The reasonable damage evaluation method for tunnel structure can be used to determine the overall safety state of the tunnel structure and can help to establish the maintenance plan of the tunnel structure. As a fuzzy system, the evaluation process of tunnel damage has the characteristics of randomness and fuzziness. Traditional tunnel damage evaluation methodologies do not account for the fuzziness and randomness of the system. Therefore, this study puts forward a visual evaluation method based on cloud theory for evaluating tunnel damage. Damage evaluation for a shield tunnel section of Changsha Metro Line Two in China has been taken as a case study. This method effectively considers the fuzziness and randomness of the evaluation system, improves robustness of the results of the structural damage evaluation, and is a simple and visual method.

The deformation of existing pipelines caused by the tunneling of a shield machine along curved sections has not been sufficiently researched, and a corresponding theoretical prediction formula is lacking. This paper derives a prediction formula for the deformation of an existing pipeline caused by shield machine tunneling along a curved section. Further, a finite difference model (FDM) corresponding to an actual project is built. Finally, the deformation of the surface and existing pipelines caused by shield machine tunneling along the curved section is analyzed. The research results show that the results of theoretical prediction, FDM calculation, and field monitoring data are consistent. In addition, the deformation of the surface and the existing pipeline are asymmetrically distributed when the shield machine tunnels along the curve section instead of symmetrically distributed (for straight line segment). When the pipeline is perpendicular to the tunnel axis, the maximum deformation position of the existing pipeline deviates from the tunnel axis by about 0.5 times the tunnel radius. In addition, as the angle β between the pipeline axis and the tunnel axis increases, the maximum deformation position of the pipeline gradually approaches the tunnel axis.

With the development of urban metro systems, shield tunnels that pass through existing bridge pile foundations have become an inevitable engineering problem. Therefore, ensuring the stability of the strata and existing bridge piles during tunnel construction is a common goal in engineering practice. Currently, research on the mechanical responses of strata and existing piles under different conditions of upper-soft and lower-hard composite strata during shield tunneling has not been conducted extensively. This paper presents a numerical simulation of a shield tunnel passing through an existing bridge pile foundation in upper-soft and lower-hard composite strata. Subsequently, the surface subsidence and mechanical responses of a single pile were analyzed and evaluated. Additional stresses generated in the soil by existing bridge piles and the selection of grouting pressure were considered to optimize the driving pressure of the slurry shield. Allowable values were proposed to evaluate the construction disturbances caused by the tunnel excavation. The results show that the disturbance to the soil and existing piles is significantly influenced by the hard-rock height ratio, and the surface subsidence increases when the hard-rock height ratio decreases. The displacement and internal force of a single pile are significantly influenced by the load applied to the pile. This study demonstrates the changes in the mechanical responses of a single pile during shield tunnel boring, and provides in-depth insights into the deformation control caused by shield underpassing structures in upper-soft and lower-hard composite strata.

This study defined the height ratio of soft-rock strata and established a numerical model for analyzing shield construction in upper-soft, lower-hard composite strata together with field monitoring data. In this way, the influence of shield tunneling while passing under the pile foundation of the culvert at a short distance (the shortest distance is 1.4 m) in the typical upper-soft, lower-hard composite strata in Guangzhou can be examined. Moreover, the reinforcement effects of the ground, the bridges, and the culverts, using the strata-reinforcing plan dominated by the metro jet system (MJS) in a narrow space, are evaluated. Based on the results, (i) the maximum ground subsidence is found at the position in which the height ratio of the soft rock is 1.0. (ii) However, differential subsidence might be found in the subsequent shield construction when the soft-rock height ratio of the adjacent excavated surface ranges from 0 to 0.2 and from 0.5 to 1. (iii) The concentrated release of stress has a greater impact on the structure than the geological conditions of the shield tunneling face. (iv) Reinforcing with the MJS method contains the concentrated release of stress. This study can provide a reference for controlling the deformation of the under-crossing structure in the shield construction of the upper-soft, lower-hard composite strata.

Affected by the coupling of excavation disturbance and ground stress, the heterogeneity of surrounding rock is very common. Presently, treating the permeability coefficient as a fixed value will reduce the prediction accuracy of the water inflow and the external water pressure of the structure, leading to distortion of the prediction results. Aiming at this problem, this paper calculates and analyzes tunnel water inflow when considering the heterogeneity of permeability coefficient of surrounding rock using a theoretical analysis method, and compares with field data, and verifies the rationality of the formula. The research shows that, when the influence of excavation disturbance and ground stress on the permeability coefficient of surrounding rock is ignored, the calculated value of the external water force of the tunnel structure is too small, and the durability and stability of the tunnel are reduced, which is detrimental to the safety of the structure. Considering the heterogeneity of surrounding rock, the calculation error of water inflow can be reduced from 27.3% to 13.2%, which improves the accuracy of water inflow prediction to a certain extent.