Rock Blocks Research Articles

Preliminary estimation of rock-fall lateral dispersion by laboratory test

Lateral dispersion significantly directs the assessment of rockfall hazard and design of countermeasures. In the present study, the dependence of lateral dispersion on different controlling factors has been systematically evaluated by performing laboratory tests using three different rock block types, namely circular block, and two types of elliptical block. The three types of rock block are released onto an inclined surface with the identical initial status. Parallel, anti-parallel, and oblique impact tests set at slope angles of 22.5° and 45°are conducted to study the block-slope interaction of rockfall. Lateral dispersion of rockfall is less influenced by the block shape for the oblique impact, while the post-impact behaviors are greatly affected by the block shape. The key factors influencing the deviation of the post-impact trajectory direction are the slope angle (θ) and direction difference (Δφ). An empirical model is then developed to characterize the deviation distribution of lateral dispersion by 5th and 95th percentile values with the inclusion of the two key factors. Linear function can be used to describe the 5th percentile boundary, while hyperbolic function is good for the 95th percentile boundary, which need to be validated by field tests in the subsequent research.

Evolution of Sliding Along a Heterogenous Fault. A Large-Scale Laboratory Experiment.

A laboratory setup was constructed in IDG RAS to investigate the process of shearing the contact of rock blocks of one-meter scale. It was used to investigate deformation processes in a fault with a heterogenous structure of the sliding interface, which contained strong contact patches – analogs of the “asperity” in the model of Hiroo Kanamori. It is shown that when a large slip occurs, the rupture, that starts in the zone of maximal deficit of interblock displacement, cuts the segments of the fault with lower effective strength, the latter being decreased in previous deformation events. Those previous events may be “slow” slips with low seismic efficiency. In nature the events that “prepare” the fault interface for a large slip may be smaller earthquakes – foreshocks, or they can be either low frequency earthquakes or slow slip events, both can hardly be detected in seismic records. Thereupon a promising diagnostic indication is the shift of the spectrum of ambient seismic noise to lower frequencies caused by the decrease of fault stiffness.

Weighting Failure Mechanisms of Pre-Driven Recovery Rooms and Evaluation of Hydraulic Fracturing Applications: A Case Study

Roof weighting failures of pre-driven recovery rooms may cause huge economic losses and even casualties. The excessive dynamic load from the sliding of the broken main roof rock block causes the recovery room roof and inner supports to lose their support capacity during the last weighting. Discrete element software UDEC was used to investigate the surrounding rock deformation of the pre-driven recovery room with the main roof break at different positions. The results show that when the recovery room’s length from the main roof rock layer’s fracture region is short, the immediate roof is subjected to high deviatoric stress and the occurrence of horizontal stress concentration due to the deflection of the fractured rocks, and eventually the roof supports fail owing to the development of macroscopic shear crack zones. In this research, the hydraulic fracturing technique was applied to pretreat the main roof (fine-grained sandstone) of the 31108 panel at Huoluowan Coal Mine. Field observations suggest that the strength and duration of the periodic weighting after hydraulic fracturing treatment are both significantly reduced, effectively maintaining the bearing layer performance of the roof of the recovery room and coal pillar walls. The proposed fracturing design offers an effective method of ground control to the coal mines facing roof weighting failures of recovery rooms.

Comparative study on hydraulic fracturing using different discrete fracture network modeling: Insight from homogeneous to heterogeneity reservoirs

Conventional discrete fracture network (DFN) modeling is used to simulate hydraulic fracture propagation in fractured low permeability reservoirs. However, natural fractures have a certain degree of roughness, and reservoir rocks have significant heterogeneity characteristics. Therefore, it is necessary to compare the differences in hydraulic fracturing simulation of homogeneous and heterogeneous reservoirs caused by conventional and rough DFN modeling methods. Herein, new-generation algorithms for different DFNs are proposed. Combined the combined finite-discrete element method and different DFNs, four different simulation models are established, covering hydraulic fracturing models from relatively homogeneous to heterogeneous reservoirs. Then, the differences from different DFN modeling methods are compared and discussed. The results show that the relatively homogeneous and heterogeneous models established by conventional DFN may underestimate the bending propagation characteristics and fracturing time and overestimate the proportion of tensile failure. Meanwhile, when the nonuniform distribution of the mechanical parameters of rock blocks is considered, the bending propagation becomes more marked; thus, the fracturing time and the proportion of shear failure are further increased. The above results imply that to accurately predict the hydraulic fracture propagation in a real reservoir, it is vital to consider the roughness of real natural fractures and the nonuniform distribution of mechanical parameters in reservoir hydraulic fracturing modeling.

Rocking of rigid blocks standing on a horizontally-moving compliant base

In this paper the dynamic response of rectangular rigid blocks standing on a horizontally-moving compliant base that is not rigidly connected to its excitation source is investigated for the first time through a combination of analytical, numerical and experimental studies. A novel model combining the well-established studies of a rigid block supported by horizontally-moving rigid base and recent advances on the dynamics of a block rocking on compliant surfaces is derived. Specifically, the impact between the block and the moving base is modelled through a series of springs in parallel with dampers, leading to the generally known Winkler and Hunt–Crossley models. Model parameters are calibrated through forced harmonic rocking tests and then validated through extensive experimental tests with both free and forced rocking. Comparisons of numerically determined trajectories versus those experimentally determined highlight the accuracy of the compliant base model. The main advantage of the compliant base model over the traditionally adopted rigid base model is that it can better predict when rocking will be initiated. This feature is further highlighted from overturning charts numerically evaluated and experimentally verified.

Effects of groundwater and distilled water on the durability of evaporitic rocks

Evaporitic rock durability induced by groundwater cause several construction challenges, but representative experimental studies to evaluate such conditions are still missing. Therefore, this study intended to provide better and more realistic degradability features of evaporites with groundwater besides a comparison with distilled water as slaking fluids. Forty-eight evaporitic rock blocks were collected from Abu Dhabi area, United Arab Emirates. 96 slake durability index (SDI) tests were performed, 48 with each of the slaking fluids; groundwater and distilled water, and their textural, mineralogical, and geochemical attributes were also examined before and after the SDI tests. In comparison to mineralogical and textural modifications, slaking fluid had a greater impact on the chemical composition of evaporitic rock. The study shows that the degradability of evaporites with groundwater and distilled water indicates a wide range from very low to high. The mean weight loss values after four cycles with groundwater and distilled water vary from 11 to 77 and from 4 to 81 wt.%, respectively. Consequently, slaking with groundwater illustrates a wide range compared to the slaking with distilled water. This could be due to quick interactions between groundwater and evaporites and fast hydration-dehydration process than distilled water due to the chemical composition of the groundwater. It is recommended to investigate the attributes of evaporitic rocks as well as groundwater geochemistry for safe, cost-effective, and sustainable structures.

Response of acoustic emission and vibration monitoring data during rock block collapse in the tunnel: Small- and large-scale experiments study

Block collapse is a common disaster in the jointed rock mass of tunnels and usually involves two typical evolution stages: rock bridge breakage and rock block instability. The evolutionary characteristics of mutation induced by the gradual failure of rock mass are the mechanical basis for monitoring and assessing disasters. In this study, an acoustic emission (AE)-vibration joint monitoring method is proposed to fully investigate the two failure stages based on the disaster mechanism. It is critical to reveal the evolution law of AE and natural frequency information in block collapse. Small-scale shear tests on rock specimens are conducted to investigate the rock bridge breakage stage, while large-scale physical simulation tests are performed to investigate the block instability stage. During rock bridge breakage, AE exhibits a clearer signal response to the internal rock fracture than the natural frequency and captures brittle failure under low- and medium-stress conditions. The natural frequency exhibits a significant signal response under low-stress conditions during the block instability stage. Under medium- and high-stress conditions, the signal becomes less sensitive. Under low-stress conditions, the natural frequency of the block gradually decreases with increasing free surface, implying that the stability of the block declines. The natural frequency decreases with the decreasing stiffness of the block, which is a vital precursor to the early warning of block collapse disasters. Additionally, AE is the primary indicator in the rock bridge breakage stage, while natural frequency is the primary indicator in the rock block instability stage. From the perspective of technological innovation in underground tunneling, AE-Vibration joint monitoring prompts a new idea to evaluate the stability of key blocks in tunnel construction safety applications.

Zircon SHRIMP U-Pb Ages, Geochemistry and Nd-Hf Isotopes of ∼1.0 Ga A-Type Felsic Rocks in the Southwestern Yangtze Block, South China: Petrogenesis and Tectonic Implications

Zircon SHRIMP U-Pb Ages, Geochemistry and Nd-Hf Isotopes of ∼1.0 Ga A-Type Felsic Rocks in the Southwestern Yangtze Block, South China: Petrogenesis and Tectonic Implications

Technical safety of buildings around polish quarries against harmful seismic vibrations caused by rock blasting

This paper presents the results of measurements of the elliptical distribution of seismic vibrations generated during rock blasting.The technical safety of a building in the area of seismic vibrations is determined by the vibration velocity that does not exceed the line B included in zone II of the scale of dynamic influences [SWD]. The hypothesis proved in the paper is that for both elliptical and circular distributions of the vibration velocity in rock mining with blasting material [BM] there is a directionality of the horizontal radial component Vx and the tangential component Vy of the vibration velocity.The magnitude of the components Vx and Vy of the vibration velocity at the same distance from the vibration source depends on the directional angle "α" between the line of the blast holes and the line connecting the centre of the surface of the rock block being mined with [BM] and the place of measurement. The elliptical shapes of the graphs Vx and Vy obtained during the mining of the BM of the basalt deposit, which depend on the value of the directional angle, were compared with the shape of the circular velocity graphs Vx and Vy. New correlations are given that take into account the directional angle when calculating the maximum vibration velocity values needed to determine the damage caused to a bulding by the SWD.A dynamic impact scale [SWD] for the assessment of building damage as the vibration velocity acting on the building increases is given and discussed. Vibration velocity diagrams measured during the excavation of BM rock are presented for circular distributions in accordance with theoretical predictions. A vibration velocity diagram for an elliptical distribution, inconsistent with a circular distribution, measured during the excavation of BM rock is presented. It is shown that the directionality of the horizontal radial and tangential components of vibration velocity exists for both circular and elliptical distribution of vibration velocity in rock excavation with BM. In the conclusions, for the elliptical velocity field of the vibrations, the conditions to be observed in order to be able to direct the smallest vibrations towards the built up area are given.

Experimental study on strength and failure characteristics of sandstone rock mass with complex cataclastic structure using 3D printing models

A cataclastic rock mass is a poor type of engineering geological rock mass. The determination of the shear failure characteristics and shear strengths of cataclastic rock masses can provide key basis for the design and construction of infrastructure. Physical model samples of a sandstone cataclastic rock mass were first produced by a combination of three-dimensional (3D) printing technology and manual pouring. Shear tests were conducted with respect to the shear stresses parallel to the trace line plane and perpendicular to the trace line plane of the cataclastic rock mass model. Based on an extensive analysis of the shear failure characteristic, shear stress evolution characteristic curve and shear strength. When the shear stress was parallel to the trace line plane, and when the rock block that was cut and confined by the trace line exhibited a significant tip, the end stress concentration effect of the cataclastic rock mass was more significant during the shear process with the anisotropy of the rock block increased. In addition, the shapes of the rock blocks that were confined and cut by the joints were the main influencing factors of the strength of the cataclastic rock mass. When the shear stress was perpendicular to the trace line plane, the structure of the rock wall was the main influencing factor of the deformation and failure process of the shear failure plane and the shear strength. The physical and mechanical properties of the shear failure plane of the cataclastic rock mass were found to be closely related to the joint–rock wall system characteristics of the cataclastic rock mass. Therefore, when determining the shear strength of cataclastic rock mass, the shape and combination form of the rock block, shear direction, and structural failure characteristics of the rock wall should be comprehensively considered during the shear process.

Proterozoic evolution of the Alxa block in western China: A wandering terrane during supercontinent cycles

The tectonic affinity of the Alxa block in the western North China craton remains controversial because of the widespread Cenozoic sediments and limited Proterozoic geochronological data, especially in the western Alxa block. To establish the tectonic affinity of the Alxa block with neighbor units, we systematically investigated U-Pb age and Hf isotope composition of zircon and U-Th-Pb age of monazite from Proterozoic rocks in the southwestern Alxa block. Ages of zircon and monazite from granitic gneiss and mica schist indicate that the Paleoproterozoic Longshoushan Complex recorded a magmatic event at ∼2.0 Ga and two metamorphic events at ∼1.95–1.90 and ∼1.85–1.80 Ga. Detrital zircons from quartz schist of the Longshoushan Complex show an age peak at ∼2.0 Ga with εHf(t) values between −4.048 and 6.432. By contrast, detrital zircons from the Late Paleoproterozoic Dunzigou Group yield different Paleoproterozoic age peaks and εHf(t) values, suggesting a provenance change. Detrital zircons from the Neoproterozoic Hanmushan Group exhibit three age peaks at ∼2.5 Ga, ∼1.85 Ga and ∼0.8 Ga, and two types of εHf(t) values with wide variations. The depositional ages of the Dunzigou Group and Hanmushan Group are constrained as 1.8–1.7 Ga and 845–830 Ma, respectively. The detrital zircon age populations suggest that the Longshoushan area experienced a transition from a convergent setting (less polymodal age spectra) at ∼1.98–1.95 Ga to a divergent setting (polymodal age spectra) at 1.8–1.7 Ga and then intracontinental rifting at ∼830 Ma. Compared with previous zircon studies, we propose that the Alxa block may be connected with the Khondalite belt at ∼1.98–1.90 Ga during assemblage of the Columbia supercontinent, and located between the North China craton and the northern Siberian craton at 1.8–1.7 Ga in a divergent setting. The Alxa block probably separated from the North China craton in the Late Mesoproterozoic and moved next to the northwestern Yangtze craton in the Early Neoproterozoic during the assemblage and breakup of the Rodinia supercontinent.

Modal analysis and harmonic response analysis of energy-absorbing and anti-scouring columns

Many field observations have found that damage to the support did not increase with the magnitude of the impact ground pressure. To enhance the impact protection performance of “support and surrounding rock” system. From the perspective of preventing the resonance of the “support and surrounding rock” system, the dynamic response of energy-absorbing and anti-scouring column is studied. Using the block theory, a dynamic model of the roadway enclosure-absorbing anti-scouring column under impact loading was established, and the dynamic response equation of the rock block at the support end was obtained. Based on the structural dynamics and Love shell theory, the characteristic equations of the energy-absorbing and anti-scouring column were derived, and the theoretical equations for the natural frequency and vibration mode function of the energy-absorbing and anti-scouring column were obtained. The ABAQUS numerical simulation method was used to carry out pre-stress modal analysis and harmonious response analysis of energy-absorbing and anti-scouring columns and conventional columns. We obtained the natural frequencies and vibration modes of the two columns and analyzed the effect of the setting load on the modalities of the columns. The column dynamic response law was determined by monitoring the displacement and velocity response curves at different positions. The results show that the natural frequency and vibration mode of the energy-absorbing and anti-scouring column are related to the density, elastic modulus, and length. The vibration of the energy-absorbing and anti-scouring column has two forms: beam vibration mode and cylindrical shell vibration mode, and the first four orders of vibration mode are transverse bend. The setting load has a small effect on the natural frequency and vibration mode of both types of columns, where the natural frequency decreases as the setting load increases. When the excitation frequency is close to the vibration frequency of the surrounding rock, the radial, axial, and circumferential response amplitudes of the primary and secondary columns of the energy-absorbing and anti-scouring column are the largest. Reinforcement and strengthening measures should be implemented to reduce the column deformation amplitude.

Effects of discontinuities on the rock block geometry of dimension stone quarries: a case study

ABSTRACT The geometry of rock blocks, including shape and size, is a crucial factor affecting the quarry’s profitability. The block’s dimension is limited by the fracture network properties, especially discontinuity’s orientation, and spacing. Volumetric joint count (Jv), and weighted joint density (WJd) are two well-known indexes to determine the average block’s volume. In this investigation the discontinuity properties of eight quarries are determined through the line and aerial mapping surveys. The investigation was performed along 2258 m scanline in 63 slope benches. Different indexes were used to compare the obtainable rock block’s geometry. An empirical index was proposed considering different aspects of discontinuity network to increase the accuracy of measurements. The index was introduced based on the number of joints in each joint set, average spacing of joints in each joint set, and the total number of joints recorded during the investigation. The joint mean spacing index allows us to estimate the average volume of blocks and evaluate the quarry’s profitability. By increasing the ratio of the joint mean spacing index, the obtainable rock block’s volume and mine profitability increase.

Analysis of a Simplified Model of a Rigid Rocking Block on Winkler Foundation

It has been observed from previous large earthquakes that weakening the structural foundation can reduce the damage of the structure itself by allowing a rocking motion to release the seismic energy, and this seismic design philosophy is gradually applied to new constructions. In this paper, a simplified model of the motion process of a rigid rocking block is proposed, the rocking motion equation of rigid rocking block is derived, and the parameter analysis is carried out. It was found that the height–width ratio and damping have a great impact on the rocking response of the structure. On this basis, combined with the Winkler foundation model, the equation of motion of the rigid rocking block considering the flexibility of the foundation is established. Through the analysis of an example, it is found that damping plays an important role in the overturning resistance of high-rise buildings and the soil elastic coefficient has a greater impact on the higher structure.

Experimental and numerical simulation on the sliding process of roof rock blocks triggered by dynamic disturbance

With the excavation of underground opening, the roof rock block may fall under external dynamic disturbance. In this paper, the roof rock mass was simplified as a rock block system composed of trapezoidal rock blocks. A series of experiments and numerical simulations were performed to study the sliding process of the key block under the horizontal static clamping load and vertical impact disturbance. The propagation of stress wave in the block system were captured and analyzed by using high-speed camera and digital image correlation technique. The results reveal that a pendulum-type wave was generated due to the propagation and superposition of stress waves in the block system. Therefore, the governing mechanism of the sliding displacement of the key block was clarified based on the propagation of incident stress waves or pendulum-type waves. Meanwhile, it is found that the sliding distance of the key block decreases in a power function with the increasing friction coefficient, or decreases in a parabolic function with the increasing trapezoid internal angle. Finally, a case study on the roof block sliding of the roadway at a gold mine was conducted, and it is concluded that the sliding of the key block resulted from the coupled effects of “shear driving” and “low friction” driven by stress wave propagation, regardless of a single or multi-layer rock block system. These results may provide technical guideline for preventing rock-falling accidents caused by blasting disturbances in underground mining.

EVALUATION OF ENERGY CONSUMPTION OF DRILLING TOOLS WHEN DRILLING WELLS ON KARSTED ROCK BLOCKS

The article is devoted to the analysis of energy consumption in the process of drilling wells in karst rock blocks. The paper presents the results of experimental and analytical studies of the drilling process and energy consumption for the destruction of rock massifs with a complex structure characterized by the presence of karst cavities. The operation of the drilling machine during the drilling of the karst rock block was monitored. In the article, the use of the criterion of energy intensity of the well drilling process is proposed to assess the level of energy consumption by the drilling rig. On the basis of the conducted research, the dependence of the rotary power of the drilling machine on the productivity of drilling wells was established, and the dependence of the specific energy intensity of rock drilling on the drilling productivity was determined.
 The results of the conducted analytical and experimental studies on the determination of the geological structures of well columns by the energy intensity of their drilling process allow the development of designs of well charges for effective and safe destruction of complex rock massifs.

The Effect of Block-Matrix Interface of SRM with High Volumetric Block Proportion on Its Uniaxial Compressive Strength

The soil–rock mixture (SRM), as a heterogeneous and discrete geomaterial, can be widely found in nature and may present difficult design and construction issues for structures within or on top of them. Engineers face a difficult problem when determining the mechanical behavior of geomaterials with SRM, especially those with a high volumetric block proportion (VBP). As it is often very difficult to prepare undisturbed and representative samples of these materials. Thus, this paper proposes a novel method that can generate SRM models with a high VBP and produce a block-matrix interface (BMI) around the rock block, which can simulate unwelded SRM in nature. Then, the finite difference method (FDM) is applied to simulate uniaxial compression tests. The conformity of the numerical simulation results with the experimental results shows that the method is reasonable and effective. In addition, the effect of the strength of the BMI, the thickness of the BMI, and the geometrical shape of the rock blocks on the uniaxial compressive strength (UCS) of the SRM are also investigated. The modelling approach proposed in this paper is able to generate BMI in SRMs and enables the effect of the BMI on the SRMs’ properties to be better investigated in numerical simulations. This method can overcome the difficulties of preparing representative and undisturbed experimental cores while saving cost and improving efficiency. Simultaneously, the method proposed in this paper is promising to be extended to three dimensions.

The deformation evolution law and stability evaluation of the high-filled slope in the cutting hills to backfill ditches project

The cutting hills to back ditches (CHBD) project has been widely implemented since urbanization in hilly areas is steadily rising. The stability of the high-filled slope and the problem of foundation settlement deformation has become one of the vital issues for safe construction. This paper focused on the deformation evolution law and stability assessment of the high-filled deposit slope composed of the soil-rock mixture (S-RM) in the CHBD project, in Shiyan City, Hubei Province as examples. First, large-scale direct shear tests of S-RM with different rock block proportions (RBPs) under different various normal stresses were carried out, and its mechanical properties were analyzed. Next, the finite element method was used to simulate the processes of the step-by-step filling, and the deformation evolution law was analyzed. Then, the limited equilibrium method (LEM) was used to obtain the potential sliding surfaces and the corresponding safety factors of the high-filled slope, and the safety of the construction was assessed. Finally, automated monitoring of the step-by-step settlement and deep soil deformation was computerized for the typical locations, and the long-term stability of the high-filled slope was studied. The results demonstrate that the first layer of backfill in the F area contains the largest incremental settlement displacement in the y-direction, whereas the value in the G area occurs at the site of the fill layer close to the slope surface at each filling timestep. The displacement response value steadily declines with the increasing filling depth and horizontal displacement, presenting a clear spatial influence range, with the site of maximum incremental displacement as the center. After filling, the safety factors of the potential sliding surface in the F and G areas are 2.531 and 1.118, respectively, and the slope is in a stable state. The monitoring data show that the deformation mostly takes place within 10 m of the surface. The study’s findings are thought to offer technical and practical knowledge for the slope risks.

Investigation on mechanical behavior of pre-tensioned bolt in fractured rock mass using Continuum Discontinuum Element Method(CDEM)

The instability of engineering rock mass is usually associated with the failure of discontinuous joints. Pre-tensioned bolts can significantly improve the stress state of fractured rock mass and enhance its strength to resist tensile and shear deformation. To investigate the action mechanism of the bolt applied in the fractured rock mass, this paper developed an analytical approach to describe the performance of a pre-tensioned bolt penetrating rock joint. The stress state and deformation characteristics of the pre-tensioned bolt are analyzed considering the interaction between the bolt and rock block. Then, numerical validation is carried out and a model of fractured rock mass is established using the Continuum Discontinuum Element Method (CDEM). Uniaxial compression tests of the model under different bolting parameters are carried out. The influences of bolt spacing and pre-tensioned force are analyzed and the apparent mechanical parameters of reinforced rock mass are obtained.

A multiscale finite element method for soil-rock mixture

Soil-rock mixture is a complex multi-phase composite geotechnical material, and its strength is determined by the physical properties of constituent multi-phase materials and their coupling mechanical response between different phases of materials. Based on the Eshelby-Mori-Tanaka equivalent inclusion average stress principle, a theoretical model of multi-scale coupled shear strength of soil-rock mixture considering the interaction effect of rock block and soil is established, and the rotational freedom reflecting the microscopic motion details of rock block is introduced. Moreover, a multi-scale coupled constitutive relationship of soil-rock mixture is derived and compiled into a multi-scale finite element program. Based on the large-scale direct shear test of soil-rock mixture, the model parameters of the multi-scale finite element method are determined, and then the multi-scale finite element program is used to simulate and predict the cross-scale deformation process of the soil-rock mixture slope. The results show that the multi-scale finite element method can effectively describe the influence of the mechanism of the micro motion characteristics of the soil-rock mixture on the macro mechanical response, and can effectively overcome the pathological mesh-dependency of the classical finite element method; the rotation displacement of the rock block is mainly concentrated within the shear zone of the slope. The maximum rotational displacement of rock blocks inside the soil-rock mixture slope is 40.7°, and the rotational displacement of rock blocks outside the shear zone is about 0°. The physical mechanism of the cross scale evolution of the shear band of the soil-rock mixture slope is that: the rotation of the rock blocks weakens the strain transmission ability between the rock block and the matrix soil, thus forming the concentration and development of the plastic strain, and finally leading to the penetration of the shear bands of the slope and the overall sliding failure.