In the heart of Nanjing, China, a groundbreaking study is reshaping the way we approach urban rail transit construction, particularly in challenging geological conditions. GUO Shiqing, a lead researcher from the Nanjing Metro Line 9 Phase I Construction Contract under China Railway Construction Corporation Limited, has published a study in *Chengshi guidao jiaotong yanjiu* (translated to English as “Urban Rail Transit Research”) that delves into the complexities of slurry improvement and gushing control in water-rich silty fine sand layers. This research is not just academic; it has significant commercial implications for the energy sector and beyond.
The study focuses on Earth Pressure Balance (EPB) shield tunneling, a method used to construct tunnels in difficult ground conditions. The section between Qinghe Road Station and Green Expo Park Station of Nanjing Metro Line 9 served as the case study. This area is characterized by high friction, poor flow plasticity, and strong permeability, making it a formidable challenge for conventional tunneling methods.
GUO Shiqing and his team conducted a series of slurry modification experiments using various improvement agents, including foam, bentonite, and clay. The goal was to determine the optimal mass ratios between each agent and water. “We aimed to enhance construction safety by improving the slurry’s performance,” GUO explained. The researchers conducted laboratory tests, including mixing, slump, and permeability tests, to define the applicable range of slurry improvement in silty fine sand layers.
The results were promising. Individual agents significantly improved the slump performance, with clay showing the best flow plasticity. However, mixed agents exhibited even better results, particularly a foam-to-bentonite ratio of 2:1. “The mixed agents not only reduced the mixing current but also lowered the permeability coefficient, indicating superior improvement in reducing slurry friction and permeability,” GUO noted.
The study proposed several slurry improvement schemes for water-rich silty fine sand layers, each with specific agent injection rates. These schemes provide a practical guide for future tunneling projects in similar geological conditions.
The commercial impact of this research is substantial. By improving the efficiency and safety of tunneling in challenging environments, this study paves the way for more ambitious urban rail transit projects. It also has implications for the energy sector, particularly in the construction of underground energy storage facilities and pipelines. The ability to control gushing and improve slurry performance can significantly reduce construction costs and enhance project feasibility.
As urbanization continues to grow, the demand for efficient and safe tunneling methods will only increase. This research by GUO Shiqing and his team is a significant step forward in meeting that demand. It offers a glimpse into the future of tunneling technology, where advanced materials and innovative techniques will overcome even the most challenging geological conditions.
In the words of GUO Shiqing, “This research is not just about improving slurry performance; it’s about redefining the boundaries of what’s possible in urban rail transit construction.” As the industry continues to evolve, this study will undoubtedly serve as a valuable resource for engineers, researchers, and policymakers alike.