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Accurately predicting the stress distribution around the tunnel is crucial for designing safe and economical support systems. The stress distribution is closely related to the ground stress release induced by tunneling, as well as the initial gravity stress and boundary conditions. In this study, a two-dimensional analytical model considering the ground surface boundary conditions and gravity is presented to investigate the stress field around the tunnel. Then, a numerical model was developed to validate the proposed analytical model. Finally, parametric analyses were conducted, and the limitations of the load calculation method of the code for design of shield tunnel in China were discussed. The results indicate that: (a) Tunnel excavation induces stress redistribution in the soil, resulting in a soil arching effect around the tunnel. This arching effect causes nonlinear load changes around the tunnel. (b) The soil mass around the tunnel can be divided into undisturbed and disturbed zones. Above the tunnel, the disturbance range is C -2 D (C and D represent the burial depth and the tunnel diameter), while below and on both sides of the tunnel, the disturbance ranges are 4 D and 1.5 D , respectively. (c) Once the stress release rate reaches 0.6, a combined arching effect zone, consisting of both major and minor principal stresses, is formed in the disturbance zone above and below the tunnel. (d) The load distribution pattern calculated by the code for design of shield tunnel in China is gourd-shaped, and this calculation method is insufficient for accurately evaluating the load around the tunnel. The research results can provide a reference for the design of the shield tunnel. [ABSTRACT FROM AUTHOR]

Excavations near an existing tunnel are frequently encountered in underground construction. The excavation–soil–tunnel interaction mechanism is not yet fully understood, notably the long-term behavior. This study carried out three-dimensional centrifuge test of an existing tunnel subjected to a nearby excavation in saturated kaolin clay. Emphasis is put on the long-term behaviors of the ground and tunnel regarding the undrained shear strength, excess pore-water pressure, horizontal earth pressure, compression behavior, settlement, and bending moment. T-bar penetration tests showed that the retaining wall installation leads to a soil strength increase, whereas the excavation causes a reduction. Excess pore-water pressure below the excavation base gradually dissipates to zero. In comparison, the excess pore-water pressures above the tunnel crown and nearby the right springline (close to the excavation) experience continuous increases, although those close to the left springline (away from the excavation) exhibit a different pattern. Reduction amplitudes in horizontal earth pressures around the tunnel differ in both burial depth and horizontal relative position. The lateral earth pressure coefficient nearby the right springline decreases, and the stable value is higher than the Rankine's active earth pressure coefficient. The compressibility of soils at the left side of the excavation (tunnel exists) was lower than at its symmetrical side, and the ground surface settlement is compared with empirical estimates concerning ground conditions and excavation geometries. Long-term responses show that the excavation base exposure leads to continuous and appreciable increases in ground settlement, tunnel settlement, and bending moment. [ABSTRACT FROM AUTHOR]

Cases of closely spaced twin tunnels demonstrate that ground settlement above the 2nd tunnel, referred to as T2 constructed after the first tunnel (T1), exhibits pronounced differences from that above T1. The differences can be attributed to the disturbance induced by T1 construction. Based upon closed-form plasticity solutions for an unloading cylindrical cavity, this study employs subsurface settlement troughs to determine the shear modulus change during twin-tunnelling. Observations of 1 g model tests for twin-tunnelling in overconsolidated kaolin clay are interpreted from literature. After T1 construction, for positions with different radial distances but a constant angle with respect to the vertical line above the tunnel center, the graph of radial displacement/tunnel radius versus tunnel radius/radial distance exhibits good linearity. Further analyses demonstrate that the shear stiffness decreases as the angle increases. In comparison, during T2 construction, the shear modulus of soils close to T1 degrades, while the other side increases. In light of the observations of combined axial–torsional tests, the tendency of shear modulus change can be attributed to the rotation of principal stress axes. The findings can explain the differential settlements over closely spaced twin tunnels in clayey ground. [ABSTRACT FROM AUTHOR]

The impact of twin shields tunneling undercrossing with an oblique angle on the existing tunnels is complicated and still lacks of understanding. This paper investigated the deformation behaviors of the existing tunnels with new twin tunnels construction undercrossing obliquely based on numerical simulation on a case history in Changsha, China. The accuracy of numerical analysis was verified in comparison with the field measurement. The variation of the ground settlement trough and the earth pressure acting on the existing tunnel during the shield tunneling was analyzed. Then, the transversal deformation, internal forces and torsion behavior of the existing tunnels induced by the new tunnels excavation were obtained. Additionally, a parametric study was conducted to investigate the impact of the intersection angle between the new and existing tunnels on the deformation behaviors of the existing tunnel. The results show that due to oblique intersection, the transversal deformation and internal forces of the existing tunnel show obvious asymmetrical characteristic, and an unrecoverable local torsional deformation of the existing tunnel on both side of new tunnel can be observed after shield tunneling. The parametrical analysis indicates that the intersection angle significantly influences on the maximum settlement of the existing tunnel bottom, which is up to 27.53% larger in parallel case than that in perpendicular case, and decreases rapidly as the interaction angle varies from 30° to 60°. Nevertheless, the maximum settlement of the existing tunnel crown is unaffected by the intersection angle. [ABSTRACT FROM AUTHOR]

Earth pressure balanced shield machine (EPBS) is widely adopted for metro tunnel construction in urban areas. Support pressure on excavation face and grouting at the EPBS tail are the main measures to control the ground disturbance and settlement. The post-construction settlement is of significance to the serviceability of metro tunnel. By weakening the compression parameters of underlying soils related to soil disturbance degree (SDD) and using layer-wise summation method, this study developed a method to predict the post-construction ground and tunnel settlement. The SDD is quantitatively evaluated by the shear-strain state obtained from a series of isotropically consolidated undrained triaxial compression (CIU) tests. Based on a case history of metro tunnel constructed in structured soft soils, a suite of three dimensional finite-element analyses are performed to investigate soil disturbance during tunneling construction. The numerical simulation and the applicability of the proposed method are validated by comparing the numerical results with the field measurements. In addition, influences of support pressure and grout ratio on the tunneling-induced soil disturbance, ground and tunnel settlement are revealed. The SDD shows remarkable falloff within 0.32 D above the tunnel crown, while 0.24 D below the tunnel invert. Furthermore, within the above distance range, the linear relation between the SDD and distance from the tunnel crown or invert can be built. The analysis results show that the excessively high or low support pressure and grout ratio can both cause severe SDD which results in the significant post-construction settlement. Grout ratio of about 200% and support pressure of 2.2–2.4 P 0 are effective for reducing both the post-construction ground and tunnel settlement. The research presented in this paper provides a reference for controlling the post-construction ground and tunnel settlement constructed in structured soft soils. [ABSTRACT FROM AUTHOR]

• An AIoT-based system is designed to real-time control of tunnel construction information. • The AIoT-based system was applied to a practical tunnel engineering. • RF-based models are developed for predicting tunneling-induced settlement and shield operational parameters. Shield machine performance and tunnelling-induced settlement are the main concerns during the tunnelling process. This study proposes an artificial intelligence Internet of Things (AIoT)-based system for real-time monitoring of tunnel construction. Shield machine operational parameters and tunnelling-induced settlement can be transferred and stored in real time by an AIoT system. Thereafter, shield operational parameters and tunnelling-induced settlement prediction models based on machine learning algorithm random forest (RF) are established based on the collected data. The models are further employed to predict shield operational parameters and ground response at the next step. This dynamic system was applied to a practical tunnel engineering. The results indicate the implementation of such process from the data collection, training and updating of RF-based models, and decision making of controlling shield machine performance can be completed within 15 minutes, which is much less than the time of excavating and installing a segmental ring, ensuring the real-time control of shield machine. Based on the predicted shield operational parameters, maximum and mean prediction error of the tunnelling-induced settlement can be controlled within 5 and 2.5 mm, respectively. The AIoT-based system improves the information and automation level during the construction process, facilitates decision-making and avoids accidents. [ABSTRACT FROM AUTHOR]

Tunneling in mixed ground faces great challenges in control of shield machine, and improper operation easily trigger hazards without warning. Recently, an unexpected ground surface settlement of approximately 0.05 m was observed in the mixed ground of Changsha, China. When the shield machine advanced from the low-permeability ground to the high-permeability ground, the lag in the regulation of chamber pressure allowed the water inflow from the excavation face, hydraulic pressure loss at the tunnel face thus induced large settlement. To further investigate ground responses induced by tunneling crossing the interface of water-bearing mixed ground, a 3D fluid-solid coupling finite element model is established in this study. The results indicate obvious drawdown of the groundwater occurs when the shield machine crosses the interface of low-permeability and high-permeability ground with low chamber pressure, leading to significant ground consolidation settlement with close to the measured results. Three typical settlement development modes that are related to the relative position of the monitoring section to the interface are proposed to describe the tunneling-induced settlement in the water-bearing mixed ground. The experience of this case history provides an important lesson for the future control of shield tunneling in the water-bearing mixed ground. [ABSTRACT FROM AUTHOR]

To explore the development law of tunnel uplift during tunnelling in hard rock and its inherent relationship with the deformation of segmental rings and bolt force, this study carried out field measurements on the deformation and mechanical behaviors of shield tunnel during construction based on the North Extension Project of Changsha Metro Line 1. Five monitoring items were conducted in field measurements, including tunnel uplift, the dislocation between segmental rings, circumferential joint opening, lining circumferential and longitudinal strains, and longitudinal bolt axial force. The measured results indicated distinct stages of tunnel uplift, including the initial rapid uplift stage (Stage I), the relatively gradual uplift stage (Stage II), the second rapid uplift stage (Stage III), and the final stable stage (Stage IV). The uplift was more significant in the location of 4∼8 rings away from the shield tail, and it took approximately 40∼65 hours to be stabilized after detachment from the shield tail. The process of uplift was influenced by factors such as the buoyancy of bedrock fissure water and unsolidified slurry, grouting pressure, and the interaction between the segmental rings. Meanwhile, a notable synchronization between the transverse deformation of the tunnel, dislocation between segmental rings, circumferential joint opening, longitudinal bolt axial force, and the development of tunnel uplift was observed. The flattening effect caused by longitudinal differential deformation of the tunnel resulted in a "horizontal elliptical" shape of the tunnel cross-section. During the process of tunnel uplift, the maximum dislocation between segmental rings was reached, which gradually recovered with the stability of the uplift. Notably, the monitoring conducted over three months after construction confirmed a continuous increase in both the circumferential joint opening and the longitudinal bolt axial force at corresponding locations, providing evidence of longitudinal stress relaxation in the tunnel. Additionally, the curved section of the tunnel showed a trend of recovering toward the inner side of the curve. [ABSTRACT FROM AUTHOR]

Settlement control is an essential part of the tunnel construction process. This paper proposes two novel computational models based on the Random Forest (RF) algorithm for supporting automatically steering Earth Pressure Balanced (EPB) shield. The first model is utilized for predicting tunneling-induced settlement and the other estimates shield operational parameters. A PSO-RF hybrid algorithm which intergrates the Particle Swarm Optimization (PSO) and the RF algorithms is proposed to optimize shield operational parameters when the settlement exceeds the tolerated value. The proposed models are adopted in the case study of Changsha Metro Line 4 project. The results indicate that the predicted settlements show great agreement with the measured settlements. The face pressure and grout filling are the most significant shield operational parameters to control the settlement as a result of Global Sensitivity Analysis (GSA). The anomalous settlement (≥10 mm) can be controlled under tolerated value after the face pressure and grout filling values are optimized by the PSO-RF hybrid algorithm. Simultaneously, the consistency of the face pressure and grout filling values calculated by the PSO-RF and the grid search method demonstrates the feasibility and applicability of proposed hybrid algorithm. • Random forest models are established for predicting tunneling-induced settlement and shield operational parameters. • A hybrid algorithm is proposed for optimizing shield operational parameters. • Combining settlement and operational parameters prediction models achieves the automatic control of shield machine. [ABSTRACT FROM AUTHOR]

• Anti-uplift portal frame to control the tunnel uplift induced by overlying excavation. • Observed deformation behaviors of the existing tunnel under overlying excavation. • Control effect of the anti-uplift portal frame on the tunnel uplift. • Relationship between the tunnel uplift and the unloading ratio at different construction stages. Excavation above the tunnel will inevitably cause release of the ground stress and the associated tunnel uplift. The control of tunnel uplift is a tough problem that troubles the engineers. This paper introduces a new technology (namely anti-uplift portal frame technology) to control the tunnel uplift caused by long-distance collinear overlying excavation which adopted in the construction of an urban underground expressway in Shenzhen, China. The anti-uplift portal frame (AUPF) is composed of anti-uplift piles and anti-uplift slab, forming a portal frame between the bottom of the foundation pit and the tunnel to hoop the underlying tunnel. In order to minimize the impact of shaft excavation on the underlying tunnel during the AUPF construction, the AUPF was divided into sections in longitudinal direction and avoid excavation of the adjacent shafts at the same time. The field data indicated the median uplift after shaft excavation in the AUPF construction stage was 12.8 mm in Zone A and 5.3 mm in Zone B, and recovered by 62.5 % in Zone A and 85 % in Zone B after backfill. During the foundation pit excavation in expressway tunnel construction, the median uplift was 7.2 mm, recovered by 61 % after tunnel structure was constructed. When the tunnel uplift reached 8 to 8.5 mm, further excavation did not cause increase of the tunnel uplift, which indicates the AUPF can effectively control the tunnel uplift. The reported case provides valuable referrence to guide the similar overlying excavation projects. [ABSTRACT FROM AUTHOR]

• A reinforcement learning (RL) based optimizer is proposed. • Extreme learning machine based tunneling-induced settlement prediction model is established. • Framework of hybrid RL based optimizer and machine learning algorithms is proposed. Prediction of ground responses is important for improving performance of tunneling. This study proposes a novel reinforcement learning (RL) based optimizer with the integration of deep-Q network (DQN) and particle swarm optimization (PSO). Such optimizer is used to improve the extreme learning machine (ELM) based tunneling-induced settlement prediction model. Herein, DQN-PSO optimizer is used to optimize the weights and biases of ELM. Based on the prescribed states, actions, rewards, rules and objective functions, DQN-PSO optimizer evaluates the rewards of actions at each step, thereby guides particles which action should be conducted and when should take this action. Such hybrid model is applied in a practical tunnel project. Regarding the search of global best weights and biases of ELM, the results indicate the DQN-PSO optimizer obviously outperforms conventional metaheuristic optimization algorithms with higher accuracy and lower computational cost. Meanwhile, this model can identify relationships among influential factors and ground responses through self-practicing. The ultimate model can be expressed with an explicit formulation and used to predict tunneling-induced ground response in real time, facilitating its application in engineering practice. [ABSTRACT FROM AUTHOR]