Deformation Characteristics Of Rock Research Articles

Development of Soft Computing-based Predictive Tools for Estimating the Young Modulus of Weak Rocks

The deformation characteristics of rocks are of vital importance in addressing most geomechanical issues as they are one of the most critical input parameters in rock engineering analyses. For this reason, robust forecasting models are required when analysing the stability of tunnels, slopes, mine galleries, and other underground excavations. In this research, novel predictive models are proposed to estimate the tangential Young modulus (Eti) of weak rocks. To achieve this, an extensive literature review is performed to obtain a comprehensive database including critical physico-mechanical properties of various weak rocks. Thanks to the advantages of soft computing methods such as genetic algorithm (GA), adaptive neuro-fuzzy inference system (ANFIS), artificial neural networks (ANN) and multivariate adaptive regression splines (MARS), novel predictive models are established. The effectiveness of the developed predictive models is investigated using various statistical measures and it is concluded that empirical models utilizing ANN and ANFIS methodologies are the most effective tools for estimating the Eti of weak rocks. In addition, a practical design chart is also developed for assessing the Eti of weak rocks.

A damage rock model considering shear failure by modified logistic growth theory

Localized rock failures, like cracks or shear bands, demand specific attention in modeling for solids and structures. This is due to the uncertainty of conventional continuum-based mechanical models when localized inelastic deformation has emerged. In such scenarios, as macroscopic inelastic reactions are primarily influenced by deformation and microstructural alterations within the localized area, internal variables that signify these microstructural changes should be established within this zone. Thus, localized deformation characteristics of rocks are studied here by the preset angle shear experiment. A method based on shear displacement and shear stress differences is proposed to identify the compaction, yielding, and residual points for enhancing the model's effectiveness and minimizing subjective influences. Next, a mechanical model for the localized shear band is depicted as an elasto-plastic model outlining the stress-displacement relation across both sides of the shear band. Incorporating damage theory and an elasto-plastic model, a proposed damage model is introduced to replicate shear stress-displacement responses and localized damage evolution in intact rocks experiencing shear failure. Subsequently, a novel nonlinear mathematical model based on modified logistic growth theory is proposed for depicting the shear band's damage evolution pattern. Thereafter, an innovative damage model is proposed to effectively encompass diverse rock material behaviors, including elasticity, plasticity, and softening behaviors. Ultimately, the effects of the preset angles, temperature, normal stresses and the residual shear strength are carefully discussed. This discovery enhances rock research in the proposed damage model, particularly regarding shear failure mode.

A Time-Dependent Damage Constitutive Model for Brittle Rock Materials Based on Subcritical Damage Theory.

In the domain of geotechnical engineering, a profound understanding of the long-term mechanical deformation characteristics of rocks is indispensable for the design and construction of structures, dams, tunnels, and various engineering projects. The deformation behavior of rocks under long-term loads directly impacts the stability and safety of engineering structures. This study employs micromechanical methods to investigate the subcritical extension of microcracks under stress corrosion. By examining the accumulated damage resulting from this phenomenon, the research explores the patterns of aging damage development and establishes a constitutive model for aging that incorporates cumulative damage over the stress history. The accuracy of the proposed model is evaluated through a comprehensive comparison of numerical results with experimental data. The experimental data set encompasses traditional triaxial compression tests, single-stage creep, multistage creep, and single-stage relaxation tests conducted under varying confining pressures. The predicted results exhibit strong consistency with the entire data set. Furthermore, this paper employs crack damage stress as an indicator characterizing the long-term strength of rock. Through frictional damage coupling analysis and derivation, an analytical expression for the long-term strength of rock materials containing microcracks is provided, serving as a theoretical basis for investigating the long-term mechanical performance of brittle rock materials and ensuring the long-term stability of large-scale rock engineering projects.

Research into mechanical properties of ore and rocks in the ore deposits with assessment of the mass stress state natural field

Purpose. The research aims to conduct a comprehensive study of the mechanical properties of ores and rocks within the Zhilandy Group field, as well as to assess the natural field of mass stress state to solve geomechanical problems in optimizing mining operations. Methods. To determine the boundary conditions when measuring the stress-strain state of the mass, a complex methodology is proposed, including stress measurements using hydraulic fracturing methods of the wells and determining the physical-mechanical properties of rocks. Five rock probes have been tested. Twelve tests (six tests in natural and six in water-saturated states) have been conducted for each probe. Findings. Hydraulic fracturing tests at the metering stations show significant tectonic stress due to the shape of structural folds and the mass fracturing. It has been revealed that the hard rock mass is characterized by non-uniform fracturing. It is of tectonic origin and averages between 10-15 and 15-25 fractures per meter for different lithological varieties. The maximum horizontal stress at the stations is oriented along an azimuth of 70° ± 10. Originality. The influence of water saturation on the reduction of strength and deformation characteristics of rocks has been determined for the conditions of the Zhilandy Group field, which shows significant variations depending on the rock type. Especially important is the revealed fact of a significant decrease in uniaxial compression and uniaxial tensile strength, as well as a decrease in Young’s modulus and cohesion factor. Linear dependences of stresses occurring with depth have been obtained from the measurement results. Practical implications. The results obtained are of significant importance for the mining industry. Understanding the extent of reduction in strength characteristics during water saturation and assessing the natural field of the stress mass state allows more accurate prediction of rock behavior.

Investigation on the damage model of rock subjected to freeze-thaw cycles considering its fracture voids compaction

The investigation on the mechanical properties and damage model of rock subjected to freeze-thaw cycles (FTCs) holds significant theoretical for assessing the deformation of rock mass engineering in cold regions. When the rocks subjected to FTCs, the fracture voids of rocks increase with increasing number of FTCs, and the rocks exhibit nonlinear deformation characteristics as its fracture voids compaction. Based on the dissipation energy evolution law and distribution characteristics of rocks under loading, the critical point of rock compaction deformation was determined. A constitutive model for rock subjected to FTCs considering its fracture voids compaction was established based on macroscopic and microscopic damage levels. The rationality of the model was validated using experimental results, and a comparison was made between the calculation results of proposed model and model that not consider fracture voids compaction. The evolution properties of rock damage variable and stress under different FTCs were analyzed. The variation of model parameters with the FTCs and the influence of model parameters on the deformation characteristics of rock was analyzed.

Study of longitudinal deformation profiles in high-ground-stress mega-section tunnels based on the Hoek–Brown criterion

In rock tunnel construction, the analysis of rock deformation characteristics is an essential aspect of the overall safety evaluation. In this study, the high-ground-stress section of the Tongzi tunnel was taken as the research object and the longitudinal wave velocities of the disturbed and undisturbed areas of the surrounding rock were measured using on-site drilling to determine the disturbance range of the surrounding rock excavation. The uniaxial and triaxial compressive strengths of the rocks sampled in the field were measured through indoor tests. Through a combination of the field acoustic test and indoor test results, the Hoek–Brown (H-B) failure criterion parameters of the surrounding rock were quantitatively obtained. A numerical model was developed for the analysis, and the following conclusions were drawn: At the pre-deformation stage, the influence of the crown settlement, horizontal displacement, and the tunnel face extrusion deformation were all within the range of one times the tunnel diameter. The location and area of the first tunnel face influenced the extent of the surrounding rock’s pre-deformation. A more pronounced effect on the pre-deformation of the tunnel crown settlement was obtained the closer the first tunnel face was to the tunnel crown. In addition, the closer the first tunnel face was to the arch waist, the more pronounced the impact was on the pre-deformation of the horizontal displacement, and the pre-deformation increased exponentially with the increase in the significance of the excavation area of the first tunnel face. The deformation varied in tunnels that had been excavated using different construction methods. The three-step method employed in this study resulted in the most considerable deformation, followed by the CD method, and the double-side heading method resulted in the smallest deformation. The results show that increasing the number of working faces and using small cross-sectional staggered slot excavation are beneficial to tunnel stability. The field monitoring data are generally consistent with the numerical simulation results, providing a degree of validation for the numerical simulation results. The intrinsic model used in the numerical simulation influences the simulation results. When compared with the Hoek–Brown principal structure model, using the Mohr–Coulomb central structure to simulate the high-ground-stress rock tunneling may result in more considerable elevation arch uplift and tunnel face extrusion deformation. Therefore, it is more reasonable to use the Hoek–Brown principal structure model.

A new elasto-visco-plastic damage model and numerical simulation method used for time-dependent behavior prediction of deep tunnel

Accurately predicting the time-dependent behavior of surrounding rock is crucial for supporting design, revealing the mechanism of lining cracking and understanding long-term stability in deep-buried tunnels engineering. Based on the component combination model method and continuous damage mechanics theory, a New Elasto-Visco-Plastic Damage (NEVPD) model was proposed considering the characteristics of viscoelastic-plastic and the damage evolution of rocks. Three groups of experimental data were used for validating the model, and the results indicate that the model can effectively describe the time-dependent deformation characteristics of rocks at different stress levels. The dynamic link computer application program of the NEVPD model was procured through the secondary development interface of the FLAC3D software, and its validity was ascertained through test simulations. By investigating the influence of stress levels on creep parameters, a creep simulation approach considering the impact of rock mass stress state on the creep parameters was proposed for used in the long-term stability analysis of underground rock engineering. Finally, the time-dependent behavior of deep tunnel was predicted using two simulation approaches (the traditional method and the proposed method) based on the Burger-Creep Viscoplastic (CVISC) model built-in FLAC3D and the NEVPD model. The findings suggest that the proposed tunnel creep simulation approach provides a more precise reflection of the local deformation features of the surrounding rock compared to traditional methods. The simulation outcomes based on the NEVPD model exhibit the highest agreement with the field monitoring data.

Experimental study on frost heave deformation characteristics of rock and soil based on pore distribution model

Experimental study on frost heave deformation characteristics of rock and soil based on pore distribution model

Numerical study of the fluid fracturing mechanism of granite at the mineral grain scale

Hydraulic fracturing is an essential technique for reservoir stimulation in the process of deep energy exploitation. Granite is composed of different rock-forming minerals and exhibits obvious heterogeneity at the mesoscale, which affects the strength and deformation characteristics of rocks and controls the damage and failure processes. Therefore, in this paper, based on the discrete element fluid-solid coupling algorithm and multiple parallel bond-grain based model (Multi Pb-GBM), a numerical model of a granite hydraulic fracturing test is established to study the evolution of hydraulic fractures in crystalline granite under different ground stress conditions. The main conclusions are as follows. The crack propagation of hydraulic fractures in granite is determined by the in situ stress state, crystal size, and mineral distribution, and the ground stress is the main controlling factor. The final fracture mode affects the maximum principal stress and shear stress, and the generation of cracks changes the distribution of the stress field. The hydraulic fracturing initiation pressure decreases with decreasing crystal size. The influence of the crystal size on the crack inclination angle is mainly reflected in local areas, and the general trend of the fissure dip angle distribution is along the direction of the maximum in situ stress. This study not only has important theoretical significance for clarifying the propagation mechanism of hydraulic fractures but also provides a theoretical basis for deep reservoir reconstruction and energy extraction.

A novel meso-damage constitutive model of rock under true triaxial stress with three-dimensional cracking strength, threshold and closure effect

Deep underground engineering is in a true three-dimensional stress state, and the adjustment of the three-dimensional stress state caused by engineering excavation will induce the fracture or even instability of the surrounding rock. However, three-dimensional mechanical model research suitable for the stability analysis of deep surrounding rock is very scarce. Therefore, a series of tests under different true triaxial stresses on two rocks (rhyodacite and marble) were conducted, and the characteristic strength (crack stable propagation initiation stress, crack unstable propagation initiation stress and peak strength) and deformation characteristics were further analyzed. After that, using the Lemaitre strain equivalence hypothesis and rock statistical damage theory, a new statistical damage constitutive model at true triaxial stress states was proposed, which introduced the three-dimensional strength criterion Modified Wiebols Cook to characterize the three-dimensional strength of the rock microelement. Therefore, the intermediate principal stress can be reasonably considered. The damage threshold, initial compaction effect and residual strength of the rock microelement at different true triaxial stress conditions were also considered. Then the relationships between the proposed model parameters and σ2 and σ3 were analyzed. Furthermore, sensitivity analysis of the influence of parameters m and F0 in proposed model on the shape of rock stress–strain curve and peak strength was also investigated. The comparison between the results predicted by proposed model and the experimental data shows that the new model established in this study can well simulate the prepeak and postpeak deformation characteristics of rock and the intermediate principal stress effect under true triaxial stress conditions.

Comparative analysis of quasi-static penetration characteristics of slotted granite and intact granite

The stress release method with rock slotting in the bottom hole by ultra-high-pressure water jet is proposed as a solution to the problem of increased rock strength due to high in-situ stress. However, the failure mode of rock with annular grooves under the simultaneous action of geostatic stress and hydrostatic pressure is still unclear. The failure characteristics, penetration force, failure mode and deformation characteristics of rock under geostatic stress are studied by numerical simulation. The results showed that the presence of an annular groove changes the rock failure mode. The radial crack propagation direction dominated by extrusion shear is deflected and will be connected to the peripheral area of the groove’s bottom. It becomes the primary crack propagation dominated by tensile shear, controlled by the crack formation zone and the stress concentration zone at the peripheral area of the groove’s bottom. The annular groove can significantly reduce the peak penetration force by about 72%. There is a critical value for the influence of groove depth on the peak penetration force. The presence of an annular groove changes the load-penetration curves from ductile failure to brittle failure mode. The groove modifies the stress propagation mode, altering the rock response and crack propagation zones. In addition, the annular groove decreases the radial force that restricts the extension of rock in the surrounding area, allowing the rock to expand more easily in the surrounding area. Therefore, this stress release method and the study’s findings are instructive for improving rock-breaking efficiency and gaining a deeper understanding of the technique.

Progress on rock mechanics research of Beishan granite for geological disposal of high-level radioactive waste in China

The mechanical behavior of host rock for a deep geological repository of high-level radioactive waste plays a key role in ensuring the isolation function of host rock as a natural barrier under the multi-field coupling environment. For a better understanding of granite in China's Beishan pre-selected area for geological disposal of high-level radioactive waste, a series of investigations were carried out on in-situ stress field of rock mass at depth, strength and deformation characteristics of rocks under different stress and temperature conditions, and rock boreability and adaptability to Tunnel Boring Machine (TBM) technology. The results indicate that Beishan granite shows typical characteristics as a hard and brittle rock with a quite low permeability, and it is favorable to geological disposal. Meanwhile, a new rock mass suitability evaluation system was proposed, and the rock mass mainly composed of Beishan granite was proven to be suitable for geological disposal. Besides, the constructability of Beishan granite at engineering scale was tested and verified through field tests in the Beishan Exploration Tunnel (BET). Here, we summarize the main outcomes of rock mechanics research on Beishan granite in the past years and introduced the current progress of Beishan underground research laboratory (URL) for geological disposal.

The creep model based on nonlinear Newton body under different temperature conditions

Mastering the creep deformation characteristics of rock under different temperature conditions is of great significance for studying the long-term stability and deformation mechanism of geotechnical engineering. Based on the classical Burgers model, the creep model under different temperature conditions is established by introducing a nonlinear Newton body. The parameters of the creep model are identified and the influence law of different parameters on rock creep deformation is analyzed. The relationship between model parameters and temperature is quantitatively expressed. The results show that the newly established model can describe the characteristics of the rock in the decay creep stage and the constant creep stage, especially can quantitatively characterize the relationship between the strain and the time of the rock in the tertiary creep under different temperatures conditions. The model fitting curve is highly consistent with the test data, and the correlation coefficient R2 is above 0.98, which thoroughly verifies the accuracy and rationality of the model. It is found that when the temperature is constant, the creep increases with the increase of the shear modulus of the elastomer G1, the shear modulus of the viscoelastic body G2, and the viscosity coefficient of the viscous body η1 in the constant creep stage. The decay creep property of rock is more obvious with the increase of the viscosity coefficient η2, and the axial strain tends to a constant value. The achievement can be used to predict the deformation trend of geotechnical engineering with time under different temperature conditions and provide the theoretical basis for long-term stability analysis.

Triaxial creep damage characteristics of sandstone under high crustal stress and its constitutive model for engineering application

AbstractThe creep characteristics of rock under high crustal stress are of important influence on the long‐term stability of deep rock engineering. To study the creep characteristics and engineering application of sandstone under high crustal stress, this study constructed nonlinear creep damage (NCD) constitutive mode based on the triaxial graded loading‒unloading creep test of sandstone in the Yuezhishan Tunnel. A numerical NCD constitutive model and a breakable lining (BL) model were developed based on FLAC3D and then applied to the stability analysis of the Yuezhishan Tunnel. Based on the creep test results of sandstone, a power function of creep rate and stress level was constructed, by which the long‐term strength was solved. The results show that the long‐term strength of the red sandstone based on the related function of the steady‐state creep rate and stress level is close to the measured stress value in engineering. The NCD model considering damage factors reflects the instantaneous and viscoelastic plasticity deformation characteristics of the red sandstone. The numerical NCD constitutive model and the BL model can reflect surrounding rock deformation characteristics and lining failure characteristics in practical engineering. The research results provide theoretical references for long‐term stability analysis of rock engineering and the deformation control of surrounding rock under high crustal stress.

Time-Dependent Creep Constitutive Model of Roadway Surrounding Rock Based on Creep Parameters

In order to better study the creep deformation characteristics of rock under different stresses, the generalized Burgers model was used as the basic model after analyzing the creep characteristics of rock and its relationship with stress and strain, and its application scope was verified. Based on the damage mechanics theory, a viscoplastic body considering aging damage was established, which was connected with the generalized Burgers model in series. A new nonlinear creep constitutive model was obtained, which was extended to three dimensions. In addition, the relationship between model parameters and damage variables was established by introducing damage variables that considered damage effects. The unsteady creep constitutive model of rock is obtained, and the correctness and rationality of the model are verified by test data. The results show that this model not only accurately reflects the creep characteristics of attenuation and steady creep stage but also overcomes the defect that the generalized Burgers model is difficult to describe the accelerated creep. Considering the deterioration of creep parameters with time, the creep damage process of rock under different stress states can be better described, which provides a new idea for establishing unsteady creep model and determining model parameters.

A Case Study on Surrounding Rock Deformation Control Technology of Gob-Side Coal-Rock Roadway in Inclined Coal Seam of a Mine in Guizhou, China

Surrounding rock deformation control of gob-side coal-rock roadway in inclined coal seams (GCRICS) is a major problem in gob-side entry technology application practice. This paper describes a case study of the surrounding rock deformation characteristics and control technology of a typical GCRICS in Guizhou, China. As according to data obtained during a field investigation, the reasons for the deformation and failure of 151509 tailentry and the shortcomings of the original support scheme were analyzed. In combination with existing theory and field experience, the “anchor cable + U-shaped steel + shotcreting + grouting” (CUSG) support method was proposed. The plastic zone distribution, displacement, and stress evolution law of the roadway-surrounding rock under the four support modes were analyzed and compared by numerical simulation. The results show that the supporting effects of several support methods varied from good to poor; CUSG was the best, followed by anchor cable support, U-shaped steel support, and then no support. Based on the previous seepage grouting theory, a slurry diffusion model of hollow grouted anchor cable (HGC) was established and the calculation formulas of slurry diffusion radius and grouting time were deduced, which provided guidance for field construction. Finally, the CUSG surrounding rock control technology was applied to 151509 tailentry subsequent roadway support. Through drill holes, analysis of the surrounding rock of the non-grouting area and the grouting area was conducted. It was found that the surrounding rock of the grouting area was high in integrity and strong in bearing capacity. Throughout the excavation period to the end of roadway mining, the roadway did not have to be repaired. This case study has high practicability, high popularization value, and provides a useful reference for the engineering support design of the GCRICS.

Experimental study on frost heave deformation characteristics of rock and soil based on pore distribution model

Experimental study on frost heave deformation characteristics of rock and soil based on pore distribution model

Fracture and deformation behaviors of saturated and dried single-edge notched beam sandstones under three-point bending based on DIC

It is of great significance to study the fracture and deformation characteristics of rock with different moisture conditions for the safety assessment of “fragile surface with cracks” in rock engineering such as dams and underground chambers affected by groundwater. Therefore, in this work, three-point bending tests were conducted on single-edge notched beam sandstone specimens with different moisture conditions (natural condition, dried condition, and saturated condition) under complex stress environment. Additionally, the digital image correlation (DIC) method was used to quantitatively research the fracture parameters and deformation behavior of specimens during pure mode I fracture and mixed mode I-II fracture. The results show that (1) the average peak load of dried sandstone is 42.18–116.08% higher than that of saturated sandstone. (2) By increasing the offset distance of the pre-notch (0–72 mm), the specimen is transformed from pure mode I fracture to mixed mode I-II fracture, with an increase in average peak load of 152.83–284.24%. (3) When the pure mode I fracture occurs in saturated sandstone, the fracture toughness is 66.74% of that natural sandstone, which is 46.28% of that dried sandstone. (4) In the mixed mode I-II fracture, the effective fracture toughness of sandstone with a consistent moisture condition is 1.05–1.70 times that of the pure mode I fracture. (5) The fracture toughness of saturated sandstone is most significantly affected by the loading mode. When the offset distance of pre-notch increases from 0 to 72 mm, the average effective fracture toughness increases from 4.324 MPa·mm0.5 to 7.357 MPa·mm0.5, increasing by 70.14%. Besides, according to the trend of the ap, which was calculated by the DIC method, the post-peak macroscopic crack propagation is divided into two stages: the post-peak stable propagation stage and the post-peak unstable propagation stage.

Fracturing mechanisms and deformation characteristics of rock surrounding the gate during gob-side entry retention through roof pre-fracturing

To study the fracturing mechanism and deformation characteristics of the rock surrounding the gate during gob-side entry retention through roof pre-fracturing, the roof fracture laws and mechanism of the gob-side entry were analyzed. Based on the results, a 6-zone distribution law of the gob-side entry was developed through theoretical analysis. In this study, the fracturing mechanism of the gate roof in different zones and the plastic zone expansion law of the coal side were clarified through numerical simulations based on a gate in the Halagou Coal Mine. The numerical simulation results showed that the fracture mechanism of the gate roof above the coal side is closely related to the tensile strengths of the immediate roof and the main roof. The fractures above the solid coal are the main cause of the dramatic appearance of dynamic pressure in the gob-side entry. The slewing subsidence of the main roof causes the deformation of and damage to the surrounding rock to sharply increase. To ensure the stability of the gob-side entry, a support design scheme consisting of a high-pretension force, constant resistance, and the use of large deformation cables + single hydraulic props + steel beams + U section steel is proposed. The field test results showed that after the working face was mined, although the fractures in the overlying strata penetrated to the ground surface, the maximum roof and floor convergence was only 196–212 mm, which is within a reasonable range. The results of this study provide an important support design for gob-side entry retention under similar conditions.

Experimental study on the failure process of sandstone subjected to cyclic loading and unloading after high temperature treatment

To understand the influence of temperature on sandstone failure process, the cyclic loading and unloading tests under the action of seepage and stress were carried out on sandstone after different temperature (25–800 °C) treatments. Based on the experimental results, the stress-strain curve, Young's modulus and crack volume strain of rock were analysed during cyclic loading and unloading, and the energy calculation equation was established considering the confining pressure and seepage pressure. The main research results are as follows: (1) with the increase in temperature, the stress-strain curve of the rock sample after heat treatment shows obvious signs of hysteresis loop, showing the characteristic of a three-stage evolution, that is, “sparse→dense→sparse”. (2) the Young's modulus in the unloading process is clearly larger than that in the loading stage, but both increase first and then decrease with the increase in temperature, with 400 °C as the critical temperature. (3) temperature can affect the deformation characteristics of rock, which results in an evident correlation between the crack volume strain and the temperature during each cycle of loading and unloading. (4) based on the established energy calculation equation, the energy evolution characteristics in the process of rock deformation and failure are obtained. Compared with the sample treated at lower temperatures than 400 °C, the cumulative dissipation energy of the sample increases after higher temperature (above 400 °C) treatment. The results are expected to enhance the understanding of mechanical properties and failure process of sandstone after temperature treatment, and provide guidance in engineering stability analysis under multi-physical field coupling.