Abstract
Shield tunneling in highly fractured karst water-rich conditions easily results in water inrush disaster or even causes the roof of the karst caves to collapse. Severe water inrush disasters have occurred during the EPB (earth pressure balance) shield machine of the Jinan Metro Line R1 advanced through a karst and fissure groundwater-rich limestone ground in the spring area. To cope with the extreme water inrush risk, a multi-step combined control technology was put forward. First, a detailed geological exploration was carried out by ahead geophysical prospecting using high-density resistivity method, geological radar, etc., and geological borehole drilling was conducted from the ground surface before excavation. As a result, the distribution orientation, size, fissure development degree, and water inflow channel within the surrounding rock of the karst caves were detected. Second, multi-step grouting was performed to reinforce the surrounding rock, including pre-grouting treatment and filling rock blocks to the big karst caves from the ground surface, multiple grouting with a small amount of inert slurry each time inside the tunnel, and secondary circumferential hoop grouting at the shield tail. Third, the tunneling process was optimized, including optimizing the tunneling parameters, making full use of the air-pressurized tunneling technology of the EPB to press bentonite into the fractures around the excavation cabin to seal the fissure water, and using the drainage system of EPB and muck improvement technology to reduce the water inrush disaster. Meanwhile, shield protection slurry technology is applied to cutter inspection and replacement in the pressurized chamber under dynamic water flow environment of the spring terrain. The practice shows that the water inrush on the tunnel face is obviously alleviated after the shield machine advanced into the grouting area. According to statistics, the water inflow on the tunnel face decreases from about 4 m3/h before treatment to less than 0.3 m3/h after the abovementioned control, and the water seepage between the segmental linings reduces to almost zero. The average advance rate increased from 3 m/day without stopping or even zero when the shield machine needs to shut down 2–3 days for drainage to about 6 m/day. In addition, the treatments prevented the shield machine from jamming and the head descending disaster. This study provided a reliable control method for shield tunneling through the karst and fissure water-rich area and played an essential role in protecting the spring water.
Highlights
With the continuous increase of metro lines, more and more metro tunnels will inevitably be built in complex hydrogeological environments
After geophysical prospecting and borehole drilling detection, the karst caves and broken rocks’ distribution orientation, size, fissure development degree, and water inflow channel were detected in the limestone section (Figures 2, 8)
26 karst caves are exposed within 0–5 m above the tunnel roof; three karst caves are exposed beyond 5 m above the roof
Summary
With the continuous increase of metro lines, more and more metro tunnels will inevitably be built in complex hydrogeological environments. Karst terrains are widely distributed in China, which is the most common geological problem during metro construction (Li et al, 2020a; Kang et al, 2021; Zheng et al, 2021) Because of their strong concealment, high complexity, and difficulty in treatment, they are prone to cause the shield machine heading down and subsidence, water and mud inrush disaster, and tunnel face instability. Because of the impact of the dynamic water environment in the spring area, various geological disasters such as ground subsidence, karst cave collapse, and surrounding rock instability are often encountered during the metro tunnels construction, as well as various water environmental problems such as water inrush disaster, groundwater table decline, and water pollution. The mud outbursts and water inrushing in the karst cave have become the most severe geological disaster at present, which may lead to flooding of tunneling equipment or even fatal crash
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
