When excavating through muddy sandstone formations, ultra-large-diameter slurry shield machines often experience rock debris retention, causing severe secondary wear on cutting tools and frequent cleaning of the excavation chamber, which reduces excavation efficiency. To address this issue, this study employed a coupled Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) approach to develop a full-scale two-phase flow model covering the excavation chamber, working chamber, cutterhead, and slurry pipeline network system. The model was used to identify debris movement patterns and flow field characteristics under the combined effects of pipeline flushing and cutterhead rotation. The influence of cutterhead speed, pipeline flow distribution, and intra-chamber recirculation on debris removal was quantitatively analyzed. Results showed that most debris settled at the chamber bottom and moved toward the discharge port by sliding. When the cutterhead speed exceeded 1.2 rpm, circumferential flow dominated and hindered debris transport to the working chamber. Increasing the flow rate of Pump 0.1 improved discharge performance, while increasing Pump 0.2 flow reduced it. Optimizing intra-chamber recirculation by redirecting the jet to a 30 degrees downward angle and setting the flow rate to 1200 m3/h increased debris discharge by 5.8 %. Based on the simulation results, an optimized scheme was proposed and successfully applied, effectively alleviating the issue of rock debris retention. The findings provide guidance for optimizing flushing pump layout and operational parameters in ultra-large slurry shield tunneling projects.

Cutterhead is the core component of the tunnel boring machine (TBM). In slurry TBM engineering, conventional and atmospheric cutterheads are usually associated with different cutterhead structure, cutter change mode and auxiliary system configurations, which may lead to different responses under complex geological conditions. To explore the tunneling performance and differences, this study presents a comparative field case analysis of two slurry TBM system configurations featuring conventional and atmospheric cutterheads in the parallel tunnels of the Haizhuwan Tunnel Project. First, the tunneling performance under four representative geological conditions was analyzed based on tunneling data, equipment modifications, and cutter failure characteristics. Subsequently, the Kruskal-Wallis test was used to compare the tunneling differences between the two machine configurations, with tunneling time per ring and construction time per ring taken as the main evaluation indicators. The results show that, under the investigated project conditions, in challenging environments, such as soft soil strata with poor formation stability, the atmospheric cutterhead configured system demonstrates better tunneling performance. In contrast, in hard rock strata, particularly under high rock hardness conditions, conventional cutterhead configured system exhibits superior tunneling performance. These findings provide practical engineering reference for slurry TBM equipment configuration and construction organization under similar geological conditions.

Traditional ultra-large diameter slurry shields rely solely on slurry entrainment for debris removal, and under complex operating conditions, rock debris retention and clogging in the excavation chamber are difficult to avoid, reducing tunneling efficiency and compromising construction safety. To improve debris removal performance, an ultra-large-diameter slurry shield used in a subsea tunnel project was equipped with a short screw conveyor, establishing a hybrid debris discharge mode based on fluid entrainment and mechanical removal. In this study, a coupled CFD-DEM approach was used to develop a full-scale slurry discharge simulation model that includes the cutterhead, excavation chamber, flushing pipelines, and short screw conveyor. The model captures the staged characteristics of the discharge process and the corresponding flow field distribution under the combined effects of pipeline flushing, cutterhead rotation, and short screw operation. Based on this model, response surface methodology (RSM) was applied to quantify the effects of cutterhead speed, advance speed, and short screw speed on slurry discharge performance and to evaluate their interactions. The results indicate that short screw speed and advance speed have the most significant influence on slurry accumulation within the excavation chamber. Matching schemes for short screw rotation speed under different operating conditions were further proposed and validated using field monitoring data, resulting in a recommended speed range of 8-9 rpm for this project. This study provides a reference for optimizing the construction parameters of shield machines adopting this innovative discharge mode.

Accurate in situ measurement of the lubricating film in spherical valve plate pairs is important for understanding efficiency loss and durability limits in large-displacement pumps, yet the film is difficult to access and its stiffness response under operating conditions is rarely quantified. This paper develops an in situ measurement and stiffness-identification method for the spherical valve plate pair of an industrial 750 mL center dot rev(-1) pump. Three noncontact gap sensors and embedded pressure/temperature sensors are integrated with minimal modification to obtain synchronous time histories during steady operating sweeps. After calibration with a material-matched target, the gap signals are converted to local film thickness and expanded to the full film-thickness field by sparse-point spherical reconstruction, yielding the cylinder-block tilt angles (phi, theta). Force-moment equilibrium is then used to evaluate the local scalar pressure-thickness sensitivity kappa, or its secant form kappa sec, and to derive interface-level directional stiffness measures associated with the 2 & times; 2 rotational stiffness representation K; these descriptors separately characterise local pressure-film coupling and the moment-tilt response of the interface. Pressure concentrates the sampled kappa sec response near the high-pressure leading edge and increases the directional stiffness contrast; speed thickens the film and reduces fluctuations; displacement amplifies overturning excitation and circumferential non-uniformity while the mean film thickness changes only slightly. The workflow provides practical indicators for comparing operating points and supporting design and condition monitoring of valveplate interfaces in large-displacement pumps.

Abstract The running-in process is critical to the efficiency and service life of the valve plate pair (VPP) in axial piston pumps. Stepped speed variations during the running-in process have a significant impact on the VPP’s tribological characteristics. This study investigates the effects of speed step number, variation direction, and time proportion on the VPP's running-in tribological performance. Friction and wear tests were conducted using a ring-on-block tribometer. The results demonstrate that increasing the speed step number can reduce the size of abrasive particles and Spk values. However, excessive steps drastically reduce the Svk value by approximately 82.44%, thereby compromising the surface's oil retention capability. Acceleration running-in significantly outperforms deceleration running-in. Compared to deceleration running-in, the friction coefficient decreases by 63.89%, and the wear rate is halved. In contrast, deceleration running-in induces deeper micro-cutting marks and adhesive wear. Furthermore, optimizing the time distribution by extending the low-speed stage can minimize surface damage and abrasive wear. These findings suggest that a multi-stage acceleration strategy with an optimized time proportion can effectively enhance the running-in quality and tribological performance of VPPs.

To address the problem of low mechanical excavation efficiency for cutter in extremely hard rock, the rock-breaking influence law of microwave-assisted TBM cutter mode is investigated. Rock-breaking experiments using microwave pretreatment and small-scale cutters were conducted. The fragment size distribution, cutting forces, and energy efficiency for microwave-assisted cutter were analyzed. And the influence of microwave parameters on the rock-breaking performance has been researched. Results show that under an equivalent energy input of 900 kJ, the 3kW-5 min group achieved a 41.94% increase in rock-breaking volume and a 36.34% reduction in specific energy compared to the 1kW-15 min group. Evidently, the high-power, short-time scheme significantly outperforms the low-power, long-time alternative. Furthermore, the total specific energy index identified the 3kW-5 min combination as the optimal energy efficiency window, with a total energy consumption of 135.3 MJ/m³. And the normal and rolling forces reduced by 13.66% and 15.38%, respectively, relative to the untreated condition. The study provides a quantitative scientific basis for the parameter optimization of microwave-assisted cutter breaking rock system for TBM.

The bearing reliability of TBM cutter-holder system directly determine tunnelling efficiency and construction safety. To investigate failure mechanism of the cutter-holder, static and fatigue finite element simulations are carried out and the engineering results are presented in this study. The results reveal that five high-risk failure locations exist on inner cutter-holder plate of traditional cutter-holder. Locations 1 and 5 bear alternating compressive stress and easily produce crushing failure, while locations 2, 3 and 4 mainly suffer tensile stress and tend to tensile fracture failure. The engineering field failure investigation validates the reliability of above results. To relieve the risk of the traditional cutter-holder, a new cutter-holder with removable block and tangential-direction locking mechanism is proposed. Comparative simulation results show that the maximum equivalent stress of inner cutter-holder plate decreases from 259.94 MPa to 174.53 MPa with a reduction of 32.9%. The improved structure limits potential failure of the cutter-holder on the removable block, which realizes convenient on-site maintenance and significantly improves the service performance of TBM cutter-holder.

The automation of hazard warning and decision-making in tunneling projects is critical for ensuring safety and efficiency. This paper presents a novel automated inspection and intelligent decision-support system for the realtime prediction of tunnel-face stability. Specifically, a sensing unit captures muck images and point clouds to extract quantitative morphological and volumetric-flow features. These features are then fused with the operational data from a tunnel boring machine and processed by a model based on long short-term memory integrated with a multi-head attention mechanism. The system provided continuous risk assessment and real-time warnings for tunnel-face stability, achieving an overall accuracy of 94.5%. Comparative analyses demonstrated that the spatiotemporal fusion model outperformed single-source baselines, such as those relying only on operation parameters (65.69% accuracy) or muck features (79.38% accuracy). Validated in a real-world tunneling project, the proposed automated inspection and risk forecasting system has proven its capability to provide reliable and real-time decision support for tunnel engineers.

Disc cutters on Tunnel Boring Machines (TBMs) fracture rock by rotating passively under the combined action of thrust and cutterhead motion. Consequently, their rotational speed is a key measurand for fault diagnosis and wear prediction. However, in harsh tunneling environments, this signal is heavily contaminated by noise and transient shocks; such contamination obscures weak but informative features. To address this, an adaptive denoising method, ICEEMDAN-EK-WSTD is proposed. It integrates improved complete ensemble empirical mode decomposition (ICEEMDAN), envelope kurtosis (EK), and wavelet soft-threshold denoising (WSTD). An EK-based intrinsic mode function (IMF) selection strategy is introduced to adaptively identify noise-dominated IMFs, thereby replacing fixed empirical thresholds. The selected IMFs are then denoised via WSTD and recombined to reconstruct the signal. Experiments are conducted on a laboratory-scale linear rock-cutting platform to evaluate performance under four typical health states-normal, evenly wear, chipping, and uneven wear. Across these states, the proposed method achieved an average signal-to-noise ratio (SNR) of 29.12 dB and a root-mean-square error (RMSE) as low as 0.1381, yielding up to a 10.73 dB improvement in SNR (average 3.35 dB) relative to baseline methods. These results demonstrate the method's feasibility at a laboratory scale. The resulting higherfidelity rotational-speed signal enables more accurate cutter-wear estimation and fault identification, thereby strengthening TBM condition monitoring. In practice, more reliable measurements can facilitate earlier maintenance decisions, reduce unplanned downtime, and enhance logging of rock-machine interaction for construction planning. As next steps, we will embed the sensing module into a full-scale disc cutter and conduct short-duration in situ tests on an operational TBM to assess method performance under production conditions.

Disc cutters installed on conical cutterheads play a critical role in rock-cutting during the downward excavation process for shaft boring machines (SBMs). The rock-cutting characteristics of inclined cutters constitute an essential basis for cutter layout and optimization of operational parameters. This study investigates the rock-cutting characteristics of disc cutters at different installation angles under various cutting parameters through full-scale cutting tests. Compared with traditional TBM normal cutters, the penetration direction of the SBM inclined cutter does not coincide with its symmetry axis. As the cutter installation angle increases, the cutter-rock contact area decreases, and the dense core and crushed zone deviate toward the lower side of the symmetry axis. The normal force and the rolling force of rock-cutting decrease, while the side force of the inclined cutter is significantly larger than that of the normal cutter, and the degree of rock fragmentation on the lower side of the cutter blade is higher than that on the upper side. The cutting specific energy tends to decrease with the increase of cutter installation angle. When the cutter spacing to penetration depth ratio is 30, the SE of disc cutters with installation angles of 0°, 15°, and 25° are 66.2, 85.9, and 147.8 MJ/m3, respectively. Furthermore, large-sized rock debris is more prone to appearing under the rock-cutting by the cutter with a lower installation angle. The findings of this study provide valuable guidance for the design of the installation angle for the SBM inclined cutters.

This study investigates the rock fragmentation performance of a swing-arm hob in a new cutting condition with experimental and numerical approaches. At this cutting condition, two tilted slots are cut before the swing-arm hob penetrates the rock. Then, the regulatory effects of slotting depth (D) and cutting spacing (S) at this cutting condition on fragmentation process, penetration load, and efficiency are analyzed. Results indicate the existence of a critical S for a given D, within which the tilted slots effectively induce macro crack propagation, enabling the detachment of blocky rock fragment and improving rock fragmentation efficiency. Beyond this critical value, the auxiliary function vanishes. The critical S grows with increasing D, demonstrating that larger D enhances the auxiliary range and function. Optimal performance is got through the reasonable design of D and S. This study can offer support for optimizing penetrating parameters of swingarm hob in hard rock conditions.

To investigate the impact of groove angle on rock-crushing behavior of a TBM cutter, the finite element method was employed to simulate both rock cutting and rock-crushing processes. Then, the average vertical load, average rolling load, and specific energy required for rock-crushing by TBM cutter were calculated and analyzed under varying groove angles and groove spacings. Furthermore, some rock-crushing tests were performed to show the cutter's crushing behavior regarding the groove angle and groove spacing. The study's results indicate that the effectiveness of crack propagation to the groove is influenced by the groove angle and groove spacing. Specifically, for the given groove angle, when the groove spacing remains at a low value, the cracks produced can effectively extend to grooves. However, when the groove spacing surpasses a certain threshold, the cracks fail to sufficiently reach the grooves. This threshold is referred to as the critical groove spacing, which varies with different groove angles. Notably, as the groove angle increases, the critical groove spacing also tends to increase. Furthermore, when the two cutting grooves can facilitate rock crushing, a rise from 0 degrees to 60 degrees in the groove angle results in a decrease in both the cutter's vertical load and rolling load. Additionally, the specific energy initially falls and then rises with the growth of the groove angle. An optimal groove spacing that minimizes the specific energy exists for a certain groove angle. In particular, the optimal groove spacings at groove angles of 0 degrees, 15 degrees, 30 degrees, 45 degrees, and 60 degrees are 70 mm, 70 mm, 80 mm, 80 mm, and 90 mm, respectively. Notably, when the grooves with different groove angles and groove spacings can provide an auxiliary crushing effect, the crushing load of the cutter is minimized at a groove angle of 60 degrees, while the specific energy of the cutter reaches its lowest point at a groove angle of 30 degrees.

Pistons in bent-axis piston motors are designed with a specific tapered angle. This tapered angle induces a rotational angle difference between the cylinder block and the shaft, influencing the output characteristics of the motor. However, the mechanism of this influence remains insufficiently investigated. To address this, this paper proposes a model that incorporates the piston tapered angle and theoretically analyzes its effects on the motor output characteristics. Experimental investigations are conducted using two types of pistons to verify the influence of the tapered angle on the output speed and pressure of the motor. The results indicate that increasing the piston tapered angle from 3.333° to 3.934° leads to an increase in the maximum rotational angle difference from 0.176° to 1.696°. Performance measurements under the operating condition of 250 rpm and 20 MPa reveal that the motor speed fluctuation rises from 9.08% to 31.72%, and the pressure fluctuation rises from 2.141% to 6.379%. An increase in the piston tapered angle beyond its baseline design significantly intensifies fluctuations in both the speed and pressure of bent-axis piston motors.

To study the rock-crushing mechanism of the TBM ball-tooth cutter in water jet slotting condition, the rock-crushing process and phenomenon in slotting condition was simulated and observed with finite element simulation and experimental test, respectively. Then, the difference in rockcrushing features in varying slot depths and cut breadths were compared. The research findings indicate that the rock surface exhibits some intermittent pits in the cut trajectory while the ball-tooth cutter cut rock in slotting condition. For a certain slot depth, there exists a critical cut breadth within which the slotting condition has an auxiliary effect for the ball-tooth cutter. While the cut breadth is beyond the critical cut breadth, the auxiliary effect of the slotting condition will disappear. The critical cut breadths for the ball-tooth cutter at slot depths of 5 mm, 15 mm, 25 mm, and 35 mm are 20 mm, 30 mm, 30 mm, and 40 mm, respectively. At a certain slot depth condition, both the vertical and tangential loads rise then stabilize, but the side load firstly reduces and eventually stabilize with the growth of the cut breadth. Furthermore, the efficiency index initially grows with the growth of the cut breadth, but after reaching a peak, it begins to reduce and ultimately stabilizes. For each slot depth, there exists an optimal cut breadth that maximizes the efficiency index and enhances rock-crushing efficiency, and the optimal cut breadth corresponds to the critical cut breadth. Additionally, for a certain cut breadth which is below the critical cut breadth, both the vertical load and the tangential load tend to reduce, whereas the average side load and efficiency index of the ball-tooth cutter show an upward trend with the growth of slot depth from 5 mm to 35 mm. While for the certain cut breadth which is beyond the critical cut breadth, both the rock-crushing loads and efficiency index of the ball-tooth cutter under varying slot depth are similar. Overall, by the assist of water jet slotting condition, the rock-crushing loads and the efficiency index of the ball-tooth cutter could be evidently improved.

Compared with plane cutterhead, the cone-shape cutterhead has better rock-breaking performance with a free surface during the rock-breaking process. Tunneling parameters of cone-shaped cutterhead have great influence on the rock-breaking efficiency and cutterhead thrust. A full-scale excavation model of cone-shape cutterhead was constructed using LS-DYNA to characterize the rock-breaking process accurately and efficiently. The effects of penetration depth and rotation speed on the damage, cutterhead thrust, and rock-breaking efficiency in each area were investigated. The results show that the penetration depth is more sensitive to the field penetration index and thrust fluctuation index than the rotation speed. When the penetration depth and rotation speed is 4 mm/r and 4.5 r/min, respectively, the cone-shape cutterhead performs best with high rock-breaking efficiency and smallest fluctuation of cutterhead thrust under specific geological conditions. It provides suggestions for the selection of tunneling parameters during cone-shape cutterhead construction.

This study proposes a approach for enhancing and predicting ventilation and heat dissipation performance in large-diameter shield tunnels through Computational Fluid Dynamics (CFD). A comprehensive steady-state airflow model was developed to analyze heat-flow coupling in Phi 15 m shield tunnels. The numerical model's reliability was rigorously validated through field measurements of velocity and temperature distributions at the construction site. Extensive steady-state CFD simulations were performed to systematically evaluate the average velocity and temperature variations under diverse ventilation conditions. The results reveal that implementing a double-duct air supply configuration in the shield ventilation system significantly improve flow uniformity, reducing the non-uniformity coefficient by 33.6 %. Optimal operational parameters are identified for Phi 15 m shield tunnels: an air supply volume of 22-24 m3 /s, a duct outlet-to-shield tail distance of 10-12 m, and a duct diameter range of 1.0-1.2 m through systematic analysis. Furthermore, the study establish empirical correlations between key influencing factors and velocity/temperature distributions based on simulation data, providing a valuable tool for assessing ventilation performance and optimizing design parameters in shield tunnel engineering applications.

The downward excavation of a shaft boring machine (SBM) is realized by dozens of disc cutters mounted on the conical cutterhead to break the rock. The cutterhead drives the inclined-mounted cutter to penetrate the inclined rock surface in the direction of excavation, with the cutter symmetry axis forming an acute angle relative to the thrust direction. It leads to significant differences in the rock-breaking method between the inclined-mounted cutter on the conical cutterhead and the normal-mounted cutter on the planar cutterhead. To study the rock breaking characteristics of inclined-mounted cutters on SBM conical cutterheads, a series of full-scale rock cutting experiments using an inclined-mounted cutter with an installation angle of 25 degrees and a cutter spacing of 80 mm were conducted. Three different rock types were used in the tests to represent the changing geological conditions during downward excavation. The cutting force, particle distribution of rock muck, and specific energy under varying geological conditions and cutting parameters were analyzed. The results indicate that the relationship between vertical force and penetration depth can be fitted by a power function, while the rolling force and side force exhibit a linear function relationship with penetration depth. The vertical force is linearly positively correlated with rock compressive strength. The maximum coarseness index values obtained during the cutting of sandstone, marble, and granite are 746.11

The safety and tunneling efficiency of shield machine is one of the most important issues highly concerned. In order to explore the feasibility of high-speed tunneling, the three-dimensional cutterhead dynamic tunneling simulation model is established by means of dynamic simulation software. The cutting rock volume, tunneling load of cutterhead and stress distribution characteristics of surrounding rock can be obtained to represent the tunneling performance of cutterhead. The coupled influence of different tunneling parameters combination on the tunneling performance of cutterhead is investigated. The results show that when the penetration depth is 40 mm/r and the rotational speed is 3 r/min, the stress of surrounding rock is the largest, where the average and the largest stress of excavation surface is 5.28 MPa and 28.8 MPa. When the rotational speed of the cutterhead is 2.5 r/min, the tunneling efficiency is high and the disturbance of surrounding rock is least. It means that it is feasible to increase the rotational speed while ensuring the stability of the surrounding rock so as to improve the tunneling efficiency under uniform soft rock stratum.

Surface defects in the segmental lining of shield tunnels, such as water leakage and damage, pose significant threats to safety. Currently, manual inspection methods are inefficient and inaccurate. Most artificial intelligence techniques for detecting tunnel features and surface defects face challenges, including poor data quality and high computational costs in real-world settings. This paper introduces an automated system for tunnel information acquisition and defect detection, offering a comprehensive solution for identifying surface features and defects. An intelligent tunnel inspection vehicle was designed for automatic image acquisition, and a preprocessing method combining adaptive local tone mapping (ALTM) with contrast-limited adaptive histogram equalization (CLAHE) was used to improve image illumination and contrast. An enhanced deep-learning method based on segmenting objects by locations version 2 (SOLOv2) was proposed, which incorporates an F-ResNeSt backbone with a focus structure from split-attention networks with 101 layers (ResNeSt101), and an improved bi-directional feature pyramid network (BIFPN) with a convolutional block attention module (CBAM) in the feature fusion module. Applied to the Xiangya Road Tunnel, the method proves to be efficient, lightweight, and accurate, offering novel approaches for detecting tunnel surface features and defects.