Double-shield TBM is more efficient than shield tunnel construction in hard rock strata. It is widely used in subway tunnel construction, such as in Qingdao and Chongqing in China. However, construction vibration problems caused by double-shield TBM critically affect human comfort in surface buildings. In order to study the vibration influence law of double-shield TBM, the on-site monitoring plan of double-shield TBM is developed, relying on a tunnel section of Qingdao Metro Line 4. Then, the vibration monitoring results are analyzed, and the time domain and frequency domain characteristics of vibration acceleration are obtained. Subsequently, taking vibration peak acceleration as the research object, the transverse and longitudinal vibration laws of double-shield TBM construction are studied. Finally, according to the standard of human comfort in buildings, the vibration influence ranges of double-shield TBM construction are obtained. The research results can provide a reference for the vibration effect of double-shield TBM passing through houses, highways and bridges. Moreover, it can also provide a basis for the disputes that double-shield TBM tunnel construction affects the lives of inhabitants.

Excessive surface settlement poses significant challenges to shield tunnelling construction, resulting in damage to adjacent buildings, infrastructure, and underground pipelines. This study focused on investigating the surface settlement induced by shield tunnelling during the construction of Qingdao Metro Line 6 between Haigang Road Station and Chaoyang Road Station. Firstly, the settlement data from the left line of the shield tunnel were evaluated by grey relational analysis. The relational coefficients were calculated to assess the correlation degrees of each influential parameter. Subsequently, the four critical influential parameters with the highest relational degrees were chosen to investigate their effects on surface settlement through numerical simulations under different scenarios. The results show that the four parameters with the highest relational degrees were thrust, grouting pressure, earth pressure, and strata elastic modulus. It should be noted that the strata elastic modulus significantly affects surface settlement, while the grouting pressure influences the settlement trough width in weak strata. Moreover, improper thrust magnitude can lead to an increase in surface settlement. Based on these findings, recommendations are proposed for the right-line tunnel construction and practical countermeasures for surface settlement during shield tunnelling construction are provided.

When shield machine traverses through hard rock mass, disc cutters will be abraded to different degrees. Excessive height difference exists between adjacent disc cutters, which critically affects the rock‐breaking efficiency. Relying on a shield section of hard rock mass in Qingdao, the disc cutter abrasions are measured on site, and the reason for low construction efficiency is analysed. Subsequently, the discrete element method is used to study the rock‐breaking law under different height differences of disc cutters. The ultimate cutter height difference for rock breaking is obtained. According to this, the cutter adjustment scheme is proposed to reduce the cutter height differences on site. Comparing shield tunnelling parameters before and after the cutter adjustment, it is found that the construction efficiency is significantly improved. The results are of great significance for improving the rock‐breaking efficiency and increasing advancing speed of shield in hard rock mass.

For tunnel-support engineering, the bed separation of surrounding rock has a great influence on the support performance of bolts. In order to reveal the mechanical properties of the full-grouted prestressed bolt under the influence of bed separation, three typical working conditions of single-separation, multi-separation and different separation positions were set up, and theoretical models and numerical models were established. Furthermore, the characteristics of bolt axial force and anchorage–interface shear stress were analyzed by numerical method, and the sensitivity based on an orthogonal test was studied by means of range analysis and variance analysis. The results showed that: (1) under the single-separation condition, the separation value has a significant effect on the mechanical properties of the bolt, and with the increase in the separation value, the sliding failure unit of the bolt increases; (2) for multi-separation conditions, if the total separation value is the same, the increase in the number of separation interfaces is beneficial to the force of the bolt; (3) for the case where the separation layer is located at different positions, the separation layer on the right side is more likely to cause the overall slip failure of the bolt; and (4) for the above three influencing factors, the separation value has the greatest influence on the mechanical properties of the bolt, and the separation position has the least influence.

In order to compare the mechanical characteristics and supporting performance of the lengthened anchored pre-stressed bolt, the full-length anchored bolt and the full-length anchored pre-stressed bolt under the bed separation conditions, theoretical and numerical analysis models of the three typical bolts were established, respectively. The influences of preload, bed separation values, bed separation numbers and bed separation positions on the mechanical properties of the three typical bolts were studied by numerical simulation method, and the mechanical properties of the three typical bolts were compared and analysed, and the sensitivity analysis of the crack opening of the three typical bolts was carried out. Results indicate that the initial preload can exert obvious restraint on the surrounding rock, in which the preload transmission range of the full-length anchored pre-stressed bolt is larger, and the restraint effect on the surrounding rock is better. Under the different bed separation conditions, the stress characteristics of the three typical bolt bodies at the bed separation basically follow the same law except for the free section of the lengthened anchored pre-stressed bolt. Under the action of the bed separation, the initial bonding section of the full-length anchored pre-stressed bolt and the free section of the lengthened anchored bolt have a certain influence on the distribution of the axial force and shear stress at the anchorage interface. The sensitivity of the two kinds of full-length anchored bolts is higher than that of the lengthened anchored pre-stressed bolt under the left bed separation condition. There is little difference in sensitivity between three typical bolts under the middle and right bed separation conditions. The research results can provide theoretical guidance for the selection of bolts in roadway support.

The double-shield TBM has been widely adopted in urban subway tunnel construction in China. TBM excavation inevitably induces ground vibrations, which may pose risks to adjacent structures and adversely affect human comfort. However, current vibration assessment methods rely heavily on field monitoring and lack a quantitative relationship with TBM excavation parameters. To address this gap, this study proposes a novel approach to predict vibrations based on thrust, torque, and monitoring distance. Based on field tests conducted in the double-shield TBM section of the Qingdao Metro, a test segment consisting of 1063 rings was selected for analysis. Excavation parameters were systematically adjusted, and both the parameter values and corresponding vibration accelerations were recorded. Using Spearman’s rank correlation coefficient, the relationship between the excavation parameters and the root mean square (RMS) value of the vertical vibration acceleration was examined. The results indicate that both thrust (r = 0.72, p < 0.01) and torque (r = 0.47, p < 0.01) are significantly correlated with the vertical vibration acceleration. Using the improved GA-BP algorithm, a prediction model for vibration acceleration was established based on tunnelling parameters and monitoring distance. The results indicate that the model relying on thrust and distance yields the best performance, achieving a mean squared error (MSE) of 0.92888. The single-point prediction error ranges from 0.02 to 1.63 mm/s². Compared with a model that uses distance alone, the proposed model reduces the single-point prediction error by 73.6%, representing a significant improvement in accuracy. The predictive model was further validated in the left tunnel, where the prediction error ranged from 0.03 to 1.07 mm/s², confirming its feasibility. This study provides a method for real-time prediction of TBM-induced construction vibrations and offers a basis for adjusting tunnelling parameters to mitigate vibrations during tunnel construction.