Abstract:Research purposes: Aiming at the road traffic problems confronted by the open-cut method of subway station construction in the water-rich sandy pebble layer, this paper relies on the successful project of Chengdu subway station construction in water-rich sandy pebble layer for the first time using the concealed excavation method to carry out a study on the key technology of concealed excavation method, indicating the key technology of the concealed excavation guide hole setting and its excavation sequence, the way of over-advanced pre-strengthening of the strata, the type of initial support, the steel pipe columns with permanent-temporary combination, and the arched cover buckling arch and so on, and clarifying the feasibility of the shallow buried large span metro station with water-rich sandy pebble layer for the first time. The feasibility of using the concealed excavation method for the first time in the construction of the shallow buried large-span subway station in water-rich sand and pebble layer was clarified. Research conclusions: (1) Based on the concept of modular tunneling approach, with the pre-support of tube curtain with large rigidity, the basic principle of the pilot tunnel is clarified, and then multiple pilot tunnels are adopted in the construction of steel pile pillars, tunnel roofs. The underground excavation of metro stations with large spans and shallow buried depth can be realized. (2) The precise control of construction accuracy and stratum disturbance of tube curtains with large rigidity plays a key role in the control of stratum settlement. The corresponding basic construction principle is accurate positioning, timely correction, not enough slagging, strict control of over-digging, low-speed drilling at the beginning, and then even speed drilling. (3) Based on the passive bearing properties of initial support, grid steel has a relatively better economic effect and construction convenience, the overall flexural stiffness after shotcrete increases to nearly 8 times. The corresponding stiffness of grid steel is larger than H plate steel after shotcrete. So, grid steel should be adopted as far as possible. (4) In the center pilot tunnel, the snakelike middle column embedded with inverted L-shaped steel plate at the top can realize the effective connection of the lining structure on both sides and the effective horizontal force transmission. The hydraulic reverse circulation drilling machine can meet the need for high-precision permanent steel pipe pillar construction within a small headroom. (5) This paper can provide a reference for the similar project in the sand and gravel stratum in the future.
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