Disintegration Of Rocks Research Articles

Acoustic emission and 4D X-ray micro-tomography for monitoring crack propagation in rocks

Acoustic emission (AE) and 4D X-ray computed tomography (4D XCT) were used simultaneously to study crack initiation and propagation in two different types of quartz-rich sandstones during the four-point bending experiments. Statistical analysis of the AE response indicated the failure mechanisms and their dynamics. The characteristic changes observed in the AE response defined the timing of the bending interruptions for XCT scanning to reveal the development of the crack. It was possible to quantitatively describe the developing cracks in their dimensions and volume and relate this information to the rate of decrease in the post-peak region of the material response. It could be concluded that the combination and concurrent use of AE and XCT techniques represents a highly effective and reliable instrument for observation, description, analysis of the crack propagation process, and rock disintegration in detail at a microscale level. With regard to the specific sandstones studied, Mšené sandstone is softer, respectively, less brittle, while Kocbeře sandstone is characterised by a more brittle behaviour accompanied by an AE signal with higher amplitudes compared to those of Mšené.

A NOVEL WAY TO CLASSIFY THE SLAKE DURABILITY INDEX OF ROCKS

Slaking, the disintegration of rocks upon exposure to moisture and air, poses significant challenges in engineering applications, such as in slope stability and embankment design. This study improves the slake durability index test by introducing several enhancements to better reflect the field conditions of rocks. A new test methodology is developed which includes a revised slake durability classification table, a novel Discard Method for calculating weight retention in the test drum, and an updated classification chart. The improved methodology considers parameters such as porosity and strength, evaluated through index, Schmidt hammer rebound and point load tests. The new classification table categorizes rocks into durability classes according to the field observations and laboratory test results. The Discard Method improves accuracy by eliminating broken pieces from the durability calculation, addressing the limitations in the suggested method. A Configured Discard Method equation further defines the durability estimation by combining porosity, strength and slake durability data. Field investigations and laboratory tests conducted with various rock types demonstrate that the new classification system provides more accurate and practical assessments of rock durability. This study highlights the importance of effective porosity and strength impact which enhance the reliability of slake durability evaluations, offering a revised classification framework that simplifies field assessments while maintaining the accuracy. Future research should focus on developing these methods and expanding their applicability to diverse geological contexts by including more material to test.

Influence of wet–dry cycles on the disintegration characteristics of Cretaceous siltstone, China

Cretaceous siltstone, which is widely distributed in the Yichang region, is a type of soft rock characterized by its low strength and its susceptibility to softening and disintegration when exposed to water. To gain a better understanding of the impact of wet–dry cycles on the disintegration characteristics and mechanisms of Cretaceous siltstone, a series of rock disintegration experiments were conducted. These experiments involved microscopic structure analysis and solution ion concentration tests on the specimens. The results of the experiments revealed that with an increase in the number of wet–dry cycles, the Cretaceous siltstone progressively fractured and disintegrated, with larger fragments transitioning into smaller ones. Microscopic structure analysis indicated that continuous wet–dry cycles altered the specimen's microscopic structure, resulting in the formation of new microcracks and pores. The results of solution ion concentration tests showed significant mineral dissolution losses during specimen immersion in the solution. Furthermore, a comparative analysis of various disintegration parameters highlighted that each metric emphasized specific aspects of Cretaceous siltstone disintegration characteristics. Therefore, adopting a multi-metric approach allows a comparison of the validation and assessment of the disintegration features of Cretaceous siltstone from many aspects. Finally, based on the experimental findings, a concise description and summary of the disintegration mechanisms of Cretaceous siltstone under wet–dry cycle conditions are provided; then, combined with its disintegration mechanisms, engineering prevention and control suggestions for timely drainage and a reduction in thermal contact are put forward from the perspectives of waterproofing and heat insulation, which can be used for reference.

Features and processes of rock weathering in central Dronning Maud Land, Antarctica

In this study, we have investigated rock weathering phenomena in the central part of Dronning Maud Land, Antarctica. The area is characterized by low mean annual temperatures (−18 °C), strong katabatic winds, and minimal liquid water at the surface. Weathering features, including ventifacts, tafoni, and grus accumulations, are characterized through field observations, rock surface temperature measurements, and microscopic analysis. Abrasion by sand and ice particles transported by strong winds has locally resulted in ridge-shaped ventifacts and rock surfaces with elongated pits, furrows, and grooves. The abrasion-caused features, such as polished facets, keels, and grooves, indicate a northeast-facing wind direction, aligning with the present-day wind regime. The dominant weathering processes in coarse-grained intrusive rocks are oxidation and granular disintegration. Fe-oxidation induces cracking, increasing the porosity and enhancing susceptibility to further weathering. Additionally, temperature fluctuations on rock surfaces caused by solar radiation create thermal stress, which can lead to the formation of microcracks. These microcracks, formed due to thermal expansion, are likely to propagate through subcritical cracking, which is a slow, long-term process. Together, Fe-oxidation, thermal expansion, and subcritical cracking are important mechanisms contributing to long-term weathering and rock decay. Salt weathering, facilitated by snow and ice meltwater, particularly within tafoni, leads to flaking and disintegration of the parent rock. These findings shed light on the complex interactions shaping the geomorphology of central Dronning Maud Land and provide insights into long-term weathering processes operating in Antarctica's extreme environment.

Physico-mechanical parameters of rock materials used in open pit reclamation – a case study of CTL Maczki-Bór S.A. mine in Poland

The aim of the research was to assess the variability of selected physical and mechanical properties of Carboniferous barren rocks in the Upper Silesian Coal Basin and to analyze the impact of time and increasing vertical pressure on the mechanical parameters of the mixture of these rocks used in the reclamation of the open pit. Both type of tests were conducted in a strength press. For lithologically and stratigraphically differentiated rock samples, strength parameters in various states of humidity (air-dried and capillary saturation state) were determined, including compressive strength, cohesion and the angle of internal friction. It was found that the strength of all types of rock increases with geological age, however saturation of these rocks with water causes their structural weakening, which is especially noticeable in the case of sandstone and claystone. In the case of mudstone, due to their structure, the reduction of strength after saturation with water is not so significantly noticeable. In the second part of the laboratory tests, 5 samples of Carboniferous post-mining waste with different storage times in the open pit were subjected to the assessment of changes in density and compressibility in relation to increasing values of vertical pressure. It was found that the long-term depositing of waste in the excavation is conducive to the intensive development of hypergenic processes. This contributes to the disintegration of sedimentary rocks, which causes changes in their physical and mechanical parameters. This phenomenon is additionally intensified by the increasing vertical pressure with thickness of waste layers.

Study on Shear Failure Process and Zonal Disintegration Mechanism of Roadway under High Ground Stress: A Numerical Simulation via a Strain-Softening Plastic Model and the Discrete Element Method

Fracture expansion in rock masses can be observed by monitoring the break of contacts between the bounding particles via the discrete element method. The latter’s realization in this study via the PFC2D program tracked the evolution process of the zonal disintegration in an exemplary roadway-surrounding rock affected by mining. Besides, the damage evolution pattern in a high-stress soft rock roadway was simulated by the FLAC2D program using a strain-softening plastic model, revealing the effects of rock mass strength, stress state, and anchor support on the zonal disintegration of the roadway. Numerical simulation results show that in a roadway with high-level stress, the obvious fractures spread from the roadway surface to the depth of the surrounding rock along a series of geometric planes and cut the surrounding rock into rock mass blocks. Under high crustal stress, conjugate shear fractures occur near the roadway surfaces and form a closed-loop fractured zone after intersecting the conjugate fracture faces. The closed fractured zone becomes a free face, from which conjugate shear fractures develop, forming new closed fractured zones in the deep surrounding rock. By repeatedly generating the closed fracture zones, a fracture network appears in the roadway-surrounding rock. The development of zonal disintegration of roadway-surrounding rock mainly depends on the rock mass strength and its stress state. Zonal disintegration only occurs when the crustal stress of the roadway-surrounding rock exceeds its strength. When the horizontal stress is low and the vertical stress exceeds the rock mass strength, zonal disintegration only occurs on two sides of the roadway. When the vertical stress is low and the horizontal stress exceeds the rock’s mass strength, it only appears on the roof and floor. When the values of cohesion, internal friction angle, and tensile strength are reduced in the same proportion, cohesion has the greatest impact on the expansion of the zonal disintegration zone, followed by the internal friction angle, while the tensile strength effect is the least. In anchor-supported roadways undergoing zonal disintegration processes, the intact zone blocks slide relatively along the fracture surface during the process of loosening and deformation of the surrounding rock, making the anchor rods susceptible to tensile, shear, and bending actions.

Study of rock fracture patterns for obtaining the basis for energy-efficient ore ball milling

The study is conducted using methods of analysis (in proving the possibility of assessing the disintegration of rocks by energy consumption), methods of free vibration theory (to determine the motion of a falling ball over an elastic connection), methods of energy balance, methods of theoretical mechanics and material resistance (to study amplitude characteristics of mechanical systems), methods of rock fracture theory (to determine fracture work), physical modeling (to design test benches) and experimental methods (to find relationships between parameters). The strength of bulk crushed material in the first stages of ore preparation is practically independent of its coarseness and solid form, which allows the estimated volume of disintegrated ore (particle concentration) to be determined by the energy expended, translated into other physical quantities. Results of experimental studies support the theoretical dependences. The proposed approach of automatic stabilisation of solid concentration in the ball mill pulp at the optimum level allows to increase the productivity of ore preparation on the finished grade in the first stages by 10% at reduction of specific power consumption for ore grinding.

Effect of different buried depth on the disintegration characteristic of red-bed soft rock and the evolution model of disintegration breakage under cyclic drying-wetting

The disintegration of red-bed soft rock exhibits a strong correlation with various geological disasters. However, the investigation into the evolutionary mechanisms underlying disintegration breakage has not yet received extensive exploration. In order to comprehensively examine the disintegration characteristics of red-bed soft rock, the slake durability tests were conducted to red-bed soft rocks of varying burial depths. Subsequently, an investigation was carried out to examine the disintegration characteristics and the evolution of disintegration parameters, including the coefficient of uniformity (Cu), coefficient of curvature (Cc), disintegration rate (DRE), disintegration ratio (Dr), and fractal dimension (D), throughout the disintegration process. Finally, employing the energy dissipation theory, an energy dissipation model was developed to predicate the disintegration process of samples at various burial depths. The findings demonstrate a decrease in the abundance of large particles and a concurrent increase in the abundance of small particles as the number of drying-wetting cycles increases. Furthermore, as the number of drying-wetting cycles increases, a significant alteration is observed in the content of particles larger than 10 mm, whereas the content of particles smaller than 10 mm undergoes only minor changes. The disintegration parameters, including the curvature coefficient, non-uniformity coefficient, disintegration rate, and fractal dimension, exhibit a positive correlation with the number of drying-wetting cycles. Conversely, the disintegration index demonstrates a decreasing trend with the increasing number of cycles. Nevertheless, as the burial depth increases, a notable trend emerges in the disintegration process, characterized by a gradual increase in the content of large particles alongside a progressive decrease in the content of small particles. Concurrently, the curvature coefficient, non-uniformity coefficient, disintegration rate, and fractal dimension exhibit a gradual decline, while the durability index experiences a gradual increase. In addition, based on the principle of energy dissipation, it is revealed that the surface energy increment of red-bed soft rock increases with the increase of the number of drying-wetting cycles, but decreases with the increase of burial depth. Ultimately, by leveraging the outcomes of energy dissipation analyses, a theoretical model is constructed to elucidate the correlation between surface energy and both the number of drying-wetting cycles and burial depth. This model serves as a theoretical reference for predicting the disintegration behavior of samples, offering valuable insights for future research endeavors.

Spatio-temporal distribution and carcinogenic assessment due to potentially toxic elements in aquifer water of Ganga and Yamuna River basins, India

The spatial and temporal dispersion of potentially toxic elements (PTE) are evaluated for shallow groundwater samples of Delhi and Patna considering PTE pollution index (HPIPTE), evaluation index (HEIPTE), cancerous and non-cancerous effects, hazard coefficient index (HQI) and overall hazard index (HInc) considering fuzzy entropy weights and source identification is done through PCA. The evaluation of groundwater indicators as pH, TDS and PTE (As, Ni, Mn, B, Pb, Fe and Zn) indicated 6.67% and 3.33% of sampling stations exceeded the threshold limit, HPIPTE > 100 for arid and humid periods of Delhi, whereas 3.33% and 13.33% of sampling stations come under high contamination in the banks of the Ganga in arid and humid seasons respectively. The hazard coefficient index (HQI), only 18% and 21% of the specimens were in the grade of low pollution in both the seasons of Delhi and Patna. The trend of HQI is followed as, HQIAs>HQIPb>HQIFe>HQIMn>HQINi≥HQIZn>HQIB in Delhi region for both Young and elders in both seasons, while the sequence is followed as, HQIAs>HQIPb>HQIFe>HQIMn>HQIZn>HQINi>HQIB in the Ganga River basin area for elders and Young. The index (HInc) found 4 Young & 3 elders and 4 Young & 4 elders (Patna, arid and humid seasons) whereas 6 Young and 5 elders (Delhi, arid and humid seasons) affected as per the index per 1000 cases reported. The PC1 (As, Fe, Mn, and Pb) and PC2 (pH, As, Fe, and Pb) extracted from PCA pointed to the effects of evolution of contamination, hydrogeochemical reaction, disintegration of rocks, its dissolution, dispersion, and dilution in unconfined deep aquifers. Rapid depletion of groundwater table may cause the influx of As contamination in the shallow groundwater, whereas high Pb, Fe, Mn and Ni may be the reasons of nearby industries and improper waste disposal process. The findings and GIS mappings may put some light on the PTE over the Rivers which can help the local government and decision makers to formulate safe and protective bounds, to reduce the rate of contamination and to protect the water ecology and environmental system.

DESTRUCTION OF ROCKS BY EXPLOSION DURING OIL TRANSPORTATION

When oil and gas wells are ready for operation, when drilling is carried out at the bottom of the well to establish contact with the formation, it is considered that the degree of crushing of the rocks is proportional to the speed of application of the load. As a result of the stresses created by them, the degree of fragmentation is higher. In the article, it is proposed to take into account the quality of crushing of the necessary rock by using some empirical coefficients in the calculation formulas. The dynamics of the rock dispersion process is studied on the basis of the hydrodynamic hypothesis. Here, the solution of the system of differential equations is given based on the fundamental laws of conservation of mass, energy and momentum. Based on the strength properties of mountain rocks, broken lines are found in the continuum of the whole environment, which determines the final effect of rock crushing. However, the accepted assumptions about the incompressibility of the rock and the transfer of the explosive impulse to the immediate environment significantly reduce the practical value of the results. It should be noted that in the immediate area directly adjacent to the load, the mountain rock is under uneven volume compression. In this case, the largest tangential stresses occur mainly in planes oriented at an angle of 450 to the radial direction. Thanks to this, a system of spiral sliding lines breaks the rock into small blocks. Outside this zone, a system of radial cracks is formed as a result of the expansion of the massif. When the pressure in the gas cavity decreases and the mass moves back in the direction of the load, tangential cracks appear. The combination of the volume compression zone and the reach zone constitutes the controlled crushing area. When the compression wave reaches the bare surface, it becomes a stress wave. As this wave travels from the surface to the load, it forms a system of jump cracks. The high explosive effect of explosive gases with sufficient explosion energy causes the release of such shattered rock. Obviously, this concept is very important for the development of the theory of explosive disintegration of mountain rocks. Because there is no unequivocal relationship between the nature of the dissolution of the rock and the acoustic hardness. One of the first to clearly describe the mechanism of shock wave formation and its transformation into a more explosive and seismic wave when detonation reaches the boundary of the charge cavity. In rocks, shock waves are formed during the entire time of expansion of the gas cavity. It explains in detail the mechanism of cracking phenomena by considering the cracks as a source of multiple reflections of the stress wave. Keywords: rock strength, constant material, scale effect, rocks, destruction probability, fractured, robustness theory, microcrack, mineral, experience constant, density of defects, displacement, compression.

Origin of Fracture-Controlled Conduits in Calcite-Rich Highly Productive Aquifers Impregnated with Diagenetic Silica

The origin of highly permeable flow paths in carbonate-siliciclastic rocks, such as large-aperture fractures in aquifers in the Eastern Bohemian Cretaceous Basin (EBCB), is poorly understood. The karst potential was assessed from the rock carbonate content and the degree of disintegration after leaching in HCl. Surprisingly, dissolution of calcite in EBCB usually did not lead to rock disintegration until calcite > 78%. Instead, porosity increased significantly. High-porosity rock is held together by microns-thick secondary silica cement with a foam-like structure and considerable tensile strength. Three types of conduits occur in the EBCB: (i) bedding-parallel conduits associated with calcite-rich layers, (ii) subvertical fracture swarm conduits that develop on damaged zones of fracture swarms, and (iii) conduits formed by dissolution of calcite veins by groundwater flow. These are ghost-rock karst features where calcite is leached from the rock in the first phase and the residue is washed out by conduits under steep hydraulic gradients in the second phase. Very similar features have been described in Minnesota and Wisconsin, USA. Research has shown that fractures with sharp-edged walls that give the impression of an extensional tectonics origin may actually be ghost-rock karst features in which dissolution and piping have played an important role in their enlargement.

Effects of pH on Disintegration Characteristics of Gypsum Karst Breccia under Scouring Action

Water–rock interactions and scouring actions are recognized key factors that significantly influence the disintegration of rock on the surface of slopes. However, the research on rock disintegration, specifically under the action of scouring, is limited, which makes it difficult to understand the characteristics of rock disintegration. Therefore, in this study disintegration tests were performed on the gypsum karst breccia collected from the Zhoukoudian site in Beijing, using a self-made disintegration test device. Further, this study investigated the impact of solution pH, flow velocity, and the number of cycles on the characteristics of rock disintegration. The changes in pore structure, microstructure, and mineral composition of the rock were analyzed using nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), X-ray diffraction (XRD), and inductively coupled plasma optical emission spectrometer (ICP-OES) methods. The findings reveal that the cumulative relative disintegration amount of the gypsum karst breccia experiences an increase as the pH value of the soaking solution decreases and the number of cycles increases. Once a specific flow rate is attained, the cumulative relative disintegration amount stabilizes (about 73%) and no longer exhibits significant changes. This phenomenon signifies the presence of a stabilizing flow rate for disintegration. The stable flow rate concerning rock disintegration is influenced by both the solution’s pH and the number of cycles. Following acid contamination, the rock sample’s particle morphology undergoes disruption, leading to the dissolution of cement. This, in turn, leads to an augmented release of Ca2+, Al3+, and Ma2+ ions in the solution, intensifying the disintegration of the rock samples. Conversely, alkali contamination prompts secondary cementation, mitigating localized damage. This results in a marginal increase in the calcite content within the rock samples (from 15.3% to 19.2%), while the release of Ca2+ in the solution experiences a decrease. Additionally, there is a slight increase in the release of Al3+ (a maximum increase of 1.71 mg/L), which minimally inhibits the disintegration of the rock samples. Notably, the rock disintegration predominantly occurs around macropores, and the effect of solution pH on the disintegration characteristics and stable flow rate is primarily due to the changes in the relative proportion of macropore volume in the rock samples. The findings of this study have significant implications for the prediction and control of slope-related issues.

Numerical investigation on blast-induced rock fragmentation with different stemming structures

Stemming is one of the main concerns in blast of rock engineering due to its impact on explosion energy consumption and rock excavation performance. In this study, blast-induced rock fragmentation under different stemming conditions is numerically studied using combined numerical modelling and image processing. After careful determination the parameters of constitutive material models, the developed numerical model in LS-DYNA is verified based on the blast testing results including rock fracturing and fragment size distribution (FSD). The calibrated constitutive models are then used to model the pressure variation and rock disintegration produced by blasting with different stemming structures. The size data of simulated rock fragmentation are obtained by image-processing the cut surfaces of the numerical model with the program ImageJ, and the blast-created rock FSD is characterized using a three-parameter generalized extreme value function. The effects of the combination of explosive, air/sand deck and stemming on blast-induced rock fragmentation are quantitatively analysed, considering various stemming modes, stemming lengths and air/sand deck lengths. The results show that the blast-created fragment size decreases with an increase in stemming length, a decreasing in air/sand deck length, replacement of top stemming (stemming at borehole collar with air deck) with bottom stemming (stemming directly contact explosive) and alteration of air deck to sand deck, while the FSD range exhibits the opposite tendency. Bottom stemming is recommended for practical blasting due to its efficiency in rock fragmentation and robustness with respect to stemming length.

Basic consolidation and impermeability laws for nano-silica-sol grouted mudstone

The engineering characteristic of the water absorption, swelling, softening, and disintegration of muddy soft rocks can cause long-term large deformation and instability in muddy tunnels. Due to the poor injectability of conventional cement slurry into rock microcracks and insufficient reinforcement and anti-seepage effects on mudstone, this research performed tests on the modification and reinforcement with silica sol. Taking nano-silica sol as the research subject, this study analyzed the injectability of the slurry, the anti-seepage performance of the gel, and the macro and micro characteristics of the pore closure of consolidated mudstone. Ultimately, the basic laws of silica sol grouting and anti-seepage reinforcement for mudstone are obtained. Besides, the impact of silica sol consolidation on grouting is examined, with its performance being compared with traditional slurries. Research indicates that the silica sol slurry exhibits superior injectability and permeability, with its gel demonstrating enduring volume stability and a compact structure. When applied to mudstone, silica sol grouting markedly diminishes both porosity (by 1.68–1.88%) and permeability, reaching an ultra-low level of 10-9 cm/s. NMR tests further elucidate that silica sol is more efficacious in sealing medium and large pores (with T2 > 10 ms, >0.1 μm) compared to smaller ones (with T2 < 10 ms, below 0.1 μm). Therefore, silica sol is a prime candidate for grouting and sealing applications in micro-cracked mudstones of coal mine tunnels, particularly in muddy tunnel projects necessitating extended maintenance and anti-seepage measures. The research is expected to provide solutions to the anti-seepage and reinforcement of mudstone.

Origin of chromitites in the Norilsk-1 intrusion (Siberian LIP) triggered by assimilation of argillaceous rocks by Cr-rich basic magma

Сhromite-rich rocks and monomineralic chromitites occur in mafic-ultramafic layered intrusions worldwide, and are economically important as they host major resources of chromium and platinum group elements. One of the acknowledged genetic concepts for such mineralization advocates bulk chromite crystallization in a response to hybridization of Cr-rich basic magma with felsic melts, derived from partial melting of the wall rocks. However, there has been lack of direct insights into this process and its details have been remaining largely obscured. In this study, we report data on chromite-rich assemblages of the Noril'sk-1 intrusion (Siberian LIP), with a particular focus on chromite-hosted multiphase inclusions. Composition of the latter is different from the rocks of the Noril'sk-1 intrusion and inherits geochemical fingerprints of the wall rock argillites and, therefore, represent snapshots of the heavily-contaminated medium of the magma-wall rock reaction front. Mineral relationships in chromite-rich breccias with fragments of the wall rocks also provide valuable insight into chromite mineralization mechanisms. Our results, along with geological evidence and data on other Noril'sk-type intrusions, indicate that bulk crystallization of chromite, aided by partial suppression of silicate crystallization, occurred in the hybrid medium during digestion of the wall rocks by ascending and emplacing basic magma. Continuous flow of the magma around outshoots of the wall rocks or through a “magmatic karst” in the wall rocks, allowed for a continuous precipitation of chromite. Concentration of chromite grains to form dense mineralization apparently occurred due to formation of chromite-rich blobs around the wall rock fragments, and selective collection and transport of chromite by fluid bubbles, which formed via degassing of wall rocks and then carried chromite and relics of the wall rocks (xenoliths) to the upper parts of the pluton. We propose that assimilation-driven formation of chromite-rich lithologies in intrusions requires: (1) sufficient Cr contents in magma, which allow for its oversaturation in Cr-spinel only by a sudden cooling and addition of SiO2, K2O or/and H2O; (2) efficient disintegration and digestion of the host rocks, releasing considerable amounts of these components to the magma, and (3) a mechanism ensuring accumulation of excess chromite within a small volume (e.g. continuous reaction of Cr-rich magma with the products of the host rocks' assimilation or/and mechanical concentration of chromite).

Mathematical modeling of rocks plasma disintegration process at borehole reaming

The mathematical model of thermal disintegration of rocks during the reaming of boreholes, which takes into account the compatibility of the thermogas dynamic problem for a high-temperature heat transfer agent and the thermal problem for the rock heated by this heat transfer agent, has been developed. The mathematical model is based on the laws of conservation of mass, quantity of motion and energy and takes into account the dependences for determining the thermal stresses and the temperature of brittle fracture of rocks. As a result of solving the equations of the mathematical model, the temperature distribution in the rock mass (magnetite quartzite) during heating in the process of borehole plasma reaming and productivity of the borehole plasma reaming process are obtained. Calculated and experimentally determined productivity of the process of plasma reaming of the borehole were compared.

Preparation Method of Similar Materials for the Progressive Disintegration of Red-Bedded Soft Rock Based on Diagenesis Simulation

Solid waste formed during the excavation of soft red stratum rock is often encountered in engineering practice. However, its reuse has been limited because it often shows a gradual degradation mechanism during water–rock interactions. Similarity simulation experiments of geotechnical materials have been developed to be environmentally friendly; however, their application in soft rock mechanics is still limited. Based on these limitations, this study aims to prepare red-bedded soft rock-like materials by referring to the diagenetic process of sedimentary rocks using low-melting-point glass powder (STGP) and high-temperature and vertical stress to accurately simulate the progressive disintegration properties of red-bedded soft rock. For this purpose, a series of laboratory tests were conducted to verify the function of STGP in the embedment of skeleton particles of soft rock as a cement material for resisting the dry–wet cycle. Micro-scanning electron microscopy, disintegration experiments with dry–wet cycles, and basic physical and mechanical property tests were conducted for the synthetic red soft rock-like material. Finally, the synthetic and natural materials were compared based on their density, microstructure, disintegration breakage, and uniaxial compression mechanical properties. The results showed that adding STGP promoted embedded solidification between aggregate particles. The simulated material exhibited the same characteristics of gradual disintegration breakage as natural red-bedded soft rock. Meanwhile, the basic physical and mechanical properties were in substantial agreement when the STGP content was 0.5~2%.

Simulation and Experimental Study on Rock Disintegration Characteristics of Special-shaped PDC Cutters

In order to analyze the rock disintegration characteristics of special-shaped Polycrystalline Diamond Compact (PDC) cutters, numerical simulation and micro-drilling test on four kinds of special-shaped PDC cutters are carried out. Simulation results show that, the surface stress of each PDC cutter is quite different. For the dual-chamfer PDC cutter, the second chamfer can expand the stress on the cutting edge to a larger area; for the conical PDC cutter, the maximum stress is concentrated at the tip of the cone; for the ridged PDC cutter, the stress is distributed in a triangular fan shape from the lower edge of the cutting edge upward along the ridge, and for the triangular ridge PDC cutter, the stress is mainly distributed on the lowermost ridge. The conical PDC cutter has advantages in rock disintegration stability and efficiency, but it requires a higher weight on bit; the ridged PDC cutter has advantage in rock disintegration efficiency, but it tends to swing sideways when breaking rock; the dual-chamfer structure of PDC cutter is beneficial to extend the cutter’s life, but its rock disintegration efficiency is poor. Anchor bits with these special-shaped PDC cutters are produced, and electro-hydraulic micro-drilling test are carried out, the results of micro-drilling test and numerical simulation show the same law excluding conical PDC cutter. The research results can provide guidance for the application of special-shaped PDC cutters in drill bit.

SEISMIC INHOMOGENEITIES IN THE UPPER CRUST OF THE ALDAN-STANOVOY SHIELD AND IN ITS TOTAL CRUST (PROFILE 3-DV)

In accordance with the detailed first-arrival data, the near-surface part of the Earth’s crust consists of three layers. The upper discontinuous layer is represented by the Mesocenozoic deposits in local basins. The two inhomogenous layers decrease in thickness towards the north from 1.5 km to total thinning in the Stanovoy block and from 4 km in the Chulman basin to 1 km in the Aldan. It is implied that the nature of thinning lies in weathering and disintegration of crystalline rocks. Their underlying boundary at a depth of 1–4 km with a longitudinal wave velocity of 6.0–6.2 km/s can be assigned to the unchanged Early Precambrian basement surface.The deep seismic sounding data show that the two-layer crust thickness of the Stanovoy block reaches 40 km, and the three-layer crust in the Aldan block is as thick as 50 km. These blocks are separated by the vertical zone beneath the Stanovoy ridge with contrast inhomogeneities in the crust and step-like increase in the Moho depth beneath the Chulman basin.There was discovered an isostatic imbalance of the lithosphere, correlated with seismicity of the Chulman basin.

ІНТЕРПРЕТАЦІЯ 3D ГЕОЕЛЕКТРИЧНОЇ МОДЕЛІ РАЙОНУ ПЕРЕТИНУ ЗВІЗДАЛЬ-ЗАЛІСЬКОЇ ТА НЕМИРІВСЬКОЇ ЗОН РОЗЛОМІВ

The interpretation of the deep three-dimensional geoelectricalal model of the central part of the Zvizdal-Zaliska and Brusyliv fault zones of the Ukrainian shield, which was built with the involvement of data from experimental observations of the Earth's low-frequency electromagnetic field conducted in 2019 by the Institute of Geophysics named after S.I. Subotin of the National Academy of Sciences of Ukraine, within the Ordyntsi-Lobachiv and Zoziv-Stryzhavka profiles was done. Experimental materials were processed with the PRC_MTMV software package, tipper estimates were obtained for periods of geomagnetic variations from 50 to 3400 s and curves of apparent resistivity (amplitude values and impedance phases) from 10 to 10000 s. Based on the qualitative analysis of magnetovariational profiling parameters, magnetotelluric sounding curves and pseudo-sections, several local near-surface structures of complex orientation in space were identified, which are confined to the Pogrebyshchensky and Ogiivskyi faults, areas of separate parts of the Zvizdal-Zaliska, Brusyliv and Nemyriv fault zones, as well as their convergence , and outside the fault zones in the crystalline massive of the Ukrainian shield. The main result of the geological-geoelectrical interpretation of the 3D model is the discovery of new anomalies of low resistivity in the near-surface part of the earth's crust (from the surface to 0.5-2 km), which correspond to the structural and metallogenic features of the study area; confirmation and detailing of the anomalously heterogeneous distribution of resistivity in the tops of the upper mantle at depths from 70 to 120 km west of the Ukrainian shield. The area of intersection of the Zvizdal-Zaliska and Nemyrivs fault zones is characterized by both a galvanically connected spatially diverse system and local separate near-surface anomalies with low resistivity from 5 to 100 Ohm·m, most of which dip to 0.5-1 km. It is shown that there are connections between conductivity and structural features of the Zvizdal-Zaliska, Brusyliv and Nemyriv fault zones. In addition, some anomalies are found in the granite migmatites of the Ros' structural-formation zone, outside the tectono-metasomatic mineragenic zones. As a rule, anomalies are confined to zones of disintegration of crystalline basement rocks, elongated zones of metasomatization, and areas of distribution of graphitized rocks; moreover, some of the surface anomalies correspond to regions of weathering crusts. The conducted geological-geoelectrical analysis of the model showed that several areas require further study, namely the sub-latitude anomaly west of the Zoziv-Stryzhavka profile and the complex-shaped anomaly in the eastern part of the study area. As promising for the search for minerals, which meets the geoelectrical criteria, the area of the anomaly within the Brusyliv fault zone with a depth of up to 2 km is highlighted.