Due to the lack of living space and the increase in population, there has been a construction boom in the underground space to improve the quality of human life. Tunnel engineering plays a vital role in the development of underground space. In addition to traditional methods, some intelligent methods such as artificial neural networks (ANNs) have been applied to various problems in the tunnel domain in recent years. This paper systematically reviews the application of ANNs from different aspects of tunnel engineering. It reveals that the backpropagation algorithm (BPA) and Levenberg-Marquardt algorithm (LMA) are the most widely used. Due to the limitations of some original models, some scholars use optimization algorithms such as particle swarm optimization (PSO) and genetic algorithm (GA) to optimize the original ANNs to obtain better prediction results. A comparison between the ANN-based methods and methods like statistical methods is conducted. Finally, the following conclusions can be drawn: (1) The recommended ratio of the training set and test set is 3:1; (2) The advantage of optimized ANNs is not apparent when the optimization algorithm varies. Additionally, the performance of ANNs is always better than that of statistical methods.

By selecting the ratio of the cumulative maximum deformation of the retaining structure to the excavation depth as the control parameter of the retaining structure deformation, this paper established a sidewall unloading model which can consider the deformation of the retaining structure and the spatial effect of foundation pit excavation. Meanwhile, the impact region of the sidewall was divided to calculate the distribution of additional stress caused by foundation pit excavation. On this basis, through introducing the collaborative deformation model for rotation and dislocation of a shield tunnel, this paper studied the longitudinal deformation of the adjacent shield tunnel due to foundation pit excavation. Moreover, several engineering cases were given to verify the reliability of the proposed method, and the influencing factors were analyzed. The following conclusions were obtained: the axial horizontal displacement of the shield tunnel by the side of the foundation pit was normally distributed, and the calculated value was in good agreement with the measured value; the longitudinal deformation of the shield tunnel was mainly induced by the unloading effect of the sidewall of the foundation pit, which was parallel and closed to the tunnel; the soil excavation in the vicinity of the buried depth of the tunnel would result in a significant increase in longitudinal deformation; with the increase in the retaining structure deformation of the foundation pit, the longitudinal deformation of the adjacent shield tunnel and its influence scope also increased; the longitudinal deformation of the shield tunnel decreased with the increase of clearances between the foundation pit and tunnel; and finally, the excavation of the foundation pit had a great influence on the shallowly buried shield tunnel nearby, and the effect of foundation pit excavation on the tunnel decreased with the increase of the burial depth of the shield tunnel.

In order to research the theory for the variety of transverse forces of the adjacent shield tunnels caused by foundation pits excavation, the effect mechanism of foundation pit excavation on the adjacent shield tunnel was analyzed. The sidewall unloading model of the foundation pit, considering the deformation of the retaining structures, was introduced to calculate the additional stress of soil caused by foundation pit excavation. On this basis, the additional confining pressure variation model of the adjacent shield tunnel was established, considering the influence of the longitudinal deformation. Take the deep foundation pit project by the side of the shield tunnel of Hangzhou Metro Line 2 as a case study, the variation in confining pressure distribution of the adjacent shield tunnel caused by foundation pit excavation was analyzed, and a simplified finite element model was established to calculate the internal force of the segment ring structure. Moreover, the influence factors were analyzed, such as the deformation of the foundation pit retaining structure, the clearance between the foundation pit and the adjacent tunnel, and the buried depth of the tunnel. The present study suggests that the foundation pit excavation reduces the confining pressure of the adjacent shield tunnel, increases the absolute value of bending moment and shear force, and decreases the axial force at the top and bottom of the tunnel’s segment ring. With the increase in the deformation of the foundation pit’s retaining structure, the absolute value of the additional confining pressure on the adjacent tunnel increases, and the response of the bending moment to the foundation pit excavation unloading is more obvious than the variation in the confining pressure. When the buried depth of the adjacent shield tunnel is deeper than the excavation depth of the foundation pit, the influence of the excavation on the tunnel will be obviously weakened. With the decrease in the distance between the pit and tunnel, the influence of the excavation on the tunnel will be enhanced.

Aiming at studying the harm caused by sudden ground loadings on existing shield tunnels, a indoor scaled model test with a geometric similarity ratio of 1:15.5 was adopted. Considering the influencing factors such as ground loading, burial depth of the shield tunnel, loading position and soil properties, tunnel convergence deformation, tunnel settlement and deep settlement of soil caused by sudden ground loadings are studied. A three-dimensional finite element simulation is carried out using the Midas software, and deep settlement of soil is calculated by a theoretical method. The purpose of this model test is to further understand the influence of ground surcharges on shield tunnel deformation. The results show that the greater the ground surcharge, the greater the settlement and vertical convergence deformation of the shield tunnel; The further away from the ground surcharge, the smaller the settlement, vertical convergence deformation and lateral convergence deformation of the tunnel. When the pile load size is constant, the greater the burial depth of the tunnel, the smaller the vertical convergence deformation and settlement of the tunnel; the maximum value of deep settlement of the soil always remains at the closest point to the ground surcharge; compared with the use of dry sand, the vertical convergence deformation and settlement of the tunnel are significantly reduced when using wet sand. Both the theoretical calculation results and the numerical simulation results are in good agreement with the indoor model test results.