Work in winter conditions. Method of thawing soil with the development of it in the thawed state

Defrosting occurs due to heat exposure and is characterized by considerable labor-intensiveness and energy costs. It is used in rare cases when other methods are unacceptable or unacceptable - in the vicinity of existing communications and cables, in cramped conditions, during emergency and repair work.

Thawing methods are classified according to the direction of heat propagation in the soil and according to the heat carrier used (fuel combustion, steam, hot water, electricity). In the direction of thawing, all methods are divided into three groups.

Thawing soil from top to bottom . Heat is distributed in a vertical direction from the surface to the bottom of the ground. The method is the simplest, practically does not require preparatory work, is most often applicable in practice, although from the point of view of economical energy consumption is most imperfect, since the heat source is located in the cold air zone, therefore significant energy losses to the surrounding space are unavoidable.

Thawing soil from the bottom up. Heat propagates from the lower boundary of the frozen soil to the surface. The method is the most economical, since thawing occurs under the protection of a frozen soil crust and heat loss into space is practically excluded. The required heat energy can be partially saved by leaving the upper soil crust in a frozen state. It has the lowest temperature, therefore, it requires a lot of energy for thawing. But this thin layer of soil in 10 ... 15 cm will be freely developed by an excavator, for this the power of the machine is enough. The main disadvantage of this method is the need to perform labor-intensive preparatory operations, which limits its scope.

Radial thawing of soil takes an intermediate position between the two previous methods on the consumption of thermal energy. Heat is distributed in the ground radially from the vertically installed heating elements, but in order to install and connect them, considerable preparatory work is required. . To perform soil thawing in any of these three methods, it is necessary to clean the area from snow in advance so as not to waste thermal energy on its thawing and it is unacceptable to overwet the soil.

Depending on the heat carrier used, there are several defrosting methods.

Thawing direct burning of fuel . If in winter time it is necessary to dig 1 ... 2 pits, the simplest solution is to get along with a simple fire. Keeping the fire going during the shift will thaw the soil beneath it by 30 ... 40 cm. After extinguishing the fire and well warming the heating place with sawdust, thawing of the soil inside will continue due to the accumulated energy and during the shift can reach a total depth of 1 m. you can again burn a fire or develop a thawed ground and make a fire at the bottom of the pit. The method is used extremely rarely, since only a small part of the heat energy is spent productively.

The firing method is applicable to extracting small trenches, a link construction (Fig. 3.1) from a series of truncated metal boxes is used, from which a gallery of the required length is easily assembled, in the first of them a solid or liquid fuel combustion chamber is arranged (firewood, wood and gas). fuel burned through a nozzle). Thermal energy moves to the exhaust duct of the last duct, which creates the necessary traction, thanks to which hot gases pass along the entire gallery and the soil under the ducts is heated along its entire length. It is advisable to warm the top of the box, often using thawed primer. After the change, the unit is removed, the strip of thawed soil is filled with sawdust, further thawing continues due to the heat accumulated in the ground.

Electric heating . The essence of this method consists in passing an electric current through the soil, as a result of which it acquires a positive temperature. Use horizontal and vertical electrodes in the form of rods or strip steel. For the initial movement of electric current between the rods, it is necessary to create a conductive medium. Such an environment can be thawed soil, if the electrodes

kind to another. Under the influence of heat, the underlying layers of soil thaw. In the subsequent distribution of thermal energy is carried out mainly in

thicker than the ground, sawdust only protects the heated area from the loss of heat into the atmosphere, for which purpose it is advisable to cover the layer of sawdust with rolled materials or shields. This method is quite effective when the depth of soil freezing or thawing is up to 0.7 m. Electricity consumption for heating 1 m3 of soil varies between 150 ... 300 kWh, the temperature of heated sawdust does not exceed 80 ... 90 ° С.

The thawing of the soil by strip electrodes placed on the surface of the soil, cleaned of snow and debris, as far as possible aligned. The ends of the iron strip are folded upward by 15 ... 20 cm for connection to electrical wires. The surface of the heated area is covered with a layer of sawdust 15 ... 20 cm thick moistened with a solution of sodium chloride or calcium consistency of 0.2 ... 0.5%. Since the soil in the frozen state is not a conductor, in the first stage the current moves along the sawdust moistened with the solution. Next, the upper layer of the soil warms up and the thawed water begins to conduct electric current, the process eventually goes deep into the soil, sawdust begins to play the role of thermal protection of the heated section from heat losses to the atmosphere. Sawdust on top is usually covered with tar, plexiglass, shields, and other protective materials. The method is applicable at a depth of warming up to 0.6 ... 0.7 m, since at greater depths the voltage drops, the soils are less intensively involved in the work, they heat up much more slowly. In addition, they are sufficiently saturated with water in the fall, which requires more energy to go to the thawed state. Energy consumption ranges from 50 ... 85 kWh per 1 m3 of soil.

Ground thawing with rod electrodes (Fig. 3.2). This method is carried out from top to bottom, from bottom to top and combined methods. When ground is thawed by vertical electrodes, bars of reinforced iron with a pointed lower end are hammered into the ground in a staggered manner, usually using a 4x4 m frame with crosswise tensioned wires; the distance between the electrodes is in the range of 0.5 ... 0.8 m.

When heating from top to bottom , the surface is cleared of snow and frost, the rods are driven into the ground by 20 ... 25 cm, a layer of sawdust soaked in a solution of salts is laid. As the soil warms up, the electrodes hammer deeper into the ground. The optimum depth will be within the range of 0.7 ... 1.5 m. The duration of thawing of the soil by exposure to an electric current is approximately 1.5 ... 2.0 days, after which the increase in the depth of thawing will occur due to the accumulated heat for 1 ... 2 days The distance between the electrodes is 40 ... 80 cm, the energy consumption compared with the strip electrodes is reduced by 15 ... 20% and is 40 ... 75 kW • h per 1 m3 of soil.

When warming up, wells are drilled upwards and electrodes are inserted to a depth exceeding the frozen ground depth by 15 ... 20 cm. The current between the electrodes goes through thawed soil below the freezing point, when heated, the soil warms the overlying layers, which are also included in the work. With this method, a layer of sawdust is not required. Energy consumption is 15 ... 40 kWh per 1 m3 of soil.

The third, combined method will take place when the electrodes are buried in the underlying melt soil and the device is placed on the day surface of the sawdust soaked in saline. The electric circuit closes at the top and bottom, the ground will thaw from the top down and bottom up at the same time. Since the complexity of the preparatory work with this method is the highest, its use can be justified only in exceptional cases when accelerated thawing of the soil is required.

Thawing by high frequency currents. This method makes it possible to drastically reduce preparatory work, since the frozen ground retains conductivity to high-frequency currents, therefore there is no need for a large penetration of the electrodes into the soil and in the device for sawdust backfilling. The distance between the electrodes can be increased to 1.2 m, i.e., their number is almost halved. The process of soil thawing proceeds relatively quickly. The limited use of the method is due to the insufficient release of high-frequency current generators.

One of the methods that have now lost their effectiveness and have been supplanted by more modern ones is the thawing of the soil with steam or water needles. This requires the presence of sources of hot water and steam, with a small, up to 0.8 m depth of soil freezing. Steam needles are a metal pipe with a length of up to 2 m and a diameter of 25 ... 50 mm. A tip with holes with a diameter of 2 ... 3 mm is mounted on the lower part of the pipe. The needles are connected to the steam line with flexible rubber hoses in the presence of taps on them. The needles are buried in wells that are pre-drilled to a depth of approximately 70% of the depth of thawing. The wells are closed with protective caps, fitted with glands for the passage of the steam needle. Steam is supplied under a pressure of 0.06 ... 0.07 MPa. After installing the accumulated caps, the heated surface is covered with a layer of insulating material, most often sawdust. The needles are placed in a staggered manner with a distance between centers of 1 ... 1.5 m. Steam consumption per 1 m3 of soil is 50..100 kg. Due to the release of steam in the soil latent heat of vaporization, the heating of the soil passes particularly intensively. This method requires a consumption of thermal energy of about 2 times more than the method of vertical electrodes.

Soil thawing by heat electric heaters. This method is based on the transfer of heat to frozen ground by contact method. Electromates are used as the main technical means. They are made of a special heat-conducting material through which electric current is passed. Rectangular mats, the dimensions of which can cover the surface from 4 ... 8 m2, are placed on the thawed area and connected to a 220-volt electricity source. At the same time, the heat generated effectively spreads from top to bottom into the frozen ground, which leads to its thawing. The time required for thawing depends on the ambient temperature and the depth of soil freezing and averages 15-20 hours.