Application of Bio-enzyme Soft Soil Reinforcement Technology on the Road Above Metro Interval Tunnels

With the acceleration of urbanization in China, massive population influx into cities has brought economic prosperity but also exacerbated traffic congestion and increased transportation loads. To alleviate severe traffic conditions, subway tunnel construction continues to expand while municipal road projects flourish, leading to increasingly close proximity or even intersection of road/bridge engineering works above subway tunnels, which imposes higher requirements on soft ground treatment technology. This paper addresses the soft ground reinforcement challenges of the planned Second Road project above the Shuiwan-Shenzhen Pazhou Branch Line Tunnel in Panyu District, proposing a novel bio-enzyme-based soil solidification technique for subgrade treatment. Comparative analysis with traditional high-pressure jet grouting piles and deep cement mixing piles reveals technical shortcomings of conventional methods, including significant soil displacement effects, construction disturbance sensitivity, prolonged construction periods, and potential additional stress on subway tunnels. This study employs a bio-enzyme composite solidification system, forming a solidified subgrade through layered paving (20 cm ± 2 cm thickness) and vibration compaction. The construction process eliminates the need for drilling operations, avoiding soil displacement effects and pore water pressure increases characteristic of traditional methods. Field tests demonstrate that the solidified layer achieves 92.4%~95% compaction with deflection values 121 mm~142 mm, saving approximately 51 days of construction time and reducing direct costs by 2.6378 million yuan compared to conventional techniques. This technology provides a non-invasive solution for soft ground treatment in subway protection zones, offering significant technical and economic advantages that can serve as a reference for similar projects.