Engineering Solutions

Imagine a geography that is both swampy, very cold and geologically very hard rocks in places. You will build a city in such a place. How would you do it?

Because the area is swampy, you have to drive piles, but sometimes you come across very hard rock masses underground. Moreover, the depth of the swamp is hundreds of meters, but at the same time it is very cold, so the swampy soil is frozen. In the short summer period, the upper levels soften.

Here is an engineering problem.

This is the situation in the northern mining city of Norilsk.

When you drive piles into the swampy ground, you can't find solid ground below. The piles have to bear the load through surface friction.

If you place the building on the ground on piles like on normal soft ground, the swampy ground softens due to the heat of the building and the piles cannot bear the load on them and sink.

Moreover, if you try to drill the soil with a normal piling machine during the pile construction phase, the drilling system of the piling machines does not withstand due to the soil structure formed by the hard rocks of the region, and quickly dulls the diamond drilling system. You cannot manufacture piles by drilling.

The Russians had the good sense to use Soviet-era hammer-type piling machines. These machines have a heavy hammer and they lift it and drop it on the ground and break these hard rock stones to make the pile hole. The machines are very old and it takes weeks to make a single pile. Lift and lift and drop, the hammer weighing several tons slowly breaks the rocks and ice inside the pile pit. Every now and then they change the bit and clean the inside of the pit, then put the hammer back on and keep going, lifting and lifting the hammer, breaking rock and ice, for days on end, for a single pile. The machines run on diesel, but they can also be connected to electricity if you have the opportunity. At least it is quieter with electricity, but these old machines break rocks for days on end. It's really tiring.

Sometimes a big rock mass is encountered down below, immediately the project managers check their calculations, a few tests are done, if the rock is close to the surface it is useless, if the soil softens it will sink to the bottom under additional load because the area is swampy. The size of the rock is measured with ultrasound tests and if necessary, the project is modified at that point. But the pile tip must penetrate at least one meter into the rock. What I mean by hard rock is granite, basalt, very hard rock. It takes at least a day or two to dig a one meter hole in that rock. Sometimes, as I said, if it is a small rock, it has to be drilled through. So you just keep at it. Bam bam, keep breaking.

I won't talk about the methods of pouring concrete in the cold, but you can imagine that special precautions have to be taken.

The piles are ready now, but as I said, the piles carry the load by surface friction, and the swampy ground is like mud when it softens, it doesn't carry any load. Therefore, it is necessary not to allow the ground to soften during the long winter period. In the short summer period, the lengths of the piles should be designed to extend to the frozen ground under the softened ground close to the surface.

As a solution, buildings are built one and a half to two meters above the ground, that is, the buildings are on piles, but underneath they are open to cold weather conditions. Thus, the ground is not affected by the heating of the buildings in winter. The ground floor can also be walled up, but with window openings for air to enter and exit, so that the ground can remain frozen in winter.

The heating is centralized, as in many Russian cities, with insulated hot water pipes running to the buildings and the heating system running on boiling water.

But I saw some abandoned buildings in the city. When I asked, they told me that due to malfunctions in the hot water pipes, hot water escaping into the ground caused the piles of the buildings to sink, so the buildings were evacuated.

In short, I found these engineering solutions to be difficult conditions, but interesting at the same time.

Special cooling systems were installed around the piles under some of the city's bridges to keep the ground frozen even in summer. Due to the traffic load and heavy vehicle vibration, these bridges were collapsing in the summer due to the softening of the ground surface, so they had to take such a precaution. The system worked like a refrigerator, with rods driven into the ground around the piles and refrigerated with freon gas or a similar gas. This was also an interesting solution.

In short, when human beings want to, they can find ways to live even in the -60°, -70° cold regions of the north. Of course, I didn't encounter such cold when I worked there. The lowest I saw was -54°C, but I guess even that is cold enough. You can only get to the house a hundred meters away from the construction site by car, and even in the twenty meters you walk from the construction site building to the car, you freeze if you are not dressed warmly. Of course, the icy wind blowing at 12 meters per second has a big effect on this.

I want to keep the memories of cold and difficult conditions, good and bad, but I wanted to share some information in terms of engineering solutions.

Love and respect to everyone from Moscow.