Jointed Rock Mass Research Articles

Monitoring of ground surface deformation at Taimyrsky Mine using Sentinel-1 radar imaging for geodynamic risk assessment

The modern stage of mineral mining involves prediction of geotechnical risks. One of the major methods in this regard is the geodynamic zoning. The key target is to assess the cross-effect of mining operations and blocks structure of the Earth’s crust. This article presents the information on ground surface subsidence within the boundary of the mining lease of Taimyrsky Mine as a result of processing of paired images from Sentinel-1A sate llite. The implemented probabilistic kinematic analysis revealed some features of movements in overlying rock mass, in particular, local uplifts of ground surface. The detailed information on vertical deformations was obtained. Such approach enabled detecting the deformation areas subjected to the effect of the global tectonics which is, as a rule, neglected in geotechnical risk assessment while it directly affects mining safety. Despite the apparently consistent patterns resulted from processing of satellite images, the method InSAR is only used as a supplemental technique since the relevant regulatory framework is yet absent. In combination with the conventional surveying for monitoring ground surface deformations, the method InSAR enhances efficiency of monitoring and improves accuracy of geodynamic risk prediction in the course of mineral mining, inclusive of observations over the global tectonic processes. The probabilistic kinematic analysis allows for getting insight into the mechanism of overlying rock mass movement with regard to rock mass jointing and, jointly with InSAR, can be used in the artificial intelligence systems for learning models of prediction of overlying rock movement parameters during mineral mining.

Prediction of bolt supporting the controlling influence angle based on a synthetic weight factor.

The purpose of a rock bolt is to improve the strength capacity of a jointed rock mass. The strengthened arch controlling area can be formed based on the superposition of the controlling influence range of the bolt with the controlling influence angle of rock bolt playing an important role. However, quantitative research on the influence angle is still rare. In this study, numerical simulations and mathematical analysis are used to study the law of stress field distribution and the controlling influence angle through a single bolt, and the following conclusions can be obtained. (1) The compressive stress field is roughly distributed in an "Apple shape" and in a "conical" spatial distribution. (2) The bolt controlling angle is not a constant 45°, and it is influenced by the rock mass strength and bolt parameters. It decreases with the increasing elastic modulus of the bolt, bolt diameter and bolt length. It also increases with the increasing pretension and rock mass strength. The length has less influence on the supporting range. (3) Based on the experimental results, an optimal analytical model to predict the bolt’s controlling influence angle was developed. The analytical model includes the influences of the rock mass strength and bolt parameters. (4) A comparison between the model predictions with the results from the Dabei Mining 103 face transportation tunnel and the existing results shows the rationale behind the original support design scheme and an improvement over the existing results.

Research on Seismic Wave Quality Factor of Marble Jointed Rock Mass under SHPB Impact

In order to quantitatively describe the energy dissipation law of jointed rock mass, we obtained the jointed cores in laboratory conditions using marble from the roof and floor of Jinchanghe Lead–zinc mine in Baoshan. The dissipative degree of stress wave in marble jointed rock mass is measured by introducing quality factor Qs parameter. Based on the experimental principle of Split Hopkinson Pressure rod loading device (SHPB), we proposed a three-wave energy method of incident wave, reflected wave and projected wave for calculating jointed rock samples’ quality factor Qs based on stress wave energy. Using the SHPB test system for multiple specimens taken from the same piece of rock mass shock compression experiment, the three groups of specimens under different loading conditions gained incident wave and reflected wave and transmission wave experimental data, using the method of stress wave energy to deal with stress wave data, and calculate the joint sample maximum storage energy, dissipation energy and Qs quality factors. The results show that: ① The non-destructive breaking time–history strain of Dali rock mass under impact load is obtained by SHPB dynamic test system; combined with the deformation energy and dissipation energy calculation principle of quality factor, six groups of Qs experimental values are obtained. Although the Qs experimental values are discrete, the overall deviation is small with an average of 43.07. ② AUTODYN-Code was used to simulate the damage and fracture characteristics of rock mass with different quality factors under explosive dynamic load. The results showed that the radius of rock mass compression shear damage area gradually increased with the increase in porosity, but it was not obvious.

The effect of rock hardness and integrity on the failure mechanism of mortar bolt composite structure in a jointed rock mass

The appearance of joints in the rock tunnels makes the rock mass show obvious anisotropy and discontinuity in physical and mechanical properties, which has a significant influence on the rock mass stability. As one of the normally used support structures in tunnel construction, Mortar bolts will inevitably pass through the joints during the process. Both rock hardness and rock mass integrity will directly affect the anchorage performance of mortar bolts in joint rock. Considering this, this paper designs a mortar bolt pull-out experiment to investigate the joint rock failure modes and bolt-grout composite structure failure modes under different conditions of rock hardness and rock mass integrity. By taking the two influencing factors of rock hardness and integrity into account, the calculation formulas of ultimate pull-out load and ultimate displacement of mortar bolts in joint rock are established and proposed.

Energy evolution and damage constitutive model of anchored jointed rock masses under static and fatigue loads

During propagation, cyclical impact loads transform into low-frequency fatigue loads, which induce the release of energy from far-field anchored jointed rock masses (AJRMs) under long-term disturbance loads. Shear tests of marble under static and fatigue loading rates were conducted using a servo-controlled compression shear test machine equipped with an improved specimen fixture system. The effects of static and fatigue loads on the mechanical behaviour of samples, for example, the stress–strain curve, peak stress, shear modulus, peak strain and failure strain, were explored. The energy evolution of different types of AJRMs was studied in detail. In addition, a damage constitutive model for AJRMs was developed based on the Weibull distribution under static loading and deformation characteristics under fatigue loading. The results showed that fatigue loading could reduce the strength and increase the deformation of specimens, while static loading had a cumulative effect on the deterioration of specimens, which could decrease the elasticity of AJRMs. In the energy transformation process, the total energy included elastic energy, which described the elastic deformation, and dissipated energy, which could be converted to describe the anchor deformation, fracture extension and plastic damage, depending on the application. The proposed damage constitutive model was established by considering the influence of static and fatigue loads, and a damage constitutive equation of AJRMs was derived. A comparison between the calculated and experimental data showed that the damage equation could accurately describe the effects of static and fatigue loading rates on the stress–strain responses of specimens, and its parameters had definite physical meanings. Thus, the proposed model is a very good tool for the analysis of load coupling problems involved in deep rock mass engineering.

Experimental study on the shear performance of a prestressed anchored jointed rock-like mass under different corrosion levels

To illustrate the influence of corrosion on the shear performance of jointed rock masses reinforced by prestress anchors, four kinds of concrete specimens reinforced by anchors with different joint distributions were designed, and prestress was applied to the anchors using the posttensioning method. The deterioration effect of the shear performance of jointed rock-like masses reinforced by prestress anchors (JRLM-PA) under different corrosion levels was studied by means of electrochemical accelerated corrosion tests and direct shear tests . The research shows that (1) prestress improves the cohesion of the joint surface of jointed rock-like masses reinforced by anchors (JRLM-A) but has almost no influence on the internal friction angle of the joint surface of JRLM-A, (2) the shear strength of JRLM-PA increases first and then decreases with increasing pitting rates, and (3) the greater the prestress, the higher the connectivity rate, and the more significant the deteriorated influence of equivalent corrosion on the shear strength of JRLM-PA. Finally, an equation to calculate the shear strength of JRLM-PA under different corrosion levels is proposed, and the rationality of the equation is verified by comparison with the results of the laboratory tests. • Bolt corrosion mainly affects the equivalent cohesion of the rock mass. • The loss of prestress is related to the joint rock mass and prestress size. • A method is proposed to calculate the shear strength of a JRLM-PA under corrosion.

Bearing capacity of strip footings on jointed rock mass

Rock masses are non-homogenous, discontinuous media composed of rock material and naturally occurring discontinuities such as joints, fractures and bedding planes. Due to the presence of the geological discontinuities such as joints, faults and bedding planes, the compressive strength and modulus of elasticity of jointed rock mass are significantly reduced and the measurement of the strength behaviour of these jointed rock masses below the foundation becomes a challenging task. Previous researches have dealt with the bearing capacity of strip footings on the jointed rock mass for concentric, eccentric, inclined loading, separately. But, very limited work has been carried out for determining the bearing capacity of footings on jointed rock mass under eccentric-inclined loading together. In this study, the behaviour of rock masses under the pressure of strip footing has been investigated. To make the problem, more realistic, eccentric-inclined load was applied on the strip footing resting on horizontal jointed rock mass. A parametric study has also been carried out to develop some non-dimensional correlation between different parameters including GSI, e/B ratio, inclination, bearing capacity, etc. Three-dimensional analysis has been carried out by the finite element method using PLAXIS 3D software. Modified Hoek–Brown criteria was used to simulate the behaviour of rock mass and elastic behaviour of foundation was taken into the consideration for analysis. From the results, it can be concluded that the bearing capacity values drop as the eccentricity of the load increases. This indicates that as the eccentricity of the load increases, the bearing capacity of jointed rock mass diminishes. The bearing capacity value decreases with increasing loading inclination with respect to vertical. In the current study, non-dimensional correlations have been developed using data from non-linear elasto-plastic FEA to forecast footing’ bearing capacity, settlement and tilt of shallow foundation. These connections rely on the inclination of the load as well as the eccentricity to breadth ratio. The results obtained from the non-dimensional correlations holds goods on comparing the results obtained from the FEM analysis.

Analyzing the shear strength of jointed magmatic rock mass excavatability using the hybridization of metaheuristic model of ELM-SVM

Analyzing the shear strength of jointed magmatic rock mass excavatability using the hybridization of metaheuristic model of ELM-SVM

Study on Interfacial Crack Initiation of Jointed Rock Mass Based on Interface Fracture Mechanics

The fracture of interfacial crack is the main failure type of jointed rock mass. Therefore, it is very important to study the interfacial fracture of jointed rock mass. For the similarity of jointed rock mass and composites (all are composed by two parts, intact materials and their contact interfaces), the interface fracture mechanics widely used for analysis the interface crack of the composites (bimaterials) can be applied to study the interfacial fracture of jointed rock mass. Therefore, based on the basic theories of interface fracture mechanics, the interfacial fracture of jointed rock mass was analyzed, and one new criterion of interfacial crack initiation for jointed rock mass is proposed. Moreover, based on the proposed interfacial crack initiation criterion, the effect of main influence factors on the interfacial crack initiation of jointed rock mass was analyzed comprehensively. At last, by using the triaxial compression numerical tests on a jointed rock mass specimen with interfacial crack, the theoretical studies were verified.

Rock Chip Properties of TBM Penetration in Jointed Rock Masses Based on an Improved DICE2D Simulation

Rock Chip Properties of TBM Penetration in Jointed Rock Masses Based on an Improved DICE2D Simulation

Shear strength deterioration effect of rock mass joint surface under cyclic shear load

Understanding the shear strength degradation mechanism of a rock mass joint surface under cyclic shear load and determining a corresponding analytical model is an important foundation for accurately evaluating the safety of rock mass engineering under seismic loads. It is worth noting that, to date, there has been a dearth of studies on the strength characteristics of joint surfaces that consider the number of loading cycles, normal load, and initial undulant angle of the structural plane. In this study, focused on the behaviour of sandstone, the particle flow code (PFC) modelling framework was used to simulate a joint surface cyclic shear test considering first- and second-order undulations. Based on the experimental results, the comprehensive effects of the number of cyclic shear cycles, the normal stress, first- and second-order undulation and the dilatancy angle on shear stress during cyclic shear were analysed. Formulas for the joint surface shear basic friction angle and dilatancy angle under cyclic shear were proposed, and a method for calculating the joint surface peak shear strength under cyclic shear considering the deterioration of the dilatancy angle and basic friction angle was established. The peak shear strength of a sample after five cycles of shearing was calculated using the proposed formula and compared with the results of numerical simulations, the Barton method, and the Homand method. The results showed that the calculated values have good consistency with the results of the numerical simulations, demonstrating the effectiveness and accuracy of the proposed formula. However, under a low normal stress, there could be errors in estimating the cyclic shear strength of the joint surface.

Numerical simulation of stress wave propagation in joint rock specimens with cavity defects

The process of crack initiation, propagation, and coalescence is the essential cause of rock failure. A three-dimensional numerical model based on microscopic damage mechanics is adopted to simulate the failure process and acoustic emissions (AEs) of a jointed rock mass containing a pre-existing hole subjected to stress waves. The numerically simulated results demonstrate that transmission energy plays an important role in the failure process of specimens. The greater the energy of joint transmission is, the greater the damage to the joint transmission area of the rock mass is. Furthermore, the joint width could significantly influence crack propagation patterns and the damage of the joint transmission area of rock specimens. Moreover, the degree of damage to the local joint transmission area of the rock mass is small but then becomes more obvious when the joint angle grows larger. In addition, the wavelength of the stress wave can also affect the failure modes of the rock when stress waves are applied. As the wavelength of the stress wave reduces, the larger the damage of the rock mass is and the smaller the effect of the joint on crack propagation is. Finally, the numerical results demonstrate that the width of the specimen has a significant effect on its dynamic failure mode and degree, showing an obvious size effect. This finding could explain the lateral growth of an existing flaw in its own plane, which is a phenomenon that has not been observed in laboratory experiments.

A method for full three-dimensional kinematic analysis of steep rock walls based on high-resolution point cloud data

The predisposition of a slope to generate rockfalls is related to the intensity of rock mass jointing and the geometric arrangement of discontinuities intersecting the rock face. With the increasing use of terrestrial laser scanner (TLS) in rock slope surveying, methods have been proposed to semi-automatically extract the spatial properties of outcropping discontinuities from high-resolution topographic data. The present paper builds upon one of such methods (named DiAna), and extends it to enhance the assessment of rockfall susceptibility over steep rock walls. In particular, a Matlab routine (named DiAna-K) that incorporates a full three-dimensional derivation of kinematic analysis principles is introduced. Kinematic tests for plane, wedge, block toppling, flexural toppling, and free fall failure are formulated by explicitly accounting for the presence of overhanging areas of the rock face as well as varying frictional strengths across different discontinuity sets, planes, or intersections between planes. Results from a test application at an abandoned quarry site highlight the ability of the proposed procedure to provide detailed insights into the kinematic feasibility of structurally controlled instabilities. They also demonstrate the importance of properly defining failure mechanisms over steep (and usually undersampled) topographies in order to derive realistic quantifications of rockfall hazards.

Study on the shear creep characteristics of anchored jointed rock masses under creep fatigue loading

Study on the shear creep characteristics of anchored jointed rock masses under creep fatigue loading

Strength and deformation behavior of columnar jointed rock masses under different confining pressures

Strength and deformation behavior of columnar jointed rock masses under different confining pressures

Experimental and numerical investigation on compressive strength and crack behavior of rock-like specimens with open flaws under confining loads

Engineering problems are related to the failure of geological material, especially that of jointed rock masses. To investigate the influence of confining stress and inclination angle β on cracking behavior and failure mechanism, triaxial compression tests are conducted on rock-like samples containing parallel opening flaws. There are two patterns, namely, tensile failure and tensile-shear failure, and each occurrence has an equal frequency. Nine crack modes are summarized, and the most special one is mode 8, which is mainly observed in samples with β = 60° at high confining pressure. Both the compressive strength and internal friction in samples with β = 60° are the smallest in the experiments, and those in samples with β = 65.31° based on the improved theory are the smallest. The compressive strength decreases with the increase of inclination angle β when 0°≤β≤60°; however, it increases as inclination angle β increases when 60°<β≤90°. This phenomenon is found in laboratory experiments and numerical tests and is almost even in accordance with theoretical results. Numerical compression tests are performed to investigate the influence of the width-to-length ratio of opening flaws on compressive strength and to verify the improved theory reliability. Compared numerical results with the two kinds of theoretical results, the width-to-length ratio has an obvious impact on compressive strength and the opening fracture intensity factor KⅠ.

Anisotropic mechanical characteristics and energy evolution of artificial columnar jointed rock masses subjected to multi-level cyclic loading

Columnar jointed rock masses (CJRM) are natural geological structures with regular and irregular polygons. Because of the joints throughout, the rock mass mechanical properties are severely degraded. This study focused on the effect of joint dip angle, fatigue effect, and stress level on the anisotropic strength, deformation behavior, energy evolution characteristics, and failure mode of CJRM specimens. Triaxial compression and multi-level cyclic loading tests were performed on artificial CJRM specimens with a similar geological structure under a 7 MPa confining pressure. Energy dispersive spectroscopy (EDS) tests were performed on the hexagonal prism and joint structure to investigate the failure mechanism of the CJRM specimens. The experimental results show that the relationship between the characteristic stress and the joint dip angle is a typical U-shaped pattern. The anisotropy of characteristic stresses decreases gradually under triaxial compression. The fatigue effect increases peak strength's anisotropy and decreases residual strength's anisotropy. The plastic strain and strain energy depend on stress level, fatigue effect, and joint dip angle. Three failure modes were observed. Disintegration and fracture of hexagonal prisms, and joint cracking result in the failure of CJRM specimens. Overall, the fatigue effect increases the number and distribution of cracks in CJRM specimens.

Experimental Study on the Influence of Hydromechanical Boundary Conditions on Shear-Flow Coupling Characteristics of Granite Joints

The instability of jointed rock mass is usually the shear process of the rock mass along discontinuities under the influence of groundwater flow. By conducting laboratory tests and numerical experiments on the shear-flow coupling of rock joints under constant normal stiffness (CNS) and constant normal stress (CNL) boundary conditions, the influence of normal boundary conditions and seepage pressure on the shear mechanical and flow characteristics of joints were investigated. The test results were as follows: The joint shear stiffness, peak, and residual shear strength under the CNS boundary condition were predominantly larger than those under the CNL boundary condition. Overall, these parameters were positively correlated with the initial normal stress σ n 0 . When σ n 0 > 2 MPa, the postpeak shear stress of the CNS boundary condition showed a sharp decrease, whereas that of the CNL boundary condition changed from a slowly decreasing type ( σ n 0 = 4 MPa, 6 MPa) to a sharply decreasing type at σ n 0 = 8 MPa. The peak dilation rate under the CNS boundary condition at all levels of normal stress was lower than that of CNL, and the strain softening in postpeak of the latter was more remarkable. In the process of joint shear, the hydraulic aperture displayed a four-stage variation law of “steady-sudden increase-slow increase-basically stable.” Moreover, the hydraulic aperture under the CNS boundary condition was always lower than that under the CNL boundary condition. The seepage pressure increased from 0.5 MPa to 1.5 MPa, and the average hydraulic aperture in the stable stage under normal stress at all levels increased from 0.146 mm to 0.187 mm. In addition, the average peak shear stress and average shear stiffness decreased by 0.9 MPa and 0.83 GPa/m, respectively. We also established a numerical model of a real rough three-dimensional joint, compiled a calculation program for the shear-flow process of a joint under CNS boundary conditions, and visualized the flow channel inside the joint. The seepage flow bypassed the area where the joints contacted each other, forming obvious flow channels. The flow rate increased at the intersection of the flow channels.

Strength and Failure Behaviors of a Jointed Rock Mass Anchored by Steel Bolts: A Numerical Modeling Study

Strength and Failure Behaviors of a Jointed Rock Mass Anchored by Steel Bolts: A Numerical Modeling Study

An Improved Method for Estimating the Strength of Jointed Rock Mass Using Drilling Technology

During underground excavations for civil and mining engineering purposes, the variations in mechanical properties of jointed rock mass are important, especially for the design of underground structures. The unreasonable evaluation of strength properties for rock masses can lead to the structure instability of underground construct, which subsequently causes collapse accidents in underground engineering and poses a serious threat to the structures safety. Rock mass classification system is an effective method for determining the strength parameters for rock masses. Firstly, the existing approaches for determining the strength parameters of rock masses are reviewed using classification systems such as the joint factor, jointing index methods, rock mass rating (RMR), Q-system (Q), geological strength index (GSI), and rock quality designation (RQD). Since in some cases, rock quality designation (RQD) is the only information available, a comparative study with other methods then is conducted to verify the limitation and deficiencies of RQD method. On this basis, a newly developed method from RQD classification system based on drilling special energy is established to estimate the rock mass strength. Finally, the developed method is applied in the tunnel engineering in the Daheba hydropower station in Hanjiang to the Weihe River project of China, and the results are compared with those from the previous works. The in situ test results show that the developed method can give appropriate values compared to various suggested relationships from RMR, Q, and GSI. The results can be treated as an important design reference for the prevention and treatment of surrounding rock instability and underground excavations in the Daheba hydropower station.