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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.

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.

The purpose of this study is to achieve better understanding of associated mechanisms and to recommend and identify new strategies to develop new rock breaking technology for Tunnel Boring Machines (TBMs). Tunnel Boring Machine tunnelling mainly depends upon the rock breakage caused by cutters moving on a rock surface in a rolling and sliding motion while under the action of thrust force. The rock breaking behaviour is controlled by the mechanical interaction between the cutters and the rock. Due to the high hardness and high abrasiveness of rock, the cutters have to work under very high thrust force and suffer heavy‐load‐impact and abrasive wear, causing serious wear and low rock breaking efficiency. Rock‐boring organisms exist in nature, which achieve drilling and/or tunnelling in rocks through a tribochemical interaction. This phenomenon is called bioerosion and the organisms are natural ‘TBMs’ to some degree. In this study, the interaction between TBM cutters and rock is presented, and current measures to improve cutter wear and rock breaking efficiency and their limitations are reported. Then, the connotation, mechanism and typical cases of bioerosion are presented. Finally, inspired by bioerosion, a new chemically assisted rock breaking technology is proposed for TBMs.

Introduction. Pellet impact drilling method which is basically the destruction of rocks by blows of pellets, has been studied by many researchers. Despite this, the rheological properties of the drilling fluid used in pellet impact drilling have not been investigated yet. All bench and field tests were carried out using service water. The use of a drilling fluid with a higher viscosity than water has the potential to expand the field of application of pellet impact drilling. Therefore, it becomes urgent to study the effectiveness of destruction of rocks when using flushing fluids with different rheological parameters. Objective of this research is to investigate the efficiency of rock destruction in the process of drilling wells using the pellet impact drilling method at various rheological parameters of the drilling fluid. Methods of research. A scaled laboratory bench was used in the research. The bench was a closed system of circulation of the drilling fluid (drilling mud). The solution was prepared separately on a high-speed mixer. The main part of the bench was a scaled pellet drill bit located in a simulated well. After the experiment, the destructed rock volume and the rheological parameters of the flushing fluid were measured. A series of experiments was carried out with a gradual increase in the viscosity of the flushing fluid. A biopolymer (xanthan gum) in various concentrations was used to thicken the flushing fluid. Drilling fluid rheological parameters were measured using an eight-speed rotary viscometer and a Marsh funnel. Results. For the first time, a relationship has been established between the efficiency of rock destruction during pellet impact drilling and the rheological parameters of the drilling fluid used. It was found that with an increase in the concentration of biopolymer and an increase in viscosity, at first, there was a significant increase in the volume of drilled rock per unit time, and with a further increase in concentration, a gradual decrease occurs. Conclusions. The results obtained expand the field of application of pellet impact drilling. The reliability of predicting the drilling speed is improved depending on changes in the properties of the drilling fluid. Based on the results, recommendations were made for the selection of the optimal parameters of the drilling fluid, depending on the drilling conditions.

Improving the rock-breaking efficiency of hard rock formation has always been of concern in drilling. Compound impact drilling technology is a new method to achieve efficient crushing of hard rock by exerting axial and torsional impacts on the drilling bit. In this study, to investigate the dynamic rock-breaking process and mechanism under compound impact, a numerical model was developed based on cohesive elements. Dynamic impact tests on sandstone were conducted to verify the effectiveness of the method. Then, the dynamic rock-breaking process under compound impact was simulated using the proposed model. Finally, the effects of impact parameters and cyclic loading on the rock-breaking performance were systematically studied. The results indicate that the stereoscopic crushing effect of rock can be achieved under compound impact. The amount of broken rock increases with the increase in the impact load amplitude and impact loading times, whereas both the impact angle and duration have an optimal range. When the impact angle is 30°, the impact duration is 2.5 ms, the amount of broken rock is maximum. A novel compound impact drilling tool was designed based on the analysis of the rock-breaking mechanism, the laboratory and field tests were carried out and the parameters were optimized.

In order to grasp the rock breaking mechanical characteristics of arc-shaped PDC bit, and guide the optimization design of bit structure, theoretical calculation models of cutting parameters of PDC cutters were established. Taking Φ 94 mm tri-wing arc-shaped PDC bit as an example, theoretical calculation results show that, with the increase of radial distance, the cutting area, cutting arc length and cutting force of cutters approximately increase first and then decrease; the maximum cutting force is concentrated on number 5 and 6 cutters, which makes these two cutters very easy to be damaged in advance. Based on this, a Φ 94 mm four-wing arc-shaped PDC bit was designed, and the maximum cutting force is distributed on number 4, 5, 6 and 7 cutters, also the force value is greatly reduced, which is beneficial to the uniform wear of the cutters. At the same time, numerical simulation and field test were carried out, simulation results are in good agreement with the theoretical calculation results, and the wear conditions of the cutters in the field test are basically consistent with the theoretical and simulation results, which indicate the reliability of the theoretical calculation and the simulation results.

Compound percussive drilling technology is a new method to improve the rock‐breaking efficiency in deep hard formation. In order to study the rock‐breaking mechanism of compound impact drilling, the thermal‐structure coupling simulation of the dynamic rock‐breaking process with a single PDC cutter was investigated by using ABAQUS software. The influence of impact parameters on the rock‐breaking performance and cutting temperature was analyzed. The results proved that the compound impact load changes the rock failure mode and improves the rock‐breaking efficiency. Compared with steady load cutting, the rock broken volume under compound impact increased by 7.5%, and the mechanical specific energy (MSE) decreased by 12.3%. As the axial impact load amplitude increases, the MSE increases gradually. With an increase in torsional impact load amplitude and impact frequency, the MSE decreases first and then increases, and the optimal torsional static load ratio is 0.3, and the optimal impact frequency is 30 Hz. In addition, the cutting temperature of the compound percussive drilling is higher than that of the steady load cutting, and it increases with the impact load amplitude and decreases with the frequency. For the three impact load waveforms—sine, triangle, and square in this paper, the rock‐breaking efficiency under the condition of sine waveform is the largest when the dynamic amplitude of the pulse force is fixed, and the cutting temperature under the condition of square waveform is the highest. Finally, based on the analysis of the rock‐breaking mechanism, a novel compound percussive drilling tool was designed and tested in the field.

Rock breaking technique plays an important role in rock excavation engineering, such as mining, tunnel construction and hydropower engineering. Pneumatic fracturing with carbon dioxide (CO2) ice powder is potentially a safe and efficient rock breaking method, which is one of the most pertinent research topics in rock breaking. A site test of pneumatic rock breaking with CO2 ice powder was carried out on a tuff hill with a compressive strength of 80 MPa. The attenuation of peak particle velocity (PPV) induced by pneumatic rock breaking with CO2 ice powder was studied and the vibration effect on surrounding buildings was evaluated. The research results demonstrate that: (1) the pneumatic rock breaking with CO2 ice powder is greatly affected by quasi-static pressure of high-pressure gas with many macrocracks formed near boreholes; (2) with increase in distance, the PPV decreases in the form of a power function with dominant frequency less than 100 Hz, And when the charge of CO2 ice powder is 4 kg, the PPV reduced down to 21.9 mm/s at the distance of 2.8 m; (3) a simplified motion model of vibration waves propagating in slope is established, showing that the steeper the slope, the faster does the PPV attenuate; and (4) pneumatic rock breaking with CO2 ice powder is safer than traditional liquid CO2 and explosive blasting, and it can significantly improve rock breaking efficiency.

Purpose is to substantiate design factors and technological parameters of next-generation facilities of hydromechanical drilling basing upon the determined features of interaction between breaking pellets and rock mass. Methods. The studies of directionality features and bottomhole processes for rock mass breaking have been carried out using the current analytical methods and laboratory experiments. Among other things, certain mathematical and physical simulation techniques, methods of theoretical processing and interpretation of the research results under SolidWorks, Statgraphics, and Маthсаd environments, and a number of relevant instruments and materials have been applied. Following their technological sequence, the well bottomhole rock-breaking processes were simulated using a special laboratory stand equipped with a control-and-measuring unit (inclusive of a flowmeter, manometer, tachometer, and coordinate spacer among other things). Findings. Application perspectiveness of the combined techniques for rock breaking has been proved. Structural designs of the next-generation facilities for well drilling have been proposed. The pellet-impact drilling features have been analyzed from the viewpoint of its significant dynamic component during the rock mass breaking. Nature of the effect of breaking load rate on the results of bottomhole deformation processes has been identified. Efficiency of the proposed scheme to improve pellet-impact drilling based upon maximum use of a well bottomhole deformed by pellets has been proved. Measures to increase technical and technological indicators of pellet drilling have been considered. Requirements for the conditions stabilizing operation of a collar of the pellet-impact device have been outlined. Further research tendencies have been specified. Originality. It has been determined that compliance with specific geometrical and hydromechanical ratios, corresponding to the stable mode of a well sinking, is the factor required for reliable operation of hydromechanical drilling facilities. Practical implications. The results of stand-based tests as well as analytical studies may become the foundations to develop efficient engineering decision for hydromechanical well drilling with high technical and economic indicators. The data, concerning bottomhole rock breaking processes, are the basic ones to work out rational standard parameters of well sinking processes.

In the process of drilling and coring by the rock-breaking rig, the drill rod is affected by the intermittent impact force, which reduces the efficiency of the rig to break the rock and increases the cost of the drilling and coring. Therefore, it is very important to improve the impact resistance of the drill pipe during the rock-breaking process. To achieve this goal, a flexible design of the drill pipe was carried out, and a dynamical model of the drilling rig based on a series elastic actuator was established. Considering the dynamic performance of the system, a torque feedforward link is introduced and a control model based on the force source is established. The influence of the equivalent inertia of the transmission system and the series elastic actuator damping coefficient on the system stability was analyzed by drawing the frequency domain characteristic curve of the system. By using the control and Simulink simulation software, the electromechanical simulation of the model is carried out, and the torque step tracking response of the system is obtained. A torque feedforward link is introduced to establish the control model of the system based on force source. Through dynamic simulation software ADAMS, dynamic and static impact simulation experiments were carried out on the system. The results show that when a force of 200 N is applied to the output end of the drill pipe in the tangential direction, the maximum moments received by the joint under static and dynamic environments are 34.1 N·m and 57.9 N·m, respectively. When the impact force disappears, the time required for the flexible drill pipe to reach a stable state is only 0.15 s, which verifies that the series elastic actuator–based drill pipe model can alleviate the impact of the external environment and protect the internal structure of the rig.

In order to improve the ROP (rate of penetration) of complex structure and deep wells and reduce the energy consumption of rock breaking during the drilling process, a core drill bit with negative ...

To compare the rock breaking performances caused by the arc and wedge hob with two blades, a rock cutting model with two hob blades is established and a series of rock cutting simulations are performed based on the particle flow code. Meanwhile, the rock breaking process, crack extension pattern, rock cutting force and rock cutting efficiency etc. are investigated in this study. The results present that the rock breaking area and the lateral crack length induced by the arc blades is much greater than that induced by the wedge blades. The optimal cutting spacing of the arc and wedge blades is 60 mm and 30 mm respectively. It confirms that the wedge blades can significantly reduce the rock cutting force and raise the rock cutting efficiency compared with the arc blades, which can provide a reference for the hard rock tunneling by the tunnel boring machine.

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.

This paper presents a new drilling tool with multidirectional and controllable vibrations for enhancing the drilling rate of penetration and reducing the wellbore friction in complex well structure. Based on the structure design, the working mechanism is analyzed in downhole conditions. Then, combined with the impact theory and the drilling process, the theoretical models including the various impact forces are established. Also, to study the downhole performance, the bottom hole assembly dynamics characteristics in new condition are discussed. Moreover, to study the influence of key parameters on the impact force, the parabolic effect of the tool and the rebound of the drill string were considered, and the kinematics and mechanical properties of the new tool under working conditions were calculated. For the importance of the roller as a vibration generator, the displacement trajectory of the roller under different rotating speed and weight on bit was compared and analyzed. The reliable and accuracy of the theoretical model were verified by comparing the calculation results and experimental test results. The results show that the new design can produce a continuous and stable periodic impact. By adjusting the design parameter matching to the working condition, the bottom hole assembly with the new tool can improve the rate of penetration and reduce the wellbore friction or drilling stick-slip with benign vibration. The analysis model can also be used for a similar method or design just by changing the relative parameters. The research and results can provide references for enhancing drilling efficiency and safe production.

Microwave technology is increasingly used in laboratory tests and field applications as an effective rock breaking technique. The underlying mechanism of rock fracturing induced by microwave energy...

As a new tool of hard rock breaking, abrasive slurry jet (ASJ) is of great potential in tunneling and mining. Therefore, this paper presents a new system, shearer drum assisted by ASJ, to exploit thin seam with complex geology, in which coal rock will be broken by the coupled forces of ASJs and cutting picks. Then, an orthogonal experiment is carried out to study the effects of parameters (mass fraction of polymer additives, jet pressure, impact angle, standoff distance, and impact time) on the ASJ ability in rock breaking. Furthermore, a prediction model is established to quantify the rock breaking ability of ASJ with different parameters based on the multivariable linear regression method. Results show that only impact angle has a significant effect on the crushing pit width, and the jet pressure, impact angle, and impact time are the significant effect parameters on the crushing pit depth. The conclusions can provide theoretical and data support for designing the most efficient system of ASJ and shearer drum in thin seam exploiting.

Directional rupture is one of the most important and most common problems related to rock breaking. The goal of directional rock breaking can be effectively achieved via multi-hole linear co-directional hydraulic fracturing. In this paper, the XSite software was utilized to verify the experimental results of multi-hole linear co-directional hydraulic fracturing., and its basic law is studied. The results indicate that the process of multi-hole linear co-directional hydraulic fracturing can be divided into four stages: water injection boost, hydraulic fracture initiation, and the unstable and stable propagation of hydraulic fracture. The stable expansion stage lasts longer and produces more microcracks than the unstable expansion stage. Due to the existence of the borehole-sealing device, the three-dimensional hydraulic fracture first initiates and expands along the axial direction in the bare borehole section, then extends along the axial direction in the non-bare hole section and finally expands along the axial direction in the rock mass without the borehole. The network formed by hydraulic fracture in rock is not a pure plane, but rather a curved spatial surface. The curved spatial surface passes through both the centre of the borehole and the axial direction relative to the borehole. Due to the boundary effect, the curved spatial surface goes toward the plane in which the maximum principal stress occurs. The local ground stress field is changed due to the initiation and propagation of hydraulic fractures. The propagation direction of the fractures between the fracturing boreholes will be deflected. A fracture propagation pressure that is greater than the minimum principle stress and a tension field that is induced in the leading edge of the fracture end, will aid to fracture intersection; as a result, the possibility of connecting the boreholes will increase.

Jet breaking using a high‐pressure nozzle is one solution for breaking natural gas hydrate (NGH) formations, creating a larger breaking volume and fluidizing broken solid fragments. Based on the analysis of various jet breaking mechanisms for the variation of the flow velocity of the internal and outlet sections of different nozzles, a straight‐swirling mixed nozzle (SSMN) was designed. We obtained different jet breaking effects for a single nozzle, including the influences of the working pressure and target distance on the hole shape, as well as working pressure on hole parameters and target distance on hole parameters. In addition, we analyzed the influences of the nozzle number, type of NGH rock, and construction parameters on the rock‐breaking efficiency and selected the best combination mode of multiple nozzles. The research results of the rock‐breaking mechanism and efficiency of the SSMN promotes the development of commercial mining technology for nondiagenetic NGH in deep‐sea shallow areas.

Underground radial drilling technique is a novel hydraulic stimulation technology, which is one of the important ways to realize precise, intelligent, and efficient extraction of the gas resources. There are many factors influencing the hole‐forming effect by water jet, such as nozzle arrangement and so on. Recently, the self‐rotatory multinozzle drilling bit is frequently used to improve the rock‐breaking effect of water jets. In this paper, to study the effects of inclination angle of forward nozzles and standoff distance, the ANSYS FLUENT combined with RNG turbulence model was adopted to analyze the multinozzle jets flow field. The results indicate that the components of axial velocity and tangential velocity of forward nozzle jets are different with inclination angles of forward nozzles. Moreover, there exists an optimal standoff distance of multinozzle drilling bit for rock breaking. Besides, the drilling test was conducted using the self‐developed drilling simulation system to investigate the effect of inclination angle, radial angle, standoff distance, and jet pressure on the rock‐breaking effect of water jet. Based on the rotating characteristic of rotary jet, the asymmetric inclined linear nozzle arrangement was proposed for the multinozzle drilling bit. And the results also show that the drilling bit with three forward nozzles has larger rock‐breaking zone in terms of jetted hole diameter. Besides, the depth of jetted hole decreased, while the hole diameter increased with the inclination angle of forward nozzle.

Rock breaking using conical picks is a complex process affected by several factors; its performance is directly related to the excavation rate of rock tunnels, which is important in terms of the economic benefits and social impact of a project. This study investigates the effects of cutting depth and water pressure on rock breaking performance using a conical pick assisted by an abrasive water jet (AWJ). To measure the weakening effect of the AWJ on rock strength and evaluate the practical application of this approach, further analyses of a secondary cut of rock with a fracture pit and rock breaking economy are included in this study. The results show that a conical pick can efficiently break hard rock when assisted by the strong impact of an AWJ; the cutting resistance and specific energy (SE) decrease with the use of the AWJ. With a fracture pit and surrounding tiny cracks, the cutting resistance during the secondary cut is further reduced and rock fragments become smaller. In addition, with a decrease in cutting depth and an increase in water pressure, the stability of the cutting resistance is improved, reducing conical pick costs resulting from impact fracture and wear. According to the rock breaking economy analysis of the proposed approach, there is an optimal cutting depth under certain conditions that can provide a reference for practical application.

Water-jet drilling (WJD) is an effective method for stimulating, exploring, and developing oil and gas resources. The self-rotatory water-jet bit (SRWJB) is a type of potentially efficient bit appl...

To investigate the matching rules of cutters with different blade widths in hard rock and extremely hard rock environments, this study carries out a full-scale cutting test of 432-mm disc cutters with blade widths of 12 mm, 19 mm and 30 mm. A multifunctional cutter performance experimental system was used to test the cutting loads and rock-breaking quantity of rust stone granite (hereinafter referred to as hard rock) and granite (hereinafter referred to as extremely hard rock) as well as to analyse the specific energy consumption for rock breaking under different cutting parameters. The experimental results show that (1) the blade width has a greater influence on the normal force than on the rolling force. The rock-breaking resistance of the 12-mm-blade-width cutters under extremely hard rock conditions is 36.7% lower than that of conventional cutters. (2) Under the same conditions, the smaller the blade width is, the smaller the specific rock-breaking energy consumption is and the smaller the optimal cutter spacing is. Under extremely hard rock condition, the specific energy consumption of the 12-mm-blade-width cutters is 37.9% lower than that of conventional cutters. (3) With a certain gross thrust of a single cutter, the rock-breaking quantity of a single 12-mm-blade-width cutter is much larger than that of the 19-mm-blade-width cutter, regardless of the types of rock. Under extremely hard rock conditions, the S/P of the 12-mm-blade-width cutter with the highest rock-breaking efficiency is approximately 10–12.

Blasting is an economical technique for rock breaking in hard rock excavation. One of its complex undesired environmental effects is flyrock, which may result in human injuries, fatalities and property damage. Because previously developed techniques for predicting flyrock are having less accuracy, this paper develops a new hybrid intelligent system of extreme learning machine (ELM) optimized by biogeography-based optimization (BBO) for prediction of flyrock distance resulting from blasting in a mine. In the BBO-ELM system, the role of BBO is to optimize the weights and biases of ELM. For comparison purposes, another hybrid model, i.e., particle swarm optimization (PSO)-ELM and a pre-developed ELM model were also applied and proposed. To do so, 262 datasets including burden to spacing ratio, hole diameter, powder factor, stemming, maximum charge per delay and hole depth as input variables and flyrock distance as system output were considered and used. Many models with different combinations of training and testing datasets have been constructed to identify the best predictive model in estimating flyrock. The results indicate capability of the newly developed BBO-ELM model for predicting flyrock distance. The coefficient of determination, coefficient of persistence and root mean square error values of (0.93, 0.93 and 21.51), (0.94, 0.95 and 18.84) and (0.79, 0.85 and 32.29) were obtained for testing datasets of PSO-ELM, BBO-ELM and ELM model, respectively, which reveal that the BBO-ELM is a powerful model for predicting flyrock induced by blasting. The developed BBO-ELM model can be introduced as a new, capable and applicable model for solving engineering problems.

The purpose of this study is to investigate the dynamic characteristics of a roadheader for breaking rocks containing different numbers and sizes of predrill holes. A series of experiments was performed to quantitatively measure the cutting torque, thrust force, and specific energy during the cutting of a cutterhead. Experimental results show that the cutting torque, thrust force, and specific energy decrease as the number of predrill holes increases. When the number of predrill holes is nine, type 9‐2 exhibits the minimum cutting load and specific energy. In addition, three‐dimensional numerical simulations were conducted using LS‐DYNA software, and the results were further validated with experimental data. Numerical results reveal that the confining pressure has significantly affected the rock‐breaking process, and under the confining pressure of 10 MPa, values of the cutting torque and thrust force are 8.9% and 8.6% higher than those without confining pressure. The optimal diameter of the predrill holes is set as 12.5% of the maximum diameter of the cutterhead. Furthermore, the number of the holes is set as six, that is, one central hole and five circumferential holes, with a diameter of 45 mm according to the arrangement of type 6‐1.

Mining transport systems largely determine effectiveness of mining enterprises. The study aim is developing new technical solutions for progressive mining transport systems based on the harmonization of technological solutions and equipment. The aim is achieved through the introduction of new mine transport designs compatible with tunneling machinery, enabling change from cyclic concept of a mining enterprise activity to in-line system concept. The option is considered on development of designs of steeply inclined and curving conveyors in transport workings, including overhead and floor pipe belt conveyors and airdraulic pipeline systems for delivering lump ore from the face to the surface in the mine. At the same time, the basis of the proposed technology and equipment is the method of contactless hard rock breaking by using hydroimpulsive facilities. The proposed solutions allow decreasing mineral mining and processing capital and operating costs.

The raise boring machine, which plays a crucial role in wellbore construction, has been widely applied in subway tunnels and mine construction projects. High levels of quality and safety, make it recognized and promoted by an increasing number of users. The tipped hob as a rock-breaking cutter of the raise boring machine poses a direct influence on the efficiency of the well-bore construction. In this paper, the finite element software LS-DYNA is employed to establish the model of the crushed rock with the tipped hob, and the accuracy of the model is examined by experiments. On this basis, the variation laws and correlations of feed force, lateral force and positive force under different penetration depths are studied. The results show that as the penetration depth increases, the feed force, lateral force and positive force all grow exponentially. In the geological environment with high rock hardness, spherical tooth can effectively reduce cutter wear and conical tooth can achieve higher crushing ability. The research results provide a theoretical basis for the selection of a suitable tipped hob to improve rock breaking efficiency.

Rock breaking is a complex physical process that can be influenced by various factors, such as geometrical shape and cutting angle of rock breaking tools. Experimental study of the rock breaking mechanism of personalized bits is restricted due to long cycle and high cost. This study simulated the rock breaking mechanism of polycrystalline diamond compact (PDC) bit by combining finite element method and experiment. The simulation was performed to shorten the period and reduce the cost of studying the rock breaking mechanism of PDC bits. A rock breaking finite element model for sting cutters of personalized PDC bit was established to simulate the rock breaking process. The crack propagation pattern, dynamic stress of rock breaking, and rock breaking mechanism of sting cutters of personalized PDC bit were analyzed. The correctness of the simulation results was verified through experiments. Results demonstrate that the rock breaking load increases with the crack propagation in the fracture initiation and propagation stages, with the maximum tangential force of 1062.5 N and maximum axial force of 1850.0 N. The load changes in a small range when the crack penetrates the rock, with the tangential force of 125.0–500.0 N and axial force of 375.0–875.0 N. The rock breaking mechanism of the sting cutters of bit is consistent with maximum tensile stress theory. The rock begins to break when the tensile stress of rock is 36.9 MPa. The sting cutters of personalized PDC bit have better wear resistance than the sting cutters of conventional bit. The average wear rates of personalized PDC and conventional bits are 1.74E-4 and 2.1E-4 mm/m, respectively. This study serves as reference for shortening the study period of rock breaking mechanism, efficiently designing personalized PDC bit structure, reducing bit wear, and enhancing rock breaking efficiency.

Sonic drilling technology uses the longitudinal vibration of a drill string to realize fast and effective drilling. By setting the top and bottom boundary conditions of the drill string during drilling, a dynamic model of flexible sonic string percussive drilling is established in this article. At a certain drilling depth, with the excitation frequencies as the control parameters, the maximum impact force and rock breaking energy utilization rate are used to evaluate the rock breaking capability of the sonic drilling system under the linear bit–rock model. A surface diagram of the maximum breaking force reached within the working frequencies and at varying drilling depths is obtained. The curve graph of the rock breaking energy utilization rate varying with drilling depth under the first six orders of resonance is also calculated. Analysing the influence of changing drilling parameters on the rock breaking capability of sonic drilling systems can provide theoretical guidance for the actual drilling process.

Microwave energy has been demonstrated to be able to assist mechanical rock breaking in geotechnical and mining engineering. The aim of this research is to study the influences of the interaction between microwave energy and rocks on the performance of disc cutters on a TBM (tunnel boring machine). By applying an open-type microwave-induced fracturing apparatus of hard rocks, cuboidal basalt samples were subjected to microwave irradiation for different times. Full-scale linear cutting tests were conducted on specimens subjected to microwave treatment on condition of having same penetration depth and cutting spacing. The results showed that high temperatures were mainly measured at the zone directly facing the microwave applicator and the surface temperature of the samples approximately increased in a quasi-linear manner with the duration of exposure to microwave irradiation. On condition of having a fixed penetration depth and cutting spacing, the amount of rock breaking by the TBM disc cutter increased with increasing exposure: the longer the exposure duration was, the more significant the fracturing effect of the samples. During cutting, the average normal and rolling forces applied to the disc cutter both linearly reduced with exposure time while the specific energy of the disc cutter for breaking rocks exhibited an exponential reduction relationship with exposure time. It can be seen that microwave irradiation can increase the amount of rock breaking by the disc cutter and reduce the cutting forces required by the cutter, thus further improving the efficiency of rock breaking with a TBM.

Using various tools to obtain downhole data to reach a precise pore pressure model is an important means to predict overpressure. Most downhole tools are connected to the lower end of drill string and move with it. It is necessary to understand the motion state and dynamic characteristics of drill string, which will affect the use of downhole tools. In this paper, a drilling process considering rock-breaking process in vertical wells is simulated using finite element method. In the simulation, gravity is applied to the whole drill string. The contact force between PDC bit and formation is the weight on bit (WOB). And a rotation speed is applied to the upper end of drill string. Analysis of the results shows that the vibration amplitude of bottom hole WOB (contact force between PDC bit and formation, which is the real WOB in drilling process) is bigger than the amplitude of wellhead WOB (acquired through conversion using Hook load, which is on behalf of the WOB obtained on drilling site). Both wellhead WOB and bottom hole WOB decline with a fluctuation in drilling process. In small initial WOB and low rotation speed conditions, the fluctuation of wellhead WOB focuses on low frequency, the fluctuation of bottom hole WOB focus on high frequency, and the phase of them are not identical. In large initial WOB and high rotation speed conditions, the fluctuation of wellhead WOB and bottom hole WOB both become more irregular. As for wellhead torque and bottom hole torque, the fluctuation of them mainly focuses on low frequency. And in high rotation speed conditions, wellhead torque may become negative. The research results are beneficial to the usage of downhole tools.

A reliable and robust visual perception system is often a key-enabler for autonomous robotic systems working in at least partially unknown environment. For autonomous robotic rock breaking system, boulder detection and localization system is an essential part that must be able to operate under challenging environments. The problem can be summarized as detecting unstructured objects in a structured environment. A key to robust boulder detection is an effective clustering algorithm, that can segment a point cloud, captured by e.g., a Time-of-Flight (TOF) camera, into clusters of individual boulders. This information is crucial for an autonomous robotic secondary breaking system, that uses it to break each individual boulder by a hydraulic impact hammer. This study proposes a novel algorithm for point cloud segmentation that can be used for the boulder detection application. The method is designed using features of the Point Cloud Library (PCL), and it is benchmarked against other readily available algorithms in the PCL. The results indicate robust performance with an impressive 97.4% accuracy on our dataset. acceptedVersion

In this study, a two-dimensional SPH-FEM/DEM coupled model is developed to investigate rock breaking behavior under water jet impact based on the LS-DYNA software, where the SPH method is adopted to model the water jet and the FEM/DEM method is adopted to simulate rock breaking response, respectively. To better approximate the micro-structure of rock, a Voronoi tessellation technique is adopted to generate the random polygonal grains. A zero-thickness cohesive element is inserted along the boundaries of the Voronoi grains to model the mechanical interaction between grains as well as the breaking process of rock. Numerical water jet impact tests on sandstone are firstly conducted to verify the proposed method as well as calibrate the corresponding micro-parameters. Then, using the verified method, the effects of micro-structure and micro-mechanical properties on the rock breaking performance under water jet impact are systematically investigated. The numerical results show that the rock breaking performance is greatly affected by grain size and irregularity, ductility, microscopic strength and the heterogeneity of micro-parameters, whereas the contact stiffness ratio has little effect on the rock breaking performance under water jet impact.

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.