Jointed Rock Mass Research Articles

Model test study on the dynamic failure process of tunnel surrounding rocks in jointed rock mass under explosive load

The presence of joints can significantly reduce the integrity and stability of an engineering rock mass. Under dynamic loads, such as from blasting excavation, the key blocks divided by joints may be destabilized and prone to sliding, potentially leading to engineering geological disasters like rockbursts. To study the dynamic instability process, similar materials for the rock mass and joints were developed based on the similarity theory, and a tunnel model in the jointed rock mass was constructed. Subsequently, a detonating fuse was used to generate a dynamic load, and the dynamic instability process of the tunnel surrounding rock in the jointed rock mass under explosive load was studied using the geotechnical multifunctional testing device. The deformation characteristics and dynamic instability process of the tunnel surrounding rock were analyzed using acceleration sensors, resistance strain gages, linear variable displacement transducers and motion camera. The study shows that the acceleration at the tunnel vault is significantly greater than at the straight wall and floor under blast loads, with differences reaching an order of magnitude. Acceleration waveforms were classified into three categories based on peak characteristics, explained through the propagation of explosive stress waves. Additionally, strain and displacement at the tunnel arch were also significantly greater than in other areas, indicating more severe stress concentration and dynamic damage at the arch, necessitating reinforced support in tunnel excavation. The entire dynamic instability process of the tunnel surrounding rock was successfully recorded using a motion camera. The dynamic failure process was divided into several phases, the appearance of cracks on the joint surface, particle ejection accompanied by the dropping of jointed blocks, a significant drop of the jointed blocks, and return to calm. The dynamic failure modes include the dropping and rotation of jointed blocks, local particle ejection, and shear cracks on jointed block.

Shear creep deformation of rock fracture distrubed by dynamic loading

The long-term stability of jointed rock masses is usually dominated by fault activation, which may be triggered by the dynamic disturbance generated by blasting during mining activities, leading to the occurrence of disasters such as landslides in open-pit and rockbursts in deep mining. The initial stress and dynamic disturbance are key factors that strongly affect the shear creep behavior of rock fractures. In this work, the shear failure instability of rock fractures of sandstone under creep-impact loading was experimentally investigated by using a creep-impact test machine, which allows for applying creep loading and an additional dynamic disturbance on rock fractures. Three stages of shear creep deformation, creep strain rate, and time-to-failure are examined under different creep stress levels and impact energies. Experimental results show that the tangential and normal creep rates increase with the increase of creep stress and impact energy, but the increment of tangential creep rate is higher than that of the normal creep rate. The time-to-failure of the creeping specimen is shortened under high creep stress and large impact energy, while the time-to-failure after the last dynamic disturbance of the specimen is determined by the total impact energy and creep stress level. By using high-speed photography, it is found that the failure types of rock depend on the magnitude of impact energy and creep stress level; that is, rock mainly slides with low stress levels and shears off with high stress levels. In addition, under different impact energy and creep stress levels, the variation of height is between 0.38 and 0.52, while the defined fracture factor, which describes the degree of failure of serrations, is between 0.30 and 0.54. The findings can provide deep insight into the fault sliding mechanism caused by mining activities, which provides theoretical support for the safe mining of ore in fault fracture zones.

Experimental Study on Strength and Deformation Moduli of Columnar Jointed Rock Mass—Uniaxial Compression as an Example

Experimental Study on Strength and Deformation Moduli of Columnar Jointed Rock Mass—Uniaxial Compression as an Example

Numerical simulation of failure and micro-cracking behavior of non-persistent rock joint under direct shear

Persistency, as a key geometric parameter of joints, significantly affects shear strength parameters of jointed rock mass. A good understanding of how persistency affects shear behavior of joint is therefore crucial for better evaluation of stability of rock slope. To investigate the failure and micro-cracking behavior of non-persistent rock joint under direct shear, a novel Voronoi generation algorithm is first used to establish an improved grain-based model (GBM) of granite which considers the shape of feldspar. The calibrated model is then used to simulate the direct shear test of numerical models possessing different joint persistency under various normal stresses. The results reveal that the developed micro-cracks generally increase rapidly when the shear strain reaches to a value approximately 50 % of the peak shear strain and the grain boundary tensile micro-crack is dominant among these initiated micro-cracks. Micro-cracks generally initiate at the ends of rock bridge, and then gradually propagate to the central of rock bridge, forming en-echelon fractures. The failure mode of numerical model is closely related to the generated en-echelon fractures. An increase in both joint persistency and normal stress can lead to a shear failure. The finding in this study provides an important basis for understanding the mechanical behavior and failure mechanism of jointed rock mass.

The grouting plugging mechanism of layered jointed rock mass considering the time-varying yield stress of grout

Slurry retention in fractures decreases after grouting is completed and the pressure supply is stopped, which affects the grouting sealing effect and prevents or restrains the occurrence of such adverse conditions. Based on the time-varying yield stress of grout, a theoretical analysis model of grouting diffusion decay is established, the decay height variation function and the minimum pressure stabilisation time calculation formula are derived, and the sealing mechanism of a jointed rock mass with multiple joints is studied. Moreover, a 3D visualisation laboratory test device for grouting diffusion decay of a jointed rock mass with layers was developed to analyse the diffusion and decay process of grout with different water-cement (W/C) ratios visually, and the correctness of the theoretical model was verified. The results show that: (1) the W/C ratio of grout should not be greater than 2, otherwise it is difficult for grout to remain in the cracks; (2) a large fissure opening easily spreads grout but is not conducive to the retention of grout; and (3) the time of stable pressure determines the retention rate of the slurry in the crack. When the horizontal crack opening width is 3 mm and the W/C ratio of the slurry is 1, the minimum stable pressure time to achieve a better sealing effect is 810 s. The research results can be used to reasonably plan the grouting time and improve the grouting efficiency to ensure the grouting effect, which is crucial for improving the theoretical system of grouting technology.

Failure characteristics and pressure relief effectiveness of non-persistent jointed rock mass with holes

In tunnel engineering, the rock mass contains a significant number of irregularly distributed joints, and typically exhibits high energy accumulation, thereby posing a risk of rockburst occurrence. Therefore, it is of paramount importance to investigate the fracture propagation behavior in jointed rock masses and assess the impact of borehole pressure relief on mitigating rockburst occurrences for effective prevention and control measures. This paper focuses on failure characteristics and pressure relief effectiveness of non-persistent jointed rock mass with holes through laboratory testing and numerical simulation. In laboratory experiments, rock samples are prepared to include a range of crack dip angles and circular holes. Then, the crack propagation law of crack inclination and circular hole is studied by AE and DIC technology. The experimental results show that with the increase of fracture dip angle, the peak strength and energy change of the sample decrease first and then increase. Due to the existence of holes, the crack propagation direction of the original crack is changed. After drilling, the strain energy of the sample is obviously reduced, which shows that the drilling pressure relief effect is obvious, which can effectively reduce the energy accumulated inside the rock mass and reduce the risk of rockburst. Finally, the PFC numerical simulation software is used to analyze the micro-failure process and energy change law of the sample from three aspects: the relative position of cracks and holes, the diameter of boreholes and the spacing of boreholes. Further understanding of the energy dissipation law and mechanical behavior characteristics of jointed rock mass provides a reference for exploring the pressure relief effect of rock mass and preventing rockburst.

Challenges of slope design for high cut slopes in jointed rock masses

AbstractThe construction of the 275 m high Yusufeli arch dam and auxiliary structures required the execution of very steep cut slopes with more than 400 m height. Uncertainties regarding the geotechnical conditions imposed a serious challenge for the cut slope design. The design approach evolved from initial back‐calculations to a robust methodology, which was constantly revised and updated as excavation proceeded. The article explains the modular design procedure that allowed continuous interaction, adjustments and updates of and between different design and construction activities. It briefly describes the process of geological data collection and parameter determination and elaborates on the calculation tools utilised for the design. Finally, the verification and updating of the design during construction is explained on a selected case study. The excavation of the Yusufeli Dam was completed in 2018, dam concreting and grouting in 2022, and the final impounding level was reached by the end of 2023.

Automatic interpretation of geometric information of discontinuities and its influence on the stability of highly-jointed rock slopes

The discrete fracture system of a rock mass plays a crucial role in controlling the stability of rock slopes. To fully account for the geometric shape and distribution characteristics of jointed rock masses, terrestrial laser scanning (TLS) was employed to acquire high-resolution point-cloud data, and a developed automatic discontinuity-identification technology was coupled to automatically interpret and characterize geometric information such as orientation, trace length, spacing, and set number of the discontinuities. The discrete element method (DEM) was applied to study the influence of the geometric morphology and distribution characteristics of discontinuities on slope stability by generating a discrete fracture network (DFN) with the same statistical characteristics as the actual discontinuities. Based on slope data from the Yebatan Hydropower Station, a simulation was conducted to verify the applicability of the automatic discontinuity identification technology and the discrete fracture network-discrete element method (DFN-DEM). Various geological parameters, including trace length, persistence, and density, were examined to investigate the morphological evolution and response characteristics of rock slope excavation under different joint combination conditions through simulation. The simulation results indicate that joint parameters affect slope stability, with density having the most significant impact. The impact of joint parameters on stability is relatively small within a reasonable range but becomes significant beyond a certain threshold, further validating that the accuracy of field geological surveys is critical for simulation. This study provides a scientific basis for the construction of complex rock slope models, engineering assessments, and disaster prevention and mitigation, which is of great value in both theory and engineering applications.

Experimental investigation of failure mechanism of fissure-filled sandstone under hydro-mechanical conditions

Fissure fillings are critical to the hydro-mechanical properties of jointed rock masses in rock engineering. In this study, triaxial seepage tests were performed on standard cylindrical fissure-filled sandstone. The characteristics of stress–strain relationships, absorption and consumption of energy, variations in deformation resistance, and permeability evolution during the experimental process, along with the crack development observed in post-failure computed tomography scan images of the sandstone specimens were analyzed. The results demonstrate that the fillings improve the energy capacity and reduce the damage accumulation of sandstone specimens, with sand-filled specimens performing better than mud-filled specimens, especially at lower bridge angles. The fillings can reduce the depth of crack extension and lessen the influence of prefabricated fissures on sandstone failure, with this effect diminishing as the rock bridge angle increases. Permeability decreases in the pre-peak failure stage as the fillings improve the deformation resistance of the sandstone specimens. In the post-peak failure stage, the fillings and rock debris generated by the sandstone failure move within the developed fractures, causing significant fluctuations in permeability. These findings deepen the understanding of the hydro-mechanical properties of jointed rocks and provide a scientific basis for stability analysis in rock engineering.

Weakly confined slotted cartridge blasting in jointed rock mass

Directional fracture blasting can improve the smooth blasting effect of layered jointed rock masses. However, few studies have comprehensively considered the interaction between joints and slit blasting, and there is a lack of quantitative research and analysis on slit blasting. Therefore, this study combined slit blasting, pouring model test blocks for explosion testing, and numerical simulations for auxiliary research. Finally, practical engineering applications were conducted. The results showed that the weakly constrained PVC material has a high instantaneous strength under impact and can achieve a good energy accumulation guidance effect. The joint angle has a significant impact on the isolation effect of explosion stress and crack propagation. The isolation effect of the explosion stress gradually weakened with an increase in joint angle. The smaller the angle, the more vulnerable the crack propagation direction is to the “traction” of the joint and tends to the trend of the joint, and the more serious the phenomenon of crack turning, deviation and bifurcation. The results show that the explosion energy propagates preferentially from the cutting seam direction, and the stress in the cutting seam direction reaches the peak value first. The energy in the cutting seam direction has a strong transmission ability and a directional fracture effect on the joints, and the application of weakly restrained slotted pipes in layered rock tunnel blasting construction has a good effect.

Optimal mine pitwall profiles in jointed anisotropic rock masses

ABSTRACT A new methodology based on the limit analysis upper bound method for the topological optimisation of slopes is presented, to determine geotechnically optimal slope profiles in anisotropic jointed rock masses. The methodology accounts for the effects of discontinuities such as joints, bedding planes, and tension cracks. We applied this methodology to the context of open pit mines, with the goal of achieving geotechnically optimal pitwall profiles. The optimal profiles maximise the Overall Slope Angle (OSA) while maintaining a prescribed Factor of Safety (FoS) and satisfying the geometric constraints imposed by benches and ramps. The method, implemented in the software OptimalSlope, utilises direction-dependent cohesion and internal friction angle parameters to replicate the effect of joints on slope stability. Key inputs include joint orientation, non-persistence, and probability of occurrence. We tested the methodology on a Mexican open pit mine to be excavated into Cretaceous siltstone featuring eight different joint sets and a primary bedding plane. Optimal pitwall profiles were determined for various combinations of bedding dip angles (0°, 15°, 30°, 45°, 60°, 75°, 90°) and mine pitwall orientations (hanging wall, footwall, side walls), considering the three-dimensional kinematics of the joints through anisotropic functions of cohesion and friction angle. Results indicate that the optimal pitwall profiles generally exhibit higher OSA compared to planar profiles with the same FoS, except in one bedding dip direction. Additionally, stability analyses performed using Rocscience Slide2 independently verified the FoS values of the optimal profiles.

Effects of joint persistence and testing conditions on cyclic shear behavior of en-echelon joints under CNS conditions

Cyclic shear tests on rock joints serve as a practical strategy for understanding the shear behavior of jointed rock masses under seismic conditions. We explored the cyclic shear behavior of en-echelon and how joint persistence and test conditions (initial normal stress, normal stiffness, shear velocity, and cyclic distance) influence it through cyclic shear tests under CNS conditions. The results revealed a through-going shear zone induced by cyclic loads, characterized by abrasive rupture surfaces and brecciated material. Key findings included that increased joint persistence enlarged and smoothened the shear zone, while increased initial normal stress and cyclic distance, and decreased normal stiffness and shear velocity, diminished and roughened the brecciated material. Shear strength decreased across shear cycles, with the most significant reduction in the initial shear cycle. After ten cycles, the shear strength damage factor D varied from 0.785 to 0.909. Shear strength degradation was particularly sensitive to normal stiffness and cyclic distance. Low joint persistence, high initial normal stress, high normal stiffness, slow shear velocity, and large cyclic distance were the most destabilizing combinations. Cyclic loads significantly compressed en-echelon joints, with compressibility highly dependent on normal stress and stiffness. The frictional coefficient initially declined and then increased under a rising cycle number. This work provides crucial insights for understanding and predicting the mechanical response of en-echelon joints under seismic conditions.

Experimental Investigation on Failure Characteristics of Pre-Holed Jointed Rock Mass Assisted with AE and DIC

Experimental Investigation on Failure Characteristics of Pre-Holed Jointed Rock Mass Assisted with AE and DIC

Spatio-temporal evolution law of anisotropic shear damage on rock mass joint surface affected by joint morphology

The spatial–temporal evolution law of shear damage on the joint surface is closely related to its morphological characteristics. Understanding the heterogeneous failure behavior of the joint surface is essential for revealing the controlling role of the joint morphology. The diorite from the Guanshan Tunnel is investigated through anisotropic direct shear tests in this study. Based on shear damage quantification and acoustic emission (AE) localization techniques, the heterogeneous damage evolution law of joint surfaces under different joint compression strength (JCS), normal stress (σn), and morphology parameter (M) is studied. The results indicate that the joint surface morphology, shear damage, and AE parameters exhibit similar anisotropic characteristics in different shear directions. An increase in the morphology parameter leads to an increase in shear failure, with shear fracture energy and the number of fracture events showing an increasing trend. Meanwhile, the occurrence of a large number of fracture points shifts from the pre-peak nonlinear period to the post-peak period. However, the evolution process of fracture events exhibits certain similarities, though the morphology parameters are different in two opposite shear directions. Additionally, shear damage volume and fracture energy demonstrate consistency in spatial distribution and quantitative characteristics, while the linear scale factor between cumulative shear fracture energy and damage volume decreases with increasing joint surface strength. These findings assist in a better understanding of the anti-sliding property of joint surfaces and provide crucial clues for further exploration of joint surface failure mechanisms.

In Situ Shear Test and Numerical Simulation of the Paleoweathered Jointed Rock Mass in the K1/J2 Contact Zone of the Ordos Basin

In Situ Shear Test and Numerical Simulation of the Paleoweathered Jointed Rock Mass in the K1/J2 Contact Zone of the Ordos Basin

Directional fracture patterns of excavated jointed rock mass within rough discrete fractures

The influence of the fractures on the anisotropic mechanical behavior of excavated fractured rock mass is important for the stability of rock tunnels. Rough joints were generated using fractal principles, and the Monte Carlo method was employed to create joint network faces. Biaxial compression numerical simulations were conducted using the discrete element method to analyze the behavior of the rock mass containing these networks. Quantitative analysis was carried out to evaluate the strength variability and total number of cracks in the jointed rock mass. A linear regression analysis was conducted to establish the relationship between rock strength and excavation size. The findings demonstrate significant disparities between the linear and fractal models regarding rock damage mode, stress–strain curves, and crack evolution patterns. Tensile rupture and local shear damage were found to be the primary fracture modes for the fractured rock tunnels, forming a V-shaped damage zone within the central tunnel. The shape of this zone was influenced by fracture direction and excavation ratio. Excavation at the center of the rock mass substantially impacted the variability of rock strength and the occurrence of internal cracks. An increase in the slope ratio led to a greater variability of rock mass strength, transitioning from nearly isotropic to weakly anisotropic behavior. The total number of cracks exhibited a W-shaped trend, initially increasing and later decreasing as the slope ratio decreased. Additionally, a clear linear correlation was observed between rock strength and excavation ratio at the center of the rock mass.

A Comparison of Statistical Validity of In-Situ Hydraulic Conductivity Prediction Models of Rock Mass Inferred from Borehole Logs and Lugeon Test Data

In-situ hydraulic conductivity is a vital property in rock engineering for jointed rock mass. Understanding its correlation with rock mass parameters is crucial for water circulation. Therefore, a study was carried out to develop statistically significant empirical relationships between hydraulic conductivity and various rock mass parameters to estimate in-situ hydraulic conductivity from Lugeon test and various rock mass parameters obtained from borehole logs.The study initially aimed to establish a correlation between hydraulic conductivity and Rock Quality Designation (RQD). However, the outcomes were unsatisfactory, prompting further research. Later, two more robust models were developed, namely the HC-model and modified HC-model. The HC-model incorporated four rock mass parameters, including Rock Quality Designation Index, Depth Index, Gouge Content Designation Index, and Lithology Permeability Index, achieving a maximum coefficient of determination (R2) of 0.46. The modified HC-model included six parameters, encompassing fracture frequency and theoretical aperture, resulting in an improved R2 of 0.69. Both models significantly outperformed RQD-alone predictions (R2 < 0.10), highlighting the need for incorporating multiple rock mass parameters in predicting hydraulic conductivity due to a complex interplay of various factors. However, the effects of joint persistence and roughness are limiting in the present analysis.

Analysis of progressive collapse disaster and its anchoring effectiveness in jointed rock tunnel

AbstractThe complexity and variability of the structural distribution and combination characteristics of jointed rock masses make the response mechanism of tunnel rock collapse different, and there is a lack of systematic research on the existing perimeter rock instability mode and bolt support scheme. Based on numerical simulations of the block system structure of a nodular rock mass, the existing theory of bolt support is compared and analyzed to explore the scope of their respective applications. Combined with the spatial and temporal transport law of block instability, a new batch instability model of jointed rock tunnels is proposed, which reveals the progressive collapse catastrophe evolution mechanism of a collapsed interlocking block system after the instability of the key blocks and elucidates the coupling mechanism between the bolts and the block system structure as well as their anchoring effectiveness. Finally, for the actual tunnel project, the instability batches of the surrounding rock are identified, and the corresponding optimized design of the bolt support is presented, which has achieved good support effects. The research results can provide important theoretical guidance and practical engineering value for risk avoidance, disaster identification and targeted prevention and control of dangerous rock fall and chain collapse instability disasters in jointed rock body tunnels.

A complementary approach to quantify the basic GSI chart considering scale effect on rock structure

Geological strength index (GSI) has been widely used as an input parameter in predicting the strength and deformation properties of rock masses. This study derived a series of equations to satisfy the original GSI lines on the basic GSI chart. Two axes ranging from 0 to 100 were employed for surface conditions of the discontinuities and the structure of rock mass, which are independent of the input parameters. The derived equations can analyze GSI values ranging from 0 to 100 within ±5% error. The engineering dimensions (EDs) such as the slope height, tunnel width, and foundation width were used together with representative elementary volume (REV) in jointed rock mass to define scale factor (sf) from 0.2 to 1 in evaluating the rock mass structure including joint pattern. The transformation of GSI into a scale-dependent parameter based on engineering scale addresses a crucial requirement in various engineering applications. The improvements proposed in this study were applied to a real slope which was close to the time of failure. The results of stability assessments show that the new proposals have sufficient capability to define rock mass quality considering EDs.

Influence of 3D joint roughness on fracture behaviours of rock mass subjected to compression

Jointed rock mass with internal rough structural planes have a significant influence on the mechanical behaviour and damage mode of the rock mass. Based on the Weierstrass-Mandelbrot (W-M) fractal function, a numerical model containing a single rough fracture was established. Multi-parameters sensitivity analysis was carried out to determine the key parameters affecting the mechanical properties. By conducting experimental research on the single fracture inclination, fractal dimension, and surface precision of numerical model uniaxial compression, the influence laws of different parameters and the model cracking process were revealed. The results show that the cracks go through the process of sprouting from the single fracture and expanding to both sides, and the expansion of shear cracks in the structural plane reflects the roughness pattern of the structural plane. The higher the roughness was, the lower the peak uniaxial compression strength of the model was. The change of the parameters influenced the macroscopic cracking morphology of the model, and the model finally showed the destruction along the diagonal, the V-shaped destruction, the X-like destruction, and the X-type destruction. The results have an outstanding reference value for further researches on the application of three-dimensional rough discrete fracture networks.