Figure - available from: Rock Mechanics and Rock Engineering
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Structure of cutterhead and specimen box and layout of disc cutters: a front view of the cutterhead; b left view of the cutterhead; c outer ring—illustration of the assembly of specimen-box segments, inner part—illustration of the half cross section of specimen and cutter spacing
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Rock penetration is the most important function of tunnel boring machines (TBMs). Based on a detailed review of TBM rock penetration research, this study introduces a rarely reported full-scale experimental cutterhead system that combines the advantages of in situ penetration tests and laboratory rock-breaking tests. The main focus of this study is...
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Citations
... To obtain the peak and frequency of the cutting force, the full-scale rotary cutting machine (RCM) (Geng et al. 2022) was used for the experiments under different rock strengths and operating parameters. It has a force sensor and vibration sensor to monitor the normal force, tangential force and lateral force, and vibration of the cutterhead, as shown in Fig. 4a. ...
Dynamic information about the cutting force of each cutter, such as peak and frequency of normal force, is essential to address the deformation and vibration of the cutterhead during tunnel construction using tunnel boring machines (TBM). Existing theoretical/empirical models of cutting forces and models of cutterhead deformation and vibration often use static forces for simplified analysis. It will have an impact on cutterhead design and performance analysis. In this study, a dynamic cutting force model is established based on the cavity expansion model and discretization method. This model calculates the period of the cutting force from cutter size, operation parameters and rock strength. Then, it is applied to the equation of motion of the cutterhead as the external load. The natural frequency, mode shape, deformation, and forced vibration of the cutterhead are analyzed. Finally, the cutterhead vibration response was calculated under typical geological conditions and operating parameters. The results show that increased installation radius of cutter, rotational speed and penetration of cutterhead increase the volume of rock extruded by the cutter per unit of time. The core boundary velocity and the frequency of cutting forces are also increased. Furthermore, the dynamic response of the cutterhead is significantly correlated with the geological conditions and operation parameters. Using greater advance rate and rotational speeds on stronger rocks results in most severe vibration of the cutterhead. These results demonstrate that the model provides theoretical support for cutterhead vibration analysis.
... In recent years, with the rapid increase in the demand for the development of underground space, a full-face rock tunnel boring machine (hereinafter referred to as TBM) is widely used in highway tunnels, railway tunnels, diversion tunnels, and other industries due to its advantages of high excavation efficiency and good safety, and low environmental impact, which has brought a widespread attention in TBM field [1][2][3][4]. ...
Rock breaking by laser-assisted disc cutters is a novel high-efficiency rock breaking mode that combines mechanical stress induced by the disc cutters with thermal cracking by laser. This paper presented a “step-by-step” simulation modeling concept, and conducted an in-depth study on potential influencing factors of simulation accuracy at each key step. First, the prediction accuracy of laser holes in laser drilling simulation was discussed. Second, the SHPB simulation and experiment were carried out to evaluate the accuracy of the selected material constitutive model in simulating the dynamic fracture damage of rock. Then, taking the laser-assisted rock-penetrating process of the scaled disc cutter as an example, the simulation prediction accuracy of rock-breaking by the disc cutter was analyzed. Finally, the simulation and experiment of laser-assisted disc cutter penetration into rock was carried out, and then the feasibility of the “step-by-step” concept was analyzed. The results show that: (1) in the laser drilling simulation, the predicted accuracy of laser hole size is higher when the power is low; with the laser power increases, the large amount of glass glaze will affect the subsequent modeling accuracy; (2) the HJC model can be used to simulate the transient nonlinear fracture damage behavior of granite; (3) the damage morphology of the granite obtained by the penetration simulation is highly similar to the experimental results, and the load curve should be corrected by the peak point fitting method. The results show the application prospects of the proposed numerical modeling method in future laser-assisted TBM tunnelling.
In the Tunnel Boring Machines (TBMs) construction of soft rock tunnels, adverse geological conditions, such as water-rich and wet strata are often encountered. Water in strata can change the stress state and weaken the mechanical performance of rock mass, further affecting the tunneling process and rock breaking efficiency. To study the effect of water content on mudstone fragmentation characteristics and cutter force during TBM cutter indentation, the water softening effect is considered in the moisture diffusion-fracture coupling model based on the finite-discrete element method (FDEM). Then, the micro parameters (fracture energy release rate, swelling coefficient and moisture diffusion coefficient) of mudstone are calibrated by uniaxial, triaxial compression and swelling tests. Subsequently, the water content and swelling deformation evolution of mudstone samples during water migration are revealed. Finally, the coupling model is utilized to investigate the fragmentation characteristics and cutter force of mudstone samples with different water contents under various confining pressures during TBM cutter indentation. The fragmentation zone, cutter force, acoustic emission (AE), and crack number during cutter indentation are quantitatively analyzed. Results indicate that the vertical extent of fragmentation range (Ev) decreases with the increase of water content, while the horizontal extent of fragmentation zone (Eh) does not decrease obviously until the water content reaches 3%. The increase of confining pressure reduces the effect of water content on Ev, and the increase of water content also reduces the effect of confining pressure on Ev, indicating that confining pressure and water content have a mutual inhibition effect on Ev. Besides, both the peak value of normal force and the fluctuation range of tangential force for the TBM cutter decrease with the increase of the water content. The AE counts show that the failure pattern of mudstone is mainly shear failure during TBM cutter indentation. Specifically, many shear cracks are generated in the compression zone under the cutter, while few tensile cracks propagate in mudstone on both sides and deeper below the cutter. For mudstone under different confining pressures, the proportion of shear cracks increases with the increase of water content. Moreover, the effect of cutter penetration velocity on mudstone fragmentation characteristics and cutter force is discussed. The results in this paper have theoretical guidance for TBM construction of soft rock tunnels in water-rich and wet strata.
Cutter spacing is one of the key factors affecting the rock breaking efficiency of Tunnel Boring Machine (TBM). In the excavation of deep soft rock tunnels, the water content can change the fragmentation behavior by TBM cutters, and further influence rock breaking efficiency. This study takes mudstone as an example to study the influence mechanism of water content on the optimum cutter spacing and rock breaking efficiency when TBM disc cutters penetrate soft rock. Firstly, the FDEM water migration-fracture coupled model considers the water weakening effect based on existing experimental fitting results. Secondly, several numerical experiments are conducted to calibrate the microscopic parameters input in FDEM. Finally, a series of numerical experiments of TBM double disc cutters penetrating in water-soaked mudstones are carried out using the coupling model. The crushing characteristics, cutter force, acoustic emission (AE), and crack pattern with different water content and cutter spacing are discussed in detail. Moreover, a novel recognition algorithm is proposed to calculate the rock chip distribution and area. The crack number, work done by the cutters, and specific energy (SE) are quantitatively analyzed. The results indicate that the water content of 2%–3% and the cutter spacing of 60–80 mm can lead to the lowest SE and highest rock breaking efficiency. Overall, the optimum cutter spacing decreases with the increase of water content. The modeling results can supply guidance for the optimization of cutter spacing during TBM tunneling in water-rich soft rock ground.
The disc cutters of shield machines exhibit unsatisfactory adaptability and performance during the soft–hard varied strata tunneling process. To analyze the rotation state, cutting performance, and adaptability of disc cutters during shield tunneling in soft–hard varied strata, the Holmquist Johnson Cook and Federal Highway Administration constitutive models are introduced to numerically simulate the failure process of materials on the excavation face and to calculate the load of disc cutters. Additionally, the parameters of the models are modified based on laboratory disc cutter excavation test results. The results of numerical calculation can reflect the load level and the behavior of the disc cutters during operation. The tangential loads of the disc cutters during the cutting of four typical soft-strata excavation face models are numerically calculated, thus providing reference values for the starting torque of the disc cutters. A greater penetration is suggested for soft-strata tunneling to allow the disc cutters to rotate smoothly and continuously as well as to guarantee a better cutting effect. The disc cutters in the center of the cutterhead should be specified with a lower starting torque to prevent uneven wear, rotation stagnation, cutterhead clogging, and other adverse phenomena.
Estimation of cutting forces has been used in the design and performance prediction of tunnel boring machines. The relationship between rock strength and integrity, cutting force, torque, and vibration response was investigated by the synchronous monitoring system of the full-scale rotary cutting machine. The results showed that the penetration and rotation speed of the cutterhead were important operating parameters affecting the cutting force. Moreover, the penetration also greatly influenced the cutting force. The size, position, and frequency of the cutting force significantly correlated with the vibration of the cutterhead. The root mean square (RMS) of the acceleration component in the tunnel direction was the key feature. Soft–hard mixed stratum could be identified by the RMS of vibration. Based on these results, an empirical formula for predicting cutting force was constructed. The Colorado School of Mines model underestimated the normal forces acting on soft rocks, and the gradient boosting decision tree has the best effect in predicting the cutting force.
