Gate protection for navigation locks

Abstract

The gates are the most vulnerable structures in the thrust front of navigation locks in internal waterways. Vulnerability of the gates is dictated, above all, by a high probability that ships will strike them on entering the lock when the motion of the regime is disturbed. Since it is rather difficult to create a safe motion regime in the chamber, impingement of a gate is a frequent phenomenon. Each strike results in damage to the gates, and occasionally to loss of stability of the fold of the gates due to its contact with support pads and hinging devices, as a result of which impact by a ship may lead not only to shutdown of the lock, but also to breaching of the thrust front of the hydraulic facility. Considering that it is virtually impossible to avoid a strike by ships in navigation locks, protective devices are established in advance of the gates of the lower head at all locks abroad. There are no such devices in the majority of locks on the waterways of Russia, although existing Russian standards (Construction Rule and Regulation II-56–79) call for their mandatory installation. Each protective device consists of two elements: — a barrier element that spans the navigation bay in advance of the gates of the lock; and, — shock absorbers, which are connected to the barrier element, and are intended to dissipate the energy of a strike. Beams (trusses) are used as barrier elements in locks where the navigation bay is narrow (up to 12 m), and chains and cables where the locks are wider. In selecting the barrier element, the method of its installation in advance of the ship’s entry to the lock and opening of the navigation bay prior to the ship departing the lock are major problems. The barrier element is raised above the superstructure of the ship, or lowered onto the bottom of the lock below the base of the ship. The design employed for installation of the barrier element by means of a maneuverable truss operating in accordance with a “toll-gate” scheme is also used (Fig. 1). Friction drums are used in the barrier installations to dissipate the impact energy of ships with a displacement of 2800 tons in the Welland Canal (Canada) where the locks are 24.4 m wide and the travel speed of the ships is 1.63 msec. Two drums mounted on the walls of the lock will bring the ship to a standstill in a total braking distance of 22 m; here, the maximum force of the impact amounts to 2870 kN, and the force in the arresting cable is 1740 kN. The friction system of shock absorbers will stop the ship only when the length of the braking path is sufficient; to return the barrier device to its initial position, moreover, the operation of additional mechanisms is required. Springs, counterweights, hydraulic cylinders where the fluid flows from the rod to piston cavity, etc. have also been tested as shock absorbers in the designs of protective de