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The mechanism of surface subsidence induced by shallow buried excavation construction and the failure mode under ultimate state were not unclear. In view of this situation, a scaled model experiment based on particle image velocimetry(PIV)was conducted to simulate the construction process of shallow buried tunnels in sandy soil and Ⅴ-grade surrounding rock. PIV technology was used to analyze the deformation images of the surrounding rock during the construction process of the tunnel, and to obtain displacement cloud maps of geological deformation induced by construction disturbance. By analyzing the characteristics and gradual evolution of surface deformation induced by underground excavation construction disturbance, the shape and range of the failure surface and collapse induced by underground excavation tunnel construction in different strata under the limit state were summarized. The equation of the failure surface induced by the collapse of the arch top strata during underground excavation construction was derived by using the upper limit theorem of limit analysis and variational principle, and the collapse surface graph was drawn. The validity of the model test results was verified by comparing the range of collapse induced by underground excavation construction in the arch crown strata obtained from the model test with the theoretical calculation results. [ABSTRACT FROM AUTHOR]

Underground excavation is usually accompanied by complex soil-structure interaction problems in practical engineering. This paper develops a novel multi-scale approach for investigating the soil arching effect through trapdoor tests. This approach adopts the finite element method (FEM) and smoothed particle hydrodynamics (SPH) method to handle the particle-rigid body interaction in the trapdoor tests, incorporating a micromechanical 3D-H model to derive the nonlinear material response required by the SPH method. The variation of the earth pressure on the trapdoor in simulations exhibits good agreement with those of the experiments. Extensive parametric analyzes are performed to assess the effects of soil height and inter-particle friction angle on the evolution of load transfer and soil deformation. Three deformation patterns are observed under different buried conditions, including the trapezoid, the triangle, and the equal settlement pattern. Results indicate that the planes of equal settlement develop progressively with the trapdoor movement and then enter the range of experimentally observed values. Additionally, three failure mechanisms are identified that correspond to the three deformation patterns. Due to the advantages of the micromechanical model, mesoscale behavior is captured. The anisotropy of stress distribution in the plastic region is found during the arching process. [ABSTRACT FROM AUTHOR]

The transition from an open-pit to an underground space is inevitable to exploit deposits from greater depth. Crown pillar, a remnant ore usually left in between open-pit to underground mining that supports the terrain and aids in carrying out underground mining operations safely and its stability is vital. The design of crown pillar is majorly influenced by its thickness, span, slope angle, ore dip, depth of open-pit mining, rock mass quality, cohesion and friction angle. When the crown pillar is situated near the surface (shallow depth), it is synonymously named as the surface crown. The behaviour of the crown pillar is different from the surface crown due to variation in geo-mining conditions. As underground mining progresses, displacements around the crown pillar are generated and stresses reorients around it. This can be assessed through numerical simulation. To have a better understanding, this paper concentrates on crown pillar's stability and geometrical parameters influence on its stability. The field study is carried out at Ramrama manganese ore mine, where the transitioning takes place at shallower depth and FLAC3D 5.0 is used for numerical simulation work to analyse the behaviour of the crown pillar. From the results interpreted, it is found that the maximum amount of principal stresses decreases for the lower span, 8 m, of crown pillar with increase in slope angle and for the larger span as in case of 22 m span; the stresses generated are reduced in case of 38° slope angle and increased for 45° slope angle. Higher dip of orebody generates high amount of stresses in the pillar and with an increase in the depth of mining, high amount of displacements and stresses are observed around the crown pillar. [ABSTRACT FROM AUTHOR]

Estimation of in situ stresses based on back-analysis of measured stress changes and displacements has become an alternative to the direct stress measurement methods. In order to help users conduct own measurement and analysis, this paper presents in detail a field stress back-analysis approach directly from borehole strain changes measured during nearby underground excavation. Essential formulations in major steps and the procedure for the entire analysis process are provided to allow users to follow. The instrument for borehole strain change measurement can be the CSIR or CSIRO stress cells and other borehole strain cells that can measure strains on borehole walls. Strain changes corresponding to the stress changes at a borehole location are calculated in borehole environment. The stress changes due to nearby excavation can be calculated by an analytical model for a single circular opening and simulated by a numerical model for non-circular and multiple openings. These models are based on isotropic, homogeneous and linear elastic assumptions. The analysis of borehole strain changes is accomplished by multiple linear regression based on error minimization and an integrated process provides the best-fit solution directly to the in situ stresses. A statistical technique is adopted for screening outliers in the measurement data, checking measurement compatibility and evaluating the reliability of analysis results. An application example is included to demonstrate the practical application and the analysis procedure.

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In the last few decades, rock mass classification had been used intensively in engineering design. The concern arises for the potential occurrence of localized or global rock mass failure due to geological (such as discontinuities, water, weathering) and non-geological (such as construction load, vibration) factors should be taken into consideration. The ability of a classification system to represent the rock mass condition in a straightforward and effective way can assist in engineering works. Two classification systems can be applied in underground construction such as tunneling and mining. In tunnel construction, the Rock Mass Rating (RMR), Q System, Japanese Highway (JH) Method, Geological Strength Index (GSI) and Rock Mass Quality Rating (RMQR) are commonly used. However, these systems cannot be applied for rock mass covered by shotcrete due to difficulty in observing the discontinuity planes. Therefore, a new investigation method and rock mass classification for rock mass covered by shotcrete is vital to overcome this limitation. [ABSTRACT FROM AUTHOR]

Construction of huge metro projects in congested areas in Cairo City, Egypt, calls for optimization of the underground excavation process. The soil profile in Cairo city, Egypt, is generally characterized as soft soil containing layers of clay and sand. To control the ground movements and shotcrete stresses, it is necessary to optimize the ground surface settlements and excavation step. In this paper, several tunnel sections were compared to illustrate how the tunnel shape affects the soil deformations and straining actions results. Results of numerical modeling using plane-strain finite elements are presented; different types of sequences for the tunneling excavation of each section are compared. Analysis results from different models show that using different tunnel section excavation sequences affects the soil behavior differently, and that suitability of the sequence is determined by the soil properties and the dimensions of the tunneling section. [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 work systematically quantifies groundwater's effect on the roof stability of underground openings in shallow coal mines and indirectly assesses the potential for sinkhole formation. A specific stratigraphy was analyzed where the opening instability can lead to sinkhole formation, given the geological conditions, the overburden stratigraphy, and the depth of the openings. The groundwater recharge was investigated as an individual rainfall infiltration (short-term) and as groundwater dynamics (long-term), representing the accumulation of infiltrated rainwater with time. In the latter case, two approaches were employed for the porewater pressure calculation: (a) phreatic line with hydrostatic conditions and (b) steady-state flow based on constant groundwater head on the vertical boundaries at the model's edges. The safety analysis was based on a simplified statics model relating the stability to the bending of the roof, and numerical analysis was employed for the stress analysis. The short-term safety remained unaffected as rainfall water accumulated on the aquitard to form perched water. The long-term safety deteriorated due to the increase of the tensile stresses in the roof of the underground openings with the rise of the groundwater table. The phreatic line approach is the most conservative, resulting in lower safety than steady-state flow. [ABSTRACT FROM AUTHOR]

The anisotropy combined with the time-dependency of rock mass is commonly observed in tunnel construction. In this study, a comprehensive analytical investigation is performed on analysing time-dependent ground responses induced by tunnel excavation in an anisotropic rheological rock mass. An innovative analytical solution for the anisotropic viscoelastic problems is first proposed, which can be applied to the general cases that the rheological behaviours in anisotropic principal directions are independent and arbitrary. Using the generalized corresponding principle, the analytical model, which can precisely and rapidly address the problem, is then presented for the deformation and stresses around tunnels in transversely isotropic viscoelastic rock mass, considering different viscoelastic characteristics, different anisotropic angles, and circular/elliptical tunnel shapes. The analytical solutions agree very well with the numerical predictions for the consistent models, and can also be reduced to the isotropic viscoelastic case. Furthermore, the application of analytical solutions in practical engineering is validated by the good agreements between analytical solutions and field measurements. A parametric analysis is then performed to investigate the time-dependency of stress, and the effects of anisotropy ratios and anisotropy angles on displacements and stresses. The proposed analytical solution has a valuable contribution to the field of rock rheological mechanics, as it offers a benchmark for anisotropic viscoelastic problems, insights into the complex behaviour of anisotropic rock masses and provides a more accurate prediction of the ground response that may be useful to optimize the design of tunnel excavation in anisotropic rock masses. [ABSTRACT FROM AUTHOR]

Given the increased environmental concerns in excavation works, particularly in urban areas, the search for new and more accurate mathematical models for blast-induced ground vibration amplitudes prediction is mandatory, as these mathematical models are good tools for the minimization and mitigation of the environmental impacts related to these dynamic events. This paper presents the methodology-based proposal, selection and validation of multiple linear models in which the predictors are not only distance and explosive weight per delay but also RMR as a quantitative predictor and building type, as a qualitative predictor. The methodology was successfully applied to a case study of blast monitoring during excavation works of granite rock mass in Porto (Portugal). The obtained best-fitted model, with a coefficient of determination of 0.91 and sum squared error of 471.02, shows that these new predictors greatly improves the prediction ability of the blast-induced ground vibration amplitudes compared with conventional models. Moreover, the results show also that RMR has an important influence on blast-induced ground vibration amplitudes on ground vibration target structures. [ABSTRACT FROM AUTHOR]

Induced seismicity associated with underground space creation and resource extraction has become a matter of global concern. However, our ability to predict and mitigate anthropogenic geohazards is still woefully inadequate. This review provides an overview of unloading-induced seismicity and highlights the mechanisms behind fault instability from a view of rock mechanics. Based on numerous fault instability cases, reduction and rotation of in situ stresses on pre-existing faults are possible causes of excavation-induced seismicity. Fault instability during resource extraction is related to many geological and operational factors, including mining depth, pore pressure, stress distribution, and production rate. Most of these cases can be explained by the Mohr–Coulomb failure criterion, and some exceptional cases could offer us new clues to improve the understanding of the mechanisms behind and the ability to predict and mitigate the induced seismic events. The current challenges include how to control remote triggering of fault instability and how to manage unseen threat of undetected faults. Emerging technologies, such as data analytics and machine learning, combining with physical models could be the next frontier for fault instability research.

Highlights: The entire disturbing slope is divided into four regions. The critical sliding surface shows an L-shaped or a W (double L)-shaped broken line. When the advancement exceeds a certain value, the safety factor suddenly drops. This study offers a basis for selecting an appropriate working face stop line. In this study, the Lagrange element strength reduction method is used to explore slope stability and as an evaluation method of underground mining of end-slope coal in a rock-stability analysis. A numerical analysis model is established herein using the geological conditions for mining in a coordinated open pit with an underground mining area of the Anjialing Open-Pit Mine and Underground No. 2 Mine. Additionally, the evolution law of slope stability in open-pit end-slope mining is studied using the proposed numerical simulation method. According to our findings, the steps show obvious horizontal movement and deformation under the influence of underground mining disturbances. Taking the horizontal displacement at the slope tops of the steps as the deformation index, the entire disturbed slope is divided into four regions: upper, middle-upper, middle-lower, and lower steps. When a step is fully affected by underground mining, its subsidence value first increases rapidly and then slowly. An exponential function is used to reflect the change rule in the step-subsidence value as the working face advances. In the underground mining process, the critical sliding surface of the slope develops along the soft rock or coal seam, showing an L-shaped or a W (double L)-shaped broken line. As the working face advances, the initial position of the sliding mass is unchanged while the cutting position alternately changes up and down in the weak plane. The safety factor suddenly drops when the advancing distance exceeds a certain value. [ABSTRACT FROM AUTHOR]

Blast-induced vibration produces a very complex signal, and it is very important to work out environmental problems induced by blasting. In this study, blasting vibration signals were measured during underground excavation in carbonaceous shale by using vibration pickup CB-30 and FFT analyzer AD-3523. Then, wavelet analysis on the measured results was carried out to identify frequency bands reflecting changes of blasting vibration parameters such as vibration velocity and energy in different frequency bands. Frequency characteristics are then discussed in view of blast source distance and charge weight per delay. From analysis of results, it can be found that peak velocity and energy of blasting vibration in frequency band of 62.5–125 Hz were larger than ones in other bands, indicating the similarity to characteristics in the distribution band (31–130 Hz) of main vibration frequency. Most frequency bands were affected by blasting source distance, and the frequency band of 0–62.5 Hz reflected the change of charge weight per delay. By presenting a simplified method to predict main vibration frequency, this research may provide significant reference for future blasting engineering. [ABSTRACT FROM AUTHOR]

The generalized Hoek-Brown (GHB) failure criterion can estimate the rock mass parameters required for rock mechanics–related analyses such as numerical modeling in geomechanics. The determination of GHB parameters has been developed in the field of rock mechanics. Due to the wide use of the Mohr-Coulomb criterion and the lack of an existing relationship for determining its parameters for a rock mass, equivalent Mohr-Coulomb parameters (EMC) can be derived from the GHB. To determine the differences in the use of these two criteria, we analyzed the behavior of a deep circular tunnel in nine stress states for three metamorphic rocks recovered from the Canadian Shield from rock masses that present a very blocky structure. We carried out 241 simulations using the finite element code RS2 to assess the effect of the geological strength index (GSI), in situ stress, and rock type on the deviation of wall displacement, the number of yielded elements, and the differential stress obtained by the GHB and EMC parameters. A combination of low in situ stress and high GSI yielded similar results when using both failure criteria. [ABSTRACT FROM AUTHOR]

Stress cycle disturbances induced by underground excavation can trigger fault activation and slip, leading to earthquakes and other dynamic hazards. This study investigates shear slip induced by cyclic unloading in sawed faults through laboratory experiments. We examine the effects of unloading rate, amplitude, and initial stress on fault slip behavior. Results suggest that cyclic unloading induces fault slip and modifies fault failure characteristics, leading to a gradual rise in confinement pressure during activation. Fault displacement correlates positively with higher unloading rates, amplitudes, and initial stress levels on the fault. Fault slip rate is mainly influenced by unloading rate, whereas initial stress primarily impacts the initial slip rate. Due to fault roughness, higher unloading amplitudes can induce several acceleration events on the fault. Moreover, data from all sub-slipping events demonstrate a positive correlation between the magnitude of stress drop and maximum slip rate. This study offers a theoretical framework for the rational selection and optimization of underground development strategies, aimed at effectively mitigating the dynamic instability of faults. • Cyclic unloading drive fault slip and alters activation conditions. • Increasing unloading rate enhances fault slip rate. • Increasing unloading amplitude drives fault multiple accelerations. • Lower initial stress enhances the both the displacement and rate of initial fault slip. • A positive correlation exists between fault stress drop and maximum slip rate under cyclic unloading driving. [ABSTRACT FROM AUTHOR]

Historically, the idea of designing and installing rockbolts in rockmasses can be traced back to the construction of the Snowy Mountain hydroelectric scheme in Australia, which was completed in 1974. The use of rockbolts as a ground support system has been widely applied to enhance the stability of structures in mining and to resist the movement of keyblocks in underground excavations. The strength of a rockbolt as a rock support tool lies in its ability to improve the tensile and shear strength needed to maintain the load-bearing capacity of a rockmass. Currently, rockbolts are extensively used as reinforcement methods in mining and civil engineering projects to support deforming rockmasses in coal and hard rock mining, tunnelling and underground openings. The performance of a rockbolt depends on the design parameters such as load-bearing capacity of the bolt, strength of the bolt, bolt diameter, length of the bolt and bolt spacing. This study provides a detailed review of the various applications of rockbolts in mining operations. In addition, the integration of smart sensors in rockbolts to enhance monitoring of displacement measurements, stresses, subsidence of pillars and ground pressure on structures are discussed in this paper. The use of smart rockbolt devices, which has improved the monitoring and evaluation of critical parameters in rockbolts such as the axial force, corrosion occurrence, grout quality and resin delamination, are also discussed. This review shows that with the numerous applications of rockbolts in mining, especially in underground excavations and tunneling engineering, rockbolts can be used as supports in rocks with different geological conditions. Nevertheless, this paper highlights that there are still some areas that need improvement in rockbolting technology. [ABSTRACT FROM AUTHOR]

Underground excavation is a necessary process for constructing mines, tunnels and depots in granite rock mass. In this study, the numerical granite specimens were established by the discrete element method and confirmed by laboratory experiments in order to investigate the peak stress, cracking development and failure properties of pre-holed granite under coupled biaxial loading and unloading conditions. The results show that, for the specimens containing D-type and square holes, the peak biaxial unloading strengths first decrease, then increase and finally decrease as the inclination angles of the holes increase. For the specimens with elliptical holes, the peak biaxial unloading strengths first decrease and then increase with the increases in the inclination angles of the holes. The biaxial unloading strengths of specimens containing elliptical, circular, D-type and square holes decrease in that order. The cracks initially appear near the crossover points between the X-type shear fracturing plane and the pre-hole in the center and gradually expand along the X-type shear direction, which indicates that the failure of pre-holed granite is primarily shear failure. When the overall length of cracks expanding along the X-type shear direction extends to the size of the pre-hole in the center, the failure of the pre-holed specimen occurs. When the existing pre-hole in the center of the granite specimen extends to connect with the shear slip in the vicinity of the hole, this triggers overall failure. [ABSTRACT FROM AUTHOR]

• A Burgers-viscoplastic strain-softening (BVSS) model has been implemented into CODE_BRIGHT. • The BVSS is capable to simulate the time-dependent plastic behavior of geomaterials. • A coupled solid-fluid model is used to simulate the interaction between solid deformations and fluid flow. • The coupled solid-fluid response of tunnel excavation in saturated time-dependent plastic rock masses has been analyzed. This article provides a general numerical approach for modelling the response of deep tunnels excavated in saturated time-dependent plastic rock masses, considering a coupled solid-fluid interaction and time-dependent plastic behaviour. In order to do that, a Burgers-viscoplastic strain-softening model has been developed and implemented into the finite element method software CODE_BRIGHT, and a coupled solid-fluid model is used to simulate the interaction between solid deformations and fluid flow. Parametric analyses are then performed to analyse the influence on the tunnelling response of different time-dependent models, different standstill times and different excavation rates. It has been observed that the time-dependent model selection is crucial to simulate the response of underground excavations. Additionally, the coupled solid-fluid results are significantly different from the purely mechanical ones. The liquid pressure build-up in the vicinity of the tunnel face and the overpressure dissipation with time due consolidation can be accounted for. Moreover, the higher the excavation rate, the larger build-up of liquid pressures occurs. [ABSTRACT FROM AUTHOR]

Stability is the main problem in underground excavations that can result in rock-related accidents or closure of mines. This is often controlled by the geological condition of the rockmass and the in situ stress field where excavation is being carried out. Over the years, conventional support systems such as bolts, shotcrete and mesh have been the standard support systems used in difficult ground conditions to maintain stability of underground openings. The novel Thin Spray Liner (TSL) is a technology with an improvement in terms of support capabilities for difficult geological conditions. This technology is predicted to replace conventional support systems, as it offers a significant yielding capacity that is better than that of the traditional techniques of controlling strata. The performance of the TSL lies between that of shotcrete and wire mesh. The TSL has numerous advantages regarding rock reinforcement such as rapid curing period, fast application, high tensile strength, high adhesion properties that prevent movement of rock keyblocks, improved cycle times, reduction in material-handling compared to shotcrete, and a significant ability to penetrate joints. These advantages increase the allowance for mechanisation and improvement of safety in excavations. Despite various benefits of TSLs, there are shortcomings which make end-users to be sceptical about the technology. This study provides a detailed review of the mechanism, properties, composition and types, as well as the general and mining applications of TSLs. It also describes the challenges faced by the mining industry and other end-users in accepting the technology as a solution for stability issues in underground openings. In addition, some insightful suggestions are made as recommendations for future work on the development of suitable, effective and efficient thin surface rock support technology within limitations/constraints. [ABSTRACT FROM AUTHOR]

Abstract With the increase in mining depth and the deterioration of surrounding rock conditions, large deformation failure of deep roadway surrounding rock is still very common. To solve the support problem, it is necessary to understand the deformation and failure mechanism of the deep roadway. This paper presents a case study on the deformation failure behavior and support design of a deep roadway in the Tangyang mine by field tests and numerical simulations. The rock mass properties were first evaluated based on field data and the mechanical parameters of rock specimens. Then, the numerical model of the deep roadway surrounding rock was established based on the calibrated microparameters. The deformation features and cracking behavior of the roadway were investigated in detail. The results show that the cracking process of crack initiation, crack propagation, and rock separation in the surrounding rock of this kind of roadway is a gradual process developing from a shallow to deep depth. A combined support “bolt‐cable‐mesh‐steel ladder” was proposed based on the failure characteristics of the roadway. Finally, a numerical simulation and field experiment were conducted to evaluate the rationality of the proposed support scheme, and the results show that the new support method can effectively control the surrounding rock. This study can provide valuable references for support design in deep underground engineering.

In an assault on a military fortress, the attacking side often attacks the fortress through the use of underground mining, so that the defensive side cannot be prepared. The existing monitoring methods make it difficult to monitor such underground excavation. One effective way to monitor for tunneling activity is to detect and identify seismic signals generated by underground excavation. However, the main problem facing the practical application of this technology is that many behaviors on the ground may generate seismic signals, and the monitoring system cannot identify whether a signal is generated by underground excavation or by someone walking on the ground, resulting in a high false alarm rate. To effectively identify underground excavation signals, we propose an approach for estimating speed based on a double point synchronization measurement. In our approach, we first formulate mathematical models of the velocities of underground and ground-level objects. Then, signals acquired by different seismic detectors are used to estimate the velocities of underground and ground-level objects. By analyzing the differences between velocities, signals due to human movement and underground excavation are effectively identified. Lastly, simulations and a field test are performed. It is found that the proposed approach can effectively distinguish between signals generated by a human moving at ground-level and underground excavation. Our approach can be helpful for reducing the false alarm rate of a monitoring system.

During underground excavation, rocks are generally subjected to weak dynamic disturbances caused by blasting, machine vibration, rockburst. To investigate the failure characteristics of hard rock subjected to weak dynamic disturbance, two types of tests, dynamic and static true triaxial tests, with different minimum principal stresses σ3 (0.5, 5, 10, 15, 20, 25, and 30 MPa) were conducted on granite specimens. In the former type of true triaxial test, a weak dynamic disturbance was included; while in the latter type of true triaxial test, only a static stress state was considered. Then, the strength and failure mode of the tested specimens were systemically investigated. The experimental results indicate that the rock strength from the dynamic true triaxial tests is lower than that from the static true triaxial tests, indicating a reduction effect of the weak dynamic disturbance on the rock strength. This reduction effect will gradually increase with σ3. In addition, the failure of the tested specimens from the dynamic true triaxial tests is much more serious than that of the tested specimens from the static true triaxial tests, which may be due to the promotion effect of the weak dynamic disturbance on the crack development. Specifically, when σ3 is low, the dynamic disturbance primarily promotes the development of subdominant cracks (vertical tensile cracks and short oblique tensile-shear cracks) within the tested specimens; when σ3 is high, the dynamic disturbance primarily promotes the development of predominant cracks (through oblique tensile-shear cracks). [ABSTRACT FROM AUTHOR]

Frequency-based criteria for control of blasting vibrations require methods to predict both peak particle velocity and dominant frequency. In this study, based on the theory of dynamics of structures a mechanical model is built firstly to derive vibration response to a cylindrical explosion source. According to model analysis, a theoretical formula is proposed to predict the frequency-dependent attenuation of vibration induced by cylindrical explosion source. With the application of dimensional analysis, a mathematical relationship is established between the dominant frequency and its principal influencing factors. The prediction formulae derived from model analysis, and dimensional analysis showed completely consistency in the formula form, indicated that the formula obeys both the method of dynamics of structures and the dimensional homogeneity. In the end the applicability of the proposed formula is verified by single-hole blasting experiments. The prediction accuracy of the proposed formula is compared with some other prediction formulae and the new proposed formula proved to be superior with a higher fitting degree and lower deviation. In addition, application of the prediction method in multi-hole blasting is discussed. With a simplified equation to predict dominant vibration frequency, the research would give a significant guiding path for future blasting engineering. [ABSTRACT FROM AUTHOR]

When the drill and blast technique is used to excavate a roadway in underground coal mines, the relationship between the carriage and roadway space affects the automated hole positioning of a computer-controlled drill jumbo. This leads to low efficiency in hole positioning and high safety risks. This study analyzes the effects of deviations in carriage positioning, left-stacked stones, and inappropriate hole-position design and proposes solutions. This method builds a functional relationship between the size of the drill-bit coverage area and the hole-position parameters based on the drill-arm workspace and its projection. Based on the real-time carriage positioning results, the program checks the alignment between the hole positions and drill-bit coverage area. The crucial angle parameters were adjusted based on the extent to which the blast holes exceeded the coverage area. The analysis showed that the carriage deviation from the midline of the roadway and the height of the remaining stacked stones should not exceed 35–45 cm. Hole drilling and blasting tests demonstrate that this strategy ensures continuous high operational efficiency of the jumbo, thereby safeguarding the blasting efficiency. [ABSTRACT FROM AUTHOR]

In this study, the Lagrange element strength reduction method is used to explore slope stability and as an evaluation method of underground mining of end-slope coal in a rock-stability analysis. A numerical analysis model is established herein using the geological conditions for mining in a coordinated open pit with an underground mining area of the Anjialing Open-Pit Mine and Underground No. 2 Mine. Additionally, the evolution law of slope stability in open-pit end-slope mining is studied using the proposed numerical simulation method. According to our findings, the steps show obvious horizontal movement and deformation under the influence of underground mining disturbances. Taking the horizontal displacement at the slope tops of the steps as the deformation index, the entire disturbed slope is divided into four regions: upper, middle-upper, middle-lower, and lower steps. When a step is fully affected by underground mining, its subsidence value first increases rapidly and then slowly. An exponential function is used to reflect the change rule in the step-subsidence value as the working face advances. In the underground mining process, the critical sliding surface of the slope develops along the soft rock or coal seam, showing an L-shaped or a W (double L)-shaped broken line. As the working face advances, the initial position of the sliding mass is unchanged while the cutting position alternately changes up and down in the weak plane. The safety factor suddenly drops when the advancing distance exceeds a certain value.

The generalized Hoek-Brown (GHB) failure criterion can estimate the rock mass parameters required for rock mechanics–related analyses such as numerical modeling in geomechanics. The determination of GHB parameters has been developed in the field of rock mechanics. Due to the wide use of the Mohr-Coulomb criterion and the lack of an existing relationship for determining its parameters for a rock mass, equivalent Mohr-Coulomb parameters (EMC) can be derived from the GHB. To determine the differences in the use of these two criteria, we analyzed the behavior of a deep circular tunnel in nine stress states for three metamorphic rocks recovered from the Canadian Shield from rock masses that present a very blocky structure. We carried out 241 simulations using the finite element code RS2 to assess the effect of the geological strength index (GSI), in situ stress, and rock type on the deviation of wall displacement, the number of yielded elements, and the differential stress obtained by the GHB and EMC parameters. A combination of low in situ stress and high GSI yielded similar results when using both failure criteria.

Pressure arch utilises the self-stabilizing capacity of surrounding rock and is benefit to the roof stability of underground excavations. The analysis of it provides a new stability assessment tool for underground engineering. In this paper, a series of numerical simulations were carried out to investigate the formation and properties of pressure arch and the self-stabilisation mechanism of surrounding rock. It is found that stress redistribution results in the formation of the pressure arch. The inner and outer boundary of arching area are determined as the principal stress trajectories through the inflection points of the principle stress-depth curves on the centre line of caverns. Furthermore, parametric analysis illustrates that in situ stress ratio and excavation size have more significant effect on the inner and outer boundaries and the arch thickness than roof shape and overburden depth. Finally, it can be observed that the various trends of the inner boundary height with different influence factors are same with the displacement of the crown, and it could be used as an indicator for stability assessment. Based on the observed phenomena, a design scheme is proposed to determine the maximum size of the underground openings cross-section without support in agreement with the geomechanical conditions. [ABSTRACT FROM AUTHOR]

Underground excavation is a necessary process for constructing mines, tunnels and depots in granite rock mass. In this study, the numerical granite specimens were established by the discrete element method and confirmed by laboratory experiments in order to investigate the peak stress, cracking development and failure properties of pre-holed granite under coupled biaxial loading and unloading conditions. The results show that, for the specimens containing D-type and square holes, the peak biaxial unloading strengths first decrease, then increase and finally decrease as the inclination angles of the holes increase. For the specimens with elliptical holes, the peak biaxial unloading strengths first decrease and then increase with the increases in the inclination angles of the holes. The biaxial unloading strengths of specimens containing elliptical, circular, D-type and square holes decrease in that order. The cracks initially appear near the crossover points between the X-type shear fracturing plane and the pre-hole in the center and gradually expand along the X-type shear direction, which indicates that the failure of pre-holed granite is primarily shear failure. When the overall length of cracks expanding along the X-type shear direction extends to the size of the pre-hole in the center, the failure of the pre-holed specimen occurs. When the existing pre-hole in the center of the granite specimen extends to connect with the shear slip in the vicinity of the hole, this triggers overall failure.

Steel reinforced shotcrete lining (SRSL) support is the primary structure to maintain the stability and mobilize the self-bearing capacity of surrounding rock. However, the structural design of SRSL in underground excavation still relies on experience-based method and lack of quantitative mechanical analysis. This paper aims to propose a modified analytical model of support characteristic curve (SCC) that represents the mechanical behavior of SRSL structures in underground construction, through which the interface bond-slip behavior between steel arch and shotcrete layer is taken into consideration. Four-point bending test of SRSL composite beam was carried out to study the bearing mechanism and failure performance. Test results show that the shotcrete-steel interface is prone to slip failure which significantly reduces the overall strength of SRSL. The laboratory test is complemented by non-liner finite element parametric studies considering the bond-slip properties to clarify the design principles and to obtain the flexural stiffness of tunnel primary lining structures. Based on above studies, the simplified formulas for the SCC of SRSL is constructed. The research results provide a theoretical basis for the design and application of SRSL structure in related projects. [ABSTRACT FROM AUTHOR]

Weak dynamic disturbance caused by drilling and blasting, adjacent rockburst, and machine vibration is a key factor to rock failure/rockburst during underground excavation. Meanwhile, the propagation direction of weak dynamic disturbances varies when different underground constructions are encountered. To investigate the effect of the propagation direction of the weak dynamic disturbance on rock failure, a general true triaxial test (applying a loading state of "six stressed faces") and a modified true triaxial test (applying a loading state of "one free face and five stressed faces") are conducted. For the former test, Pd1 (weak dynamic disturbance along the direction of σ1), Pd2 (weak dynamic disturbance along the direction of σ2), and Pd3 (weak dynamic disturbance along the direction of σ3) are involved. For the latter test, only Pd1 and Pd2 are involved due to the limitation of the testing machine used. After testing, the rock strength and macroscopic failure characteristics of the tested specimens are systematically investigated. The experimental results indicate that the rock strength of the tested specimen without weak dynamic disturbance is higher than those with weak dynamic disturbance, indicating a reduction effect of the weak dynamic disturbance on the rock strength. Pd3 has the greatest reduction effect on rock strength due to its greatest promotion effect on crack development, while the reduction effect of Pd1 on rock strength, as well as its promotion effect on crack development, is smallest. In addition, for the tested specimens with a free face, the failure process is observed and investigated. Rockburst characterized by rock fragment ejection occurs during the testing process of these specimens. The kinetic energy of the ejected blocks without weak dynamic disturbance is higher than that with weak dynamic disturbance, showing that the weak dynamic disturbance has a reduction effect on kinetic energy. In addition, the kinetic energy of ejected blocks is lower under the Pd2 condition than that under the Pd1 condition; consequently, Pd2 has a greater influence on the kinetic energy of the ejected blocks, i.e., the intensity of rockburst. [ABSTRACT FROM AUTHOR]

As our understanding and modeling capabilities evolve, an ever-increasing complexity of models representing the behaviour of geologic medium are analyzed. One way to evaluate these substantial problems is to optimize the underlying discretization of the governing differential equations by concentrating finite elements where solution accuracy counts the most. This paper develops and evaluates the performance of a priori local p-refinement method for finite element mesh improvement for stress analysis of underground excavations. This type of refinement entails a mesh with higher-order elements near the region of interest and lower-order elements elsewhere. The focus of the paper is the automated insertion of transitional elements at the interface of the two regions. The method relies on transitional finite elements in order to connect a mesh of quadratic interpolation order elements with a mesh of linear interpolation order elements. Four types of transitional elements were considered (4-node and 5-node triangles, 5-node and 7-node quadrilaterals). These were incorporated into a finite element code, and their performance was tested using representative problems such as a pressurized cavity or tunnelling through rock. For these problems the global stiffness matrix size was reduced on average by 85% and by 81% for the models using triangles and quadrilaterals, respectively, as a result, the calculation times were considerably shortened as well. While the average percentage of error with respect to the models without improvement, measured at critical points, was 0.04% and 0.02% in the case of triangular and quadrilateral elements, respectively.

With the increase in mining depth and the deterioration of surrounding rock conditions, large deformation failure of deep roadway surrounding rock is still very common. To solve the support problem, it is necessary to understand the deformation and failure mechanism of the deep roadway. This paper presents a case study on the deformation failure behavior and support design of a deep roadway in the Tangyang mine by field tests and numerical simulations. The rock mass properties were first evaluated based on field data and the mechanical parameters of rock specimens. Then, the numerical model of the deep roadway surrounding rock was established based on the calibrated microparameters. The deformation features and cracking behavior of the roadway were investigated in detail. The results show that the cracking process of crack initiation, crack propagation, and rock separation in the surrounding rock of this kind of roadway is a gradual process developing from a shallow to deep depth. A combined support "bolt‐cable‐mesh‐steel ladder" was proposed based on the failure characteristics of the roadway. Finally, a numerical simulation and field experiment were conducted to evaluate the rationality of the proposed support scheme, and the results show that the new support method can effectively control the surrounding rock. This study can provide valuable references for support design in deep underground engineering. [ABSTRACT FROM AUTHOR]

The borehole method is quite commonly utilized in underground excavation engineering, such as for mining and tunneling, to release high pressure in brittle rock materials for safety control. In this paper, with the purpose of better understanding the failure behavior of brittle rock material with en echelon boreholes, a series of uniaxial compression tests were carried out on sandstone samples in the laboratory. The geometric layout of boreholes was the focus in this study and varied in terms of the number of borehole rows and orientation. In accordance with the experimental results, three failure modes were observed to occur in the sandstone samples, which are tensile failure across the borehole row, tensile failure along the borehole row, and a mixed failure mode. The strength and deformability of sandstone samples are found to significantly depend on the layout of boreholes. The variation in the brittleness of the rock materials was also analyzed with respect to the ratio of the initial stress over peak stress. The findings of this study would enhance the understanding of the borehole method and provide guidance for underground excavation engineering. [ABSTRACT FROM AUTHOR]

The stability of a fractured rock mass around a subsurface opening is critical to tunnel excavation. The traditional underground excavation analysis is based on a continuum description of randomly distributed discrete pre-existing fractures. In contrast to this, we have developed an improved hybrid finite element method (FEM) to investigate the stability of fractured rocks around an excavation by incorporating the outputs into the FEM codes. The proposed model consists of a discrete fracture network (DFN) model and cohesive zone model (CZM). The DFN model automatically generates a fracture network with a given fracture opening distribution and provides grid generation strategy to the FEM. The CZM captures material failure and intersection and surface contacts through the fracture element with different constitutive laws. As a case study, a DFN model was formulated for the underground excavation at Jinping Hydropower Station, in light of the input requirements of our model, and its deformation analysis was performed. The comparison analysis of rock deformation was made for excavation in both intact rock mass and fractured rock mass under the same boundary conditions. The numerical results show that two different modes of rock failure exist in these two rock masses and that intense deformation at the fractures intersected by the tunnel is responsible for fractured rock mass instability. The proposed approach was verified using data from field investigations. A larger displacement can be produced if the rock mass is weakened by a key block. A sensitivity analysis was carried out to investigate the effects of different model parameters on deformation variations. This study provides an insightful understanding of the deformation of fractured rock mass during tunnel excavation. [ABSTRACT FROM AUTHOR]

As our understanding and modeling capabilities evolve, an ever-increasing complexity of models representing the behaviour of geologic medium are analyzed. One way to evaluate these substantial problems is to optimize the underlying discretization of the governing differential equations by concentrating finite elements where solution accuracy counts the most. This paper develops and evaluates the performance of a priori local p-refinement method for finite element mesh improvement for stress analysis of underground excavations. This type of refinement entails a mesh with higher-order elements near the region of interest and lower-order elements elsewhere. The focus of the paper is the automated insertion of transitional elements at the interface of the two regions. The method relies on transitional finite elements in order to connect a mesh of quadratic interpolation order elements with a mesh of linear interpolation order elements. Four types of transitional elements were considered (4-node and 5-node triangles, 5-node and 7-node quadrilaterals). These were incorporated into a finite element code, and their performance was tested using representative problems such as a pressurized cavity or tunnelling through rock. For these problems the global stiffness matrix size was reduced on average by 85% and by 81% for the models using triangles and quadrilaterals, respectively, as a result, the calculation times were considerably shortened as well. While the average percentage of error with respect to the models without improvement, measured at critical points, was 0.04% and 0.02% in the case of triangular and quadrilateral elements, respectively. [ABSTRACT FROM AUTHOR]

As more and more TBM tunnels are constructed under complex conditions such as high stress and fault fracture zones, large deformation disasters of squeezing soft surrounding rocks occur frequently. However, TBM method shows poor adaptability to major engineering challenges. Equipment damage, track deviation and support structures failure are widely observed. It is important to propose an effective support scheme and to fully clarifying the mechanical properties of the support structures in TBM tunnel. In this case, this paper aims to conduct laboratory and numerical tests considering steel–concrete interface bond-slip behavior so as to verify the effectiveness of the proposed support scheme. Thus, the quantitative relationship between arch type, arch spacing, longitudinal connection strength, concrete strength, steel fiber content, and tunnel surrounding rock deformation can be obtained. The research results show that the support scheme proposed in this paper shows good applicability for deformation control of TBM tunnels under squeezing soft rock conditions, which provides a reference for TBM tunnel support under squeezing soft rock conditions. [ABSTRACT FROM AUTHOR]