Displacement Of Rock Mass Research Articles

A hybridized DDA-DDM for modeling jointed rock masses

The complexity of geo-materials’ behaviors surpass the capabilities of conventional numerical methods alone, particularly when realistically modeling rock structures. Coupling methods can enhance the realism of numerical modeling. Discontinuous deformation analysis (DDA) and displacement discontinuity method (DDM) are combined to model block displacement and crack propagation mechanisms in a blocky rock mass. DDA calculates stresses, strains, rotations, and displacements of the blocks, while DDM predicts crack propagation paths based on specified boundary conditions. The displacements result from DDA are transformed into stresses, followed by investigating crack propagation mechanisms within each block using Kelvin's solution. Boundary stresses are adjusted as cracks propagate, updating stress boundary conditions in DDA. This iterative process continues until crack propagation halts or a new block emerges. In this paper, the complete failure process of a rock slab with one pre-existing non-persistent joint located on the crest of a rock slope and compression test on the rock-like specimen with a single random crack with a 45° slope angle is simulated using the proposed numerical approach. The proposed numerical solution is compared with existing numerical results. This comparison confirms the accuracy and effectiveness of the proposed procedure, as the predicted crack propagation paths from the coupled numerical method align well with the corresponding numerical results from the rock-like samples.

Evolution Law and Grouting Treatment of Water Inrush in Hydraulic Tunnel Approaching Water-Rich Fault: A Case Study

Tunnel construction adjacent to the fault fracture zone is prone to water inrush disasters, which pose a serious threat to the safety of tunnel construction. To provide theoretical support for the early warning and prevention of water inrush disasters of the tunnel adjacent to the water-rich faults, a numerical analysis based on the three-dimensional discrete element method (DEM) was performed to study the evolution of the displacement and seepage fields of the water-resistant rock mass of a tunnel adjacent to a water-rich fault during the water inrush process by taking the Xianglushan tunnel as the research project. With reference to the obtained results, a grouting reinforcement scheme was developed, and its effectiveness was evaluated. The results indicated that as the tunnel face approached the water-rich fault fracture zone, the effect of water pressure gradually became obvious, and the displacement at the face continuously increased. When the tunnel face was excavated to the position 5 m from the fault, the displacement at the center of the face changed suddenly with a sudden increase in water pressure. The water-resistant rock mass ahead of the center of the face was damaged, and a water inrush disaster occurred in the tunnel. Numerical simulation results demonstrated the feasibility of the grouting reinforcement scheme. The assessment based on the borehole acoustic waves, borehole TV, geological radar detection, and convergence monitoring as well as the excavation results confirmed that the water inrush disasters in the 2# adit of Xianglushan tunnel adjacent to the water-rich fault were effectively prevented and controlled, which can provide a reference for the prevention and treatment of the frequent water inrush disasters in underground projects constructed in the water-rich fault area.

Slope stability analysis of an open pit mine with considering the weathering agent: Field, laboratory and numerical studies

Freezing-thawing (F-T) processes can affect the slope instability of open pit mine wall in cold regions, resulting the increase of mining operations cost and decrease the safety of personnel and equipment. Therefore, estimating the degradation of rockmass geomechanical properties under the weathering agent is crucial for slope stability analysis of an open pit mine in mountain areas. Accordingly, for optimal slope stability analysis of Angouran open-pit mine in this research, variations of physico-mechanical properties of pit wall schist rock including dry density, and uniaxial and triaxial compressive strengths were firstly measured during the defined F-T cycles. Then, the related properties of slope rock mass were determined using the generalized Hoek-Brown criterion. Based on the estimated rock mass characteristics, a numerical model of mine slope was constructed and pit stability conditions was analyzed. According to the obtained results, the displacement of slope rock mass varied from 0 to 14.6 m, occurred in highly weathered schist, indicating the low probability of large collapses. To validate the achieved results, 30 prisms were installed in the north-west wall of mine and in-situ displacements were recorded three times in week for one year. Results indicated that the measured displacements from in-situ monitoring and numerical model are in good agreement, so that the determination coefficient (R2) was obtained 0.80.

Penerapan Sistem Monitoring Pergeseran Tanah berbasis Internet of Things (IoT) di Daerah Aliran Sungai (DAS) Kahayan, Kota Palangka Raya

Landslides occur as a result of a geological process caused by the displacement of rock or soil masses. In general, landslides are caused by shifting soil and excessive water content due to high rainfall. One of the processes that occur in rivers is sedimentation With the entry of sediment into the river flow, it will result in increased river surface flow and deposition which causes siltation of the river. This siltation will greatly affect the capacity of the river when the rainy season arrives, because it can cause floods. For this reason, assistance and training are needed to increase community knowledge about the use of Internet of Things (IoT) based monitoring system tools around the Kahayan river basin. IoT is a technology that allows smart objects, things, and machines to be connected via the internet so that data can be received in real time. The people of Pahandut Village were enthusiastic in participating in the socialization activities provided and felt the benefits of increasing knowledge starting from an understanding of the Internet of Things and the use of monitoring system tools for land shifts. Based on the evaluation results, it is known that participants have increased knowledge and insight into the Internet of things and its application in this case the soil shift monitoring system tool which will later be installed in residential areas around the watershed (DAS).

Stress redistribution in a multilayer chamber for compressed air energy storage in abandoned coalmine: Elastic analytical insights and material choice

AbstractCompressed air energy storage (CAES) is attracting attention as one of large‐scale renewable energy storage systems. Its gas storage chamber is one of key components for its success. A successful utilization of an abandoned coalmine roadway depends on the stability of the gas storage chamber. The chamber is a multilayer structure and the redistribution of the stress and displacement in each layer is critical to the chamber stability. So far, this redistribution mechanism under any lateral pressure coefficient and internal air pressure has been unclear and thus a quick and easy evaluation on the CAES chamber stability becomes difficult. In this study, the redistributions of stress and displacement in each layer are analytically solved based on complex variable function theory. First, the stress and displacement in three CAES multilayer structures are obtained under any lateral pressure coefficient and internal air pressure. Then, a comprehensive parameter b1 is obtained to describe the redistribution of stress and displacement in rock mass, lining layer, and grout layer. Its linkage with lateral pressure coefficient, internal air pressure, and material properties is analytically expressed. Thirdly, an analytical expression is obtained for the influence range of internal air pressure on chamber stress. Finally, the role and selection of lining and grouting layers are explored at different lateral pressure coefficient and internal air pressure. It is found that the CAES chamber stability can be effectively and quickly evaluated by these analytical solutions and comprehensive parameters and enhanced by a material with low bulk modulus but high shear modulus.

Influence of underground mining activities on the topographic surface, case study of Nui Beo Coal Mine (Vietnam)

Purpose. Coal mining activities by underground mining method will disrupt the equilibrium of the surrounding rock mass. In underground mining, determining the influence zone of exploiting the longwall on the topographic surface is extremely important.Through analyzing the displacement and deformation of the rock mass when exploiting the longwall 21103 in Seam 11 at Nui Beo Coal Mine, the influence is to be determined of exploiting this longwall on the topographic surface in order to forecast the boundary of the influence zone that may affect the surface works, ensuring the safety of such works. Methodology. To achieve the research results, actual field survey methods, data analysis and numerical modeling methods are used in this article. Findings. Analysis of the results from the numerical model determined that the total height of the collapsed and cracked area when exploiting the longwall 21103 in Seam 11 is about 85 m. The subsidence to the ground is about 10 cm from the center of the subsidence area. The analysis results from the numerical model also show that the roof collapse angle is 69°, thereby determining the area of influence on the topographic surface in the range of 55 m. Results on the cross-sections show that the boundary of the influence of mining on the topographic surface is the closest section 6–6, which is about 12 m. The stability time of the collapsed rock mass is determined to be about 5 months. Originality. On the basis of UDEC (Universal Distinct Element Code) software, the authors have developed a simulation model for the mining process of the longwall 21103 in Seam 11. Analysis of the results from the model has shown the state of displacement and deformation of the surrounding rock mass. In this study, the numerical modeling method is applied to simulate the displacement of the longwall, which is consistent with the actual production of the underground mine. This enabled the authors to assess and identify the affected area with the required degree of reliability. Practical value. The research results of the paper are used as a basis for implementation in actual production at Nui Beo Coal Mine. On the basis of the analysis of the surrounding rock mass displacements and deformations, when exploiting the longwall 21103 in Seam 11 at Nui Beo Coal Mine, the affected boundary of the topographic surface has been determined. At the same time, the stability time of the collapsed rock mass is also calculated. So, this is also the basis for Nui Beo Coal Mine to plan construction works on the site outside the determined affected areas to ensure the safety of such works.

Determination of the rock mass displacement zone by numerical modeling method when exploiting the longwall at the Nui Beo Coal Mine, Vietnam

Purpose. It is important to conduct a study to identify the displacement zone caused by mining operations. By numerical modeling the process of mining the longwall 31104 in Seam 11 at the Nui Beo Coal Mine, Vietnam, the authors have deter-mined the total height of the rock mass displacement zone and the boundary of the affected area on the topographic surface. Methods. In this study, the authors use a numerical modeling method. The models are developed based on the UDEC (Universal Distinct Element Code) software. In addition, field survey methods and statistical analysis methods are used. Findings. Based on the analysis of the numerical modeling results, it has been determined that the total height of the displacement zone, when exploiting the longwall 31104 in Seam 11, is about 63 m. The analysis of the numerical modeling results also shows that the roof collapse angle is 52°, which determines the area of influence on the topographic surface in the range of 160 m. Originality. Based on the UDEC software, the authors have developed a simulation model for the mining process of the longwall 31104 in Seam 11. Analysis of the model results has shown the state of the displacement zone of the surrounding rock mass. In this study, the numerical modeling method is applied to simulate the longwall displacement zone, which is consistent with the actual production of the underground mine. Practical implications. Based on the analysis of the surrounding rock mass displacements zone, when exploiting the longwall 31104 in Seam 11 at the Nui Beo Coal Mine, the affected boundary on the topographic surface has been determined. At the same time, the height of the rock mass displacement zone has also been calculated. Thus, the research results can be used as a basis for implementation in actual production at the Nui Beo Coal Mine.

Study on effects of highly deviated well on thin interbedded reservoirs fracturing

Highly deviated well is widely applied in thin interbedded reservoirs fracturing in changqing oilfield. the oil production data shows that highly deviated fracturing well can increase the oil production compared with horizontal well fracturing, which suggests that highly deviated well fracturing is more efficient. However, it still needs deeper understanding for the mechanism of highly deviated well increase oil production, to study this problem, True-axial hydraulic fracturing physical simulation test is carried out on two kinds of cement specimen with interlayers, the results show that cement specimen for highly deviated well is more productive because fractures are more likely to cross the interbedded layers and connect oil reservoirs that separated by interlayers. Further research on the mechanism of highly deviated well fracture crossing interbedded layers is conducted via numerical simulation. Cohesive zone model is adopted to simulate the propagation of fracture in highly deviated well and horizontal well to compare the difference of thin interbedded layers stress. the results show that due to the deflection of highly deviated well fracture during propagation, the reservoir mass is divided into two parts, which causes relative displacement of rock mass on both sides of the fracture under the effect of vertical principal stress, thin interlayer eventually got broken under the action of tensile and shear stress. Both laboratory tests and numerical simulation results show that highly deviated wells have stronger interlayer penetration capability, which can improve the fracturing effect of thin interbedded reservoirs.

Wave-like character of rock pressure in a longwall face

Introduction. Coal seam extraction causes rock mass displacement, which often leads to negative consequences. It is important to take into account the process patterns within the undermined rock mass to reduce the negative effect. Intensifi ed mining operations, increased lengths of faces and extraction panels, and increased per face output inevitably cause changes in all geomechanical processes in the face. Research theory. When designing and developing the working area, it is important to examine and forecast the geomechanical situation, as well as take into account the parameters and elements of the displacement processes caused by coal seam mining. The research objective is to determine the infl uence patterns in the rock seam that exerts pressure on mine support. The article presents the results of pressure area construction when mining longwall faces in gently sloping coal seams. Methods of research. Rock pressure on a power support unit was monitored based on pressure readings in the legs using Marko company data. The Surfer software product was used to build the pressure area and its profi les. The pressure area is obtained by converting the fl uid pressure in power support legs into rock pressure. The variation of the longwall support pressure during coal seam mining is shown. Results and analysis. The paper proposes an algorithm for calculating the thickness of the seam that exerts pressure on the longwall face support. The algorithm considers its wave-like changes along the length of the panel. The thickness of rocks exerting pressure on the support is up to 10 seam thicknesses. Conclusions. The height of the pressure arch generally coincides with the parameters for the disordered collapse zone. It is 4–8 times as big as the thickness of the extracted seam. The process of roof collapse and displacement a longwall face is wave-like. The height of the pressure arch can be determined using a sinusoid and the concepts of rock mass structuring according to the algorithm presented in this paper

Analytical Solutions for a Deep-Buried Tunnel with Noncircular Cross Sections in Orthotropic Rock Mass

For the generalized plane strain problem of a deep-buried tunnel excavated in orthotropic rock mass under far-field biaxial compression, the stress and displacement are the most important basis for determining tunnel support design. First, by using the complex variable method, the conformal mapping and affine transformation functions are represented by the same variable. Two stress functions are obtained by the integral method, and thus, the analytical solutions for stress and displacement in orthotropic rock mass are obtained. Second, taking a horseshoe-shaped tunnel as an example, the stress and displacement distributions around the tunnel are given by using the analytical and the finite element method software ANSYS, respectively. The analytical and numerical results are in good agreement, especially at the tunnel edge. Finally, compared with isotropic rock mass, the results show that material constants of the rock mass have little effect on the stress and significant effect on the displacement.

Assessing the impact of underground working (tunneling) in the II section of Seam 14 on surface construction works at Ha Lam Coal Mine (Vietnam)

Purpose. Tunneling in the ground changes the initial equilibrium stress state of the rock, which is also the cause of displacement and deformation of the surrounding rock mass. To determine the impact of tunneling on surface construction works in order to ensure the safety of surface works by analyzing the displacements and deformations of the rock mass during tunneling in the IIsection of Seam 14 at Ha Lam Coal Mine. Methodology. To achieve the research results, actual field survey methods, data analysis and numerical modeling, as well as combined blasting vibration methods are used. Findings. After analyzing the numerical modeling results, an area has been identified in the II section of Seam 14 of the Ha Lam Coal Mine that affects the surface construction works and is located within a radius of about 20 m from the portal of two inclined shafts. The results of blasting vibrations are calculated on the basis of the passport of blasting operations in tunnels. Thus, the affected area has been identified within a radius of 30.5m. However, at a distance of 30.5 m, surface construction works are not in the area of influence. Originality. On the basis of FLAC software, the authors have developed a simulation model for tunneling, thereby analyzing and describing the best state of deformation and displacement of the surrounding rock mass. In this study, a numerical modeling method is applied to simulate the driving order for each tunnel, which is consistent with the actual production of underground mines. Based on the passport of drilling and blasting operations in tunnels, the authors calculated the impact of blasting vibrations on surface construction works. After that, the authors assessed and identified the affected area with the required degree of reliability. Practical value. The research results are used as a basis for implementation in actual production at Ha Lam Coal Mine. On the basis of analysis of the surrounding rock mass displacements and deformations, when tunneling in the II section of Seam 14 at Ha Lam Coal Mine, the affected area of the surface construction works has been determined. This is also the basis for Ha Lam Coal Mine when planning construction works on the site outside the determined affected areas to ensure the safety of such works.

Rancang Bangun Alat Deteksi Tanah Longsor Berbasis IoT dengan NodeMCU ESP8266 dan MPU6050

Landslide is a geological process caused by the displacement of rock and soil mass. In general, landslides are caused by geographical conditions in the form of mountains and slopes as well as high rainfall which causes the soil to become unstable. This study aims to make a landslide detection tool using NodeMCU ESP8266 as a microcontroller and MPU6050 as a sensor so that it can detect the acceleration of the earth on the x, y, and z axes and the slope of the ground. This landslide detection tool is based on the Internet of Things (IoT) so that it allows the acceleration of the earth and the slope of the ground to be monitored in real-time. This tool is linked to applications built using cloud services on a real-time database of firebase and MIT APP Inventor to build applications. From this study, it can be concluded that landslide detection tools and applications can work according to the design that is able to display the acceleration of movement and slope of the ground in real-time and can convey the condition status, namely safe, beware and alert with an average error of 0.419%

Ground Characteristic Curve and Convergence Confinement Method - A case study

Ground Characteristic Curve (GCC) describes the relationship between the initial stress of rock mass and the displacement of rock mass on the boundary of tunnels. Another way that indicates the relationship of support pressure and the level of Convergence Confinement of tunnels by percent. The using GCC to design supports in the underground construction has many advantages to ensure full utilization of the loading bearing capacity of rock mass, and release a part of initial stress in the rock mass around tunnels. However, this method is limited in the field of underground mines in Viet Nam. This article analyzed and applied GCC and Convergence Confinement Method (CCM) to design the supports of underground constructions and applied them to the geological conditions of the Nam Mau coal mine - Vinacomin. The research results show that at the geological conditions of the drift at level +125 in Nam Mau coal mine, TH section steel ribs with flange width 124 mm, section depth 108 mm, weight 21 kg/m, maximum support pressure 1.98 MPa, and spacing 700 mm were applied. Results of research in this method can be applied to design rock supports for deep roadways and other drifts in the underground mines in Quang Ninh province of Viet Nam. By a factor of safety, mobilized support pressure, wall displacement of roadways, and convergence of roadways the designation and selection of rock support around roadways will become clearer. Near future this method should be widely applied in the combined protection design in deep roadways in underground mines in Viet Nam. Although the method has great advantages, it is still necessary to have complete and detailed monitoring data of the geological and hydrogeological conditions in the area under consideration.

Study on the stability of rock mass around large underground cavern based on numerical analysis: A case study in the Cai Mep project

Geotechnical problems are complicated to the extent and cannot be expected in other areas since non-uniformities of existing discontinuous, pores in materials and various properties of the components. At present, it is extremely difficult to develop a program for tunnel analysis that considers all complicated factors. However, tunnel analysis has made remarkable growth over the past several years due to the development of numerical analysis methods and computer development, given the situation that it was difficult to solve the formula of elasticity, viscoelasticity, and plasticity for the dynamic feature of the ground when the constituent laws, yielding conditions of ground materials, geometrical shape and boundary conditions of the structure were simulated in the past. Actual problems have been successfully analyzed in addition to simple analysis and more reasonable design and construction management materials have been obtained. The stability of rock mass around an underground large cavern is the key to the construction of large-scale underground projects which have to divide into different parts stages. Rock bolt and shotcrete are important means to ensure the stability of the underground cavern. The objective of the paper is to evaluate the stability of a large cavern in the Cai Mep project in Ba Ria- Vung Tau by numerical method. The results from numerical simulations show that the stability of rock support of the cavern is in fair agreement with the original design calculation. The maximum displacement of rock mass surrounding caverns, maximum compressive stress and tensile stress in shotcrete, and the maximum axial force of rock bolt obtained by Rocscience -RS2- Phase2 software are the main parameters in the stability assessment.

Investigation on the evolution mechanism of water and mud inrush disaster in fractured rock mass of mountain tunnel

Water inrush is one of the major disasters during tunnel construction. Due to its characteristics of great harm and difficult prediction, it has always been the focus of research. In order to reveal the mechanism of fault water inrush, a laboratory experiment is adopted to simulate tunnel excavation. The results show, firstly, the pore water pressure and soil pressure of model are unchanged before the fault is exposed; after the fault is exposed, the pore water pressure and soil pressure of vault decrease first, followed by the arch and haunch, and the decline of arch and vault is greater than that of haunch. Secondly, excavation has the greatest impact on the displacement of rock mass directly above the tunnel axis, and the farther away from the axis, the smaller the impact. Thirdly, the seepage channel around vault begins to expand, and clear water begins to seep out after the fault exposure. As the sediment in the crack is carried out by water flow, the clear water gradually becomes turbid, seepage channel changes from pore flow to fissure flow and then to pipe flow. Finally, Comsol is used to analyze the fault water inrush mechanism from the perspective of permeability change, and the correctness of model test is verified by comparing with engineering practice.

Characteristics and Evolution of Tunnel Collapse in Fully-Weathered Coastal Red Sandstone Strata

Xu, H.; Shao, Z.; Chen, C.; Wang, Z.; Cai, L.; Li, Z., and Huang, C., 2022. Characteristics and evolution of tunnel collapse in fully-weathered coastal red sandstone strata. Journal of Coastal Research, 38(2), 289–301. Coconut Creek (Florida), ISSN 0749-0208. Understanding characteristics of tunnel collapse and its evolution is the premise of effective prevention and control. Fully-weathered coastal red sandstone is widely distributed in coastal areas, and the characteristics of tunnel collapse under this stratum are not clear. This paper studies characteristics of tunnel collapse and its evolution by conducting a model test of tunnel excavation in fully-weathered coastal red sandstone with digital image processing, where the whole process of rock mass failure, displacement, and strain variations are studied. The results show that: (1) the instability failure of the fully-weathered coastal red sandstone rock mass is a progressive process under the load. Three major collapses occur consecutively, where the first and the second start at the arch foot and arch waist, respectively; both manifested as cracks developing upward to the middle until the cracks penetrate. The third is mainly manifested as the collapse of rock mass block above the tunnel crown. (2) The displacement and shear strain around the tunnel increase first with the load and then stabilize. The vertical displacement is more significant than the horizontal displacement. Tunnel crown is where the vertical displacement increases the fastest and accumulates the most, which directly threatens the rock mass stability and thus deserves special attention. The arch waist has the most intense change of shear strain. (3) All three collapses end up forming a stable balanced arch. The three collapses show the evolution that the foot of the balanced arch gradually moves horizontally outward, and the height of the balanced arch gradually expands upward. The shape of the balanced arch can be well fitted by a parabolic function. Practical suggestions on tunnel collapse prevention and control of fully-weathered coastal red sandstone are also put forward.

Three-Dimensional Measuring Device and Method of Underground Displacement Based on Double Mutual Inductance Voltage Contour Method.

Landslide is a very common and destructive geo-hazard, and displacement monitoring of it is integral for risk assessment and engineering prevention. Given the shortcomings of current landslide displacement monitor technologies, a new three-dimensional underground displacement monitoring technology is proposed based on the double mutual inductance voltage contour method. The underground displacement measuring device mainly consists of an information processing unit and sensing array, connected by power and RS-485 communication lines. An underground displacement measurement model to convert the double mutual inductance voltages and the inter-axis angle into the relative displacement between adjacent sensing units is established based on the interval-interpolation and contour-modeling. Under the control of the information processing unit, the relative displacement between any two adjacent sensing units can be calculated through the underground displacement measurement model, so as to obtain the total displacement from underground depth to surface, and the measurement data can be further sent to the Internet of things cloud platform through the 4G module; thus the remote real-time monitoring of underground displacement three-dimensional measurement for the rock and soil mass from underground depth to the surface is realized. The measurement model is verified by building an experimental platform to simulate the underground displacement of rock and soil mass. The experimental results show that for each measuring unit, when the horizontal displacement and vertical displacement are within the measurement range of 0–50 mm, the maximum measurement error will not exceed 1 mm, which can meet the accuracy requirements of underground displacement monitoring of landslide.

Mechanical Behavior of the Rock-Concrete Interface for a Bridge Anchorage Structure Using Discrete Element Method

Traditionally, the numerical simulation work of a bridge gravity anchorage structure is performed with a continuous method, such as the finite element method (FEM). However, since the rock mass and gravity anchorage structure are assumed to be continuous in the FEM, the interaction between the rock mass foundation and the concrete of the anchorage is not frequently considered. This paper aims to investigate the problem of the interaction between the rock mass foundation and the concrete of the anchorage. The discrete element method (DEM), which has been verified to be suitable for the modelling of contact problems of discrete blocks, is introduced in this paper to simulate the mechanical behavior of the rock-concrete system of the gravity anchorage structure and its rock mass foundation. Based on the in-situ scale model test for a bridge, the mechanical behavior of the rock-concrete interface was discussed with the DEM method. With the calibrated DEM model, the displacement of the foundation rock mass, contact stresses, and yield state on the rock-concrete interface were numerically investigated. The anti-sliding effect of the keyway and the step at the bottom of the gravity anchorage structure was analyzed. The results show that the anchorage deformation under the design conditions is basically characterized by the rigid rotation around the keyway of platform #2, and that such rotation subsequently affects the anti-shear capacity of the entire gravity anchorage to a large extent. The anchorage scale model could remain stable under the design lateral load such that the rock-concrete interface would remain intact and sufficient shear resistance could be provided by the keyway and steps.

Improvement of engineering solutions on friction-anchored rockbolting in mine support in difficult geological conditions

Increasingly deeper level mining in highly complicated geological conditions dictates improvement of the existing systems of mine support. The pilot commercial testing which have been implemented for 13 years in mines in Russia, Kazakhstan, Uzbekistan and Kyrgyzstan makes it possible to develop and improve friction-anchored rockbolting technologies of different geological and geotechnical conditions. The promising mine support technologies should be based on integration of mixed-type support designs including friction-anchored rock bolts, reinforcement and, sometimes, pre-treatment of adjacent rock mass. Under conditions of rockburst hazard, it is recommended to combine various rockbolting systems. The system of friction-anchored rock bolts and reinforcement ensures sufficient load-bearing capacity in case of adjacent rock mass displacement owing to the use of a special friction-anchored bolt insert of a smaller diameter. In this case, given low yielding of the rock bolt material, it is possible to provide its sufficient extension. After a series of tests, it is found that the limiting load preceding displacement of the face plate is 128.8 to 141.2 kN. The ‘yield’ of the face plate, from the load of 50 kN up to the limiting load, is 8.1–9.2 mm. When the limiting load is reached, the external diameter of the thrust decreases and the thrust ‘passes through’ the hole in the plate, which favors stability of a roadway in case of dynamic events. Neither the thrust no the rod experiences damage in this case. The essential scatter in the values of the limiting loads is conditioned by the difference (instability) in heating time of the rod before the formation of the thrust. The optimal heating time is 2.5 s, and it is maintained and held in case of complete automation of friction-anchored rock bolt manufacture. The promising design solutions on mine support systems using friction-anchored rock bolts are identified.

Predicting rock displacement in underground mines using improved machine learning-based models

Displacement of rock mass in tunnels and underground mines is considered one of the most hazardous phenomena that can cause the collapse of the structures. In this study, the rock properties, such as the depth of the tunnels (H), the angle of rock layers (α), anti-bending moment (Wc), the width of the tunnels (b), the tensile strength of rock layers (Rn), and monitoring distance (Lb), and observation time (t), were investigated to predict rock displacement in tunnels and underground mines. Two novel soft computing models, namely Harris Hawks optimization algorithm (HHOA)-based support vector machine (SVM) model (i.e., HHOA-SVM) and Grasshopper optimization algorithm (GOA)-based SVM model (i.e., GOA-SVM), were developed for this aim based on the field measurements. A total of 12 measurement stations and 63 observations of vertical rock mass displacement, rock properties, and observation time in some underground coal mines in the Donbas region (Ukraine) were compiled as the dataset for developing soft computing models. In addition, a constraint was also added to the proposed HHOA-SVM and GOA-SVM models to prevent the model from offering negative results in predicting rock displacement. The conventional models, such as SVM (without optimization) and artificial neural network (ANN), were also investigated to compare favorably with the two proposed HHOA-SVM and GOA-SVM models. Furthermore, linear and nonlinear equations were also established to predict rock displacement and compared to the soft computing models. The results showed that the novel HHOA-SVM and GOA-SVM models provided better performances than conventional SVM and ANN models. Besides, the sensitivity of the input variables was also analyzed to discover the certain characteristics of the rock displacement phenomenon through the properties of rock and observation time. The findings show that H, Lb, t, and α are the most influential parameters for predicting rock displacement in tunnels and underground mines. In contrast, the contribution of b in rock displacement is tiny, and Wc did not relate to the rock displacement in tunnels and underground mines.