Rock Mass Deformation Research Articles

Evaluation of slope stability through rock mass classification and kinematic analysis of some major slopes along NH-1A from Ramban to Banihal, North Western Himalayas

The network of Himalayan roadways and highways connects some remote regions of valleys or hill slopes, which is vital for India's socio-economic growth. Due to natural and artificial factors, frequency of slope instabilities along the networks has been increasing over last few decades. Assessment of stability of natural and artificial slopes due to construction of these connecting road networks is significant in safely executing these roads throughout the year. Several rock mass classification methods are generally used to assess the strength and deformability of rock mass. This study assesses slope stability along the NH-1A of Ramban district of North Western Himalayas. Various structurally and non-structurally controlled rock mass classification systems have been applied to assess the stability conditions of 14 slopes. For evaluating the stability of these slopes, kinematic analysis was performed along with geological strength index (GSI), rock mass rating (RMR), continuous slope mass rating (CoSMR), slope mass rating (SMR), and Q-slope in the present study. The SMR gives three slopes as completely unstable while CoSMR suggests four slopes as completely unstable. The stability of all slopes was also analyzed using a design chart under dynamic and static conditions by slope stability rating (SSR) for the factor of safety (FoS) of 1.2 and 1 respectively. Q-slope with probability of failure (PoF) 1% gives two slopes as stable slopes. Stable slope angle has been determined based on the Q-slope safe angle equation and SSR design chart based on the FoS. The value ranges given by different empirical classifications were RMR (37–74), GSI (27.3–58.5), SMR (11–59), and CoSMR (3.39–74.56). Good relationship was found among RMR & SSR and RMR & GSI with correlation coefficient (R2) value of 0.815 and 0.6866, respectively. Lastly, a comparative stability of all these slopes based on the above classification has been performed to identify the most critical slope along this road.

The novel strength criterion and the associated constitutive model based on the finite deformation behavior for the rock under the disturbance stress paths

To develop a novel 3D Hoek–Brown strength criterion and an associated constitutive model based on the finite deformation behavior of rock under the disturbance stress paths, a series of mechanical tests are initially conducted under designed disturbance stress paths (hydrostatic stress stage (HSS), initial loading–unloading stage (ILUS), and disturbance stage (DS)). Additionally, low disturbance (LD), medium disturbance (MD), and high disturbance (HD) modes are taken into consideration. Then, the finite deformation theory is employed to study the nonlinear behavior. This nonlinear behavior can be regarded as a nonlinear relationship between the stress and strain of rock under loading, especially the initial compression stage and plastic stage, as well as a complex deformation field, which is described by the finite deformation theory and featured by the mean rotation angle (Θ). Afterwards, the damage variable (DV) regarding Θ is proposed and used to establish a novel strength criterion (NSC) based on the current Hoek–Brown strength criterion. Finally, by considering the NSC, an associated elasto-plastic constitutive model is developed. The results show that the initial confining pressure (ICP) and disturbance mode have a significant effect on the elastic modulus (E). Meanwhile, the ICP has a higher effect on E than the disturbance mode. Then, the evolution of Θ is closely associated with the nonlinear deformation of rock masses because the σ1−Θ curves can be divided into three stages. Those stages can match well with the initial compression stage, elastic stage, and plastic stage, respectively. Regarding Θ as a parameter of the damage variable (DV), the NSC is established. Additionally, it can be observed that the failure envelopes of the NSC scale down gradually with increasing Θ on the deviatoric plane. Meanwhile, as the value of the coefficient of determination (DC) is higher than that of other strength criteria, the NSC may exhibit better agreement with the experimental data. Furthermore, a constitutive model based on the aforementioned strength criterion and the hardening function that takes Θ and the disturbance of rock masses (D) into account is proposed and validated as a solution to predict the nonlinear behavior of rock specimens under the disturbance stress paths.

Damage Evolution and Integrity Assessment of Jointed Rock Mass Based on Synthetic Rock Mass Approach

The integrity coefficient Kv of bed rock is one of the important approaches to evaluate the stability of engineering rock mass, but this parameter is difficult in frequent field tests. The integrity coefficient is the quantitative index for evaluating the complete deformation of rock mass, while the damage variable represents the level of damage of the jointed rock mass, and both have similar physical meanings and represent the degree of deterioration of surrounding rock. Damage variables and damage constitutive models were constructed based on Weibull distribution damage model and Synthetic Rock Mass (SRM) model. The relationship between damage variables and numerical calculation and damage constitutive curves of different weathered granite rocks in Hongtuzhang tunnel was calculated. A new method for evaluating integrity coefficient of rock mass is proposed.

A Coupled Seepage–Deformation Model for Simulating the Effect of Fracture Seepage on Rock Slope Stability Using the Numerical Manifold Method

Modeling seepage problems in rock fractures is an interesting research approach to evaluating rock slope instability that is attracting increasing attention. In the present study, a coupled seepage–deformation model based on the numerical manifold method (NMM) is proposed, and the flow of groundwater in a fracture network coupled with the effects of seepage pressure and rock deformation are discussed. A global equilibrium equation of the system and a local factor of safety (FoS) of arbitrary rock fractures are derived based on the principle of minimum energy, and a series of verification examples are calculated. The simulation results show the robustness and effectiveness of the proposed numerical model. Finally, a rock slope collapse accident caused by seepage effects is simulated by the proposed method, and the failure process of the slope is reproduced. The simulation results show that excessive hydraulic pressure caused the vertical fractures to open and augmented the rock mass deformation, eventually leading to the failure of the slope. The proposed method possesses the potential to simulate larger-scale engineering problems.

Study on Time-Dependent Failure Mechanisms and CBAG Differential Support Technology of Roadway in Steeply Inclined Coal Seam

In Sichuan Province, China, most coal seams that are mined are steeply inclined; their roadways’ surrounding rocks are asymmetric, with non-equilibrium deformations and unstable anchorage structures, thus making major safety hazards highly likely. Using field observations and a universal distinct element code (UDEC) numerical simulation method, this paper analyzed the time-dependent failure of the ventilation roadway of Working Face 1961 of the Zhaojiaba Mine, revealing the preconditions for such damage and a bidirectional deterioration mechanism for the deformation as well as stress of surrounding rocks. Moreover, this paper built an anchorage mechanical model for the thick layer of the roadway roof and proposed a cross-boundary anchor-grouting (CBAG) differential support technique. Calculations proved that the new support was particularly effective in restraining the expansion of tension cracks, thus preventing the slipping and dislocation deformations of rock masses on the curved roof side. The feedback of engineering applications showed that the maximum development depths of cracks in the arc roof and straight inclined roof of the roadway 150 m behind the working face are only 1.5 m and 1.10 m, decreasing by 61.3% and 47.6%, respectively, compared with the primary support. The proposed technology offers an overall thick-layer bearing structure for the surrounding rocks of roadways, effectively restraining the non-equilibrium large deformations of roadways in steeply inclined coal seams.

Assessment of long-term large deformation in deep roadways due to roof fracturing impact loading

The rock mass around deep roadways has obvious creep characteristics in high-stress environments. Meanwhile, the cyclic impact load induced by roof fracturing also causes dynamic damage to the surrounding rock, leading to long-term large deformation. This paper examined the rock mass deformation mechanism around deep roadways based on the theory of rock creep perturbation effect considering perturbation sensitive zone. This study proposed a long-term stability control guideline for deep roadways under dynamic load. An innovative support system was developed for deep roadways, with concrete-filled steel tubular support being recommended as the main supporting body. A case study was conducted to validate the proposed supporting system. Monitoring over one year in the case study mine showed that the overall convergence deformation of the roadway was 35 mm, indicating that the roadway’s long-term large deformation induced by creep perturbation was effectively controlled by using the proposed bearing circle support system.

Mathematical modelling of displacement during the potash ores mining by longwall faces

In favourable mining conditions, in particular at the Starobinskoye potash deposit (Belarus), longwall mining systems are used. They cause a high human-induced load on the subsoil, including intense deformation of the ground surface. The presented investigations are aimed at studying the dynamics of the ground surface displacement during the longwall face advance. Mathematical modelling was carried out in an elastic-plastic formulation with numerical implementation by the finite element method. The condition for the roof rocks collapse was opening of the contact between the seams when its boundaries were reached by shear fractures or formation of the tensile stresses area at the outcrop. With the working front advance, an increase in subsidence is observed, followed by its stabilization to a value determined by the process parameters of mining operations and the physical and mechanical properties of collapsed rocks. In this case, each point of the ground surface experiences sign-alternating horizontal deformations: when the front approaches, it causes tension, and when it moves away, compression. The obtained results of mathematical modelling are in good agreement with the data of instrumental measurements of the ground surface displacements, which indicates the adequate description of the rock mass deformation during the slice excavation of sylvinite seams by longwall faces.

Anisotropic Strength, Deformability, and Failure Behavior of Artificial Columnar Jointed Rock Masses under Triaxial Compression

Columnar jointed rock masses (CJRMs) have a complex network structure and, therefore, present a great challenge to geotechnical engineering design. A series of triaxial compression tests is performed on artificial CJRM specimens subjected to a confining pressure of 5 MPa, considering various pore pressures (pw=0 MPa, 2 MPa, and 4 MPa). In this work, the influence of the joint dip angles and pore pressure on the anisotropic strength, deformation, and failure modes of the CJRM is investigated. The anisotropic characteristic stresses, strength parameters (c and φ) and elastic modulus of the CJRM specimens show a U-shaped pattern with increasing joint dip angles (β), while Poisson’s ratio changes inversely. The elastic modulus has a stronger anisotropy than Poisson’s ratio. Moreover, with increasing pore pressure, the characteristic stresses decrease, while the anisotropy of stresses and deformations increases. Finally, three failure modes of CJRM specimens with different joint dip angles are observed under triaxial compression conditions.

Development of ideas about the mechanism of coal-overlaying formation displacement in terms of its influence on local gas-drainage parameters in the Western Donbas conditions

Purpose. The research purpose is to study the mechanism of the influence of geomechanical-technological factors on the location parameters of the gas-drainage wells behind the longwall face in the area of stope operations under the conditions of weakly metamorphosed rocks. Research methodology. An integrated approach is used, including an analysis of existing research on the gas release patterns in the mine workings of extraction sites and local gas-drainage parameters, analysis of geomechanical processes, development of schemes for modeling by the finite element method, substantiation of methodological approaches for conducting experimental research into the rock pressure manifestations in extraction working, taking into account existing tendencies of the influence of stoping face advance velocity. Research results. The views on the mechanism of the stratified mass texture transformations of weak rocks have been developed during the study of the optimal extraction site gas-drainage parameters. The deformation development schemes have been constructed for any layer of the main roof behind the area of longwall face conjugation with the extraction working, displacement of coal-overlaying formation rocks along and across the extraction site with the location of gas-drainage wells. Based on the conducted research, recommendations on the rational location of gas-drainage wells have been obtained. Scientific novelty. The main characteristics of the weakly metamorphosed rock displacement process in the area of stope operations are studied in a spatial formulation, and the mechanism of the influence of geomechanical-technological factors on the expedient location parameters of gas-drainage wells behind the longwall face is represented on the relevant schemes. Practical value. The reliability of the proposed location parameters for gas-drainage wells behind the longwall face in the conditions of weakly metamorphosed rocks of the Western Donbas has been analyzed, taking into account the stoping face advance increased velocities.The conclusions drawn on the basis of rock displacement tendencies in the coal-overlaying formation are summarized in the schemes for identifying the mechanism of rock mass deformation near the area of stope operations.

Machine-learning method applied to provide the best predictive model for rock mass deformability modulus (Em)

Machine-learning method applied to provide the best predictive model for rock mass deformability modulus (Em)

Investigation of the Microstructure Characteristics and Deformation Mechanisms of the Carbonaceous Slate under Hydromechanical Coupling

Carbonaceous slate inevitably possesses microscopic pores, microcracks, cleavages, and bedding planes in complex geoenvironment during the diagenesis processes. The microstructure of carbonaceous slate changes apparently under the effects of underground water infiltration, tectonic stress, and engineering disturbance, which induces the large deformation of rock mass and influences the stability of geotechnical engineering projects. To investigate the microstructure characteristics and reveal deformation mechanisms of carbonaceous slate under the influence of water pressure and stress, the variations of the pore size distribution(PSD), connectivity of pores, and porosity of samples during water injection and triaxial compression were studied using multiple methods. The results indicated that voids include plate-like micropores and microcracks, which are discontinuous without external stress. The micropores with a size of less than 1 μm dominate in number. The flaky particles were extruded and bent at a confining pressure, which caused the intermediate pores to form and altered the PSD of the samples. Hence, the connectivity dramatically improved and resulted in increased permeability. Water with dissolved clay minerals and small particles could move between micropores and microcracks during the water injection process. The elastic deformation of the particles recovered, and the intermediate pores disappeared when the imbalanced forces on two sides of the particles were narrowed. Pore water pressure affected the effective stress state and decreased the cohesion and stiffness of the rock. In the lower stress state, the porosity had a certain range of decrease (about 0.2%) mainly due to micropore compression, while the microcrack sprouted and expanded with the increase of compressive stress, resulting in the extension of porosity. The interaction of the stress and water seepage on the slate reduced the rock strength and favored the deformation, leading to a large macrodeformation of the soft rock in the long run.

Analysis of Thermally Induced Strain Effects on a Jointed Rock Mass through Microseismic Monitoring at the Acuto Field Laboratory (Italy)

The study of the deformation of rock masses in response to near-surface thermal stresses is nowadays considered crucial in the field of geological risk mitigation. The superposition of heating and cooling cycles can influence the mechanical behavior of rock masses by inducing inelastic deformations that can trigger shallow slope instabilities, such as rockfalls and rock topples. This study reports the main outcomes obtained from the analysis of 20 month long microseismic monitoring at the Acuto field laboratory (Central Italy), where an integrated geotechnical and geophysical monitoring system has been operating since 2015. A preliminary event classification was performed through the analysis of time- and frequency-domain characteristic features of the extracted waveforms. Furthermore, the evolution of the local microseismicity was explored as a function of environmental factors (i.e., rock and air temperature, thermal gradients and ranges, and rainfalls) to highlight potential correlations. The here presented results highlight nontrivial insights into the role played by continuous near-surface temperature fluctuations and extreme thermal transients in influencing the stability of rock masses. In particular, the comparison of monitoring periods characterized by the most intense microseismic activity highlights a peculiar distribution of microseismicity during the heating and cooling phases of the rock mass in relation to different environmental conditions. These behaviors can be interpreted as the consequence of different driving mechanisms at the base of local failures.

Factors influencing fault-propagation folding in the Kuqa Depression: Insights from geomechanical models

Understanding the rock mass deformation and strain state is critical to a range of endeavors. Geomechanical modeling is an excellent approach simulating the formation processes of faulting and folding, which can reproduce the geometry of fold structures and track strain and stress through the whole deformation process. In this study, five series of two-dimensional (2D) elastic-plastic finite element models were built to investigate the influences of shortening distance, ramp cutoff angle, interlayer slip, fault friction, fault number and fault slice width on structural styles and strain distribution patterns during fault-propagation folding in the Kuqa Depression of Tarim Basin. The results indicate that, i) All above mentioned factors can influence the structural style and strain distribution of fault-propagation fold (FPF) to varying degrees. Fault friction, interlayer slip and fault slice width are the most important parameters influencing the deformation geometry and strain patterns of FPF; ii) There are critical values for fault friction coefficient and shortening distance to create a secondary fold besides the FPF; iii) A “step pattern” occurs both in the forelimb and backlimb of the FPF when fault slice width reaches a certain high value; iv) Structural position in the FPF controls volumetric changes. The evolution of FPF can be divided into two stages: layer parallel shortening and volume loss, and folding; v) The steep forelimb region of FPF develops more natural fractures, which may serve as a favorable location for potential reservoirs in the Kuqa Depression. The results are also expected to provide clues for the exploration and development of oil and gas in regions with similar geological conditions.

Experimental study on the shear performance of quasi-NPR steel bolted rock joints

Quasi-NPR (negative Poisson’s ratio) steel is a new type of super bolt material with high strength, high ductility, and a micro-negative Poisson’s effect. This material overcomes the contrasting characteristics of the high strength and high ductility of steel and it has significant energy-absorbing characteristics, which is of high value in deep rock and soil support engineering. However, research on the shear resistance of quasi-NPR steel has not been carried out. To study the shear performance of quasi-NPR steel bolted rock joints, indoor shear tests of bolted rock joints under different normal stress conditions were carried out. Q235 steel and #45 steel, two representative ordinary bolt steels, were set up as a control group for comparative tests to compare and analyze the shear strength, deformation and instability mode, shear energy absorption characteristics, and bolting contribution of different types of bolts. The results show that the jointed rock masses without bolt reinforcement undergo brittle failure under shear load, while the bolted jointed rock masses show obvious ductile failure characteristics. The shear deformation capacity of quasi-NPR steel is more than 3.5 times that of Q235 steel and #45 steel. No fracture occurs in the quasi-NPR steel during large shear deformation and it can provide stable shear resistance. However, the other two types of control bolts become fractured under the same conditions. Quasi-NPR steel has significant energy-absorbing characteristics under shear load and has obvious advantages in terms of absorbing the energy released by shear deformation of jointed rock masses as compared with ordinary steel. In particular, the shear force plays a major role in resisting the shear deformation of Q235 steel and #45 steel, therefore, fracture failure occurs under small bolt deformation. However, the axial force of quasi-NPR steel can be fully exerted when resisting joint shear deformation; the steel itself does not break when large shear deformation occurs, and the supporting effect of the jointed rock mass is effectively guaranteed.

Influence of intermittent opening density on mechanical behavior and fracture characteristics of 3D-printed rock

To investigate the influence of intermittent opening density on the mechanical behavior and fracture characteristics of rock, sand 3D-printed specimens containing different opening numbers are prepared using quartz silica sand and furan resin adhesive as printing substrates. Uniaxial compression testing is performed on these rock-like specimens. Based on digital image correlation (DIC) technology, a methodology for identifying crack types and evaluating rock damage is proposed to quantify the mechanical mechanism of crack evolution during loading. The experimental results are verified and explained using the rock failure process analysis (RFPA) code. The results show that with increasing intermittent opening density, the stress–strain curves of the specimens are similar. Meanwhile, the increase in intermittent opening density causes the stress field distribution of the specimen to change, which in turn leads to a decrease in the uniaxial compressive strength and elastic modulus. The types of cracks around the opening can be grouped into tensile cracks (T) and shear cracks (S), and the coalescence modes of the rock bridge between the openings can be grouped into shear coalescence (C1) and traction coalescence (C2). As the intermittent opening density increases, the coalescence type between openings changes from C1 to C2, and the overall failure pattern is converted from tensile-shear failure to tensile failure. The damage factor (Df) evolution is closely related to the intermittent opening density of the specimens. A one-way exponential decay correlation between the stress ratio and the damage factor is found. The above study is expected to deepen the understanding of the deformation and fracture mechanism of rock masses with openings and to provide a reference for the application of 3D printing technology in the rock mechanics field.

КОНТРОЛЬ СДВИЖЕНИЙ И ДЕФОРМАЦИЙ ПОРОДНОГО МАССИВА В ОКРЕСТНОСТИ ГОРНЫХ ВЫРАБОТОК

The paper describes implementation of geomechanical monitoring of movements and deformations in rock mass and mine structures in hybrid open pit/underground mining. The case-study of extraction ofAikhal kimberlite pipe reserves under bottom of an open pit ofAL- ROSA allows examining the pitwall rock mass stability control using subsurface check points arranged in boreholes in underground roadways. The authors assess the occurrence time of dynamic deformation in pitwall rock mass, duration of the dynamic deformation period and the limit displacements at the moment of slope falls. The developed assessment method of the rock mass stress-strain behavior uses the data of borehole measurements of check point displacementsThe proposed method is included in integrated projects of hydrogeomechanical monitoring of crown pillars under pit bottoms in Aikhal andInternatsionalny Mines of ALROSA.

Improving Rock Pillar Stability Guidelines Through Detailed Numerical Investigation

Pillar stability guidelines have been presented by numerous authors in the past, based on a combination of empirical observations (mostly visual) from mining applications and simple numerical (elastic or simple continuum plasticity) models. In many cases, the resulting design limits for pillar dimensioning are presented as universal for all rockmass conditions and stress regimes. There have been numerous developments in the past decades in mechanistic classification (brittle spalling, effective continuum rockmass, structural control) and mechanism-appropriate modelling and design metrics. These new tools and paradigms for rockmass behaviour allow for a modelling-based revision of the empirical guidelines from the past century that still form the basis of many performance critical designs. This paper includes the consideration of rockmass deformation and yield (rockmass strength approach), brittle strength, and damage behaviour where appropriate. This paper presents correlations for residual GSI and the effects of Hoek-Brown dilation on pillar behaviour. The investigation includes generating 3D FEM synthetic pillar models with equivalent elastic and plastic continuum.

Hardening soil model in prediction of plastic deformation zone in soft rock mass of Yakovlevo iron ore deposit

The authors propose a sizing procedure for the zone of plastic deformation (possible failure) in rock mass in the vicinity of stoping using the method of numerical modeling and the Hardening Soil Model (HSM). The relevance of HSM application in the conditions of Yakovlevo deposit is confirmed, among other things, by the dependence of the deformation modulus of rocks in the volumetric stress state on the effective stresses. The subject of research is the Yakovlevo deposit of high-grade iron ore, which holds the largest reserves in the Belgorod Region of the Kursk Magnetic Anomaly. Stoping and mine support operations induce continuous rock falls and caving because of the unreliable prediction of rock mass stability in the vicinity of stoping and due to the low strength of enclosing rock mass. Selection and validation of HSM parameters for iron–mica–martite ore of Yakovlevo deposit included processing of laboratory testing results obtained using equipment of the Saint-Petersburg Mining University. The triaxial tests of ore samples at different values of lateral pressure were computationally reduced to a reference abutment pressure value pref set by the software designer. The numerical experiments and virtual testing of the material behavior model, as well as the justification of the possible failure zone size were implemented in the certified software environment Bentley Systems PLAXIS-3D. Finally, on the basis of the integrated research of different-density ore samples, including laboratory tests and numerical experiments, the rock mass behavior models are constructed and the parameters of plastic deformation zones (possible failure) in the vicinity of a single stone are predicted.The study was supported under the state contract for scientific work in 2021, Grant No. FSRW-2020-0014.

A twisted yieldable rock bolt as a tool for dissipation of the ground pressure energy

An innovative design of a twisted yieldable rock bolt has been developed using the system analysis of conventional rock bolt technology, a thermodynamic approach, and a theory of technical creativity. This bolt consists of one single piece of a metal cylindrical rod having longitudinal feathers that provided its maximal reliability and minimized the cost. The bolt can be driven into a hole with a pneumatic hammer and creates a set of dissipative structures during rock mass deformation that facilitates and intensifies the dissipation of ground pressure energy causing stress relief around an underground opening. A 30 cm section of the bolt was successfully tested in special laboratory equipment, one 1.8 m bolt in a mechanic workshop, and fifty-five 1.8 m bolts in an underground entry of a coal mine. The behavior of this bolt was simulated on the FLA3D model to verify its basic parameters and to understand deeper abilities to yield and resist rock mass deformation. This bolt is fastened to the hole's wall for its entire length, thus the resistance and the energy dissipation indicators of this bolt are extensive parameters, hence the 2-m-length bolt can exceed the performance of the best modern prototypes. This bolt is relevant to provide stability to underground openings in hard squeezing conditions.

Effect of the Number and Distribution of Circular Holes on the Damage and Fracture of Limestone Using PFC2D

The common occurrence of various number and distribution of hole flaws complicates the mechanical behavior and fracture mode of the rock masses that contain them. This study develops seven numerical models of limestone samples with different numbers and distributions of circular hole flaws using 2-D particle flow discrete element code (PFC2D) to investigate their impact on the mechanical properties of limestone while maintaining the same flaws area. In addition, it analyzes the effect of these factors on the mesomechanical features of each model, including the characteristic stress values (peak stress, crack initiation, and damage stress), crack evolution, stress, and displacement field. The results showed that the peak stress, crack initiation, and damage stress of the single-hole model are between those of multihole models. As the arrangement of dip angle increases, the peak stress, crack initiation, and damage stress of models with the same number of multihole flaws exhibit a V-shaped change. The characteristic stress values are the largest when the holes are vertically aligned. Model differences in crack development path, shape, and number, as well as stress concentration area and failure mode, are primarily due to the number and distribution of holes. The circular holes are arranged at approximately 45°, and the greater the number of defects, the more likely the model is to fail. The study’s findings can provide support and reference for the research system of deformation and failure of rock mass with hole flaws.