Since entering the site, Shucheng has carried out a series of studies on the solution of plateau permafrost, and wants to know how to solve the problem of plateau permafrost in railway construction. Pen & Fun & Pavilion www.biquge.info

After a week of discussion with Lin Xiaoyong, he finally understood the solution to the plateau permafrost.

And today, Shucheng held this meeting to popularize the treatment method of plateau permafrost.

Hearing Shu Cheng's words, Lin Xiaoyong paused and said: "Plateau permafrost, this name, presumably everyone will not be unfamiliar, in fact, plateau permafrost refers to the ice-containing soil that has been frozen on the plateau for two years or more, and the soil contains ice slag. In winter, it produces freeze swelling, causing the soil to bulge, while in summer it occurs hot thaw, which is when the soil surface sinks, repeatedly, making the ground uneven. ”

In fact, to put it bluntly, the soil freezes when it is cold, and once it freezes, the water mixed in the soil breaks into ice, and when the volume increases, it will expand, causing the soil to rise.

As soon as the temperature rises, the ice melts, and the ice mixed in with the soil turns into water, which decreases in volume and sinks.

In the plateau, as the temperature rises and falls, the two states are repeated.

If a railroad were built on this kind of soil, it would be imaginable to anyone.

As soon as the soil swells in winter, the railway swells, and this one bag and that one package causes the railway to be uneven.

In the summer, when the ice melts into water, the soil becomes a pit, and the railroad on top of it sinks.

In some severe areas, as the year increases, the ice frozen below does not melt and accumulates, resulting in thicker and thicker ice, and the heaving is very violent.

On the railway, there is a regulation on the slope of the rail and the height difference between the two rails, and once this regulation is exceeded, there is a high probability of derailment accidents.

Therefore, no one dares to build a railway in this soil until the problem of permafrost is solved.

It can be seen from the construction of railways on the frozen soil in foreign countries that after the completion of the railway, there has been no running car.

After the construction of railway embankment on permafrost, the heat exchange conditions between the surface and the atmosphere have been changed, and the temperature of the permafrost has been re-adjusted to the thermal balance.

Due to the cold expansion and thawing characteristics of permafrost, there are serious diseases in permafrost subgrades.

"After more than half a century of hard work, the older generation, one after another, has finally found several solutions to the construction of railways on the frozen soil." Lin Xiaoyong continued.

For Lin Xiaoyong's speech, everyone was not disturbed, not only the technicians, but even the other members of the project department looked at Lin Xiaoyong curiously, wanting to know the solution to the frozen soil.

"Among the existing solutions to the plateau permafrost, there are three more general methods that can solve the problem of plateau permafrost, and these three methods to solve the problem of plateau permafrost are divided according to the depth and severity of permafrost freezing." Lin Xiaoyong continued: "For the general permafrost, the thickness of the permafrost is not particularly deep, and there is no water and swamp on the surface of the permafrost. ”

The first kind of permafrost is that the freezing depth is not too severe, because the water content of this permafrost is slightly less, winter and summer have less impact on its volume, but it still has an impact, but the uplift and sinking amount are not particularly much.

Even so, the factor of foundation sinking must be considered, after all, the heavenly route can be said to be a century-old plan, and the party and state leaders attach great importance to it.

Even if it sinks one centimeter and rises one centimeter, causing triangular pits on the railway, the train may overturn.

Therefore, no one dares to be careless.

"The second type, which is considered moderate permafrost, is the depth of freezing, which is more severe than the first, the depth of freezing is deeper, and the soil rises and falls more severely as the temperature changes." Lin Xiaoyong said again.

For the second type of permafrost, it is on the first type of permafrost, which freezes deeper.

Within the distance from Kunlun Mountain to Tanggula Mountain, the boundary of Kunlun Mountain begins, and the thickness of permafrost changes as you go to Tanggula Mountain, showing a stepped shape.

At the beginning of the Kunlun Mountains, the permafrost was not very serious, and continuing to the Tanggula Mountains, the permafrost gradually became serious, and finally there was a permanent frozen layer.

"The last and most complex type of permafrost can also be called severe permafrost. This part of the permafrost, which is generally located in swampy areas, and the depth of the permafrost is several hundred meters, and below it is the permafrost, and how to build a railway on this permafrost is the most difficult. Lin Xiaoyong continued: "Because with the change of temperature, the swamp is like a quagmire, the frozen soil is compacted, you can pass the car, and it will sink deep in summer, and the impact on the foundation is very serious!" ”

For a long time, how to build a railway on a permafrost swamp has been the most concerned thing for railway researchers, and research in this area has lasted for more than half a century.

The main reason why the permafrost is divided into three types and three different solutions is based on the budget investment and other things.

After distinguishing the three types of frozen soil, Lin Xiaoyong continued: "The answer given by the design institute for the solution to the frozen soil is: try not to disturb the original formation, and keep the temperature of the frozen soil within a range through some method. Let the frozen soil not be uplifted and sunk due to temperature changes, so as to ensure the stability of the line and ensure the safety of driving. ”

To put it bluntly, it is to control the temperature of the frozen soil, once the temperature of the frozen soil is controlled within a small range, it will not be affected by the outside temperature, and there will be no sinking and uplifting.

This approach is the principle of active protection of permafrost by means of 'cooling the roadbed'.

But how to achieve this goal is the key.

For the construction of projects such as the Qinghai-Tibet Highway, there are also frozen soil areas and pre-construction sections, but this is not considered.

At that time, when the Qinghai-Tibet Highway was built, the common method was to increase the thermal resistance as a means to protect the frozen soil in the frozen soil section.

This method is to take the principle of not excavating and filling the roadbed, but when the temperature changes greatly, when the freezing and melting thickness are inconsistent, there will still be a situation such as severe sinking, which eventually leads to serious damage to the road surface.

"For the first kind of slight frozen soil, the method given by the design institute is called stone masonry cold roadbed, also called stone-throwing roadbed, and stone-throwing roadbed is divided into two kinds, one is called stone-throwing slope protection roadbed, and the other is called stone-throwing air-cooled roadbed." Lin Xiaoyong introduced.

In fact, before proposing this kind of rubble roadbed, scientific researchers first did another experiment, and there is another way, which can also solve the problem of plateau permafrost.

This method is called ventilation duct subgrade.

The ventilation pipe subgrade, as the name suggests, is buried side by side under the roadbed, just like we have seen, a water pipe is buried from under the road, but the ventilation pipe subgrade is buried in a large row of pipes.

In winter, the air has a large density, and under the action of self-weight and wind, convection is generated, which takes away the temperature in the tube, and continuously takes away the heat of the surrounding soil, reduces the temperature of the substrate, and achieves the purpose of protecting the frozen soil.

To put it bluntly, in winter, cold air passes through the tube, taking away the temperature of the tube and the surrounding soil, and the temperature of the frozen soil will not be unable to transfer heat due to the roadbed laid on it.

However, the ventilation pipe subgrade has certain limitations, which are affected by factors such as pipe diameter, wind direction, snow and sand accumulation in the pipe.

For example, if the diameter of the pipe is not large enough, the temperature in the pipe cannot be carried out when the temperature in the pipe is convected in summer, which will have an impact on the frozen soil.

There is also the direction of the wind, on the plateau, the direction of the wind can not be exactly the same as your subgrade ventilation pipe, the wind can just pass through the ventilation pipe, once the wind can not pass through the ventilation pipe, the heat inside can not be taken away, and it also has an impact on the frozen soil.

In addition, not to mention the snow and sand in the pipe, the air convection is not passable, and the heat cannot be carried out.

In addition, there is another most critical reason, the ventilation pipe subgrade, the cost is too high, if the day route uses this form of roadbed, the budget of the day route, it is not good to do a few more.

Because of the limitations of the ventilation pipe subgrade, the railway researchers pondered, is there any other way to replace the ventilation pipe?

After a long period of research, the leading figure in the railway field, by chance, discovered a strange phenomenon.

They found that the temperature around the ground where the stones were piled up was generally low, so they began to study the stones.

After research, it was found that the stones were stacked together, and in the absence of other debris, had a diode heat conduction effect.

That is, the stones that are piled up together can create a convection of air, which takes away the temperature in the soil and lowers the temperature of the soil.

"Rubble slope protection roadbed, that is, on the roadbed slope, add a rubble layer; Rubble air-cooled roadbed is to set a rubble layer of a certain thickness and porosity on top of the roadbed cushion. Due to the porosity of the riprap layer, air can circulate freely in it. When the surface is heated in summer, the hot air rises, and the gas in the rubble is in a state of heat conduction, taking away the heat, and can still maintain a low temperature to prevent the heat from spreading downward. Lin Xiaoyong said.

In Shucheng's view, the purpose of the rubble roadbed is one, in summer, through air convection, take away the temperature in the soil, and at the same time, the rubble can also block the sunlight and prevent the temperature from entering the permafrost, so that the permafrost can remain in a relatively stable state and not melt and sink.

In winter, the cold air can infiltrate through the rubble, and the rubble in the rubble is still in a state of hot convection, and more cold air is introduced into the foundation, and the frozen soil is more compact, stabilizing the roadbed.

This method of 'cooling the roadbed' is also the most widely used method of the day route, and the cost of this roadbed is not very high, which is conducive to popularization and application.

The only thing to note is that there are certain regulations on the selection of the particle size of the rubble, and there can be no debris between the rubble, so as not to affect the air convection effect.

When Lin Xiaoyong finished introducing the first solution to the plateau permafrost, he began to introduce the second solution. (To be continued.) )