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.

In fracture zones, tunneling with a double-shield Tunnel Boring Machine (TBM) presents significant challenges, including deformation overrun of the surrounding rock, TBM jamming, and excavation face collapse. To assure the tunnel construction safety and efficiency, it is necessary and crucial to conduct a stability analysis of the tunnel surrounding rock when a TBM passes through the fracture zones. The tunnels from Jiadingshan Road Station to Anshan Road Station in Qingdao Metro Line 8 are constructed by double-shield TBMs. It inevitably passes through fracture zones with different deterioration levels and dip angles. In this study, based on this construction section, numerical models of fracture zones with different deterioration levels and dip angles were developed to analyze the displacements of tunnel vaults, inverts, and haunches. In addition, the maximum shear stresses of the surrounding rock were analyzed. Finally, the displacement and shear stress variation patterns of the surrounding rock with different deterioration levels and dip angles were obtained. The findings reveal the stability behavior of tunnels under various fracture zones. They can serve as a valuable reference and theoretical foundation for future tunnel construction projects utilizing double-shield TBMs in areas with fracture zones.

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.

Existing component-based models have difficulty interpreting the field response of earth pressure balance (EPB) shield tunneling parameters when the excavation face gradually changes from hard rock to sandy strata. To address this problem, this study proposes a mechanism-informed semi-empirical analysis based on a continuous face sand fraction function, $\eta \left(z\right)$, which represents the evolution of the sand-bearing area fraction at the excavation face along the shield advance direction. The function is constructed from the geological profile and is used as a continuous reformulation of existing face-composition descriptors such as rock/sand ratio and composite ratio. Based on $\eta \left(z\right)$, engineering-equivalent models for total thrust and cutterhead torque are developed and evaluated using field tunneling data from Qingdao Metro Line 15 and Line 5. The Dandan right-line data are used for parameter calibration, while the Basi right-line data from Rings 590–650 are used for independent validation without further parameter tuning. The results show that the η-related correction term improves the independent validation performance of the total thrust model, reducing the MAPE from 22.56% to 14.25%. In contrast, cutterhead torque exhibits stronger operational variability and interval-specific baseline offset. After applying a baseline correction determined from the stable hard-rock section of the Basi interval, the ring-scale torque MAPE decreases from 44.07% to 17.25%, but the additional $\eta$-related torque contribution remains limited. These results indicate that total thrust is more sensitive to the gradual increase in face sand fraction, whereas cutterhead torque is more strongly influenced by machine condition, cutter wear, and operational control. The proposed approach provides a field-based semi-empirical reference for interpreting tunneling parameter responses in similar hard-rock-to-sandy-strata transition zones.