Construction Sequence Optimization for Diaphragm Wall Obstruction Removal Using a Horizontal Full-Rotation Drilling Rig
This paper proposes and validates a construction sequence optimization for removing diaphragm wall obstructions beneath an existing metro station using a horizontal full-rotation drilling rig, demonstrating through numerical simulation and field monitoring that this method significantly reduces structural deformation compared to direct shield cutting and that specific interval group construction sequences yield the most favorable ground stability outcomes.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
Imagine the underground world beneath our cities as a giant, bustling library where trains are the books zipping through the stacks. Sometimes, a new train line needs to be built right underneath an old, busy station. But here's the problem: the old station is held up by massive, concrete "bookends" called diaphragm walls, reinforced with steel beams, that were built decades ago. To build the new tunnel, these stubborn walls have to go. If you try to smash them with a giant, noisy machine (like a shield tunneling robot), it's like trying to break a chocolate bar with a sledgehammer: you get the job done, but you shake the whole library, crack the shelves, and risk dropping the books. On the other hand, if you try to chip them away by hand, it's slow, dangerous, and messy. Engineers have been looking for a way to remove these walls that is precise, quiet, and gentle enough not to disturb the sleeping trains above. This is the challenge of "obstruction removal" in underground engineering: how to take out a giant obstacle without waking up the whole neighborhood.
This paper tells the story of a clever new solution tested in Hangzhou, China, where a new metro line needed to pass under an existing station. The researchers proposed using a "horizontal full-rotation drilling rig," which is essentially a giant, high-tech drill that can spin horizontally to eat away the concrete wall piece by piece, rather than smashing it all at once. To see if this new method was better than the old way of just driving a shield tunnel right through the wall, the team built a massive 3D computer simulation (a digital twin of the real world) to watch what would happen to the ground and the station.
The results were quite clear. When they simulated the old method of "direct shield cutting," the ground shook and settled significantly, with the station moving up to 3.6 mm and the wall itself shifting 3.9 mm. It was like the sledgehammer approach: it worked, but it caused a lot of unnecessary wiggling. In contrast, the new drilling method was much gentler. In the computer model, the station only moved 2.1 mm, and the wall shifted just 2.7 mm. The disturbance was much more focused, like a laser beam rather than a shockwave. The simulation showed that this new method could reduce the maximum deformation of the station by about 42% and the wall by 31%, proving it is a much safer bet for keeping existing structures stable.
But the researchers didn't stop there. They realized that how you order the drilling matters just as much as what you use. Imagine you have a row of cookies to eat; do you eat them from top to bottom, or bottom to top? Or do you eat every other one first? The team tested different "eating orders" for the drilling holes. They found that within a single row of holes, drilling from the bottom up was slightly better than top-down, causing less movement in the retaining piles (the safety walls holding the dirt back). When it came to the order of the rows themselves, they compared going left-to-right, right-to-left, or doing an "interval" pattern (skipping rows, like A, then C, then E, then B, then D). The simulation showed that the "interval" method was the champion. By skipping around, the construction crew allowed the un-drilled parts of the wall to act as temporary supports, preventing the stress from piling up in one direction. This approach kept the ground settlement and wall deformation to the lowest levels of all the tests.
In short, the paper suggests that for removing these tough underground walls under busy stations, the "small-hole drilling" method is superior to the "big smash" method. It also suggests that the best way to do it is to drill from the bottom up and to skip around the rows rather than marching in a straight line. While these findings come from computer simulations and field data that matched the model, they offer a strong recipe for engineers to build new tunnels without waking up the city above.
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