Until then, the landfill crew literally climbed down into the steel structure to install the wooden planks from the inside in order to control the outflow of water into the landfill and the settling time of the dredged material.
YES scan
A long calculation and design process followed at Boskalis’ head office in Papendrecht, the Netherlands. It involved not only the Central Fleet Support department but also staff from the Research & Development department and dredging projects. “During the history of Boskalis, we have always used the water boxes as we have known them: by installing the planks from the inside. But as projects have got bigger and bigger, and after a number of incidents (and near-misses), we knew we had to change the design to make things safer for our colleagues,” says Van de Zande, operations director for the cutter suction dredgers at Boskalis. “Go figure: with what we know now, working in the water box could never pass the YES scan in our own NINA (No Injuries, No Accidents) safety programme. YES stands for Yourself, Equipment and Surroundings; these three areas must be safe and checked before you can start work. With the old approach, two out of three failed to comply with the standards and values we set out in our own NINA programme.”In a nutshell, the design modification meant that, instead of going down to the water level in the landfill from the inside, personnel on the landfill can now use a safe stairway to access a manually operated platform that allows them to move up and down the outside of the water box. The planks are then put into position from that platform, which resembles those used by window cleaners on high buildings. Van de Zande: “It’s actually a very simple solution that immediately makes things lots safer for our colleagues. Every dredging company in the world deserves a water box like this: it makes a direct contribution to safety on a project.”
Design
However, large and impressive the water box may be from up close, the updated design is modular and so it can be used on any type of project. The water box consists of three “containers” with different colours: a blue lower box connected to the pipeline through which the water exits from the landfill, a yellow “middle box” that can be used to raise the structure and the top box in a red warning colour that is connected to the platform. “Each water box consists of at least one blue, one yellow and one red container with a maximum height of 10 metres,” explains Van der Hulst. Boskalis now has 19 of the new water boxes. 15 of them are being deployed on the largest dredging project in the history of Boskalis: the Manila International Airport project in the Philippines.Preventing implosion
The new water box was designed and produced to eliminate the risk of implosion due to soil pressure when the pressure of the soil in the landfill becomes too large for the structure. So the new design is a lot stronger. “You can base your calculations on three types of soil pressure: active, neutral and passive. The load differs by a factor of three for each approach. Neutral soil pressure is three times as high as the passive soil pressure and the active soil pressure is three times as strong as the neutral soil pressure,” says Van der Hulst. “So we decided to design the new water box to withstand active soil pressure. From practical experience, we know that the pressure on a landfill never reaches the active pressure we have now used as the theoretical basis for our calculations. So we are confident that this box is the safest there is.”Obviously, during the design process, Van der Hulst and his colleagues used the prevailing Quality Assurance and Quality Control (QA QC) requirements, which state that the quality of the structure has to be easy to measure in the long term and that the production process must be optimised. “The design meets the highest standard in terms of strength and resilience to soil pressure and, when it comes to quality, we measure the steel thickness of the water box after every operation and conduct visual inspections. This allows us to see how much wear there has been during the project and whether repairs need to be made efore the box is used again,” says Van der Hulst. “Working with the water box in this way allows us to eliminate risks during operations.”
Practical test
Of course, a water box is not the only way our dredging colleagues can control water levels and settlement time in the landfill. Another widely used method is placing a pipeline in the dike around the landfill at a certain height so that all the water above that level is discharged through the pipeline. Another alternative is covering the dike with a tarp so that all the excess water flows over the dike naturally. Van de Zande: “These are also excellent approaches and they are also typical of the enterprising approach in the sector to manage situations in inventive ways. But our aim with the new, safer water box is that, when a project manager decides to use this method, it will be the safest option.”Support from project managers is certainly crucial for the success of the new water box, explains Van der Hulst. “I’m an engineer, a numbers man. So you need colleagues with hands-on experience to check whether an idea is the best possible option. We sometimes come up with fantastic solutions but they are useless if they don’t pass muster with our colleagues on the projects. For example? We thought about whether it would be possible not to have people going down alongside the water box and to position or remove the planks automatically. That turned out to be impractical: the colleagues on the platform also have to remove the non-sandy material that always ends up in a landfill so that the water can continue to flow out. Another example is the type of material used for the planks. There were drawbacks to every alternative we proposed. But wood, which has been used for decades – or perhaps even centuries – proved to be the most effective material by far.”
Many of these aspects were tested at a Boskalis yard in the Netherlands, where a special test array was set up. Project managers, landfill masters and colleagues from Research & Development, Central Fleet Support and numerous other departments met there to come up with the ultimate design. Van de Zande: “So you can honestly say that this water box was a team effort from Boskalis as a whole: a perfect example of our internal motto ‘Making the difference together’. And all that after that clear moment and the comment from the landfill master in Australia.”
