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Controlling the ground settlement and building deformation triggered by shield tunnelling, particularly within water-rich strata, poses a significant engineering challenge. This study conducts a finite element (FE) analysis focusing on the ground settlement and deformation of adjacent structures (with a minimum distance of 2.6 m to the tunnel) due to earth pressure balance (EPB) shield tunnelling. The analysis incorporates the influence of groundwater through a 3D fluid–solid coupling model. This study assesses the effects of tunnelling on the behaviour of nearby buildings and introduces two mitigation strategies: the vertical partition method and the portal partition method. Their effectiveness is compared and evaluated. Our findings reveal that the deformation curves of the stratum and the building are influenced by the accumulation and dissipation of pore pressure. The vertical partition method reduced surface settlement by approximately 70%, while the portal partition method further minimized building deformation but required careful application to avoid issues like uplift. Both methods effectively mitigate the impacts of tunnel construction, with the portal partition method offering superior performance in terms of material use and cost efficiency. This research provides a scientific foundation and technical guidance for similar engineering endeavours, which is vital for ensuring the safety of metro tunnel construction and the stability of adjacent buildings. [ABSTRACT FROM AUTHOR]

Soil conditioning is essential for addressing the stratum applicability problem of earth pressure balance (EPB) shields. Under high water pressures, EPB shields spew water and soil when excavating coarse-grained strata. Typically, foam combined with polymers and slurry is used to solve spewing. However, in current techniques, slurry, foam, and the other agents are mixed with soil separately, their synergistic effect is seldom realized. In this study, an anionic surfactant was used to foam in bentonite slurry to form bubble–slurry to maximize the synergy between bubbles and slurry. The slump, volume stability, and permeability test of bubble–slurry-conditioned sand was conducted to examine the conditioning effect, and the stratum applicability of bubble–slurry was determined from the perspective of permeability. It was found that the conditioning effect of bubble–slurry in coarse gravel soil was excellent and could expand the applicability of EPB shields. The main stabilization mechanism of bubble–slurry is that bentonite particles provide a space barrier for bubbles. And three seepage modes of bubble–slurry-conditioned sand were innovatively defined, and the occurrence conditions of the three seepage modes were analyzed according to the permeability coefficient of sand, initial dynamic shear force of bubble–slurry, and hydraulic gradient. [ABSTRACT FROM AUTHOR]

Ground volume loss is an important parameter for settlement control and prediction in shield tunneling. This parameter is usually determined empirically, while its variation along the tunnel is not predictable. In this study, an analytical formula for ground volume loss is obtained based on physical derivation. The ground volume loss is divided into two components. Key operational parameters, i.e. face pressure, grouting pressure and grouting volume, are used to calculate the two components. The proposed formula is then validated against the field data collected from Changzhou Metro in thick silty clay layer. The validation shows that the new formula gives reasonable prediction of ground volume loss. Furthermore, the three model coefficients derived from physical calculation are very close to the regression coefficients based on statistical method. For EPB tunnels excavated in silty clay layer, the ground volume loss along a specific tunnel can be predicted by the new formula. The analysis also indicates that the surface settlement of EPB tunnel should be controlled by a balanced combination of varied operational parameters.

Foam conditioning is a widely adopted technique in earth pressure balance (EPB) shield tunneling for the purpose of reducing sand permeability and preventing water spewing. The permeability of foam-conditioned sands differs from that of natural sands due to the presence of foam bubbles. This study investigated the effect of water pressure on the permeability of foam-conditioned sands using novel laboratory permeability tests. The water pressure, for the first time, is decoupled with the hydraulic gradient, owing to a newly developed permeameter with the controllable downstream hydraulic pressure in the laboratory. The results show that the permeability is significantly affected by the water pressure, and the effect is also predominantly dependent upon the foam injection ratio. The initial hydraulic conductivity increases with the increasing water pressure, while the initial stable period duration decreases. The water-plugging structure formed by foam bubbles and sand particles is prone to be damaged under high water pressure due to the shrinkage of foam bubbles. This means that the existing permeability tests with low water pressure underestimate the permeability of foam-conditioned sands. The underlying mechanism of water pressure in modifying the permeability of foam-conditioned sands is also examined from a particle-scale perspective. [ABSTRACT FROM AUTHOR]

Ground volume loss is an important parameter for settlement control and prediction in shield tunneling. This parameter is usually determined empirically, while its variation along the tunnel is not predictable. In this study, an analytical formula for ground volume loss is obtained based on physical derivation. The ground volume loss is divided into two components. Key operational parameters, i.e. face pressure, grouting pressure and grouting volume, are used to calculate the two components. The proposed formula is then validated against the field data collected from Changzhou Metro in thick silty clay layer. The validation shows that the new formula gives reasonable prediction of ground volume loss. Furthermore, the three model coefficients derived from physical calculation are very close to the regression coefficients based on statistical method. For EPB tunnels excavated in silty clay layer, the ground volume loss along a specific tunnel can be predicted by the new formula. The analysis also indicates that the surface settlement of EPB tunnel should be controlled by a balanced combination of varied operational parameters. [ABSTRACT FROM AUTHOR]

Both foam and bentonite slurry are commonly employed in soil conditioning to prevent water spewing during earth pressure balance (EPB) shield tunnelling. A novel calculation model to estimate the permeability coefficient of soils conditioned with foam and bentonite slurry is developed. In this model, bentonite particles are assumed to adhere to the foam film in a monolayer of bridging particles, and the permeation channels within the conditioned soil are updated using the Kozeny-Carman equation. A series of permeability tests on conditioned soil, varying conditioning parameters and water heads, validate the accuracy of the model. The measured results that the value of permeability coefficient can be well captured by the calculation results, which indicates that the model can accurately predict the permeability of soil conditioning by foam and bentonite slurry. While there is a slight reduction in accuracy for conditioning states with high foam and bentonite slurry injection ratios, the model remains conservative for tunnelling engineering safety due to calculated values consistently exceeding measured ones. Furthermore, the model performs well in cases of foam-conditioned soil from previous studies. Additionally, the model underscores the significant influence of bentonite slurry on the permeability coefficient by altering soil grain gradation. [ABSTRACT FROM AUTHOR]

At present, the determination of tunnel parameters mainly rely on engineering experience and human judgment, which leads to the subjective decision of parameters and an increased construction risk. Machine learning algorithms could provide an objective theoretical basis for tunnel parameter decision making. However, due to the limitations of a machine learning model's performance and parameter selection methods, the prediction model had poor prediction results and low reliability for parameter research. To solve the above problems, based on a large number of construction parameters of a composite section subway in Shenzhen, this paper combined dimensionality reduction data with service analysis to optimize the selection process of shield tunneling parameters, and determined the total propulsion force, cutter head torque, cutter head speed, and advance rate as key tunneling parameters. Based on an LGBM algorithm and Bayesian optimization, the prediction model of key tunneling parameters of an earth pressure balance shield was established. The results showed that the average error of the LGBM model on the test set was 8.18%, the average error of the cutter head torque was 13.93%, the average error of the cutter head speed was 3.16%, and the average error of advance rate was 13.35%. Compared with the RF model, the prediction effect and the generalization on the test set were better. Therefore, an LGBM algorithm could be used as an effective prediction method for tunneling parameters in tunnel construction and provide guidance for the setting of tunneling parameters. [ABSTRACT FROM AUTHOR]

Based on the overlapping tunnel of Tel Aviv Red Line Light Rail Project in Israel, this study established a three-dimensional numerical model by using Rhino6 and FLAC3D software on the basis of analysis of on-site monitoring data, to investigate the ground settlement and stratum displacement laws of shield overlapping tunnel at different overlapping angles.Results show that when the two tunnels gradually transit from horizontal to overlapping state, with the increase of overlapping angle of the two tunnels, the accumulated settlement at the measuring points in the middle of the two tunnels increases, but the accumulated settlement is not only affected by overlapping angle, but also closely related to the stratum traversing situation.Under the stratum condition of the project, when the overlapping angle is 60°, the accumulated surface settlement reaches the maximum because both tunnels pass through the loose reservoir K1 stratum.When the overlapping angle of the rear-built tunnel is less than 45° after excavation, the width of the settlement trough increases.When the overlapping angle is larger than 45° and smaller than 60°, the width of the settlement trough remains unchanged.The width of settlement trough decreases when the overlapping angle is larger than 60°.When the overlapping angle reaches 90°, the settlement trough is symmetrical on both sides.After excavation of tunnels on both sides, when the overlapping angle of the tunnels reaches 75°, the strata on both sides change the direction of movement.This research offer reference for the design and construction of overlapping tunnels.

The water permeability of conditioned soils is one of the most essential properties for Earth Pressure Balance (EPB) tunnelling in coarse-grained soils. Permeability tests are conducted to study the influence of water heads on the permeability of foam-conditioned sands. The initial permeability coefficient of foam-conditioned sands increases with the water head, while the stable permeability coefficient and the initial stable period duration decrease. Meanwhile, a novel analytical model is proposed to estimate the initial permeability coefficient. In this model, the effect of the water head on the initial permeability coefficient is incorporated by calculating void ratios of the foam and effective diameters of foam bubbles under different water pressures. Experimental results are in close agreement with analytical solutions, indicating the excellent performance of the proposed calculation method. In addition, the physical mechanisms of how the water head affects the permeability of foam-conditioned sands are discussed from the contraction and evolution of foam bubbles.

Earth pressure balance (EPB) shield excavation in cohesive strata frequently encounters cutterhead clogging, consuming time and economic costs. Engineering practice shows that cutterhead aperture ratio, soil chamber pressure and soil conditioning have important influences on the clogging behavior of EPB shields. In order to study these factors, a series of laboratory tests were conducted using a setup that can closely simulate the shield tunnelling process. The indicators analyzed were excavation speed, torque, specific energy and soil distribution on the cutterhead. The results indicate that cutterhead aperture and cutter arrangement are important factors in clogging potential. Clogging creates a significant reduction in excavation speed. Torque is not a sensitive parameter reflecting clogging because of the effect of the consolidated soil on the cutters. The presence of soil chamber pressure makes it difficult to remove the clogging through the shearing action of the excavation surface. The injection of a sufficient amount of foam can reduce the risk of shield clogging, but it may lead to an increase of soil adhesion on the cutterhead. The amount of soil that adheres to the cutterhead cannot be used as a classification criterion for clogging potential. Based on experimental phenomena and established studies, a mechanical model called 'beam-bridge' was proposed to study the behavior of the soil through the cutterhead opening and damage form of clogging. The results will help to the excavation control of EPB shields. [ABSTRACT FROM AUTHOR]

Ground loss is the volume of soil excavated in excess of designed excavation. It defines the boundary conditions for ground deformation field and thereby dominates the magnitude of tunneling-induced ground settlement. In practice, it is generally quantified by a parameter called ground loss parameter. To date, there is no unanimously agreed formulation for ground loss parameter despite its indispensable role in developing both empirical and analytical solutions for tunneling-induced ground settlement. Herein, a comprehensive field database is utilized to quantitatively assess existing formulations of ground loss, and to unravel its role in settlement prediction via inverse analysis. It reveals that remarkable errors can be generated by classical solutions for tunneling-induced ground settlement. This implies that the reliability of classical solutions for tunneling-induced settlement can be potentially improved with a more accurate formulation of ground loss. A data-driven formulation for ground loss is developed with aid of the random forest algorithm, and it can well capture the target value with an R-value equaling 0.84. The developed formulation is further implemented in the O'Reilly and New solution, yielding a hybrid model for settlement prediction. The hybrid model can accurately predict the actual settlement with an R-value of 0.84, outperforming the purely data-driven model and further confirming the accuracy of the proposed formulation of ground loss. [ABSTRACT FROM AUTHOR]

Soil conditioning is essential for addressing the stratum applicability problem of earth pressure balance (EPB) shields. Under high water pressures, EPB shields spew water and soil when excavating coarse-grained strata. Typically, foam combined with polymers and slurry is used to solve spewing. However, in current techniques, slurry, foam, and the other agents are mixed with soil separately, their synergistic effect is seldom realized. In this study, an anionic surfactant was used to foam in bentonite slurry to form bubble–slurry to maximize the synergy between bubbles and slurry. The slump, volume stability, and permeability test of bubble–slurry-conditioned sand was conducted to examine the conditioning effect, and the stratum applicability of bubble–slurry was determined from the perspective of permeability. It was found that the conditioning effect of bubble–slurry in coarse gravel soil was excellent and could expand the applicability of EPB shields. The main stabilization mechanism of bubble–slurry is that bentonite particles provide a space barrier for bubbles. And three seepage modes of bubble–slurry-conditioned sand were innovatively defined, and the occurrence conditions of the three seepage modes were analyzed according to the permeability coefficient of sand, initial dynamic shear force of bubble–slurry, and hydraulic gradient. [ABSTRACT FROM AUTHOR]

Abstract The spewing of a screw conveyor easily occurs from the earth pressure balance (called EPB) shield in a water‐rich sand stratum. This may lead to the collapse of the tunnel face and even serious subsidence of the ground surface. To understand the spewing mechanism of the shield screw conveyor and explore the critical hydraulic condition of soil spewing in a shield–soil chamber, a simplified theoretical model for the spewing of the screw conveyor was developed based on the equation of groundwater flow in the screw conveyor under turbulent state. Thus, coupling Darcy's law with Brinkman's equation, this model was implemented within the COMSOL Multiphysics framework. The underground water flow in the shield screw conveyor was simulated so as to obtain its velocity and flow rate. Numerical simulations show that the water pressure distribution is concentrated in the lower part of the soil chamber after the groundwater enters the soil chamber. When the groundwater enters the screw conveyor, its pressure gradually decreases along the direction of the screw conveyor. When the water flow reaches the stratum–shield interface, the flow velocity changes markedly: first increases and concentrates at the entrance of the lower soil chamber, plummets and stabilizes gradually, and increases again at the exit. The soil chamber and screw conveyor are significantly depressurized. It is also found that the soil permeability coefficient can be reduced to k

During EPB (earth pressure balance) shield tunnelling in cohesive soils, the excavated soil may stick to the cutters, causing clogging. Clogging could reduce the efficiency of tunnelling as the cutters may be covered with excavated soil, the opening ratio of the cutterhead may be reduced by the sticked soil, and increased torque may be required. This paper studies clogging by testing adhesion strength and tangential adhesion strength with modified pullout tests and direct shear tests, respectively. Strong weathered granite and 11 artificial soil samples are tested to check the feasibility of the modified pullout tests and direct shear tests in the clogging study. The repeatability and accuracy of the modified pullout test are improved by building a new soil container and using a new loading method. Soil conditioning by injecting chemical additives such as foam and dispersant into the excavated soil can be used to reduce the clogging potential during shield tunnelling. The influences of foam and dispersant on Atterberg limits, adhesion and tangential adhesion in strong weathered granite are also studied. Test results show that the Atterberg limits decreased in conditioned soil, and soil conditioning has a greater influence on tangential adhesion than on adhesion. A new clogging potential assessment method for conditioned soil is proposed based on the pullout and direct shear test results. Validations using strong weathered granite show that this method is more suitable for conditioned soils than the traditional methods. [ABSTRACT FROM AUTHOR]

At present, the determination of tunnel parameters mainly rely on engineering experience and human judgment, which leads to the subjective decision of parameters and an increased construction risk. Machine learning algorithms could provide an objective theoretical basis for tunnel parameter decision making. However, due to the limitations of a machine learning model’s performance and parameter selection methods, the prediction model had poor prediction results and low reliability for parameter research. To solve the above problems, based on a large number of construction parameters of a composite section subway in Shenzhen, this paper combined dimensionality reduction data with service analysis to optimize the selection process of shield tunneling parameters, and determined the total propulsion force, cutter head torque, cutter head speed, and advance rate as key tunneling parameters. Based on an LGBM algorithm and Bayesian optimization, the prediction model of key tunneling parameters of an earth pressure balance shield was established. The results showed that the average error of the LGBM model on the test set was 8.18%, the average error of the cutter head torque was 13.93%, the average error of the cutter head speed was 3.16%, and the average error of advance rate was 13.35%. Compared with the RF model, the prediction effect and the generalization on the test set were better. Therefore, an LGBM algorithm could be used as an effective prediction method for tunneling parameters in tunnel construction and provide guidance for the setting of tunneling parameters.

Spewing is a key issue during earth pressure balance (EPB) shield tunneling in a water-rich sandy stratum. This paper proposed the bubble-slurry as a new type of soil conditioning agent. The foamability and stability of the bubble-slurry were studied, and the volume stability, fluidity, and permeability of bubble-slurry-conditioned sands with hydraulic gradient of 2 to 10 were analyzed. The stability mechanism was explored by the zeta potential and microstructure of the bubble-slurry system. The formulation of bubble-slurry with a half-life of 121–383 h was determined through laboratory tests. The results of soil conditioning experiments showed that the bubble-slurry-conditioned soil exhibited appropriate fluidity, excellent volume stability and low permeability in a certain period. The use of bubble-slurry can save approximately 3.0–8.2% of the slurry consumption compared with the method of slurry conditioning. The zeta potential and the distribution of slurry particles of the bubble-slurry system were key mechanisms affecting the stability of the bubble-slurry. The high absolute value of zeta potential of the system increases the dispersion of bubbles, and the slurry particles uniformly distributed on the bubble liquid film and in the Plateau boundary are conducive to enhancing the anti-disturbance ability and inhibiting the decay of bubbles. [ABSTRACT FROM AUTHOR]

To control tunneling risk, the prediction of the surface settlement rate induced by shield tunneling using earth pressure balance plays a crucial role. To achieve this, ten independent variables were identified that can affect the amount of settlement. The nonlinear relationship between maximum ground surface settlements and ten influential independent variables was considered in artificial neural network (ANN) models. A total of 150 genuine datasets derived from the Southern Development Section of the Tehran Metro Line 6 project were used to train, validate, and test ANN techniques. Hence, the ground surface settlements of the mentioned project were predicted by the most accurate back propagation ANN technique. Ultimately, the importance level of different influential parameters on ground settlement at tunneling is relatively determined based on the results of the optimal neural network. The results used in this paper to evaluate the relative importance of each variable involved in the rate of ground surface settlement demonstrate that the parameters of grout injection and permeability equivalent to the proportions of approximately 16.91% and 5.07% have the highest and lowest impact, successively. [ABSTRACT FROM AUTHOR]

The cutterhead of an earth pressure balance (EPB) shield usually relies on a large torque when tunneling through a water-rich and high-permeability sand layer. Sandy soils may lead to severe wear of the cutter tools and make the screw conveyor vulnerable to spewing. In this study, we investigate the characteristics of the soil conditioned by means of foam, bentonite slurry, and carboxymethyl cellulose solution. The mechanical and friction properties of the conditioned soil were tested by the triaxial shear, Laboratoires Central des Ponts et Chaussees (LCPC), and sliding tests, under considering the influence of soil consolidation time. The test results showed that the conditioned sand presents dilatancy, and its cohesion enhances but its internal friction angle decreases. The changing trend of these properties is more prominent with the increase of consolidation time but they stabilize after 12 h. The starting torque of the shield machine in 3-h shutdown reaches 60% of the rated torque, while the starting torque in 6-h shutdown exceeds 80% of the rated torque. To avoid a large starting torque, we suggest that the cutterhead is idled for a short time within 12 h after the shield machine is shutdown. Finally, the theoretical calculation method of torque on cutterhead was developed, and the prediction by such method is in good agreement with the in situ measured data in the cutterhead. [ABSTRACT FROM AUTHOR]

Based on the construction practice of the Beijing Metro Line 10 shield tunneling project, this paper describes research on soil improvement technology for Beijing stratum characteristics (sandy gravel stratum) and covers similar engineering conditions. It also describes the development of a new type of mud improver. Based on the laboratory tests with bentonite as the base mud and different additives, the effects of guar gum, CMC, xanthan gum, and clay medium particles on mud performance are analyzed. Then, two kinds of mud were used to conduct indoor simulated muck improvement tests (mixing test, slump test, sliding plate test, and adhesion resistance test), and the improvement effects of new mud and ordinary mud applied in pebble/round gravel and sandy soil layers were compared. The results show that xanthan gum is the best material to improve the performance of slurry, using the contrast test of bentonite-based slurry and different additives. The optimum slurry preparation scheme is 4% bentonite, 0.2% xanthan gum, 0.04% soda ash, and 1% clay particles. Using indoor simulated muck improvement tests (mixing test, slump test, slide plate test, and adhesion resistance test), the improvement effects of applying new mud and ordinary mud in pebble/round gravel and sandy soil layers are compared, and the advantages of the new mud in the application of the above two formations are verified. Among them, the new slurry has great advantages for improving the two parameters of the soil adhesion resistance coefficient and slump during shield tunneling. When the improved soil mass reaches the flowing plastic state, the proportion of new mud added to different soil mass is different. The proportion of new mud added to improved pebble/pebble soil is 28%, and that of sand and clay is 32%. It can be seen that new mud is more suitable for improving pebble/pebble soil. [ABSTRACT FROM AUTHOR]

Copyright of Railway Standard Design is the property of Railway Standard Design Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

When excavating tunnels in the clay stratum by using earth pressure balance (EPB) shields, the cutterhead is prone to clogging and may lose its ability to excavate. To investigate the clogging mechanism, a cutterhead device equipped with a driving system was developed to emulate the cutterhead behavior of the EPB shield in conditioned soils. The influences of water content, consolidation time, and soil conditioning factors on clay adhesion were evaluated and compared based on general laboratory and cutterhead model tests. The mixing test results showed that the water content influenced considerably clay adhesion. A water content interval near the liquid limit caused a decrease in the adhesion coefficient, and the change in water content was more effective than that in clay conditioning. Direct shear tests revealed that soil conditioning could reduce clay strength, and the effect was evident when the consolidation time was less than 6 h. A peeling point was observed in the adhesion curve of the clay and steel blocks. The peeling point for unconditioned clay was greater than the corresponding shear failure strength, which indicated that the clay had failed before it was detached from the steel block surface. However, contrasting results were obtained for conditioned clay. The cutterhead model test also showed that the water content had the greatest influence on clay adhesion according to the torque and thrust. [ABSTRACT FROM AUTHOR]

Soil conditioning of an earth pressure balance shield in a saturated sand layer aims to impart adequate flow plasticity and impermeability. Thus, the effect of soil conditioning on the saturated sand layer was analyzed for Harbin Metro Line 2 in the tunnel section project from Harbin North Station to Dagengjia Station, and the optimal soil conditioning ratio was obtained through experiments on medium sand using foam, bentonite, and carboxymethyl cellulose. In addition, the microscopic pores and shape characteristics of the soil before and after conditioning were compared using computerized tomography (CT) scanning and scanning electron microscopy (SEM) to evaluate the microscopic effect of soil conditioning. The current research results revealed that the soil conditioning reduced the particle size dispersion and improved the particle gradation, and the conditioned soil particles were more uniform than the original soil sample. Moreover, the CT scanning images processed using the threshold method illustrated that the pores of the conditioned soil were independent of each other, no continuous channels were formed, and the porosity of each layer was under 4%. In addition, the SEM images confirmed that the clay mineral composition improved the angularity and sharpness of the sand particles, and the flocculent aggregate structure, formed in combination with the sand particles, reduced the soil permeability. Furthermore, the practical application of the optimal ratio of conditioning materials, obtained experimentally and verified through the aforementioned observation, yielded proper results in the field construction, and the spewing of the screw conveyor during the shield tunneling process was avoided. [ABSTRACT FROM AUTHOR]

For the safety and efficiency of earth pressure balance (EPB) shield tunnelling, the dynamic characteristics of the muck in the excavation chamber and the screw conveyor should be considered. However, the velocity and pressure distribution of the muck in the EPB shield, reflecting muck flowability and face stability, are rarely observed at the jobsite. Therefore, a computational fluid dynamics (CFD) model with a modified inlet boundary was established to investigate the muck characteristics in the chamber and the screw conveyor during tunnelling in a full chamber mode. A compressible Bingham model was adapted to describe the muck compressibility and rheology. The time-dependent tunnelling parameters obtained from the simulation excellently matched the field-measured data. The simulation results show the nonuniform velocity distribution of the muck at the excavation face and the low-velocity zones where clogging potentially occurs. The muck pressure reaches a peak at the excavation face and then decreases along the cutterhead openings, chamber and screw conveyor for inflow. The simulation also captures the pressure imbalance at the cutterhead and bulkhead, which may destabilize the excavation face. The proposed discharge efficiency is 56.7% in the simulated condition, indicating that tunnelling with these muck properties has no risk of muck spewing. [ABSTRACT FROM AUTHOR]

• Reveals spatial motion trajectories and distribution patterns of granules during shield tunneling. • Introduces novel metrics for evaluating the cutterhead's cutting and guiding performance. • Clarifies the impact of shield tunneling parameters on the movement characteristics of granules. An investigation into the movement characteristics of granules during Earth Pressure Balance (EPB) shield tunneling contributes significantly to understanding the interaction between the shield machine and the soil. This understanding also enables researchers to gain deeper insights into the cutting and guiding effects of the shield cutterhead on the soil, thus providing a scientific basis for optimizing shield tunneling parameters and cutterhead designs. To achieve this, indoor model shield tunneling experiments were conducted using independently developed shield tunneling equipment and spatial positioning devices developed by our research group. The research investigated the spatial movement trajectories, radial diffusion, and axial movement characteristics of granules at the face subjected to the action of a spoke-type cutterhead. Furthermore, the study proposes the use of average diffusion degree and movement rates of granules as metrics for evaluating the cutting and steering performance of the cutterhead. The influence of cutterhead rotational speed and advance rate on the movement characteristics of granules was further explored based on these two indicators. The study's findings reveal the following: (1) Granules at the face predominantly exhibit a spiral movement trajectory when the EPB shield tunneling machine operates in a dynamic equilibrium state. (2) The cutting and steering performance of the cutterhead's various areas is enhanced progressively from the center to the outer edge, as evidenced by a gradual decrease in the average diffusion degree of granules and an increase in the average axial movement rate (AMR). (3) The AMR and average diffusion degree of granules are influenced by both the rotational speed of the cutterhead and the advance rate of the shield machine. Optimal matching of the rotational speed and advance rate maximizes the average AMR of granules, minimizes the average diffusion degree, reduces the torque on the cutterhead to its lowest point, and consequently, optimizes the efficiency of shield tunneling. This research presents a novel perspective and methodology for understanding the movement characteristics of granules during shield tunneling operations. The outcomes of this study provide valuable insights for the structural design of shield machine cutterheads and the optimization of tunneling parameters. [ABSTRACT FROM AUTHOR]

As metro lines continue to expand rapidly in urban areas, the excavation of twin tunnels in shallow depths using shield tunnelling methods has become widespread. By analysing field data obtained from an actual shield tunnelling project, it has been observed that the post-ground settlement occurring over the preceding tunnel during the excavation of the following tunnel in silty sand is approximately 42% of the green field settlement, which cannot be disregarded. Accurate approximation of the post-ground settlement is useful for preventing any damage due to excessive deformation and to determine the total ground settlement profile during twin tunnel construction stage. And yet, only a few number of studies have focused on investigating and predicting the post-ground settlement that occurs during twin tunnel construction in soft soils. Therefore, this study develops a transparent model using the multi-gene genetic programming (MGGP) method, enabling the prediction of post-ground settlement during twin tunnelling. Comparative analysis demonstrates that the proposed model is user-friendly and capable of generalising to unseen data. The reliability of the MGGP-based model has been validated through sensitivity and parametric analyses. Additionally, when estimating post-settlement during twin tunnelling, it is essential to consider the spacing between twin tunnels, soil cohesion, and crucial operational parameters of the shield, such as torque and face pressure. [ABSTRACT FROM AUTHOR]

To control tunneling risk, the prediction of the surface settlement rate induced by shield tunneling using earth pressure balance plays a crucial role. To achieve this, ten independent variables were identified that can affect the amount of settlement. The nonlinear relationship between maximum ground surface settlements and ten influential independent variables was considered in artificial neural network (ANN) models. A total of 150 genuine datasets derived from the Southern Development Section of the Tehran Metro Line 6 project were used to train, validate, and test ANN techniques. Hence, the ground surface settlements of the mentioned project were predicted by the most accurate back propagation ANN technique. Ultimately, the importance level of different influential parameters on ground settlement at tunneling is relatively determined based on the results of the optimal neural network. The results used in this paper to evaluate the relative importance of each variable involved in the rate of ground surface settlement demonstrate that the parameters of grout injection and permeability equivalent to the proportions of approximately 16.91% and 5.07% have the highest and lowest impact, successively.

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the process of earth pressure balance (EPB) shield tunneling at silty clay stratum, it is easy to occur shield clogging with cutterhead and poor plasticity characteristics of the muck, so it is necessary to carry out soil conditioning to ensure the safe and efficient tunnel-construction of the shield. Taking one construction section of Hangzhou Metro Line 10 as an example, this study conducted liquid and plastic limit tests for soil conditioner selection, and then applied for the improvement of silty clay. The validity of selected conditioner and its parameters was verified through the slump test and compressive strength test of conditioned soil, and field soil conditioning test on the basis of the laboratory test. It was found that foam could significantly reduce the plastic limit of silty clay. Silty clay stratum was more sensitive to the increase of water content (w) and foam injection ratio (FIR). The slump value of conditioned soil increased with the increase of water content and foam injection ratio, and its compressibility also improved with the increase of foam injection. After optimizing the improvement parameters of conditioned soil, the torque of the shield cutter plate was significantly reduced, and the driving parameters of the shield remained stable, which indicated that the optimization and improvement parameters of the stratum were set reasonably, and that the improvement effect of the silty clay stratum using foam agent was significant. [ABSTRACT FROM AUTHOR]

The rheological properties of sands conditioned with different conditioners and injection ratios were examined. The conditioned sands were prepared with a 40% and 60% volume injection ratio of a bentonite slurry or a carboxymethyl cellulose (CMC) solution. The experiment results show that the tested bentonite-conditioned sand exhibits the characteristics of a Herschel-Bulkley fluid at shear rates in the range of 0–10 s−1 while the CMC-conditioned sand conforms to the power law model. The flow curves of all of the samples show a marked shear-thinning behavior. They also indicated that the existence of a yield stress (τ0) depends only on the rheological behavior of the conditioner and that the yield stress (τ0 if present) and the plastic viscosity (μp) increase with an increase in the volumetric concentration of the sand. Furthermore, to characterize the thixotropy of the conditioned sand, experiments were carried out by using three loading histories with shear rate accelerations of 0.1, 0.2 and 0.4 s−1/s. In the measured results, the thixotropy of the conditioned sand is heavily dependent on the recent flow history. Based on the experimental data, a simple thixotropic prediction model was developed to analyze and predict the transient flow curves of bentonite-conditioned sands. [ABSTRACT FROM AUTHOR]

In order to solve the problem of EPB (earth pressure balance) shield muck accumulation and transportation impact on the urban environment, relying on the shield tunnel project in a work area of Hangzhou Metro Line 10, for the clay soil layer, the shield muck reuse was proposed as synchronous grouting material. In the scheme, the slurry performance was tested by uniform test method. Linear regression and single factor analysis were performed on the test results. Among them, the 28 d compressive strength and the 2 d hardening rate were both increased significantly with the increase of the proportion of muck, while the 3 h bleeding rate decreased accordingly. It was found that when the waterbinder mass ratio was 0.65，the cement-sand mass ratio was 0.7，the residue mass fraction was 5%，and the cement mass fraction was 30%, all the parameters of the slurry met the requirements. The influence of each factor on the key performance indicators of the slurry was explored to provide a new idea for the reuse of earth pressure balance shield muck. [ABSTRACT FROM AUTHOR]

• Revealed the failure process of cobble particles with different diameters. • Evaluated the roles of cobble particle with different diameters in keeping tunnel face stable. • Clarified the influence of panel opening ratio and rotating speed of cutter head on face stability. This paper aims at revealing the failure mechanism of deep earth pressure balanced (EPB) shield tunnels in dry graded cobble-rich soil, considering the influence of kinematic differences of filler and skeleton cobble particle. The work was performed by three dimensional discrete element method (DEM). Results show that particle size greatly influences the movement of cobble particles. The coarse particles serve as the skeleton of the ground and provide the stability, while the fine and middle particles are filler materials. The erosion of fine particles has little influence on tunnel face stability, while the erosion of middle particles weakens tunnel face stability much. Existing researches overestimate tunnel face stability as the erosion of filler particles is ignored. The collapse developing from the tunnel face to the ground surface experiences three phases, i.e. local, ultimate and global. The proposed angles of 0.6(45°+ φ p /2) (φ p = the peak friction angle) to the horizon and 0.4(45°- φ p /2) to the vertical are suggested to shape the local failure zone in the longitudinal and transverse direction, respectively. The collapse pressure and size of the failure zone increase with increasing cutter head panel opening ratio and rotating speed. [ABSTRACT FROM AUTHOR]

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Predicting the tunneling-induced maximum ground surface settlement is a complex problem since the settlement depends on plenty of intrinsic and extrinsic factors. This study investigates the efficiency and feasibility of six machine learning (ML) algorithms, namely, back-propagation neural network, wavelet neural network, general regression neural network (GRNN), extreme learning machine, support vector machine and random forest (RF), to predict tunneling-induced settlement. Field data sets including geological conditions, shield operational parameters, and tunnel geometry collected from four sections of tunnel with a total of 3.93 km are used to build models. Three indicators, mean absolute error, root mean absolute error, and coefficient of determination the (R2) are used to demonstrate the performance of each computational model. The results indicated that ML algorithms have great potential to predict tunneling-induced settlement, compared with the traditional multivariate linear regression method. GRNN and RF algorithms show the best performance among six ML algorithms, which accurately recognize the evolution of tunneling-induced settlement. The correlation between the input variables and settlement is also investigated by Pearson correlation coefficient. [ABSTRACT FROM AUTHOR]

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To avoid water spewing out of the screw conveyor, foam is often used to reduce the permeability coefficient of the soil during earth pressure balance (EPB) shield tunneling. Whether foam can effectively reduce the permeability or not strongly depends on soil gradation characteristics. A series of permeability tests were carried out on foam-conditioned soil with changing effective grain size (d10), curvature coefficient (Cc), and uniformity coefficient (Cu), further, three characteristic times were defined to evaluate the permeation safety of the conditioned soil, including critical time (tc), flow rate safety time (ta) and flow quantity safety time (ts). The test results show that with an increase in d10, the initial permeability coefficient of the conditioned soil increased greatly, however, it only changed slightly with increases in Cc and Cu. In addition, permeability coefficient was still much lower than that of the unconditioned soil, even though entered the slow growth period for a long time. It is shown that as the Cc and Cu increased, the ta and ts changed slightly, however, as the d10 increased, the ta and ts decreased significantly. The results indicate that d10 can greatly affect the permeability characteristics of conditioned soil, more specifically, the initial permeability coefficient and the permeation safety. By contrast, Cc and Cu have less effects. In addition, it is not reasonable to consider that the permeability coefficient of the conditioned soil will reach or be close to that of unconditioned soil when most, or all, of foam in the foam-conditioned soil dissipates. [ABSTRACT FROM AUTHOR]

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A computational scheme coupling PFC3D (Particle Flow Code in 3 Dimensions) and FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) was performed to investigate influences of sand conditioning on the tunneling behaviour of earth pressure balance (EPB) shield in sandy ground. A detailed EPB shield and its near ground were modelled in the PFC3D while the other ground was simulated in the FLAC3D. Decreasing friction coefficients were used to characterize the fluidity improvement of conditioned muck particles. The results indicate that the residence time of muck in the excavation chamber is associated with its position and rotation directions of the spoke. The muck pressure and its difference in front of and behind the cutterhead decrease with the improvement of conditioning degree in a certain conditioning range, and an appropriate soil conditioning scheme can facilitate the control of chamber pressure. In addition, the torque of cutterhead decreases more significantly than the thrust with an improvement of soil conditioning degree within a normal conditioning range. [ABSTRACT FROM AUTHOR]

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Tunnel Construction / Suidao Jianshe (Zhong-Yingwen Ban) is the property of Tunnel Construction Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to determine the appropriate model for predicting the maximum surface settlement caused by EPB shield tunneling, three artificial neural network (ANN) methods, back-propagation (BP) neural network, the radial basis function (RBF) neural network, and the general regression neural network (GRNN), were employed and the results were compared. The nonlinear relationship between maximum ground surface settlements and geometry, geological conditions, and shield operation parameters were considered in the ANN models. A total number of 200 data sets obtained from the Changsha metro line 4 project were used to train and validate the ANN models. A modified index that defines the physical significance of the input parameters was proposed to quantify the geological parameters, which improves the prediction accuracy of ANN models. Based on the analysis, the GRNN model was found to outperform the BP and RBF neural networks in terms of accuracy and computational time. Analysis results also indicated that strong correlations were established between the predicted and measured settlements in GRNN model with MAE = 1.10, and RMSE = 1.35, respectively. Error analysis revealed that it is necessary to update datasets during EPB shield tunneling, though the database is huge. [ABSTRACT FROM AUTHOR]