Shield Construction Research Articles

Impact of tunneling parameters on disc cutter wear during rock breaking in transient conditions

The assessment of disc cutter wear in subway shield construction beneath operational airports is a critical endeavor for evaluating the structural integrity of shield machines. This study delved into the linear tunnel project linking Station T1 to T3 within the Baiyun airport, focusing on the intricate relationship between tunneling parameters during rock-machine interactions and the impact of disc cutter installation radius on wear amount. In addition, dynamic impact transient rock-breaking tests of shield disc cutters were performed under the coupled thermo-hydro-mechanical triaxial conditions to ensure the validity of the relationship between mass-point velocity and the transient rock-breaking behavior of the disc cutter. The analysis revealed that when the shield thrust was between 17000 kN and 21000 kN, the total thrust of the shield had a significant effect on the advancement speed and cutterhead torque. Notably, the wear amount of the cutter increased approximately linearly with the installation radius, while the wear of the gauge cutter was also affected by the inclination angle. Furthermore, the study uncovered a linear correlation between the cutting length of the disc cutter and the magnitude of wear. Within a cutting length range between 440 km and 2276 km, the disc cutter's installation position had minimal impact on the wear coefficient. Simultaneously, this study employed the mass-point velocity to simulate the thrust and rolling forces in the equivalent shield tunneling processes. The findings underscored a positive correlation between disc cutter wear and shield advancement speed, cutterhead rpm, and mass-point velocity. When the mass-point velocity of the shield reached the maximum value of 0.666 m/s, the wear of the shield disc cutter also reached the maximum value of 27.5 mm, providing the quantitative reference for evaluating the influences of shield tunneling parameters on the cutter wear under transient impact rock breaking conditions.

Research on the application of a hybrid intelligent algorithm in reducing the negative response of shield tunneling construction

Traditional shield project control relies on manual monitoring and management, which suffers from poor reliability, lag, and other defects. In this paper, a hybrid algorithm based on Bayesian optimization (BO), light gradient enhancer (LGBM), and nondominated sorting genetic algorithm-III (NSGA-III) is proposed to realize intelligent control of shield construction safety. The BO-LGBM-NSGA-III is a multiobjective optimization algorithm that takes cutterhead wear and shield energy consumption as objective functions and the nonlinear mapping function of surface settlement and construction parameters as fitness functions. Based on the Pareto distribution of the optimized backing structure construction parameters, reasonable limits of the control parameters of the shield tunneling machine are obtained. The conclusions are as follows. (1) The R2 of the test set for surface subsidence prediction is 0.916, and the RMSE is 2.655. (2) The proposed method can achieve multiobjective optimization, and the surface settlement, cutter head wear, and shield energy consumption are optimized by 49.92%, 24.38%, and 41.88%, respectively. (3) By using this method, both prediction and optimization can be realized, and the optimal control scheme can be obtained. The negative impact of shield tunneling construction has been significantly reduced.

Characteristics of Vibration Sources and Their Propagation Properties in Shield Construction

The vibration generated during the shield construction process may have an impact on the surrounding environment and structures, so it is particularly important to study the characteristics of its vibration sources and propagation properties. This paper analyzes the characteristics of the main vibration sources of the shield machine during the construction process, including the vibration frequency, amplitude distribution and so on. Through the literature research of various experts and scholars, the change rule of vibration sources under different working conditions is explored, and the propagation characteristics of vibration in the soil body are studied. This study can provide reference basis for vibration control and environmental protection during shield construction. The main conclusions are as follows: 1) the vibration during shield construction is mainly generated by the interaction between the cutter plate and the surrounding rock; 2) the frequency of vibration caused by shield construction is mainly in the range of 0~80Hz, and the amplitude is related to the nature of the excavated soil and the construction parameters; 3) the vibration tends to decrease with the increase of the distance, and the high-frequency vibration propagates faster than the low-frequency attenuation in the soil body.

How Do We Analyze the Accident Causation of Shield Construction of Water Conveyance Tunnels? A Method Based on the N-K Model and Complex Network

In the construction of water conveyance tunnels with the shield method, accidents have occurred from time to time, such as collapses and explosions, and it is of practical significance to explore the cause mechanism of the accident. However, previous research has not considered the effects of dependence between risks on the risk spread. In response, we propose a method based on the Natural Killing Model (the N-K Model) and complex network theory to analyze the cause of shield construction accidents in water conveyance tunnels. By deeply exploring the transmission mechanism and action intensity between system risks, this method can scientifically clarify the accident cause mechanism and provide support for engineering construction safety management. The method constructs a risk index system. Secondly, we introduce the N-K model to reveal the risk coupling mechanism. Then, based on complex network theory, we construct the incident causation model and revise the node’s centrality with the coupling value. Finally, the network topology parameters are calculated to quantitatively describe the causal characteristics of accidents, revealing the risk evolution process and critical causes. The research results indicate that the key causes of accidents are failure to construct according to regulations, inadequate emergency measures, poor ability of judgment and decision-making, and insufficient understanding of abnormal situations. The front end of critical links is subject to human or management risks and should be carefully controlled during construction.

Effects of shield construction on dynamic characteristics and deformation of interlayer soil: A case study in Changchun, China

Effects of shield construction on dynamic characteristics and deformation of interlayer soil: A case study in Changchun, China

Effects on upper masonry structures caused by double-line parallel shield cutting group pile construction

The effects on the upper masonry structure and the construction parameters of shield cutting piles were studied during shield construction, focusing on a shield interval of Zhengzhou Metro Line 5. The study utilized the actual engineering case of left and right double-lane shields superimposed on cutting cement soil group pile composite foundations beneath masonry structures. Findings revealed that masonry structures within approximately 30 m (5.0 times the tunnel diameter) were impacted before and after shield cut pile construction, resulting in deflection and twisting deformations of houses along the central axes of the left and right tunnel lines. Implementation of “clay shock” grouting outside the shield shell, radial grouting through small conduits, shield tail synchronous grouting, and secondary reinforcement grouting effectively mitigated the disturbance caused by shield construction to the ground. When shield cut piles passed beneath masonry structures, pressure on the soil chamber, total thrust, and cutterhead speed were consistently controlled. Furthermore, the cutterhead torque was appropriately reduced, and slurry injection volume increased, contributing to better control of house settlement.

Dynamic prediction and optimization of tunneling parameters with high reliability based on a hybrid intelligent algorithm

In this paper, a hybrid intelligent framework comprising Bayesian optimization (BO), gradient boosting with categorical features (CatBoost) and the nondominated sorting genetic algorithm-III (NSGA-III) was proposed to support multiobjective optimization of shield construction parameters without large sample datasets, improve the shield performance, and ensure reliable and interpretable results. First, with the use of the specific tunneling energy, advancing speed and cutter wear as objective functions, a BO-CatBoost prediction model for shield construction parameters and various objectives was constructed, and the key influencing factors were identified via the SHapley Additive exPlanations (SHAP) method. Then, a BO-CatBoost-NSGA-III model was developed to obtain Pareto solutions under different scenarios involving the adjustment of the key influencing factors. Finally, adopting the Wuhan Metro as the background, the accuracy, stability, and generalizability of the constructed algorithm were verified. The results indicated that (1) the developed BO-CatBoost algorithm is superior to 9 other algorithms. The R2 values of the proposed approach were 0.976 and 0.901–0.976 on the test set. (2) The developed BO-CatBoost-NSGA-III algorithm could be used to obtain Pareto solutions under different scenarios via the adjustment of the key influencing factors with the SHAP method, and the optimal solutions could facilitate improvements in the advancing speed, specific tunneling energy and cutter wear of 3.45 %, 6.09 %, and 0.52 %, respectively, with an overall average reliability of 90.5 %. (3) By comparing various prediction algorithms, optimization schemes of different objectives and geological conditions, the accuracy, stability, and generalizability of the constructed algorithm were verified. The developed BO-CatBoost-NSGA-III framework could enable dynamic adjustment of shield construction parameters for decision-making purposes in the event of conflicting shield construction objectives and exhibits generality.

Study on the Rules of Ground Settlement and Pipeline Deformation Considering the Combined Effects of Pipeline Damage Leakage and Shield Tunneling Construction

A pipeline with long-term “hidden leakage” will greatly reduce the stability of the ground between the pipeline and tunnel in the process of tunneling through existing pipelines in unsaturated soil. Excessive settlement of the surrounding strata and pipelines can occur when the shield excavation face approaches below a pipeline, which can lead to engineering accidents. This study is based on a self-developed model experimental system for tunneling through an existing pipeline with a double-line tunnel shield. The ground settlement and pipeline deformation caused by shield construction with small-scale and no leakages are investigated. An experimental study is conducted and the accuracy of the results is verified through a comparison with theoretical solutions. The results demonstrate that there is a significant increase in ground settlement and pipeline deformation under the influence of leakage water. It is also determined that the displacement field generated by the excavation of a double-line tunnel is not simply a superposition of the displacement field generated by the excavation of a single-line tunnel. The repeated disturbances caused by the excavation of a double-line tunnel significantly influences the redistribution of the displacement field. Additionally, a three-dimensional (3D) model of shield construction considering the influence of pipeline leakage is established. This study discusses the ground settlement and pipeline deformation patterns caused by changes in the vertical and horizontal leakage diffusion ranges. The computational results indicate that the diffusion depth of a leakage is the primary factor controlling the extent of settlement.

Optimizing Grouting Parameters to Control Ground Deformation in the Shield Tunneling

In urban shield tunneling, reducing the disturbance of underground construction to the surrounding environment is important for both tunnel engineers and researchers. Among other factors, the quality of synchronous grouting is one of the crucial factors affecting the safe construction of shields. In order to determine a reasonable grouting pressure and grout amount during shield construction, the relationships among synchronous grouting pressure, grout amount and shield chamber pressure are analyzed using field monitoring data. Based on the tunnel face pressure and the ultimate yield conditions of the soil at the gap edge, a method for calculating the grouting pressure considering the overburdening load of the tunnel was proposed. Then, by linking the grout amount and the grouting pressure, an accurate calculation method for the simultaneous grout amount in shield construction was proposed. These methods were then used in the construction of the Jurong shield tunnel. The results show that the adopted grouting pressure and grout amount calculated by the proposed method, which considered the change of the overburdening load of the tunnel, can well control the ground deformation caused by the shield construction and significantly reduce the uneven settlement of the surface buildings. The proposed methods in this paper may provide a reference for other shield construction projects.

Contract, network or hierarchy? Selecting governance mechanisms in megaprojects from the perspective of contractor alliances

Understanding the evolving governance mechanisms in megaprojects is crucial for reducing transaction costs and ensuring project success. However, previous literature primarily discusses the results of selecting governance mechanisms at different phases, with little research exploring the reasons behind these choices. To fill this gap, this article addresses the question of how to select effective governance mechanisms at different phases from the perspective of contractor alliances, based on transaction cost economics (TCE). We employ a longitudinal exploratory case study method to analyse the governance mechanism selection process across three phases (i.e. contractor alliance formation phase, shield construction phase and crisis response phase) of a large infrastructure project in China. The results indicate that the likelihood of opportunistic behaviour, uncertainty and the duration of the phase jointly explain the reasons for selecting specific governance mechanisms. Additionally, we also find that contractual governance, network governance and hierarchical governance are typically complementary in multiple phases of megaprojects. This article provides valuable managerial insights for future governance practices in megaprojects.

Study on the Reuse of Shield Mud from Clay Stratum in Synchronous Grouting Slurry

The purpose of this study is to investigate the feasibility of replacing the fly ash in synchronous grouting material by reusing the shield mud produced in the clay stratum during the shield construction of Wuhan Rail Transit Line 11. The test utilizes the shield mud from the clay stratum to replace the fly ash material in synchronous grouting at percentages of 20%, 40%, 60%, 80%, and 100%, and research and analyses are conducted on the fluidity, stability, strength, and resistance to water dispersion of the slurry after the replacement; at the same time, improvements in the undesirable phenomenon produced by the synchronous grouting slurry are also examined after the replacement. The results show that, when the fly ash is replaced by shield mud at 80%, the mortar still has good stability and strength performance, but, at the same time, the initial value of consistency and the phenomenon of flow time loss is too large. Through the adjustment of the water–binder ratio and the addition of an appropriate amount of a polycarboxylate superplasticizer agent, the adverse phenomenon of the slurry is effectively improved, and the compressive strength and ease of the slurry are also improved. At the same time, when adding an appropriate amount of hydroxyethyl methyl cellulose (HEMC), the slurry has good water dispersion resistance, but, with the gradual increase in HEMC, the fluidity of the slurry deteriorates and the compressive strength decreases. The test proves that the shield mud in the clay stratum can be used to replace most of the fly ash in an appropriate proportion, which not only solves the problem of the shield mud being difficult to work with, but also provides more valuable insights for tunneling projects.

Vibration reduction technique of shield construction in water-rich karst strata

In shield tunneling within karst formations, the vibrational effects often impact the safety of surrounding residents and buildings. The study of construction vibration mitigation measures holds significant importance. Based on the shield tunneling project in the Huang-Shang section of the Xuzhou Metro Line 6, this paper studies the causes, propagation characteristics and influencing factors of ground vibration caused by shield construction. Three effective mitigation measures were identified: (1) Optimization adjustment of shield tunneling parameters; (2) Grouting with mixed bentonite; (3) Layout of vibration reduction boreholes. Each mitigation measure was individually tested for its impact on ground vibration. The comprehensive application of the three measures in shield tunnel construction was analyzed to assess their combined effectiveness. The integration of actual engineering measurements indicates that boreholes provide the best damping effect. Furthermore, the application of multiple mitigation measures resulted in an overall 60% reduction in ground vibration, significantly mitigating the impact on residential structures on the ground. This study provides valuable references for vibration reduction measures in other engineering projects.

Active learning-based research of foaming agent for EPB shield soil conditioning in gravel stratum

Injecting soil conditioner into the soil during EPB shield construction is crucial for soil enhancement. Foam agent consumption is common but developing their composition and qualities is time-consuming. Hence, there is an urgent need for a novel approach to material design. This study presents the development of an active learning-based model for foam agents to enhance soil conditioning in gravel strata during EPB shield operations. Foaming volume and half-lift time were forecasted using six machine learning algorithms. The Extra Tree Regression (ETR) model was the most effective for volume prediction, while CatBoost Integration (CB) model performed best for time prediction. The new foam has a half-life of 945 s and the Foam Expansion Ratio (FER) of 21, suitable for EPB shield soil conditioning. The results of slump value and shear strength experiments show a positive correlation between soil slump value, shear strength, and an increase in Foam Inject Ratio (FIR).

A facile superlithiophilic 3D host with a transition metal oxide heterostructure for ultrastable zero-volume-expansion lithium metal anodes

Lithium metal batteries (LMBs) are widely recognized as the candidate for next-generation energy devices due to their unprecedented capacity and low electrochemical potential. Nonetheless, their practical implementation has been hindered by the dendrite formation and unstable solid electrolyte interface (SEI). In this study, we introduce a novel approach involving the in-situ growth of a ZnO–CuO heterostructure within a crack shield construction on a three-dimensional (3D) copper foam host. Computational COMSOL simulations reveal remarkable improvements in homogenizing lithium ion flux subsequent to decoration. Through galvanostatic measurements, the Li@ZnO-CuO-CF electrode exhibits an exceptionally low 0.2 V hysteresis, no volume expansion and uniform lithium deposition in symmetry cells under a 50 mA cm−2 current density. Furthermore, the electrode retains 95.4 % initial capacity after 600 cycles at 0.5C and 85.5 % initial capacity after 220 cycles at 1 C when coupled with a LiFePO₄ (LFP) cathode. This work sheds light on the facile fabrication of practical Li metal anodes for high-energy-density LMBs.

Study on the Distribution Law of External Water Pressure with Limited Discharge during Shield Construction of Soft Rock Tunnel in Western Henan Province

When shield tunneling is carried out in poor geological areas with high water head and low strength, there is a great construction risk, and the external water pressure is one of the key factors affecting the stability and safety of the tunnel during shield tunneling. Taking the Yinguruxin tunnel of Xin’an County as the engineering background, the geological conditions and water-bearing characteristics of the water-rich area in the tunnel excavation path are analyzed by means of drilling and high-density electrical method, and the pumping test is used to evaluate the groundwater linkage in the water-rich area. The 2022 version of Midas GTS NX is used to study the distribution characteristics of external water pressure during tunnel excavation in fault zones, and the influence of different drainage rates on the external water pressure of the tunnel is analyzed. The results show that the rock mass in the unfavorable geological section of the tunnel excavation is broken and rich in water, but the complexity of the stratum leads to uneven water richness in the axis direction of the tunnel. The drainage rate is the key to affecting the external water pressure of the lining. The drainage rate is the key to affecting the external water pressure of the tunnel. The correct drainage rate is an effective measure to reduce the external water pressure of the tunnel. The internal and external water pressure of the tunnel decreases with the increase of the drainage rate. When the drainage rate reaches 66.67% of the water inflow, the external water pressure of the tunnel can be reduced to 0.3 MPa to ensure the safety of the earth pressure balance shield machine in the tunneling process. The conclusion provides a useful reference for the high water pressure control of the tunnel shield tunneling process.

Multisource information fusion for real-time prediction and multiobjective optimization of large-diameter slurry shield attitude

Abnormal large-diameter slurry shield attitudes (SA) lead to safety and quality problems in shield construction. To achieve intelligent prediction and optimization of the large-diameter slurry SA, a combination of Bayesian optimization categorical boosting (BO-CatBoost) and a multiobjective evolutionary algorithm based on decomposition (MOEAD) is proposed for the prediction and optimization of the tunnel large-diameter slurry SA, as well as the corresponding digital twin framework. Using the Yangtze River large-diameter slurry shield project in Wuhan as an example, data were collected for three soil conditions, namely, silty fine sand, angular gravelly soils and chalky clays, and gravelly soil. The results show that: (1) The R2 values of the three predicted types of soils are all above 0.9, the RMSE values are less than 1.2, and the MAE values are less than 0.9. (2) Based on the results of the SHapley Additive exPlanations (SHAP), the propulsive thrust had the greatest influence on the large-diameter slurry SA. (3) The large-diameter slurry SA optimization improves when the number of adjusted construction parameters increases, with a maximum optimization rate of 23.436%. In addition, a digital twin framework based on BO-CatBoost-MOEAD is proposed, which can effectively control large-diameter slurry SAs and improve overall project safety and quality.

Three-Dimensional ERT Advanced Detection Method with Source-Position Electrode Excitation for Tunnel-Boring Machines

Tunnel-boring machines (TBMs) are widely used in urban underground tunnel construction due to their fast and efficient features. However, shield-tunnel construction faces increasingly complex geological environments and may encounter geological hazards such as faults, fracture zones, water surges, and collapses, which can cause significant property damage and casualties. Existing geophysical methods are subject to many limitations in the shield-tunnel environment, where the detection space is extremely small, and a variety of advanced detection methods are unable to meet the required detection requirements. Therefore, it is crucial to accurately detect the geological conditions in front of the tunnel face in real time during the tunnel boring process of TBM tunnels. In this paper, a 3D-ERT advanced detection method using source-position electrode excitation is proposed. First, a source-position electrode array integrated into the TBM cutterhead is designed for the shield-tunnel construction environment, which provides data security for the inverse imaging of the anomalous bodies. Secondly, a 3D finite element tunnel model containing high- and low-resistance anomalous bodies is established, and the GREIT reconstruction algorithm is utilized to reconstruct 3D images of the anomalous body in front of the tunnel face. Finally, a physical simulation experiment platform is built, and the effectiveness of the method is verified by laboratory physical modeling experiments with two different anomalous bodies. The results show that the position and shape of the anomalous body in front of the tunnel face can be well reconstructed, and the method provides a new idea for the continuous detection of shield construction tunnels with boring.

Study on the Fracture of a Shield Segment in a Fully Excavated Hard Rock Section under the Influence of Construction Loads

In this paper, the initiation of the fracture of a segment caused by the pressure of the jack and other factors during shield construction is discussed. Based on the Rots model in the finite element software Diana 10.4, the fracture width is solved. Combined with in situ measurements, the mechanisms of concrete fracturing of a segment under external loads, such as the jack thrust deflection angle and uneven jack thrust caused by the changes in the segment due to the upward buoyancy and shield attitude, are studied; additionally, the occurrence conditions and engineering control measures for segment fracture are summarized. The results show that when the attitudes of the shield and segment are identical, the total thrust of the shield is recommended not to exceed 21,000 kN, and is strictly limited to 24,000 kN. When the attitude inclination angle between the shield machine and the segment is less than 1°, the impact on the segment quality is small. When the inclination angle reaches 2°, the total thrust of the shield is recommended not to exceed 16,000 kN, and is strictly limited to 18,000 kN. When the inclination reaches 3°, a fracture is easily produced. When the total thrust is 19,000 kN, it is recommended that the loading increase or decrease in the left and right four grippers should not exceed 20%, and they are prohibited to exceed 30%. The fracture width increases exponentially with the increase in misalignment between adjacent segment rings. These research results provide a theoretical basis for jack pressure control during shield construction.

Optimisation of Synchronous Grouting Mix Ratio for Shield Tunnels

During shield construction in underground spaces, synchronous grouting slurry is poured between the surrounding rock and tunnel lining to ensure stability. For synchronous grouting slurries, few studies have investigated the relationship between the rheological parameters and physical properties, grout-segregation mechanism, and anti-segregation performance. Therefore, we explored the relationships between the slurry rheological parameters, segregation rate, and bleeding rate. Cement, sand, fly ash, and bentonite were used to prepare the slurry, and the effects of different polycarboxylate water-reducing agents and dispersible latex powder dosages were studied. The rheological parameters of 16 groups of uniformly designed slurries were tested, and the data were fit using the Herschel–Bulkley model. The optimal mix ratio lowered the slurry segregation rate, and its rheological behaviour was consistent with the Herschel–Bulkley fluid characteristics. High-yield-shear-stress synchronous grouting slurries with high and low viscosity coefficients were less likely to bleed and segregate, respectively. The optimised slurry fluidity, 3 h bleeding rate, 24 h bleeding rate, segregation rate, coagulation time, and 28 days compressive strength were 257.5 mm, 0.71%, 0.36%, 3.1%, 6.7 h, and 2.61 MPa, respectively, which meet the requirements of a synchronous grouting slurry of shield tunnels for sufficiently preventing soil disturbance and deformation in areas surrounding underground construction sites.

Analysis of sensor parameters for ultra close range lateral penetration of subway tunnel full section sand layer soil pressure shield tunneling

In order to solve the problem of large disturbance to the stratum caused by shield tunneling in the full face sand layer geology by using the earth pressure balance full bin tunneling technology in the subway tunnel shield construction, this paper presents a parameter analysis of the ultra close side penetration of the full face sand layer earth pressure shield in the subway tunnel. By analyzing the monitoring data of surface settlement caused by subway shield construction, it is concluded that the law of surface horizontal settlement basically conforms to peak settlement theory, and the law of surface vertical settlement basically shows a steady downward trend. Through the mathematical modeling of the cumulative settlement data affected by the shield passing of the right line tunnel at the surface monitoring point, the influence of the shield passing of the left line tunnel on the surface settlement is predicted, and the prediction result is accurate. The experimental results show that the maximum deviation is 1.47 mm and the minimum deviation is 0.03 mm. The prediction accuracy is high and meets the accuracy requirements of practical engineering. Under the same geological conditions and construction parameters, the disturbance law of tunnel shield construction on the ground surface has important guiding significance in practical engineering.