Search

The cavitation cloud impingement of the jet in the rock breaking process was experimentally investigated to reveal the jet erosion mechanism in drilling of petroleum exploitation. Serial erosion tests and flow visualization were performed, where the cavitation cloud motion in the erosion crater was obtained with the designed transparent specimen. Various erosion patterns were identified in the whole erosion process based on the eroded specimen topography. The shallow eroded crater with a shrinking erosion area is generated by the combination of impinging and scattering cavitation clouds. The increase of ld promotes the development of cavitation cloud σc but reduces the impingement frequency fd, suggesting that the jet aggressive ability is enhanced when the balance between σc and fd is reached. The cavitation cloud motion in the erosion crater was investigated with the transparent specimen. The erosion in the crater at shorter exposure periods Te is generated by the combination of impingement and restricted scattering of cavitation clouds. With the continuous development of the erosion damage, the jet's aggressive ability is diminished due to the erosion expansion on sandstone, where the cavitation clouds impinge on the target and then collapse and vanish without restricted scattering. [ABSTRACT FROM AUTHOR]

In this paper, a discontinuous rock breaking method under combined action of impact and splitting is presented. A dynamic model of rock splitting was established to study the fracture law of rock under impact pressure, with granite as the medium. Firstly, a numerical simulation of the rock splitting under static pressure was conducted. The applicability of the dynamic model was verified by comparison with the experimental results. On this basis, the numerical simulations of rock impact splitting with single frequency and multi frequency were carried out by different loading modes. The stress and damage, crack, splitting force and element failure were analyzed by comparing with static pressure splitting, and the "failure abrupt point", which can be used as a direct evaluation index of rock impact splitting effect, was proposed. The results indicate that the rock can be completely broken only when the loading pressure reaches 3 MPa in the case of static pressure, while just 1.8 MPa for impact splitting. The required pressure of rock breaking by impact splitting is 60% of that by static pressure splitting, which greatly reduces the requirement on pressure. For single frequency impact splitting, frequency 35 Hz and 25 Hz have the best rock breaking effect, and 40 Hz has a better cracking effect. For multi frequency, the alternating frequency of 30 Hz and 40 Hz has the best effect. [ABSTRACT FROM AUTHOR]

In this research, the finite-element numerical software COMSOL Multiphysics is used to simulate the electric pulse rock-breaking process, and the novel numerical model takes into account the multiple fields of electrical, thermal, and mechanical physics. The electric field strength inside the rock under the action of the electric pulse is updated by the full coupling function of COMSOL (version 6.1) software, and the electric damage variable χ is used to describe the process of electric breakdown inside the rock, to simulate the formation of plasma channel in the process of electric pulse rock-breaking. The voltage change curves and plasma channel trajectories in the electric breakdown process of the model in this paper are compared with the literature to verify the accuracy of the model. The formation process of plasma channels captures the temperature and stress changes during the whole process of electric pulse rock-breaking, to reveal the mechanism of the electric pulse rock-breaking process. With the presence of conductive particles inside the rock, the particles can effectively promote the formation of plasma channels, increase the area of electrical damage, and improve rock-breaking efficiency. Before the formation of the plasma channel, the internal temperature of the rock is about 600 K, and the stress is about 10−2 MPa; when the channel is formed, the energy of the electric pulse is mainly concentrated in the plasma channel, and the temperature of the plasma channel rises to 104 K. When the maximum stress exceeds the critical stress of the rock, the rock undergoes fracture. Furthermore, an appropriate increase in the rise time of the electric pulse increases the speed and area of rock-breaking, subsequently improving the efficiency of rock fracture. The results of the numerical modeling in this paper help to better understand the mechanism of the electric pulse rock-breaking process, which is of great engineering significance for the development of new electric pulse rock-breaking technology in the realm of geotechnical engineering. [ABSTRACT FROM AUTHOR]

Rock macro-indentation plays a fundamental role in mechanical rock breaking for various rock engineering application, such as drilling, tunneling, cutting, and sawing. Over the past decades, extensive research has been conducted to understand the indentation mechanisms and responses through various approaches. This review aims to provide an overview of the current status and recent advancements in theories, experiments, numerical simulations, and applications of macro-indentation in rock engineering. It starts with elaborating on the mechanisms of macro-indentation, followed by a discussion of the merits and limitations of commonly used models. Influence factors and their effects on indentation test results are then summarized. Various numerical simulation methods for rock macro-indentation are highlighted, along with their advantages and disadvantages. Subsequently, the applications of indentation tests and indentation indices in characterizing rock properties are explored. It reveals that compression-tension, compression-shear, and composite models are widely employed in rock macro-indentation. While the compression-tension model is straightforward to use, it may overlook the anisotropic properties of rocks. On the other hand, the composite model provides a more comprehensive description of rock indentation but requires complex calculations. Additionally, factors, such as indentation rate, indenter geometry, rock type, specimen size, and confining pressure, can significantly influence the indentation results. Simulation methods for macro-indentation encompass continuous medium, discontinuous medium, and continuous-discontinuous medium methods, with selection based on their differences in principle. Furthermore, rock macro-indentation can be practically applied to mining engineering, tunneling engineering, and petroleum drilling engineering. Indentation indices serve as valuable tools for characterizing rock strength, brittleness, and drillability. This review sheds light on the development of rock macro-indentation and its extensive application in engineering practice. Specialists in the field can gain a comprehensive understanding of the indentation process and its potential in various rock engineering endeavors.

Copyright of China Petroleum Machinery is the property of China Petroleum Machinery Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Pulsed water jet technology has broad application prospects in the field of rock breaking. The pressurized pulsed water jet (PPWJ) is a new type of pulsed jet that offers high-amplitude pressurization, variable pulse pressure and frequency, and a high energy usage rate. To achieve a more destructive and powerful pulsed water jet, a dynamic simulation model of the device was established by using the AMESim software (v1400) based on the operational principle of PPWJs, and the simulation model was validated against the experimental results. The relationships between the key structural parameters of the PPWJ device and the pulse parameters were quantitatively investigated. The pulse pressure and frequency can be increased by appropriately increasing the nozzle diameter or boost ratio, and the pulse pressure will drop if the nozzle diameter or boost ratio exceeds a threshold value. Increasing the maximum displacement or action area of the piston will increase pulse length while decreasing pulse frequency; a proper match of the maximum displacement or action area of the piston will assure pulse peak pressure. The maximum outer diameter of the piston only affects the pulse frequency. The key structural parameters of the device were optimized on that foundation. Compared to the original device, the optimized device resulted in an increase in pulse frequency and jet output energy, leading to larger diameter and volume of erosion pits at the same stand-off distance and erosion time. The findings of this study offer valuable scientific insights for achieving efficient rock breaking with PPWJ. [ABSTRACT FROM AUTHOR]

The vibration of rock breaking in tunnel excavation may cause serious damage to nearby buildings if it is not controlled properly. With reference to a hard rock tunnel in China, the vibration response to the high-pressure gas expansion method (HPGEM), an emerging rock-breaking approach, was investigated with field tests, theoretical derivations, and numerical simulations, then comparisons with the traditional dynamite blast were performed. Firstly, the vibration velocity prediction formulas of the two methods were fitted based on the field tests. Subsequently, the accuracy of the formula was verified by numerical simulation, and the vibration attenuation law of the HPGEM was explored. Comparisons were made between the blast and HPGEM, particularly the differences in peak particle velocity (PPV) for different agent qualities, distance from the blasting center, and engineering conditions. Furthermore, this study also analyzed the relationship between the agent qualities and the rock-breaking volume under different cases, finding that the HPGEM has slight vibration and good rock-breaking effect. The HPGEM is thus fully capable of replacing dynamite blasting to carry out rock-breaking operations in certain special areas. [ABSTRACT FROM AUTHOR]

Abstract Disc cutters are essential for full-section hard-rock tunnel boring machines. The performance of these devices directly affects tunnel engineering costs and duration. This paper proposes a sinusoidal variable cross-section (VCS) cutter ring and design method and establishes a digital model. Rock-like materials are simulated with a finite element model, and the model validity is verified via rock simulation mechanics tests. A disc cutter rolling rock simulation model for a linear cutting machine is also established, and simulation tests are performed for single- and three-cutter rolling using sinusoidal VCSs and constant cross-section (CCS) cutter models, respectively. The stress and energy changes for the cutters and rock-like material damage area were compared via simulation, confirming that some sinusoidal VCS cutter rings do less work on rock-like materials and cause larger crushing areas under the same engineering parameters; therefore, these cutter rings have smaller specific energies. The sinusoidal VCS cutter ring performance is 7% greater than that of CCS on average under single-cutter simulation, and the intermediate cutter performance of the intermediate cutter is 9% greater than that of CCS on average under three-cutter simulation. Thus, sinusoidal VCS cutter rings offer improved rock damage performance, and further research and application of this technology will improve the working efficiency of tunnel boring machines.

With the gradual implementation of China’s deep-earth engineering strategy, deep resource extraction and underground space construction have brought in some new opportunities, but they also face many challenges, with extreme geological conditions such as high geopathic stresses, high ground temperatures and hard rock bodies popping up all the time. Rock breaking technology is the main engineering activity for all resource extraction and underground space construction, and it is the main factor determining the construction process and engineering efficiency. Under extreme geological conditions, tool-based rock breaking technology has become a key technical bottleneck to affect the smooth implementation of deep-earth engineering strategy due to fast tool wear and low rock breaking efficiency. In order to solve the problem of high-efficiency rock breaking in deep-earth and to guarantee the smooth implementation of deep-earth engineering strategy, there is an urgent need for a revolutionary rock breaking technology. As an important supplement to the tool-based breaking technology, the non-tool rock breaking technology is a feasible solution to break through the bottleneck of the tool-based breaking technology. To this end, the non-tool rock breaking technology is summarized into three types of technological systems, namely, impact rock breaking, thermal stress rock breaking and erosion and abrasion rock breaking. Sixteen types of rock breaking technologies, such as water jets, lasers and abrasive air jets, etc., are systematically analyzed. Also, the history of the development of each technology and their technical principles are summarized, and the advantages of the rock breaking and the technological bottlenecks are analyzed. It is concluded that the main reasons why the current non-tool rock-breaking technologies are not widely used in resource extraction and underground space construction are high energy consumption, poor adoptability and complex technical equipment. Compared with tool-based breaking, non-tool breaking technology has a lower energy utilization rate for breaking rock. The specific energy consumption of water jet breaking is 40−70 times that of a tool breaking. Microwave, laser and plasma technologies require high-standard operation environment and cannot be applied in drilling, tunneling and other restricted and harsh environments. In order to solve the problem of rock breaking in extreme geological conditions, the idea of synergistic rock breaking by multiple non-tool rock breaking technologies is proposed, giving full play to the technological advantages of each non-tool rock breaking technology. The rock breaking concept of unloading high geo-stress by jet slit and breaking hard rock by particle impact volume is constructed to minimize the energy consumption of rock breaking, simplify the system equipment, and provide a theoretical support for the development of non-tool rock breaking technology.

In order to effectively improve the drilling speed in deep hard rock and save drilling costs, this study explores the transformation mechanism and critical velocity range of ultra-high-speed diamond drilling technology on rock breaking effect, using marble as an example. The study establishes an ultra-high-speed single diamond fragmentation model using the finite element method (FEM) and solves for the unknown critical velocity of marble in this drilling technique. Additionally, small diameter bit drilling experiments were conducted on our self-developed ultra-high-speed diamond drilling test bench. Based on existing simulation results and experimental studies, we discuss the critical velocity problem and compare and analyze the change in the rock-breaking mechanism and mechanical specific energy (MSE) under conventional drilling versus ultra-high-speed rotary drilling conditions. Our results indicate that changes in rock breaking mechanisms under ultra-high-speed diamond drilling conditions are limited to a specific speed range and do not persist with increasing speeds. Furthermore, experimental verification confirms that ultra-high-speed diamond drilling can effectively reduce MSE and increase the rate of penetration (ROP) by altering the rock-breaking mode. It is hoped that these findings will provide valuable insights for applying this technology to various hard rocks. [ABSTRACT FROM AUTHOR]

In this article, authors attempt to estimate the volume of rock pieces using the laser scanning technique supported by measurements from the RGB camera. Laboratory tests were performed, based on which the error in estimating the size of the fragments was determined based on the available perspectives. With a known estimation error, the volume of the ore chunks was estimated based on data from a single perspective. The presented methodology makes it possible to determine a unital numerical measure to compare Hydraulic Breaker Hammers (HBH) and Lekatech Electric Hammer (LEH) by estimating the energy consumption determined through electric current measurements. [ABSTRACT FROM AUTHOR]

In recent years, mining automation has received significant attention as a critical focus area. Rock breaking robots are commonly used equipment in the mining industry, and their automation requires an accurate and fast visual perception system. Currently, rock detection and determination of rock breaking surfaces heavily rely on operator experience. To address this, this paper leverages multi-sensor fusion techniques, specifically camera and lidar fusion, as the perception system for the rock breaking robot. The advanced PP-YOLO series algorithm is employed for 2D detection, enabling the generation of specific detection results based on the breaking requirements. Furthermore, 3D reconstruction of rocks detected in the 2D area is performed using point cloud data. The extraction of rock breaking surfaces is achieved through point cloud segmentation and statistical filtering methods. Experimental results demonstrate a rock detection speed of 13.8 ms and the mAP value of 91.2%. The segmentation accuracy for rock breaking surfaces is 75.46%, with an average recall of 91.08%. The segmentation process takes 73.09 ms, thus meeting the real-time detection and segmentation needs within the specified rock breaking range. This study effectively addresses the limitations associated with single sensor information. [ABSTRACT FROM AUTHOR]

Disk cutters, as the main component of rock fragmentation, are prone to various types of breakages during rock cutting due to the unevenness of rocks in nature, which can affect rock breakage efficiency. This study has numerically simulated stress and strain changes for different rocks under rock breaking using disk cutters. This study has used several behavioral models, including elastic- plastic constitutive, plastic-kinematic, and elastic constitutive models, to analyze stress and strain in rock breakage. The aim was to determine different rocks' strength and deformation ability under the action of TBM disk cutters. In three simulation models, the maximum stress in the elastic model exceeded those of plastic-kinematic and elastic-plastic models by 15.5 and 8.7 times, respectively. The plastic model is very susceptible to deformation and damage. On the other hand, the elastic model requires significant stresses to produce partial strains and releases the stress faster as the disk shear continues. [ABSTRACT FROM AUTHOR]

High-voltage electric pulse(HVEP)drilling has become a new and efficient rock breaking method, which is also the research focus in the field of drilling speed increase. To probe into rock breaking mechanism of high voltage electric pulse, this study establishes a two-dimensional numerical model of multi-physical field coupling electric breakdown of single pair of electrodes. The model reproduces the generation of plasma channels in homogeneous red sandstone from the coupling of current field, electric breakdown field and circuit field. This paper analyzes the effect of electrode pair angle, voltage and electrode spacing on rock electrical breakdown(that is, the formation of plasma channel in rock). The model includes the circuit structure parameters of pulse tool, the occurrence and development of electrical breakdown, and the relationship between electrical breakdown intensity and time. Results indicate that the plasma channel begins to sprout from the partial area near the top of the discharge electrode and develops towards the partial weak dielectric strength. With the voltage value of loading pulse increasing gradually, the time of electrical breakdown decreases gradually; comparatively, the equivalent failure volume of rock model increases gradually, and there is a positive correlation between them. On the precondition that the rock can be electrically broken, increasing the electrode spacing can improve the rock breaking efficiency of high voltage electric pulse. The equivalent failure volume of rock shows significant fluctuations during the gradual increase of electrode inclination angle of discharge electrode, and its extreme value mostly appears in the range of electrode inclination angle of 35°~ 55°. To further promote the industrial application of high-voltage electric pulse rock breaking, this paper proposes a three-dimensional numerical model of multi-physical field coupling dynamic electric breakdown of red sandstone based on two-dimensional model, reproducing the appearance of the fracture crater in the rock during the rock breaking process with electrode bit. At the same time, the self-designed coaxial electrode bit is selected for experiments of electric breakdown, and the laboratory experimental results of electric breakdown confirm the simulation experimental results.

Pulsed water jet technology has broad application prospects in the field of rock breaking. The pressurized pulsed water jet (PPWJ) is a new type of pulsed jet that offers high-amplitude pressurization, variable pulse pressure and frequency, and a high energy usage rate. To achieve a more destructive and powerful pulsed water jet, a dynamic simulation model of the device was established by using the AMESim software (v1400) based on the operational principle of PPWJs, and the simulation model was validated against the experimental results. The relationships between the key structural parameters of the PPWJ device and the pulse parameters were quantitatively investigated. The pulse pressure and frequency can be increased by appropriately increasing the nozzle diameter or boost ratio, and the pulse pressure will drop if the nozzle diameter or boost ratio exceeds a threshold value. Increasing the maximum displacement or action area of the piston will increase pulse length while decreasing pulse frequency; a proper match of the maximum displacement or action area of the piston will assure pulse peak pressure. The maximum outer diameter of the piston only affects the pulse frequency. The key structural parameters of the device were optimized on that foundation. Compared to the original device, the optimized device resulted in an increase in pulse frequency and jet output energy, leading to larger diameter and volume of erosion pits at the same stand-off distance and erosion time. The findings of this study offer valuable scientific insights for achieving efficient rock breaking with PPWJ.

The vibration of rock breaking in tunnel excavation may cause serious damage to nearby buildings if it is not controlled properly. With reference to a hard rock tunnel in China, the vibration response to the high-pressure gas expansion method (HPGEM), an emerging rock-breaking approach, was investigated with field tests, theoretical derivations, and numerical simulations, then comparisons with the traditional dynamite blast were performed. Firstly, the vibration velocity prediction formulas of the two methods were fitted based on the field tests. Subsequently, the accuracy of the formula was verified by numerical simulation, and the vibration attenuation law of the HPGEM was explored. Comparisons were made between the blast and HPGEM, particularly the differences in peak particle velocity (PPV) for different agent qualities, distance from the blasting center, and engineering conditions. Furthermore, this study also analyzed the relationship between the agent qualities and the rock-breaking volume under different cases, finding that the HPGEM has slight vibration and good rock-breaking effect. The HPGEM is thus fully capable of replacing dynamite blasting to carry out rock-breaking operations in certain special areas.

To improve the rock breaking ability, cavitating waterjet and abrasive waterjet are combined by using a coaxial low-speed waterjet generated around the periphery of a high-speed abrasive waterjet, and a new type of waterjet called unsubmerged cavitating abrasive waterjet (UCAWJ) is thus produced. The rock breaking performance of UCAWJ was compared with submerged cavitating abrasive waterjet (SCAWJ) and unsubmerged abrasive waterjet (UAWJ) by impinging sandstone specimens. Moreover, the effects of jet pressure, standoff distance, abrasive flow rate and concentration were studied by evaluating the specific energy consumption, and the area, depth, and mass loss of the eroded specimen. The results show that the artificially generated submerged environment in UCAWJ is able to enhance the rock breaking performance under the same operating parameters. Furthermore, the rock breaking performance of UCAWJ is much better at higher jet pressures and smaller standoff distances when compared with UAWJ. The greatest rock breaking ability of UCAWJ appears at jet pressure of 50 MPa and standoff distance of 32 mm, with the mass loss of sandstone increased by 370.6% and the energy dissipation decreased by 75.8%. In addition, under the experimental conditions the optimal abrasive flow rate and concentration are 76.5 mL/min and 3%, respectively.

TBM hob wear is an important factor that affects the TBM tunneling efficiency and construction cost.Different blade types differ in rock breaking efficiency and wear.By analyzing the rock-breaking mechanism of the arc blade wedged hob, this study established the calculation model of hob normal cutting, and analyzed the influence of hob edge angle on normal cutting force.This study then designed three kinds of hobs with different cutter spacing and three types of hobs with different blade for rock breaking tests in laboratory.Results show that the reasonable cutter spacing is 15mm, sharp blade is prone to be worn, the tooth-like blade, which has higher rock breaking efficiency and wear resistance, is better than arc blade.Combined with the actual situation of the project site, a new hob with wedge-shaped blade is developed, which are applied to inclined shaft TBM tunneling at engineering site.Results show that the wear rate of the new wedge-shaped hob is 20 % less than that of the conventional ones, and the service life of former is longer than that of latter.Under the same geological conditions, new wedge-shaped hob can reduce the number of hobs consumption and improve efficiency of tunnelling.The development and application of the new type successfully solved the problems of hob wear and frequent replacement of hobs in the TBM inclined shaft excavation.It can provide technical support for TBM long distance inclined shaft driving, which not only shortened the construction period, but also saved the construction cost.

A high-energy gas rock-breaking material and method suitable for shallow hole blasting has been proposed. The rock-breaking principle and law of high-energy gas were analyzed through laboratory rock-breaking experiments combined with CT scanning and three-dimensional reconstruction technology. The results showed that the specimen after the action of high-energy gas was broken evenly and the energy utilization rate was high. However, with the increase in the dosage, energy would be wasted and the rock would be over-crushed. According to the analysis of the deflagration pressure curve of high-energy powder, the action process of high-energy gas could be roughly divided into four stages: crack initiation, high-speed expansion, low-speed expansion, and pressure reduction. At the same time, the multi-level interaction mechanism of "gas expansion + detonation impact" between high-energy gas and rock mass was proposed. Finally, the superior rock-breaking effect of high-energy gas was verified through engineering application, which provides scientific guidance for the later scheme optimization. Highlights: Propose a high-energy gas rock breaking method applied in the field of shallow hole blasting, which is based on an energetic material. CT scanning technology can accurately describe the internal damage of rock mass. Revealed the multi-level interaction of "gas expansion + detonation impact" between high-energy gases and rock masses. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In recent years, the drilling technology applied to deep and ultra-deep formations has developed rapidly, but the drilling speed for hard formations is low. Therefore, it is very important to study the drilling methods for deep and hard strata. Particle pulsed jet drilling is a new drilling method based on particle jet impact drilling technology and high-pressure pulsed water jet impact drilling technology. In this paper, the mathematical models of the shear layer amplification coefficient and wave velocity are established based on a similar network theory, and the motion equations of a single particle and particle swarm are established according to the motion of particles in a pulsed jet environment. Then, based on the self-designed particle jet impact rock-breaking experimental platform, the numerical simulation results are compared, analyzed, and verified. The results show that the rock-breaking efficiency increases with the increase in the average velocity of the particle pulsed jet. When the average speed exceeds 160 m/s, the rock-breaking efficiency increases significantly. With the increase in the particle concentration, the rock-breaking efficiency of the particle pulsed jet also increases, but there is an optimal value. When the concentration is too high, the impact of particles on the rock is affected by the collision between particles, and the wear of the drill intensifies. This research is helpful for understanding deep-well drilling-speed-increasing technology and promotes the development and engineering applications of particle jet impact drilling theory. [ABSTRACT FROM AUTHOR]

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to effectively improve the drilling speed in deep hard rock and save drilling costs, this study explores the transformation mechanism and critical velocity range of ultra-high-speed diamond drilling technology on rock breaking effect, using marble as an example. The study establishes an ultra-high-speed single diamond fragmentation model using the finite element method (FEM) and solves for the unknown critical velocity of marble in this drilling technique. Additionally, small diameter bit drilling experiments were conducted on our self-developed ultra-high-speed diamond drilling test bench. Based on existing simulation results and experimental studies, we discuss the critical velocity problem and compare and analyze the change in the rock-breaking mechanism and mechanical specific energy (MSE) under conventional drilling versus ultra-high-speed rotary drilling conditions. Our results indicate that changes in rock breaking mechanisms under ultra-high-speed diamond drilling conditions are limited to a specific speed range and do not persist with increasing speeds. Furthermore, experimental verification confirms that ultra-high-speed diamond drilling can effectively reduce MSE and increase the rate of penetration (ROP) by altering the rock-breaking mode. It is hoped that these findings will provide valuable insights for applying this technology to various hard rocks.

The single polycrystalline diamond compact (PDC) cutter test is widely used to investigate the mechanism of rock-breaking. The generated cuttings and cutting force are important indexes reflecting the rock failure process. However, they were treated as two separate parameters in previous publications. In this study, through a series of rock block cutting tests, the relationship between them was investigated to obtain an in-depth understanding of the formation of cuttings. In addition, to validate the standpoints obtained in the aforementioned experiments, rock sheet cutting tests were conducted and the rock failure process was monitored by a high-speed camera frame by frame. The cutting force was recorded with the same sampling rate as the camera. By this design, every sampled point of cutting force can match a picture captured by the camera, which reflects the interaction between the rock and the cutter. The results indicate that the increase in cutting depth results in a transition of rock failure modes. At shallow cutting depth, ductile failure dominates and all the cuttings are produced by the compression of the cutter. The corresponding cutting force fluctuates slightly. However, beyond the critical depth, brittle failure occurs and chunk-like cuttings appear, which leads to a sharp decrease in cutting force. After that, the generation of new surface results in a significant decrease in actual cutting depth, a parameter proposed to reflect the interaction between the rock and the cutter. Consequently, ductile failure dominates again and a slight fluctuation of cutting force can be detected. As the cutter moves to the rock, the actual cutting depth gradually increases, which results in the subsequent generation of chunk-like cuttings. It is accompanied by an obvious cutting force drop. That is, ductile failure and brittle failure, one following another, present at large cutting depth. The transition of rock failure mode can be correlated with the variation of cutting force. Based on the results of this paper, the real-time monitoring of torque may be helpful to determine the efficiency of PDC bits in the downhole. [ABSTRACT FROM AUTHOR]

Diamond bit is an important tool for drilling. In recent years, with the application of new composite materials and the continuous progress in precision machining technology, combined with the continuous innovation of drilling equipment, diamond bits have achieved rapid development. This paper briefly introduces some new progress of efficient rock breaking technology with diamond bit, and puts forward the possible development directions in the future.

In order to measure the variation of temperature and pressure inside rock subjected to pulsed discharge, a device for measuring the temperature and pressure inside rock is designed in this work. The device is composed of an excitation module and a signal module. Based on the analysis of pulsed discharge process, the structure of key components of the device was designed. The experiment of rock breaking by single pulsed discharge was conducted. The peak values of temperature and pressure inside sandstone rock samples of 20 cm*20 cm*20 cm were measured when they were broken at 8 different voltage levels in the range of 2.5 kV–20 kV. It was found that with the increase of voltage level, the temperature and pressure inside the rock were also significantly increased when the rock was broken. At the maximum 20 kV voltage, the temperature peak inside the rock is 398 °C and the pressure peak is 2.4 MPa. The temperature and pressure inside the rock rose dramatically as it broke. This device can monitor temperature and pressure inside rock during the rock breaking process, and its embedded computer can construct time-varying temperature field and pressure field with transmitted temperature and pressure signals. This technically supports theoretical research on rock breaking by pulsed discharge.

A cutter ring is a consumable tool used by a tunnel boring machine (TBM) to break rock, affecting the cost and time limit of tunnel engineering. In this paper, based on the working principle of the cutter ring, the failure form of cutter rings, and the mechanical properties of rock, a variable cross-section (VCS) cutter ring is optimized based on the existing constant cross-section (CCS) cutter ring. The finite element method was used to model the Beishan granite, and the mechanical properties of the granite were simulated. The average discrepancy rate of the four key parameters was 1.19% compared with the experimental results. The linear rock cutting experiment of the disc cutter in Beijing University of Technology was simulated, the simulation results of normal force are similar to the reality. The digital models of the 20-in CCS cutter ring and 30 types of VCS cutter rings are established, and modal, impact response, and cutting rock simulations are conducted. The results demonstrate that the natural frequencies of the two types of cutter rings are very close to 6.72 rad/s, confirming the feasibility of interchange. The impact resistance of most of the 30 VCS rings is higher than that of CCS rings, and the rock-breaking effect of all VCS rings outperforms that of the CCS rings. The VCS ring with the highest crushing adaptability of the rock model in this simulation experiment was obtained by statistical analysis of 3D data. This experimental method of rock adaptability can obtain the optimal design parameters of VCS cutter rings for a particular rock model. VCS cutter rings have the potential to support establishing a tool selection system with rock adaptability based on extensive experimental data in the future. Highlights: According to the working principle, failure mode of TBM disk cutter and rock characteristics, a variable cross-section (VCS) disk cutter is designed. The simulation model of linear rock cutting is established according to the real experiment, and the validity of the simulation model is verified. The impact resistance and damaged rock performance of 30 kinds of VCS cutter rings were ranked using a statistical analysis method with 3D data. [ABSTRACT FROM AUTHOR]

During hard rock excavation in the process of tunnel construction, the hard rock excavator wears seriously and quickly and reduces its excavation efficiency. Aiming at this problem, this paper proposes a composite rock breaking method by impact rolling and cutting as a solution. In this paper, the composite rock breaking characteristics of impact hob are studied. The impact cutting load of the hob was analyzed, and the hobbing force equation and the rock crushing volume equation were established. The effects of different impact frequencies and impact loads on the cutting force and rock crushing characteristics of the hob were analyzed by experiments. The results show that under a certain thrust and hob spacing, with the increase of the impact frequency, the rock ridge between the two hobs gradually decreases, while the crushed volume of the rock increases gradually. Under the same axial load and cutter spacing conditions, with the increase of the impact frequency, the hob shear force decreases significantly. Under a certain axial load and impact frequency, with the increase of impact load, the crushing volume of rock and the hob shear force decrease significantly. These test results are of great significance for guiding the efficient excavation of hard rock tunnels. [ABSTRACT FROM AUTHOR]

Rock breaking under impact load has a wide application prospect in hard‐rock roadway excavation because of its environmental protection and strong rock‐breaking ability, but the key factors affecting the rock‐breaking effect are not clear enough. Based on a percussive penetration experimental system (PHPB) into rock by combining the Hopkinson Pressure Bar and a detachable indenter, the effects of impact velocity, waveform and rock strength on the force‐penetration curves, percussive efficiency, and crushing work ratio are studied by model simplification, experimental analysis, and theoretical verification. The results show that the peak percussive force and percussive depth are linearly related to the impact velocity; the penetrative coefficient and crushing work ratio are decayed exponentially with the increase of the thickness‐width ratio of the specimens; the rectangular wave can significantly improve the penetration efficiency; the newly established shear‐tensile model with a double‐V structure can accurately predict each stage of rock breaking, which is consistent with the experimental results. The conclusions can be used to speed up the project progress in mechanical excavation of hard‐rock roadway. Highlights: The PHPB system is established to replace rock breaking by a hydraulic breaker.The shear‐tensile breaking model is proposed to predict each stage of rock breaking.The theoretical analysis in the paper can explain the experimental results well. [ABSTRACT FROM AUTHOR]

The exploitation of deep resources and energy needs to break hard rock. Aiming at the problem of deep hard rock fragmentation, this paper proposes a variable cross-section squeezing pulsed water jet technology (SPWJ). SPWJ was generated under pump pressures of 5.2, 6.8, 8.5, 10, 11.9, and 13.8 MPa to carry out erosion experiments. Features such as rock spalling area, erosion depth, volume loss, and decomposition per unit inlet pressure are used to characterize the erosion performance of SPWJ. The results show that SPWJ can effectively crush granite under low input pressure. Granite crushing modes caused by SPWJ are mainly divided into three types: I: drilling type, II: erosion type, and III: cracking type. Compared with continuous water jet (CWJ), SPWJ has better overall erosion ability than CWJ when the erosion pressure is higher than 60 MPa, the dimensionless target distance is greater than 200, and the erosion time is less than 90 s. In addition, the erosion ability of SPWJ is better than that of CWJ under the condition of unit input pressure. The research results provide a reference for further optimizing the performance of SPWJ crushed granite in the future. [ABSTRACT FROM AUTHOR]

Rock breaking by laser-assisted disc cutters is a novel high-efficiency rock breaking mode that combines mechanical stress induced by the disc cutters with thermal cracking by laser. This paper presented a "step-by-step" simulation modeling concept, and conducted an in-depth study on potential influencing factors of simulation accuracy at each key step. First, the prediction accuracy of laser holes in laser drilling simulation was discussed. Second, the SHPB simulation and experiment were carried out to evaluate the accuracy of the selected material constitutive model in simulating the dynamic fracture damage of rock. Then, taking the laser-assisted rockpenetrating process of the scaled disc cutter as an example, the simulation prediction accuracy of rock-breaking by the disc cutter was analyzed. Finally, the simulation and experiment of laser-assisted disc cutter penetration into rock was carried out, and then the feasibility of the "step-by-step" concept was analyzed. The results show that: (1) in the laser drilling simulation, the predicted accuracy of laser hole size is higher when the power is low; with the laser power increases, the large amount of glass glaze will affect the subsequent modeling accuracy; (2) the HJC model can be used to simulate the transient nonlinear fracture damage behavior of granite; (3) the damage morphology of the granite obtained by the penetration simulation is highly similar to the experimental results, and the load curve should be corrected by the peak point fitting method. The results show the application prospects of the proposed numerical modeling method in future laser-assisted TBM tunnelling. [ABSTRACT FROM AUTHOR]

The development of high-efficiency polycrystalline diamond compact (PDC) bits plays a major role in developing unconventional oil and gas. Thereby, a series of single cutter tests have been conducted in the past few years. However, most of them were performed under atmosphere conditions due to the limitation of the experimental setup. In the present study, a series of single cutter experiments were performed under pressurized conditions, in which both principal stress and hydrostatic pressures were loaded with a self-developed facility. The cutting force, topography of cutting grooves, and mechanical specific energy (MSE) were analyzed to evaluate rock failure efficiency. Furthermore, a theoretical model was developed to study stress evolution. Combined with experimental results, the rock failure mechanism and the effects of bottom hole pressures on rock breaking characteristics were revealed. The results indicate that the increase in principal stress and hydrostatic pressures cause larger cutting forces and reduced rock cutting efficiency. Additionally, a larger hydrostatic pressure will promote the propagation of subsurface cracks, leading to larger roughness of cutting grooves and facilitating the subsequent rock cutting process. In this study, the hydrostatic pressure has the greatest impact on rock failure process, followed by the principal stress when parallel to the cutting direction. Comparing the experimental and simulation results, we can find that only a fraction of cutting force is directly utilized in breaking rocks, while the remaining force is applied to overcome the friction induced by the flow of cuttings along the cutter surface. Consequently, measures should be taken to prevent bit balling and decrease the friction force, thus weakening the effects of hydrostatic pressures and improving the efficiency of PDC bits.

With the deepening of drilling depth, the difficulty of drilling engineering increases gradually due to the complex geological conditions. The traditional mechanical drilling method shows the problems of high energy consumption, low efficiency, long cycle and high cost. Because of the characteristics of rock, the high abrasiveness of rock causes great wear to the bit, which becomes an important factor affecting the drilling rate. High voltage electric pulse (Abbreviated as HVEP later in this paper) drilling technology is a new technology developed in the past several decades. The technology uses plasma channel, water jet or shock wave generated by high voltage electric pulse discharge to break rock. It has the characteristics of environmental protection, directional breaking, easy control of rock breaking process and fast speed in the face of complex hard rock. In this paper, the mechanism and technology of rock breaking by high voltage electric pulse method in deep drilling are studied, and the functional test is carried out. [ABSTRACT FROM AUTHOR]

During the guided drilling process as part of shale gas exploration and development, shale is damaged by a polycrystalline diamond compact (PDC) bit cutter. It is essential to carry out research on rock breaking by a PDC cutter. In this paper, we study the mechanism of shale fragmentation by a PDC cutter based on the discrete element method. Additionally, we consider the effects of bedding angle, bedding thickness, cutting depth and cutting rate on the rock-breaking efficiency of a PDC cutter. The results show the following: (1) With the increase in bedding angle, the number and area of microcracks first increase and then decrease, and the proportion of tension cracks is relatively unchanged; there is no significant change in the morphology of the failure zone, and the average particle size of the cutting fragments first decreases and then increases. (2) With the increase in the bedding thickness, microcracks continue to extend in a horizontal direction, the total number of cracks shows a fluctuated change, and the proportion of tension cracks increases. The failure zone extends in a conical shape in the horizontal direction, and the average size of the cutting fragments gradually increases. (3) With the increase in cutting depth and cutting rate, the number and area of microcracks increase, and the proportion of shear cracks increases; the area of the failure zone increases and the size of the cutting fragment decreases. [ABSTRACT FROM AUTHOR]

TBMs rely on the cutters to directly cut into the rock surface for excavation. The design of the disc cutter parameters can significantly affect the TBM's tunneling performance. In this study, a three-dimensional numerical model of a TBM disc cutter cutting Chongqing sandstone is established by the FEM-CZM coupling method, and verified with laboratory tests. The mechanical characteristics of rock breaking using a disc cutter and rock crack propagation laws were investigated. An orthogonal test was designed to analyze cutter parameter optimization under multiple factors (blade width, blade angle, penetration, and cutting speed). The results show that the force of cutter during the cutting process increases as the blade width and angle increase. Cracks that extend laterally in the rock are more sensitive to the blade angle, and the choice of blade angle needs to be taken into account when designing the cutter spacing. The degree of influence of each factor on rock-breaking efficiency is as follows: penetration > cutting speed > blade angle > blade width. The design of the cutter parameters should give priority to determining the optimum penetration depth, other parameters can be changed to meet the energy consumption and wear requirements of different engineering geologies. [ABSTRACT FROM AUTHOR]

During tunnel boring machine (TBM) construction, the rock breaking effect of the disc cutter in complex formations affects the progress and cost of the entire project. Therefore, it is necessary to better understand the rock breaking mechanism of TBM in complex formations. In this study, matrix discrete element method (MatDEM) software is used to study the rock breaking mechanism of the disc cutter at the interface of soil and rock. Based on the theoretical study and analysis of rock breaking process of the disc cutter in the soil-rock composite formations, the three-dimensional dynamic rock breaking process of the disc cutter in soil-rock formations with different rock dip angles (0°, 15°, 30°, 45°, 60°, 75°) is simulated by using MatDEM, and the simulation results are analyzed from three aspects: the unit force, the fracture number of unit connection, and the system energy. The main conclusions are as follows: when the disc cutter is used to roll and break the rock at the soil-rock interface of composite formations, the unit force and the fracture number of unit connection are positively related to the contact area S of the rock and blade at the front edge of the disc cutter. The energy to break the rock by the disc cutter is mainly affected by the broken rock volume per unit time Vdt. The greater the Vdt is, the more energy the disc cutter needs to break the rock is. The total force P is affected by the contact area S (β, t). The change of the maximum total force is small when β = 15°, 30°, and 45°, and is obviously lower at 60° and 75°, respectively. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to solve the problem of huge consumption of traditional water jet rock breaking resources, it is urgent to develop an efficient and energy-saving jet rock breaking technology in order to achieve the purpose of energy conservation, emission reduction and green sustainable development. Based on the computational fluid dynamics method, the quantitative gas phase was added to the water jet to form the gas-liquid two-phase jet, and its numerical simulation was carried out. The characteristics of the velocity field and pressure field of the gas-liquid two-phase jet were studied, and the effects of gas volume fraction, incident pressure and jet distance on the rock breaking performance parameters of the gas-liquid two-phase jet were analyzed. The results show that the maximum axial velocity of gas-liquid two-phase jet with gas volume fraction of 30% is 288 m/ s, which is more than 19% higher than that of pure water jet. When the jet is ejected from the nozzle, the high-pressure bubble collapse will form a high-speed collapse micro jet, which will improve the jet velocity and jet impact force. With the increase of gas volume fraction, the maximum axial velocity of jet increases, while the stagnation point pressure decreases slightly. With the increase of incident pressure, the maximum axial velocity of jet increases, but the increase decreases gradually. When the jet distance increases to 35 mm, most of the bubbles in the jet collapse near the target surface and produce pulsating impact on the target surface, so that the stagnation point pressure rises to 26 MPa. At this time, the stagnation point pressure is high, the jet diffusion is small, and the rock breaking performance of the jet is good. [ABSTRACT FROM AUTHOR]

Hydraulic impact hammers used for rock breaking play a crucial role in the mining industries, but their operation is complex and inefficient. To address these challenges, this paper investigates the rock breaking process of impact hammers. Utilizing stress wave theory, a mathematical model for impact rock breaking is established, and the size of broken rock is estimated. Subsequently, the DEM-based numerical analysis verifies the reliability of the mathematical model and elucidates the working mechanism of impact rock breaking. Additionally, the study explores the influence of different hammer parameters on the rock breaking performance. The results indicate that the essence of rock breaking lies in the formation of a rock crushed zone and the initiation and growth of cracks under the impact load, with the main macrocrack extending towards the free surface closer to the operating point. Regarding rock breaking efficiency, the impact velocity has a relatively minor influence, while the drill rod diameter shows a positive correlation with efficiency. The drill bit angle significantly affects the rock breaking efficiency and is accompanied by changes in the rock breaking pattern. [Display omitted] • A theoretical model of the rock breaking process under impact is established. • DEM simulation reveals the rock breaking mechanism with impact hammer. • The effect law and significance of operation parameters are obtained. [ABSTRACT FROM AUTHOR]

The exploitation of deep resources and energy needs to break hard rock. Aiming at the problem of deep hard rock fragmentation, this paper proposes a variable cross-section squeezing pulsed water jet technology (SPWJ). SPWJ was generated under pump pressures of 5.2, 6.8, 8.5, 10, 11.9, and 13.8 MPa to carry out erosion experiments. Features such as rock spalling area, erosion depth, volume loss, and decomposition per unit inlet pressure are used to characterize the erosion performance of SPWJ. The results show that SPWJ can effectively crush granite under low input pressure. Granite crushing modes caused by SPWJ are mainly divided into three types: I: drilling type, II: erosion type, and III: cracking type. Compared with continuous water jet (CWJ), SPWJ has better overall erosion ability than CWJ when the erosion pressure is higher than 60 MPa, the dimensionless target distance is greater than 200, and the erosion time is less than 90 s. In addition, the erosion ability of SPWJ is better than that of CWJ under the condition of unit input pressure. The research results provide a reference for further optimizing the performance of SPWJ crushed granite in the future.

The single‐cone bit has become the first choice for slim hole sidetracking and deep well drilling with its unique rock breaking method and high ROP (rate of penetration). The single‐cone bits currently used in the oil field all use cemented carbide inserts, with its main failure mode being of early excessive wear of the cutting teeth. In order to improve the adaptability of single‐cone bits to hard and highly abrasive formations, a single‐cone PDC composite bit is designed. According to the characteristics of the tooth profile, the way of tooth arrangement and the way of contact between the cutting teeth and the rock, the acceleration equation to the cutting teeth of the single‐cone PDC composite bit is established. The shaft inclination angle of the cone, the position and height of the PDC teeth, the radius of the PDC teeth, the lateral rotation angle, and the front inclination angle on the acceleration are studied. The acceleration of the single‐cone bit is verified by numerical simulation and drilling experiment of rock‐breaking. Rock formation properties have an impact on the acceleration of the cutting teeth, with the acceleration of the cutting teeth in hard rock formations being higher than that in soft rock formations. On the premise that the bearing life of the single‐cone bit is allowed, the value of the shaft inclination angle β can be approached to 70°. This research lays a theoretical foundation for the dynamic research and wear analysis of single‐cone PDC composite bit. [ABSTRACT FROM AUTHOR]

The rock breaking efficiency of drill bit is deeply affected with the increase of drilling depth. The increase length of the drill string leads to torsional stiffness decrease, which may even result in the stick-slip phenomena. In order to improve the rock breaking efficiency and reduce the stick-slip, this paper proposed a longitudinal–torsional coupled impactor. The internal working mechanism was carried out by theoretical analysis and experimental test. Moreover, comparing the computation and test results, the following conclusions can be obtained and verified. This innovative design can provide appropriate longitudinal-torsional coupled impact to drill bit during drilling process, and the movement of the hammer and pendulum is periodic. With the increasing flow rate of drilling fluid, this tool can generate corresponding larger impact force, torque and higher impact frequency. The theoretical analysis results are consistent with the experimental test results, which verify the reliability of the innovative design and the accuracy of theoretical analysis. This paper can provide reference for the innovative design of downhole drilling tool, the development of drilling dynamics and the improvement of drilling efficiency especially in the conditions of complex and ultra-deep wells. [ABSTRACT FROM AUTHOR]

The demand for the usage of hydraulic rock breakers in excavating rock masses has increased recently for environmental and economic reasons. The conventional method (i.e., drill and blasting technique) has many restrictions due to environmental aspects. In this paper, we propose a methodology for the prediction of the performance of hydraulic rock breakers in the excavation of a rock mass. The case study area is located in Northwest Egypt on the shoreline of the Mediterranean Sea. Extensive site investigation was implemented using exploration boreholes showing that the majority of the site is limestone with lenses of sands. Based on the collected rock properties, mapping of both the rock quality (RQD) and the uniaxial compressive strength (UCS) for the rock mass was conducted. Such mapping of the mechanical properties helps in the zoning of a rock mass and grouping the similar rock zones of nearly matched properties. Due to economic and machinery availability concerns, this study focuses on very small, small, and medium capacity hydraulic breakers. For each type of rock breaker, calculations of the net breaking rate (NBR) are implemented for each group of the rock with similar properties. The challenge of this methodology is that the excavation of the rock mass shall be implemented in a very limited time frame (only one year ≈ 300 workdays). Therefore, two scenarios of light-duty and medium rock breakers are applied providing the number of machines required with specifications and working days. The first scenario is assigned to medium duty machines, while the second scenario concerns very small to small rock breakers. In general, such a sequence could be adopted for other cases with different rock mass properties, hydraulic breakers specifications and any desired time frame.