Rock Mass Deformation Research Articles

Response Characteristics of Electric Potential and Its Relationship with Dynamic Disaster during Mining Activities: A Case Study in Xuehu Coal Mine, China.

Across the world, coal resource is widely utilized in industrial production. During coal mining activities, dynamic disasters may be induced, such as coal and gas outbursts, or rock burst, resulting in serious accidents or disasters. Previous studies have shown that electric potential (EP) signals can be produced during the deformation and fracture process of coal and rock mass under load. The abnormal response characteristics of EP can reveal the damage evolution and failure feather of coal mass. In this paper, the response characteristics of EP signals are analyzed with high gas testing during mining activities within deep coal seams, and the relationship between the EP response and outburst disaster hazard is studied. The results show that: (1) Under the comprehensive action of mining stress and gas effect, the coal mass was damaged and fractured, which can produce abundant EP signals, while the temporal EP response characteristics can reflect the loading state and damage evolution process inside the coal seam. (2) When coal cannon and a sudden increase of gas concentration occurred in the coal mass, the EP signal was at a high level and fluctuated violently. This can be regarded as precursory information for an outburst risk, which was verified by monitoring the results of mining stress and electromagnetic radiation (EMR). (3) Based on the unilateral inversion imaging method, EP spatial distribution law was studied and abnormal zones with high-value were identified. The zone is close to, or coincident with, the high value interval of EMR intensity and count indexes, which revealed the distribution characteristics of coal damage localization. Hence, EP monitoring results can forecast precursor information of outburst hazards temporally, and identify local zones with outburst hazard spatially. This study provides a new idea and application basis for using the EP method to monitor and prevent coal and rock dynamic disaster hazards in the field.

Research on stability of steep bank slope and reserved thin-walled rock cofferdam during excavation of intake foundation pit

The intake of water diversion project is generally located on the bank slope above the large reservoir or deep water area of a river. Due to the influence of water level change and hydraulic action, the rock mass of bank slope is seriously weathered and broken, leading that the rock mass has low strength and is easy to collapse or landslide. In this paper, the water intake engineering of the long-distance diversion project in central Shanxi Province is selected as the research object. The multi-point displacement meter is used to monitor the slope deformation after anchorage and concrete retaining wall support. Based on the FLAC3D V6.0 software, the numerical simulation of the excavation process of the steep reinforced river bank slope is carried out, and the long-term deformation of the slope is predicted. The excavation scheme of retaining outer thin-walled rock wall as water cofferdam is proposed. The excavation process of foundation pit, which is supported with concrete-filled steel tubular pile reinforcing cofferdam and concrete supporting beam, is simulated. It is found that the upper part of the steep slope supported by anchor cable and concrete retaining wall is stable, and the large deformation and plastic failure of the water-retaining thin rock wall are mainly affected by the disturbance of foundation pit excavation. The concrete-filled steel tubular pile support avoids the collapse of the reserved thin-walled cofferdam, and the horizontal beam in the foundation pit improves the stress state of the external wall of the foundation pit. The research results of this paper reveal the evolution mechanism of rock mass deformation and failure during excavation of foundation pit on steep bank slope, and provide guidance for excavation and support of foundation pit for similar bank slope.

Numerical Simulation of Crack Evolution Mechanism and Subsidence Characteristics Effected by Rock Mass Structure in Block Caving Mining

In the block caving mining, the significant rock mass deformation and surface subsidence will be formed with the continuous extraction of ore. However, the internal crack evolution mechanisms in rock mass and associated subsidence characteristics present one of the key issues in rock mining engineering. Although block caving method has been used for many years, current knowledge of the crack evolution mechanisms, the subsidence characteristics under the influence of rock mass structure and subsidence prediction capabilities are limited. Based on the rock mechanics model provided by CEMI (Centre for Excellence in Mining Innovation), crack evolution mechanisms and subsidence characteristics effected by the rock mass structure in block caving are numerically investigated using RFPA 2D, a numerical code based on FEM (Finite Element Method). Crack formation, propagation and coalescence in the overlying strata and the stress-balancing arch evolution in the stress field are represented visually during the whole process of extraction. The numerically obtained crack evolution shows that the stress-balancing arch has a significant influence on the fracture development of rock mass, and directly determines the slump form and rate of the rock mass. After understanding of the crack evolution mechanism in rock mass, the characteristics of surface subsidence are analyzed. Numerical experiments emphasize the geometrical configuration of joints and faults about mechanisms of subsidence development, including joints orientation, faults location and inclination, which can provide significantly meaningful guides for investigation of subsidence mechanisms and implementation of remedial measures.

Damage Constitutive and Failure Prediction of Artificial Single-Joint Sandstone Based on Acoustic Emission

The effect law of deformation and failure of a jointed rock mass is essential for underground engineering safety and stability evaluation. In order to study the evolution mechanism and precursory characteristics of instability and failure of jointed rock masses, uniaxial compression and acoustic emission (AE) tests are conducted on sandstones with different joint dip angles. To simulate the mechanical behavior of the rock, a jointed rock mass damage constitutive model with AE characteristic parameters is created based on damage mechanics theory and taking into account the effect of rock mass structure and load coupling. To quantify the mechanism of rock instability, a cusp catastrophe model with AE characteristic parameters is created based on catastrophe theory. The results indicate that when the joint dip angle increases from 0° to 90°, the failure mechanism of sandstone shifts from tensile to shear, with 45° being the critical failure mode. Sandstone's compressive strength reduces initially and subsequently increases, resulting in a U-shaped distribution. The developed damage constitutive model's theoretical curve closely matches the test curve, indicating that the model can reasonably describe the damage evolution of sandstone. The cusp catastrophe model has a high forecast accuracy, and when combined with the damage constitutive model, the prediction accuracy can be increased further. The research results can provide theoretical guidance for the safety and stability evaluation of underground engineering.

Excavation compensation method and key technology for surrounding rock control

The change in the stress state of the underground rock caused by excavation is the root cause of the deformation instability. Compensating for the stress change is one of the keys to effectively control the instantaneous deformation of rockbursts and the slow deformation of soft rocks in deep underground engineering. At present, the Platts pressure arch theory and the New Austrian Tunneling Method are commonly used in ground control, but their applicability to high-stress deep rock masses is limited. The strength and elongation of the traditional support materials are insufficient, the prestress is low, and it is difficult to effectively control the large deformation of deep rock masses. In this work, the excavation effect and support compensation effect of the rock are analyzed from the mechanics perspective, and an excavation compensation method suitable for controlling large deformation of deep rocks is proposed. The excavation effect verification experiments are carried out to examine the large deformation failure characteristics. Based on the excavation compensation method, a high prestress excavation compensation control technology is developed by using a new Negative Poisson's ratio (NPR) material. This technology is successfully applied to deep buried hard rocks and soft rocks to realize the effective control of the large deformation, which proves the applicability of the excavation compensation method and technology.

Experimental Test and Field Observations of an Electric Potential Monitoring Device for Dynamic Hazards during Mining Activities

The EP (electric potential) signals can be generated during the deformation and fracture process of coal and rock mass. Meanwhile, the EP response is closely related to its stress state and damage evolution, which is expected to be used in monitoring and coal and rock dynamic disaster hazards. Based on this, this paper developed an EP monitoring device for mining to continuously monitor the temporal response characteristics and spatial distribution of coal seam internal EP signals in real time. Further, the experimental tests were carried out, whose results showed that the device has high monitoring sensitivity and little error for the EP signals and can reveal the loading state and damage degree of the coal and rock specimens during the deformation and fracture process. Moreover, the tests and application of EP monitoring were carried out during mining activities in the field. The results showed that the EP signals fluctuate during the coal mining stage and remain relatively stable during the maintenance stage. When the abnormal mining stress or the coal cannon phenomenon occurs, the intensity of EP signals increases rapidly and fluctuates violently, which has precursory response information for the hazards of dynamic disasters. Considering the advantages of sensitive response and nearly non-destructive monitoring, the study results can provide key monitoring equipment and research basis for field testing the EP signals during the mining process, to monitor and forecast the hazards of coal and rock dynamic disasters.

Study on Quantitative Characterization of Coupling Effect between Mining-Induced Coal-Rock Mass and Optical Fiber Sensing.

The monitoring of mine pressure, division of vertical zoning of the overburden, discrimination of key stratum structure of the overburden and monitoring of advanced abutment pressure are still the main research problems in the field of coal mining. Therefore, the promotion of development of a monitoring technology of mining-induced rock mass deformation has important research value in the mining field. There are many problems to be solved in the application of optical fiber sensing (OFS) to deformation monitoring, such as the corresponding relationship between actual deformation and optical parameters, the coupling relationship between the optical fiber and rock mass and the reasonable division of vertical zoning of the overburden. In this study, a quantitative index of coupling action between the mining rock mass and optical fiber is put forward, and the coupling coefficient of different vertical zonings is quantitatively analyzed and discussed. Based on this, five different media in contact with optical fiber are proposed. The relationship between the strain curve form, the development height of the fracture zone and the activity of key stratum is established. It is of great academic value and research significance to establish a characterization system of displacement, deformation and structural evolution of overlying strata based on optical fiber sensing technology.

Experimental study on the evolution law of mining‐induced fractures and deformation rock mass structure of gently inclined layered slope

AbstractLandslide induced by underground mining is the main type of geological disaster in Guizhou Province. The spatial position of the mined‐out area is the key factor affecting the deformation evolution of mining landslides. Three typical mining‐induced slopes in western Guizhou Province are selected to establish the engineering geological model. The orthogonal experimental design is carried out with the position of the mined‐out area relative to the slope shoulder (PM) and the slope height (SH) as variables, and the discrete element simulation test is carried out. The influence of the two variables on the evolution of overlying strata fractures and the structure of slope surface deformed rock mass is analyzed by gray relational method. The results show that under the effect of mining, the overlying strata rock on the mined‐out area gradually collapses and produces cracks through the surface. The force chain arch gradually develops from the lower part to the surface rock layer, and the slope surface rock layer is transformed from a cantilever beam embedded at one end to a multisegment articulated beam. Depending on the number of segments of the articulated beam structure, it can be divided into three categories, and the rock mass where the slope collapse occurs is mainly concentrated at the end of the multisegment articulated beam. The central subsidence of the subsidence basin, the length of the end of the articulated beam, the position of the fulcrum, and the rotation angle of the beam structure are the key indicators affecting the stability of the multisegment articulated beam. Gray relational analysis shows that PM is the primary factor to control the output of these indicators. The multiple linear regression model of gray relational degree between PM and SH was constructed, and the prediction formula of gray relational grade was obtained, which realized the multiobjective prediction of the overlying strata rock structure model under the same slope parameters. The results provide the theoretical basis for disaster prevention and mitigation of gently inclined layered mining slopes.

Stability Analysis on the Steeply-Inclined Small-Angle Layered Surrounding Rock Masses at the Upstream High Sidewall of a Large-Span Cavern

The underground powerhouse of China’s Wudongde hydropower station is one of the world’s underground powerhouses with the largest span and height. Because the underground powerhouse is all located in steeply-inclined layered rock masses, and the bedding plane strike of the rock mass has a small angle with the axis of the main caverns, there is a serious risk of high sidewall instability. According to the basic principles of the structurally-controlled concept, the mechanical properties of bedding planes and other discontinuities are largely attributed to this problem. A thorough investigation was conducted into the Wudongde underground powerhouse throughout the excavation process to clarify the possible mechanisms behind these failures and to realize the dynamic adjustment of construction. First, the geological conditions and mechanical properties of the rock masses in the study area were introduced in detail. The stability of the right bank underground powerhouse’s surrounding layered rock mass was then investigated using a discontinuum-based numerical method. Special attention was paid to the excavation-induced failure mechanisms of the steeply-inclined small-angle layered rock masses at the upstream high sidewall. The results show that the failure of steeply-inclined small-angle layered surrounding rock masses presents significant three-stage characteristics, i.e., 1) rock plate forms due to the unloading opening of the bedding plane; 2) rock plate cracks due to bending; and 3) rock plate buckles or slides due to crack penetration. Based on the understanding of the deformation and failure mechanisms of steeply-inclined small-angle layered rock masses, the excavation sequence needs to be optimized according to local geological conditions. In practice, it is vital to insist on the principles of excavation by thin layers and finish all the supports before the next-step excavation.

Rockburst mechanism of rock mass with structural planes in underground chamber excavation

Natural rock mass generally contains discontinuous structural planes, such as joints, fractures and faults, which have great influence on the occurrence of rockburst. The rockburst mechanism of rock mass with structural planes in underground chamber excavation is studied by means of model test and numerical simulation in this paper. Firstly, quartz sand, barite powder, gypsum powder, cement and water are selected as raw materials to configure the similar materials suitable for the rockburst model test. Secondly, four working conditions of none structural plane, single structural plane, multiple structural planes and through structural plane are designed, and the corresponding rockburst model tests are carried out. The stress and displacement laws of surrounding rock during excavation are analyzed. Finally, the numerical calculation of chamber excavation is conducted under the above four working conditions and the model test is verified. The failure modes and laws of surrounding rock mass with different structural planes during chamber excavation are obtained. The results show that: (i) After the tunnel excavation in rock mass with single structural plane, the tension of structural plane and the expansion of fractures occur, accompanied by small-scale rockburst. (ii) After the tunnel excavation in rock mass with multiple structural planes, the stress level of surrounding rock mass decreases significantly and no rockburst occurs, but the surrounding rock is prone to large-scale collapse or spalling. (iii) After the tunnel excavation in rock mass with through structural plane, the fractures appear in the vault and arch bottom and expand rapidly, accompanied by rockburst phenomena such as granules ejection. The research results of this paper are of great significance for understanding the deformation and failure mechanism of rock mass with structural planes in the underground chamber excavation.

Experimental evaluation of precise monitoring of multi-scale deformation failure of rock mass based on distributed optical fiber

To realize the precise monitoring of multi-scale deformation and failure of rock mass by distributed optical fiber, the mechanical model of optical fiber and rock strata is established to analyze the mechanical characteristics and strain response of rock strata under the stages of elastic deformation, elastoplastic deformation. Finally, an optical fiber quantitative monitoring method for multi-scale deformation and failure of rock strata is presented to quantify the deformation characteristics of rock mass at different scales and failure modes in different regions. On this basis, the distributed optical fiber is embedded in a similar model to monitor the internal deformation of the strata of the model. Meanwhile, Digital image correlation (DIC) is used to observe the deformation of the strata in real-time to verify the accuracy of the proposed method. The research results can promote the application of optical fiber sensing technology in the field of mine engineering.

Intelligent prediction of rock mass deformation modulus through three optimized cascaded forward neural network models

Intelligent prediction of rock mass deformation modulus through three optimized cascaded forward neural network models

Empirical estimation of rock mass deformation modulus of rocks: comparison of intact rock properties and rock mass classifications as inputs

Deformation modulus of rock mass (Em) is an important parameter for the analysis and design of mining engineering projects. However, field tests for measuring deformation modulus of rock mass are difficult, time-consuming, and capital intensive. This has led to the development of numerous empirical models for estimating rock mass deformation modulus, which are in different forms and scattered in the literature. The numerous models available in the literature use different types of inputs. Therefore, this study provides a comprehensive compilation of different empirical models for estimating the deformation modulus of rock masses. The compiled models are grouped based on their type of input parameter(s) into three categories such as those using intact rock properties, rock mass classification indices, and combination of intact rock properties and rock mass classification indices. Then, a comparative analysis was performed using absolute average relative error percentage (AAREP) and variance accounted for (VAF) to assess the reliability of using different types of inputs for estimation of deformation modulus of rock masses using data from two sites. The results of the analyses show that rock mass classification indices are the most reliable indices for estimating the deformation modulus of rock masses among the categories considered for analyses. For AAREP analyses in the two illustrative examples considered in this study, models (7 out of 10) using rock mass classification indices in the estimation of Em have the best performances with AAREP values ranging from 24.07 to 55.15%. For VAF analyses in the two examples, models (8 out of 10) using rock mass classification indices in the estimation of Em have the best performances with values ranging from 59.81 to 88.11%. The lowest errors and highest deviation similarities from models using rock mass classification indices indicate that they produce the most reliable estimations of Em. It is important to note that the reliability of deformation modulus estimated from empirical models depends on the quality of input data as the models performed differently across the sites used in this study. This study therefore provides a compilation of available models for estimating deformation modulus, performance evaluation of available models for estimating deformation modulus, and guidelines for selecting appropriate model for estimating deformation modulus of rock mass.

Rock fracturing observation based on microseismic monitoring and borehole imaging: In situ investigation in a large underground cavern under high geostress

During the excavation of deep rock engineering projects under high geostress, the brittle failure of hard rock often occurs. To understand the excavation-induced fracturing process of the surrounding rock of a large underground powerhouse, in situ observation schemes have been proposed, including microseismic (MS) monitoring, imaging with a digital panoramic borehole camera, multipoint extensometer measurements and on-site surrounding rock failure investigation. First, a MS system is used to capture the microfractures inside the rock mass, revealing the potential high-risk failure regions. The spatial distribution of MS events shows that the excavation-induced MS events are progressively clustered in the upstream spandrel and downstream foot of the powerhouse, approximately parallel to the direction of the maximum principal stress. Second, the digital panoramic borehole camera and multipoint extensometer are arranged in the high-risk region to further reflect the rock mass fracture evolution and deformation response characteristics in the monitored section. The borehole camera observations of the top arch and sidewall indicate that the excavation unloading not only causes surrounding rock fracturing near the periphery of the cavern but also induces deep fracturing at a certain depth from the periphery of the cavern. From these comprehensive observation results, the mechanism of rock mass mechanical behaviour is clarified; that is, the macroscopic deformation or failure characteristics of the surrounding rock are directly related to the evolution of microfractures. The research results of this paper are valuable for the stability analysis and excavation optimization of similar underground caverns.

Numerical investigation of creeping rockmass interaction with hardening and shrinking cemented paste backfill

Revealing the interaction mechanism between the time-dependent deformation of rockmass and hardening backfill are important for successful mining design. Based on laboratory tests and numerical simulation, a framework has been established to simulate the hardening CPB in backfilled stope, which could consider the strength evolution characteristics, stress curing conditions, filling rate and shrinkage strain of hardening CPB. Results show that three interaction process could be happened after the CPB poured into stope; the stress distribution in CPB affected by the combination of stress arching and squeezing effect when the rheological effect of rockmass is significant in deep backfilled stope, and the squeezing effect makes the stress in CPB exceed its self-weight stress; The hardening process, filling rate, stress curing conditions and shrinkage deformation of CPB influences significantly on the stress distribution of CPB itself and lateral deformation of the surrounding rockmass. It is necessary to consider the delayed supporting effect of CPB having obvious shrinkage characteristics, and this delayed supporting effect becomes more significant with to prolong of the delay filling. By analyzing the hardening process, curing stress, filling rate and shrinkage deformation of CPB during hardening process, the new mechanism of the interaction between CPB and surrounding rockmass is revealed, which can provide a theoretical basis for improving the support design of mine backfill.

Mathematical Model and Numerical Simulation of Coalbed Methane Migration Considering the Adsorption Expansion Effect

The influence of gas adsorption and desorption on the volumetric strain of coal was measured by a self-designed, fluid–solid coupling triaxial coal adsorption deformation experimental system. The experimental results show that coal deformation has a threshold value with an increase in gas content. Before the gas content reaches the threshold value, coal deformation is not obvious. When the gas content reaches the threshold value, the deformation will increase sharply. At the same time, coal volume strain changes with coal gas content in accordance with exponential law ε = ε0(eϒc-1). Based on the experimental results, considering the coupling effects of heat transfer, water seepage, coal and rock mass deformation, and coalbed methane desorption and seepage, a mathematical model of heat transfer–deformation–seepage coupling coalbed methane migration was established, and a numerical simulation study was carried out on the heat injection-enhanced coalbed methane mining project. The results show that (1) With continuous heat injection, the gas in the coal seam is rapidly desorbed, and the adsorbed gas content forms an elliptical funnel that extends from the extraction hole to the deep part of the coal body and takes the fracturing crack as the center to the upper and lower boundaries of the coal seam. At day 30, the adsorbed gas content in the whole drainage area has decreased to 0.1 m3/t within 2m from the fracture zone. (2) On the basis of considering the gas adsorption expansion effect, the strain of the coal body decreases from roof to floor. With the increase in the heat injection time, the strain value will also increase, and the strain increase will decrease. When the heat injection is 30 days, the maximum strain at the roof is 0.015. The research results have important guiding significance for predicting coal rock deformation and determining gas extraction efficiency in the process of heat injection-enhanced coalbed methane extraction.

Relative deformation of matter at the micro- and macrolevel under the conditions of changing space weather

Research subject. Deformations and stress state of rock masses at subsoil use objects.Materials and research methods. Extensive experimental data about the relative deformation of matter and, in particular, about the deformation of rock masses (earth’s crust) allowed the authors to find a solution to this problem using the very behavior of the rock mass during its response to technogenic activity.Results. Novel results were obtained on the relative deformation of matter under the conditions of changing external factors: 1) deformation of rock mass itself; 2) deformation of a surveying tape as a measuring instrument, 3) deformation of a quartz tube in a deformometer as a measuring instrument. Using the results of measurements over the 11-year nanocycle of solar activity available to us, regularities in the emergence of deformations and stresses of rock masses were revealed. A justification was obtained for changing the physical state of measuring instruments based on electromagnetic waves: satellite navigation systems, light and radio range finders. At the same time, it was found that all these parameters change in time continuously and endlessly, thereby requiring constant monitoring for making a reliable forecast of their impact on technogenic activity.Conclusion. The results presented in the article extend previous publications of the authors, the main conclusions of which are as follows. 1. The results about the deformations of rock masses, which are currently being obtained by methods based on various physical principles, are relative; therefore, these results do not allow one to judge about their absolute values. 2. The international community of scientists should develop a mechanism for tracking changes in the deformations and stress state of rock masses.

Numerical Modeling of Stand-Up Time of Tunnels Considering Time-Dependent Deformation of Jointed Rock Masses

Numerical Modeling of Stand-Up Time of Tunnels Considering Time-Dependent Deformation of Jointed Rock Masses

3D simulation of complex fractures with a simple mesh

AbstractRock masses are 3D in nature. The contained complex fracture networks pose great difficulty to its computer‐aided design (CAD) modeling and bring meshing burdens to classic finite element analysis (FEA). Considering the efficiency of digital images capturing complex geometries, as an extension of the previous 2D work, the 3D implementation of the image‐based simulation is carried out in this work. Continuous‐discontinuous deformations of complex rock masses are simulated in 3D with a simple structured mesh based on the numerical manifold method (NMM). Characteristics of the developed voxel crack model and its differences with discrete and smeared crack models are summarized. Based on this voxel crack model, the generating algorithm of 3D physical patches to construct the continuous‐discontinuous trial function is introduced in detail. In the developed method, the three spatial resolutions, respectively of the image model, integration voxels, and mathematical elements, are independent. These resolutions can be chosen freely by trading off the accuracy need and the computational expenses. Numerical examples investigate the accuracy and convergence of this method. Its 3D simulation capability of complex rock masses is demonstrated by calculating the continuous‐discontinuous deformation of El Capitan rock located in the Yosemite National Park with assumed complex fracture networks.

Seepage Deformation and Failure of Rock Mass Under High Water Pressure With a Discrete Element Method

The seepage failure induced by high water pressure along the fault structural plane is one of the main factors for the deformation and failure of underground caverns. Based on the pipe domain seepage model with the discrete element particle flow method, the law of flow conservation is introduced, and the pressure renewal equation is improved by connecting the change of mechanical volume in timestep with the effective stress. The model for pipe domain seepage analysis of fractured rock mass is established, and the sample seepage model is used to simulate and verify the seepage process. Then, seepage failure induced by water pressure in an underground tunnel is analyzed by using this model. The results show that the improved pipe domain seepage model conforms to Darcy’s law, the seepage velocity of the model can be changed by controlling the viscosity coefficient, and the tunnel failure phenomenon is consistent with the actual phenomenon in the practical project. The research results can provide a theoretical basis and method for investigating the deformation and failure of underground caverns under complex seepage.