Underground concrete balloons can keep leaning Amsterdam houses built on wooden piles upright, and do it cheaply, according to Almer van der Stoel.
The balloons will also be used during subway tunnel construction.
Many pre-war buildings in Amsterdam lean over quite severely. In fact, some are threatening to subside. The wooden piles forminmg their foundations sink down further on the street-side than on the garden side, because Amsterdam’s streets are often raised. This elevation means extra force is applied on the street side, causing the clay and peat layers below to settle more deeply. The ground pulls the piles downwards, via ‘negative skin fraction’ (see drawing on page 9).
If cracks appear in the houses, then a new foundation must be laid from within the building. But, if Almer van der Stoel has his say, there’s a cheaper (half the cost) and more convenient solution for keeping structures upright. And shops won’t need to close during renovations. ”In prime shopping areas, temporary closure means thousand of guilders are lost in daily turnover.”
Van der Stoel will keep the houses upright by injecting a mix of water, sand and cement, called grouting, underneath or beside the piles from street level. ”You can extract water from the sand layer below the pile’s toe and replace it with this sort of glue, the grout, thus consolidating the existing sand frame,” Van der Stoel says. ”By doing so you can support the pile’s toe, which must supply the most weight-bearing capacity.” There is, however, one small problem. ”My opponents will surely attack me during my dissertation defence on this point: it’s not always certain where the piles are underneath an old building. And that’s true.”
But grouting can be done in many ways. ”You can also inject the grout so that you seem to inflate a concrete balloon obliquely from below or underneath the pile. Then the ground surrounding the pile’s toe strengthens and stiffens, so the toe can move less.”
Controversial
To examine the grouting effects on Amsterdam’s wooden piles, Van der Stoel found a test location in north Amsterdam that had the same ground conditions as the inner city. Wooden and concrete piles equipped with many sensors were driven into the ground, and heavy constructions and sandbags were placed on top. Near the piles, a mobile grouting installation unit provided grout injections and various types of concrete balloons.
”My test location was in an out-of-the-way place.” An important fact, because the four million guilder experiment was paid for by the city of Amsterdam. For the construction of a, then controversial, subway track through the middle of Amsterdam, the ground had to be consolidated with grout. Before constructing this North-South subway line, the city wanted to know if grouting would have a negative effect on the wooden piles of old canal houses.
”Of course, I couldn’t perform my experiments on Amsterdam’s Damwith a big sign proclaiming ‘North-South track’, because at that time the politicians hadn’t yet decided if a subway track would be built.”
Van der Stoel devised all his experiments for Ingenieursbureau Amsterdam. ”The TU engaged me for two days a week and in this way was able to participate in this super expensive experiment for a song.”
Massive
After a few years of research, consultants for the North-South track recommended that a kind of rocky layer be built beneath Amsterdam’s wooden-piled houses to keep them upright during the tunnel drilling. But they did so without actually testing a rock layer. ”Such an experiment is terribly expensive, because it’s very expensive to excavate such a block, installed twenty meters deep, in order to examine it thoroughly.” Van der Stoel did dig up some of his concrete balloons, so called grout bodies, to investigate their composition.
After the city council finally decided to build the subway, engineers began working on a more viable solution. When the tunnel construction commences in six month’s time, tubes with holes will most likely be placed in the ground. Once installed, the holes will be opened from street level, allowing grout to be injected through them. This idea has already been tested in London. ”During the drilling, we’ll measure if the houses threaten to subside. Only when that happens will we inject grout at that place underneath the piles.” This new method, which is much cheaper than applying massive blocks, must still be tested in the coming months.
Underground concrete balloons can keep leaning Amsterdam houses built on wooden piles upright, and do it cheaply, according to Almer van der Stoel. The balloons will also be used during subway tunnel construction.
Many pre-war buildings in Amsterdam lean over quite severely. In fact, some are threatening to subside. The wooden piles forminmg their foundations sink down further on the street-side than on the garden side, because Amsterdam’s streets are often raised. This elevation means extra force is applied on the street side, causing the clay and peat layers below to settle more deeply. The ground pulls the piles downwards, via ‘negative skin fraction’ (see drawing on page 9).
If cracks appear in the houses, then a new foundation must be laid from within the building. But, if Almer van der Stoel has his say, there’s a cheaper (half the cost) and more convenient solution for keeping structures upright. And shops won’t need to close during renovations. ”In prime shopping areas, temporary closure means thousand of guilders are lost in daily turnover.”
Van der Stoel will keep the houses upright by injecting a mix of water, sand and cement, called grouting, underneath or beside the piles from street level. ”You can extract water from the sand layer below the pile’s toe and replace it with this sort of glue, the grout, thus consolidating the existing sand frame,” Van der Stoel says. ”By doing so you can support the pile’s toe, which must supply the most weight-bearing capacity.” There is, however, one small problem. ”My opponents will surely attack me during my dissertation defence on this point: it’s not always certain where the piles are underneath an old building. And that’s true.”
But grouting can be done in many ways. ”You can also inject the grout so that you seem to inflate a concrete balloon obliquely from below or underneath the pile. Then the ground surrounding the pile’s toe strengthens and stiffens, so the toe can move less.”
Controversial
To examine the grouting effects on Amsterdam’s wooden piles, Van der Stoel found a test location in north Amsterdam that had the same ground conditions as the inner city. Wooden and concrete piles equipped with many sensors were driven into the ground, and heavy constructions and sandbags were placed on top. Near the piles, a mobile grouting installation unit provided grout injections and various types of concrete balloons.
”My test location was in an out-of-the-way place.” An important fact, because the four million guilder experiment was paid for by the city of Amsterdam. For the construction of a, then controversial, subway track through the middle of Amsterdam, the ground had to be consolidated with grout. Before constructing this North-South subway line, the city wanted to know if grouting would have a negative effect on the wooden piles of old canal houses.
”Of course, I couldn’t perform my experiments on Amsterdam’s Damwith a big sign proclaiming ‘North-South track’, because at that time the politicians hadn’t yet decided if a subway track would be built.”
Van der Stoel devised all his experiments for Ingenieursbureau Amsterdam. ”The TU engaged me for two days a week and in this way was able to participate in this super expensive experiment for a song.”
Massive
After a few years of research, consultants for the North-South track recommended that a kind of rocky layer be built beneath Amsterdam’s wooden-piled houses to keep them upright during the tunnel drilling. But they did so without actually testing a rock layer. ”Such an experiment is terribly expensive, because it’s very expensive to excavate such a block, installed twenty meters deep, in order to examine it thoroughly.” Van der Stoel did dig up some of his concrete balloons, so called grout bodies, to investigate their composition.
After the city council finally decided to build the subway, engineers began working on a more viable solution. When the tunnel construction commences in six month’s time, tubes with holes will most likely be placed in the ground. Once installed, the holes will be opened from street level, allowing grout to be injected through them. This idea has already been tested in London. ”During the drilling, we’ll measure if the houses threaten to subside. Only when that happens will we inject grout at that place underneath the piles.” This new method, which is much cheaper than applying massive blocks, must still be tested in the coming months.
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