Rock Breaking Process Research Articles

Numerical Simulation and Field Test of a PDC Bit with Mixed Cutter Arrangement to Break Non-Homogeneous Granite

As the depth of petroleum drilling increases, the strata environment becomes more complex. The efficiency and lifespan of Polycrystalline Diamond Compact (PDC) drill bits fail to meet current drilling demands. However, the structure and arrangement of PDC cutters are valuable determinants of drilling efficiency, although related research still has gaps and deficiencies. This study focuses on PDC cutters in axe, triangular prism, and circular forms. It establishes an inhomogeneous granite model based on the actual measurements of granite and verifies the accuracy of this model through uniaxial compression simulation. Finite element models of three types of cutters in various combination schemes are constructed to examine rock-breaking effects, with the best scheme optimized using Box-Behnken response surface methodology. The rock-breaking process of the optimal PDC drill bit layout has been compared to that of a single cutter bit. Field drilling has demonstrated the effectiveness of a mixed cutter arrangement. The results show that the inhomogeneous granite model can be trusted. The optimal arrangement involves axe cutters in the front row and an alternate arrangement of triangular prism cutters and axe cutters in the back row. The optimal lateral and longitudinal distances for the triangular cutters from the front row of axe cutters are 10 mm and 7 mm, respectively, while those for the back row of axe cutters from the front row are 10.06 mm and 7 mm, respectively. The ROP standard deviation in the drilling process of mixed cutter bits decreases by 53.06% and 43.08% compared to axe and triangular prism cutter bits, respectively. The drilling efficiency increases by 16.8% and 16.6%, respectively, demonstrating higher efficiency and stability. Field drilling results indicate that a mixed cutter bit increases efficiency by 23.5% compared to a bit with only triangular prism cutters. This study posits that research on the combination schemes and parameters of PDC cutters can significantly enhance drilling efficiency, thereby reducing the drilling cycle and costs.

Comparative research of rock breaking by heat effect of continuous and pulse laser with experiment and simulation

Laser rock breaking is a novel rock breaking technology to raise the rock breaking efficiency in deep and ultra-deep strata. Continuous and pulse lasers are two types of laser that are usually used in laser rock breaking research at present. However, the present studies’ main focus is on the breaking mechanism and character optimization of continuous laser. Studies to pulse laser and the differences between the two types of laser are rarely reported. The pulse and continuous laser with 800 W power were used in the laser rock breaking experiment, and the morphology of ablation pits was measured and compared. Then, a FEM simulation model was established by the results of the experiment. The distribution condition and the evolution process of temperature, ablation pit, yield condition, and equivalent strain at test points generated by two types of laser were measured and compared. The experiment results show a thick enamel layer covering the ablation pit generated by the continuous laser, which referring a higher ablation ability but with a shallower ablation pit in measurement. And the simulation results not only represent the higher ablation ability of continuous laser at the end of simulation but also show the circular heating–cooling process, stepping expansion process of ablation pit, faster ablation pit generation speed (0.03 s earlier), higher yield volume, and higher equivalent plastic strain (about three times higher) in radiated part with a pulse laser. Referring that it has higher ablation ability in short radiation time, stronger thermal stress effects on the radiated part, and less molten materials generated in the laser rock breaking process than continuous laser. This research can offer some references to the laser type selection in laser rock breaking and explain the rock breaking theory more comprehensively.

Numerical simulation of rock-breaking mechanisms by triple-ridged PDC cutter in hard rocks

As basic cutting element of PDC bit, PDC cutters play crucial roles in breaking rocks for PDC bit. Conventional PDC cutter usually gets broken when drilling into deep formations due to high hardness and strong abrasion. To help solve such a problem, triple-ridged PDC cutters have been developed and utilized in the design of hybrid-cutters PDC bit, which have achieved enhanced rate of penetration and high life cycle. Nevertheless, few researches have focused on the rock-breaking mechanisms of triple-ridged PDC cutter. Thus, this research carries out a series of numerical simulations to reveal the rock-breaking mechanisms of the triple-ridged PDC cutter. The numerical analysis and the visualization of the rock-breaking process are shown in the paper. Parametrical analyses have also been conducted to reveal effects of cutting parameters, rock strength, and cutter structural parameters on the rock-breaking performances of the triple-ridged PDC cutter. Numerical results show that the triple-ridged PDC cutter is more easily to break the rock than the conventional PDC cutter by combining the shearing and the crushing effects, predominantly leading to much smaller cutting force. Given the same cutting depth and the cutting angle, the triple-ridged PDC cutter can exhibit higher rock-breaking efficiency than that of the conventional PDC cutter. Also, optimal analysis should be done for the structural design of the triple-ridged PDC cutter. These research findings help the readers understand the rock-breaking mechanisms and the further application of the triple-ridged PDC cutter in deep hard formations.

Damage evolution law and failure mechanism of rock impacted by high-pressure water jet under in-situ stress condition.

To investigate the real physical mechanism of rock fragmentation subjected to water jet under in-situ stress condition, a numerical model based on the SPH algorithm was established using the rate-dependent constitutive model to simulate the rock-breaking process. First, the damage evolution law of rock impacted by high-pressure water jet under in-situ stress conditions was studied by analyzing the distribution characteristics of the damage field in the dynamic process of water jet impinging. The results showed that the damage field, widths of surface damage, maximum widths of damage and mean depths of damage of rock decreased with the increase of in-situ stress, indicating that the existence of initial in-situ stress had a strong inhibitory effect on rock fragmentation. The attenuation of the maximum widths of damage could be divided into two stages. The mean depths of damage of rock played a leading role in the number of damage elements. Furthermore, on this basis, the real physical mechanism of rock fragmentation subjected to water jet under in-situ stress condition was revealed by analyzing the stress states and damage history variables of the particles in the selected five typical regions. The study showed that the failure type of the upper rock elements in the crushing zone was brittle failure caused by a combination of compressive stress and shear stress with or without in-situ stress. However, the failure mechanisms of rock elements in crack zone were completely different with or without in-situ stress. In the absence of in-situ stress, the failure type of rock impacted by water jet was the coexistence of damage caused by compressive-shear stress and tensile stress, while in the presence of in-situ stress, the failure type of rock impacted by water jet was mainly the damage caused by compressive-shear stress.

True-triaxial experimental study on the brittle failure of granite conditioned by the TBM disc cutter

The brittle failure induced by high in-site stress occurring at the tunnel face significantly affect the TBM performance. To study the rock mass failure mechanism under the combined effect of high stress and TBM cutters, three groups of true-triaxial rockburst tests were conducted, simulating the failure processes using the loading scheme “one-single face free and the remaining five surfaces loaded”. Conditioned granite specimens previously cut by the TBM cutter were prepared, and the different stressed conditions were determined based on the in-situ stress field of the Yinhan water conveyance tunnel. As the confining stress increased, the peak strength of the rock specimen also increased, and the final rupture was more violent, leading to a rockburst. The failure process recorded by the high-speed camera and the failure pattern showed a clear change. The rock conditioned by the TBM cutter was more susceptible to brittle failure under high stress, and the failure depth was greater. The stress-strain curves in the σ1 direction and the AE characteristics indicated that as the loading stress increased, the damage in the rock changed from a dominant tensile failure to a dominant shear failure, gradually extending to deeper areas of the rock. This alteration changed the rock mass mechanical behavior of the tunnel face, i.e., its stability and boreability, consequently influencing the rock breakage process by TBM cutters. As the severity of failure increased, the TBM performance shifted from a low efficiency rock-breaking performance limited by the cutter thrust to a high efficiency rock-breaking performance limited by the muck capacity and safety control.

Prediction of Disc Cutter Wear Considering the Argillization Effect

When a tunnel boring machine (TBM) excavates in the mudstone layer, the slacking mudstone will be formed under the action of the disc cutter due to the argillization effect. Therefore, the cutter wear mechanism differs significantly from that in the hard rock layer, and the hazard of flat wear increases rapidly. To predict the cutter wear in the mudstone, a novel prediction model based on the “mixture lubrication-cavity expansion” theory is established in the present study, which takes the argillization effect into consideration. Initially, the cutter wear mechanism in the mudstone was revealed by the mixture lubrication theory. Then a modified cavity expansion model was proposed and the thickness of the slacking mudstone in the rock was determined. Subsequently, according to the force acting on the disc cutter, the motion of disc cutter during the rock breakage process, and the critical condition for flat wear, formulas for the normal and flat wear of a disc cutter considering the argillization effect were derived. Finally, the proposed model was employed to predict the wear loss of a disc cutter in a tunnel project in Chongqing. The effectiveness of the proposed model was verified. It was found that the force acting on the disc cutter is borne by the slacking mudstone and the cutter simultaneously. In the modified cavity expansion model, the zone of the rock beneath the cutter is divided into the core zone (0 ≤ r ≤ T/2), argillization zone (T/2 ≤ r ≤ ra), plastic zone (ra ≤ r ≤ rp), and elastic zone (r ≥ rp). The stress caused by the cutter is equal to the stress at the argillization zone. The argillization effect can reduce the wear loss to some extent due to the mixture lubrication, however, it aggravates the risk of flat wear. This study will enrich the understanding of the cutter wear mechanism during the tunneling. Furthermore, it will provide some references for the design of the TBM and the scheme of the tunneling project.

Numerical investigation of rock breaking by a dish-shape cutter with advance slotting

A numerical model of rock breaking by dish-shape cutter wedge cracking assisted by advanced slotting was established by coupling the finite element method (FEM) and cohesive element method (CEM). The accuracy of the model was verified by uniaxial compression and cutter cutting rock experiments. The rock-breaking process of cutter wedge cracking was analyzed by combining the characteristics of thrust load and the ratio of tensile damage. The effects of the slotting feature and tool geometric parameters on the rock-breaking performance were studied. The results showed that advanced slotting can weaken the strength of rock, reduce the load of the cutter, and improve the rock-breaking efficiency. Shear failure was the main fracture mode of uncut rock extruded by the cutter, while tensile failure was the main fracture mode of extruded rock advanced slotting. The propulsion load of the cutter and the size of the rock fragment increased with increasing cutting thickness and inclination angle. The optimal values of cutting thickness and inclination angle of cutter were 30 mm and 40°, respectively. The load and specific energy consumption of cutter rock breaking decrease with increasing advanced slotting depth. However, the downward trend was no longer obvious when the slotting depth was more than 15 mm. The rock-breaking performance of the cutter increased with increasing radius, but the increasing amplitude tended to be constant when the cutter radius was greater than 70 mm.

Theoretical and numerical studies of rock breaking mechanism by double disc cutters

A plane mechanical model of rock breaking process by double disc cutter at the center of the cutterhead is established based on contact mechanics to analyze the stress evolution in the rock broken by cutters with different spacings. A continuous-discontinuous coupling numerical method based on zero-thickness cohesive elements is developed to simulate rock breaking using double cutters. The process, mechanism, and characteristics of rock breaking are comprehensively analyzed from five aspects: peak force, breaking form, breaking efficiency, crack mode, and breaking degree. The results show that under the penetrating action of cutters, dense cores are formed due to shear failure under respective cutters. The tensile cracks propagate in the rock, and then rock chips form with increasing penetration depth. When the cutter spacing is increased from 10 to 80 mm, the peak force gradually increases, the rock breaking range increases first and then decreases, the specific energy decreases first and then rises, and the breaking coefficient of intermediate rock decreases from 0.955 to 0.788. The area of rock breaking is positively correlated with the length of the tensile crack. Furthermore, the length of the tensile crack accounts for 14.4%–33.6% of the total crack length.

The sensitivity analysis of dynamic electric breakdown damage model and simulation of granite by high voltage electric pulse

The use of high-voltage electrical pulse (HVEP) technology for improving the rate of penetration in deep, complex formations has been reported; however, its rock fragmentation mechanism is not fully understood, and the parametric design of electric drilling tools is not perfect. This research paper realized the whole process of single-pulse HVEP rock-breaking by using the electric breakdown model, combining circuit parameter coupling, Kirchhoff’s law, electric breakdown criterion, heat transfer process, and solid mechanical field. The sensitivity simulation of HVEP rock-breaking parameters, which considers the structural parameters of pulse power supply, the deterioration of rock during the electrical breakdown process, the correlation between dynamic dielectric strength of rock and time, and rock heterogeneity, is analyzed. The simulation results indicate that the shape of the plasma channel has little relationship with the pulse peak voltage, and the rock-breaking volume of a single pulse is positively related to the pulse peak voltage; the electrode spacing is positively correlated with the breakdown voltage of the rock in a first-order function shape and has a positive correlation with the failure volume; large electrode spacing can promote HVEP rock-breaking; electrode tilt has little effect on the minimum breakdown voltage and failure volume, and its optimal design should be combined with the flow field analysis of the electric bit structure; the heterogeneity index of granite results in breakdown voltage amplitudes within 3 kV and differences in the fragmentation effect of HVEP. The research results can be used as theoretical support for optimizing HVEP matching drilling tools.

Study on key factors and influence law of structural design of high-voltage electro-pulse bit

The High-voltage electro-pulse (HVEP) rock-breaking technique is considered a promising technique for deep well drilling due to its low energy consumption and relatively low drilling cost. The proper design of HVEP drill bits is indispensable for implementing Electro-pulse Drilling (EPB) and achieving rock breakdown through electric discharge. This paper designs and manufactures three kinds of electrode bits in diameter of 60 mm with different electrode structure arrangements, including coaxial cylindrical bits, multi-electrode pair bits, and electrode crossing bits, to investigate the influence of key parameters in electrode arrangement and structural design on HVEP rock-breaking. Finite element models are established for each of the three different bits to simulate and analyze the influence of factors such as drill bit structural design, circumferential spacing, grounding width, cone angle of the low-voltage electrode, and the electric field distribution inside rocks during the HVEP rock-breaking process. Simulation results show that the coaxial cylindrical drill bit exhibits the highest maximum electric field intensity among these three kinds of electrode bits, indicating its superior electric breakdown ability. An HVEP rock-breaking testing system is established, and real-time parameters, such as discharge current, are recorded during the drilling processes. An HVEP discharge process prediction model is also established based on time-varying resistance, and an improved integral electrode bit is tested experimentally. The experimental results show a significant improvement in terms of maximum drilling depth and removed rock volume. HVEP rock-breaking tests are conducted on different electrode bits, confirming the superior performance of the coaxial cylindrical drill bit. Tests are also conducted on different coaxial cylindrical drill-bit diameters in red sandstone, indicating that the drilling energy consumption decreases, and the energy utilization rate increases with an increase in drill bit diameter. This paper can guide the design of HVEP drill bits and explores the key factors that influence HVEP rock-breaking, which is significant for improving the efficiency of rock-breaking and reducing energy consumption.

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.

Experimental investigation of the rock cutting process with blunt PDC cutters

Wear of drill bit is a common and unavoidable phenomenon in drilling process, which not only reduces the aggressiveness of drill bit, makes it difficult for the drill bit to penetrate into the rock, but also further reduces the rock-breaking efficiency and prolongs the well construction period, which is extremely obvious in the drilling process of deep strata and hard strata. In addition, the complexity of bottom hole environment (BHE) also leads to the complexity of drill bit wear mechanism, resulting in the unclear rock-breaking behavior and mechanism of worn cutter. Therefore, in order to study the influence of bit wear on rock-breaking performance and explore the rock-breaking behavior of blunt cutter, in this paper, sandstone was selected as the experimental object, and a series of indoor rock cutting experiments were carried out with worn Polycrystalline Diamond Compact (PDC) cutter obtained by mechanical process, and the influence of cutter wear on the rock-breaking process was studied from the aspects of cutting force, mechanical specific energy (MSE), cuttings and cutting groove. The results show that, compared with sharp cutter, the forces and MSE of blunt cutter are increased during cutting. In addition, the wear of cutter reduces the aggressiveness of cutter, and the aggressiveness of cutter is decreased with the aggravating of wear of cutter. Similarly, the wear of cutter leads to the increase of cutter-rock contact area, resulting in a greater squeezing and grinding effect on rocks, which leads to the reduction of the size of cuttings and the production of more powdery cuttings during cutting. Besides, the cutting groove obtained by blunt cutter is rougher and wider than that obtained by sharp cutter; Moreover, the cutting groove obtained by sharp cutter is smoother and deeper. The experimental research results can provide relevant guidance and enlightenment for the study of rock-breaking behavior and the understanding of rock-breaking mechanism of worn cutter.

Experiment study and numerical simulation on the dynamic rock-breaking process of rotary percussive drilling with different cyclic and stress-wave frequencies

The rotary percussive drilling tool was designed to improve rock-breaking efficiency, and the tool’s cyclic frequency and stress-wave frequency are the key influencing factors on the rate of penetration, but the correlative research reports are few. In view of this situation, the cyclic frequency of the rotary percussion drilling tool and the frequency of stress waves generated during impact were measured. A numerical model of polycrystalline diamond compact (PDC) cutter cutting hard rock was established, and the measured frequency parameters were imported into the numerical model. The effects of cyclic frequency and stress-wave frequency on the penetration depth, rock breaking volume, and rock debris size were studied. The finding demonstrated that the average penetration depth increased with the increase of cyclic frequency, and decreased with the rise in stress wave frequency. When the two parameters were simultaneously high, it was conducive to generating smaller rock cuttings and wellbore cleaning. When the cyclic frequency was high and the stress wave frequency was low, the effect on the drilling tooth penetration was the best. The research results can provide a practical reference for optimizing the structure of rotary impact drilling tools and improving the penetration rate.

Influences of Microwave Irradiation on Rock-Breaking Efficiency of a Reduced-Scale TBM Cutter

To explore the influences of microwave irradiation on the rock-breaking efficiency of tunnel boring machine (TBM) cutters, a multimode cavity with a microwave power of 2100 W was used to conduct microwave irradiation tests on Chifeng basalt for different durations. A combined abrasion test device for the reduced-scale SP3-I TBM cutter was adopted to conduct cutter wear and rock-breaking tests on basalt samples before and after microwave irradiation. Influences of microwave irradiation on the wear loss of the reduced-scale TBM cutter, rock removal, cutting force, and specific energy were investigated. The results show that the wear loss of the reduced-scale TBM cutter linearly reduces while the rock removal linearly increases with increasing exposure to microwave irradiation. When the penetration depth and the cutter spacing are fixed, the cutting force and the work done by the cutting force exerted by the reduced-scale TBM cutter decrease linearly with increasing exposure to microwave irradiation. The rock-breaking specific energy decreases with increasing exposure to microwave irradiation in an exponential manner. These results indicate that microwave irradiation can prolong the service life of the TBM cutter in the rock-breaking process, reduce the required thrust and torque of the cutter, and improve the rock-breaking efficiency of the TBM.

A Case Study of Cutting Performance by a Transverse Cutting Head Based on Three-Dimensional Particle Flow Model

Roadheaders have been increasingly used in a variety of tunnel cross-sections and roadway excavations. The appropriate setting of key construction parameters of the roadheader can maintain the excellent cutting performance of the roadheader during excavation. In this respect, this paper reviews in detail the previous studies on various experiments and numerical simulations affecting the cutting performance parameters of roadheader. A method for simulating the breaking process during the mechanical cutting of rock was then introduced using the Particle Flow Code in 3 Dimensions (PFC3D). In the numerical simulations, we used the parallel bond model to simulate the studied rock material and completed the calibration of the mesoscopic parameters by numerical simulation tests. In the simulations, we set different cutting modes, cutting depths and cutting thicknesses to study the rock breaking process of the transverse cutter head in a highly weathered granite environment from a microscopic perspective. The simulations indicated that the cutting mode, cutting depth and cutting thickness have significant effects on the cutting force and specific energy consumption. It is feasible to use the available space to the fullest and effectively reduce the wear of the picks by adopting the undercutting mode. The cutting efficiency can be improved and the specific energy consumption of cutting can be significantly decreased by increasing the cutting depth. The optimal cutting depth for highly weathered granite is 13 cm. As the cutting thickness increases, the cutting head's normal and rolling forces increase linearly, and the cutting efficiency improves. Under the condition of highly weathered granite, the maximum cutting thickness of the Erkat ER1500 transverse cutting head is 12.5 cm. Overall, the results indicate that the discrete element method is a powerful tool for simulating rock cutting process.

Research on expression method of PDC bit wear uncertainty and influence of lateral force

PDC (Polycrystalline Diamond Compact) bit is the main rock-breaking tool for oil and gas drilling nowadays. The analysis of the lateral force and wear of PDC bits is the basis of the bit design. In this article, combined with the uncertainty analysis theory, the mathematical expression method and model for PDC cutters with uncertain wear are established according to the application of PDC bits in drilling sites. The wear characteristics of different cutting teeth on PDC bits show different distribution patterns. Moreover, the numerical simulation of the uncertain wear process of PDC bit rock-breaking is established. And the wear results and process of the cutter of the PDC bit are consistent with the actual situation. According to the force analysis of the single cutter test, combined with the numerical simulation of the uncertain wear process, the lateral force of the PDC bit under uncertain wear is calculated. It concluded that the lateral force of the PDC bit is gradually increasing during the uncertain wear process, always obeying the normal distribution. After rock breaking with footage of 3.5 mm per revolution of the bit, the mean values of lateral force FS increased by 20.9%. With a gradual increase in the wear uncertainty of the PDC bit, the value of its lateral force gradually increases, and the direction of the lateral force changes by 180°. Therefore, this article has studied the mathematical characterization of uncertain wear of cutter on PDC bit during the drilling process for the first time, which lays a foundation for the design of PDC bits.

Study on the Efficiency of Cutting Granite with Ridge Teeth

In order to explore the crushing effect of roof teeth on granite in Qinghai Oilfield, the rock breaking efficiency of roof teeth was studied. Through the indoor single tooth rock breaking experiment, rock mechanics parameter experiment and numerical simulation of the rock breaking process of roof teeth, the influence of cutting parameters (depth and rake angle) of roof teeth and tooth arrangement mode on the rock breaking efficiency of roof teeth is judged. Through analysis, the best cutting parameters of plane teeth are 5 °, 3mm; The best cutting parameter of ridge teeth is 5 °, 2mm deep, and the rock breaking effect of ridge teeth is better than that of plane teeth.

Numerical study of rock-breaking mechanism in hard rock with full PDC bit model in compound impact drilling

Geothermal reservoir rocks have the characteristics of high stress, high hardness and high abrasiveness, which makes the drilling rate low and the drilling cost high, and hinders the application of geothermal energy. Improving drilling efficiency in hard rock strata is the prerequisite for large-scale application of geothermal energy. Impact drilling is considered to be the most effective drilling method in hard formations. PDC (Polycrystalline diamond Compact) bit compound impact drilling is one of the impact drilling methods, which has been widely concerned in recent years. In order to further improve the drilling efficiency of this method, the mechanism of PDC bit compound impact rock breaking is studied. Drucker–Prager criterion was used as rock constitutive relation, equivalent plastic strain was used as rock failure criterion, MSE (mechanical special energy) was used as evaluation method of rock-breaking efficiency, and a three-dimensional simulation model of full-size PDC bit for compound impact rock-breaking was built. The rock breaking law in PDC bit compound rock breaking process and the impact vector angle and impact duration on rock breaking efficiency are analyzed. The results show that the compound impact drilling can effectively alleviate the stick–slip vibration phenomenon, and improve drilling efficiency. In the compound impact mode, compressive stress failure and tensile stress failure occur at the same time, and the tensile stress failure is the main failure mode. The peak stress of the rock is 5.49% larger, and the residual plastic deformation is about 4.28% smaller than that of non-impact mode. With the increase of impact angle, the MSE decreases first and then increases a little. The optimal impact vector angle is in the range of 30°–50°. With the increase of the impact time, the MSE decreases in a wavy manner. In the range of 0.2 ms–1.0 ms, the optimal impact time is 0.8 ms–1.0 ms.

Mechanical characteristics of a tunnel boring machine cutterhead during rock breaking: Physical model tests and transient dynamic analysis

During tunnel excavation using a tunnel boring machine (TBM), the interaction between the cutter and the rock causes the cutterhead to generate abrupt vibrations, which could lead to engineering problems, such as bearing seal failure and even cutterhead cracking. In this study, large-scale physical model tests with various cutter spacings were performed to study the vibration and load characteristics of the cutterhead during the rock-breaking process. Through a TBM modal comprehensive test bench, the real-time acceleration of the cutterhead was obtained using a monitoring system. The test results showed that the complete time-domain curves were stepped and periodic. When the cutterhead was stuck or rock peeled off during the excavation, the monitoring curves showed abrupt vibrations, which were mainly concentrated at 0–3 Hz and were typical low-frequency vibrations. Taking measured data as the driving parameter, the real-time mechanical characteristics of the cutterhead were determined through transient dynamic analysis. Numerical simulation results showed that the vibration trend during excavation was the superposition of random vibrations generated by rock breaking and tunneling without rock cutting. During the tunneling process, the wear of the edge cutters should be highlighted in actual construction. The related methods and results can provide an essential reference for the selection of cutterheads.

Disk cutter wear prediction of TBM considering sliding and rolling friction

Abstract Considering the serious wear of disk cutters in tunnel project and the low prediction accuracy of existing methods, a new method for wear prediction of disk cutters from an energy perspective was proposed. Based on contact mechanics, the rock breaking process of cutters was analyzed, and the combined action of sliding and rolling friction was considered. Furthermore, the wear prediction model of disk cutters was established, which realized the predicted wear of disk cutters under different geological conditions throughout the construction line. In addition, considering the influence of penetration on the wear prediction model, the predicted wear values under different penetrations were obtained, and their average values were taken as the predicted wear values of disk cutters considering penetration. Finally, the predicted wear values were compared with the actual wear value of disk cutters. The results showed that the average relative error between the predicted wear value of disk cutters considering sliding and rolling friction and the actual wear data was 12.8%. The average relative error between the predicted value of wear considering only sliding friction and the actual value of disk cutters is 18.3%. The average relative error between the predicted value of disk cutter wear considering penetration and the actual wear data was 12.2%, which proved the feasibility and accuracy of the prediction model. Meanwhile, it is more accurate than the model only considering sliding friction. The research results provided a scientific theoretical basis for the design of a tool change scheme in tunnel construction.