Risk of draining the canal
Given the historic nature of the existing lock complex, a choice was made to equip the second lock chamber with water-control structures that are not visible above ground level (no lift-gate towers like the ones for the first lock chamber). The top end of the lock will be fitted with a Tainter gate and the bottom end will get a set of mitre gates. The water level in the Twente Canal will be controlled artificially using pumping stations. The difference between the canal’s water level and that of the River IJssel can, depending on the level of the River IJssel, be as much as 8 metres. A problem with the lock gates could create an open connection between the canal and the River IJssel, which could lead to the canal draining into the hinterland. This has been designated as the main risk of this lock.
Use of a Tainter gate
The tender design proposed to use a Tainter gate at the top end of the lock chamber. This type of water-control structure is normally used for emergency water defences, primarily because this kind of gate can be operated with relatively little force, even under great strain. When a storm or strong current leads to the water putting a great strain on the gate, the rounded shape of a Tainter gate diverts these forces to the gate’s hinge, so that the gate basically ‘balances’ on its hinges. As a result, it takes relatively little lateral force to close the gate. In the event of a contingency with an open lock chamber situation, it is highly important to have certainty that the gate can be closed.
Robust and reliable system
The water level in a lock is normally raised or lowered by opening or closing orifices in the water-control structures. Given that a Tainter gate is extremely easy to operate in a controlled manner, all it takes to raise the water level in the lock chamber is to just open the Tainter gate slightly. The Tainter gate comes with a kind of notch in the radial wall through which water can flow into the chamber in a highly controlled manner. This method makes the system simpler and also more robust and reliable.
Stilling basin to absorb water level differences
Given the great difference between the water level at either end of the Eefde lock, a stilling basin has been built underneath the gate, just like on the canal side of the original lock. When the Tainter door is opened, the water first flows into the stilling basin. Inside the stilling basin, there are pillars on the canal bed that break the water’s fall. Next, the water flows from the stilling basin into the lock chamber through a so-called resistance grid that reduces the water’s flow rate and distributes the water evenly. This makes sure that ships will remain stable in the chamber as water flows into it.
A first in the Netherlands
It is the first time this kind of Tainter gate is used in a lock in the Netherlands. It is far more common to see Tainter gates used as an emergency closing structure. An emergency closing structure, however, is used only sporadically, while a lock gate is opened and closed dozens of times every day. This means that the design had to meet more specific requirements.
The Tainter gate moves and closes off the chamber along precast steel grooves. The gate has a plastic seal on the rounded side, which is an active seal that does not come into contact, or only slightly, with the steel profiles during movement, so as to prevent wear. The water pressure pushes the seal against the gate. A plastic seal has also been fitted to the bottom side, which pushes against a sill profile. The seals have a service life of at least 10 years.
Umbrella position for maintenance
If the seal were to need replacing early, such as when it has been damaged due to an impact, or for maintenance, the gate can easily be turned around to the so-called ‘umbrella position.’ The Tainter gate is operated on one side by an electro-hydraulic system. The cylinder is connected to the gate through a mechanism of rods. By changing the mechanism, the cylinder stroke can now be used twice, meaning that the Tainter gate can be turned 180° instead of the normal 90°. The result is that the whole gate can be lifted out of the water and any maintenance on it can be done much quicker.
The use of a Tainter gate at the top end of the lock chamber is one of the risk control measures in the design. At the bottom end, mitre gates are used, which is a regular type of lock gate, albeit that they are unusually high in Eefde, on account of the great water level difference between the Twente Canal and the River IJssel. To protect these gates against collisions, a barrier with a steel cable across the lock chamber will be installed, which will slow down ships when the skipper is too late in hitting the brakes. If a ship were to still collide with the gates, the gates’ operating mechanism would also sustain an unwanted impact. To prevent damage to the operating mechanism in the event of such a collision as much as possible and to limit the time needed for repairs, Hollandia Infra has opted to use hydraulic cylinders. The cylinders offer greater impact resistance.
New hybrid operating technology
Hollandia Infra asked Bosch Rexroth to install new hybrid operating technology that combines the benefits of an electromechanical linear actuator with those of a traditional hydraulic drive system. This project is the first in the whole world to use this combination in the civil engineering domain.
The new electro-hydraulic drive system is used for the cylinders that are used to operate the lock gates. It is a completely closed system with specially designed cylinders, where the hydraulic oil moves only between the chambers of each separate cylinder. This reduces the amount of oil the systems need by a factor of twenty, which means that a large hydraulic reservoir is not needed. The cylinder rod is moved by a compact plug-and-play power box with servomotor and hydraulic pump. Thanks to this space-saving concept, the lock does not need a separate space for a generator. On top of that, the new technology is 25 percent more efficient compared to traditional systems, meaning that the drive system helps improve the lock’s energy efficiency.
• The vertical lift gates of the historic lock are approx. 13.3 metres wide and differ in height. The gate on the IJssel side is approx. 10.65 metres tall, while the Twente Canal-side gate is approx. 5 metres tall. The vertical lift gates of the historic lock were replaced in 2003 and 2004.
• Each mitre gate in the second lock chamber is a steel composite structure of approx. 13.4 x 7.7 x 0.68 metres, weighing approx. 50,000kg.
• The Tainter gate is approx. 15.1 x 4.6 x 5.6 metres and weighs approx. 51,000kg.