Search Results (42)

This study investigates the deformation characteristics and control measures for existing metro shield tunnels induced by large-section rectangular pipe jacking over-crossing, focusing on the Chengbei Road Comprehensive Utility Corridor project in Suzhou. A 9.1 m × 5.5 m pipe gallery was installed 73.6 m through clay strata over operational subway tunnels, with a minimum clearance of 4.356 m above the tunnel. Finite element simulations and field monitoring were employed to analyze the deformation of the existing tunnels, particularly the effectiveness of anti-uplift counterweights. The results revealed that excavation-induced unloading caused significant tunnel uplift, with maximum vertical displacements of 5.51 mm and 4.95 mm for the down line (DL) and up line (UL) tunnels, respectively. The addition of counterweights reduced these displacements by 30.3% and 37.1%, while also decreasing lateral displacements by up to 61.6% and bending moments by approximately 33%. The study demonstrates that counterweights, combined with slurry lubrication, real-time monitoring, and over-excavation control, effectively mitigate deformation and stress variations during large-section pipe jacking. The successful completion of the project without disrupting subway operations highlights the practical applicability of these measures. Full article

In slurry shield tunneling projects, leakage from floating seals frequently leads to abnormal failures of disc cutters. To investigate the leakage characteristics at the floating seal end faces of the cutters, a numerical method is proposed for analyzing the dynamic leakage behavior of the floating seal end faces, considering the effects of wear. The elastohydrodynamic lubrication problem of the floating seal was addressed using the Reynolds equation and the slicing method, leading to the development of a computational model for the pressure and thickness distribution of the oil film on rough surfaces. Based on the Archard wear equation, a dynamic surface roughness model considering wear was established. Furthermore, a numerical model for dynamic leakage of the floating seal end faces in shield machine cutters, incorporating wear effects, was developed. Simulated friction and wear tests of the floating seal end faces, along with cutter seal leakage experiments, were conducted for validation. The results demonstrate that the dynamic surface roughness model considering wear can effectively predict the roughness evolution of worn surfaces. The trend of the theoretical leakage rate is generally consistent with that of the experimental results, verifying the effectiveness of the proposed model. Full article

The ground settlement induced by shield tunnel construction should be carefully monitored and controlled during construction as a compulsory measurement to ensure construction safety. In the existing literature, gap parameter theory is adopted to predict ground settlement; however, the influence of slurry grouting on ground settlement during the construction process has been ignored. Regarding this drawback, a novel optimized gap parameter theory is proposed and combined with 3D finite element analysis to investigate ground settlement caused by shield tunnel excavation. Considering that construction technology plays an important role in ground settlement, numerical studies are carried out to investigate the sensitivities of the grouting filling ratio, pressure of the tunnel face, and the strata conditions in ground settlement. The practical engineering of Wuhan Metro Line 7 is introduced to verify the superiority of the proposed method. The results show that the proposed method can reflect ground settlement well, compared to the existing methods and the measured data. Then, 3D finite element analysis and orthogonal test are adopted to conduct sensitivity analyses of the grouting fill rate, support pressure ratio, and strata conditions. The results illustrate that the grouting filling rate has the most obvious impact on ground settlement, while the support pressure ratio and strata conditions also have a certain impact on ground settlement. Taking the binary structure stratum of the terrace geological environment of the Yangtze River in Wuhan as the research object, this study employs a three-dimensional numerical simulation approach to analyze six distinct binary structure stratum models. The parameter value ranges, considering formation conditions, are determined through integrated theoretical analysis. Finally, based on the deviation analysis results between the optimized gap parameter theory and numerical simulation, it is concluded that there is no significant difference in the surface settlement values obtained from the two methods. To summarize, the proposed optimized gap parameter theory, combined with the corresponding numerical simulation technology, provides a good tool for the control of ground settlement caused by shield tunnel excavation in complex strata, such as binary structure strata. Full article

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

The TBM disc cutter, which is the main cutting tool of tunnel boring machines (TBMs), is replaced when it is excessively worn during the boring process. Disc cutters are usually monitored by workers at cutterhead chambers, and they check the status and wear of disc cutters. Manual measurement occasionally results in inaccurate measurement results. In order to overcome these limitations, real-time disc cutter monitoring techniques have been developed with different types of sensors. This study evaluates the distance measurement performance of an eddy-current sensor for measuring disc cutter wear via a series of laboratory experiments. This study focused on identifying the effects of various measurement environments on the sensor’s accuracy. The study considered conditions that the eddy-current sensor may encounter in shield TBM chambers, including air, water, slurry, and excavated muck. Experiments were conducted using both a small-scale disc cutter and a 17-inch full-scale disc cutter. The results indicate that the eddy-current sensor can accurately measure the distance to the disc cutter within a specific range and that its performance remains unaffected by different measurement environments. Full article

During slurry shield tunneling in hard rock or cobble strata, the discharge pipes suffer serve wear and damage. However, the effect mechanism of pipe wall wear defects on the flow characteristics of two-phase flow is unclear. In this study, a three-dimensional slurry particle model of pipeline transport was established using the coupled computational fluid dynamics–discrete element method (CFD-DEM) considering the pipe wall wear defect, and the typical pipeline forms of straight pipe and 90° elbow pipe were selected as the research targets. The results indicated that the localized wear defect of pipes can lead to increased inhomogeneity in the velocity distribution, generating localized low-flow zones and resulting in a reduced flow rate or stagnancy in parts of the pipe. Meanwhile, the wear defect of the pipe results in local shape changes, so that the fluid flow path through the pipe is no longer smooth, causing more vortex/turbulence and secondary flow, where an increased vortex promotes localized kinetic energy reduction and creates larger pressure losses at the elbow. In addition, for the elbow pipe without wear defect, the pressure drop of the elbow increases quadratically from an increase of 6.5% to an increase of 16.9%, with the maximum wear depth increasing from 4 mm to 19 mm. For the straight pipe without wear defect, the pressure drop of the elbow increases linearly, from an increase of 2.2% to an increase of 10.2% with the maximum wear depth increasing from 4 mm to 19 mm. The paper investigates the potential mechanism of pipe flow characteristics influenced by wear defect and provides practical guidelines for the efficient operation of a slurry shield circulating system. Full article

To investigate the mechanism by which clay shock slurry fills excavation gaps and reduces ground layer deformation during shield tunneling, we conducted a study using the project example of Beijing Metro Line 19 from Youanmenwai Station to Niujie Station, which passes through Guang’anmennei Station to CaiShiKou Station of Beijing Metro Line 7 at a close distance. We employed physical and mechanical testing, numerical simulation calculations, and other methods to examine the deformation law and mechanism of the clay shock method in shield tunneling construction. Our results indicate that (1) as the mass concentration of clay shock slurry increases, its permeability decreases significantly; at a mass concentration of 400 kg/m³, clay shock slurry can prevent synchronous grouting slurry from flowing forward, providing optimal filling and support for excavation gaps. (2) Clay shock slurry can reduce friction between the shield shell and soil body by 50%, avoiding super-consolidation, shear damage, and volumetric expansion of the surrounding soil body. (3) Radial grouting with a two-fluid slurry of cement–water glass at a 1:1 ratio within 15 rings after shield tail removal effectively reduces settlement of the existing tunnel. (4) Numerical simulations demonstrate that using clay shock slurry to fill shield tunnel gaps not only significantly reduces construction settlement but also effectively inhibits strata displacement along the tunnel axis. Full article

As shield tunnels increase, managing shield muck strains construction and the environment. To mitigate this problem, shield muck replaced bentonite in silty clay to improve synchronous grouting slurry. Initially, the physical attributes and microstructural composition of shield muck were obtained, alongside an analysis of the effects of the muck content, particle size, and general influencing factors on the slurry properties through standardized tests and regression models. Subsequently, leveraging three-dimensional response surface methodology, admixture interactions and multiple factor impacts on the slurry were explored. Finally, utilizing the SQP optimization technique, an optimal slurry blend ratio tailored for actual project needs was derived for improved muck slurry. The findings reveal with the decreasing bleeding rates as the muck content rises, the particle size diminishes. An inverse relationship exists between the muck content and slurry fluidity. At soil–binder ratios below 0.6, a decrease in the soil–binder ratio intensifies the influence of the water–binder ratio on the slurry density, bleeding rate, and setting time. The fly flash–cement ratio inversely correlates with the slurry bleeding rate, while the ratio greater than 0.6 is positively correlated. For muck particle sizes under 0.2 mm, the fly flash–cement ratio inversely impacts the density, while over 0.2 mm, it correlates positively. The optimal proportion for silty clay stratum synchronous grouting slurry, substituting muck for bentonite, includes a water–binder ratio of 0.559, binder–sand ratio of 0.684, fly flash–cement ratio of 2.080, soil–binder ratio of 0.253, particle size under 0.075 mm, and water-reducing admixture of 0.06. 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

The high permeability of gravel sand increases the risk of water spewing from the screw conveyor during earth pressure balance (EPB) shield tunnelling. The effectiveness of soil conditioning is a key factor affecting EPB shield tunnelling and construction safety. In this paper, using polymer, a foaming agent, and bentonite slurry as conditioning additives, the permeability coefficient tests of conditioned gravel sand are carried out under different injection conditions based on the factorial experiment design. The interactions between different concentrations of conditioning additives are analyzed. A prediction model for soil conditioning during shield tunneling based on particle swarm optimization (PSO) and relevance vector machine (RVM) algorithms is proposed to accurately and efficiently obtain the soil conditioning parameters in the water-rich gravel sand layer. The experimental results indicate that the improvement effect of the foaming agent on the permeability of the conditioned gravel sand gradually diminishes with the growing concentration of bentonite slurry. Under conditions of high polymer concentration, further increasing the concentration of bentonite slurry and foaming agent has a weak impact on the permeability coefficient when the concentration of bentonite slurry exceeds 10%. The significance of main effects, first-order interactions, and second-order interaction on the permeability of conditioned gravel sand are as follows: polymer concentration (A) > foaming agent concentration (B) > bentonite slurry concentration (C) > first-order interactions (A × B, A × C, B × C) > second-order interaction (A × B × C). The first-order interaction mainly manifests as a synergistic effect, while the second-order interaction primarily exhibits an antagonistic effect. Case studies show that the maximum relative error between predicted and experimental values is less than 3%. A field application of shield tunneling demonstrates the good performance of real-time optimization of soil conditioning parameters based on the PSO–RVM algorithm. This research provides a new method for evaluating the effectiveness of soil conditioning in the water-rich gravel sand layer. Full article

A bentonite slurry mixed with seawater is prone to sedimentation, which will reduce the quality of the filter cake and lower the stability of the excavation surface in undersea tunnels. It is necessary to study the performance and influencing factors of the bentonite slurry mixed with seawater. This article simulates the process of undersea slurry shield tunnel construction, where the pressurized slurry penetrates into the sand layer and forms a filter cake when the shield stops pressurizing. We investigated the effects of bentonite, additives (CMC), fine sand, pressure, and formation permeability on the performance of the seawater slurry and filter cake. The sedimentation of mud caused by seawater interfered with the experiment, which manifested as the increase in bentonite, and delayed the formation of the filter cake. Fine sand with a particle size close to the average value of the formation can improve the speed and quality of filter cake formation. By conducting a sensitivity analysis on experimental data, the degree of influence of various factors on the formation rate, thickness, and porosity of the filter cake was determined. Fine sand and bentonite are the factors that have the greatest impact on the formation rate, thickness, and porosity of the filter cake. Full article

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. Full article

The rapid and accurate control of air chamber pressure in slurry pressure balance (SPB) shield tunneling machines is crucial for establishing the balance between slurry pressure and soil and water pressure, ensuring the stability of the support face. A novel air chamber pressure control method based on nonlinear adaptive robust control (ARC) and using a pneumatic proportional three-way pressure-reducing valve is proposed in this paper. Firstly, an electric proportional control system for the air chamber pressure is developed. Secondly, a nonlinear state space model for the air chamber pressure regulation process is established. Utilizing experimental data from the SPB shield tunneling machine test bench, nonlinear adaptive identification is conducted through the nonlinear recursive least square algorithm. The results demonstrate the model’s effectiveness and accuracy. Then, a nonlinear ARC for air chamber pressure is designed based on the backstepping method, and its Lyapunov stability is proved. Finally, the feasibility and effectiveness of the controller designed in this paper is verified through simulation and experiments. The results demonstrate that the developed control system can compensate for the nonlinearity and disturbance in the air chamber pressure regulation process. It can achieve good transient and steady-state performance and has good robustness against uncertainty. Full article

Insufficient investigations have been conducted on the analysis of shield tunneling parameters and the prediction of the tunneling excavation speed in formations composed of volcanic ash strata. To address this issue, we employ a comprehensive approach utilizing literature research, mathematical statistics, and other methodologies, centered on the analysis of the No. 1 Tunnel of the Jakarta–Bandung High-Speed Railway. Our focus is on examining the evolution patterns and inter-relationships of shield tunneling parameters within volcanic ash strata. Subsequently, we propose an optimized strategy for these tunneling parameters. By employing six machine-learning algorithms to construct prediction models, we compare and analyze their performance in predicting the tunneling excavation speed. The results indicate a positive correlation between slurry pressure and tunnel depth in volcanic ash strata, suggesting that the grouting pressure should exceed the slurry pressure by approximately 0.22 MPa. In the composite stratum of “volcanic ash debris + round gravel”, the cutter torque exhibits a strong negative correlation with the total thrust (−0.77). Due to tool wear and ground resistance, the excavation speed and cutter speed are weakly negatively correlated. Compared to other strata, shield tunneling in volcanic ash strata exhibits larger grouting pressure fluctuations, slower tunneling excavation speed, greater total thrust, higher cutter torque, and lower cutter speed. Regarding shield tunneling excavation speed prediction, the ranking of the algorithm performance is RF > DNN > ANN > BPNN > MNR > SVM, with RF achieving a decision coefficient of 0.829. The RF model is well-suited for predicting the shield structure tunneling excavation speed. Full article

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. Full article