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For the purpose of revealing the effect of fracturing fluids on rock breaking, wellbore stability, and fracturing reformation. A multi-scale evaluation method is initially established in th...

In this paper, the numerical simulation is used to study the rising mechanism of rotary-percussive drilling, which is under the combination of rotary cutting and axial impact. The main objective of the present work is to compare and investigate the breaking process of rock element and the motion state of drilling bit under the conventional drilling and rotary punching drilling. Additionally, the single-factor analysis is used to analyze the effects of impulse load, impulse frequency, rotary speed and formation hardness on rock breaking efficiency and acceleration effect of rotary percussion drilling. Through the investigation, it is found that there are more areas of tension stress breakage in rock elements under rotary-percussive drilling. Rotary percussion drilling can effectively alleviate the stick–slip vibration of drilling bit. At the same time, the relationship between the average penetration rate of the bit and the impulse load, impulse frequency, rotary speed and formation hardness is shown. The results of the study will be beneficial to provide some theoretical reference for the development of tools and the selection of working parameters of rotary-percussive drilling technology, as well as for the drilling methods of deep wells and hard rocks.

High-frequency torsional vibration percussive drilling is considered a promising approach to improve drilling performance in deep hard formations, so studying its rock breaking mechanism and effect...

The construction efficiency and quality of tunnel boring machines (TBMs) is largely determined by the service life of cutting tools, which is the result of contact loads in the crushed zone between cutter ring and rock. In this paper, a series of rock breaking tests were conducted with a 216 mm diameter disc cutter and concrete samples. Based on the superposition principle, the distribution of contact loads between disc cutter and rock were obtained by using the truncated singular value decomposition (TSVD). The results show that both the peak value and the whole numerical distribution of the radial strains on the cutter ring increase with the increase of the penetration. The distribution curves of the contact loads show an approximate parabola going downwards, which indicates contact loads are more concentrated. The front non-loading area with a ratio from 1.8% to 5.4% shows an increasing trend with the increase of penetration. However, the change of rear non-loading area is not obvious. It is believed that the conclusions have guidance for the study of rock breaking mechanism and manufacturing process of the disc cutter.

Imaging cracks is a direct way to learn the rock breaking mechanism beneath a PDC cutter. In this study, a series of linear cutting tests and precise observations of cracks were conducted. The formation of major cracks was captured in-situ with a high speed camera in the process of cutting rock sheets. Then the cracks under the cutting groove (subsurface cracks) were studied by reproducing the cutting groove after cutting some rock blocks and further observed by means of thin-section optical microscopy. Finally, the development sequence of the cracks and adjacent crushed zone was determined by recording the cutting process on a rock-like silica glass block. The results show that the shape of major cracks is mainly curved, both upward and downward curves were observed. The major cracks mainly initiate at the tip of the cutter when cutting sandstone and granite, while they initiate more randomly in marble. The length and angle of the subsurface cracks vary with the rocks: the subsurface cracks extend the longest in granite, while propagating more vertically in sandstone. Finally, it is determined that the major cracks initiate after the formation of crushed zone. And the initiation of major cracks will enlarge the crushed zone and lead to the initiation and propagation of the subsurface cracks. The results in this paper are expected to further reveal the rock breaking mechanism beneath a PDC cutter.

The feasibility of a cuttings waterjet directly modulated in the bottom hole is discussed from the aspects of cuttings suction and rock‐breaking efficiency. The particle waterjet modulation mechanism using a Helmholtz oscillating cavity is studied through numerical simulation and the rock‐breaking efficiency of five types of particles (including cuttings, steel balls, steel emery, garnet, and silicon carbide) is studied through experiment. The influences of particle parameters (such as diameter, density, and concentration) and operation parameters (such as standoff distance, pump pressure, and confining pressure) on the suction and rock‐breaking effect of different particles are analyzed. The results show that all particle types with different parameters could be indrawn into the Helmholtz oscillating cavity with two symmetrical suction ports and could be accelerated to considerable velocity amplitude to impact rock. The rock‐breaking efficiency of pure cuttings was lower than fractional cuttings (ie, 50% cuttings and 50% steel balls) and pure steel balls, but the pure cuttings can be used as an effective assisted rock‐breaking method. The research results lay a foundation for development of a cuttings waterjet directly modulated in the bottom hole for assisting rock‐breaking technology.

The arrangement of disc cutter on a cutter head is important to improve the performance of TBM (tunnel boring machine) cutter, cutter life and cutter disc bearing life, then reduce vibration of TBM and reduce the noise. The rock breaking with double disc cutters is the basis of study on the distribution of disc cutter on cutter head, and it plays an important role on optimum arrangement of disc cutter on cutter head. In the process of rock breaking with double disc cutters, the axial vertical distance between two cutters is an important construction parameter, which directly affects rock breaking efficiency. Therefore, research on optimal cutter spacing and analysis of adaptability between cutter spacing and rock characteristics play an important role in optimizing the arrangement of cutter on the cutter head and improving the rock breaking efficiency of TBM. This paper analyzed the breaking rock force of double disc cutters. Taking granite samples as an example, the process of rock breaking with double disc cutters was simulated. Then rock fragmentation analysis based on different cutter spacing was carried out. Finally, the rock of different cutter spacing adaptability was studied. A series of conclusions about double disc cutters breaking rock were drawn.

Contraposing the problem of cutter wear and other issues in TBM boring in erosive and hard strata, this paper analyzes the boring parameters and cutter wear amount in the trial 2 km of TBM section in Qinling Tunnel of Han River to Wei River Water Diversion Project. Then several pieces of advice are proposed and analysis results suggest that the inadequate amount of cutters around No. 43 cutter causes their relatively high wear. Experiments of disc cutter breaking hard rock are conducted, showing that the specific energy of TBM used for breaking rock is relatively low while the efficiency high when the S/p (the ratio of cutter space to penetration) is between 25 and 30. Relevant scaled experiments indicate a critical penetration value beyond which the mass wear rate of disc cutter surges. The experiment also proves that round-blade disc cutter could effectively reduce the wear. The research could provide reference for the cutter-head design and parameter control of TBM in similar geologies.

The authors express their gratitude to V.P. Teplyi, Chief Project Designer at the Department of Vibropneumatic Transport Systems and Complexes of the Institute of Geotechnical Mechanics named by N. Poljakov of National Academy of Sciences of Ukraine, and to S.V. Shniakin, Chief Engineer at the Department of Vibropneumatic Transport Systems and Complexes of the Institute of Geotechnical Mechanics named by N. Poljakov of National Academy of Sciences of Ukraine, for their valuable help during the experimental studies. The authors are also grateful to L.T. Kholiavchenko, Candidate of Technical Sciences (Ph.D), Senior Researcher at the Department of Rock Breaking Problems of the Institute of Geotechnical Mechanics named by N. Poljakov of National Academy of Sciences of Ukraine, for his valuable guidelines and comments in the discussion of the results obtained through experimental and theoretical studies.

Predicting the cutter consumption and the exact time to replace the worn-out cutters in tunneling projects constructed with tunnel boring machine (TBM) is always a challenging issue. In this paper, we focus on the analyses of cutter motion in the rock breaking process and trajectory of rock breaking point on the cutter edge in rocks. The analytical expressions of the length of face along which the breaking point moves and the length of spiral trajectory of the maximum penetration point are derived. Through observation of rock breaking process of disc cutters as well as analysis of disc rock interaction, the following concepts are proposed: the arc length theory of predicting wear extent of inner and center cutters, and the spiral theory of predicting wear extent of gage and transition cutters. Data obtained from 5621 m-long Qinling tunnel reveal that among 39 disc cutters, the relative errors between cumulatively predicted and measured wear values for nine cutters are larger than 20%, while approximately 76.9% of total cutters have the relative errors less than 20%. The proposed method could offer a new attempt to predict the disc cutter's wear extent and changing time. Keywords: Full-face rock tunnel boring machine (TBM), Disc cutter, Wear prediction

As an important equipment for wellbore construction, the raise boring machine (RBM) has been widely used in subway tunnels and mine construction projects. Its tipped hob cutter for rock breaking is directly related to the cost, safety, and overall performance of the project. However, few open studies research on the rock-breaking by the tipped hob cutter, and there is still a lack of enough understanding of how the cutter breaks rock and the form of the rock breaking. In this paper, we study how the tipped hob cutter breaks the rock, and how to establish the finite-element model of the rock breaking by the cutter, with using the numerical simulation software LS-DYNA to analyze the rolling process and rock fracture form of the cutter. By studying the fracture morphology of rocks, it is proposed that there are three fracture modes of rock breaking: forward slip, no slip, and backward slip, using the experimental verification. On this basis, study the variation laws and correlations of feed force, lateral force, and positive force under different moving speeds and penetration depths. The results in this paper can provide a theoretical basis for improving the tool design of the tipped hob cutter on the RBM against the efficiency of rock-breaking.

To solve a major problem faced by drilling technicians, that of how to improve rock breaking efficiency in complex strata, this paper introduces a polycrystalline diamond compact (PDC) drill bit with a special structure. Static-pressure breaking tests show that the breaking work ratio of a single tooth on a ridge is much smaller than that on flat rock samples, and the effect of ridge height on breaking work ratio is greater than that of ridge width. Single-tooth scrape tests show that the tangential force, axial force, and breaking work ratio of PDC teeth when scraping on a ridge are greatly reduced compared with flat rock samples, and the ridge width has a greater influence on the breaking work ratio than ridge height. A test bit with a diameter of 215.9 mm and the possibility of zero, one, or two annular grooves is designed and manufactured. Compared with the conventional, full-coverage PDC bit, the specific energy of the double-groove bit is reduced by 26.9%. The annular-groove PDC bits achieve large-scale cuttings when breaking the ridge created by the bit, and the rock breaking efficiency is greatly improved. At the same time, the raised ridges of the bottomhole increase the stability of the drill bit, providing a feasible solution for rock breaking when drilling complex strata.

Rock cutting efficiency is the most common parameter used to evaluate the performance of polycrystalline diamond compact (PDC) bits. Many studies have shown that cuttings size might be used to evaluate rock breaking efficiency; however, there are few quantitative studies of the relationship between rock cutting efficiency and cuttings size in rock cutting when a PDC bit is used. Several linear cutting tests were conducted to explore the relationship between the mechanical specific energy (MSE) and cuttings size to solve this problem. The cuttings size distributions were also discussed. Then, the coarseness index (CI) was selected as the most appropriate indicator of cuttings size and its relationship with the MSE was investigated. In addition, rock cutting tests based on the Taguchi method were conducted to analyze cutting parameters such as the depth of cut (DOC), the back rake angle (θ) and the cutting speed (v) effects on the CI and MSE. The contribution of each parameter to the response was obtained. The results show that the distribution of cuttings size conforms to the Rosin–Rammler equation, and there is a significant relationship between the MSE and cuttings size. The MSE decreases with increased cuttings size, furthermore, the relationship between the MSE and the CI could be described by an exponent function. The Taguchi experiment results show that DOC and θ have significant impacts: the CI value increases with increased DOC, and the CI increases slightly with increased θ. The most influential factor on the CI is the DOC, followed by θ. However, within the range of experiments, the cutting speed has an insignificant effect on the CI value. This work is highly pertinent to better understanding of the relationship between rock cutting efficiency and cuttings size in rock cutting using a PDC cutter.

The coal rock breaking ability of disc cutters directly affects the construction efficiency and safety of rescue tunnels in collapsed coal rock formations. This paper establishes the plastic constitutive relationship under the Drucker-Prager (D-P) plasticity criterion, builds up a finite-element analysis (FEA) model for the coal rock breaking with a single cutter on Abaqus FEA, and explores the influence laws of different penetrations and cutting velocities on the rock breaking performance of the cutter. The results show that: as the penetration increased from 3.0 mm to 7.0 mm, the mean vertical force of the cutter grew from 16.97 kN to 23.36 kN, and the mean rolling force rose from 1.79 kN to 3.95 kN. The increase of the cutter's vertical force improves the cutting efficiency, but intensifies the vertical impact, which undermines construction safety. As the cutting velocity increased from 0.6 rad/s to 1.5 rad/s, the mean vertical force grew from 15.64 kN to 22.94 kN, and the mean rolling force rose from 1.46 kN to 4.23 kN. With the increase of cutting velocity, the cutting force grew at an increasing speed. The increase of cutting velocity can improve cutting efficiency, but an excessively fast cutting velocity will weaken the stability of the cutting operation, and add to the wear of the tool. The research method provides theoretical supports to the cutterhead design of tunnel boring machine (TBM) and tunnelling control in broken coal rock formation.

Crushing of blasted ore is an essential phase in extraction of valuable minerals in mining industry. It is typically performed in multiple stages with each stage producing finer fragmentation. Performance and throughput of the first stage of crushing is highly dependent on the size distribution of the blasted ore. In the crushing plant, a metal grate prevents oversized boulders from getting into the crusher jaws, and a human-controlled hydraulic manipulator equipped with a rock hammer is required to break oversized boulders and ensure continuous material flow. This secondary breaking task is event-based in the sense that ore trucks deliver boulders at irregular intervals, thus requiring constant human supervision to ensure continuous material flow and prevent blockages. To automatize such breaking tasks, an intelligent robotic control system along with a visual perception system (VPS) is essential. In this manuscript, we propose an autonomous breaker system that includes a VPS capable of detecting multiple irregularly shaped rocks, a robotic control system featuring a decision-making mechanism for determining the breaking order when dealing with multiple rocks, and a comprehensive manipulator control system. We present a proof of concept for an autonomous robotic boulder breaking system, which consists of a stereo-camera-based VPS and an industrial rock-breaking manipulator robotized with our retrofitted system design. The experiments in this study were conducted in a real-world setup, and the results were evaluated based on the success rates of breaking. The experiments yielded an average success rate of 34% and a break pace of 3.3 attempts per minute. publishedVersion

The speed of drilling has a great relationship with the rock breaking efficiency of the bit. Based on the above background, the purpose of this article is to predict the position of shallow bit based on the vibration signal monitoring of bit broken rock. In this article, first, the mechanical research of drill string is carried out; the basic changes of the main mechanical parameters such as the axial force, torque, and bending moment of drill string are clarified; and the dynamic equilibrium equation theory of drill string system is analyzed. According to the similarity criterion, the corresponding relationship between drilling process parameters and laboratory test conditions is determined. Then, the position monitoring test system of the vibration bit is established. The acoustic emission signal and the drilling force signal of the different positions of the bit in the process of vibration rock breaking are collected synchronously by the acoustic emission sensor and the piezoelectric force sensor. Then, the denoised acoustic emission signal and drilling force signal are analyzed and processed. The mean value, variance, and mean square value of the signal are calculated in the time domain. The power spectrum of the signal is analyzed in the frequency domain. The signal is decomposed by wavelet in the time and frequency domains, and the wavelet energy coefficients of each frequency band are extracted. Through the wavelet energy coefficient calculated by the model, combined with the mean, variance, and mean square error of time-domain signal, the position of shallow buried bit can be analyzed and predicted. Finally, by fitting the results of indoor experiment and simulation experiment, it can be seen that the stress–strain curve of rock failure is basically the same, and the error is about 3.5%, which verifies the accuracy of the model.

With the continuous increase of human demand for oil and natural gas, the exploration and development of oil and gas wells have gradually moved from conventional formation to deep formation. PDC bits are widely used in oil and gas exploration and development because of its high rate of penetration (ROP) and drilling efficiency.

Актуальность. Требования к буровому породоразрушающему инструменту заключаются в обеспечении высокой механической скорости, ресурса, широкой области применения и небольших материальных затрат на его приобретение. Иными словами, буровой инструмент должен быть прочным, износостойким и изготовлен из относительно недорогого материала. Достижения в области синтеза поликристаллического алмаза и изготовления из него резцов высокой прочности значительно расширили возможности производителей бурового инструмента. Синтетический сверхтвердый материал стали применять при изготовлении режущих элементов и всей рабочей части породоразрушающего инструмента. Новшества материаловедения позволили производить резцы типа PDC разной формы, размеров, прочности, что особо актуально при создании долот, коронок и буровых головок с комбинированным вооружением. Как известно, состав и условия спекания композита влияют на свойства получаемой заготовки резца PDC. Изменяя прочностные параметры и геометрию расположения режущих элементов PDC с учетом области применения инструмента, можно добиться наилучшего эффекта разрушения горной породы. Таким образом, при создании нового бурового породоразрушающего инструмента актуальным является объединение знаний и умений в области химии, материаловедения и конструирования, что приведет к получению перспективного породоразрушающего инструмента. Цель: определить направления совершенствования бурового инструмента типа PDC, а именно возможности материаловедения в области спекания сверхтвердого материала PDC, преимущества применения композита различного состава при проектировании новых конструкций бурового инструмента типа PDC. Объекты: состав материала, процесс спекания и получаемые свойства резцов PDC, конструктивные особенности бурового инструмента PDC. Методы: аналитические исследования, эксперимент, анализ. Результаты. Изменение состава композита позволяет регулировать прочностные свойства получаемого резца PDC. Добавление такого материала, как графен, повышает прочностные, тепло- и электропроводные свойства резца PDC. Объединение возможностей материаловедения и опыта конструирования позволяет добиться положительных результатов в области разработки нового перспективного породоразрушающего инструмента. Relevance. Requirements for rock cutting tools are to ensure high mechanical speed, resource, wide range of application and low material costs for its purchase. In other words, the drilling tool must be durable, wear-resistant, and made of relatively inexpensive material. Advances in the synthesis of polycrystalline diamond and the manufacture of high-strength cutters from it have significantly expanded the capabilities of drilling tool manufacturers. Synthetic superhard material began to be used in the manufacture of cutting elements and the entire working part of rock cutting tools. Innovations in materials science have made it possible to produce PDC cutters of various shapes, sizes, strengths, which is especially important when creating bits, crowns and drill heads with combined weapons. As is known, the composition and sintering conditions of the composite affect the properties of the resulting PDC cutter blank. By changing the strength parameters and the geometry of the PDC cutting elements, taking into account the field of application of the tool, you can achieve the best effect of rock breaking. Thus, when creating a new drilling rock cutting tool, it is relevant to combine knowledge and skills in the field of chemistry, materials science and design, which will lead to obtaining a promising rock cutting tool. The aim of the research is to determine the directions of improving the PDC-type drilling tool, namely, the possibilities of materials science in the field of sintering of superhard PDC material, the advantages of using a composite of various structure in the engineering of new designs of PDC-type drilling tools. Objects: composition of material, sintering process and obtained properties of PDC cutters, design features of PDC drilling tools. Methods: analytical research, experiment, analysis. Results. Changing the structure of the composite allows you to adjust the strength properties of the resulting PDC cutter. Addition of such a material as graphene increases the strength, thermal and electrical conductive properties of PDC cutter. Combining the capabilities of materials science and design experience makes it possible to achieve positive results in the development of a new promising rock cutting tool.

In this chapter, we will introduce three base instances: the interaction of pile and soil, tunnel simulation, and the TBM cutter rock breaking numerical simulation model.

The effects of initial stress conditions and rock breaking parameters on rock fragmentation were investigated through indentation tests and numerical analysis with a discrete element metho...

The concept of tunnel boring machine (TBM) disc cutter rock breaking coupled with high-pressure water jets has been proposed to overcome the difficulties that occur when TBMs encounter extremely hard rocks. Thus, to meet actual engineering requirements for the TBM construction of tunnels as part of the Wan’anxi water diversion project in Longyan City (Fujian Province, China), experiments were conducted on high-pressure water jet-assisted TBM disc cutter rock breaking. By varying kerf depth and width under different water jet parameters and performing disc cutter rock breaking tests on rock surfaces with no kerf, single kerf, and double kerfs, the effects of different kerf depths on the disc cutter rock breaking process, load, and efficiency were examined. The test results showed that high-pressure water jets can generate the regular kerfs required for the coupled disc cutter rock breaking of granite. Employing the coupled rock breaking method also resulted in a decrease in specific energy and an approximately 40% decrease in the normal force of the disc cutter, thereby significantly improving rock breaking efficiency. These results provide key technical parameters for the design and manufacture of high-pressure water jet-assisted rock-breaking TBMs and serves as a reference for similar processes.

As a new type of drilling method, with adding a certain proportion of steel particles into high-pressure pipe, high-velocity particle is formed to impact on rock surface to produce very large rock-breaking stress and achieve to drill rapidly. Therefore, based on cavity expansion theory, firstly, mathematical model of stress of particle impact rock was established, and the stress distribution of rock-breaking was numerical calculated. Then, the dynamical rock-breaking process under particle impact was simulated, and simulation results were compared with numerical calculation results. The results showed that there was a good agreement with each other, and rock-breaking stress could increase with increase of particle impact velocity. It would be of great significance to the development and improvement of particle impact drilling theory.

The study of bit-rock interaction model is essential to describe the rock breaking process. In practice, it is difficult to get downhole measurement, and the downhole rock-breaking data is difficult to obtain. Therefore, this paper uses finite element simulation to obtain the kinetic data of bit-rock interaction, based on the analysis and comparison of existing models, an effective analysis method is provided for bit-rock interaction. Firstly, by using the Drucker-Prager rock criterion, actual bit and rock parameters, we develop the finite element bit-rock interaction experiments, and we obtain the data of rotating speed, rate-of- penetration, weight-on-bit. Then, based on multiple nonlinear regression method, we identify the existing Young model, Jorden and Shirley model, Richard model, Ritto model parameters. Through the analysis and comparison of identification effects and characteristics of each model, we obtain the relationship among parameters of the bit-rock interaction.

Microwave-induced rock fracture is one of the promising approaches of achieving non-blasting continuous mining and assisted mechanical rock breaking. It is of great theoretical and practical significance to study the temperature effect and fracture characteristics of rocks of different sizes under microwave heating, however, there are few studies in this field. Microwave heating of &phi, 50 &times, 100 mm, &phi, 50 mm, and &phi, 25 mm sandstone samples with different heating powers and times was performed to measure the temperature of the sample, the microwave energy absorbed, the mass, and the P-wave velocity before and after heating. The results show suppress that (i) under the same heating conditions, the mass difference and the temperature increase range of &phi, 100 mm and &phi, 50 mm samples are larger than that of the &phi, 25 mm samples, (ii) the wave velocity change rate and the damage factor of samples increase with the increase of heating power and time, (iii) different size specimens have different crack- propagation modes. The main crack of &phi, 100 mm specimens usually starts from the middle of the height of the specimen, for the &phi, 50 mm specimens, it usually starts from the middle or bottom-end surface of the specimen height, the main crack of &phi, 25 mm specimens starts from the vertical surface of the specimen. With an increase in the heating time, the length and width of the main crack continuously increase and secondary cracks are generated. The fracture mode of the sample is also related to the size of the sample. The fracture mode can be divided into three parts: melt fracture, thermal-expansion fracture, and secondary thermal-expansion fracture. The relationship between the sample temperature and the absorbed microwave energy is approximately linear.

Particle jet impact drilling technology is an efficient method which mainly uses high-velocity particles to break rock. As the important criterion for evaluating rock-breaking effect, rock-breaking depth and damage area were studied in this paper. Firstly, a particle jet impact rock-breaking test device was developed, and laboratory experiments have been carried out. Then, based on the spherical cavity expansion theory, the mathematical model of rock-breaking depth and damage area under particle jet impact was established. Afterward, the effect of water-jet impact velocity, impact angle, and particle diameter on rock-breaking depth and damage area was analyzed by comparing experimental results and mathematical calculation. The results show that rock-breaking depth and damage area would increase with increase of water-jet impact velocity and decrease slightly with increase of particle diameter. And the combination of 8° and 20° is recommended for nozzle layout. The experimental results and mathematical calculation are basically consistent, which could verify the correctness of the mathematical model. The study has significance for development and application of particle jet impact rock-breaking technology and perfection of theoretical research.

The rock-breaking characteristics and the influence factors of laser perforation are investigated in this study. A series of fiber laser perforation experiments on basalt, sandstone, and granite were conducted. Experimental measurements of rock failure morphologies and composition tests showed that the main surface features are thermal cracks and glazed layer formed by the melting and condensing of rock in laser perforation. It is also found that higher quartz content could help reduce the glazed degree of rock. Comprehensive results showed that the laser rock perforation is mainly formed by thermal fractures, the decline of molten pool, and the evaporating and splashing of the special melted rock components. The depth of rock perforation and SE usually increase with the laser irradiation time, while the ROP gradually decreases. With the increase of laser power, the perforation depth and ROP gradually increase, while the SE initially decreases and then increases indicating that there is an optimal power that maximizes perforation efficiency. It is believed that the strength of rock is the main factor affecting laser perforation efficiency, and the lower rock strength resulted in deeper perforation depth, higher ROP, and lower SE.

Directional rupture is one of the most important and common problems in rock breaking engineering. The purpose of directional rock breaking can be effectively realized by using multihole linear codirectional hydraulic fracturing. In this paper, realistic failure process analysis (RFPA) software is used to verify the experimental results of multihole linear codirectional hydraulic fracturing and investigate its basic law. The following results are demonstrated: (1) RFPA software can be very helpful to study the basic law of multihole linear codirectional hydraulic fracturing; (2) the process of multihole linear codirectional hydraulic fracturing can be divided into four stages: water injection boost, fracture initiation, stable fracture propagation, and fracture connection; and (3) multihole linear codirectional hydraulic fractures propagate along the direction of borehole distribution. Multihole codirectional hydraulic fracturing is influenced by the angle between the direction of the hole distribution and maximum principal stress, the difference of the principal stress, and the spacing of the boreholes. The smaller the angle, the difference value of the principal stress, and the hole spacing, the better the multihole codirectional hydraulic fracturing effect.

The rock cutting process with a circular sawblade and the rock breaking mechanism of rock are studied with a numerical simulation method in this paper. The influence of cutting parameters of the circular sawblade on cutting force, rock damage, and specific cutting energy in the process of circular sawblade cutting rock is researched. The cutting force increases with the feed speed and an increase in cutting depth and decline in rotation speed. Cutting rock with double circular sawblades can reduce cutting force. However, the specific cutting energy declines with the increase in cutting depth and the decline in the distance between the double circular sawblades. Cutting parameters have a great influence on the damage range of rock. The research results can be applied to rock processing with a circular sawblade.

The new method of rock breaking based on the combination of circular sawblade and conical pick was proposed to improve the effectiveness of hard rock breaking. The numerical simulation method was applied to research the conical pick cutting arc rock plate by ANSYS/LS-DYNA. The conical pick cutting arc rock plate numerical simulation model was established to research the influence of arc rock plate structural parameters and cutting parameters on cracks formation and propagation of the arc rock plate and the cutting force in the process of conical pick cutting arc rock plate. The amount of cracks is positively correlated with arc rock plate thickness, the cutting speed, and distance of cutting point to arc rock plate central axis and negatively correlated with the cutting angle. The mean peak cutting force is positively correlated with the thickness of arc rock plate and the distance of cutting point to arc rock plate central axis; however, it is negatively correlated with the arc rock plate height and width and cutting angle of conical pick. The simulation results can be used to predict the conical pick work performance with various cutting parameters and structural parameters.

The authors express their gratitude to V.P. Teplyi, Chief Project Designer at the Department of Vibropneumatic Transport Systems and Complexes of Institute of Geotechnical Mechanics named after M.S. Polyakov of the National Academy of Sciences of Ukraine, and S.V. Shniakin, Chief Engineer at the Department of Vibropneumatic Transport Systems and Complexes of Institute of Geotechnical Mechanics named after M.S. Polyakov of the National Academy of Sciences of Ukraine, for their valuable help during the experimental studies. The authors are also grateful to L.T. Kholiavchenko, Candidate of Technical Sciences (Ph.D), Senior Researcher at the Department of Rock Breaking Problems of Institute of Geotechnical Mechanics named after M.S. Polyakov of the National Academy of Sciences of Ukraine, for his valuable guidelines and comments relating to the experimental studies.

Extensive and detailed investigations have been made to better understand the rock-breaking mechanism of the tunnel boring machine (TBM) disc cutter, but the crack propagation and failure modes induced by the disc cutter when the confining stresses and joint characteristics vary have not been comprehensively investigated. To address this area of research, a triaxial testing machine (TRW-3000) is modified to investigate the effect of different confining stresses (0, 2.5, 5, 7.5 and 10 MPa) on the rock breaking of different joint angles (0°, 30°, 60°, and 90°) induced by the disc cutter. In this series of tests, the crack propagation and failure modes of the intact and jointed rock with different confining stresses are analysed. During the experiments, four different types of failure modes have been observed. The failure mode is affected by the joint orientation at low confining stress. The existence of joints has no obvious effect on the failure mode when the confining stress increases to a certain extent.

Hydrothermal jet spallation drilling (HJSD) is a new drilling method suitable for drilling deep wells in hard rock formations. The characteristics of HJSD are that the rock surface is impinged by a high-velocity hydrothermal jet, causing rock breaking into small spalls. In this study, we develop an analytical model to evaluate the heating conditions (surface temperature and surface heat flux) in HJSD, in which the effect of jet impact on the heating conditions is first considered. Meanwhile, we conduct thermal spallation experiment using sandstone and granite samples. After that, the effects of jet impact on the heating conditions are investigated. Furthermore, the impacts of all physical parameters on the heating conditions are compared to clarify the key factors. Additionally, we compare the rate of penetration and heating conditions between sandstone and granite, which can provide direct understanding about the suitability of HJSD for sandstone and granite. Our study provides a further understanding of critical physic affecting the rate of penetration and heating conditions in HJSD.

A liquid carbon dioxide blasting experiment was carried out under free field conditions, alongside a liquid carbon dioxide rock breaking experiment, to investigate explosion pressure variation and rock breaking characteristics under liquid carbon dioxide blasting. The experimental results show that the internal and external explosion pressures of the liquid carbon dioxide fracturing devices all rapidly increased at first, before attenuating vibrantly after blasting. When the explosion pressure was raised, the internal explosion pressure increased first exponentially and then linearly, while the external explosion pressure increased exponentially throughout. The duration time of the blasting effect stage was about 45 ms. Under the combined effect of jet impingement and a gas wedge of high-pressure carbon dioxide, the rock is subjected to tensile failure. The impact failure and the “gas wedge effect” of high-pressure carbon dioxide play a key role in the rock breaking of liquid carbon dioxide blasting technology.

Microscopic damage and macroscopic fragmentation are induced in rocks when they are impacted by water jets. A combination of macroscopic and microscopic methods was developed into an effective way of revealing the mechanism underlying rock breaking. Based on Computed Tomography (CT) and digital image processing, this paper proposes a quantitative approach to study the microscopic damage induced by water jets on coal. 3D reconstructions of induced damage filed were established by segmenting the greyscale slices. Relying on the established 3D reconstructions, the distributions of the induced damage in the horizontal and vertical directions were discussed. The results show that the distribution range of microscopic damage induced by pure water jets was significantly larger than that induced by abrasive jets due to different erosion mechanisms. Furthermore, the damage induced by both pure water jets and abrasive jets decreased as the punching depth increased, which resulted from the energy consumption caused by the resistance of the mixture composed of the initial arrival liquid and the coal debris.

Delay blasting with relatively long-delay intervals is widely used in mining engineering since the former detonated blast-holes can produce new free surfaces for the later detonated blast-holes. With the application of electronic detonators, which have a minimum delay and a delay accuracy of 1 ms, a new blasting pattern using short-delay intervals is proposed in the present study in order to improve rock breaking and control blast-induced vibrations in cutting blasting with single free surface in underground mines. Theoretical analyses are firstly conducted to investigate the mechanisms of blasting crater formation and vibration reduction of short-delay blasting. Then a series of blasting crater tests with different delay intervals are performed to compare the characteristics of blasting craters and blast-induced vibrations produced by short-delay and simultaneous blastings. The results of crater sizes show that it is possible to form a common blasting crater only when the delay intervals are shorter than the formation time of a new free surface. It is also found that the short-delay blasting can effectively reduce PPV compared with the simultaneous blasting, particularly in the near-field. Spectral analysis indicates that there is less energy in the low-frequency content in short-delay blasting than simultaneous blasting. The possibility and feasibility of reducing vibration via short-delay blasting in underground mines are also discussed in this study.

In order to solve the problems of low rate of penetration (ROP) and short service life of the bit drilling in hard formation, and further improve the performance of conventional hybrid bit, a hybrid bit, disc-like hybrid bit (DLHB) is put forward. The hybrid bit has the advantages of conventional Polycrystalline Diamond Compact (PDC) bit and disc-like roller bit. With analysis on the structural characteristics and rock-breaking mechanism of DLHB, comparison experiments on DLHB and conventional hybrid bit are conducted. The results show that pre-fracturing of the disc inserts is quite significant. The circumferential coverage of the grooved craters produced by disc insert-rows is 40% higher than conventional teeth-rows, and the dynamic load factor is much lower. Besides, ROP of DLHB is 30% higher and weight on bit (WOB) fluctuation is 15%–25% lower than the conventional one in hard formation. DLHB can make the PDC cutters and bearings more durable and it has longer service life compared with conventional hybrid bit.