the rotor system. Finally, by gathering and examining the vibration data set from a test platform for rotor-casings with bolted joints, the correctness of the numerical simulation findings was confirmed. Additionally, the results of the experimental investigation agreed with that of the simulation. The dynamic distinguishing characteristics that were noticed can be used as an indicator for determining whether the fixed-point rubbing fault between the rotor and casing has become worse. [ABSTRACT FROM AUTHOR]

Rock-support interaction is the basis and premise of support structure design in tunnel engineering. In the conventional convergence-confinement method, the imperfect rock-lining interface is usually ignored. In this study, we present a mechanical model considering the imperfect interface and corresponding solution method for the analysis of rock-support system. Parametric study on the influence of interface on rock-support interaction indicates that: (1) rock-support system without considering imperfect interface is the limit cases in which rock-lining interface initial stiffness is very large or rock-lining interface maximum displacement is close to 0; (2) the smaller the interface initial stiffness and the larger the interface maximum displacement, the larger the displacement, plastic zone and load taken by rock mass, but the smaller the load shared by support structures; (3) no matter how the interface parameters change, rock mass is always the dominant load-bearer, while support structures share less load; (4) compared with surrounding rock and systematic bolt, the influence of interface on load taken by lining is more significant. This study can improve our understanding of rock-support interaction and determine the loads shared by surrounding rock and support structures, which contributes to the rational design and the safety of tunnel engineering. [ABSTRACT FROM AUTHOR]

In mechanical and aerospace engineering, different components are usually integrated together via bolted connections. Compared to the rivet joint and welding joint, the bolted connection is preferred in some cases due to its easy-to-operation and low-cost. However, the bolt self-loosening caused by vibration or other issues (e.g., improper installation and chemical corrosion) may induce severe accidents. Therefore, in this paper, the author proposes a new strategy based on the acoustic emission (AE) technique to detect bolt looseness. To the best of the author's knowledge, this research is the first attempt to identify multi-bolt looseness via the AE-based method. Particularly, the main contribution is that the author proposes a new shapelet-enhanced AE method that employs a newly developed dual-shapelet networks classifier to discriminate AE waves. The dual-shapelet networks classifier consists of sample-specific shapelets, which is sensitive to the difference among various categories, and category-specific shapelets derived from auxiliary binary classifiers. The objective of category-specific shapelets is to address the imbalanced classification task, that is, discriminating minority categories. Then, the sample-specific shapelets and category-specific shapelets are combined to extract features from AE signals under different multi-bolt looseness cases, and the final classification is achieved by feeding the extracted features into a softmax layer. Finally, the author conducts an experiment to verify the effectiveness of the proposed method. Moreover, by comparing the proposed method's performance with two baselines, the advantages of the shapelet-enhanced AE method can be demonstrated. Overall, this research demonstrates that the AE technique is valid to characterize friction and collision between asperities on the bolted interface, thus providing a new direction for multi-bolt looseness detection, and the proposed shapelet-enhanced AE method has substantial potential in the field of structural health monitoring (SHM). [ABSTRACT FROM AUTHOR]

In this study, the mechanical behavior of fully grouted rock bolts in hydraulic tunnels subjected to elevated ground temperatures was investigated. A differential equation for axial displacement of the rock bolt was formulated, which considers the force equilibrium of infinitesimal bolt segments and the stress transfer mechanism at the anchor–rock interface. The distribution functions for axial stress within the bolt and the interfacial shear stress were obtained by solving the differential equation, which incorporated the displacement of the surrounding rock mass as a parameter. This study showed that the effectiveness of the bolt–shotcrete support system decreases over time, considering the displacement relaxation rate of the surrounding rock mass. The mechanical model's variation laws at 20 °C, 50 °C, and 80 °C were summarized by integrating the thermal deformation equation for material parameters, and the numerical simulation results were compared and analyzed. The findings revealed that the bond strength between the rock bolt and the rock mass diminishes as the temperature of the surrounding rock increases, leading to a reduction of interfacial shear stress at both extremities of the bolt. Moreover, the maximum axial force within the bolt escalates as the neutral point migrates farther from the tunnel wall. [ABSTRACT FROM AUTHOR]

Bolt-ball joints are widely adopted in grid structures due to their high installation accuracy and short construction period. Since the bolt is inside the joint, it is challenging to evaluate its health status from outside the structure. A finite-element plane-truss structure model, based on the actual grid structure, was constructed to investigate the influence of the rod's preload on the overall stiffness and bearing capacity of the grid structure. Moreover, a model of the grid structure, with a bolt-ball joint connection, was constructed to analyze the influence of the preload loss in bolted-ball joints on the overall mechanical performance of the local members and structures. The results show that the release of preload on the outer web rod is less effective in terms of the overall stiffness and bearing capacity of the structure than on the inner web rod. The preload of the larger span direction rod plays an important role, and the preload of the upper chord has a greater impact, while the preload of the web rod and the upper chord in the smaller span direction has no significant effect on the normal stress in the surrounding rods. [ABSTRACT FROM AUTHOR]

Copyright of New Building Materials / Xinxing Jianzhu Cailiao is the property of New Building Materials 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.)

The effect of the curing temperature of cement mortar on the mechanical and deformation characteristics of the full encapsulated rock bolting system was not considered in most previous studies. To reveal the temperature-dependent behavior of cement mortar and bolt-grout interface in terms of strength and deformation characteristics, extensive tests over a curing temperature range of 2–60 ℃ were carried out in this study, including uniaxial compression tests of cement mortar, direct shear tests of cement mortar under both constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions, and direct shear tests of the bolt-mortar interface under CNL boundary conditions. The results showed that the uniaxial compression and shear strength of cement mortar increase with curing temperature at 2–40 ℃ and reduce slightly at 40–60 ℃. Moreover, the effect of CNS boundary conditions was discussed. Furthermore, the evolution of shear strength and dilation limit of bolt-mortar interface with curing temperature was revealed. Based on the experimental results, suggestions for supporting the design of rock bolting systems under high- or low-temperature geological environments are given. [ABSTRACT FROM AUTHOR]

The development of deep geotechnical engineering is restricted by the complex geological conditions of deep rock masses and the unknown creep mechanism of rock in water-rich environments. To study the shear creep deformation law of the anchoring rock mass under different water content conditions, marble was used as the bedrock to make anchoring specimens, and shear creep tests of the anchoring rock mass under different water contents were carried out. The influence of water content on rock rheological characteristics is explored by analysing the related mechanical properties of the anchorage rock mass. The coupling model of the anchorage rock mass can be obtained by connecting the nonlinear rheological element and the coupling model of the anchorage rock mass in series. Related studies show that (1) shear creep curves of anchorage rock masses under different water contents have typical creep characteristics, including decay, stability and acceleration stages. The creep deformation of the specimens can be improved with increasing moisture content. (2) The long-term strength of the anchorage rock mass shows an opposite change law with increasing water content. The creep rate of the curve increases gradually with increasing water content. The creep rate curve shows a U-shaped change under high stress. (3) The nonlinear rheological element can explain the creep deformation law of rock in the acceleration stage. By connecting the nonlinear rheological element with the coupled model of anchoring rock mass in series, the coupled model of water‒rock under water cut conditions can be obtained. The model can be used to study and analyse the whole process of shear creep of an anchored rock mass under different water contents. This study can provide theoretical support for the stability analysis of anchor support tunnel engineering under water cut conditions. [ABSTRACT FROM AUTHOR]

Due to the influence of the ground stress, mining disturbance, and other factors, the roadway surrounding rock in deep underground engineering such as mines, tunnels, and underground caverns is prone to looseness and deformation with the excavation of roadways. In such engineering, the bolt support is frequently employed to stabilize the surrounding rock. In this work, a part of the anchor and the surrounding rock were taken as a simplified model of the anchorage rock mass, and the laboratory compression test was performed on the similitude model. Then, the FLAC3D software was used to simulate varying numbers of bolts and different lateral pressure conditions, and the peak stress, the maximum principal stress field, and the anchor stress field distribution of the anchorage rock mass were obtained. The influence of bolt pretightening force and row spacing on the stability of surrounding rock was discussed using the combined arch theory. The results show that increasing the number of bolts and lateral pressure in the anchorage rock mass can significantly improve the stress value and distribution range of the maximum principal stress field and the anchorage stress field. The fluctuation of the anchorage stress field at different anchorage distances can be lessened by increasing the number of bolts (bolt density). When the lateral pressure exceeds 3 MPa, the anchorage mechanical characteristics of the anchorage rock mass tend to remain stable. The coverage of the effective anchorage stress field and the thickness of the surrounding rock anchorage composite arch can be increased by increasing the bolt pretightening force and decreasing row spacing, consequently improving the anchorage mechanical characteristics of the anchorage rock mass. The research results can be used as a theoretical reference for choosing appropriate bolt support parameters for the roadway surrounding rock. [ABSTRACT FROM AUTHOR]

Regarding the issue of intense mining pressure appearing in the underlying gateway below the remaining coal pillar in the close‐distance coal seam (the remaining coal pillar is perpendicular to the underlying section coal pillar), 401 working face is used as the engineering background. Field measurements, laboratory experiments, numerical simulations, and engineering verification techniques are used to study the abutment pressure's evolution properties and the plastic zone's propagation laws before and after the underlying coal seam roadway experienced the mining impact. The conclusions are as follows: ① The maximum plastic area on the two sides and the roof of the roadway underlying the gob are up to 2 and 1.5 m, whereas the maximum plastic area on the two sides and the roof of the roadway underlying the remaining coal pillar are up to 5 and 4.5 m, respectively. Moreover, the plastic area extends along the two sides, and the section coal pillar is completely broken when the working face is mined below the remaining coal pillar. ② The stress increase coefficient K in the overlap area of the remaining coal pillar and the underlying section coal pillar reaches 3.4 when the mining face penetrates the underlying remaining coal pillar and the advance abutment pressure is overlaid with the concentrated stress of the coal pillar. ③ When the underlying working face is mined to 4, −2, −8, and −14 m away from the remaining coal pillar, the damage range of the roadway 5–10 m ahead increases in turn. At the same time, the maximum plastic area of the roof passes through the plastic area of the upper coal seam floor. Therefore, the underlying and transition areas on both sides of the remaining coal pillar are divided into Area I (15 m) → Area II (the most complicated area to control under the remaining coal pillar, 20 m) → Area III (25 m) according to the width. Furthermore, the divisional differentiated combined control technology of channel steel truss anchor cable with joint double‐way locking control function of roof and coal pillar in Areas I and III, while channel steel truss anchor cable with joint double‐way locking control function of roof and side + high resistance integral door‐type support is proposed in Area II. Field engineering practice shows that the deformation of the roadway surrounding rock can be controlled within 210 mm after adopting the above divisional combined control technology. Finally, the mining operation can safely and efficiently pass through the remaining coal pillar. The research results have important reference values for surrounding rock control of mining roadways in the overlapping area of similar "+"‐type cross‐working face. [ABSTRACT FROM AUTHOR]

Rock bolts are widely employed as an effective and efficient reinforcement method in geotechnical engineering. Sandwich composite structures formed by hard rock and weak rock are often encountered in practical projects. Furthermore, the spatial structure of the rock mass has a direct influence on the effect of the anchorage support. To investigate the impact of rock mass structure on the mechanical characteristics of anchorage interfaces, pull-out tests on reinforced specimens with different mudstone thicknesses and fracture dip angles are conducted. The experimental results indicate that the percentage of mudstone content and fracture dip angle have a significant influence on the pullout load of the samples. A weaker surrounding rock results in a lower peak load and a longer critical anchorage length, and vice versa. The results also show that 70% mudstone content can be considered a critical condition for impacting the peak load. Specifically, the percentage of mudstone content has a limited influence on the variation in the peak load when it exceeds 70%. Optical fiber deformation results show that compared to the rock mass with fracture dip angles of 0° and 60°, the rock mass with a fracture dip angle of 30° has a more uniformly distributed force at the anchorage interface. When the fracture dip angle exceeds 60°, the dip angle is no longer a key indicator of peak load. The accuracy of the experimentally obtained load-displacement curves is further verified although numerical simulation using the discrete element method. [ABSTRACT FROM AUTHOR]

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

This paper presents the results of 10 laboratory tests performed on closely spaced built-up members fabricated from hot-rolled angle sections. Such members are of special interest in the construction and reinforcement of steel lattice towers used for telecommunication or electrical transmission lines. The angle sections used in this study were star-battened with pinned support conditions. In particular, two configurations were studied: star-battened angles with equal sections (SBE) (composed of two chords with the same section), and star-battened angles with unequal sections (SBU) (composed of two chords with different sections). The influence of connection spacing along the members and different types of connections (fully preloaded bolts, partially preloaded bolts) were also studied. In addition, the important influence of geometric imperfections on failure load and failure mode were analyzed. In this paper, a numerical model is introduced after the laboratory tests are presented. The model was built in ANSYS version 18.2 and was validated based on the results obtained during the experimental campaign. The numerical results highlighted the sensitivity of failure modes to initial imperfections (out-of-straightness, load eccentricity). Last, the validated numerical model is thought to be used in a wider parametric study with the aim of developing new design recommendations. [ABSTRACT FROM AUTHOR]

The failure characteristics of geotechnical materials are quite complex, among which there are obvious differences between soil materials and rock materials. In order to describe the failure characteristics of soil materials and rock materials uniformly, a new failure and yield criterion, called VML criterion, is proposed in this paper. This strength criterion has the following characteristics. (1) On the deviatoric plane, the criterion can be expressed as a power parameter expression of von Mises criterion and spatial mobilized plane (SMP) criterion, so it can be used to describe cohesive materials such as metals or frictional materials such as sand. (2) On the meridian plane, another power parameter expression can be used to consider tensile stress strength. On the meridian plane, the material strength envelope can be expressed as a curve, so the hydrostatic pressure effect of soil material can be reasonably considered. (3) In order to consider the volumetric compression yield properties of soil materials under isotropic compression, a yield criterion considering the volumetric compression yield properties is also proposed on the deviatoric plane. Since geotechnical materials are often in plane strain condition in engineering, a VML criterion expression considering plane strain condition is proposed in this paper. The criterion shows that the internal friction angle of soil under plane strain is usually 1.1 times of that under conventional triaxial compression. The comparison between the predicted and tested data shows that the VML criterion proposed in this paper can be widely applied to the failure simulation of rock and soil materials, and the plane strain VML criterion can also be applied to the failure prediction with plane strain state. [ABSTRACT FROM AUTHOR]

The interaction between bolt and rock is crucial to its reinforcing efficacy. Effective bolt installation depends on the bonding/coupling type and its ability to adhere to the rock in a drilled borehole. In this study, three bond types were considered for rock bolting: resin, Fasloc, and an organic mineral glue, Verpensin T, both of which were provided by DSI Underground and a CEM I 42.5R cement bond. The bonds were tested in the laboratory. The bonding properties were checked and then pull-out tests on bolts installed in concrete were carried out. During the investigations, both bond strength and bond stiffness were determined. Based on the experiment data, ABAQUS numerical models were established based on a Fasloc-bonded specimen to investigate the mechanical behavior of the three bond types. The results indicated that the numerical model could favorably support the pull-out test results. Afterward, a series of numerical simulations were carried out by a finite element program RS2 from Rocscience. The simulations were based on two fictitious engineering scenarios with different geologies. The results indicated a weak relationship with the bonding materials and this was suitable for all models. It seemed that the strata selected for simulation played a decisive role. In addition, interesting results such as stress/displacement distribution zones were established. Finally, the Rocscience results were compared to FLAC results for calibration and optimization. The results of this study can deepen our understanding of the interaction between bolts and rock, especially when their mutual mechanical response is transmitted by different types of materials. Highlights: Three kinds of bonding materials for rock bolts were tested considering different curing times. Pull-out tests of rock bolts bonded by different bonds indicated a favorable impact of curing time on mechanical performance. Multiple numerical approaches including ABAQUS, Rocscience, and FLAC were employed to better understand the inner mechanism. [ABSTRACT FROM AUTHOR]

Grouting is a fundamental technology in engineering construction, and its grouting quality evaluation is a critical scientific problem. Proper and reasonable grouting quality evaluation is vital to ensure engineering safety. Standard research on grouting quality evaluation does not consider the uncertainty in the evaluation process and lacks multi-index comprehensive analysis. Because of the above problems, this paper puts forward a comprehensive evaluation method of grouting quality based on FRES-VFS. Firstly, based on the systematic analysis of relevant factors affecting grouting quality, the comprehensive evaluation of grouting quality is divided into three parts: the groutability before grouting, the rationality of design and construction, and the quality evaluation after grouting. Then, twelve indexes, such as the number of joints in the rock mass, the opening degree of the joint in the rock mass, the water permeability before grouting, the water–cement ratio of grout, the grouting pressure, the design parameters, the hole position, the borehole deviation rate, the construction parameters, the permeability, the compactness, and the durability after grouting, are selected to construct the rating index system. Secondly, the weight of each index in the index system is calculated based on the fuzzy rock engineering system (FRES) method. Furthermore, considering the uncertainty in the comprehensive evaluation of grouting quality, the uncertain mapping between evaluation grade and evaluation index is established using variable fuzzy set (VFS) theory. Finally, the comprehensive evaluation method based on FRES-VFS is applied to the Huanggou Pumped Storage Power Station grouting project in China, which provides a new idea for the comprehensive evaluation of grouting quality. [ABSTRACT FROM AUTHOR]

Copyright of Guangdong Architecture Civil Engineering is the property of Guangdong Architecture Civil Engineering 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.)

In recent decades, the number of applications of fiber-reinforced polymer (FRP) reinforcement for concrete has significantly expanded. This fact is mainly due to the FRP reinforcement cost competitiveness, the increasing availability of design provisions, and due to the advantageous physical-mechanical and chemical properties of this composite material, which open up new possibilities for the design and implementation of extremely durable elements. Currently, the most commonly used types of reinforcement bars are those containing glass FRP (GFRP) or basalt FRP fibers, which is mainly the result of their favorable price and high resistance to aggressive environments. The use of composites in construction is wide-ranging: it is possible to apply FRP bars not only in the design and strengthening of concrete structures but also in the installation of shear dowels in concrete pavement, as rock bolts or as anchors for overhanging facade components. In the case of the design of load-bearing elements subjected to a combination of tensile and shear force, it is necessary to quantify their shear resistance and concisely describe the effect of the interaction of the tensile and shear force on the load-bearing capacity of the reinforcing element. This is a broadly addressed area as regards composite laminates and fabrics, but when it comes to FRP bars, there are very few available experimental results. For that reason, this research deals with the experimental testing and quantification of the influence of the interaction of normal and shear force. The behavior of GFRP bars from two different manufacturers, with three different diameters, different surface treatments, and mechanical characteristics, was experimentally verified. The findings are presented, a material failure curve is compiled, and the results are compared with those predicted according to the available relationship for composite laminates and von Mises theory. The presented research was driven foremost by industry demand concerning prestressed fiber-reinforced polymer (FRP) rock bolts. In situations where such bolts are used, the slippage and displacement of parts of rocks can be expected, and consequently, the creation of a shear plane in the prestressed anchor occurs. However, there are no existing methods for determining the load-bearing capacity of such loaded FRP bars. This paper aims to determine the short-term behavior of specimens under the combined action of tensile and shear forces (failure envelope) and to compare their load-bearing capacity with available relationships for steel and composite laminates. [ABSTRACT FROM AUTHOR]

This paper presents details of an experimental program evaluating the behavior of six half-scale glass fiber–reinforced polymer (GFRP) reinforced concrete beam–column precast members connected together through pocket connections, which are subjected to cyclic loading. The novel beam–column connection was constructed by incorporating either epoxy resin or tensioned or untensioned GFRP rock bolts in conjunction with different-sized pocket connections. The effects of an additional connection bar between the column and beam components in the connection, as well as the confinement of the concrete around the pocket region, were also investigated. An innovative test setup was designed so that the beam–column joint could rotate without restraint provided by the supports. All specimens were tested under an incrementally increasing cyclic load. The load-carrying capacity, deformational behavior, failure modes, energy dissipation, and hysteretic damping were all recorded and evaluated. All specimens failed as a result of column failure within the pocket connection region. This was attributed to the relative rotational flexibility of the column with respect to the beam, owing to the low elasticity of the epoxy resin used in the pocket region, and hence the stress concentration at the column ends within the pocket area. According to the results, a pocket connection containing GFRP reinforcement providing confinement around the embedded area yielded the highest capacity, ductility, and energy dissipation under cyclic loading. The connection containing a GFRP bolt, regardless of whether or not the bolt was prestressed, did not significantly improve the performance of the connection. The findings presented here can be used for the design of precast elements reinforced with GFRP bars. Of particular relevance is application to jetties and other offshore concrete infrastructure where steel reinforcement (because of corrosion issues) needs to be replaced with GFRP reinforcement. [ABSTRACT FROM AUTHOR]

A steel plate shear wall (SPSW) is a useful component for resisting lateral action. To improve the performance of frame columns, some studies focus on a two-side connected SPSW, in which the wall plate is not connected with the frame columns. However, few studies conducted on a two-side connected SPSW consider the effect of frame constraints or the connections between the infill plates and frame beams. In this study, by using finite element modeling (FEM), two unstiffened SPSW models with two-side fixed connections and six unstiffened SPSW models with two-side bolt connections were simulated. Their performance under the presence of out-of-plane frame beam flange constraints and different numbers of bolts between the infill plates and frame beams was analyzed. The mechanical performances such as hysteretic behaviors, the capacity of energy dissipation and the out-of-plane deformation of the members were investigated by applying monotonic and cyclic loading. The results revealed that non-negligible deformation would be generated at the lateral border of the bolt connections and that the out-of-plane deformation of the frame could be significantly affected by constraints. These findings can guide the engineering design of SPSWs in the future. [ABSTRACT FROM AUTHOR]

Copyright of China Sciencepaper is the property of China Sciencepaper 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.)

• A novel support approach involving partitioned parallel anchoring in coal or semi-coal entry heading faces can balance timely and efficient anchoring and enhance heading speed. • Spatially, anchoring operations are categorized into local anchoring and reinforcement anchoring. Temporally, cutting, local anchoring, and reinforcement anchoring are carried out simultaneously. • A reasonable partitioned parallel anchoring can effectively keep the entry within acceptable limits. • Partitioned parallel anchoring approach can offer valuable insights for efficient rock anchoring and rapid heading. Rock support is a complex challenge in coal mine heading operations. In particular, heading faces with moderately stable surrounding rock are constrained by unsupported roof /sidewall distance and duration. The ability to provide rapid and effective support directly impacts surrounding rock stability and heading efficiency. This study focused on the anchoring mechanism in rapid heading faces in a specific entry of the No. 2 Coal Mine of Huangling Mine, characterized by moderately stable surrounding rock. The geological conditions, heading status, and factors limiting rapid heading were analyzed. A novel partitioned parallel anchoring (PPA) model was proposed, and its mechanism and impact on the surrounding rock stability were investigated. The findings show that the surrounding rock is significantly affected by heading disturbances; however, a reasonably implemented effective PPA strategy can control surrounding rock deformation. Spatially, anchoring operations are categorized into local anchoring and reinforcement anchoring. Temporally, cutting, local anchoring, and reinforcement anchoring are performed simultaneously, effectively reducing the cycle time and enhancing the overall heading speed. Combining these findings with the actual geological conditions, a specific scheme of PPA was proposed, and the optimization of the rapid heading and PPA processes, along with the effectiveness of PPA, were validated through field experiments. Finally, recommendations for effective PPA in rapid heading faces were provided, offering valuable insights into efficient rock anchoring and rapid heading under similar geological conditions. [ABSTRACT FROM AUTHOR]

• Reinforced shotcrete arches can function as permanent support in soil tunnelling. • Compacted and stiff tills of Norway provide stability under tunnel excavation. • Innovative use of RRS-support can substitute cast concrete liners in soil tunnels. • Optimal support design in soil tunnels demands elaborated designs and monitoring. • Significant cost savings can be achieved from the use of reinforced shotcrete. Ground support in tunnels excavated through weak ground conditions in Norway has normally consisted of reinforced shotcrete methods. However, in cases where exceptionally poor ground or soil tunnel conditions were expected, final support consisted of cast-in-place solutions designed in advance. Although reinforced shotcrete methods have proved satisfactory for a wide range of weak ground conditions, the adequacy of such support method solely to act as the final, permanent support and fully substitute cast concrete liner in soil tunnels has not been realized until the recent construction of the Bergås highway tunnel in northern Norway. In this tunnel, an unexpected portion of 70 linear m of the tunnel consisted of sedimentary deposits of glacial origin (tills) and a weathered, soil-like rock mass. In the present study, the ground behavior and the performance of reinforced shotcrete arches as permanent, final support in this soil portion are investigated. The findings suggest that the compact and over-consolidated tills pose favorable excavation conditions as evidenced by the monitored ground stability under full face excavation passes, and the low support loading during the advance through the soil zone. As such, a pragmatic design considering a permanent functional and stable ground support made of reinforced arches in the soil section was possible from the combination of the elements of the Scandinavian hard rock tunnelling with the principles of weak ground engineering, and pre-stabilization methods with grouted forepoling. The permanent tunnel support finally consisted of ribs of reinforced shotcrete (RRS), fiber reinforced shotcrete (FRS) and fully grouted steel rebar rock bolts, which substituted the pre-determined cast concrete lining that is traditionally used in soft tunnelling conditions. The approach is therefore innovative as it considers a cost-effective alternative with significantly lower concrete consumption, on the basis of a shotcrete-based support solution designed from a combination of elaborated design work, monitoring, ground characterization, and advanced numerical analyses. [ABSTRACT FROM AUTHOR]

BFRP rock bolts have broad application prospects in the field of geotechnical engineering due to their excellent mechanical properties. Large-scale direct shear tests were conducted to explore the shear performance of BFRP rock bolts reinforcing joint surfaces in rock masses. The study analyzed the effects of bolt materials and anchoring angles on the mechanical characteristics of anchored joint surfaces. A theoretical model of bolt shear deformation was established, treating BFRP rock bolts as an anisotropic material. By applying the Tsai-Hill strength criterion, a formula for calculating the shear strength of BFRP-anchored joint surfaces was derived. The results indicate that in the elastic phase, the bolt primarily provides shear resistance similar to a "dowel action," while after yielding, axial constraint effects gradually come into play. The anchoring angle significantly influences the shear strength of BFRP rock bolt anchored blocks, with optimal performance observed around 30°. Under the combined influence of epoxy resin and basalt fibers, BFRP rock bolts exhibit an "expansion-type" fracture under tensile shear loading conditions. The improved method for calculating the shear strength of joint surfaces under tension with BFRP rock bolts aligns well with experimental results. [ABSTRACT FROM AUTHOR]

To effectively control and reduce engineering dynamic disasters such as rockfalls, instability of underground chambers, and rockbursts in deep, high-stress rock masses, this research proposes a new type of energy-absorbing rock bolt. This bolt, designed for hard rock in deep mines, incorporates laminated rubber. The energy-absorption effect of the new bolt primarily depends on the performance of the laminated rubber. To systematically evaluate rock the laminated rubber’s energy absorption characteristics against rock impacts, this research employed Ansys numerical simulation software to simulate Hopkinson pressure bar impact compression tests. Impact tests on laminated rubber specimens, conducted under various impact air pressure conditions, revealed the material’s energy absorption behavior and efficiency. The results show that the energy absorbed by the laminated rubber increased linearly with incident energy, indicating a constant ratio of absorbed energy to incident energy. There is an optimal absorption capacity for laminated rubber materials of different thicknesses; the optimal thickness is between 16 and 24 mm for an incident energy range of 600 to 800 J. These findings will provide theoretical and empirical support for the development of energy-absorbing rock bolts. [ABSTRACT FROM AUTHOR]

• The failure characteristics of boreholes under different drilling modes are revealed. • A novel experimental system for measuring rock properties during drilling is developed. • A cutting mechanics model is established to analyze the failure mechanisms in drilling. Drilling failure is a key factor limiting the effectiveness of surrounding rock identification during coal roadway drilling. While most studies focus on the failure mechanisms of large-scale drilling projects, limited attention has been given to small-sized drill bits, such as rock bolt drill bits. This study, based on the use of a two-wing polycrystalline diamond compact (PDC) drill bit in coal roadways, developed a novel experimental system to detect rock mass properties during drilling. Drilling tests were conducted on specimens with varying uniaxial compressive strengths to analyze the failure characteristics under F t - n and V - n drilling modes, revealing the underlying failure mechanisms of PDC bolt drilling in coal roadways. The results show that in the F t - n mode, higher rotational speed and thrust increase the likelihood of failure, particularly in rocks with lower uniaxial compressive strength. Failure is preceded by a gradual reduction in drilling speed and an increase in torque, driven by reduced rock-breaking energy and increased friction energy. In the V - n mode, higher drilling speed combined with lower rotational speed makes rocks with higher uniaxial compressive strength more susceptible to failure. In this case, failure is indicated by a sharp increase in thrust and torque, leading to friction energy buildup. Additionally, the reliability of the findings was validated through chip particle size distribution and cutting depth measurements. This study provides new insights into the failure behavior of small-diameter PDC bits, with implications for both engineering applications and future research directions. [ABSTRACT FROM AUTHOR]

A new hybrid steel-PFRP (Pultruded Fiber-Reinforced Polymer) bolted joint stiffened by steel plates is proposed in this paper to improve the joint efficiency for hybrid steel-PFRP lattice structures. The performance of the new steel-stiffened hybrid steel-PFRP joint (SHJ) was investigated and compared with that of ordinary steel-PFRP bolted joint (OBJ) using finite element method (FEM) and experimental test. In the numerical simulations, three-dimensional (3D) progressive damage joint models were developed and validated by joint tests, in which damage was investigated by employing Hashin failure criterion for PFRP part. Moreover, full-scale structural tests were also performed to further calibrate the performance of SHJ and OBJ in hybrid steel-PFRP lattice structures. The results from both joint level and structure level indicate that the performance of SHJ including ultimate bearing capacity, stiffness and joint efficiency is prominently superior to that of OBJ. SHJ is feasible and effective for application in hybrid steel-PFRP lattice structures. Parametric studies on SHJ were further conducted. The influences of the geometric parameters, such as the end distance to bolt diameter ratio (e/d) and the PFRP width to bolt diameter ratio (w/d), on the failure mode of SHJ were also discussed with the validated 3D progressive damage models. • A new stiffened steel-PFRP hybrid joint (SHJ) with better mechanical performance compared with ordinary joint was proposed. • Steel-PFRP lattice column adopting SHJ can achieve strong joint / weak member design concept. • The factors affecting the failure mode of SHJ were analyzed with finite element models. • The value of end distance to bolt diameter ratio and width to bolt diameter ratio for bearing failure of SHJ was suggested. [ABSTRACT FROM AUTHOR]

• An evaluation method of rockburst prevention effect for anchoring rock masses is presented. • The proposed method provides a quantitative basis for the optimization of rockbolt parameters. • The rockburst prevention effect by anchoring is negatively correlated with excavation damage. • Anchorage can compensate for the damage of rock mass to assist in rockburst prevention. • Rockbolts with a large-diameter and densely spacing is conducive to improving prevention effect. Anchoring rock masses is a commonly applied measure to prevent rockburst, whereas many deep tunnels still encountered rockburst after anchoring with rockbolts. Currently, the absence of suitable evaluation methods impedes the timely grasp and improvement of the rockburst prevention effect. This paper first investigates the alterations of rockburst pit depths before and after anchoring in three deep tunnels. The results indicate that the potential rockburst pit (PRP) depth exhibits two mitigation trends, i.e., "From small to none" and "From large to small". Subsequently, the analysis model of PRP depth after anchoring and the quantitative evaluation method of prevention effect are presented. In this method, the evaluation of prevention effect is based on the decrease rate of PRP depth after anchoring, which is calculated after obtaining parameters associated with rock mass properties, geostress, excavation damage and rockbolts. Furthermore, the variation of PRP depth after anchoring and the rockburst prevention effect under different excavation damage and rockbolt parameters are quantitatively analyzed. It is found that the prevention effect is negatively correlated with excavation damage. Specifically, when the damage is minor, a smaller PRP depth is observed, and the rock mass strength is significantly enhanced after anchoring, leading to a noticeable shallowing or even disappearance of PRPs. In such cases, relying solely on anchor support can achieve good prevention effects. Conversely, when excavation damage is severe, the reduction in PRP depth after anchoring is quite limited, necessitating the implementation of more measures. In addition, the application of large-diameter and densely spaced rockbolts contributes to diminishing the PRP depth and improving the prevention effect. [ABSTRACT FROM AUTHOR]

To control the asymmetric failure of tunnel surrounding rock and lining structure caused by anisotropy of layered soft rock, a study was conducted on the directional support effect of rock bolt under varying large deformation grades in three typical layered soft rock tunnel sections of the Jiuzhaigou-Mianyang Expressway. Initially, based on statistical analysis of maximum deformation and strength–stress ratios in typical tunnels, the deformation grades of layered soft rock tunnel were categorized into slight, moderate, and severe grades. Subsequently, model tests with a 1/50 scale ratio were conducted to investigate the effect of rock bolt directional support on the asymmetric deformation and stress of surrounding rock and lining structures under different large-deformation grades. Furthermore, numerical simulations were employed to verify the accuracy and rationality of rock bolt directional support. Study found that the asymmetric failure of layered soft rock tunnel mainly occurs where the tunnel contour line intersects the bedding plane, due to the combined influence of geo-stress field distribution and the orientation of soft bedding. This asymmetric characteristic phenomenon becomes more apparent as the large-deformation grade increases. Nevertheless, rock bolt directional support can effectively mitigate asymmetric failure in layered soft rock tunnels and enhance control over the anisotropic behavior of the surrounding rock. [ABSTRACT FROM AUTHOR]

Anisotropic rock has a very different failure mechanism from isotropic rock, and the layers significantly influence the mechanical properties and failure process of surrounding rock. In this study, the bedding plane structure was coupled with the proposed Voronoi grain-based breakable block model (VGBBM) to characterize the layered hard rock, and a simple and effective parameter calibration method was proposed to conduct uniaxial and triaxial compression tests. The numerical results show that the VGBBM can effectively capture the adaptive fracture process under the interaction between the bedding plane and the rock matrix. With increasing layer angle, the following failure modes sequentially occur: matrix dominated (type I), mixed matrix-bedding plane (type II), bedding plane dominated (type III), and type II again. The reasonable range for the strength reduction factor is 0.6–0.8. Under different layer angles, the transition of the failure mechanism controlled by the confining pressure is significantly different. Moreover, the simulation of the interaction between rock and bolts reveals that the confining pressure and reinforcement angle significantly affects the reinforcement effect. This study provides useful insights for the stability analysis of layered surrounding rock and optimization of the support design. [ABSTRACT FROM AUTHOR]

Determining the axial load transfer mechanism of rock bolts under various conditions is paramount for ensuring efficient reinforcement in rock structures, advancing our understanding of rock support and ability to design robust engineering solutions. This paper presents the results of an experimental study aimed at investigating the factors affecting axial load transfer mechanisms in fully encapsulated rock bolts including embedment length, mechanical characteristics of bonding materials, and host rock conditions. The results show that increasing the embedment length improves the pullout capacity, but only up to a critical length, beyond which the ultimate strength and bond stress distribution remain constant. Amongst the mechanical characteristics, shear modulus of the bonding materials was found the most significant factor influencing axial load transfer and the bond stress distribution. Compressive strength of bonding materials, which is commonly used to assess performance, should not be the only factor considered, as shear properties were found more representative. The expansion characteristics of the bonding agents were also found to be effective in improving pullout performance. The study also provides a detailed explanation of how the mechanical properties of host rocks affect the pullout capacity of bolts. Specifically, it states that greater stiffness result in higher pullout strength. [ABSTRACT FROM AUTHOR]

The incidence of multiple impact events is frequently linked to rockburst phenomena in subterranean roadways. An in-depth investigation and analysis of the deterioration process of surrounding rock and the performance of bolt support systems under repeated impact loads are imperative. This research employs an innovative drop hammer impact simulation apparatus to develop a similar model of an impact roadway. A comparative analysis was conducted on the macroscopic failure processes of surrounding rock, the distribution of dynamic compressive stress, the evolution of dynamic acceleration, and the dynamic force variation characteristics of bolts under varying support conditions—namely, no support, non-preloaded bolts, and preloaded bolts—by incrementally applying impact energy from above. The findings are as follows: in comparison to unsupported roadways, bolt support systems significantly reduce roof delamination and impact-induced roof collapse, thereby augmenting the energy threshold necessary for the failure of the surrounding rock. The elevated compressive stress within the surrounding rock, subjected to progressively increasing impact energy, demonstrates a transfer effect, transitioning from the roof to the ribs, floor, and deeper strata. Furthermore, the peak acceleration experienced by the surrounding rock escalates with increasing impact energy, and the implementation of bolt support improves the rock’s capacity to endure higher acceleration levels. Repeated impacts result in cumulative damage to bolt support systems. By increasing the preload of the bolts, the compressive stress of the surrounding rock can be more evenly distributed, thereby suppressing acceleration growth and reducing the load on the bolts. Roadway damage from repeated impact loads involves the gradual weakening of bolt support and instability of surrounding rock. Strengthening weak areas between bolts is essential for maintaining rock stability. Prompt reinforcement and the implementation of energy-absorbing support components can postpone the initiation of impact failure in the surrounding rock and enhance the overall resistance of the roadway to rockburst. These findings offer significant theoretical insights for the investigation of roadway damage and the design of support systems under conditions of multiple impact loads. [ABSTRACT FROM AUTHOR]

• Ultrasonic guided wave measurements require specialized instrumentation. • 5 MHz measurements on rock bolts with low-cost (USD 1110) equipment. • Narrowband excitation, averaging and filtering used to increase SNR. • Achieved propagation distance of 9 m equivalent to 9000 wavelengths. • Pre-amplification used to overcome internal noise in low-cost USB oscilloscope. Guided wave ultrasound offers the ability to inspect slender structures from a single transducer location. However, the propagation of guided waves is more complex than the propagation of bulk waves used in conventional ultrasonic testing, and the experimental equipment required is more sophisticated. Typical equipment is expensive and may limit research and industrial application. This paper investigates what can be achieved by using low-cost instrumentation for laboratory measurements. The application is the measurement of guided waves in rock bolts (cylindrical rods) at relatively high frequencies (5 MHz). The dispersive wave propagation requires the use of narrowband excitation signals. The use of a bench-top waveform generator and oscilloscope is compared to the use of a compact and low-cost USB oscilloscope, which includes an arbitrary waveform generator. The introduction of a pre-amplifier mitigated the poorer noise performance of the USB oscilloscope, and comparable results were obtained from the two setups. It is demonstrated that waves propagated 9 m in a free rock bolt, with 10 dB/m attenuation, could be detected and analyzed with a measurement setup costing approximately USD 1110. [ABSTRACT FROM AUTHOR]

• Expansion–friction structure installed on ordinary anchor cables were designed. • Energy absorbing structure of dual energy absorption characteristics were developed. • Mechanical evaluation indices of expansion–friction structures were proposed. • Expansion–friction energy absorption enhanced critical stress of roadway rockburst. The powerful impact generated by a rock burst in a coal mine roadway can easily cause ordinary steel strand anchor cables to break, detach, and deform. To address these issues, an expansion–friction energy-absorbing structure designed for installation on ordinary steel strand anchor cables was developed, establishing a novel type of energy-absorbing anchor cable. To investigate the macroscopic deformation characteristics and mechanical properties of the expansion–friction structure and evaluate its performance, static tests were conducted on a 5000 kN servo press. The research results indicate that this energy-absorbing structure possesses dual energy absorption characteristics, namely, plastic expansion deformation and frictional sliding energy dissipation. The deformation characteristics manifest as symmetrical plastic deformation and stable friction deformation and exhibit strong controllability, repeatability, and energy absorption stability. In general, as the cone angle and expansion increase, the deformation of the energy-absorbing structure becomes more pronounced. From the perspective of constant resistance, as the cone angle and expansion increase, the constant resistance gradually increases. The stability of the constant resistance is best at cone angles of 10° and 15° and expansion amounts of 0.5 and 1.5 mm, respectively. Based on the principle of energy absorption, an evaluation index for the mechanical performance of the energy-absorbing structure is proposed. The analysis revealed that the constant resistance, unit displacement energy absorption, and total energy absorption ranges of the expansion–friction energy-absorbing structure are 139.60 to 652.88 kN, 0.41 to 0.61 kJ/mm, and 34.25 to 149.25 kJ, respectively. Therefore, it exhibits good static load control and dynamic load energy absorption mechanical performance. This structure can reduce the probability of impact failure that arises with ordinary anchor cables, thereby improving the stability control effect of energy-absorbing and anti-impact anchor cables on the rock surrounding the roadway and achieving effective control of roadway rock bursts. [ABSTRACT FROM AUTHOR]

• Anchor strength varies with the geological conditions in soft rock. • Dynamically design the pre-tension force to avoid tension failure and overestimation of pre-stress. • Effective pre-stress differs from the pre-tension force, declining after locking. • A deformation prediction model considering geology and support is established. • A dynamic design system facilitates the adjustment of support parameters in an economical and safe manner. The design of active–passive support parameters traditionally relies on rock mass classification. However, the ultimate load of anchors in soft rock is significantly constrained by geological conditions and is not considered in rock mass classification methods. Consequently, the constant pre-tension force for the same rock mass classification poses a risk of anchor system tension failure. The paper introduces a dynamic design system for active–passive combined support to bridge this gap, considering the interplay between geological conditions and pre-tension force. The system established a predictive model for pre-tension force under geological conditions using on-site monitoring data and B-P neural networks. Considering the instantaneous loss during pre-tension force locking to determine effective pre-stress, it then utilized numerical simulation, on-site monitoring, and B-P neural networks to correlate pre-stress, geological conditions, passive support parameters, and rock deformation. Support parameters were subsequently adjusted based on predicted rock deformation in a predetermined optimization sequence. The system was taken to practical application in the Muzhailing Highway Tunnel. The results indicated that the predictive model for designed pre-tension force values achieved goodness of fit of 0.701 and mean absolute percentage error (MAPE) of 6.51%, guiding pre-tension force design. Additionally, a rock deformation prediction model, considering effective pre-stress and constructed using numerical simulation and field-measured data, attained an R-squared value of 0.947 and an MAPE of 2.76%. Practical application on three cross-sections demonstrated a high proportion of anchor holes reaching the designed pre-tension force (94%, 91%, and 97%, respectively), preventing anchoring system failure during tensioning. Predicted rock deformation values under designed support parameters closely match actual values, with percentage errors of 1.13%, 6.73%, and 2.15%, respectively. These outcomes contribute valuable insights to the design methodology of active–passive combined support in soft rock tunnels. [ABSTRACT FROM AUTHOR]

• Axial behavior of protective sheathed rock bolts was investigated. • Plastic sheath modifies the load transfer mechanism and performance of rock bolts. • Bond stress distribution along the encapsulation length was analyzed. • The failure pattern of protective sheathed rock bolts was examined. • Failure at the grout-sheath interface was found to be the primary failure mode. Understanding the axial load transfer mechanism of rock bolts under diverse conditions is essential for optimizing reinforcement in rock structures, advancing our comprehension of rock support, and facilitating the design of robust engineering solutions. This paper reports the outcomes of an extensive experimental investigation, focusing on the axial behavior of protective sheathed rock bolts employed in corrosive environments, assessed through pullout tests. Three distinct testing setups were designed to evaluate comprehensively the performance of these rock bolts in various scenarios. The results indicated that the failure characteristics and axial behaviors of sheathed rock bolts differ significantly from conventional counterparts. The findings revealed two primary failure modes in sheathed rock bolts: bolt rupture and slip at the grout-sheath interface, based on the testing arrangement and encapsulation length. The lack of adhesion and interlocking at the grout-sheath interface prevents shear stress at the bolt-grout interface from reaching its maximum potential strength, resulting in grout damage manifesting as circumferential cracks. This, in turn, initiates crack formation, reducing the system's bond strength. Additionally, it causes slip at the grout-sheath interface to occur at lower pullout loads. It can be inferred that the inner surface of the plastic sheath lacks the necessary structural integrity to withstand high loads, significantly impacting bond stress distribution and failure modes. The results demonstrate that the protective sheath remains intact up to an axial displacement of 28 mm, irrespective of the testing configuration. Additionally, it was observed that the maximum bond stress at the bolt-grout interface falls within the range of 6–8.7 MPa, which is below the shear strength of the grout. Consequently, achieving failure at the bolt-grout interface is not feasible. [ABSTRACT FROM AUTHOR]