Search Results (27)

The large-diameter slurry tunnel boring machine (TBM) is widely used in the construction of tunnels across rivers and seas. However, cutter wear has become a critical issue that severely limits the tunnelling efficiency. Taking the Qingdao Jiaozhou Bay Second Subsea Tunnel Project as the background, the wear patterns of disc cutters on the atmospheric cutterhead of a large-diameter slurry TBM under complex geological conditions were analyzed. The flat wear of disc cutters induced by factors such as rock chip accumulation in front of the cutterhead, the jump trajectory when changing disc cutters, alloy-insert disc cutter mismatch, cutter barrel clogging, and severe wear of scrapers is discussed. Furthermore, the impacts of measures such as slurry circulation to remove rock chips during TBM stoppage, clay dispersant injection into the slurry chamber, cutter barrel flushing, and the wear resistance optimization of cutters and cutter barrels on reducing cutter wear were investigated. Based on numerical simulations and field data, a methodology for determining the optimal timing for cutter replacement is proposed. The results indicate the following: The circulation system effectively reduces accumulation, minimizing secondary wear of the disc cutters and lowering the risk of clogging in the cutter barrel. Adopting measures such as shield shutdown, a circulation system to carry away the slag, cutter barrel flushing, and soaking in 2% dispersant for 8 h can effectively reduce the accumulation of rock chips and mud cakes on the cutterhead, which in turn reduces the flat wear of the disc cutter. Measures such as making the cutter body and cutter ring rotate together and adding wear-resistant plates to the cutter barrel greatly improve the life of the cutter. The sharp increase in composite parameters can serve as an effective marker for assessing cutter conditions. The findings of this study can provide valuable insights into reducing cutter wear in similar projects. Full article

In order to realize effective attitude-predictive control during large-diameter shield tunneling, this study established an intelligent framework for attitude prediction. Specifically, a principal component analysis–support vector regression (PCA-SVR) hybrid model was constructed, based on principal component analysis. The principal component analysis method was used to mine the relevant input parameters and reduce the accompanying data noise. SVR used statistical learning and structural risk minimization to overcome data overfitting. Taking a large-diameter shield tunnel, the Zhuhai Xingye Express Tunnel, as an example, the proposed PCA-SVR model was validated by considering tunnel excavation parameters, geometric parameters, and geological parameters. At the same time, the correlation coefficient was used to analyze the relationship between input parameters and attitude parameters. The results show that the propulsion cylinder pressure is an important factor affecting the trajectory of attitude motion. The geometrical and geological parameters of the shield have a strong correlation with the attitude parameters. The attitude parameters predicted by the model are within the range of the corresponding monitoring data. The high prediction accuracy verifies that the proposed PCA-SVR hybrid model can accurately predict the attitude parameters during shield tunneling. The prediction framework can be used for reference for the attitude-prediction control of shields in similar projects. Full article

The development of the subway system in Shenyang City, China, plays a vital role in alleviating traffic congestion and promoting sustainable societal growth. However, the deformation of the surface caused by the tunneling of the shield presents a significant threat to the structural integrity of Shenyang Subway Line 2 and adjacent geotechnical structures. To tackle this challenge, a set of FEA (finite element analysis) simulations were carried out to examine surface deformation under various construction scenarios for Line 2. These simulations were compared with empirical formulas and numerical analyses conducted using Midas GTS NX 2019 software, in addition to actual site measurements. The outcomes of the finite element analysis (FEA) demonstrated a closer alignment with the empirical data than with traditional formulas. The maximum deformation was observed to be approximately twice as large as the equivalent diameter at the back of the excavation face. The analysis indicated that surface deformation is inversely correlated with overburden thickness (H), soil elasticity (E), and the grout filling rate of the shield tail (ψ), while it is directly proportional to the shield’s outer diameter (D). This study provides important methods used in the shield tunneling process employed in the Shenyang subway and suggests that the developed methodologies may be applicable to similar subway projects. Full article

Due to its inherent advantages, shield tunnelling has become the primary construction method for urban tunnels, such as high-speed railway and metro tunnels. However, there are numerous technical challenges to shield tunnelling in complex geological conditions. Under the disturbance induced by shield tunnelling, sandy pebble soil is highly susceptible to ground loss and disturbance, which may subsequently lead to the risk of surface collapse. In this paper, large-diameter slurry shield tunnelling in sandy pebble soil is the engineering background. A combination of field monitoring and numerical simulation is employed to analyze tunnelling parameters, surface settlement, and deep soil horizontal displacement. The patterns of ground disturbance induced by shield tunnelling in sandy pebble soil are explored. The findings reveal that slurry pressure, shield thrust, and cutterhead torque exhibit a strong correlation during shield tunnelling. In silty clay sections, surface settlement values fluctuate significantly, while in sandy pebble soil, the settlement remains relatively stable. The longitudinal horizontal displacement of deep soil is significantly greater than the transverse horizontal displacement. In order to improve the surface settlement troughs obtained by numerical simulation, a cross-anisotropic constitutive model is used to account for the anisotropy of the soil. A sensitivity analysis of the cross-anisotropy parameter α was performed, revealing that as α increases, the maximum vertical displacement of the ground surface gradually decreases, but the rate of decrease slows down and tends to level off. Conversely, as the cross-anisotropy parameter α decreases, the width of the settlement trough narrows, improving the settlement trough profile. Full article

With the development of large-diameter shield tunnels, how to realize effective security and stability control of shield tunnel lining has become a significant research topic. This paper investigates the deformation and failure mechanism of lining large diameter shield tunnels in depth and discusses the deformation characteristics and influencing factors of the lining of the shield tunnel with various diameters through the software of finite element analysis ABACUS. A set of models with varying diameters is built under identical stress conditions in order to maintain control over the variable. The utilization of the elastic–plastic model is observed in the application of bolts and rebar. The utilization of the Concrete Damage Plasticity model has been taken into account for the concrete lining. For the sake of comparison, the crown displacement of the shield tunnel, strain in tension and compressive zones, bolt stress and strain, deformation and intemal force distribution around the shield tunnel, and cracks in the tension zone, are carefully studied. An in-depth analysis is conducted to elucidate the variations in damage evolution mechanisms across linings of different sizes, within the framework of plastic hinge theory. The results indicate that the convergence deformation of large-diameter tunnel lining increases significantly during loading compared with that of small-diameter tunnel. Moreover, the probability of brittle failure is higher in big-diameter shield tunnels compared to small-diameter tunnels, indicating that these larger tunnel structures are more prone to suffering geometric instability. Full article

Relying on the Mawan undersea large-diameter, dual-line, mud–water-balanced shield tunnel project and focusing on the characteristics of the tunnel, such as the complex geological conditions at the expected intersection location and the existence of a superimposed perturbation or secondary perturbation effect, theoretical calculations and three-dimensional numerical simulations were used to reveal the ground disturbance situation of the large-diameter, two-lane mud–water shield when it is propelled under various working conditions. The working conditions were set for the dynamic intersection of the left and right lines, with stopping and moving as the two modes, and a traversing simulation was carried out under three conditions related to the strata. The results show that the surface settlement curve for the two-lane construction became a “W”-shaped bimodal curve due to the superposition effect; the dynamic intersection construction greatly disturbed the ground layer and there was a plastic zone expanding outward at a small angle above the tunnel, with shear damage in the soil layer and tensile damage in the rock layer. A “one line stops, and another advances” intersection can reduce the impact of disturbance; the surface settlement value after the completion of the advancement was smaller than the dual-line intersection. The surrounding rock stress and displacement under the advancement of a single shield machine did not change to a great degree, there was no obvious change in the surface settlement above the tunnel, and the effect of the secondary disturbance was small. Full article

The construction of large-diameter shield tunnels underwater involves complex variations in water and earth load outside the tunnel segment, as well as intricate mechanical responses. This study analyzes the variation laws of external loads, axial forces, and bending moments acting on the segment ring during the shield assembly and removal from the shield tail. It accomplishes this through the establishment of an on-site monitoring system based on the Internet of Things (IoT) and proposes a Bayesian-genetic algorithm model to estimate the water and earth pressure. The fluctuation section exhibits a peak load twice as high as that in the stable section. These variations are influenced by Jack thrust, shield shell force, and grouting pressure. The peak load observed in the fluctuation section is twice as high as the load observed in the stable section. During the shield tail removal process, the internal forces undergo significant fluctuations due to changes in both load and boundary conditions, and the peak value of the axial force during the fluctuation section is eight times higher than that during the stable section, while the peak value of the bending moment during the fluctuation section is five times higher than that during the stable section. The earth and water pressure calculated using the inversion analysis method, which relies on the measured internal forces, closely matches the actual measured values. The results demonstrate that the accuracy of the water and earth pressure obtained through inversion analysis is twice as high as that obtained using the full coverage pressure method. These results can serve as a valuable reference for similar projects. Full article

The aim of this research is to study the lateral deformation characteristics of the pile foundation in front of a shield construction and accurately predict its displacement in the shield tunneling direction. The impact of deep-shield construction on the pile foundations was analyzed using the Mindlin elastic solution to determine the lateral displacement. The Kerr foundation model and other factors, like additional shield thrust and uneven shell friction, were considered. The study assessed the impact of the incision distance, shield outer diameter, and additional thrust on pile displacement. The theoretical and numerical solutions of lateral displacement at various shield construction stages were compared to determine the variation law. The results indicate that the theoretical method is reliable, considering its good agreement with the numerical solutions. The buried depth of the shield means that the upper part of the pile is less affected by the additional thrust, leading to less deformation at the top. We recommend using a smaller shield thrust and outer diameter to control the pile’s end and top displacement. Full article

To reduce traffic congestion and meet the demand for rail transportation, the diameters of shield tunnels are constantly expanded. The super-large diameter, deep depth and long distance of super-large-diameter shield tunnels, coupled with the limitation of existing structures on underground construction space, cause many problems in the construction of these tunnels, such as affecting existing structures. This study takes a shield project in Wuhan as the research object, uses the finite element method to simulate the influence of super-large-diameter shield tunnelling on the displacement of the existing Line 5 tunnel segments, and analyzes the influence of the isolation pile arrangement and length on the isolation effect. The analysis indicates that (1) the displacement of Line 5 decreases with an increasing horizontal center distance between the tunnels and increases with an increasing vertical center distance between the tunnels, with a maximum displacement of 17.9 mm; (2) the displacement direction and position of the maximum displacement of Line 5 vary with changes in the vertical center distance between the tunnels, but remain essentially constant with changes in the horizontal center distance; and (3) the isolation piles closer to the shield tunnel improve support, with its isolation effect on the Line 5 segment becoming limited. Full article

The complex distribution of synchronous grouting pressure results in excessive tunnel deformation and various structural diseases, especially for ultra-large-diameter shield tunnels. In this study, to reduce the risk of tunnel failure, a three-dimensional refined finite element model was established for the Wuhan Lianghu highway tunnel project, taking into account the non-uniform distribution of synchronous grouting pressure. This study focuses on investigating the development patterns of internal forces, deformations, and damages in segment structures under varying grouting pressure ratios. The results indicate that the primary failure mode of a segment is tensile failure occurring at the outer edge of the arch. Moreover, an increased ratio of grouting pressure between the arch bottom and top leads to a higher positive bending moment value and greater tensile damage at the arch waist. The tunnel ring gradually exhibits distinct “horizontal duck egg” shape deformation. When the grouting pressure ratio is 2.8, there is a risk of tensile cracking at the outer edge of the arch waist. At this time, the segment convergence deformation is 39.71 mm, and the overall floating amount reaches 43.12 mm. This research offers engineering reference for the prediction of internal forces and deformations in ultra-large-diameter shield tunnels during grouting construction, thereby facilitating their application in the development of resilient cities. Full article

In order to accommodate more transportation-supporting facilities, the expansion of structures’ inner diameter has become the development trend of metro shield tunnels. But for large inner-diameter shield tunnels, the segment thickness design and bearing performance characteristics of tunnels under lateral unloading are still unclear. The purpose of the research was to select the optimal segment thickness and clarify the bearing performance of large inner-diameter shield tunnels. Therefore, in this study, a 3D refined numerical model was established to analyze and determine the optimal segment thickness for a shield tunnel with an inner diameter of 5.9 m. Furthermore, a full-scale test was carried out to study the bearing performance of the shield tunnel under lateral unloading. The results showed that the maximum tunnel horizontal deformation difference between the calculation and the test did not exceed 5%, and the maximum difference in the overall structure deformation between the calculation and the test did not exceed 7%. Increasing the segment thickness can reduce the convergence deformation of the shield tunnel nonlinearly; the deformation reduction was no longer significant when the segment thickness increased to 400 mm with an inner diameter of 5.9 m. Under the lateral unloading condition, the internal force of the tunnel structure increased significantly at sections of 0°, 55°, 125°, and 190°. Compared with the normal design load stage, the maximum bending moment and axial force increased by 36% and 74.1%, respectively, in the final failure stage. There was no bolt yield during the entire unloading process, indicating that the excessive strength of the bolt could not fully play a role in the entire life cycle of the large inner-diameter tunnel structure. The failure mechanism of the shield tunnel can be described as follows: in the early stage of a load, a shield tunnel will appear with joints open and dislocated. As the load increases, cracks in different directions gradually appear near the tunnel joint. In the ultimate load stage, the shield tunnel loses load-bearing capacity, and large areas of falling blocks appear at the top and bottom of the tunnel. Full article

This study focuses on investigating the surface settlement characteristics induced by the construction of a super-large-diameter shield tunnel in composite strata. By utilizing a combination of field monitoring and numerical simulation analysis, the surface settlement patterns encountered during the construction process in horizontally distributed typical soil–rock composite strata were summarized based on the 16.03 m super-large-diameter shield tunnel project in the southerly extension of He’ping Avenue in Wuhan. In addition, the collected data were used to enhance the Peck empirical formula. The results of the study show the following: (1) Significant non-uniform settlement occurs along the tunneling direction when the shield machine passes through soil–rock composite strata. The range of non-uniform settlement is approximately 3.1 times the tunnel diameter (D) in soil sections and 1.9 times the tunnel diameter (D) in rock sections. (2) The impact of composite strata on the maximum settlement is greater than its effect on the settlement trough width, with a larger impact within the soil sections compared to the rock sections. (3) The Peck correction formula, which takes into account the distance between the monitoring cross-section and the composite interface, provides more accurate predictions than the original Peck empirical formula. Full article

In recent years, there has been a rise in the construction of expansive underground structures and shield tunnels with exceptionally large diameters. These projects introduce unique challenges regarding their impact on the surrounding soil and structures, which differ from those typically encountered in conventional shield tunnels. However, the existing body of research in this specific domain remains insufficient. When such tunnels intersect deep foundation pits supported by piled-raft foundations, the discrepancies in soil deformation can become even more pronounced. At present, there is a dearth of research on the underlying principles governing these differences, and theoretical investigations have not kept pace with practical engineering applications. Consequently, the existing settlement prediction methods employed for diverse projects need to be reevaluated and adjusted to accommodate the distinctive characteristics of each individual project. Regarding the engineering focus of this paper, it is crucial to recognize that soil subsidence in the pit bottom has a significant influence on the mechanical response of the piles. Consequently, the implementation of targeted correction measures remains consistently important. Based on this concept, this paper focuses on a super-large diameter shield tunnel project that under-crossed a deep foundation pit with a piled-raft foundation. The influence of different construction methods on the settlement law of the soil at the bottom of the deep foundation pit is discussed after verification of the accuracy of the model through numerical simulation and field monitoring data. Additionally, two correction coefficients that consider the project’s load characteristics are proposed in this research. These coefficients were used to correct the surface settlement curve. The corrected soil settlement curve at the pit’s bottom can successfully reflect the numerical simulation results, which in turn can reflect the mechanical response of the pile under the influence of tunnel excavation. Full article

This paper presents a study on the influence of the construction of an ultralarge-diameter shield tunnel undercrossing the existing high-speed railway using the empirical method, numerical analysis method, and geotechnical centrifuge model experiment based on the Wuhan Lianghu Highway Tunnel project. The comparison of the results obtained from the three methods shows first, that the results obtained from the centrifuge model experiment and numerical simulation match well with the results obtained from the empirical method for the worst-case scenario and the most likely scenario, which are consistent with the unfavorable geological and construction conditions modeled in the centrifuge test and the possible geological and construction conditions modeled in numerical simulation. Second, both the results obtained from the numerical method and the centrifuge model experiment show that the asymmetry of the settlement of railway subgrade was induced by a shield tunnel, while the asymmetry of railway subgrade settlement curve is gradually weakening with tunneling. Third, the maximum settlement of the railway subgrade could vary between 20 mm (in the most likely scenario) and 65 mm (in the worst scenario). Both the results from the centrifuge test and the numerical simulation show that the allowed value of maximum differential settlement along the railway subgrade (5 mm/10 m) would be exceeded when the tunnel excavation passes the first track at 10 m. It indicates that some mitigation measures should be taken for controlling the influence of the construction of a shield tunnel, especially when the shield tunnel machine is about underneath the pass railway subgrade. It is suggested that the shield machine should underpass the railway subgrade during the skylight period of railway operation. Full article

The mechanical properties of sandy soil depend on both the confining pressure and the state of compactness. Therefore, both the buried depth of the tunnel and the relative density of the sand are key factors that affect the ground deformation induced by the tunneling of a super-large-diameter shield. In this study, the parameters of the SANISAND constitutive model are first calibrated based on triaxial test data for Foshan silty fine sand. Then, based on the actual project, a two-dimensional finite-element analysis model is established to investigate the ground deformation induced by the tunneling of a super-large-diameter shield. The width and maximum value of the settlement trough, the volume loss ratio, and the deformation characteristics of the soil are summarized and analyzed for 13 cases. The results show that as the ratio of the buried depth to the diameter and the relative density of sand increases, the anti-disturbance ability of the sand layer to the tunnel construction increases and the volume loss ratio of the stratum reduces correspondingly. The denser the sand and the smaller the confining pressure of the soil around the tunnel, the more significant the shear-induced expansion of the sand at the tunnel haunch; this expansion partially makes up the volume loss caused by the tunnel excavation and reduces the loss ratio of the stratum at the arch crown. Full article