Rock Breaking Methods Research Articles

A new dynamic fracturing method: deflagration fracturing technology with carbon dioxide

Control of damaged zone caused by impact load is the challenging issue in blasting engineering. In this paper, a new rock breaking method using carbon dioxide ice powder is developed, which is characterized by weak disturbance. Then experiments on the $$\text {CO}_{2}$$ pneumatic fracturing of concrete specimens were conducted. Generally, the $$\text {CO}_{2}$$-driven fracturing process generates medium strain rate ($$\varepsilon ^\cdot = 10^{0}$$ to $$10^{1}$$ 1/s), the large concrete specimen was fractured into 3–5 blocks, and no crushing damage occurred. The transient failure modes in the shock wave event were discussed, and the fragment size-strain rate relationship was established based on the cusp mutation theory. The theoretical calculation results are consistent with the experimental results. The research achievement may provide a new and safe rock-fracturing method for geological engineering.

A transient fluid-thermo-structural coupling study of high-velocity LN2 jet impingement on rocks

The high-velocity liquid nitrogen (LN2) jet is an efficient rock breaking method that can be applied in improving drilling rate and enhancing stimulation performances of fossil fuel and geothermal reservoirs. To determine the cooling effect during LN2 jet impingement, a transient fluid-thermo-structural coupling study was conducted in this paper. We adopted a loose coupling method in which the fluid domain and the structure domain are simulated by FLUENT and ABAQUS, respectively, and coupling quantities were exchanged across the fluid-structural interface in every real time increment through the Mesh-based Parallel Code Coupling Interface (MpCCI) server. The v2-f model was employed to calculate the flow field and heat transfer in the fluid domain, and changes of thermo-physical properties of fluid and solid with temperature were considered in the calculation. This model was validated by comparing the simulation results with previous experimental data. According to our simulation results, the velocity and turbulence intensity of LN2 jet are significantly greater than those of water jet under the same conditions. The process of high-velocity LN2 jet impingement can be divided into two stages: (1) the jet impact dominated stage and (2) the thermal dominated stage. In the former stage, stress distributions under the impacts of water jet and LN2 jet are similar. A compressive zone surrounded by a ring tensile stress zone is generated on the impact surface. In the latter stage, the compressive stress near the stagnation point transfers to tensile stress gradually under the effect of LN2 cooling. The LN2 jet induces higher tensile and shear stress in rock, and thus can achieve better rock-breaking performances than water jet. Increasing the rock temperature can further improve the stress magnitude in rock, which makes the rock-breaking performances of LN2 jet more significant.

Experimental study of the force response and chip formation in rock cutting

Mechanical rock cutting is one kind of rock breaking methods which is extensively used in oil gas drilling engineering. The force response and chip formation in rock cutting process plays an important role in studying the rock breaking mechanism of polycrystalline diamond compact (PDC) cutter, which is essential to the determination of optimum cutting parameters. In this paper, the experimental setup and discrete element model of rock cutting are developed; the force response and chip formation under various depths of cut (DOC), cutting velocities, and rake angles of PDC cutter are performed. This study shows that the average cutting force is proportional to the DOC when it is shallow; however, the average cutting force tends to deviate from the linear relationship while the DOC reaches to a threshold value. The cutting chips generated during rock cutting process can be divided into three parts, the crushed zone near the cutter tip and the plastic flow zone in front of the cutter surface, both of them in a powdery form, and another is the main part of chip in front of the crushed zone in a block-shaped form. The crushed zone will create a wedging effect on the initiation of macro-crack which causes the propagation of macro-crack in an opening mode. The cutting velocity has no obvious influence on the size and number of the formed chips. The smaller the rake angle is, the smaller size the chips will be. The research results are of great significance for deep understanding of the mechanism of rock cutting and for guiding the design of PDC bit and optimization of the drilling parameters.

Numerical research on rock breaking by abrasive water jet-pick under confining pressure

Conical pick bears great cutting force, shock, vibration and friction in breaking rock. In order to improve rock breaking efficiency and reduce cutting force as well as pick wear, high-pressure water jet assisted rock breaking technology and abrasive water jet-pick combined rock breaking method have been proposed. Numerical models of abrasive water jet-pick combined rock breaking under confining pressures are established based on FEM combined with SPH which validity are verified by experiment. A 3D numerical model is established to investigate the influence of confining pressure and jet pressure on rock breaking performance of abrasive water jet-pick. Numerical result shows that, when confining pressure increasing from 0MPa to 20MPa, stress concentration area extends on the rock and the cutting force increases by 46.69% during single pick breaking rock. However, the cutting force of abrasive water jet-pick with jet pressure of 30MPa increases by only 21.9% under the same conditions. Confining pressure can inhibit propagation of tensile stress in rock. And most tensile stress area in rock is transformed to compressive stress area, which is harder to break under confining pressure. As a result, cutting force and wear is more serious. Moreover, the cutting force decreases with the increase of abrasive water jet pressure. The reduction rate of cutting force reaches 38.14% when jet pressure increases from 0MPa to 46MPa. At the same time, stress concentration area around the rock crushing crater is more obvious, rock crushing crater and cutting groove is larger, and the weakening effect of abrasive water jet on rock strength is even more significant.

The Microwave-Induced Fracturing of Hard Rock

A new, high-efficiency technology for fracturing and breaking rocks is required. Due to various advantages including high efficiency, energy-saving, and having no secondary pollution, the technology of microwave-induced fracturing of hard rock has been considered as a potential method for rock fracturing and breaking. Aiming at the realisation of two engineering applications: microwave-assisted mechanical rock breaking and stress release from rock masses in deep underground engineering works to prevent geological disasters caused by high-stress concentrations such as rockbursts, a novel (open-type) microwave-induced fracturing apparatus (OMWFA) for fracturing hard rocks was developed. On this basis, the two modes of microwave-induced subsurface fracturing and microwave-induced borehole fracturing of hard rocks were proposed. Due to removal of the restraint of the microwave cavity, OMWFA can be used to fracture large-size rock samples and engineering-scale rock masses. Using the apparatus, the fracturing effects of the two fracturing modes on different dimensions of cuboidal basalt samples were investigated. By combining the microwave-induced fracturing apparatus with a press machine to explore the influence of unidirectional stress on the fracturing effect of microwave treatment on basalt. Moreover, field tests were carried out on rock masses encountered in underground engineering works at Baihetan Hydropower Station in Sichuan Province, China, and the fracturing effects were evaluated by applying a digital borehole televiewer and conducting acoustic wave testing. The results show that the apparatus had favourable fracturing effects on the subsurface and borehole samples of basalt. When no stress was applied, the cracks radially expanded from the approximate centre of the radiant surface and unidirectional stress promoted fracturing. The number and depth of cracks increased with prolonged microwave exposure. After microwave treatment, the P-wave velocity of the samples declined, and the longer the microwave exposure, the more significant the reduction in P-wave velocity was. The results of field test reveal that borehole fracturing can exhibit a favourable effect around boreholes. The sound velocity around the borehole and between the boreholes both declined to some extent. Microwave-induced hard rock fracturing offers guiding significance to those exploring and developing new rock breaking and tunnelling methods, and generally enhances construction safety in deep underground engineering works.

Damage Model and Numerical Experiment of High-Voltage Electro Pulse Boring in Granite

High-voltage electro pulse boring (EPB) has the advantages of high rock-breaking efficiency and good wall quality, and is a new and efficient potential method of rock breaking. The EPB process is defined as random because it is affected by many factors. At present, there is no suitable physical and mathematical model to describe the process and results of rock breakage in EPB, and the conclusions reached regarding rock-breakage mechanisms are not uniform. In this study, a complete damage model of high voltage EPB in granite is established, which includes a shock wave model and a damage model of high voltage EPB in granite. The damage model is based on the Particle Flow Code two-dimensional program. Use of a damage model of EPB accommodates the complete process of high voltage EPB, from discharge to production of a shock wave, and so rock-breaking via electro pulse can be simulated and calculated. The time-varying waveforms of shock waves with different electrical parameters are simulated and calculated on the basis of the model. Different shock wave forms are loaded into the surface and internal rock in the damage geometric model of EPB granite. Then, the breakage process of the rock surface and internally, and the mechanism of rock breakage using EPB are analyzed. This study provides a scientific basis for the quantitative expression and prediction of rock fragmentation in EPB in order to improve the drilling efficiency and reduction of energy loss in the process of EPB.

Influences on High-Voltage Electro Pulse Boring in Granite

As the exploration and drilling of oil, natural gas and geothermal wells are expanding continuously, research into high-efficiency rock drilling technology is imperative. High-voltage electro pulse boring (EPB) has the advantages of high rock breaking efficiency and good wall quality, and is a new and efficient potential method of rock breaking. The design of electrode drill bits and the selection of drilling process parameters are the main obstacles restricting the commercialization of EPB. Accordingly, it is necessary to determine the influences on high-voltage EPB. In this study, based on the equivalent circuit of high-voltage electro pulse breakdown, a mathematical model of high-voltage electro pulse discharge in rock is established. Meanwhile, a numerical simulation model of high-voltage EPB of hard granite is established based on a coaxial cylindrical electrode structure, which is often used for electrode drill bits. The simulation analysis software Comsol Multiphysics (Comsol Multiphysics®5.3a, COMSOL Co., Ltd., Stockholm, Sweden) is used to study the influences of granite composition, electrode spacing and electrode shape on the high-voltage EPB process. In addition, the influences of electrical parameters on high-voltage EPB are calculated according to a model of high-voltage electro pulse discharge in rock. Finally, it is demonstrated that high-voltage EPB is influenced by granite composition, electrical parameters, electrode spacing, and electrode shape, and the relationships between these factors are obtained. This study is of guiding significance for improving rock breaking efficiency, reducing energy loss, designing electrode drill bits and selecting drilling process parameters.

Numerical and experimental investigation of rock breaking method under free surface by TBM disc cutter

To study the rock breaking method under the free surface induced by disc cutter, the rock breaking simulations were first conducted based on the discrete element method, and the dynamic process of rock breaking under the free surface was studied including stressed zone, crush zone, crack initiation and propagation. Then the crack propagation conditions, specific energy, etc. under different free surface distance (S) were also investigated combined with linear cutting experiments. The results show that the rock breaking process under the free surface induced by disc cutter is dominated by tension failure mode. There exists a critical S to promote crack propagation to free surface effectively. And this rock breaking method can improve the rock breaking force and breaking efficiency significantly when proper.

Investigations on thermal spallation drilling performance using the specific energy method

Thermal spallation drilling is an alternative technology expected to be suitable for the development of oil and gas in hard rocks. In this paper, experiments on six types of rocks were performed to analyze characteristics of rock spallation and spall distribution. Additionally, a specific energy model for thermal spallation drilling was established. The analytical temperature results were compared with experimental values for validation. Finally, the specific energy of granite was compared with those of other rock breaking methods. Results show that it is important to control the lowering velocity of the coiled tubing (recommended in field application) to obtain the optimal penetration rate during spallation drilling. The degree of heterogeneity of rock may play an important role in the spall-ability. The shale has the largest average aspect ratio (diameter/thickness) of 30.97, with the following sequence being dolomite, limestone, granite and sandstone. The granite shows the highest penetration rate, while the limestone has the lowest. The specific energy values for sandstone, granite, shale and limestone are approximately 1000 MPa. Compared with other rock breaking methods, thermal spallation has advantages when drilling hard rocks (e.g., granite). All results in this paper can provide important implications for further study on the thermal spallation drilling.

Influences of Supercritical Carbon Dioxide Jets on Damage Mechanisms of Rock

The supercritical carbon dioxide (SC- $$\hbox {CO}_{2}$$ ) jet is potentially a new type of rock-breaking method that effectively combines pressure impact and thermal shock. Current studies show that carbon dioxide jets produce a larger damaged area and require a lower threshold pressure of breaking rocks compared with that of water jets; however, the generation mechanism of these types of jets has not been clearly explained. This study developed a fluid–solid heat coupling model using ANSYS. The simulation and experimental results show a good agreement, clearly explaining the relationships between the damage shape and thermal stress. The results of the experiment conducted indoors at ambient temperatures were first explained by simulating the stress of the rock. When the thermal effect was considered, both the maximum stress and the area wherein the stress was high increased. The increase in the elastic modulus, Poisson’s ratio, and thermal expansion of the rock transformed its damage shape from bowl to linear. The increase in the injection pressure difference increased the broken depth of the rock, while the damage area on the surface of the rock remained the same. The possible damage shapes of the rock at formation temperature were analyzed. The temperature field of the jet increased both the shear stress acting on the surface of the rock and the tensile and shear stresses inside the rock; hence, the rock developed deeper and broader volumes of breaking in the well drilling process.

Free-face-Assisted Rock Breaking Method Based on the Multi-stage Tunnel Boring Machine (TBM) Cutterhead

In order to improve the rock breaking efficiency of hard rock tunnel boring, many innovative rock breaking methods have been proposed (e.g., the water jet cutting, the high-power laser cutting, the impact-rotary drilling, and the undercutting method). However, most of the methods are not applicable to TBMs due to some structural reasons. Aiming on this problem, a free-face-assisted rock breaking method based on the multi-stage TBM cutterhead has been proposed. Series of proof-of-concept tests includes (1) the static compression test with vertical free face and (2) the rotary cutting tests in different free surface conditions were designed and carried out. The results show that the rock breaking force and efficiency can be significantly reduced and improved, respectively, with the assistance of the free face, due to the failure of the rock close to the free face is tensile-dominated failure. The influencing distance of the free face in the radial direction is at least 330 mm which covers about 5 disk cutters. Finally, the general structure of a small two-stage cutterhead (4 m in diameter) was tentatively designed in order to provide a possible approach to apply the free-face effect to TBMs.

Kinematic and bottom-hole pattern analysis of a composite drill bit of cross-scraping

For improving the drilling efficiency of polycrystalline diamond compact drill bit, a novel polycrystalline diamond compact drill bit is presented with a new rock-breaking method named as cross-scraping. In the novel polycrystalline diamond compact drill bit which is referred to as a composite drill bit, polycrystalline diamond compact cutters are mounted on rotary wheels as major cutting elements, and as a result, mesh-like scraping tracks are formed in the outer radial area of the bottom-hole. Rock-breaking method of the composite drill bit causes both shearing and fracture failure of the bottom-hole rock, which will greatly increase the rock-breaking efficiency and will prolong the bit service life. By analyzing the complex motion of cutters on the composite drill bit, velocity and acceleration models of the cutters, as well as wheel/bit speed ratio model of the bit are established in accordance with the geometric relationship between cutters and bit body in a compound coordinate system. In simulation examples, motion tracks, velocity and acceleration features of the cutter and especially the bottom-hole pattern are analyzed. Further, indoor experiments are conducted to test the mesh-like bottom-hole pattern and rock-breaking features, which have proved the accuracy of the analysis model of the composite drill bit.

The Development of the Microwave Assisted Rock Breaking Device

Microwave crag broken is a thermal assisted rock breaking method which could melt rocks. Microwave assisted rock breaking method will not bring new impact, wear and tear, instead, the microwave pretreatment on the rock reduces the difficulty of breaking rock and prolongs the service life of the drill bit. This microwave generator accumulates the microwave near the hot spot to soften and melt the rock through generating and transmitting the microwave. And we had experimented with the microwave generator to penetrate the wood, and weaken the strength of the rock. And the experiment proved the scheme of the microwave assisted rock breaking through microwave near field energy and the thermal runaway effect is feasible.

Microwave PDC Drill Bit

On the rotary drilling system, the technologies for fracturing and cutting hard rock are mainly mechanical rock breaking methods by use of improving bottomhole water horse power and bit energy, and the working life and rock breaking efficiency have much room for improvement. Microwave crag broken is a thermal assisted rock breaking method which could melt rocks. Microwave assisted rock breaking method will not bring new impact, wear and tear, instead, the microwave pretreatment on the rock reduces the difficulty of breaking rock and prolongs the service life of the drill bit. Under the combined action of microwave heat and mechanical energy of PDC bit, the rock breaking efficiency is improved greatly, and the drilling cost is reduced significantly.

ISRM Suggested Methods for land geophysics in rock engineering

Microwave assisted mechanical rock breaking is a hybrid rock breaking method that combines microwave heating and mechanical rock breaking technologies and is proven to have potential applications in mineral processing, mining, and geotechnical engineering. It is, thus, important to understand the effect of microwave-induced damage on rock fracture characteristics. In this study, granite specimens of the Cracked Straight Through Brazilian Disc (CSTBD) were used to carry out the mode I fracture test of the samples irradiated by microwave for different time and thermal cycles. The results showed that the heating rate of the surface temperature of granite is about 1 °C/s, under microwave power of 0.9 kW. When the heating time exceeds the 60 s and after 3 cycles, the fracture toughness of the granite hardly changes with the heating time and cycles. Before 100 °C, the fracture toughness and fracture energy of granite decrease by about 40% with the increase of temperature. Under microwave irradiation, the medium absorber (biotite) in granite is heated and expanded, which results in thermal damage to the rock. Moreover, the polar materials in fluid inclusions move more violently than under conventional heat conduction heating, resulting in a lower decrepitation temperature of the inclusions than under conventional heating and decrepitation degree is more severe, which further leads to an increase in the density of microcracks in mineral crystal and a significant decrease in fracture toughness. When the surface temperature is 300 °C, the bending degree of the crack increases and deviates from the straight line obviously.

Developments in rock-breaking techniques

A problem with secondary breaking at an Australian mine led to a study of new rock-breaking technologies. Many of the techniques being developed had emerged from the thrust in the U.S.A. for continuous drill-break excavation. Such approaches to rock breaking highlighted the applicability of what normally would be classified as tunnelling techniques, to the secondary breaking sector—and possibly the reverse. The investigations for suitable technologies led directly to the development of two improved rock-breaking methods specifically targeting secondary breaking, one of which could be applied to continuous excavation. Le problème d'une attaque secondaire dans une mine australienne a conduit étudier de nouvelles technologies de concassage des roches. Un grand nombre des techniques mises au point actuellement ont l'origine la poussée opérée aux Etats-Unis en faveur d'un creusement continu par foration-concassage. Ces approches sur le concassage de la roche mettent en évidence l'applicabilité de ce qui pourrait normalementêtre classé comme des techniques de creusement de tunnels au domaine des attaques secondaires, et inversement, le cas échéant. Les études portant sur des technologies adéquates ont conduit directement au développement secondaires, dont l'une peut être appliquée à un creusement en continu.

Development and estimation of rock breaking methods

Development and estimation of rock breaking methods

An analytical and experimental investigation of the effect of impact on coarse granular rocks

An Analytical and Experimental Investigation of the Effect of Impact on Coarse Granular Rocks The interaction between metallic strikers and coarse, granular rock, associated with many mechanical rock breaking methods was investigated by theoretical and experimental methods. Cylindrical steel strikers of 12.7 mm diameter with flat, conical and hemispherical tips and masses of about 18.5 g were fired by means of a gas gun at blocks of diorite and spessartite with initial energies ranging from 4 to 34 J, generating substantial fracturing. The damage pattern in the rocks was ascertained, partly with the aid of a scanning electron microscope. A synthetic model consisting of long square bars of cement paste bonded with an adhesive was constructed as a simulator of diorite and tested to further delineate the failure mechanisms in this material. As previously, it was also found here that the geometry of the striker tip significantly affects the damage pattern and extent in diorite. A crucial difference in this pattern was observed between that found in diorite, a coarsegrained rock, and in spessartite, a more finely-grained substance. The crack network in diorite consisted of numerous kinked fractures extending a distance not in excess of 20 grain lengths, whereas only 5 to 7 nearly straight cracks with a length in excess of 20 times the grain size were found in spessartite that appeared to have propagated without regard to the grain packing structure or material defects. The synthetic rock model successfully reproduced the crack pattern found in diorite under impact. An analytical model to predict the region of grain and grain boundary failure incorporating one failure criterion for grains and another for grain boundaries was constructed. The first involved the development of failure surfaces based on an empirical limiting strength analogous to the modified Griffith criterion. Grain boundary failure was stipulated upon attainment of a combination of critical tensile and Coulomb type of shear stress. The model successfully delineated the major features of damage in the synthetic rock and in diorite and established upper bound predictions for the extent of damage.

Rock mechanics and development of advanced hard rock breaking methods. Symposium : Thirumalai, K, USBM, Twin Cities, Minn. USA 20F, 3T, 14R Applications of Rock Mechanics, Proc. 15th Symp. Rock Mech., South Dakota. ASCE, 1975, P449–467

Rock mechanics and development of advanced hard rock breaking methods. Symposium : Thirumalai, K, USBM, Twin Cities, Minn. USA 20F, 3T, 14R Applications of Rock Mechanics, Proc. 15th Symp. Rock Mech., South Dakota. ASCE, 1975, P449–467

Results of practical application of the blast-excited hydraulic method of rock breaking

Results of practical application of the blast-excited hydraulic method of rock breaking