Delft council is still trying to find extra money for the desperately needed new rail tunnel. It can stop looking, because, according to a retired engineer, it can all be done much more cheaply.
At the TU, people are listening intently.
Once built to break down a barrier, Delft%s rail tunnel has become a barrier itself. From early in the morning until late at night, trains roar over the viaduct, violating the legal requirements for noise nuisance. Besides disturbing the neighbours, the trains are also inconvenienced by the viaduct. The connection between The Hague and Rotterdam consists of four tracks nearly everywhere, except in Delft, where the resulting bottleneck is responsible for many delays. A four track underground railway would solve all the problems.
But tunnels are expensive, particularly when houses have to demolished to make way for it. The construction process is also very inconvenient. Enough reasons, then, to design a tunnel that follows the existing route as closely as possible, and to build it according to a method that causes as little nuisance as possible. Difficulties hereby are that the train traffic must continue and that the existing railway viaduct is rather in the way of future tunnel. For example near student society De Bolk, where the trains narrowly ride past the houses.
Thus, the new tunnel must be located next to the viaduct, the council determinded seven years ago, and consequently a new route, passing below the current station square, was planned. To the south of the Irene tunnel the railway emerges above ground again and from there continues on the existing route. To build this tunnel, all houses bordering the Houttuinen and the Van Leeuwenhoeksingel must be demolished. New houses and offices will then be built on this empty space, once the tunnel is complete, according to a plan of Spanish urban development professor, Joan Busquets.
Worries
However, while trains continued roaring and delays kept on occurring, technology also progressed. “At the time, the council didn’t consider that one can also work underneath an operating rail track,” says Leo van Tol, a retired engineer from Breda who developed a technique for this. Van Tol suggests bringing rail traffic to a halt for a weekend, in order to lift the tracks onto a temporary viaduct, thus creating enough space below to work on the new tunnel, while trains resume travelling on the temporary viaduct.
Applying this technique means the wholesale demolition of existing properties is no longer necessary. Van Tol claims that his plan will save 180 million euro.
Van Tol’s plan, however, was not prompted by money concerns, but by worries about losing cultural-historical landmarks. “Our past would disappear. Isn’t that a terrible waste?” Moreover, he has misgivings about the return on the planned real estate developments. ”The office market is diminishing. Delft could be left with an empty part of town. Furthermore, public funds are concerned, so they must be handled carefully.” Now that Delft council is also threatened with missing out on a 68 million euro contribution from the Dutch Ministry of Transporataion (VROM), a cheaper tunnel variant is all the more attractive. Although the council doubts the feasibility of Van Tol’s proposal, it’s nevertheless preparing to sit down and discuss the planwith him.
Van Tol also proposes another construction method than the one incorporated in the council’s current plans. He opts for a sink tunnel, whereby tunnel elements of a hundred metres are manufactured in a construction dock. By closing the ends and flooding the construction dock, the elements float up. A push barge takes them to their final location, adjacent to their predecessor. By filling the element with ballast it sinks.
Many traffic tunnels underneath waterways have been constructed according to this method. In those cases, the water was already present; but it is equally effective in a canal that was dug especially for that purpose. ”Water is water,” says Dr. Han Vrijling, TU professor of hydraulic constructions. The metro in Rotterdam was also constructed this way. “The entire Coolsingel was like a canal for a while.” Either way, digging will also have to figure in the council’s plan.
Doubtful
Van Tol suggests fabricating the tunnel elements in a construction pit near the current station, constructing one element at a time. As soon as it is finished, it will be parked temporarily in the construction trench, after which the construction of the next element commences. A soon as four are ready, they are taken, by boat, to the northern end of the route. There they are assembled to form the first four hundred meters of the tunnel. ”That way, the construction of the elements is continuous and the construction time on the Phoenixstraat is as short as possible,” Van Tol contends.
Dr. Cor van der Veen, senior university lecturer in concrete constructions, sees limiting the noise and disturbance as the most important advantage of this technique. ”Construction always produces noise: think about trucks and concrete mills. By constructing the elements in one location, the nuisance is concentrated in one place and is therefore less of an inconvenience.” However, hydraulic engineer Vrijling is doubtful of the construction rate. ”It is only useful if a pile of elements can be made simultaneously, not one by one, as is the case here.”
On-site construction or submergence, that is the main question when the council’s plans are compared with Van Tol’s. ”The obstruction is equal in both cases, but for submergence it is shorter”, Vrijling says. Furthermore, construction on-site, as is required for the council’s plans, requires the driving of more piles into the ground. That is because groundwater exerts pressure from below against the construction pit, once it has been pumped dry. This can cause the construction pit to burst open, Vrijling explains. To prevent this from happening, a thick concrete floor is needed, with driven piles underneath to pull the floor down. Besides being more expensive, the driving of piles also makes a lot of noise.
Calculating
Because the trench into which the tunnel elements are sunk doesn%t have to be dry, Van Tol’s plan doesn’t require a concrete floor. Besides the nuisance, the less of a risk of sinking houses adjacent to the tunnel than in the open construction pit method. ”Particularly with the presence of historical buildings, such as in Delft, that could be decisive,” Van der Veen estimates. Because the contractor is responsible for any damages, he will calculate the risk in his tender.
To reduce construction time, manufacturing the four track tunnel elements would be ideal according to Vrijling. Van Tol maintains that there is too little space for that, however. ”You should temporarily support the rail viaduct along the entire route with an auxiliary construction. That is very costly. Now I only do it where absolutely necessary.” That’s why, just like in the council’s plan, Van Tol first creates a two track tunnel. When that’s finished, the trains startusing it and the viaduct becomes redundant. After demolition of the viaduct, construction of a second two track tunnel can commence on that spot.
Delft council is still trying to find extra money for the desperately needed new rail tunnel. It can stop looking, because, according to a retired engineer, it can all be done much more cheaply. At the TU, people are listening intently.
Once built to break down a barrier, Delft%s rail tunnel has become a barrier itself. From early in the morning until late at night, trains roar over the viaduct, violating the legal requirements for noise nuisance. Besides disturbing the neighbours, the trains are also inconvenienced by the viaduct. The connection between The Hague and Rotterdam consists of four tracks nearly everywhere, except in Delft, where the resulting bottleneck is responsible for many delays. A four track underground railway would solve all the problems.
But tunnels are expensive, particularly when houses have to demolished to make way for it. The construction process is also very inconvenient. Enough reasons, then, to design a tunnel that follows the existing route as closely as possible, and to build it according to a method that causes as little nuisance as possible. Difficulties hereby are that the train traffic must continue and that the existing railway viaduct is rather in the way of future tunnel. For example near student society De Bolk, where the trains narrowly ride past the houses.
Thus, the new tunnel must be located next to the viaduct, the council determinded seven years ago, and consequently a new route, passing below the current station square, was planned. To the south of the Irene tunnel the railway emerges above ground again and from there continues on the existing route. To build this tunnel, all houses bordering the Houttuinen and the Van Leeuwenhoeksingel must be demolished. New houses and offices will then be built on this empty space, once the tunnel is complete, according to a plan of Spanish urban development professor, Joan Busquets.
Worries
However, while trains continued roaring and delays kept on occurring, technology also progressed. “At the time, the council didn’t consider that one can also work underneath an operating rail track,” says Leo van Tol, a retired engineer from Breda who developed a technique for this. Van Tol suggests bringing rail traffic to a halt for a weekend, in order to lift the tracks onto a temporary viaduct, thus creating enough space below to work on the new tunnel, while trains resume travelling on the temporary viaduct.
Applying this technique means the wholesale demolition of existing properties is no longer necessary. Van Tol claims that his plan will save 180 million euro.
Van Tol’s plan, however, was not prompted by money concerns, but by worries about losing cultural-historical landmarks. “Our past would disappear. Isn’t that a terrible waste?” Moreover, he has misgivings about the return on the planned real estate developments. ”The office market is diminishing. Delft could be left with an empty part of town. Furthermore, public funds are concerned, so they must be handled carefully.” Now that Delft council is also threatened with missing out on a 68 million euro contribution from the Dutch Ministry of Transporataion (VROM), a cheaper tunnel variant is all the more attractive. Although the council doubts the feasibility of Van Tol’s proposal, it’s nevertheless preparing to sit down and discuss the planwith him.
Van Tol also proposes another construction method than the one incorporated in the council’s current plans. He opts for a sink tunnel, whereby tunnel elements of a hundred metres are manufactured in a construction dock. By closing the ends and flooding the construction dock, the elements float up. A push barge takes them to their final location, adjacent to their predecessor. By filling the element with ballast it sinks.
Many traffic tunnels underneath waterways have been constructed according to this method. In those cases, the water was already present; but it is equally effective in a canal that was dug especially for that purpose. ”Water is water,” says Dr. Han Vrijling, TU professor of hydraulic constructions. The metro in Rotterdam was also constructed this way. “The entire Coolsingel was like a canal for a while.” Either way, digging will also have to figure in the council’s plan.
Doubtful
Van Tol suggests fabricating the tunnel elements in a construction pit near the current station, constructing one element at a time. As soon as it is finished, it will be parked temporarily in the construction trench, after which the construction of the next element commences. A soon as four are ready, they are taken, by boat, to the northern end of the route. There they are assembled to form the first four hundred meters of the tunnel. ”That way, the construction of the elements is continuous and the construction time on the Phoenixstraat is as short as possible,” Van Tol contends.
Dr. Cor van der Veen, senior university lecturer in concrete constructions, sees limiting the noise and disturbance as the most important advantage of this technique. ”Construction always produces noise: think about trucks and concrete mills. By constructing the elements in one location, the nuisance is concentrated in one place and is therefore less of an inconvenience.” However, hydraulic engineer Vrijling is doubtful of the construction rate. ”It is only useful if a pile of elements can be made simultaneously, not one by one, as is the case here.”
On-site construction or submergence, that is the main question when the council’s plans are compared with Van Tol’s. ”The obstruction is equal in both cases, but for submergence it is shorter”, Vrijling says. Furthermore, construction on-site, as is required for the council’s plans, requires the driving of more piles into the ground. That is because groundwater exerts pressure from below against the construction pit, once it has been pumped dry. This can cause the construction pit to burst open, Vrijling explains. To prevent this from happening, a thick concrete floor is needed, with driven piles underneath to pull the floor down. Besides being more expensive, the driving of piles also makes a lot of noise.
Calculating
Because the trench into which the tunnel elements are sunk doesn%t have to be dry, Van Tol’s plan doesn’t require a concrete floor. Besides the nuisance, the less of a risk of sinking houses adjacent to the tunnel than in the open construction pit method. ”Particularly with the presence of historical buildings, such as in Delft, that could be decisive,” Van der Veen estimates. Because the contractor is responsible for any damages, he will calculate the risk in his tender.
To reduce construction time, manufacturing the four track tunnel elements would be ideal according to Vrijling. Van Tol maintains that there is too little space for that, however. ”You should temporarily support the rail viaduct along the entire route with an auxiliary construction. That is very costly. Now I only do it where absolutely necessary.” That’s why, just like in the council’s plan, Van Tol first creates a two track tunnel. When that’s finished, the trains startusing it and the viaduct becomes redundant. After demolition of the viaduct, construction of a second two track tunnel can commence on that spot.
Comments are closed.