Xijin hydro-junction is a key project of the Xijiang Golden Waterway, a two-step single lane lock has already been constructed. The proposed 2nd lane lock is designed for the maximum passing vessel with the tonnage of 3000t. The new lock is located at the right bank of the river and also the 1st lane lock, and it is a single step lock. The effective dimensions of the lock chamber are 280.0m×34.0m×5.6m (length × width × water depth over the sill), and its maximum water head is 20.3m, the designed transit time is 10～12min. Due to its large dimension and high waterhead, the comprehensive hydraulic characteristics of the new lock is close to the Three Gorges Locks and the Gezhouba Locks, so it is quite necessary to determine and improve the layout of the filling and emptying system both by hydraulic analysis and model test study.
The chamber is quite wide, so the transverse flow distribution in the chamber during the filling phase is the main influencing factor of the ship berthing safety due to the previous experiences. At the beginning, the In-chamber longitudinal culvert system（ILCS） invented by the U.S. Army Corps of Engineers is been adopted for the new lock. A physical model with the scale 1:30 is been established for the hydraulic study, and the test results of the initial layout indicate that: under the ILCS layout, the transverse flow distribution in the chamber during the filling phase especially with single valve opened is quite uneven, the flow in the center of the chamber is more concentrated than other areas, there has obvious water surface slope and the transverse hawser force of the ship far exceeds the standard valve.
Based on the test results, we change the energy dissipating type from flow jet collision to open ditch, which means we set a “T” type baffle between the two bottom culverts, and adjust the height of the ports on the “T” type baffle to improve the transverse flow distribution. At the same time, considering the uneven flow distribution problem under single valve opened or asynchronous double valves opening, we adjust the layout of the two separate culverts in the ILCS that we set two converge sections for the two culverts near the lock heads. The test results under the new layout indicate that the optimizations have achieved the anticipated goals, the transverse hawser force of the designed ship reduces by 50%, and the hydraulic characteristics under different conditions all satisfy the requirement of design and standards.
The new in-chamber double longitudinal culverts filling and emptying system has many advantages, such as obvious energy dissipating effect, high hydraulic efficiency, simple structure, economic construction and maintenance, and it is an safe and efficient filling and emptying system for high head large navigation lock. Compared to the ILCS, the new system adapts to more water head, which is recommended under 12m by the U.S. Army Corps of Engineers, and also has more efficiency and safety.