Rock Breaking Methods Research Articles

Electrode structural effects on the mechanism of high-voltage pulse rock breaking

In the oil drilling process, drilling costs account for more than 50% of total E&P costs. High-voltage electric pulse rock breaking is an economical and effective rock-breaking method that has received widespread attention. At present, there is not much research on the influence of the shape of the electrode tip on high-voltage pulse rock breaking. This paper establishes a system of equations that control the electric breakdown field based on the changes in the electric field inside the rock. Then, using this model, we conducted simulation and laboratory experiments to understand how rocks break under different conditions, such as load voltages, electrode spacing, and electrode tip shapes. The results show that the volume of broken rock is directly related to the loading voltage. The best loading voltage range is between 200 and 220 kV. Increasing the spacing between electrodes helps break more rock, but if the electrode spacing is too large, it's hard to make a hole in the rock, and the rock won't break. An electrode spacing of around 35 mm is the best. The shape of different electrode tips directly affects the high-voltage pulse breaking effect. Hemispherical electrode tips are less favorable for rock breaking, while oval electrode tips are the best. The laboratory experiments and simulations give the same conclusions and verify the applicability and correctness of our model. This study aims to help design high-voltage electric pulse devices.

Investigation of combined rock-breaking ability of sawblade and conical pick

To solve the problem of severe wear and low rock-breaking efficiency of a conical pick during rock cutting, a method of rock-breaking using a sawblade and conical pick is proposed, which can improve the rock-breaking ability and efficiency. Test benches for the sawblade rock cutting and conical-pick breaking were established to verify the numerical simulation model and improve the numerical simulation accuracy. The numerical simulation model of sawblade and conical-pick rock-cutting was used to investigate the effect of the cutting parameters on cutting performance. Based on the numerical simulation results of rock-breaking, a prediction model of the cutting force and specific cutting energy consumption for combined rock-breaking with a sawblade and conical pick was developed. This provides a comparative analysis basis for the combined rock-breaking capacity of sawblades and conical picks as well as traditional conical-pick rock-breaking. The results indicate that the cutting force, specific cutting energy consumption, and rock-breaking efficiency of combined rock-breaking with a sawblade and conical pick are better than those of the traditional conical pick. The research results provide a theoretical foundation for applying a combined rock-breaking method to sawblades and conical picks in engineering practice.

Study on the Effect of Rock Mass Structure on CO2 Transient Fissure Excavation

As a new rock breaking method, CO2 transient cracking has been widely used in rock excavation projects in recent years. However, in the actual construction process, there are often situations where the fracturing effect varies due to different rock mass structures. Through theoretical analysis and on-site cracking tests, this article studies the effect of CO2 transient cracking under the control of different rock mass structures. The results show that: (1) the dynamic compressive strength of rock directly determines the number and range of dynamic impact fractures; the original fractures of rock mass and those caused by dynamic impact in the first stage jointly determine the effect of high-pressure gas expansion in the second stage. (2) The arrangement of holes along the strata is conducive to the action of high-pressure expanding gas along the soft structural plane in the rock mass, which is conducive to the fracturing of the rock mass; the amount of crack formation is small, but the influence range is large. (3) The cracking effect of carbon dioxide transient cracking applied to massive rock mass is better than that of monolithic rock mass, while the cracking effect of layered rock mass with soil interlayer is poor. The research results are of great significance for improving the effectiveness of carbon dioxide transient-induced cracking excavation and guiding actual construction.

The rock damage mechanism of combined rock breaking with saw blade and conical pick

The combined rock breaking method with the saw blade and conical pick is proposed to improve the rock breaking efficiency. The numerical simulation of combined rock breaking with the saw blade and conical pick is established to investigate the rock damage mechanism. And verified and modified the numerical simulation model with the rock breaking comprehensive test bench, the quantitative analysis error is less than 0.05, indicated quantitative analysis system is accuracy. The result indicated that the cutting parameters of the saw blade and conical pick affect the rock damage. And the cutting parameters of conical pick and structural parameters of rock plate have been studied to influence rock breaking volume. The research result could help optimize the cutting parameters of the saw blade and conical pick to improve the rock breaking efficiency.

Experimental and numerical simulation study on the relationship between cutting depth of high-pressure water jet with high traverse speed and disc cutter penetration of TBM in hard rock tunnel

The disc cutting load of a TBM is insufficient to induce crack propagation in hard rock tunnels due to the high strength of the rock. High-pressure water jets, considered an auxiliary rock-breaking method, enhance the disc cutter's capacity to penetrate cracks by creating pre-existing fissures. In order to examine the correlation between cutting depth achieved by a high-pressure water jet operating at high traverse speeds and the penetration capability of TBM disc cutters, we conducted rock cutting experiments employing varying traverse velocities for the water jet. Additionally, we performed linear disc cutting experiments using full-size disc cutters equipped with grooves. These experiments were conducted using high-strength granite from China's Bei Shan region. We utilized the Discrete Element Software PFC2D to construct a rock breaking model based on Tyson polygons, enabling us to investigate the microfine influence mechanism of grooves with symmetry. The experiments involving high-pressure water jet grooving at high traverse velocities revealed a logarithmic decrease in groove depth as the nozzle's traverse velocity increased. These findings suggest that when high-pressure water jets are employed as an auxiliary method in TBM operations, increased distance from the center of the disc hob leads to higher traverse velocities, resulting in less efficient rock breaking. Nonetheless, increasing the nozzle diameter can enhance the rock-breaking effect. Linear disc cutting experiments indicate that, at a penetration depth of 4 mm, grooves with depths less than 4 mm have minimal impact on assisting in disc cutter rock breaking. However, when the groove depth exceeds 4 mm, there is a noticeable improvement in the disc cutter's breaking performance. The numerical simulation results provide initial validation for the linear disc cutting experiment. Lastly, considering the specific conditions of the Beishan tunnel, we propose a design scheme that involves the zoned arrangement of water jets. Additionally, we recommend appropriately reducing the rotational speed when employing high-pressure water jets as an auxiliary method for rock breaking. The research findings presented in this paper can serve as valuable references for the design and implementation of high-pressure water jet-assisted TBM cutter rock breaking.

Research on rock breaking mechanism of composite cone single cone bit

Composite cone single cone bit is a new type of single cone bit based on spherical single cone bit. Its unique structure changes the rock breaking method of traditional single cone bit, and the rock breaking efficiency and service life of the bit are improved in hard rock formation. One of the most influential is the shape of cone, which changes the trajectory and the cutter loads of the bit at the bottom of well, affecting the drilling efficiency and service life of bit. Based on experimental and numerical analysis methods, the rock breaking mechanism of two kinds of bits with different structural shapes was analyzed, and the following conclusions were obtained. 1) Rock breaking of composite single cone bit can be divided into three areas: long-distance scratch area, dense short distance scratch area and crushing pit area. 2) The direction of cutter load is determined by structure and motion mode of the cone. 3) Impact and scraping proportion of cutter with different bits structures is different, resulting in different rock breaking modes of cutter with different cutter row. This research has a profound understanding of the influence of cone shape on cutter load and cutter failure of bit, and it is of great significance for the study of composite cone single cone bit with long service life and high rock breaking efficiency.

Insights into the breaking mechanism and fragment pattern of soft rock assisted by free face under TBM wedge cutter indentation

As an innovative and efficient rock breaking method, free face-assisted rock breaking is usually applied to tunnel excavation with TBM multi-stage cutterhead. To reveal the free face-assisted breaking mechanism of soft rock, the finite-discrete element method (FDEM) is adopted to study the mudstone fragmentation characteristics, cutter force, acoustic emission (AE) and rock breaking efficiency. Then, the numerical tests of mudstone samples with different free face conditions under TBM cutter indentation are conducted. The variations of fragmentation pattern, rock breaking angle and maximum cutter force with free face spacing and height are analyzed. Finally, a fragment extraction algorithm is used to identify rock fragment distribution. The fragment area, cutter work and specific energy (SE) are calculated. Results show that free face-assisted fragmentation has a higher rock breaking efficiency with more complete and larger-area fragments compared with traditional breaking method. There are three rock fragmentation patterns controlled by several critical values of free face spacing and height. Besides, a spacing of 75 mm and a height of 125 mm can bring the largest fragment area and the highest rock breaking efficiency. The results can provide theoretical guidance for the design of TBM multi-stage cutterhead for efficient tunneling in soft rock strata.

Rock fragmentation and drilling experiment of electric impulse drilling and structural optimization of electrode bit

Due to the low rate of penetration (ROP) and high cost of natural resource development projects such as oil and gas, and mining, it's urgent to explore some new rock-breaking methods with subversive characteristics for rising ROP. Electric impulse drilling (EID) has attracted widespread attention due to its unique advantages, but its rock-breaking effect is affected by various factors such as the structures of electrode bits, pulse voltage characteristics, liquid medium type, rock type, circulation conditions, and the contact between electrode bit and rocks, etc, leading to the lack of theoretical basis for the design of the electrode bit. Therefore, to more truly reflect the interaction among electrode bits, rocks, and liquid media of EID, this study carried out rock fragmentation and drilling experiment of EID on red sandstone. Firstly, an electrical impulse generator (EIG) with a stable frequency range of 1–5 Hz and a pulse voltage of about 0–80 kV at the load terminal was developed. And an indoor EID and rock fragmentation experimental system was built, then three kinds of electrode bits with typical structures: petal-type (H type), cross-type (S type) and, coaxial type (T type) were designed. Subsequently, the rock fragmentation and drilling experiment of EID was carried out on red sandstone in three liquid media (tap water, deionized water, and hydraulic oil) under the capacitors' charging voltage of 13–17 kV (the load terminal voltage was about 45–60 kV). The general influence law of electrode bit structure, liquid medium type, circulation condition, and pulse voltage on EID was studied. Finally, the electrode bits used in the experiment were evaluated, and suggestions for structural optimization of the electrode bit were put forward based on the experiment. This study is expected to further promote the design of electrode bits and the development of EID technology.

Micro-macro fracture mechanism of heterogeneous granite in percussive drilling

The conventional rotary rock breaking method faces a technical bottleneck in improving the rate of penetration (ROP) in deep hard formations. Percussive drilling is the most potential approach to increase rock-breaking efficiency and ROP. However, the rock-breaking mechanism of percussive drilling is still unclear enough, especially the micro-fracture mechanism of rock under confining pressure (under lateral pressure and hydraulic pressure). In this paper, the impact rock breaking experiments by four kinds of Polycrystalline Diamond Compact (PDC) cutters are carried out using a drop-weight impact testing machine and an acoustic emission (AE) recording system, the influence of parameters such as cutter shape, rake angle, and impact energy on rock-breaking are systematically analyzed. This study includes a numerical simulation to examine the process of crack initiation, propagation, and cuttings formation during the impact process with the consideration of confining pressure. The results show the conical-shaped cutter is the most aggressive with high breaking efficiency. The penetration depth of the cutter is mainly influenced by the impact energy and cutter shape than the rake angle of the cutter. There exists critical impact energy makes the rock breaking efficiency the highest. The critical impact energy is about 40 J when using the conical-shaped cutter with a rake angle of 15°. The rock mainly failed in tensile mode, and the inter-grain crack is the main crack. Hydraulic pressure can inhibit the formation of horizontal cracks, while lateral pressure can inhibit the formation of vertical cracks and reduce the proportion of tensile cracks. The research results can provide some reference and basis for improving the rock-breaking efficiency in deep hard formations.

A New Linear Cutting Experimental Machine for Disc-Cutter Rock Breaking with High-Pressure Water Jets Assisted

Aiming at the low rock-breaking efficiency of TBM disc cutters in tough rock environments, A new experimental machine combined with the high-pressure water jet rock-breaking method was designed. It can flexibly change the cutting parameters of the water jet, such as spray position, spray height, pressure, etc. Moreover, the three-direction load of the disc cutter during the rock-breaking process can be obtained accurately by strain testing. The rock-breaking experiment reached the following conclusions. The experimental machine can meet the design function. In this study, the normal and rolling forces when the disc cutter breaks rock are significantly lower than the traditional, 26.90% and 28.39%, respectively. The lateral force increased slightly, about 31.17%. Although the energy consumption of water-jet-assisted is higher than the traditional rock-breaking method, the volume of broken rock per unit of time is approximately 5.85 times that of the traditional. It is feasible to increase the energy cost to increase the excavation speed. On the rock surface after the water jet experiment, a rock ridge appears on the rolling trajectory of the disc cutter, which is not conducive to further breaking the rock. The cutting depth of the water jet needs to be adjusted to reduce the height of the rock ridge.

Effect of the three-dimensional static pre-stress on the dynamic behaviours of conglomerate: True triaxial Hopkinson pressure bar tests

As the main component of gravel layer, the dynamic mechanical properties of conglomerate are closely related to the efficient rock-breaking methods while drilling in the formation rich in gravels. The characteristics of high strength and strong heterogeneity of conglomerate lead to severe vibration of drill string, causing the bottom hole rock of gravel layer is in a complex stress state of impact loads and three-dimensional confining pressure. Due to the lack of relevant study previously, this kind of dynamic mechanical behaviour is still unclear. Using the three-dimensional split Hopkinson pressure bar (3D SHPB) system, the dynamic mechanical behaviours of conglomerate under the condition of various impact loads and different levels of static pre-stress state were studied. The CT scanning results indicate that the conglomerate is characterized by strong randomness in gravel size, shape, content, and distribution, which plays an important role in the heterogeneity. The dynamic mechanical behaviours of conglomerate show a significant strain rate correlation, and that is influenced by the impact loads and static pre-stress state. There will be the highest dynamic strength and the lowest failure strain in the impact direction when the specimen is in a hydrostatic pre-stress state. With the increase of hydrostatic pre-stress, the dynamic strength of conglomerate increase linearly, while the failure strain changes the opposite. The research makes a beneficial exploration of the dynamic behaviors of conglomerate, which is expected to provide a reference for the design of high-efficiency rock-breaking methods while drilling in the stratum rich in gravels.

The partial electrical breakdown mechanism by high voltage electric pulses in multi-fractured granite

High-voltage electric pulse (HVEP) technology has currently become a new efficient rock breaking method. In order to reveal the influence of internal fracture characteristics of heterogeneous granite on electric pulse rock breaking, the two-dimensional numerical model of multi-physical field coupling electrical breakdown of fractured rock is established, which the high-voltage electric pulse plasma generation in multi-fractured heterogeneous granite is realized from the coupling of circuit field, current field, breakdown field, heat transfer field and solid mechanics. This paper analyzes the influence of fracture porosity, fracture types and granite heterogeneity on the electrical breakdown of rock (i.e. the formation of plasma channel inside the rock). At the same time, the two-dimensional numerical model of electrical breakdown parameters, which considers the circuit structure parameters of the pulsed tool, the initiation and development of the electrical breakdown, the dependence between electrical breakdown intensity and time, and rock heterogeneity, are analyzed. The simulation results indicate that with the heterogeneity H of granite changing, the plasma channel inside the rock samples are different, while the time required for breakdown t and rock breaking volume Vrock of rock samples with different heterogeneous H will show obvious fluctuations; among the rock samples with different heterogeneity H, existing a single crack requires a longer breakdown time and the extreme value of the internal conductivity is also significantly larger. And then, the formation of plasma channel is directional selective, extending towards fractures and the weak electrical breakdown intensity. With the dip angle of the fracture increasing, the required breakdown time increases accordingly, and conversely, the broken volume decreases accordingly. The larger porosity of fracture is, the larger broken volume and the shorter required break down time of the rock sample. Furthermore, with the continuous action of electric pulses, multi-fractured rock form interpenetrating plasma channels to improve the rock breaking efficiency. The research results can provide help and theoretical support for optimization of electric pulse rock breaking parameters and the development of electric pulse drilling technology.

Rock breaking mechanism of electrode bit in heterogeneous granite formation and its optimization

Electro-pulse-boring (EPB) technology is one of the most potential and nearly industrialized new rock breaking methods in geothermal drilling. However, the mechanism of EPB is not clear, and the structural parameters of EPB electrode bit are not well matched with the corresponding strata parameters and voltage parameters, which seriously hindered the commercialization process of this technology. Based on the dynamic electrical breakdown model (DEBM), a single electric breakdown of rock is realized by coupling the circuit field, the current field and the breakdown field. At the same time, considering the heterogeneity of rock, the three-dimensional numerical simulation of full-bit electrical breakdown using five kinds of electrode bits with different structures is conducted. From these five kinds of electrode bits, an electrode bit suitable for EPB is selected. Finally, the adaptability between the structural parameters and voltage parameters of the selected electrode bit is studied. The results show that the initiation and development of electrical breakdown are affected by the mineral composition, mineral quantity and mineral position of the rock. The petal-structural electrode bits with the same clearance between the high voltage electrode and all ground electrodes are more suitable for EPB drilling due to their higher chip removal function. Moreover, the minimum initial output pulse peak voltage, i.e., the adaptive voltage, of petal-structural electrode bit under different structural parameters is calculated by fitting, which is the best rock breaking voltage parameter. This research can provide reliable help for the design of EPB electrode bit, the optimization of structural parameters and voltage parameters of electrode bit to increase geothermal resources.

Research on rock breaking characteristics of impact hob of hard rock excavator

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.

Experimental study on characteristic and mechanism of simulated lunar rock destruction under high energy laser irradiation

The large load and poor heat dissipation of moon rock core drilling leads to the difficulty of rock breaking and low drilling and sampling efficiency. As a new auxiliary rock breaking method, laser rock breaking is expected to be applied to perturbation sampling in lunar rock drilling. Revealing the fracture characteristics and mechanism of rock under laser irradiation is an important basis for realizing laser-assisted lunar rock sampling. Basalt was used as simulated lunar rock sample, and its mechanical response characteristics under laser irradiation were analyzed from macro to micro point of view, and the failure law under different laser power and different irradiation time was explored. The results show that the failure of the sample under laser irradiation is mainly characterized by local rock melting and dynamic crack propagation, and the surface temperature of the sample follows the characteristics of Gaussian distribution. The laser power has a greater influence on the degree of rock weakening than the irradiation time. Laser irradiation of rocks can significantly reduce rock strength, and has obvious effects on improving rock breaking efficiency and reducing in situ disturbance. It is expected to provide theoretical and technical support for assisting lunar rock drilling and sampling in the future.

Experimental research on laser thermal rock breaking and optimization of the process parameters

The high-energy beam laser breaking of rock is an emerging noncontact physical rock-breaking method. The technology of laser thermal rock breaking has the advantages of energy concentration, high rock breaking efficiency, and no mechanical wear. An experimental study of laser thermal rock breaking was conducted to study the best combination of laser irradiated granite processing parameters. Parameters such as the total broken rock mass, mass specific energy, and cross-sectional groove area were used to quantify and analyze the efficiency of laser thermal rock breaking. The regression models of the total broken rock mass, mass specific energy, and cross-sectional groove area were established by the response surface method. Experiments verified the reliability of the regression models and the optimal parameters. The research shows that with the increase in laser power or the decrease in scanning speed, the total broken rock mass and the size of the burning groove become more significant, and the efficiency of rock breaking is improved. As the radiation distance increases, the depth of the burning groove decreases, but the width increases. With increasing radiation distance, the total broken rock mass and the cross-sectional groove area of the burning groove are approximately constant. When the laser power and radiation distance are increased, it will cause an increased energy consumption of the breaking of rock either. When the laser power is 1300 W, the scanning speed is 6.7 mm/s, and the radiation distance is 51.6 mm, the laser thermal breaking efficiency is the highest, the energy consumption is the lowest, and the best effect on rock breaking.

Mechanistic Study of a Microwave Field-Controlled Static Crushing Agent for Efficient Rock Breaking.

The long reaction time and uncontrollable reaction process of the swelling agent in the process of rock breaking by static crushing agent lead to unsatisfactory efficiency and effect of rock breaking. This paper uses physical experiments to compare and analyze the changes in temperature and pressure of the hydration reaction under different microwave conditions; utilizes microscopic analysis of the hydration reaction products under each condition, combined with numerical calculations to elucidate the mechanism of the effect of microwave field on the hydration reaction of the expansion agent; and proposes a microwave field-controlled static crushing agent rock-breaking method. The study reached the following main conclusions: (1) microwave heating is better than conventional heating in terms of heating rate, peak temperature, and peak pressure; (2) using static crushing agent rock breaking is preferable to use a low-power microwave field to control the reaction process, and to ensure that the initial temperature is not higher than the local water boiling point; (3) microwave heating to promote the reaction mechanism lies in its deep heating of the system, faster heating rate, and higher energy utilization, and is more conducive to hydration expansion reaction; (4) selective heating of microwaves can enhance the hydration reaction of calcium oxide and inhibit the production of hydrated tricalcium silicate, making the reaction more complete, while microwave heating will also improve the microstructure of hydration products.

Critical parameters investigation of rock breaking by high-pressure foam fracturing method

As a new and mild rock breaking method between blasting method with high stress loading rate and hydraulic fracturing method with low stress loading rate, high-pressure foam fracturing method has advantages of no spark, less dust, no harmful gas, controllable breaking shape and so on. In this paper, the rock breaking characteristics of 700 × 700 × 700 mm rock samples were studied by using high-pressure foam fracturing device. The influence of borehole depth, seal length and foam pressure on rock breaking were analyzed. The results show that the rock breaking weight increases with an increase of borehole depth and foam pressure, and decreases first and then increases with a decrease of seal length. When the borehole depth is 100–120 mm, the seal length is 30–10 mm and the foam pressure is 15–16.5 MPa, the failure mode of rock changed from blast crater to stripping large stone. These results have certain guiding value for revealing the rock breaking mechanism and engineering application by high-pressure foam fracturing method.

Study on the synergistic operation characteristics of disc cutter with the assistance of other rock-breaking methods

Study on the synergistic operation characteristics of disc cutter with the assistance of other rock-breaking methods

Failure Characteristics of Rock Sample during Penetration Tests with the Assistance of Different Free Surface Combinations

Abstract Free surface-assisted TBM disc cutter for rock breaking is an important direction for the optimizing of TBM cutter structure. To study the influence of free surface on TBM excavation, the free surfaces of limited-width opening and unlimited-width opening were presented, and six different free surface combinations were proposed. The penetration tests of sandstone with different free surface combinations were carried out. The results showed that the rock mass adjacent to the free surface of unlimited-width opening fell off after sample fracture. The rock mass adjacent to the free surface of limited-width opening caused the free surface to close after the rock broke. Under different free surface combinations, the auxiliary effect for rock breaking was not obvious when the free surface depth was shallow, and the failure morphology of the sample changed from vertical splitting to inclined fracture with the increase of free surface depth. The free surface-assisted rock-breaking method can reduce energy consumption during rock breaking. Among all combinations, the cumulative energy before peak load of the SDL sample dropped the most to 37.62% of the intact sample. Finally, the free surface combinations can affect the design of the cutter layout of TBM.