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The study is based on a section of the Zhengzhou Metro Line 8 quasi-rectangular shield tunnel. Field excavation trials were conducted to analyze the surface settlement patterns caused by the construction of a large-section quasi-rectangular shield tunnel in the rich water sand layer in Zhengzhou. Based on the characteristics of the rich water sand layer, ground settlement control measures were proposed. The research findings show that the surface settlement caused by the construction of the large-section quasi-rectangular shield tunnel in the rich water sand layer exhibits a temporal curve pattern of slow settlement (Stage I: pre-arrival of the shield), rapid settlement (Stage II: shield passage, Stage III: shield tail exiting 14.4 ~ 18 m), and stable settlement (Stage IV: late settlement). In Stage I, controlling the excavation rate to maintain balance between the cutter face pressure and soil pressure is effective. In Stage II, injecting lubricating mud between the shell and the sand layer to reduce soil friction and shear slip is recommended. In Stage III, increasing the synchronous grouting volume at the shield tail and adjusting grouting pressure, as well as timely filling the shield tail construction gap, are effective methods to reduce surface settlement. The Peck formula was used to fit the transverse settlement trough on the surface, with a linear correlation coefficient R²=0.983, validating the use of the Peck formula to predict surface settlement troughs for quasi-rectangular shield tunneling in the rich water sand layer. These research findings can provide data support and reference for similar projects. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Abstract The study is based on a section of the Zhengzhou Metro Line 8 quasi-rectangular shield tunnel. Field excavation trials were conducted to analyze the surface settlement patterns caused by the construction of a large-section quasi-rectangular shield tunnel in the rich water sand layer in Zhengzhou. Based on the characteristics of the rich water sand layer, ground settlement control measures were proposed. The research findings show that the surface settlement caused by the construction of the large-section quasi-rectangular shield tunnel in the rich water sand layer exhibits a temporal curve pattern of slow settlement (Stage I: pre-arrival of the shield), rapid settlement (Stage II: shield passage, Stage III: shield tail exiting 14.4 ~ 18 m), and stable settlement (Stage IV: late settlement). In Stage I, controlling the excavation rate to maintain balance between the cutter face pressure and soil pressure is effective. In Stage II, injecting lubricating mud between the shell and the sand layer to reduce soil friction and shear slip is recommended. In Stage III, increasing the synchronous grouting volume at the shield tail and adjusting grouting pressure, as well as timely filling the shield tail construction gap, are effective methods to reduce surface settlement. The Peck formula was used to fit the transverse settlement trough on the surface, with a linear correlation coefficient R²=0.983, validating the use of the Peck formula to predict surface settlement troughs for quasi-rectangular shield tunneling in the rich water sand layer. These research findings can provide data support and reference for similar projects.

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.

This paper presents a surrogate modeling approach for predicting ground surface settlement caused by synchronous grouting during shield tunneling process. The proposed method combines finite element simulations with machine learning algorithms and introduces an intelligent optimization algorithm to invert geological parameters and synchronous grouting variables, thereby predicting ground surface settlement without conducting numerous finite element analyses. Two surrogate models based on the random forest algorithm are established. The first is a parameter inversion surrogate model that combines an artificial fish swarm algorithm with random forest, taking into account the actual number and distribution of complex soil layers. The second model predicts surface settlement during synchronous grouting by employing actual cover-diameter ratio, inverted soil parameters, and grouting variables. To avoid changes to input parameters caused by the number of overlying soil layers, the dataset of this model is generated by the finite element model of the homogeneous soil layer. The surrogate modeling approach is validated by the case history of a large-diameter shield tunnel in Beijing, providing an alternative to numerical computation that can efficiently predict surface settlement with acceptable accuracy.

Section Ⅷ of Shanghai Beiheng Passageway is a super large shield tunnel with a diameter of 15. 5 m, which closely sidecrossed the inner circle viaduct after escaping from the shaft for only 54 m. The minimum covering soil burial depth ratio is 0. 5 and the shortest distance between the tunnel and pile foundation of the viaduct is only 3. 9 m. Obvious interaction between the existing pile foundation, stratum, and shield crossing is present. Comprehensive monitoring on the ground surface settlement and pile displacement within the influential zone of shield tunnelling was conducted. Based on the monitoring data, the results of a refined 3D numerical model were compared and verified. The results show that the numerical results match well with the measured data, which both reflect the characteristics of settlement in the middle and significant upheaval on the two sides of the ground above the tunnel axis. Partial upheaval will be recovered due to unloading after the excavation. There is a significant effect of tunnel-soil-pile interaction during the side-crossing of the viaduct. The existing piles have a clamping effect on the stratum displacement induced by shield excavation, which results in asymmetric ground upheaval on the two sides. In the meantime, the deformation of the stratum synergistically drives the uplift of the existing piles. On the longitudinal ground response due to excavation, restricted by the working shaft and pile foundations, the expansion of the settlement section is limited. The shield􀆳s side-crossing causes the piles to deform laterally outwards for a maximum value of 3 mm, and induces additional axial forces in a single pile that exceeds 150 kN. [ABSTRACT FROM AUTHOR]

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In complex underground conditions, the excavation of deep foundation pits has a significant impact on the deformation of retaining structures and nearby subway stations. To investigate the influence of deep excavation on the deformation of adjacent structures, a three-dimensional numerical model of the foundation pit, existing subway station, and tunnel structure was established using FLAC 3D software, based on the Shenzhen Bay Super Headquarters C Tower foundation pit project. The study analyzed the deformation characteristics of retaining structures, adjacent subway stations, and tunnels during different stages of deep excavation, and the accuracy of the numerical simulation results was validated through field monitoring data. The results indicate that during the excavation process of the foundation pit, the lateral horizontal displacement of the retaining structure is generally small, with a typical "concave inward" lateral deformation curve; the horizontal displacement value of the contiguous wall section is less than that of the interlocking pile section. The bending moments of the retaining structure show a distribution pattern with larger values in the middle and smaller values at the top and bottom of the pit, with a relatively uniform distribution of internal support forces. The maximum displacement of the nearby subway station is 8.75 mm, and the maximum displacement of the subway tunnel is 2.29 mm. The research findings can provide references for evaluating the impact of newly built foundation pits near subway stations and contribute to the rational design and safe construction of new projects. [ABSTRACT FROM AUTHOR]

Accurate settlement forecasting is essential for preventing severe structural and infrastructure damage. This paper investigates predicting tunneling-induced ground settlements using machine learning models. Empirical methods for estimating settlements are often imprecise and site-specific. Developing novel, accurate prediction methods is critical to avoid catastrophic damage. The umbrella arch method constrains deformations for initial stability before installing primary support. This study develops machine learning models to forecast settlements solely from umbrella arch parameters, disregarding soil properties. Multilayer perceptron artificial neural networks (MLP-ANN) and support vector regression (SVR) are applied. Results demonstrate machine learning outperforms empirical methods. The MLPANN surpasses SVR, with R² of 0.98 and 0.92, respectively. Strong correlation is observed between umbrella arch configuration and settlements. The suggested approach effectively estimates surface displacements lacking mechanical properties. Overall, this study supports machine learning, specifically MLP-ANN, as an efficient, reliable alternative to empirical methods for predicting tunneling-induced ground settlements from umbrella arch design. [ABSTRACT FROM AUTHOR]

The Heimaguan Tunnel in China serves as a case study to exemplify the variation laws related to surface settlement, deformation, and stress characteristics in a shallow-buried soft-rock tunnel, while emphasizing in the tunnel support requirements. The first stage of this study begins with monitoring the time-varying characteristics of surface settlement, vault subsidence, and the horizontal convergence of Grade V rock. In the second stage, Peck theory is used to calculate the distribution characteristics of surface settlement. The results of both stages are compared to create a vault settlement model, thus establishing the horizontal convergence based on exponential function, logarithmic function and hyperbolic function, and determining the optimal time of secondary lining construction. On this basis, the time-dependent variation laws and characteristics of vertical and horizontal displacement and principal stress of surrounding rock are studied. After this, using simulation and analysis, the proper support is recommended. The study reveals that the surface settlement, vault subsidence, and horizontal convergence of the shallow-buried soft-rock tunnel stabilize within 25–30 days. Peck theory closely aligns with predictions based on exponential functions, with only a 0.72% difference. The recommended time for secondary lining application is 26–27 days. [ABSTRACT FROM AUTHOR]

Electro-osmotic consolidation is a promising method to remove pore water from soft soils. Numerical models have been widely used to simulate the underlying flow-mechanical–electrical processes and predict the consolidation behavior of soft soils subjected to electro-osmotic treatment. In the present study, we proposed a method to convert a 3D electro-osmotic consolidation model to an equivalent 2D model to alleviate the notorious computational burden associated with high-fidelity numerical simulations. The accuracy of the equivalent 2D model was verified by comparing with the original 3D model in terms of surface settlement and degree of consolidation. The behavior of the equivalent 2D model was highly depended on electrode configurations. The prediction accuracy of the 2D model increased with the decrease of the spacing between electrodes with same polarity. For the cases we analyzed, the 2D model showed accurate predictions with the final relative error of surface settlement in the range of ± 6%. The equivalent method was then applied to a field test to further validate its feasibility in real-world problems. The simulated surface settlement from the 2D model coincided well with field measurements, indicating that the equivalent 2D model was able to analyze realistic scenarios with complex electrode configurations and boundary conditions. [ABSTRACT FROM AUTHOR]

Ensuring stability of the excavation surface when using the shield method during tunnel excavation is crucial to achieve engineering goals related to project progress and quality. Insufficient research has been conducted on multi-objective optimal control when considering excavation surface stability. The excavation efficiency was selected as the indicator of project progress and the maximum ground settlement resulting from shield tunnelling activities was selected as the indicator of project quality. The stratified sequencing method and NSGA-II multi-objective optimization algorithm were used to explore multi-objective optimization pertaining to shield excavation surface stability. The research sets the shield excavation surface stability as the first layer objective and the project progress, and project quality as the second layer objectives. The technique was implemented in a construction tunnel segment that traverses embankment, open area, and sensitive building areas indefinitely. The findings demonstrate that the refined shield pressure remains within the upper and lower boundary thresholds, thereby boosting construction efficacy and mitigating max ground settlement. This approach enables the refinement and optimization of control strategies in response to prevailing working conditions adaptively, enhancing adaptability and flexibility. It also offers guidance and serves as a point of reference for similar shield tunnel projects. [ABSTRACT FROM AUTHOR]

Surface settlement caused by shallow shield tunneling can occur frequently. Machine variables such as face pressure, tail-void grouting pressure, and grout volume play an essential role in the settlement control of earth pressure balance (EPB) tunnel boring machines (TBMs). Combined with literature review, theoretical derivation, case verification, and numerical simulation, methods were established for adjusting the key parameters, including the face pressure in the plenum chamber, the advance speed of the shield machine, and the rotational speed of the screw conveyor. The grouting volume required to backfill the tail void was calculated according to shield kinematics, a physical model test under high pressure and soil states during excavation,. From the mechanical properties of soil, the function between surface settlement and tail-void grouting pressure based on the Peck formula, stochastic medium theory, and Terzaghi soil arching theory was deduced for the first time. With the increase in grouting pressure, the soil was compressed after the formation of the soil arch, and the process from original settlement to upheaval was also expressed by numerical simulations. In addition, the proposed methods could control the surface settlement effectively and result in more accurate predictions. By comparing the predicted surface settlement to measured data from the Harbin Metro Line 2 project, the adaptability of the proposed methods for the face pressure, tail-void grouting pressure, and grout volume was verified. [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]

Taking the filling mining in Yungang Coal Mine 8402 working face as the background, firstly, five gangue slurry with different proportions were prepared, and bleeding rate, setting time and uniaxial compressive strength tests were tested. Reasonable gangue slurry ratios were selected according to the requirements of use and cost, and the design of filling hydraulic support and filling mining technology was carried out. Considering the change of rock mass mechanical parameters with mining stress, based on Hoek-Brown model, FLAC3D software was used to study and analyze the spatial-temporal evolution law of deformation and failure of roof overburden in 8402 working face with or without filling. The results show that: when the dosage of cement and fly ash is 180 kg/m3 and 210 kg/m3 respectively, it can meet the requirements of filling mining and cost of 8402 working face in Yungang Coal Mine at the same time; under the condition of no filling, the 8402 working face has a periodical pressure step of 18-25 m, and the height of fracture zone is 108 m. While under the condition of 85% paste filling, the periodical pressure step of the working face is 36-40 m, and the height of fracture zone is 43 m; after the working face with 85% paste filling advances 120 m, the maximum subsidence and maximum tilt of the surface are basically kept unchanged at 165 mm and 2.62 mm/m, which are less than the requirements of the code and can ensure the safety of the ground building.

To investigate the settlement behaviour under alternate vacuum preloading, a series of laboratory tests considering different influencing factors, such as vacuum pressure and alternating criterion, were conducted. Based on experimental data, a new settlement prediction model, which can synthetically reflect the effects of vacuum pressure, alternating criterion, and improvement time, was proposed. The prediction model took into account the influence of improvement depth and variations in vacuum pressure. The model was validated using several case studies and laboratory tests. Comparisons between the proposed model and layer-wise summation method results indicate that the calculated results of the proposed model are closer to the actual settlement with errors consistently less than 10%. The proposed model can conveniently and accurately predict the ultimate settlement of high water content dredger fill improved by vacuum preloading method. [ABSTRACT FROM AUTHOR]

In this study, the rectangular pipe-jacking tunnel project of the Liuye Avenue West Extension under the Changzhang Highway is used to study highway pavement settlement and deformation during pipe-jacking construction through on-site monitoring. A three-dimensional numerical simulation method is employed to analyse the factors contributing to the significant settlement and rebound of the pavement. This study identifies the fundamental law governing the development of pavement settlement over time. The findings indicate that settlement increases rapidly when the jacking distance reaches approximately 10 m and then stabilizes at a consistent growth level. Furthermore, completion of the jacking of the left pipe leads to a transition in the surface settlement groove from a "V"-type distribution to a "W"-type distribution. Comparative analysis reveals that horizontal and vertical displacements exhibit similar characteristics, with maximum displacements occurring in the lagging jacking area. On both sides of the axis, the settlement groove curve remains stable within a range of 30–40 m, while the horizontal displacement curve stabilizes within a range of 20–30 m. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ground Improvement is the property of Journal of Ground Improvement 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 Engineering Mechanics / Gongcheng Lixue is the property of Engineering Mechanics Editorial Department 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.)

Soft soil poses more challenges to the construction of shallow-buried tunnels than other soils: the surrounding rock mass is more easily disturbed, and the tunnel stability is more influenced by groundwater seepage. The research is based on the Zizhi Tunnel project, a shallow-buried twin tunnel in soft soil. This paper divides the research area into the inside and outside river-affected area respectively. From the field monitoring data, the settlement law can be summarized, which found that for a single monitoring point, outside a river-affected area, the entire settlement development stage can be clearly divided into three stages: slow growth, rapid growth stage, and gradual convergence; however, inside the river-affected area, the settlement in the last stage will not converge but will continue to develop. Compared with the vault settlement, the surface settlement inside the river-affected area develops slower than that outside the river-affected area, which shows good consistency with the monitoring data. The synchronization of the sinking rate and stability of vault settlement and surface settlement verifies that the river over the tunnel has an impact on the development of surface settlement by the groundwater seepage in the soft soil. Based on field monitoring data, a numerical model is established to investigate the influence of the river on the surface settlement of the twin tunnels, of which the numerical results show the same development law as the monitoring data. [ABSTRACT FROM AUTHOR]

To calculate the horizontal displacement of the diaphragm wall and surface settlement caused by foundation pit excavation, the three-parameter Kerr foundation model was applied to a diaphragm wall and derived the flexural differential equations of the diaphragm wall and calculated the horizontal displacement of the diaphragm wall using the finite difference calculation method. The boundary element method combined with the Mindlin displacement solution was then used to invert the additional horizontal stress near the diaphragm wall. Lastly, the Mindlin solution was used to calculate the surface settlement. The effectiveness of the proposed calculation method was verified by comparing the horizontal displacement of the diaphragm wall and the surface settlement between the theoretical calculation and the actual project. The theory proves that there is a certain connection between the horizontal displacement of the diaphragm wall and the surface settlement, and the horizontal displacement of the diaphragm wall is larger than the surface settlement. Using this theory to further analyze the foundation pit construction parameters, the greater the thickness and elasticity modulus of the diaphragm wall, and the greater the diameter and number of internal supports, the smaller the horizontal displacement of the diaphragm wall and the surface settlement. The theory can accurately predict the horizontal displacement of the diaphragm wall and surface settlement and provides guidance for the construction of foundation pit projects. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Ground Improvement is the property of Journal of Ground Improvement 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.)

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.

The construction disturbance mechanism of rectangular pipe-jacking tunnels is more intricate than that of circular tunnels, leading to potential issues such as excessive accumulation and deformation of the surrounding formation, which can result in engineering disasters. However, there is currently a lack of reliable methods for predicting these disturbances. Machine-learning techniques have the capability to analyze the influence of multiple independent variables on a dependent variable, offering a new approach for predicting surface settlement in the construction of rectangular pipe-jacking tunnels. To address the sensitivity of existing machine-learning models to initial parameters, an improved particle swarm optimization (IPSO) method is employed. This method incorporates an adaptive mutation technique, adaptive inertia weight, and postoptimization method for mutant particles to enhance the particle size and determine the probability of obtaining the optimal value. By leveraging the strong mapping and nonlinear fitting abilities of the backpropagation (BP) algorithm, the IPSO-BP algorithm model is developed and compared with the BP, support vector machine, and random forest (RF) models using actual monitoring data. The findings indicate that in the presence of specific noise in the surface settlement data, the IPSO-BP prediction model demonstrates an enhanced accuracy of 26%, 25%, and 10% for the left amplitude. This approach can serve as a valuable reference for settlement prediction in similar projects. [ABSTRACT FROM AUTHOR]

Based on the similar model test of large-section excavation under the action of pipe-roof and beam, the variation law of pipe-roof deformation and surface settlement caused by excavation was studied. In order to fully study the influence of parameter changes on the pipe-roof deformation and surface settlement, a three-dimensional numerical model was established by using the finite element software. Based on this model, the effects of the flexural stiffness of the pipe-roof and the beam on the pipe-roof deformation and surface settlement were analyzed, and the optimal stiffness matching was studied according to the fuzzy mathematical theory. The results indicate that the overall deformation of the pipe-roof structure resembles a “plate” and exhibits symmetry about the middle pipe-roof. The surface settlement of the cross section of the pipe-roof forms a “grooved” pattern, conforming to the Peck curve distribution. The pipe-roof deformation and surface settlement are exponential functions of the beam stiffness and the pipe-roof stiffness, with greater sensitivity to changes in the beam stiffness. The safety and economy can be taken into account when the beam stiffness and the pipe-roof stiffness are 0. 5D and 2K respectively [ABSTRACT FROM AUTHOR]

Surface settlement is considered a key indicator in the pipe jacking procedure of the steel tube slab (STS) pipe-roofing method. Commonly, the existing equations for this safety indicator are applied in the process of measuring surface settlement caused by the pipe with circle or rectangle cross sections. This paper proposes calculation methods for the surface settlement of a circular steel pipe with flange plates based on the modified Mindlin solution considering pipe–soil interaction and the influence of flange plates. The proposed equations in this paper are applied to calculate the surface settlement for the actual pipe jacking engineering in Shenyang, China, and the calculated results fit well with the field monitoring values. This paper analyzes the main geometric parameters affecting surface settlement, including the orientation of flange plates and pipe specification. Simultaneously, this paper obtains the mathematical relationships between the surface settlement and the geometric parameters, providing a theoretical prediction method for actual pipe jacking construction of the STS pipe-roofing method. The development of metro construction has become one of the indications of urban progress. How to build metro projects efficiently and safely has become one of the main problems of underground engineering. The steel tube slab (STS) pipe-roofing method is a new method of constructing urban underground space, which not only enhances the sideways stability of the conventional pipe-roofing system but also effectively regulates the subsidence of the ground during underground digging, thereby augmenting both the horizontal and the vertical load-bearing capabilities. This method has already been efficiently employed in the construction of the subway stations of Shenyang Metro Line 9 and Line 10. This paper proposes calculation methods for the surface settlement of a circular steel pipe with flange plates based on the modified Mindlin solution considering pipe–soil interaction and the influence of flange plates. This paper analyzes the main geometric parameters affecting surface settlement, including the position of flange plates and steel pipe diameter. Simultaneously, this paper obtains the mathematical relationships between the surface settlement and the geometric parameters, providing a theoretical prediction method for actual pipe jacking construction of the STS pipe-roofing method. [ABSTRACT FROM AUTHOR]

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In relation to the Shifu Road Station project on Line 4 of the Shenyang Metro in China, a small-pipe roof-beam method for constructing subway stations is presented. First, a numerical simulation was performed to optimize the supporting parameters of the proposed method and determine the design scheme. Subsequently, the deformation of the pipe roof and surface settlement during the construction process were investigated. Finally, the surface settlement attributed to the excavation was studied through field monitoring, and the proposed method was compared with other methods. The results show that an increase in the pipe-roof spacing has little effect on the surface settlement and pipe-roof deformation. The bearing capacity of the pipe roof can be efficiently utilized once the flexural stiffness reaches 2EI, and the flexural stiffness is not the dominant factor controlling the deformation. The essential stages in controlling surface settlement are the excavations of the transverse pilot tunnels and the soil between them. The final settlement value of the ground was 24.1 mm, resulting in a reduction in the construction period by at least five months while satisfying the control requirements. [ABSTRACT FROM AUTHOR]

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In modern urbanized areas, the increasing demand for underground structures has led to an increase in the number of tunnelling projects in soft and shallow grounds. Tunneling in such conditions poses significant challenges, primarily due to the ground's low shear capacity and high deformation potential, leading to tunnel face instability and surface settlement. Accurate calculation of surface settlement is crucial in order to prevent probable damage to nearby structures. Consequently, various field measurement techniques and analytical solutions have been developed to estimate the maximum surface settlement resulting from tunneling activities in urban areas. These methods provide valuable insights to mitigate the risks associated with excessive settlement, ensuring the integrity and safety of surrounding infrastructure. Therefore, this study employs the numerical approach to gain a comprehensive understanding on surface settlement and the tunneling operation with tunnel boring machines. The analysis considers various performance parameters, including applying pressure around the shield, grout pressure, face pressure, parameters of machine advancement, and shield conicity. The aim of this research is to compare the results obtained from the numerical model with those obtained from precision instruments. Firstly, a comprehensive background on the importance of the considered subject is outlined, and the procedure of numerical modeling is elaborated in detail which is followed by outputs, comparisons, discussion and conclusions. The findings of this study demonstrate that the difference between surface settlement obtained from the results of instrumentation and numerical modeling for the eight investigated sections was an average of 11%, which was deemed negligible. These results highlight the potential of three-dimensional modeling and simulation techniques to support accurate estimation of surface settlement in tunneling operations, thereby minimizing potential damage to the surrounding structures. The reliable assumptions and simulation techniques used in this research can be useful for future tunneling projects to reduce the construction costs. [ABSTRACT FROM AUTHOR]

To explore the ground deformation mechanism after pre-reinforcement induced by overlarge-diameter shield tunneling, a case study is conducted on a shield tunneling in Jihua west road extension line crossing underneath a dam. Three-dimensional numerical simulation is conducted to examine the ground settlement control effect by various ground reinforcement schemes. Findings are as follows: (1) The soil deformation is effectively controlled by prereinforcing the soil above the shield tunnel, and the maximum surface settlement decreases by approximately 50% after the ground reinforcement. (2) The optimal reinforcement depth is reinforcing to the bottom of the tunnel by jet grouting piles. However, the three different reinforcement depths to the arch, the arch waist, and the arch bottom have similar control effects on the ground deformation, which can be rationally selected based on the principle of economy and efficiency. (3) The different reinforcement lengths along the shield advancing direction affect the deformation of reinforced area, thus, the reinforcement area can only be determined according to the crossing length. [ABSTRACT FROM AUTHOR]

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The proposed underground tunnel for Mass Rapid Transit Line 1, Dhaka brings immense attention to the engineers and experts not only because of its construction challenges through a densely-built city, but also for the potential tunneling-induced ground settlements. This very preliminary study investigates the ground surface movement due to the progression of the tunnel boring machine (TBM) using numerical analysis. A series of finite element (FE) models have been developed using PLAXIS 3D, in which Mohr–Coulomb (MC), modified Cam-Clay (MCC), and hardening soil (HS) have been considered. The in-field data of Mashhad Metro Line-2 have been compared to verify PLAXIS 3D's efficacy in tunnel modeling. Subsequently, the outcomes of the FE analyses are compared with the existing empirical formulas. The PLAXIS 3D analysis considering the MCC soil model exhibits strong agreement with the real monitored data, with a variance of only 3.85%. After simulating different stages of the tunnel construction, results are reported in terms of the distance of the inflexion point from the center, the settlement trough pattern, the maximum transverse settlements, and the vertical settlements. They are also compared with the established empirical formula. In order to comprehend the surface settlement with various tunnel depths and diameters, a parameter dependency study has been carried out. The analysis findings showed that increasing the TBM’s depth and radius causes the inflexion point’s distance from the center of the tunnel to increase by 4% and decrease by 5%, respectively. It is also observed that as tunnel depth increases, the overall settlement of the tunnel lowers by 11% for every additional 5 meters of depth. The MCC model, out of the three, exhibits the most accurate value of the settlement compared to that obtained from the empirical solutions, and also the best-fit form to the Gaussian curve.

In complex underground conditions, the excavation of deep foundation pits has a significant impact on the deformation of retaining structures and nearby subway stations. To investigate the influence of deep excavation on the deformation of adjacent structures, a three-dimensional numerical model of the foundation pit, existing subway station, and tunnel structure was established using FLAC 3D software, based on the Shenzhen Bay Super Headquarters C Tower foundation pit project. The study analyzed the deformation characteristics of retaining structures, adjacent subway stations, and tunnels during different stages of deep excavation, and the accuracy of the numerical simulation results was validated through field monitoring data. The results indicate that during the excavation process of the foundation pit, the lateral horizontal displacement of the retaining structure is generally small, with a typical “concave inward” lateral deformation curve; the horizontal displacement value of the contiguous wall section is less than that of the interlocking pile section. The bending moments of the retaining structure show a distribution pattern with larger values in the middle and smaller values at the top and bottom of the pit, with a relatively uniform distribution of internal support forces. The maximum displacement of the nearby subway station is 8.75 mm, and the maximum displacement of the subway tunnel is 2.29 mm. The research findings can provide references for evaluating the impact of newly built foundation pits near subway stations and contribute to the rational design and safe construction of new projects.

The Heimaguan Tunnel in China serves as a case study to exemplify the variation laws related to surface settlement, deformation, and stress characteristics in a shallow-buried soft-rock tunnel, while emphasizing in the tunnel support requirements. The first stage of this study begins with monitoring the time-varying characteristics of surface settlement, vault subsidence, and the horizontal convergence of Grade V rock. In the second stage, Peck theory is used to calculate the distribution characteristics of surface settlement. The results of both stages are compared to create a vault settlement model, thus establishing the horizontal convergence based on exponential function, logarithmic function and hyperbolic function, and determining the optimal time of secondary lining construction. On this basis, the time-dependent variation laws and characteristics of vertical and horizontal displacement and principal stress of surrounding rock are studied. After this, using simulation and analysis, the proper support is recommended. The study reveals that the surface settlement, vault subsidence, and horizontal convergence of the shallow-buried soft-rock tunnel stabilize within 25–30 days. Peck theory closely aligns with predictions based on exponential functions, with only a 0.72% difference. The recommended time for secondary lining application is 26–27 days.

The experimental work of this study deals with the performance of pipe in sand with various responses subjected to incremental static loading where the backfill is reinforced with two types of reinforcement (geogrid and geocell) to investigate the effects of backfill cover. The pipes considered are installed in sand with different densities; i.e., loose, medium and dense sand, and a constant burial depth (2D, where D is the pipe diameter). It was concluded that the maximum deformation occurs at the crown of the pipe. The deformation increases when the sand density decreases. For a burial depth equal to 1.5 D, the maximum strain on the pipe crown increases by about 22.5% when the sand changes from dense to medium and 36.8% when it changes from dense to loose. The vertical stress above a pipe buried in loose sand is reduced by 8.3% when the geogrid width is 2B where B is the footing width, while it is equal to 22% when the geogrid width is B. When a geocell is used, the percent reduction is equal to 62%. The percent reduction in the vertical stress above a pipe buried in medium sand is about 28% when the geogrid width is 2B and 40% when the geogrid width is B and equal to 68% when the geocell is used.

Surface settlement due to tunnel excavation is affected by several factors. However, no explicit mapping correlation exists between surface settlement and the main influencing factors. In this study, three tree-based methodologies, including classification and regression tree (CART), random forest (RF), and gradient boosting decision tree (GBRT), were implemented to predict the tunneling-induced surface settlement of the South Hong-Mei Road tunnel in Shanghai, where a large mix-shield was used. Thirteen influencing factors within three categories (tunnel geometry, geological conditions, and shield operation factors) were employed as input variables. Results show that the ensemble methods (RF and GBDT) provide superior performance over the single-tree model (CART). Moreover, GBDT has the highest level of prediction accuracy among the three statistical learning methods. The importance of influencing factors on the tunneling-induced surface settlement was probed. The tunnel geometry had the greatest effect on surface settlement. It is followed by the influencing factors in shield operation factors. Moreover, geological conditions were not as influential as the other influencing factors. The outcomes of this study may provide a reference for evaluating tunneling-induced surface settlement in other similar tunnel projects.

The cost of subway construction is especially dependent on stations’ construction cost. In order to minimize these costs, an optimum depth for subway tunnels should be adopted. This study intends to investigate the best depth of tunnel construction for Tabriz subway, Line 2. The study is carried out in two categories of technical and financial studies. In technical studies, surface settlement is the ruling criteria, which its allowed limit is 25 mm. Results showed that depths less than 1.5 times the tunnel diameter bear settlement above the limit; therefore, tunneling in such depths is not recommended. Financial studies consist of a cost analysis of tunneling and subway station construction. To do so, the depth of station construction and their distance from each other have been analyzed. Results indicated that the construction costs are highly dependent on the stations’ depth and their distances. To put it more clearly, the least subway costs are achieved when the overburden is at minimum and station distance is at maximum. To be more specific, along the 17 km of the route, when the station depth is greater than twice the tunnel diameter, and their distance is 750 m, the unit cost of construction reaches 29 M$, while it is at its minimum (7 M$) when the stations’ depth is less than tunnel diameter, and their distances are 3000 m. Eventually, the optimum depth for Line 2 of the Tabriz subway is 1.5 to 2 times the tunnel diameter, while obviously, more distanced stations cost less. [ABSTRACT FROM AUTHOR]

The surface settlement during the tunneling process is becoming increasingly difficult to forecast as its surroundings become more and more erratic, and the maximal surface settlement raises risks posed suddenly by various uncertain factors. This paper proposes a novel approach to prediction of the surface settlement and analyzes the stability of tunnel construction. The dimensionless analysis and Buckingham’s π-theorem are adopted for this purpose, and some useful dimensionless quantities are found, which can be used to determine the surface settlement’s main properties. In this manner, the paper offers new ways of predicting surface settlement in various cases, and it sheds a new light on the tunnel’s design and safety monitoring. [ABSTRACT FROM AUTHOR]