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This study examined the influence of the effective embedment depth hef of undercut anchors and the diameter of their heads on the formation of the so-called cone failure angle α. Cone failure formation during simulated anchor pull-out tests was analyzed numerically using the Finite Element Method (FEM) with the ABAQUS software and the XFEM algorithm. The analysis was conducted for three sizes of undercut anchor heads and four embedment depths. The numerical analysis results were compared with field test results obtained during pull-out tests of anchors installed in a rock medium (sandstone). Good agreement was observed between the numerical and field test results. The results of the numerical study are highly consistent with those obtained during the field survey. Moreover, they align closely with findings from previous numerical studies conducted by members of the research team, as presented in earlier publications. For the assumed simulation and field test conditions (sedimentary rocks, gray sandstone), no clear correlation was found between the embedment depth or the anchor head diameter and the value of the cone failure angle in the initial phase of the failure zone development. This result contrasts with certain findings reported in the literature. Many existing studies on anchor bolts focus on material properties or load-bearing capacity, but lack an in-depth analysis of how anchor depth influences the geometry of the failure cone. This research addresses that gap, providing valuable insights with practical implications for design codes and safety evaluations. [ABSTRACT FROM AUTHOR]

Anchor bolts, such as rock bolts and concrete anchors, are widely used in civil, geotechnical, and mining engineering for anchorage and ground support. They are used in retaining walls, dry docks, dams, mines, and prestressed concrete structures. Evaluating the grouting condition of anchor bolts is essential to ensure the safety of these applications. Spectrum techniques have been used to develop non-destructive methods for estimating the grouting quality of grouted anchor bolts. The spectrum methods include fast Fourier transform, time–frequency analysis, wavelet transform analysis, and empirical mode decomposition. In this study, we introduce the parameter-optimized variational mode decomposition (VMD) method for the spectrum analysis of impact echo signals of anchor bolts. This method overcomes the difficulty of conventional spectrum methods that cannot separate highly coupled natural modes for advanced analysis. The parameter-optimized VMD method enables the generation of a new evaluation index for quantifying bolt grouting conditions, which has the potential to significantly enhance the quality evaluation of anchor bolts compared with conventional analysis of natural frequencies. This study uses impact response to establish a new benchmark for the integrity diagnosis of anchor bolts, paving the way for more accurate and reliable safety assessments. [ABSTRACT FROM AUTHOR]

The utilization of reinforcement cage underreamed anchor bolts is prevalent in the reinforcement of foundation pit engineering, but there are few studies on the reinforcement of soft rock slopes and the influence of its parameters on slope stability. This study combines laboratory tests to analyze the mechanical properties of reinforced and non-reinforced bolts with finite element analysis to model the anchorage support system in soft rock slopes. Key parameters affecting the stability of the slope, such as bolt diameter, expansion section diameter, and anchorage depth, were considered. The findings indicate that the inclusion of a reinforcement cage leads to a more rational distribution of mechanical properties, promoting even axial force distribution to the grouting medium. An increase in bolt diameter enhances slope stability, while the expansion section diameter has minimal impact when a strong bond exists between the grouting body and the rock mass. However, in the absence of such bonding, increasing the expansion section diameter significantly improves slope stability. Deeper anchorage also correlates with higher stability, though the rate of increase in safety factor slows as the anchorage depth approaches the critical slip plane. In conjunction with field application, the research outcomes can exert a certain directive impact on practical engineering and can be used as a reference for the design method of bolt support for soft rock slope [ABSTRACT FROM AUTHOR]

Rock bolting in underground environments is used for different fundamental reasons, including suspending potentially loosened blocks, clamping small wedges together, inducing a protective pressure arch along the contour of excavated voids to improve the self-supporting capacity of the ground, and providing passive pressure in integrated support systems. In this study, we describe a testing procedure that was developed to investigate the grouted annulus of a rock bolt using a low-cost investigation method. This diagnostic technique was based on the dynamic response of the system, where mechanical vibrations were induced within the rock bolt and the response was recorded by using geophones/accelerometers on the protruding element of the bolt (the collar and head). The collected signal was then processed to estimate the spectral response, and the amplitude spectrum was analyzed to detect the resonance frequencies. A 3D finite element model of the rock bolt and grouting was established to simulate the quality of the coupling by varying the mechanical properties of the grouting. The model's response for the studied geometry of the rock bolt suggested that a poor quality of grouting was usually associated with flexural modes of vibration with a low resonance frequency. Good-quality grouting was associated with a frequency higher than 1400 Hz, where the axial vibration was mainly excited. Our analyses referred to short rock bolts, which are usually adopted in small tunnels. The interpretation of the experimental measurements assumed that the spectral response was significantly affected by the quality of the grouting, as demonstrated by the modeling procedure. The resonant frequency was compared with the results of the model simulation. The method was used to test the quality of rock bolts in a small experimental tunnel carved from andesite rock in Chile. Low-cost shock sensors (piezoelectric geophones) with low sensitivity but a wide frequency band were used. The main research outcome was the development of a reliable method to model the dynamic response of rock bolts in mines or for experimental applications in tunnels. Albeit limited to the current specific geometries, the modeling and testing will be adapted to other anchor/bolt options. [ABSTRACT FROM AUTHOR]

In response to the problem of debonding failure of anchor rods crossing coal-rock interfaces in coal-rock roadways in Guizhou Province, China, based on bolt pull-out tests, the failure characteristics and bearing characteristics of coal-rock composite anchor bodies under different height ratios of rock to coal were analyzed. The results show that the bearing capacity of coal-rock composite anchor bodies gradually weakened with the height (proportion) of the coal, and that the load-bearing strength of the composite anchor body became closer to that of pure coal. Numerical simulation experiments were conducted using ABAQUS to reveal the debonding mechanism of coal-rock composite anchor bodies under different height ratios of rock to coal from the perspective of differences in coal-rock cooperative failure. The main stages included stress concentration zone expansion; coal failure and debonding while the rock still had bearing performance; the rock reaching critical gradual debonding; and residual strength. In addition, a load transfer model of bolts on coal-rock composite anchor bodies under different height ratios of rock to coal was constructed. This model could derive the pull-out load and displacement curves of coal-rock composite anchor bodies with different height ratios of rock to coal, which showed the same trend as the pull-out test and numerical simulation results and had high credibility. These findings can guide further theoretical research, engineering design, and on-site application of bolt support in coal-rock roadways. Highlights: Load bearing capacity of the composite anchor body differs from full-coal (or full-rock). There is a time differential development of the destruction between coal and rock. A load transfer model for bolt pull out on coal rock composite anchor was constructed. [ABSTRACT FROM AUTHOR]

This Suggested Method proposes impact tests to determine selected properties of full-scale rock bolt assemblies subject to an axis-aligned impact force. These properties include the stiffness of the bolt assembly, the rise time, the tensile strength, the ultimate displacement, and the energy absorption of the rock bolt assembly. These properties may be used to design or select ground support for burst-prone ground conditions. This Suggested Method is limited to the mass freefall impact test method. It is performed using a test frame in the laboratory. The Method specifies the requirements for the testing apparatus and measurement sensors, the test procedures, the data processing methods and the reporting items. Highlights: A Suggested Method is proposed for dynamic tests of full-scale rock bolt assemblies by a mass freefall impact Properties to be determined include energy absorption, ultimate displacement, average load, etc. The Method specifies the requirements to the testing apparatus, measurement sensors, test procedures, and data processing [ABSTRACT FROM AUTHOR]

Bolt is a safe and dependable engineering anchoring technique, and the stress transfer mechanism of the bolt has been the subject of research. Based on the bolt–grout interface deformation coordination relationship, this paper establishes physical equations using the Mindlin displacement solution and deduces the theoretical distribution of shear stress along the anchor length for fully grouted bolts. This paper also conducts an indoor bolt pullout test to verify the accuracy of the calculation results. The results show that when the bolt is subjected to tensile load, the shear stress shows a tendency to increase sharply and then decrease slowly. As the load increases, the shear stress also increases, with the extreme points gradually moving away from the pullout end. The distribution of shear stress is also directly related to the anchor length and diameter. By controlling the ratio of these two parameters, the shear stress on the bolt can be reduced by 50%–70%. Meanwhile, the ratio of the elastic modulus of the rock mass Ec to the elastic modulus of the bolt Es, Ec/Es, has a significant effect on the distribution of shear stress. The shear stress model established in this paper matches well with the experimental data, with a fitting coefficient R2 ≥ 0.9, which demonstrates high accuracy and applicability. In engineering practice, by taking into account the specific conditions of the construction site, the model developed in this study can be utilized to choose bolts of suitable size, thereby optimizing anchorage efficiency. [ABSTRACT FROM AUTHOR]

Splitting grouting is widely used to reinforce unfavorable soil stratum. Inclined steel grouting pipe is a type of structure which can achieve splitting grouting in soil stratum. It has been successfully utilized in argillaceous sandstone stratum, but its application in loess stratum has rarely been studied directly. This research aims to compare and analyze the bearing capacity and effective anchorage lengths of inclined steel grouting pipes with anchorage lengths of 6 m, 9 m, and 12 m. Firstly, bearing capacity of inclined steel grouting pipe was compared with that of ordinary grouting pipe. Secondly, bearing capacity of inclined steel grouting pipe with anchorage lengths of 6 m, 9 m, and 12 m were compared and analyzed. Thirdly, effective anchorage lengths of inclined steel grouting pipe with anchorage lengths of 6 m, 9 m, and 12 m were compared and analyzed. Finally, inclined steel grouting pipe average cohesive strength along effective anchorage length section at the interface between cement grouting and soil stratum was compared with that of rock bolt. The field experimental results illustrated that: (1) The bearing capacity of inclined steel grouting pipe with anchorage length of 9 m increases 22.6% compared with that of ordinary grouting pipe. (2) Anchorage length is not a significant influence factor for bearing capacity of inclined steel grouting pipes in loess embankment slope, while anchorage length is a significant influence factor for modulus of load-displacement curves of inclined steel grouting pipes in loess embankment slope. (3) Effective anchorage length of inclined steel grouting pipe in loess embankment slope will be slightly increased when increasing anchorage length, while the ratio of effective anchorage length to total anchorage length will be decreased when increasing anchorage length. (4) Inclined steel grouting pipe average cohesive strength along effective anchorage length section at the interface between cement grouting and soil stratum is at least three times compared with that of rock bolt. [ABSTRACT FROM AUTHOR]

The impact of rock bolts on the mechanical behavior of nonpersistent joints, including the intricate interactions between the joints, rock bridges, and rock bolts, has received limited investigation despite their effectiveness in reinforcing rock mass discontinuities. In order to tackle this issue, a variety of normal stresses were applied during direct shear tests conducted on artificial rock-like specimens with nonpersistent joints, both bolted and unbolted. Meanwhile, to measure the deformation in the rock bridge and joint plane region, a set of strain gauges were implemented. The findings indicated that the local shear deformation-shear displacement curves, whether with or without rock bolts, can be categorized into five distinct stages. Application of the rock bolts on the nonpersistent joint plane resulted in making the following two important statements: (a) The rock bolts delay the shear stress transmission along the joint plane from the joint parts to the rock bridge area; (b) The rock bolts limit the dilatancy occurring in both the joint parts and at the rock bridge area. Furthermore, the shear displacement of the bolted nonpersistent joint specimen at the peak shear strength was found to be greater than that of the unbolted nonpersistent joint specimen indicating protection of the rock bridge by the rock bolts. Whether bolted or unbolted, the stiffness values seem to be the same for the nonpersistent joint plane for a selected normal stress; this observation is significantly different from that observed for the persistent joint plane. [ABSTRACT FROM AUTHOR]

Rock masses are formed through long-term, complex geological processes, and the presence of joints significantly reduces their strength and increases their deformation. Rock bolts effectively enhance the strength and stability of rock masses and are extensively utilized for reinforcement. According to field investigations, a significant portion of the damage to bolted rock masses stems from shear deformation at joint surfaces. Moreover, roughness affects friction and surface contact, thus influencing the shear behavior between rock and rock bolts. This study considers two crucial factors affecting the shear characteristics of bolted rock joints: joint surface roughness and normal stress. Using the Particle Flow Code discrete element numerical method, the Barton standard joint profile lines were input to establish numerical models of both unbolted and bolted rock joints for direct shear tests. Results reveal that the peak shear stress and stiffness of both unbolted and bolted rock joints increase with rising normal stress and joint roughness coefficient. The peak shear stress and stiffness of bolted rock joints are notably higher than those of unbolted ones, with a maximum increase of 17.5%. Crack development in bolted rock joints occurs in stages of rapid, slow, and stable development, whereas no distinct slow development stage is observed in unbolted rock joints. Additionally, micro cracks in both unbolted and bolted rock joints are primarily tensile cracks, originating around the joint surface and extending outward with increasing shear displacement. These findings offer valuable insights into the microscopic shear mechanics of bolted rock joints and provide practical references for engineering design and applications in rock reinforcement projects. [ABSTRACT FROM AUTHOR]

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

Automatically identifying mine and tunnel infrastructure elements, such as rock bolts, from point cloud data improves deformation and quality control analyses and could ultimately contribute to improved safety on engineering projects. However, we hypothesize that existing methods are sensitive to small changes in object characteristics across datasets if trained insufficiently, and previous studies have only investigated single datasets. In this study, we present a cross-site training (generalization) investigation for a multi-class tunnel infrastructure classification task on terrestrial laser scanning data. In contrast to previous work, the novelty of this work is that the models are trained and tested across multiple datasets collected in different tunnels. We used two random forest (RF) implementations and one neural network (NN), as proposed in recent studies, on four datasets collected in different mines and tunnels in the US and Canada. We labeled points as belonging to one of four classes—rock, bolt, mesh, and other—and performed cross-site training experiments to evaluate accuracy differences between sites. In general, we found that the NN and RF models had similar performance to each other, and that same-site classification was generally successful, but cross-site performance was much lower and judged as not practically useful. Thus, our results indicate that standard geometric features are often insufficient for generalized classification of tunnel infrastructure, and these types of methods are most successful when applied to specific individual sites using interactive software for classification. Possible future research directions to improve generalized performance are discussed, including domain adaptation and deep learning methods. [ABSTRACT FROM AUTHOR]

Slope instability is a complex geological phenomenon triggered by heavy rainfall, earthquakes, tectonic forces and anthropogenic activities. Unplanned excavation of rock slopes for the development and maintenance of infrastructure such as highways, railways, and buildings in hilly regions plays a significant role in causing slope instability. The present work conducts a comprehensive stability assessment of rock slopes along the national highway (NH-44) section of the Ramban district of Jammu and Kashmir. The kinematic investigation was carried out to determine the different modes of failure of road-cut slopes, and two main modes were found: planar and wedge. Various empirical classifications have been applied for the assessment of slope stability, like geological strength index (GSI), slope mass rating (SMR), Chinese slope mass rating (CSMR), and continuous slope mass rating (CoSMR). Numerical analysis through universal distinct element code (UDEC) has been conducted to evaluate the stability of four critical rock slopes under static and dynamic loading conditions. Modelling results have provided insights into the failure mechanism, and based on these findings, remedial measures have been proposed. Three (L-1, L-3, and L-13) out of four slopes were determined to be unstable under static conditions, with factors of safety (FoS) < 1.2 and under dynamic conditions, two slopes were unstable with FoS < 1.0. However, one (L-8) slope was found to be stable under both static and dynamic conditions, with FoS 1.29 and 1.12, respectively. Installing rock bolts reduced displacement for slopes L-1 and L-13, with reductions of 11.86% and 21.05% under static conditions and 4.09% and 18.75% under dynamic conditions, respectively, while L-3 does not stabilise even after installation of rock bolts. [ABSTRACT FROM AUTHOR]

Weakly cemented soft rock roadways are prone to severe roof lowering and floor heave, especially under strong mining. The failure of bolt (cable) supports is significant. Theoretical analysis, on-site monitoring, and numerical simulation were used in the work to solve this problem. Firstly, the work explored and obtained the failure characteristics of bolts (cables) in the weakly cemented gob-side entry. The entry was mainly composed of tension fractures and tension–shear fractures in the free section, supplemented by the shear failure of floor and roof. The failure process of bolts (cables) was explored. The insufficient pre-tightening force of bolts (cables) was the internal cause of the failure mechanism of supports based on the on-site monitoring results. The large deformation of roof sinking beyond the extended range of support materials was the external cause of the failure mechanism of support. We proposed the concept of rapid support with high pre-tightening bolt–cable synergistic deformation. The support required the deformation of bolts (cables) to be coordinated with roof deformation. A design for rapid support with bolts and cables was formed. The pre-tightening force of the weakly cemented gob-side entry was optimized based on the numerical simulation. Finally, the on-site application of our method could reduce roadway deformations and the failure of bolts (cables). Highlights: In this paper, the failure patterns of bolt (cable) in weakly cemented gob-side entry were investigated, which mainly consisted of tension failure and tension-shear failure in the free section, supplemented by shear failure of the tray and roof. It was found that the breaking depth of bolts and cables in the roof is about 0.8~1.2m, which is located in the development area of the coal-rock interface fracture zone. The above research provided on-site measurement basis for the failure process and mechanism of roadway support. This paper analysed the failure process of bolt(cable) tensile fracture, tension-shear fracture, and shear fracture at the tray, and based on indoor experiments and on-site monitoring, it was found that the low pre-tensioning force of the bolt(cable) led to insufficient active support effect, which was the internal reason for the support failure. The external reason was that the extension amount of the bolt and cable was less than the lowering of the roof. This study proposed the concept of high pre-tensioning force bolt (cable) deformation synergistic support for the failure mechanism of the above bolt (cable) support, including two aspects: bolt (cable) and surrounding rock deformation synergistic support and high pre-tensioning force active support. The former required that the tensile deformation of the bolt (cable) be adapted to the lowering deformation of the roof, in order to avoid the failure of the bolt (cable) due to insufficient elongation; the latter adopted the high pre-tensioning force active support, which reduced the deformation of the surrounding rock by placing the bolt (cable) in a high supporting force stage. This study proposed a new support design method based on the actual anchoring characteristics of support materials, which can effectively solve the problem of large differences between theoretical strength verification and actual strength. At the same time, combined with the synergistic support design scheme of bolt and cable deformation, a fast support design method of bolt and cable suitable for weakly cemented soft rock roadways was formed. Based on numerical simulation, the roof stress distribution under different pre-tightening force conditions of the bolt (cable) was obtained, and the optimum pre-tightening force range was found. After on-site application, the effect was significant. [ABSTRACT FROM AUTHOR]

Hard rock formations with layered, anisotropic geological structures are rather common in Norway. The design of tunnel rock support under such ground conditions has been traditionally done with an empirical approach and assisted with engineering rock mass classification. In most cases, rock stability has been achieved with the use of fiber-reinforced sprayed concrete combined with rock bolts, sometimes supplemented with ribs of reinforced sprayed concrete (RRS) and bolt spiling. However, the discontinuous character and more complex ground behavior of layered rock can lead to design challenges as experienced during the construction of the new Skarvberg highway tunnel in Northern Norway. A significant portion of the tunnel exhibited consistent overbreak, delamination problems and a tunnel failure. In this article, the ground behavior and rock support performance at different locations of the tunnel are investigated to find a basis for design optimization of rock support under similar ground conditions. For this purpose, a thorough site investigation program was carried out, which formed the basis for further assessments and analyses with a hybrid design methodology and the numerical code UDEC (Itasca). As a result, the main challenges of classification systems to capture ground behavior and derive optimal support design in layered rocks were identified. As such, this study has investigated design optimization possibilities, which resulted in the development of, among others, a specific ground behavior classification for layered grounds and a new, optimized RRS-support concept for layered rock masses of very poor quality (e.g., Q ~ 0.1–1). Highlights: Classification systems have limitations to address ground behavior and support design in layered rock masses of poor quality. Optimal designs of tunnel rock support in layered rock masses of poor quality require a comprehensive characterization of the ground conditions. Hybrid design methodologies can address ground behavior and utilize this input to derive optimal rock support in layered rock masses. A new concept of reinforced ribs of sprayed concrete has been developed and performed satisfactorily in numerical models for layered rock masses. A hybrid method for the design of rock support in layered rock masses of poor quality can help to a significant reduction in rock support consumption. [ABSTRACT FROM AUTHOR]

The rock-socketed pier anchored by inclined anchors (RPIA) is a new type of foundation developed by combining a rock-socketed pier and inclined anchors. Current research on RPIA is relatively limited, and the impact of design parameters on its bearing performance remains unclear. To investigate the uplift-bearing performance of RPIA, a finite-element model that considers the nonlinear properties of materials and multidirectional interactions was developed and verified. Based on this model, numerical simulations were performed on twenty-five RPIA that were designed using the L25 orthogonal array proposed by the Taguchi method, and the uplift load–displacement curve for each RPIA was obtained. Based on the interpretation of the elastic limit, uplift resistance, initial stiffness, and the ductility index for each simulated RPIA, the sensitivity of each factor was examined by analyzing the signal-to-noise ratio and variance. The results indicated that rock strength and pier diameter were the main factors determining the uplift performance of the RPIAs, while the angle of inclined anchors is the most influential factor affecting the ductility of RPIA. The primary role of the inclined anchor is to reduce the extraction of the pier after failure of the side resistance between the pier and rock mass, thus significantly enhancing the ductility of the uplift-loaded RPIA. The addition of reinforcements around the connection joints of the pier and anchors may prevent concrete failure and to fully execute the role of inclined anchors. [ABSTRACT FROM AUTHOR]

The vibration waves generated by pressure fluctuations can substantially impair and jeopardize the structural integrity of roadway anchorage within adjacent rock formations, thereby presenting a significant risk to the safety and operational efficiency of mining activities. In order to address this issue and elucidate the response characteristics of roadway-anchored surrounding rock subjected to P-wave and S-wave influences, this study employs a roadway that is experiencing actual impact instability within a mine situated in Xinjiang as the engineering context. The synchrosqueezing wavelet transform, enhanced by a Butterworth filter, is utilized to isolate and filter seismic wave data, thereby facilitating the extraction of time-frequency signals corresponding to both P-waves and S-waves. Subsequently, a dynamic numerical model is developed to simulate the propagation of these vibration waves. An analysis of the dynamic behavior and response characteristics of P-waves and S-waves is performed, focusing on their interaction with roadway anchoring within the surrounding rock at various stages of propagation. The results indicate that weak rock and plastic zones can absorb vibrational waves, with S-waves exhibiting a stronger absorption effect than P-waves. S-waves contribute to increased stress and displacement in the surrounding rock, leading to the accumulation of elastic energy and an expansion of the plastic zone. The rapid fluctuations in the axial force of bolts along the roadway, caused by S-waves, can result in instability within the roadway. The research findings possess considerable reference value and practical applicability for the design of anti-scour support systems in roadways. [ABSTRACT FROM AUTHOR]

The Haidong Tunnel is one of the four soft rock tunnels of the Central Yunnan Water Diversion Project (CYWDP), where large deformation hazards of soft rock occur frequently, which seriously affect construction safety. The effect of highly prestressed anchor cable support was studied based on the active support test in the No. 3 branch tunnel of Haidong Tunnel. Firstly, the geological conditions and failure causes were analyzed on the basis of the results of geological survey, in-situ test, and rock laboratory test. Then, the Mohr circle form of the highly prestressed anchor cable active support theory for the support of bedded rock mass was given in combination with the excavation compensation method. It is considered that the prestress active compensation value required for the bedded rock mass is larger than that for the homogeneous rock mass. The deformations of rock mass under both passive and active supports were analyzed by numerical simulations. Furthermore, the 'pressure bubble' mechanical model for anchor cable support of bedded rock mass in Haidong Tunnel is given. Field monitoring results show that the highly prestressed anchor cable support can control rock mass deformation well, with a maximum deformation of about 200 mm. The prestressed anchor cable is effective in the bedded stratum, which makes the stress of rock mass uniform and reduces the risk of failure of steel arches due to local bias. Meanwhile, the expansion of plastic zone was efficiently controlled, which is of positive significance for the overall stability of rock mass. [ABSTRACT FROM AUTHOR]

In order to investigate the failure mechanism of the reinforced muddy soft rock under the influence of the hydration reaction when ground water is present, a series of confined compressive tests and Acoustic Emission (AE) recordings were conducted subject to various moisture content levels and lateral confining stresses. It was found that the failure modes of the reinforced rock specimen were affected by the moisture content level and the lateral stress σ2 in a way that the load bearing capacity of the reinforced rock would increase with the lateral stress σ2 but decrease as the moisture content increased. An increase in the moisture content would reduce the extent of the influence of the lateral stress on the load bearing capacity of the reinforced rock. In addition, much less AE counts were recorded when the moisture content increased indicating that the crack initiation and propagation in this case was easier due to the reduction of the required external input energy. With increasing moisture content, the failure mode of the specimen gradually changes from sudden and brittle to progressive and ductile. Moreover, the hydration reaction became more significant leading to a complete debonding between the grout and the rock. Consequently, the reinforcement provided by the rock bolt to the rock became negligible. [ABSTRACT FROM AUTHOR]

Fully grouted rock bolts are widely used in mining, tunneling, and pit support, and thus the study of their anchorage performance is beneficial for optimizing the anchorage system design. In this study, an FDM‐DEM coupled numerical model is established to simulate the whole process of rock bolt pullout test and to investigate the failure mechanism of fully grouted rock bolts. The accuracy of the model is verified by comparison with existing laboratory test results. Virtual experiments are conducted on different models by eliminating the anchor plate, changing the layered rock strata condition, and adding bolts. The results show that the presence of an anchor plate will reduce tensile stress to restrain the rupture of surrounding rock and thus improve the strengthening effect. Due to the different bond strength and tensile strength of the soft and hard rock mediums, the layer sequence of the rock strata affects the maximum pullout force. The upper‐soft and lower‐hard composite rock strata (S‐HCR) exhibits single‐cone damage while the upper‐hard and lower‐soft composite rock strata (H‐SCR) exhibits double‐cone damage. The superposition effect of the anchor group on the stresses and displacements is the reason leading to the reduction of the maximum load‐bearing capacity of the rock bolts. [ABSTRACT FROM AUTHOR]

Anchor rock bolts are among the essential support components employed in coal mine support engineering. Measuring the axial load of the supporting anchor bolts constitutes an important foundation for evaluating the support effect and the mechanical state of the surrounding rock. The existing methods for measuring the axial load of rock bolts have difficulty meeting the actual demands in terms of accuracy and means. Therefore, we propose a novel inverse method for determining the axial load of rock bolts. On the basis of the dynamic relationship between the axial load of the anchor bolt and the strain of the plate, a calculation model for the inverse analysis of the axial load from the plate strain is presented, and it is verified and corrected through finite element analysis and indoor physical experiments. By combining the calculation model with the digital image correlation method, a low costinversion of the axial load of the anchor bolt in actual support engineering is achieved. The experimental results demonstrate that the average errors of the load inversion of anchor bolts in three different states via the theory and method proposed in this paper are less than 8.8% (4 kN), 3.6% (3.2 kN), and 14.7% (5.5 kN), respectively, and the average error of the axial load of the rock bolts in the proposed method is only 4.23 kN. It possesses relatively high accuracy and can be effectively applied in the actual production processes of mines. [ABSTRACT FROM AUTHOR]

Understanding the shear characteristics and acoustic emission features of bolted joints is crucial for the optimization of support systems and disaster early warning. In this paper, a series of shear tests on rock joints using both full-length anchorage and partial anchorage methods were conducted. The evolving patterns of shear mechanical characteristics and acoustic emission features of bolted rock joints were obtained, elucidating the influence of anchorage methods and revealing the shear failure mechanisms of joints under different anchorage lengths. The results indicate that the "pin effect" of the bolt can be rapidly mobilized in the full-length anchorage compared to the partial anchorage method. The full-length anchorage exhibits higher peak shear stress and fracture shear stress, with maximum differences of 0.38 MPa and 0.08 MPa, respectively, when contrasted with the partial anchorage method. The deformation range of bolts in the partial anchorage method approximately doubles that observed in the full-length anchorage. Acoustic emission feature parameters exhibit a good correspondence with shear stress curves, and their evolution suggests that the most significant damage to bolted joints occurs at the shear stress peak, with the highest energy release observed when bolts fail. Under both partial anchorage and full-length anchorage, with an increase in normal stress or JRC, the b of bolted joint acoustic emissions gradually decreases. Compared to the partial anchorage method, the full-length anchorage demonstrates a higher maximum Hit rate, along with lower maximum energy release, implying more intense interaction between bolts and surrounding rock in the full-length anchorage, resulting in greater damage under the same conditions, whereas the deformation range of bolts is smaller, and the energy released upon failure is lower in the full-length anchorage. Highlights: A series of shear tests on rock joints using full-length and partial anchorage methods. Investigated the effects of anchorage lengths, normal stress, and joint surface roughness on shear behavior and acoustic emissions. The effects of the anchorage lengths on the fracture behavior of bolted joints was revealed. [ABSTRACT FROM AUTHOR]

Anchoring is a highly effective means to reinforce jointed rock masses. In addition to the axial force from the anchor bolt, the effect of its transverse force in constraining the displacement of the structural plane cannot be ignored. Thus, this paper studies the combined action of the axial and shear forces of an anchor bolt on enhancing the shear strength of the anchored joint. In this work, first, laboratory direct shear tests are conducted to study the evolution of the peak shear strength of the anchored joint with increasing angle between the shear direction and bolt inclination. Second, to further verify this trend, numerical simulation with the finite difference method is used to simulate the same direct shear tests to reveal the lateral and axial stresses and deformations of the bolt. Finally, according to classical beam theory, the mechanical analysis model of a bolt subjected to the combined action of axial tension and lateral shear is established, which takes the realistic stress and deformation patterns of the bolt from the numerical simulation into account. The results show that the lateral restraint of the bolt plays a significant role in the shear strength of the anchored joint, its enhancing effect first increases and then decreases with increasing installation angle, and the optimal installation angle providing the maximum shear strength is approximately 60°. In addition, it is concluded that the shear resistance of the bolt is mainly due to its axial force when the installation angle is relatively small; conversely, the shear resistance of the bolt is mainly due to its shear force when the installation angle is relatively large. Highlights: A new approach for calculating the anchoring force considering the combined action of the transverse restraint and axial restraint of the bolt is presented. A calculation method for the optimal anchoring angle is presented, and its value is suggested to be approximately 60° in this study. The contribution rates of the axial force and tangential force to the anchoring force are not equal and vary with the change in the anchoring angle. [ABSTRACT FROM AUTHOR]

An analytical method and numerical simulation were developed to investigate the shear performance of fiberglass rock bolts (20-tonne and 30-tonne) by conducting sixteen double-shearing tests with both clean and infilled shear interfaces. Following the preparation of the required samples, each test set-up was subjected to different ranges of pretension values. The infilled scenario involved 5 mm thick sandy clay infilled shear interfaces. The results of the double shearing tests unveiled that as pretension increased, so did the confining pressures at the shear interfaces for both clean and infilled joints. Also, an analytical model was developed utilising the Fourier transform, energy balance theory, and linear elastic theory. The result was an empirical relationship that could determine the double shear performance of fibreglass rock bolts in close agreement with the experimental data. Coefficients were incorporated to facilitate model calibration and tuning. Eventually, fast Lagrangian analysis of continua (FLAC) three-dimensional (3D) modelling was utilised to conduct numerical simulations of fibreglass rock bolts subjected to double shearing scenarios. The numerical model was calibrated against experimental data and then extended to conduct a sensitivity analysis on fibreglass rock bolts subjected to double shear test setup variations. Scenarios included rock bolt installation angles, shearing rates, and various host rock strengths. The results revealed that increasing the shear speed from the experimental test baseline yielded substantial displacement increases in the post-failure residual performance of the rock bolts. Changing the installation angle resulted in greater peak shear forces and extended residual zones. The least significant impacts were observed when changing the host rock UCS, suggesting neither rock bolt was drastically impacted by weak or strong host rocks. [ABSTRACT FROM AUTHOR]

This article investigates the application of eXtreme gradient boosting (XGBoost) and hybrid metaheuristics optimisation techniques to predict the axial load bearing capacity of fully grouted rock bolting systems. For this purpose, a comprehensive dataset of 72 pull-out tests was built, considering various influential parameters such as three water-to-grout (W/G) ratios, five ranges of curing time (CT), three different grout admixtures with two different fly ash (FA) contents, and two different diameter confinements (DCs). Additionally, to find out the effect of the mechanical behaviour of grouts on the performance of fully grouted rock bolting systems, seventy-two uniaxial compression strength (UCS) samples were cast and tested simultaneously with pull-out samples. The UCS samples were prepared with the same details as the pull-out samples to avoid any inconsistency. The results highlight that peak load values generally increase with longer curing times, lower W/G, and higher UCS and DC values. The main novelty of this paper lies in its data-driven approach, using various XGBoost models. This method offers a time-, cost-, and labour-efficient alternative to traditional experimental methods for predicting rock bolt performance. For this purpose, after building the dataset and dividing it randomly into two training and testing datasets, five different XGBoost models were developed: a standalone XGBoost model and four hybrid models incorporating Harris hawk optimisation (HHO), the jellyfish search optimiser (JSO), the dragonfly algorithm (DA), and the firefly algorithm (FA). These models were subsequently evaluated for their ability to predict peak load values. The results demonstrate that all models effectively predicted peak load values, but the XGBoost-JSO hybrid model demonstrated superior performance, achieving the highest R-squared coefficients of 0.987 and 0.988 for the training and testing datasets, respectively. Sensitivity analysis revealed that UCS values were the most influential parameter, while FA content had the least impact on the maximum peak load values of fully cementitious grouted rock bolts. [ABSTRACT FROM AUTHOR]

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This study proposes a novel system for accurately predicting grout's uniaxial compressive strength (UCS) in fully grouted rock bolting systems. To achieve this, a database comprising 73 UCS values with varying water-to-grout (W/G) ratios ranging from 22 to 42%, curing times from 1 to 28 days, the admixture of fly ash contents ranging from 0 to 30%, and two Australian commercial grouts, Stratabinder HS, and BU-100, was built after conducting comprehensive series of experimental tests. After building the dataset, a metaheuristic technique, the jellyfish search (JS) algorithm was employed to determine the weight of base models in the ensemble system. This system combined various data and modelling techniques to enhance the accuracy of the UCS predictions. What sets this technique apart is the comprehensive database and the innovative use of the JS algorithm to create a weighted averaging ensemble model, going beyond traditional methods for predicting grout strength. The proposed ensemble model was called the weighted averaging ensemble model (WAE-JS), in which the obtained results of several soft computing models such as multi-layer perceptron (MLP), Bayesian regularized (BR) neural networks, generalized feed-forward (GFF) neural networks, classification and regression tree (CART), and random forest (RF) were weighted based on JS and the new results were then generated. Eventually, the result of WAE-JS was compared to other models, including MLP, BR, GFF, CART, and RF, based on some statistical parameters, such as R-squared coefficients, RMSE, and VAF as indices for evaluating the performance and capability of the proposed model. The results suggested the superiority of the ensemble WAE-JS system over the base models. In addition, the proposed WAE-JS model effectively improved the predicting accuracy achieved from the MLP, BR, GFF, CART, and RF. Furthermore, the sensitivity analysis revealed that the W/G had the most significant impact on the grout's UCS values. [ABSTRACT FROM AUTHOR]

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

The mechanical properties of bolts are important factors affecting the shear behavior of bolted joints. In this study, tensile and pure shear tests were conducted on five kinds of bolts made from different materials to measure their tensile and shear parameters. Direct shear tests were conducted to analyze the effects of tensile and shear strength parameters on the shear behavior of bolted joints. The test results showed that the mechanical properties of bolts made from different materials were clearly different and that these differences mainly affected the plastic deformation stage of the bolted joints. The larger the bolt elongation was, the larger the joint shear displacement at bolt failure. The tensile and shear strengths of the bolts were positively correlated with the shear strength of the bolted joints. According to the standard regression analysis, the bolt shear strength had a greater influence than the bolt tensile strength on the bolt contributions when the bolts were perpendicular to the joint surface. Based on the empirical equation for the bolt contribution proposed by Spang, the maximum shear loads in the pure shear test were introduced, and a new equation was established to predict the contributions of bolts. The prediction results obtained using the modified equation were in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

This paper presents a laboratory testing rig designed to investigate the failure mechanisms and load transfer of rock masses under rock anchor loading. The study revealed that joint patterns significantly affect the strength and capacity of the rock mass, with existing design approaches based on apex angles of 90 ∘ or 60 ∘ found to be potentially overly conservative. Joint orientation and spacing should be included in the anchor design to obtain a more precise design criterion. In all the studied patterns, increasing the horizontal and vertical stress increased the block models' capacity, and load arching did not occur in the model with an unfavourable joint orientation. This study also revealed that the failure surface followed the joints in all tests and that the block model capacity was significantly higher than estimated with the design principle based on the weight of the overlying rock. The findings of this work have important implications for designing rock anchoring systems in mining and civil engineering demonstrate that joint orientation and block size significantly affect the rock mass capacity. This study confirms the need to consider the influence of in situ stresses on rock mass capacity when designing of rock anchors. Overall, this work guides the development of more precise design criteria for rock anchors, contributing to more efficient and effective rock engineering practices. Highlights: The models exhibited increase in horizontal stress upon application of a vertical anchor load to the blocks, indicative of load arching effects. The maximum vertical displacement in the blocks was in the normal direction to one of the joint sets under the influence of a vertical anchor load. The capacity of the block models was enhanced with an increase in both horizontal and vertical in situ stress. Crater-like failures were observed, with separation surfaces aligning with the joint set surfaces. Apex angles of the block patterns ranged from 90 to 140 ∘ ; symmetrical failures were observed in models with symmetrical jointing around the anchor. [ABSTRACT FROM AUTHOR]

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

The present paper reports on various test methods and techniques which have been developed throughout the last decades. These methods have been used to evaluate both axial and shear performance of tendons under impact loading mode. Based on the literature review conducted on the scientific documents, published between 1992 and 2024, the developed facilities mainly work based on the direct impact and momentum transfer methods. In the direct impact method, which can be done in-situ and in the laboratory, the impact energy is applied by a mass freely falls to the test sample. In the momentum transfer method, the test assembly, consisting of both the mass and test sample free-fall at the beginning of the test until the movement of the assembly is halted by a stopper, and the momentum of the mass is transferred to the test sample. Besides, most of the current facilities are working based on the direct impact method. It was also found that less research have been conducted on dynamic shear testing, especially high-strength cable bolts, as most of the facilities have been designed for pull testing. In addition, it was found that in dynamic pull-out tests of rock bolts, two main mechanisms of energy absorption are identified: steel plastic deformation and bolt sliding within the encapsulation medium. The first impact plays a key role in energy absorption, causing significant permanent displacements, while the energy consumed in displacing the bolt is more indicative of dynamic behavior than the total input energy. According to the results, the tendons that undergo static deformations before dynamic loading are more prone to failure as some parts of their performance have already lost. Meanwhile, differences between dynamic and static shear tests suggest that dynamic tests require less energy for failure, as friction is ineffective in impact loading. Finally, the study highlights gaps in the current understanding of tendon performance under impact loading, with potential research directions aimed at improving safety in underground excavation. [ABSTRACT FROM AUTHOR]

The complex mechanical behaviours of steeply inclined and layered surrounding rock in strong and active fault zones result in control measures that cannot adapt to asymmetric squeezing tunnel and are still unsolved. Hence, the Yuntunbao Tunnel was taken as an example to study this issue based on geological survey and indoor and outdoor tests. The results showed that strong geological structures and abundant groundwater undoubtedly deteriorate the mechanical properties of rocks containing many water-sensitive minerals, approximately 45%. The stepwise growth of deformation characteristics before reaching the rock peak strength and the gradient to abrupt failure characteristics after reaching the rock peak strength are determined via triaxial cyclic and static load tests. According to field test results, the unilateral squeezing deformation is severe and greater than 1.5 m, the average extent of the excavation loosening zone is approximately 10 m, and the highest deformation rate reaches 12 cm/d. The gradual and sudden changes in tunnel deformation are demonstrated to be consistent with the postpeak deformation characteristics of layered rock in indoor tests. Moreover, the steel arch exhibits composite failure characteristics of bending and torsion. Finally, reliable and practical controlling measures are suggested, including the optimised three-bench excavation method with reserved core soil, advanced parallel pilot tunnel, long and short rock bolts, and large lock-foot anchor pipe. Compared with tunnel deformation before taking measures, the maximum convergence deformation is reduced from 2.7 to 0.9 m, and the bearing force of the primary support is also reasonable and stable. [ABSTRACT FROM AUTHOR]

The document discusses the challenges of maintaining stability in underground openings in deep mining environments due to increasing mining depths and high in situ stress conditions. Researchers have focused on rock reinforcement and support methods to address these issues, with a special issue dedicated to stability control in underground openings. Published academic papers from China and Poland explore topics such as roadway reinforcement, rock burst issues, and rock failure mechanisms using various methods like numerical simulations and in situ observations. The research aims to improve understanding of stability mechanisms in deep mining engineering to minimize risks to underground staff and equipment. [Extracted from the article]

Undercutting anchors are structural elements used in construction and geotechnics to stabilize both structures and soils. Their main applications include stabilizing slopes and embankments, reinforcing foundations, and providing support during tunnel construction and other underground works. The authors propose the use of these anchors in rock mass detachment technology. This article presents a comprehensive analysis of the mechanism behind rock mass detachment using an undercutting anchor. Particular attention is given to the influence of parameters such as the fracture energy of the medium and the coefficient of friction between the medium and the anchor head on the detachment process of rock elements during anchor expansion in the drilled hole. Numerical FEM analysis was employed to model the effect of changes in the shape and size of failure cones under varying simulation conditions. The discussed problem is crucial for evaluating the effectiveness of this anchor design under non-standard conditions, particularly in the unconventional destruction of rock media. [ABSTRACT FROM AUTHOR]

In actual underground rock engineering, to prevent the deformation and damage of the rock mass, rock bolt reinforcement technology is commonly employed to maintain the stability of the surrounding rock. Therefore, studying the anchoring and crack-stopping effect of rock bolts on fractured granite rock mass is essential. It can provide significant reference and support for the design of underground engineering, engineering safety assessment, the theory of rock mechanics, and resource development. In this study, indoor experiments are combined with numerical simulations to explore the impact of fracture dip angles on the mechanical behavior of unanchored and anchored granite samples from both macroscopic and microscopic perspectives. It also investigates the evolution of the anchoring and crack-stopping effect of rock bolts on granite containing fractures with different dip angles. The results show that the load-displacement trends, displacement fields, and debris fields from indoor experiments and numerical simulations are highly similar. Additionally, it was discovered that, in comparison to the unanchored samples, the anchored samples with fractures at various angles all exhibited a higher degree of tensile failure rather than shear failure that propagates diagonally across the samples from the regions around the fracture tips. This finding verifies the effectiveness of the numerical model parameter calibration. At the same time, it was observed that the internal force chain value level in the anchored samples is higher than in the unanchored samples, indicating that the anchored samples possess greater load-bearing capacity. Furthermore, as the angle αs increases, the reinforcing and crack-stopping effects of the rock bolts become increasingly less pronounced. [ABSTRACT FROM AUTHOR]

In order to quantitatively calculate the critical depth and critical load of mines affected by rock burst, and to achieve effective prevention and control of rock burst in coal mines, this paper proposes a mechanical model for predicting the occurrence of rock burst in coal mine roadways based on catastrophe theory. Additionally, a theoretical calculation formula for initiating rock burst is derived. The first step was to establish a mechanical analysis model, which directly correlated with the in-situ stress, physical and mechanical characteristics of the coal-rock mass, and engineering structural parameters. Following this, a mechanical instability criterion was derived for the key load-bearing circle within the surrounding rock of the roadway. In the final step, the critical depth and load for rock burst initiation were verified for 25 distinct coal mines in China that were prone to rock burst hazards. The research results demonstrate that the discrepancy between the theoretically calculated critical depth and the actual measured statistical values was less than 35%. In addition, the difference between the theoretically determined critical depth and the value calculated by Pan Yishan was less than 32%. Notably, the ratio of the theoretically calculated critical load to the uniaxial compressive strength of the coal-rock mass ranged from 0.38 to 1.93. This aligns with empirical data on rock burst occurrences, as set out in the engineering classification standards for rock masses. These research outcomes substantiated the practical utility of the proposed theory, thereby laying a robust theoretical groundwork for the quantitative control of rock burst. [ABSTRACT FROM AUTHOR]

In this paper, the potential of the five latest artificial intelligence (AI) predictive techniques, namely multiple linear regression (MLR), multi-layer perceptron neural network (MLPNN), Bayesian regularized neural network (BRNN), generalized feed-forward neural networks (GFFNN), extreme gradient boosting (XGBoost), and their ensemble soft computing models were evaluated to predict of the maximum peak load (PL) and displacement (DP) values resulting from pull-out tests. For this, 34 samples of the fully cementitious grouted rock bolts were prepared and cast. After conducting pull-out tests and building a dataset, twenty-four tests were randomly considered as a training dataset, and the remaining measurements were chosen to test the models' performance. The input parameters were water-to-grout ratio (%) and curing time (day), while peak loads and displacement values were the outputs. The results revealed that the ensemble XGBoost model was superior to the other models. It was because having higher values of R2 (0.989, 0.979) and VAF (99.473, 98.658) and lower values of RMSE (0.0201, 0.0435) were achieved for testing the dataset of PL and DP' values, respectively. Besides, sensitivity analysis proved that curing time was the most influential parameter in estimating values of peak loads and displacements. Also, the results confirmed that the ensemble XGBoost method was positioned to predict the axial-bearing capacity of the fully cementitious grouted rock bolting system with extreme performance and accuracy. Eventually, the results of the ensemble XGBoost modeling technique suggested that this novel model was more economical, less time-consuming, and less complicated than laboratory activities. [ABSTRACT FROM AUTHOR]

Rock anchors, which can withstand substantial forces and are essential for securing the foundations of the built environment, can fail due to steel tensile failure, bond detachment, or rock mass fracturing through uplift. In this study, uplift failure of the rock mass surrounding rock anchors was simulated using both physical and numerical models. The physical models used a specially designed testing rig with predefined sizes and different joint layouts to simulate rock mass uplift failure. The numerical models were calibrated using the physical models and used to investigate scenarios involving increased complexity and greater depths. This paper presents the load distribution within rock masses with orthogonal joints when exposed to an anchor load. Extensive analysis of the numerical models revealed that symmetrical load arches were induced in rock masses that contained a joint set oriented parallel to the loading direction. However, joints that were obliquely oriented relative to the anchor axis induced asymmetrical load arching. The greatest displacement occurred in the direction parallel to the joint set with the smallest angle to the anchor loading axis. Large-scale models with zero or near-zero in situ horizontal stress revealed that the load capacity in a rock mass with continuous vertical joints was relatively low, especially when compared to rock masses with discontinuous vertical joints. It was observed that the uplift capacity of the rock mass around an anchor decreased if the load arches of adjacent anchors overlapped; consequently, a decrease in anchor spacing was found to correspond to a decrease in uplift capacity. Highlights: Symmetrical load arches are induced within a rock mass if the joint sets are oriented parallel to or close to parallel to the anchor axis. An oblique orientation of the joints relative to the anchor axis results in asymmetrical load arching in the rock mass when the anchor is loaded. Rock masses with continuous vertical joints have a low load capacity, especially compared to rock masses with discontinuous vertical joints. In a row of rock anchors, the rock mass uplift capacity of individual anchors is decreased if the anchor spacing is too low. [ABSTRACT FROM AUTHOR]

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

Tunnelling using drilling and blasting method inevitably disturbs the surrounding rock and induces a blasting damaged zone around the tunnel. Conventional mechanical analyses assume that the entire ground is damaged, leading to an underestimation of the surrounding rock stability and a conservative support design of the tunnel. This study developed a new analytical model to analyze the displacement, stress, and plastic radius of tunnels reinforced by grouted rockbolts considering the blasting damage effect. The blasting damaged zone was assumed to take a cylindrical shape with a finite radius. First, four different states of an unsupported tunnel based on the plastic zone distribution within the damaged and undamaged zones were distinguished and solved. Subsequently, ten different forms of a bolt-supported tunnel considering the ground state at bolt installation and the relative ranges of the bolt length and plastic zone were established. A method for determining the evolution paths of these possible forms for a specific tunnel project was developed using the critical displacements and longitudinal positions that define the transition between the different states and forms. Finally, an analytical algorithm for the rockbolt–surrounding rock interaction was established by introducing the concept of a fictitious pressure to simulate tunnel advancement. The proposed analytical model was verified by 3D numerical simulation and field monitoring results. Illustrative examples were presented to investigate the effect of the bolt length on tunnel displacement in both hard and soft rocks. Finally, the performance and advantages of the proposed model were investigated by comparing with the conventional analytical model. The proposed method can be used in the rockbolt design of tunnels constructed using the drilling and blasting method. Highlights: Interaction between rock and grouted rockbolts considering blasting damage zone is analyzed. Ground reaction curves for four different ground states and ten forms are derived. Analytical algorithm for possible evolution paths and critical transitions is presented. Effects of blasting damage zone and bolt length on tunnel displacement is illustrated. Proposed model validated by numerical and field test results excels existing models in rockbolts design. [ABSTRACT FROM AUTHOR]

Friction properties of rock are closely connected with the anisotropy. The anisotropy of rock friction can provide a valuable assessment for geotechnical and geological engineering. In this study, the rotary friction tests were conducted to analyze the water effect on the friction property and the friction anisotropy of the four types of rock. The drilling response model (DD-model) was employed to characterize the rotary friction behavior of the rocks. The parameters of this model include the three types of friction parameters: 1/ς, μ, and f, where 1/ς and μ are constant, and f is a variable. A quantitative method is proposed for assessing the anisotropy of rock friction. The results of the rotary friction tests indicate that the relation between torque force and thrust force conforms to the DD-model. The changes of two friction constants 1/ς and μ from dry state to water-saturated state suggest that the water effect on the friction strength of the rocks exhibits significant anisotropy. The friction strength determined by the friction variable f increases first, then decreases, and finally stabilizes with the increasing of depth. AIf is an anisotropy index calculated by the proposed method. The percentage difference of the average value of AIf between water-saturated and dry states shows the degree of the water effect on the friction anisotropy of the rocks, mudstone (MU) > granite (GR) > fine sandstone (FS) > argillaceous siltstone (AS). The quantitative model is hopefully constructed for characterizing the relation between the anisotropic friction strength of rock and the moisture state in future. [ABSTRACT FROM AUTHOR]

Unstable block collapse is an important factor affecting the safety of tunnel construction process. Based on the collapse accident of a block in Qingdao, the failure mechanism of a large-span tunnel with unstable blocks and the control effect of the length, prestress and spacing of pre-stressed rock bolts on the surrounding rock are studied through the model test and combination of numerical calculation, the on-site support optimization scheme is proposed. It is found that the surrounding rock on both sides of the vertical joint has a slight dislocation first, and then the joint opens, and the rock on both sides roughly forms a relative cantilever structure. Pre-stressed rock bolt has the function of limiting block slip and providing radial binding force, and pre-stressed rock bolt restricts the opening of joints and enhances the bearing capacity of surrounding rock. The bolt length is the key factor affecting the bolt support effect, followed by prestress force, and finally the bolt spacing. [ABSTRACT FROM AUTHOR]

Anchors of various designs are crucial, especially in mining and underground construction, where they stabilise the excavation and prevent the movement of rocks. They make it possible to control the direction of cracking during explosions, limit the dispersion of rock material and minimise damage from vibrations. The use of anchors increases the safety and efficiency of work in difficult geological conditions. The authors propose the use of modified anchor construction for the detachment of rock lumps. The paper presents the results of a numerical analysis carried out using the finite element method (FEM) on the effect of the angle of the anchor conical head of a new breakout design on the formation of the detachment crack trajectory influencing the range and, consequently, the volume of detached rock output. The analysis was carried out with a view to explaining the mechanism of separation of lumps of rock by the anchor treated as a mining tool. [ABSTRACT FROM AUTHOR]

This paper focuses on a pullout failure of anchor rods used to stabilize rock slope at the sides of a road cut in a mountainous terrain. The objectives of this work are to analyze a case study of a pullout type of failure of anchor rods at highly fractured rock slope sides of a road cut called Dhila descent in Saudi Arabia, and also to investigate the possible mechanisms that caused this peculiar type of failure of the rock anchors and the landslides along the descent. Anchor rods exit out of the hole for a distance of few meters. Results of this analysis showed that the mechanism of this rock anchor failure is of the pullout type, caused apparently by the release of the energy stored in anchor rods at the post-tension stage during the construction period. This release is caused by the reduction of the bond strength between the rod and the grout at the anchorage end inside the hole. The displacements of the rods were computed based on the conservation of energy and work-energy principles. The amount of the displacements computed for a range of possibilities are comparable with those observed in the field. The bolt failure process is explained in terms of the debonding between the bolt and the grout. Recommendations were made to improve the design of such anchors. It is recommended to use fully-grouted, inclined, static rock bolts with a more ductile grout, and locked with nuts from both sides of the bearing block. [ABSTRACT FROM AUTHOR]

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

Roadway mine pressure monitoring is one of the important means to ensure the safe and efficient mining of coal mines. However, the traditional monitoring methods have the disadvantages including lack of systematim, low accuracy, poor reliability, and difficulty in networking. In this paper, by using the grating sensor as a monitoring method, a roadway mine pressure grating monitoring system including roof separation, bolt stress, surrounding rock stress and bolt load monitoring was systematically designed and develop, to solve the shortcomings of current monitoring methods. Firstly, taking the 81303 return airway of a coal mine in Inner Mongolia as the research object, the stress distribution law of the two coal pillars was clarified by numerical simulation, and the optimal measuring point layout scheme of the roadway was determined. Secondly, the overall framwork of the roadway mine pressure grating monitoring system was built, and the design and research of the system hardware configuration and monitoring software were carried out to realize the real-time online monitoring and data processing of the roadway mine pressure. In addition, the industrial application test shows that the mine pressure law obtained by the system is generally consistent with those from the traditional method, and the relative error of the monitoring parameters is up to 1.16%, which verifies the effectiveness and adaptability of the mine pressure grating monitoring system. [ABSTRACT FROM AUTHOR]

Coal‐measure strata is a typical layered structure, a better understanding of the bearing characteristics of fully grouted bolts in layered rock mass is of great significance for roadway support. However, limited studies have been conducted to investigate the bearing performance of fully grouted bolts in layered rock mass. In this paper, a numerical model of fully grouted bolt in layered rock mass was established, and a tri‐linear bond–slip model of the anchorage interface was imported into the numerical model by the user‐defined Fish language. The effects of strata sequence, strata thickness, and strata number in layered rock mass on the bearing performance of fully grouted bolts were systematically analyzed. The results show that fully grouted bolts in soft–hard type (SH‐type) layered rock mass has higher bearing capacity. The greater the thickness of the soft rock in the layered rock mass, the more significant the influence of the strata sequence on the bearing performance of fully grouted bolts. The bearing capacity of fully grouted bolts decreases with the increase of the thickness ratio of soft rock to hard rock. The greater the thickness of the hard rock in the layered rock mass, the more beneficial to the bearing performance of fully grouted bolts. With the increase of the strata number, the bearing capacity of fully grouted bolts gradually decreases. For bolt support of layered rock mass, the deep anchoring foundation of fully grouted bolts should be arranged in hard rock or elastic zone rock as much as possible, and rock grouting can be adopted to reduce the difference in mechanical properties between layered rock mass and improve the durability of fully grouted bolts. The research results may provide useful guidance and reference for the support design of fully grouted bolts. [ABSTRACT FROM AUTHOR]

The structural compliance of annular ring gear can significantly influence the quasi-static and dynamic performance of an epicyclic gear set. As powertrain components are continually being optimized to their design limits, this influence becomes prominent and can no longer be ignored. The current paper will study the impact of ring gear compliance on the dynamic response of epicyclic gear sets in fixed ring kinematic configuration. To achieve this objective, the current study will incorporate a finite element-based ring gear formulation into the three-dimensional planetary load distribution model of Ryali and Talbot (2021, "A Dynamic Load Distribution Model of Planetary Gear Sets," Mech. Mach. Theory, 158, p. 104229). The proposed model employs a modified simplex algorithm to iteratively solve for the elastic gear mesh contacts in conjunction with a numerical integration scheme, which enables it to inherently capture the influence of several components and system-level design variations. The developed formulation is used to conduct parametric studies involving different planetary gear designs, ring gear fixtures (bolted vs. splined), and operating conditions (quasi-static, dynamic). In the case of a splined ring gear fixture, an external splined tooth contact model is developed, which will be used to validate the model against the quasi-static experiments of Kahraman et al. (2010, "Influence of Ring Gear Rim Thickness on Planetary Gear Set Behavior," ASME J. Mech. Des., 132(2), pp. 0210021-0210028). The discussed results demonstrate the fidelity of the developed model, thus making it an excellent tool for the design and analysis of planetary gears with thin annular ring gears. [ABSTRACT FROM AUTHOR]