Shield tunnelling through densely populated urban areas inevitably disturbs the surrounding soil, potentially posing significant safety risks to nearby buildings and structures. The constitutive models currently employed in numerical simulations for tunnel engineering are predominantly confined to the assumptions of isotropy and coaxiality, making it challenging to adequately capture the complexity of the mechanical response of the soil surrounding the tunnel. Based on the proposed non-coaxial and anisotropic elastoplastic Mohr-Coulomb yield criterion, this study carries out numerical simulation analyses of soil disturbance induced by urban shield tunnelling. Herein, the anisotropic parameters n and /1 jointly determine the shape of the anisotropic yield surface. The results demonstrate that rotation of the principal stress axes is observed in most areas of the soil surrounding the tunnel face, with the phenomenon being particularly pronounced at the crown and the invert of the tunnel. As the anisotropic parameter n decreases, the maximum surface settlement above the tunnel axis increases. The influence of anisotropy on higher-stress unloading coefficients is significant, resulting in the development of a wider plastic zone around the tunnel. As the coefficient of lateral earth pressure at rest K0 increases, the maximum surface settlement gradually reduces. Under the influence of anisotropic parameter /1 or non-coaxial parameter k, the maximum surface settlement exhibits an approximately linear relationship with K0. However, the anisotropic parameter n has a significant influence on the trend of the maximum surface settlement with respect to K0, which leads to a non-linear relationship. Neglecting the effects of soil anisotropy, noncoaxiality, and the coefficient of lateral earth pressure at rest may lead to design schemes that are potentially unsafe. The results of this research can provide engineers with design bases for construction parameters and soil disturbance control while shield tunnelling in sandy pebble soil.

Accurate prediction of ground surface settlement (GSS) adjacent to an excavation is important to prevent potential damage to the surrounding environment. Previous studies have extensively delved into this topic but all under the limitations of either imprecise theories or insufficient data. In the present study, we proposed a physics-constrained neural network (PhyNN) for predicting excavation-induced GSS to fully integrate the theory of elasticity with observations and make full use of the strong fitting ability of neural networks (NNs). This model incorporates an analytical solution as an additional regularization term in the loss function to guide the training of NN. Moreover, we introduced three trainable parameters into the analytical solution so that it can be adaptively modified during the training process. The performance of the proposed PhyNN model is verified using data from a case study project. Results show that our PhyNN model achieves higher prediction accuracy, better generalization ability, and robustness than the purely data-driven NN model when confronted with data containing noise and outliers. Remarkably, by incorporating physical constraints, the admissible solution space of PhyNN is significantly narrowed, leading to a substantial reduction in the need for the amount of training data. The proposed PhyNN can be utilized as a general framework for integrating physical constraints into data-driven machine-learning models. (c) 2025 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/ 4.0/).

The development of underground spaces is crucial for modern urban environments, particularly in coastal cities with prevalent soft soil conditions. Deep foundation excavation works in such areas present technical challenges due to complex deformation phenomena including soil settlement and the lateral displacement of supporting structures. This study analyzes deformation patterns associated with deep foundation pit excavations in Ningbo's soft soil areas by examining 10 cases of subway station projects. This study evaluated the relationship between the maximum surface settlement and various engineering parameters using statistical and comparative analyses and also compared the results of each relationship with those of other regional studies. The results indicate that multiple coupled parameters-the excavation depth, diaphragm-wall-embedded depth ratio, support system stiffness, and pit aspect ratio-significantly shape the deformation patterns. The average ratio of the maximum surface settlement to the excavation depth is 0.64%, notably higher than in regions such as Hangzhou and Shanghai. The maximum lateral displacement in this study averaged 0.37% of the excavation depth. The maximum lateral displacement of the diaphragm walls in this study averaged 0.37% of the depth of excavation and, in addition, the average positive correlation between the depth at which the maximum lateral displacement occurred and the depth of pit excavation was h delta hmax=He + 1.46. A positive correlation also emerged between the maximum ground settlement and lateral displacement of the diaphragm walls. But the influence of the shape of the pit on the deformation will show different types of relationships depending on the area and geotechnical conditions, which need to be further investigated.

In order to address the issue of surface deformation in wintering foundation pits in seasonal frozen soil areas due to excavation and freeze-thaw, an indoor scale model test was conducted to examine the displacement relationship between pit wall soil and supporting structures under freeze-thaw conditions, as well as the temperature change and water migration of soil surrounding the foundation pit. The distribution mode of surface settlement under excavation and freeze-thaw conditions was examined and a surface settlement calculation model was established based on the maximum value of surface settlement. The water will move from the frozen to the unfrozen region as a result of the freeze-thaw cycle. About 1.1 m is the freezing depth. An increase in surface settlement will result from the coordination of deformation between the soil and the supporting structure during freezing and thawing. The greatest surface settlement value following the initial freeze-thaw cycle is 1.082 mm, which is around 215% greater than that of excavation. The skewed distribution is comparable to the surface settlement curves produced by excavation and freeze-thaw cycles. The calculated model's results and the measured settlement values agree rather well.

This study presents a series of centrifuge model tests that were conducted to investigate the grouting mechanism and its effect during rectangular pipe jacking in soft soil. A new jacking grouting device was developed to simulate the entire grouting process in the centrifuge model tests. The influence of grouting on the friction at the lining-soil interface and vertical displacement of the tunnel lining was analysed. In addition, the impact of the grouting slurry's viscosity and fluid loss on ground surface settlement and the friction at the pipe-soil interface was also examined. The results indicate that grouting plays a significant role in mitigating the friction and vertical displacement of the tunnel lining caused by excavation. Furthermore, the study shows that reducing the viscosity of the grouting slurry can reduce the friction coefficient at the pipe-soil interface, thus facilitating the advancement of pipe jacking. The use of a low fluid loss grouting slurry is also recommended to improve control over ground surface settlement. These findings are crucial for enhancing the efficiency and safety of rectangular pipe jacking in soft soil.

Ground surface settlement is the most significant restriction when constructing shallow metro station tunnels in urban areas. The umbrella arch method (UAM) is generally applied as a tunnel support method. However, UAM becomes inadequate in some soil conditions, such as loose sand or soft clay. Innovative support systems are required to safely build shallow metro station tunnels in urban areas. The objective of this research is to investigate alternative tunnel support systems and appropriate soil models to safely construct shallow twin-tube metro station tunnels. The continuous pipe arch system (CPAS), which consists of horizontal and continuous pipes along the metro station tunnels, was modeled in three dimensions (3D) using the finite element (FE) program Plaxis3D for various pipe diameters. The ground surface settlement results of the 3D models were compared with the in situ settlement measurements to validate the geotechnical parameters of the soils used in the models. It was observed that the hardening soil (HS) model was more accurate than the Mohr-Coulomb (MC) soil model. As a result of the 3D FE model analysis, maximum ground surface settlements were obtained below 50 mm when the pipe diameters of CPAS were larger than an internal diameter (ID) of 1200 mm at a cover depth of 10 m in sandy clay soil. It is revealed that CPAS with pipe diameters between ID 1200 mm and ID 2000 mm can be utilized as a tunnel support system in urban areas to construct shallow twin-tube metro station tunnels with low damage risk.

Though a comprehensive in situ measurement project, the performance of a deep pit-in-pit excavation constructed by the top-down method in seasonal frozen soil area in Shenyang was extensively examined. The measured excavation responses included the displacement of capping beam and retaining pile, settlement of ground surface, and deformation of metro lines. Based on the analyses of field data, some major findings were obtained: 1) the deformations of retaining structures fluctuated along with the increase of temperature, 2) the deformation variation of retaining structures after the occurrence of thawing of seasonal frozen soil was greater than that in winter, although the excavation depth was smaller than before, 3) the influence area of ground settlement was much smaller because of the features of seasonal frozen sandy soil, 4) the displacement of metro line showed a significant spatial effect, and the tunnel lining had an obviously hogging displacement pattern, and 5) earth pressure redistribution occurred due to the combined effects of freezing-thawing of seasonal frozen soil and excavation, leading to the deformation of metro line. The influence area of ground settlement was obviously smaller than that of Shanghai soft clay or other cases reported in literatures because of special geological conditions of Shenyang. However, the deformation of metro lines was significantly lager after the thawing of the frozen soil, the stress in deep soil was redistributed, and the metro lines were forced to deform to meet a new state of equilibrium.

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 alpha was performed, revealing that as alpha 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 alpha decreases, the width of the settlement trough narrows, improving the settlement trough profile.

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.

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.