Jointed Rock Mass Research Articles

Evolution Characteristics of Plastic Zone in Jointed Rock Mass of High-Temperature Hydraulic Tunnel

The evolution characteristics and the extent of the plastic zone in rock mass can reflect the failure characteristics and destruction degree of a hydraulic tunnel. In this research, we derived the equation of a plastic zone range based on a gateway-like structure high-temperature tunnel through a theoretical analysis. On-site monitoring and discrete element model simulation were combined to analyze the temperature field law and plastic zone evolution characteristics of the jointed rock mass at high temperatures. The results show that the joints affect the temperature field variation in rock mass, and the vertical and horizontal joint groups pose significantly greater influence than the inclined joint group on temperature field. The sensitivity of the joint internal friction angle and thermal expansion coefficient to the range of the plastic zone is relatively small. Under various joint spacings, the influence of horizontal and inclined joint groups on the plastic zone morphology decreases, while the vertical joint group exhibits an incremental influence on the plastic zone morphology. Similar to the influence of the temperature field, the vertical and horizontal joint groups have a significantly greater influence on the plastic zone range than the inclined joint group. Under various rock mass temperatures, the plastic zone in rock mass results in the occurrence of uneven expansions along the direction of the joint dip angle, which changes the potential failure direction of rock mass and increases the potential destruction degree of rock mass, whereas it exhibits a smaller uniform expansion perpendicular to the joint dip angle, and the boundary of the plastic zone coincides with the joint surface, relatively hindering the potential destruction degree of rock mass. The research results of this study have certain reference values for the stability control of jointed rock mass in high-temperature hydraulic tunnels.

A Comprehensive Method for Similarity Evaluation in Discrete Fracture Network Modeling of Jointed Rock Masses

A Comprehensive Method for Similarity Evaluation in Discrete Fracture Network Modeling of Jointed Rock Masses

Numerical simulation study on shear resistance of anchorage joints considering tensile–shear fracture criterion of 2G-NPR bolt

2G-NPR bolt (the 2nd generation Negative Poisson’s Ratio bolt) is a new type of bolt with high strength, high toughness and no yield platform. It has significant effects on improving the shear strength of jointed rock mass and controlling the stability of surrounding rock. To achieve an accurate simulation of bolted joint shear tests, we have studied a numerical simulation method that takes into account the 2G-NPR bolt's tensile–shear fracture criterion. Firstly, the indoor experimental study on the tensile–shear mechanical properties of 2G-NPR bolt is carried out to explore its mechanical properties under different tensile–shear angles, and the fracture criterion of 2G-NPR bolt considering the tensile–shear angle is established. Then, a three-dimensional numerical simulation method considering the tensile–shear mechanical constitutive and fracture criterion of 2G-NPR bolt, the elastoplastic mechanical behavior of surrounding rock and the damage and deterioration of grouting body is proposed. The feasibility and accuracy of the method are verified by comparing with the indoor shear test results of 2G-NPR bolt anchorage joints. Finally, based on the numerical simulation results, the deformation and stress of the bolt, the distribution of the plastic zone of the rock mass, the stress distribution and the damage of the grouting body are analyzed in detail. The research results can provide a good reference value for the practical engineering application and shear mechanical performance analysis of 2G-NPR bolt.

The Mechanism of Rockbolts in Jointed Rock under Uniaxial Tension

In this research, the rockbolt mechanism of a jointed rock mass under uniaxial tension was systematically revealed with a laboratory test and a numerical simulation. It was found that the rockbolt rock mass experienced five stages under uniaxial tension, the densification stage, elastic stage, plastic deformation stage, progressive debonding stage, and complete debonding stage. The stress-strain curve and ultimate tensile strength of a rockbolt rock mass were analyzed by taking the rockbolt spacing and rockbolt angle as variables. It was found that the improvement effect of the reduction of the rockbolt spacing on the ultimate tensile strength was limited. When the rockbolt spacing was reduced to a certain limit, the stress concentration area between adjacent rockbolts was connected and destroyed, resulting in the increase of the rockbolt rock strength becoming smaller, and even having a downward trend. The increase of the rockbolt angle led to the change of the stress mode and failure mode of the whole structure, and the ultimate tensile strength first increased and then decreased. The optimal rockbolt angle was between 60° and 70°. It is worth noting that there was an obvious mechanical occlusion between the thread on the rockbolt surface and the rock mass, resulting in the multi-stage step-down characteristic of the stress-strain curve in the complete debonding stage. The results of this study can provide a reference for the design and construction of similar projects.

Experimental and Numerical Study of Joint Persistence Effect on the Non-persistent Jointed Rock Mass’ Tension Failure Behavior

Experimental and Numerical Study of Joint Persistence Effect on the Non-persistent Jointed Rock Mass’ Tension Failure Behavior

Planar Slope Failure in Heavily Jointed Rock: Tension Cracks and Nonlinear Strength

This work proposes the calculation of the factor of safety for a strongly jointed rock mass in the case of plane failure with a tensile crack whose exact position or depth is not known but is expected to exist. This calculation is performed by applying the non-linear failure criteria of the Focus Procedure of Úcar and Hoek–Brown’s and implementing the necessary formulae in a spreadsheet. The aim is to provide a simple, cost-effective, and easy-to-use procedure that is useful in the early stages of a project or as a starting point for more detailed investigations. Besides slope geometry and strength parameters, the required parameters are the RMR of the rock mass or its mi, depending on the criterion used. The proposed procedure allows for the estimation of the factor of safety, the position and depth of the tensile crack, and the inclination of the failure plane in the most unfavorable case, with reasonable accuracy, using an iterative process with the conventional tools available in common spreadsheet programs. An example is provided in which an accuracy of 86–96% for the factor of safety is obtained.

Numerical Simulation of Failure Modes in Irregular Columnar Jointed Rock Masses under Dynamic Loading

The mechanical properties and failure characteristics of columnar jointed rock mass (CJRM) are significantly influenced by its irregular structure. Current research on CJRMs is mainly under static loading, which cannot meet the actual needs of engineering. This paper adopts the finite element method (FEM) to carry out numerical simulation tests on irregular CJRMs with different dip angles under different dynamic stress wave loadings. The dynamic failure modes of irregular CJRMs and the influence law of related stress wave parameters are obtained. The results show that when the column dip angle α is 0°, the tensile-compressive-shear failure occurs in the CJRMs; when α is 30°, the CJRMs undergo tensile failure and a small amount of compressive shear failure, and an obvious crack-free area appears in the middle of the rock mass; when α is 60°, tensile failure is dominant and compressive shear failure is minimal and no crack area disappears; and when α is 90°, the rock mass undergoes complete tensile failure. In addition, in terms of the change law of stress wave parameters, the increase in peak amplitude will increase the number of cracks, promote the development of cracks, and increase the proportion of compression-shear failure units for low-angle rock mass. The changes in the loading and decay rate only affect the degree of crack development in the CJRMs, but do not increase the number of cracks. Meanwhile, the simulation results show that the crack expansion velocity of the CJRMs increases with the increase in dip angle, and the CJRMs with dip angle α = 60° are the most vulnerable to failure. The influence of the loading and decay rate on the rock mass failure is different with the change in dip angle. The results of the study provide references for related rock engineering.

Stability analysis of jointed rock mass in large underground caverns based on multi-scale analysis method

Random defects at different scales are the crucial cause of damage evolution and cascade transfer in rocks. For a large-scale underground cavern, the rock mesoscopic heterogeneity and macroscopic random joints are inevitable factors of rock stability, which needs to be further studied. In this study, a multi-scale analysis method for the stability of jointed rock mass in large underground caverns is proposed. The statistical damage theory is used to describe the mesoscopic heterogeneous rock damage. Monte Carlo simulation and measured joint geometric information are combined to reconstruct the macroscopic random joint network of rock mass. The integrated analysis of mesoscopic heterogeneity of rock and the macroscopic response of random jointed rock mass is performed by Rock Failure Process Analysis (RFPA) system. The research shows that the existence of joint affects the failure mode of rock mass and strengthens the heterogeneity. The representative elementary volume (REV) of jointed rock mass and its equivalent mechanical parameters are determined and used in the stability analysis of a large-scale underground cavern project. Results show a good agreement with the in-situ monitoring deformation of surrounding rock mass, which verifies the effectiveness of the rock mass multi-scale analysis method.

Influences of Joint Persistence on the Compressive-Shear and Tensile-Shear Failure Behavior of Jointed Rock Mass: An Experimental and Numerical Study

Influences of Joint Persistence on the Compressive-Shear and Tensile-Shear Failure Behavior of Jointed Rock Mass: An Experimental and Numerical Study

Analysis of P-wave propagation in filled jointed rock mass with viscoelastic properties

Stress wave propagation in filled jointed rock mass is an important basis for the analysis of rock dynamic stability. The presence of small cracks in rock mass often causes the rock to exhibit viscoelastic behavior, resulting in the amplitude attenuation and time delay of the stress wave. In view of the incomplete understanding of stress wave propagation in viscoelastic media, this study presents an analysis on stress wave propagation in filled jointed rock mass with viscoelastic properties based on the time-domain recursive analysis method. By introducing the quality factors of stress wave in viscoelastic medium, the propagation equation of plane P-wave in filled jointed rock mass with viscoelasticity is established. Subsequently, the transmission and reflection characteristics of P-wave are accordingly analyzed. The results indicate that the transmission and reflection coefficients of P-wave through the filled joint decrease obviously due to the attenuation effect of rock viscoelasticity on wave amplitude, but the coefficients gradually stabilize as the quality factor increases. As the propagation distance of the P-wave increases in viscoelastic rock masses, the transmission and reflection coefficients decrease gradually. The normal stiffness of joint contact interface has a decisive influence on the wave propagation. Specifically, a higher normal stiffness leads to stronger transmission and poorer reflection. The larger the thickness of filled joint, the more obvious the attenuation of P-wave becomes. Additionally, the viscoelasticity of filling layer further aggravates the influence of joint thickness on the attenuation of P-wave. The study comprehensively takes into account the effect of viscoelasticity of both the rock mass and the filling layer on transmission and reflection of waves. The research results provide certain theoretical support for the dynamic response and stability analysis of rock mass containing structural planes.

Elasto-plastic and post-yield weakening jointed rockmass response in a comparison of equivalent-continuum and explicit structural models

The strength and stiffness of a composite rockmass (intact material, defects, joints, bedding, etc.) are primary inputs for the engineering analysis of rock slopes and underground excavations. The Geological Strength Index (GSI) has served rock engineering for three decades as a rockmass assessment system based on the blockiness of the rockmass and discontinuity condition. GSI is used to factor the Hoek–Brown strength envelope for intact rock to represent jointed rockmasses in conventional equivalent-continuum numerical modelling. Modern numerical tools can represent networks of discrete (explicit) structure with assigned discontinuity properties. This provides an opportunity to compare explicit structural modelling with the conventional implicit equivalent-continuum approach. In this paper, explicit structural models are developed using elasto-plastic (constant-strength) constitutive models for intact rock and realistic parametric ranges for explicit structure properties. Explicit model results are compared to equivalent-continuum results, validating the classical implicit approach while also identifying key limitations. Explicit models with post-yield weakening of the intact and structural elements are then developed and compared to post-yield weakening implicit models that use post-yield dilation and empirical relationships between peak and residual GSI. The results provide guidance for practical modelling in strain-weakening rockmasses, including recommendations for post-yield dilation in the traditional implicit approach.

A general equivalent continuum model and elastic wave velocity analysis of jointed rock masses

The presence of joints dramatically affects the mechanical behavior of rock mass. For highly fractured jointed rock mass, it is more convenient to treat the jointed rock mass as equivalent continuum material. Consequently, several researchers have proposed continuum models to describe the mechanical behavior of jointed rock mass. These models are reviewed and their limitations are discussed. From the perspective of energy conservation, a general continuum model for jointed rock mass is proposed in this study, which incorporates a fourth-rank compliance tensor for joints. The stiffness, areas and orientations of joints are included in the compliance tensor. The proposed compliance tensor is in a general form, which is applicable for joints of arbitrary shape, such as penny-shaped joints and multi-sets of persistent/non-persistent joints etc. The directional modulus and Poisson's ratio of jointed rock mass are deduced from the proposed model. Besides, the elastic wave velocities of jointed rock mass are analyzed from the proposed model according to Christoffel equation. It is found that the square of longitudinal wave velocity is approximately proportional to directional modulus of jointed rock mass. Effectiveness of the proposed model is verified by comparisons with both in situ tests and numerical simulations.

Static pressure and dynamic impact characteristics of filled jointed rock after frozen-thaw cycle damage

In the construction project, rock mass is often destroyed from the joint plane, and the jointed rock mass is easy to be eroded by freeze-thaw environment. Therefore, the damage mechanical properties of filled jointed rock mass under freeze-thaw action are very important for construction disaster prevention, engineering safety evaluation and reinforcement. In order to research the effect of the freeze-thaw cycle on the mechanical deterioration properties and damage characteristics of filled jointed rocks, prefabricated filled jointed rock samples are tested with different numbers of freeze-thaw cycles under the temperature range of -20°C~20°C. Then the wave velocity test, static compression test and SHPB impact test are conducted on the rock samples after freeze-thaw. Based on the test results, the change regularity of wave velocity degradation, static compression mechanical properties and dynamic compression mechanical properties of filled jointed rocks under the effect of freeze-thaw cycles were analyzed. The results show that the wave velocity, static compressive strength and dynamic compressive strength of the filled jointed rocks all show a downtrend with the increase of the number of freeze-thaw cycles, and each parameter is positively correlated with the strength of the filling materials. Among them, the decrease in the wave velocity of the rock sample after 30 freeze-thaw cycles is greater than 30%, and the strength loss of the static peak compressive strength exceeds half of its initial strength. The static peak strain rises exponentially with the increase of the number of freeze-thaw cycles while the dynamic peak strain does not show a clear trend. The dynamic peak strain is about 1/10 to 1/5 of the static peak strain. Under the same freeze-thaw action, the lower the strength of filling material, the more serious the damage.

Development of a computer program from photogrammetry for assisting Q-system rating

A computer program to assist the Q-system rating of jointed rock mass is herein developed based on the photogrammetric analysis of point clouds. Three major rating terms, namely, rock quality designation (RQD), joint set number (Jn), and joint roughness number (Jr), are evaluated using predefined algorithms in the computer program without the input of an engineering expert. The random sample consensus algorithm is adopted to identify major outcrop joint surfaces. Thereafter, the major joint surface is determined to calculate the weighted joint density (wJd) and its corresponding RQD. In addition, a spherical K-means clustering is utilized to obtain the number of dominant joint sets and further convert it to the Jn value. Moreover, the a/L method is adopted to calculate the joint roughness coefficient (JRC) of those facets and convert it to Jr. The analysis results agree with manual Q-system rating results, revealing that the proposed computer program is practicable. Furthermore, we evaluate the limitation of the proposed computer program as applied to interlayered sedimentary rocks. Finally, we found that doubling the standard deviation of the distance between fitted facets to the point cloud is a reasonable estimate of the JRC20 and Jr of rock joints.

Study on damage anisotropy and energy evolution mechanism of jointed rock mass based on energy dissipation theory

Study on damage anisotropy and energy evolution mechanism of jointed rock mass based on energy dissipation theory

Shear behaviour of anchored jointed rock mass under different engineering conditions considering damage and joint surface morphology

According to different geological conditions and engineering disturbance, three dimensional numerical models of anchored jointed rock mass with two kinds of boundary conditions of constant normal load (CNL) and constant normal stiffness (CNS) were constructed considering the ductility damage of rockbolt, the stiffness degradation of grouting layer and the joint surface roughness. The effects of anchorage angle, joint surface morphology, and boundary conditions on the shear performance of anchorage system were analyzed, and the failure characteristics under different working conditions were revealed. Finally, the analytical solution of shear strength of anchored system was established. Results show that the larger the anchorage angle is, the more serious the necking phenomenon of rockbolt will be. The damage degree of the bonding layer and the horizontal displacement of the bedding rock mass decrease with the increase of the joint surface roughness. The CNL condition is to instantaneously apply high normal stress, and the CNS condition is to gradually form a high normal stress environment through the superposition of increment on the basis of the initial value, which can resist greater transverse load. This is equivalent to enhancing the ductility of the rockbolt. The shear strength of the system increases with the increase of normal stress and normal stiffness. Ignoring the normal stiffness will underestimate the shear strength.

Effect of rock joints on lined rock caverns subjected to high internal gas pressure

The storage of hydrogen gas in lined rock caverns (LRCs) may enable the implementation of the first large-scale fossil-free steelmaking process in Sweden, but filling such storage causes joints in the rock mass to open, concentrating strains in the lining. The structural interaction between the LRC components must be able to reduce the strain concentration in the sealing steel lining; however, this interaction is complex and difficult to predict with analytical methods. In this paper, the strain concentration in LRCs from the opening of rock joints is studied using finite element (FE) analyses, where the large- and small-scale deformation behaviors of the LRC are coupled. The model also includes concrete crack initiation and development with increasing gas pressure and rock joint width. The interaction between the jointed rock mass and the reinforced concrete, the sliding layer, and the steel lining is demonstrated. The results show that the rock mass quality and the spacing of the rock joints have the greatest influence on the strain distributions in the steel lining. The largest effect of rock joints on the maximum strains in the steel lining was observed for geological conditions of “good” quality rock masses.

Numerical simulation of rock bursts triggered by blasting disturbance for deep-buried tunnels in jointed rock masses

Frequent dynamic disturbances, such as explosions, vibrations, and earthquakes, may trigger the risk of rock burst disasters around neighbouring deep-buried tunnels. In this study, the PFC software was used to simulate rock bursts triggered by blasting stress waves (dynamic disturbance) to determine their effects on deep-buried tunnels in jointed rock masses. This study investigated the effects of different ground stress values and joint angles on rock bursts in tunnels under intense dynamic disturbance. An analysis of different ground stress values and joint angles revealed the changes in the ejection velocities of damaged rocks and kinetic energy under intense dynamic disturbance. The results show that higher ground stress can alter the proportion of stress waves converted into strain energy and kinetic energy. Joint angles affect the location of the rock burst. The closer the joint angle is to 90°, the greater the damage to surrounding rocks caused by stress waves. Higher ground stress and joint angles increase the risk and intensity of rock bursts, causing significant damage to surrounding rocks, which makes existing tunnels more vulnerable to impact. The findings of this research have important guiding significance to ensure the secure protection of tunnels against rock bursts.

Studying rock mass jointing to provide bench stability while Northern Katpar deposit developing in Kazakhstan

Purpose is to identify the basic joint systems, their characteristics, distribution within the rock mass, and determine impact of the joints on the bench stability. Methods. The risks of strain emergence in the form of blocks sliding along weakness surfaces within the local areas were determined based upon the definition of rock stability loss. The results of large-scale measurements of jointing were processed using circular and bar diagrams as well as stereographic grids. In the context of the paper, kinematic analysis was implemented through Dips Rocscience Inc. Software. Findings. Five basic joint systems have been identified; joints of 2nd and 5th systems are the most commonly encountered among them. The results of the jointing determination within the open pit boundaries have been represented as well as the open pit wall stability in terms of each site inclusive of consideration of potential strains along the sliding surface. Originality. For the first time, zoning of the open pit wall in terms of slide types has been performed. It has been identified that potential shear of a prismatic block is 33%; at the same time, 66% are bench destruction with the block toppling. The risk of wedge-shaped block shear is minimal. Practical implications. The research findings may be helpful to define and select both parameters and conditions of safe mineral extraction under the specific mining and geological conditions. In turn, the abovementioned will help reduce the risk of accidence while providing scientifically substantiated approach to select quarrying sequence, techniques, and system.

Impact of rock mass jointing on dilution of disseminated copper–nickel ore in Oktyabrsky Mine

Impact of rock mass jointing on dilution of disseminated copper–nickel ore in Oktyabrsky Mine