Research on the engineering practice and safety control of open-gate operation in locks

The open-gate operation (a mode in which the lock gate is opened to allow vessels to pass quickly and freely when the water level difference across the lock is minimal) can significantly enhance the navigation efficiency of locks. However, it also introduces notable navigation risks and safety challenges for lock structures and equipment. In response to the current lack of systematic and universally applicable safety control standards in the promotion and application of this mode, this study first conducted a comprehensive review of the engineering application status of open-gate operation in China. The analysis indicates that this mode is predominantly applied to two categories of locks in China: tidal estuary locks and inland canal locks with specific hydrological conditions that allow bidirectional head adaptation. While significantly boosting lock throughput—for instance, reducing passage time for a 1,000-ton vessel from 30–50 minutes to 3–5 minutes—the operation introduces two core safety risks: gate operation under dynamic flow conditions and vessel navigation within the highly confined lock chamber. To address these risks, this research established a theoretical framework based on the mechanics of gate operation under dynamic water conditions and the theory of vessel navigation in restricted channels. For gate safety, the analysis simplified the force equilibrium during miter gate operation, identifying the water level difference across the lock head as the dominant factor influencing the operating force, which is critical for preventing overload of hoisting machinery. For navigation safety, by considering the lock chamber as an extremely restricted channel with a typical cross-sectional coefficient (n) between 1.5 and 3.0, the vessel’s navigation state was theorized to be a function of chamber flow velocity, vessel speed, and inter-vessel spacing. Consequently, a safety control framework was constructed with four parameters—lock head water level difference (Δh), lock chamber flow velocity (v_w), vessel speed (v_s), and inter-vessel spacing (ΔL)—as the core indicators, covering the entire “opening–navigation–closing” cycle of open-gate operation. Building upon theoretical analysis and synthesizing practical engineering experience from multiple locks, this study proposes graded safety control standards. The recommended limits are categorized based on key influencing factors: (1) The water level differential limit (Δh_lim) is primarily related to lock chamber width (b), with suggested values of 0.30 m for b=23 m, 0.25 m for b=16 m, and 0.20 m for b=12 m, derived from both empirical practice and theoretical safety margins, despite higher values observed in some dynamic tests. (2) The chamber flow velocity limit (v_wlim) is graded according to lock class, proposed as 1.6 m/s for Class III and IV locks, and 1.4 m/s for Class V locks, representing a 70%-80% reduction from typical approach channel standards in view of the restricted chamber geometry. (3) The vessel speed limit (v_slim) is also class-dependent, suggested as 1.6 m/s, 1.5 m/s, and 1.4 m/s for Class III, IV, and V locks respectively, with a minimum speed of 1.0 m/s required to maintain steerage. (4) The vessel spacing limit (ΔL_lim) is based on vessel type and load condition, recommending a minimum of one times the vessel length for convoys and loaded vessels, and two times the length for empty or lightly loaded vessels. Based on this indicator system and the hierarchical standards, a comprehensive and operational method for establishing open-gate operational criteria was developed. This method outlines specific logic for gate opening (requiring Δh ≤ Δh_lim and v_w < v_wlim), vessel navigation (requiring v_s ≤ v_slim and ΔL ≥ ΔL_lim), and gate closing (triggered when v_w ≥ v_wlim, while still ensuring Δh ≤ Δh_lim). The proposed methodology was subsequently applied and validated using the Baishan Lock, a key node in the Yangtze-to-Huaihe Water Diversion Project, as a case study. For this Class III lock with a chamber width of 23 m, the specific operational criteria were set, demonstrating the method's practicality. The results confirm that the established indicator system and hierarchical standards can effectively quantify the safety boundaries for open-gate operation. This research provides a systematic theoretical basis and technical support for the scientific decision-making, standardized management, and safe implementation of open-gate operations, facilitating its broader and safer application. Future work should focus on validating these standards for larger locks and vessels and optimizing dynamic thresholds through real-world monitoring.