**Abstract:** The multi-section floating box gate is an innovative inspection gate designed without any permanent opening and closing equipment, combining the advantages of traditional gates and floating gates while addressing the specific requirements of the project. It ensures a stable position of the orifice and maintains stagnant water flow, making it cost-effective, easy to operate, reliable, and simple to maintain. This gate form is particularly suitable for scenarios with static water flow and steady conditions at the orifice. Key words: Multi-section design, floating gate, maintenance gate, energy dissipation, structural optimization. **1. Introduction to the Multi-Section Floating Box Gate** The multi-section floating box gate integrates the benefits of conventional stacked beam gates and floating gates, tailored to meet the practical needs of the Xiaolangdi Project. Installed at the discharge spout end of the 1# orifice, this gate system is designed to avoid the need for permanent mechanical structures. The project features three orifice flood spillways, each with two entrances, including a maintenance gate and an accident gate. After passing through the central chamber, the flow splits into two sections before merging again. Due to high flow velocity and potential damage from erosion, frequent inspections are necessary. The 1# orifice’s energy dissipation nose ridge is located at 129m elevation, with the lowest tailwater level at 134m, requiring the maintenance gate to be placed in a submerged section after more than 700 meters. To facilitate maintenance, an inspection gate must be installed at the tunnel exit, separating the power pond from the hole during operation. **2. Door Type Selection and Design Considerations** During the preliminary design phase, the layout of the maintenance door slot on the side wall was considered. However, due to the high-velocity flow, the slot area was prone to cavitation damage, posing challenges for future gate installation. Thus, the focus shifted to comparing conventional flat doors with floating doors. The environment at the tunnel exit is unsuitable for permanent gate systems due to heavy rain, mud, and limited space for equipment storage. Conventional flat doors require complex mechanical systems, increasing costs and maintenance difficulty. In contrast, floating doors use buoyancy, reducing the need for lifting equipment and simplifying operations. Given the terrain constraints, transporting and maintaining conventional gates is challenging. Therefore, the multi-section floating box-type gate was selected for its ease of transport via the lower dike and efficient operation. **3. Structural Design of the Multi-Section Floating Box Gate** The multi-section floating box gate consists of multiple sealed compartments, each designed to float independently. The structure includes upper and lower cabins connected to form a single sealed unit, allowing the entire gate to float and be transported in water. Each section has air and drainage valves, along with quick connectors for inflation and deflation. The gate is supported by sliding blocks and positioning pads, ensuring smooth movement within the slot. Sealing is achieved using P-shaped rubber seals that adapt to slight misalignments and provide a continuous watertight barrier. The embedded design includes a 1m-wide platform protruding from the outlet wall, ensuring proper alignment and stability. **4. Main Equipment and Operation Process** Key equipment includes a car crane, traction ropes, manual hoists, air compressors, and hoses. During operation, the gate is suspended into the water, floated, and pulled into the slot using manpower. Two manual hoists are mounted on the piers to adjust the gate’s position. Air compressors inflate the gate to submerge it, while drainage allows for retrieval. After maintenance, the gate is inflated and lifted back to the surface for storage. The entire process is efficient, requiring minimal personnel and time, and ensures safe and reliable operation. **5. Advantages and Operational Benefits** Compared to traditional inspection gates, the multi-section floating box gate offers several advantages: it operates entirely above water, reducing risks; all equipment can be removed for protection; no divers are needed; no underwater hooks are required; lifting capacity is reduced; and the box structure provides greater rigidity for large openings. These features make it highly economical and ideal for long-term use. **6. Conclusion** The Xiaolangdi multi-section floating box gate successfully completed its first maintenance task in 2001, demonstrating the effectiveness of the design. The installation process was smooth, and the gate performed exceptionally well in sealing water under various conditions. The design proved to be both practical and cost-effective, offering a new solution for similar projects, especially in high-speed flow environments where traditional gates are not feasible. This innovation saves significant investment and reduces long-term maintenance challenges, making it an ideal and promising gate type for future applications.

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