A City on Stilts

“GRANDPA! The ground is shaking! Is it an earthquake?” Grandfather smiles and tells his teen-age grandson who is vacationing in Amsterdam: “No, Frank, this is not an earthquake. The truck that just rumbled by caused the ground to shake. The soil in this city is so unstable that sudden pressure of weight causes surroundings to […]



“GRANDPA! The ground is shaking! Is it an earthquake?” Grandfather smiles and tells his teen-age grandson who is vacationing in Amsterdam: “No, Frank, this is not an earthquake. The truck that just rumbled by caused the ground to shake. The soil in this city is so unstable that sudden pressure of weight causes surroundings to tremble.” Frank breathes a sigh of relief: “I never experienced anything like this before. I was really scared.” “The city officials, too, have reason for concern, Frank. The heavy traffic that winds its way through the old city causes tremors. This does much damage to centuries-old structures that just weren’t built for this kind of thing.”

“The city officials, too, have reason for concern, Frank. The heavy traffic that winds its way through the old city causes tremors. This does much damage to centuries-old structures that just weren’t built for this kind of thing.”

After the two walk on for a while, Frank asks: “What I can’t understand is, How do the old houses manage to stand right side up when the soil is so miry and soft?” “Stilts, Frank.” “Stilts?” “Well, I admit, a building expert would not use that word. Would you like to know something about this method of building?”

“Of course, Grandpa.” “Let’s sit down on this bench. Now, try to eliminate all the houses, apartment buildings, towers, roads, bridges-everything. What do you see?”Frank shuts his eyes and tries to imagine that nothing is there. “I, well, I see nothing.” “Right! That’s the way it all started-a boggy area at the mouth of a river. In time a small group of persons settled there, some farmers and a merchant or two. For protection against rising tides, a dam was built across the mouth of the river Amestelle.

The houses that were constructed in the area, Frank, were nothing like those of today. People were satisfied with very little. The wooden walls were set up on a simple foundation of reeds and small branches. On top of these a roof of reeds was fashioned and made fireproof by a layer of clay mud. These early houses weighed very little. When a house caught on fire, the people living next door quickly dismantled their home and moved it to a safer spot.

“The ever-present danger of fire in time required building more substantial structures. In the fifteenth century, two major fires ravaged old ‘Amestelledamme.’ The one in 1452 destroyed more than half of the then-existing hundreds of houses. Thereafter the officials ruled out wooden walls and required that brick structures be erected.

This created a new problem for the citizens. Frank, I presume that you readily see the problem this brought.””I suppose the old foundations of reeds and branches could not support brick walls.” “Right! Better foundations were needed. The first step was to drive wooden poles, or piles, into the wet ground. At first these were just short piles, only about four or five feet [1.2 or 1.5 meters] long.

When larger houses began to be built, piles up to twenty-five feet [7.6 meters] long were used. “Still, old Amsterdam’s houses were quite primitive. Several houses used just one toilet. Sales contracts contained clauses stipulating who was responsible for emptying the toilet containers and through whose house the waste was to be transported. Not until 1528 did the city’s administrators decree that no house could be built without its own toilet facilities.

Eventually the city grew to be a busy merchant port, and the demand for more stable buildings increased. At the beginning of the seventeenth century, a thick layer of hard-packed sand was found about thirty-six feet [11 meters] beneath the mire of the city. From then on the city officials required that piles be driven down all the way to the hardpan.”

“That’s very interesting, Grandpa,” Frank remarks, “but how did they get those long piles into the ground?” “For a long time the piles were driven in by hand. First, just a simple maul was used. Later, the pile driving was accomplished with a heavier hammer block that was equipped with handles on each side and was heaved up and down by two men.

Still later, the hammer blocks were made to move up and down between two upright guide poles.This hammer would be drawn up high by means of a rope running over a wheel. Many strong men were needed to pull the hammer up and down.”

“How could so many men tug at the rope without falling over one another?”

“That’s a good question! Those early Amsterdammers had a solution. They tied many thinner ropes to the main line so that each man could pull his own rope.

Of course, it was monotonous work. To break the monotony, special pile-driving songs were sung to the rhythm of the hammer. The foreman would sing the songs, and the workers would supply the rhythm. In an effort to speed up the rhythm and the singing, strong drink would be served. But this commonly led to misconduct and rowdiness-and violation of the building code.

“For hundreds of years only wooden piles were used. As each of these can carry only eight to twelve tons, many were needed under a building of considerable size. Do you recall seeing the Royal Palace the other day? Well, it was built on 13,659 wooden piles.” “But, Grandpa, don’t those wooden piles ever decay? Don’t they have to be replaced with new piles?” “It would seem so, Frank, but when the tops of the piles are driven under the water level, they last for hundreds of years.”

“Are wooden piles still used?”

“Once in a while for smaller buildings. But usually reinforced concrete piles are used. They do not have to be driven below the water level and can bear much heavier loads than wooden ones. Now back to your question about replacing defective piles. The piles used for replacement purposes come in sections of about four feet [1.2 meters] or so. These sections have a hollow core and are so constructed that one section fits on top of the other one to form a complete pile.

These piles are pressed into the ground by hydraulic power. As a section is pressed in, the soil from its foot is removed through the hollow core. When one section is in the ground, the other sections, one at a time, are pressed into the soil until hardpan is reached.

Thereafter the hollow core is filled with concrete, adding strength to the sectioned pile and forming a broad foot to give it good bearing capacity. This method is also used in the neighborhood of buildings that would otherwise be damaged by conventional hammering or in the neighborhood of hospitals and office buildings where people would suffer from the noise of a pile driver.”

“Thank you for telling me all of this, Grandpa. When I get home I’m going to have a lot to tell all my friends about my vacation in the Netherlands.”

Arthurkingsla-21
UK

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