Engineers have made remarkable strides in ensuring the stability of existing structures during subway construction, particularly as tunneling operations frequently take place beneath inhabited buildings. A recent study led by researchers from Zhengzhou University focuses on the response of overlying masonry structures induced by double-track Earth Pressure Balance Machines (EPBM) tunneling cutting through cemented soil composite pile foundations.
This engineering investigation stems from the challenges presented by urban tunneling, where subsurface drilling often interacts with vulnerable structures. During the construction of Metro Line 5 in Zhengzhou, the research team monitored the impacts of tunneling operations on the adjacent Zhenghe 1# Building—a masonry structure subjected to the pressures of the tunneling.
The researchers utilized finite element modeling to establish parameters for their study. They simplified the composite foundation using the area-weighted composite modulus method, which allows for more efficient calculations when predicting how structures will react to subsurface disturbances. By deploying this method, they created numerical models to represent the tunnel as it passed through the cement-soil pile foundation. Notably, their computational approaches aligned closely with real-world measurements, confirming the reliability of their models.
At the heart of this inquiry was the examination of two key excavation parameters: face pressure and grouting pressure—both of which play pivotal roles during tunnel construction. According to the study, "The numerical simulation curves of settlement at monitoring points align well with the monitored values, thereby confirming the rationality of the simplified model." This alignment is significant as it demonstrates the model's effectiveness in predicting real-world scenarios.
The findings revealed fundamental criteria for mitigating negative impacts on the surrounding structures. Researchers learned from their analysis of the face pressure data—where increasing pressures suppressed surface settlements effectively up to certain thresholds. "Increasing the face pressure can effectively reduce the impact of the shield on the superstructure, but diminishing returns occur above 0.20 MPa," the study noted. This information is invaluable for urban planners and engineers, providing guidance on the necessary measures for maintaining structural integrity during tunneling.
This research does not only offer immediate solutions but also emphasizes the importance of precision engineering when addressing urban development. The study highlights several best practices for minimizing disruption to existing structures, allowing for safer and more efficient tunneling processes beneath residential and commercial buildings. Recommendations include optimizing excavation methods and increasing the pressure parameters to suit the structural conditions encountered.
Overall, this research is instrumental for the future of urban infrastructure development, particularly as cities expand and existing structures are frequently challenged by underground construction activities. Further studies will likely build on these findings, advancing techniques and modeling practices to protect structures from the risks posed by tunneling.