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After almost 100 years of service the Noordersluis (North Lock) in IJmuiden, the Netherlands, needs to be replaced. The 545 m long, 70 m wide and almost 18 m deep new lock will become the biggest in the world

 
The new lock will provide access to the port of Amsterdam for larger sea-going vessels and will thereby stimulate[ds_preview] the economy in the region. Building of the lock will start in spring of 2016. It is expected that the new facility will receive the first vessels at the end of 2019.

Study objective and starting point

In 2014 and 2015 Deltares was commissioned by Rijkswaterstaat (part of the Dutch Ministry of Infrastructure and the Environment) to perform extensive hydraulic research for the reference design of the levelling system of the new lock of IJmuiden. The main objective of the study was to determine achievable levelling times, on the condition that the forces on the vessel remain within acceptable limits. The hydrodynamic forces on a ship are not allowed to become too large during the locking cycle. Otherwise mooring line forces may exceed operating limits. This may result in potentially dangerous situations leading to unwanted ship motions or even line breakage. The design vessel for the design of the levelling system is a bulk carrier with a length of 330m and a beam of 52m. The maximum draft of vessels passing the lock is set to 13.75m in salt water, due to restrictions upstream in the North Sea Canal.

One of the most important boundary conditions is the density difference of the water, since the lock is located between salt water on one side (North Sea) and fresh water on the other side (North Sea Canal). The maximum density difference over the lock is approximately 20 kg/m3.

Two types of levelling systems have been considered: openings in the lock gates and a system with short culverts in the lock heads. When the design of the levelling system for the North Lock was made, in the 1920s, levelling through gate openings was regarded as not feasible, mainly because of the impact on the steel construction of the gate, but also due to the expected flow forces on the moored vessel in the lock. Now, based on the current state of knowledge in gate construction and lock hydraulics, it has been concluded that gate openings are feasible, provided that levelling times may be longer to some degree.

Scale model

The hydraulic designs of the two levelling systems have been investigated in a scale model, on scale of 40 to 1. The complete levelling process is simulated in the scale model, including the lock exchange flow after opening of the gate. All the relevant physical flow phenomena are automatically included in the scale model.

In the model, the zigzag weirs at the beginning of the lock approaches are used to adjust the water levels in the lock approaches. The maximum water level that could be achieved in the model is NAP+4m and the minimum water level is NAP-1.75m. The maximum head over a gate that has been considered for levelling is 4.74m. To avoid reflections of the translatory waves a constant flow is maintained over the weirs by using a suitable pipe system. The approaches in the model have been made approximately 600m long, to avoid that the reflections of the internal density waves interfere with the measurements. To establish a density difference over the lock, the density of the water in the outer approach can be increased by mixing the fresh water with brine.

More than 200 parameters have been measured, including the most important ones, such as water levels, forces on the ship and the density distribution of the water. Levelling tests with a density difference showed that the forces due to these differences in density were significant and could exceed allowable force criteria. Besides providing valuable insights in the process of the complete locking cycle, the measurements were also used to validate various numerical models.

Many aspects of the locking process that are important for the safe operation of the lock have been considered in the study, such as the influence of the position of the vessel in the lock, different valve lifting programs, different density distributions, and the type of design vessel (container vessel or bulk carrier). On the basis of the results of the scale model study and the validated numerical simulations, the contractual requirements for the levelling times have been adjusted. These new requirements have been incorporated by Rijkswaterstaat in the tender for the realisation of the lock.

Other hydraulic aspects

After levelling, when the gate is opened, the lock exchange flow, given the high density difference, brings about very high forces on the vessel, directed towards the side with the higher density. Both longitudinal and transverse forces are higher than the criteria. These high forces are independent of the type of levelling system. In the coming period, measures will be studied, meant either to reduce the forces, e.g. installation of air bubble screens near the lock heads, or to raise the force criteria, e.g. by applying extra hawsers or tug assistance.

At times, in the outer harbour of IJmuiden »seiches« occur. These are standing oscillations in the closed harbour basin which are caused by atmospheric phenomena on the North Sea. Additional tests have been carried out in the scale model to assess the effect of seiches on the vessel moored in the lock. It showed that the forces on this vessel can rise above the criterion. In the event of seiches lock operations may be restricted.

DBFM-contract

The design of the new lock is part of a DBFM-contract, which means that the contractor will bear the responsibility for the design, building, financing and maintenance (26 years) of the lock. In summer 2015 the project has been awarded to the consortium of the building companies BAM and Volker Wessels, together with financiers PGGM and DIF. The price of the lock is 350mill €.

The lock chamber will be built with diaphragm walls, and the gate recesses will be built at ground level and pneumatically lowered to the level of the lock sill. One of the reasons why these types of constructions have been chosen is the low-vibration construction methods. Deformations of the neighbouring lock structures must at all times be prevented. On the basis of the reference designs and the results of the hydraulic studies the contractor has chosen to use openings in the rolling gates instead of short culverts in the lock heads for the levelling of it. The new lock will have two operational gates, one per lock head, and one reserve gate, which are all identical. The new gates are designed by IV-Infra who is one of the subcontractors.

 


Arne van der Hout, Wim Kortlever