How to warm up the earth for excavation. Ways of warming up frozen soil and their features

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The development of the soil associated with digging a trench in winter conditions is complicated by the need for preliminary preparation and warming of the frozen soil. The depth of seasonal soil freezing is determined according to the data of meteorological stations.
In urban conditions, with a large number of operating cable lines and other underground utilities, the use of percussion tools (jackhammers, crowbars, wedges, etc.) is impossible due to the danger of mechanical damage to existing cable lines and other underground utilities.
Therefore, the frozen soil before starting work on digging a trench in the area of \u200b\u200bexisting cable lines must be pre-warmed so that earthworks can be carried out with shovels without the use of percussion tools.
Soil heating can be done by electric reflex ovens, electric horizontal and vertical steel electrodes, electric three-phase heaters, gas burners, steam and water needles, hot sand, fires, etc. Ground heating methods, in which heating needles are inserted into frozen soil by drilling wells or their plugging, have not been used, since this method is effective and its use can be economically justified at a depth of fracture more than 0.8 m, i.e. at a depth that is not used for cable work. Soil heating can also be carried out by high-frequency currents, however, this method has not yet received practical application due to the complexity of the equipment and the low efficiency of the installation. Regardless of the method adopted, the heated surface is preliminarily cleaned of snow, ice and the upper cover of the base (asphalt, concrete).

Heating of soil by electric currents of industrial frequency with the help of steel electrodes, laid horizontally on the frozen ground, is to create an electric current circuit, where the frozen ground is used as a resistance.
Horizontal electrodes made of strip, angular and any other steel profiles 2.5-3 m long are laid horizontally on frozen ground. The distance between the rows of electrodes included in opposite phases should be 400 - 500 mm at a voltage of 220 V and 700-800 mm at a voltage of 380 V. Due to the fact that the frozen soil does not conduct electric current well, the soil surface is covered with a layer of sawdust soaked in an aqueous solution salt 150-200 mm thick. In the initial period of switching on the electrodes, the main heat is transferred to the soil from sawdust, in which intense heating occurs under the influence of an electric current. As the soil heats up, its conductivity increases and the electric current passes through the soil, the intensity of the soil heating increases.
In order to reduce heat loss from dispersion, the sawdust layer is compacted and covered with wooden boards, mats, tar paper, etc.
The consumption of electrical energy for warming the soil using steel electrodes is largely determined by the moisture content of the soil and ranges from 42 to 60 kWh per 1 m 3 of frozen soil with a heating duration from 24 to 30 hours.
Work on defrosting the soil by electric current should be carried out under the supervision of qualified personnel responsible for observing the heating regime, ensuring the safety of work and the serviceability of the equipment. These requirements and the complexity of their fulfillment naturally limit the possibilities of using this method. The best and safer method is to apply voltage up to 12V.

Figure: 15. Design of three-phase heaters for warming the soil

a - heater; b - connection diagram; 1 - steel rod with a diameter of 19 mm, 2 - steel pipe with a diameter of 25 mm, 3 - steel sleeve with a diameter of 19-25 mm, 4 - copper contacts with a section of 200 mm 2, 5 - steel strip 30X6 mm 2.

Electric three-phase heaters allow heating the soil at a voltage of 10 V. The heater element consists of three steel rods, each rod is inserted into two steel pipes, the total length of which is 30 mm less than the length of the rod; the ends of the rod are welded to the ends of these pipes.
The space between the rod and the inner surface of each pipe is covered with quartz sand and filled with liquid glass for sealing (Fig. 15) - The ends of the three pipes located in the A-L plane are interconnected by a steel strip welded to them, forming the neutral point of the heater star. The three ends of the pipes located in the BB-B plane are connected to the electrical network through a special 15 kV-A step-down transformer using copper clamps fixed to them. The heater is placed directly on the ground and covered with 200 mm thick thawed sand. To reduce heat loss, the heated area is additionally covered from above with fiberglass mats.
The consumption of electrical energy for warming 1 m 3 of soil with this method is 50-55 kWh, and the heating time is 24 hours.

Electric reflex oven. As the experience of conducting repair work in urban networks has shown, the most convenient, transportable and fastest under the same conditions, determined by the degree of freezing, the nature of the heated soil and the quality of the coating, is the method of heating by electric reflex ovens. As a heater in the furnace, a nichrome or fechral wire with a diameter of 3.5 mm is used, wound with a spiral on a steel pipe insulated with asbestos (Fig. 16).
The stove reflector is made of an aluminum, duralumin or steel chrome-plated sheet with a thickness of 1 mm, bent axially into a parabola with a distance from the reflective reflector to the spiral (focus) of 60 mm. The reflector reflects the heat energy of the oven, directing it to the area of \u200b\u200bwarmed up frozen soil. To protect the reflector from mechanical damage, the oven is closed with a steel casing. There is an air gap between the housing and the reflector, which reduces heat loss from dissipation.
The reflex oven is connected to a 380/220/127 V electrical network.
When the soil is warmed up, a set of three single-phase reflex furnaces is assembled, which are connected into a star or triangle according to the mains voltage. The heating area of \u200b\u200bone furnace is 0.4X1.5 m 2; power of a set of furnaces 18 kW.


Figure: 16. Reflector oven for warming up frozen soil.
1 - heating element, 2 - reflector, 3 - casing; 4 - contact clamps
Electricity consumption for warming up 1 m 3 of frozen soil is approximately 50 kWh with a heating duration of 6 to 10 hours.
When using the ovens, it is also necessary to ensure safe working conditions. The place of warming up must be fenced off, the terminals for connection with a wire are closed, and the spirals of the leak must not touch the ground.

Warming up the frozen soil with fire.For this purpose, both liquid and gaseous fuels are used. Solar oil is used as a liquid fuel. Its consumption is 4-5 kg \u200b\u200bper 1 m 3 of heated soil. The installation consists of boxes and nozzles. With a box length of 20-25 m, the installation per day makes it possible to warm the soil at a depth of 0.7-0.8 m.
The heating process lasts 15-16 hours. During the rest of the day the soil thaws due to the accumulated heat in its surface layer.
A more efficient and economical fuel for warming the soil is gaseous.
The gas burner used for this purpose is a piece of steel tube 18 mm in diameter with a flattened cone. Hemispherical boxes are made of sheet steel with a thickness of 1.5-2.5 mm. To save money (heat losses, the boxes are sprinkled with a heat-insulating layer of soil up to 100 mm thick. The cost of heating the soil with gas fuel averages 0.2-0.3 rubles / m 3.
Heating of the soil by fires is used for a small amount of work (digging of pits and trenches for insertion). A bonfire is made after clearing the place from snow and ice. For greater efficiency of warming, the fire is covered with iron sheets 1.5-2 mm thick. After the soil has been warmed to a depth of 200-250 mm, which is installed with a special steel probe, the fire is allowed to burn out, after which the thawed soil is selected with shovels. Then, at the bottom of the formed hollow, a fire is again made, repeating this operation until the frozen soil is selected to the full depth. During work on warming up the soil, it is necessary to ensure that water from melting snow and ice does not flood the fire.
In the process of warming up the soil, the operating cables can be damaged as a result of the influence of the heat heater. Experience has shown that for proper protection of operating cables during ground heating, it is necessary that a layer of earth with a thickness of at least 200 mm remains between the heater and the cable during the entire heating period.

Our country is located in the northern latitudes. The winter period with negative temperatures takes up a lot of time for builders. However, it is possible not to stop capital construction if the soil is warmed up. This procedure is becoming more and more popular. In this article we will tell you about the main methods of heating the soil.

Why do you need soil heating in winter?

When construction is carried out within the city limits, it becomes dangerous to remove frozen soil with the help of fender equipment. You can easily damage underground communications, of which there are so many in the city: cable lines, water pipes, gas pipelines. In such places, it is often necessary to remove the soil manually. In winter, shovels cannot take the frozen ground out of the trench. Therefore, they order soil heating immediately before the start of construction work. At the same time, they order the heating of the concrete after pouring the foundation for its hydration and the correct set of hardness.

What are the ways to warm up the soil?

There are many ways to warm up the ground at the construction site. They differ not only in cost, but also in efficiency. We will list the main ones:

1. Warming up with hot water.This method is suitable for defrosting small areas of land. Labyrinths of flexible sleeves are laid over the area, which are covered with polyethylene or any heat insulator. Water heated to 70-90 degrees Celsius is allowed through the sleeves. To do this, use a heat generator or pyrolysis boiler. Defrosting speed - no more than 60 cm per day. Disadvantages - high cost of equipment and low heating rate.
2. Heating with steam and steam needles. At the site, wells are drilled with a depth of one and a half to two meters for special metal pipes with a diameter of up to 50 mm. These so-called needles have holes at the ends of no more than 3 mm. Pipes are staggered every 1-1.5 meters. Saturated water vapor is fed into the needles (temperature - more than 100 degrees Celsius, pressure - 7 atmospheres). This method is used only for deep pits - more than 1.5 meters. Disadvantages - complex preparatory work, the release of large volumes of condensate and the need for constant process control.
3. Heating by heating elements. This method is similar to the tool used with steam needles. Pipes 1 meter long and up to 60 mm in diameter are also used. They are installed in drilled wells at the same distance. Inside the pipes there is a liquid dielectric with high thermal conductivity. Heating elements are connected to the mains. Electricity consumption for 1 cubic meter meter of land - 42 kW * h. The disadvantages are high costs.
4. Heating with electric mats. The method involves the use of infrared mats, working on the principle of similar mats for a “warm floor”. Electromats heat the soil to a temperature of 70 degrees. Warm-up depth - no more than 80 cm in 32 hours. Electricity consumption - 0.5 kW * h per 1 square meter. Disadvantages - fragile material, the need for constant monitoring.
5. Heating with ethylene glycol using a Waker Neuson installation. The equipment runs on diesel fuel. From this point of view, it is autonomous and does not depend on the supply of communications (electricity). A hose is laid out over the area of \u200b\u200bthe site with a snake, through which heated ethylene glycol will circulate. This liquid has the highest thermal conductivity and a higher boiling point than water. The hoses are covered with thermal insulation mats. One installation allows you to defrost 400 square meters to a depth of 1.5 meters in 8 days.

Our company offers soil and concrete heating services using the Waker Neuson installation. This method is considered to be the most efficient in terms of cost per area and defrosting time.

When a soil section is switched on with the help of cathodes, a heating current of 120, 220 and 380 volts can be passed through it into the electric circuit.

The electrical conductivity of the soil depends on its moisture content (Fig. 3, a), the state and temperature of moisture, the concentration of solutions of salts and acids in the soil (Fig. 3, b), the structure and temperature of the soil (Fig. 3, c), etc. ...

The complexity of the structure of the soil, the physical phenomena occurring in it and the changes associated with power processes, significantly complicates the theoretical side of the electric heating of the soil, which is still at the stage of development.

Figure: 1. Installation of horizontal (string) electrodes on frozen ground filled with sawdust
1 - frozen ground; 2 - horizontal (jet) electrodes with a diameter of 12-16 mm; 3 - wires supplying current; 4 - sawdust moistened with salt solution; 5 - upper insulation (roofing paper, wooden boards, mats, etc.)

Figure: 2. Installation of vertical (rod) electrodes in frozen soil filled with sawdust
1 - vertical electrodes; 2 - wires supplying current; 3 - sawdust moistened with a solution of salt, 4-upper insulation (roofing paper, wooden shields, mats, etc.)

Thawing of the soil is performed using horizontal (sling) and vertical (rod and depth) electrodes. When thawing with horizontal electrodes (Fig. 1), the surface of the warmed-up soil area is covered with a 15-25-cm layer moistened with an aqueous solution of salt (sodium chloride, calcium, copper sulfate, etc.) intended only to bring current and warm the upper layer of frozen soil, so as the latter, even at a voltage of 380 V, practically does not pass.

With horizontal electrodes, heat is initially transferred to the ground only from the heating layer of sawdust. Only the upper, insignificant layer of soil adjacent to the electrodes is included in the electrical circuit and is a resistance in which heat is released.

The distance between the rows of electrodes included in different phases is 40-50 cm at a voltage of 220 V and 70-80 cm at a voltage of 380 V. The use of horizontal electrodes is advisable when warming up frozen bases and a small (up to 0.5-0.7 m) depth of freezing, as well as in cases where vertical (rod) electrodes cannot be used due to the low electrical conductivity of the soil or the impossibility of driving them into the ground.

When thawing with vertical rod electrodes, wet sawdust initially serves as a stimulus for heating the upper layer of the soil, which, as it thaws, is included in the electrical circuit, after which the sawdust only reduces the heat loss of the thawed soil. Instead of sawdust, the stimulus can be salt solutions poured into grooves in the soil, punched with a chisel between all the electrodes to a depth of 6 cm.

When the surface of the heated soil is covered with a layer of dry sawdust, as practice shows, the arrangement of such grooves gives good results.
The use of vertical electrodes is more effective when the frozen soil depth is more than 0.7 m, as well as when it is impossible to ensure proper contact between the horizontal electrodes and the ground. In hard (clay and sandy soils with a moisture content of more than 15-20%), electrodes are driven to a depth of 20-25 cm, and then immersed deeper as the soil thaws (approximately every 4-5 hours).

The distance between the electrodes is assigned from 40 to 70 cm, depending on the current voltage, the nature and temperature of the soil. When defrosting to a depth of 1.5 m, it is recommended to have two sets of electrodes - short and long; after thawing the soil to the depth of short electrodes, they are replaced by long ones. Warming up the soil to a depth of 2 m or more should be done in several steps, layer by layer with periodic removal of thawed layers with the current turned off. In order to save electricity and maximize the use of power, one should strive so that by the end of thawing the average soil temperature does not exceed + 5 ° and a maximum of + 20 °, and heating should be carried out in sections, periodically turning off the current.

Figure: 3. Change in soil resistivity depending on
a - from the moisture content of red clay soil, b - from the NaCi content in clay soil at 30% moisture content (by weight), 8 - from the soil temperature at 18.6% moisture

The installation for thawing the soil consists of boards and soffits (4-5 for each switchboard) for connecting the electrodes to the network.

When using deep electrodes, the frozen soil is thawed from the bottom up to its day surface. For this, electrodes made of round steel with a diameter of 12-19 mm (depending on their length and soil hardness) are staggered through the entire thickness of the frozen layer by 15-20 cm into the thawed soil. At the beginning of thawing, an electric current passing through the thawed soil heats it up and thaws the part of the frozen layer located directly next to it. Thus, the heat flux, gradually increasing in thickness from bottom to top, sequentially heats the frozen soil, and almost all the heat released by the current is used to thaw the frozen layer.
This method of thawing, in addition to reducing heat loss, provides a number of other benefits.

As you know, excavators can develop a frozen soil crust up to 25-40 cm thick without preliminary loosening, which makes it possible to accordingly reduce the depth of the thawed soil. Since the topsoil is usually the most complex and energy intensive, mining them in an unfrozen state reduces energy consumption and speeds up work.

The use of a higher voltage makes it possible to increase the distance between the electrodes. The latter, at a voltage of 220 V, is taken at 0.5 m, and at 380 V it is already 0.7 m.
The lower end of the electrode is sharpened, and a through hole with a diameter of 3-4 mm is drilled in the upper end, through which a bare copper wire 25-30 cm long is passed; one end of the wire is welded to the electrode, and the other is connected to the mains with subsequent phase rotation.

If it is difficult to drive the electrodes, boreholes with a diameter that is 1-2 mm less than the accepted diameter of the electrode pass through.
According to experimental data, loams with a moisture content of 18% at a freezing depth of 1.5 m and a voltage of 220 V are thawed for about 16 hours.
The heated area is allocated with a portable fence and multiplied by warning signals with a categorical prohibition to enter it.
When using any method of soil heating, it is necessary to strictly follow the rules set forth in the special "Instructions for the use of electric heating in construction".

Defrosting by currents of high frequency. Frozen soil is permeable to high-frequency currents, and its warming occurs due to the heat released in the soil when it is placed and an alternating high-frequency electric field.
The high frequency generator consists of a step-up transformer, a rectifier, oscillator tubes, capacitors and an oscillating circuit. The mobile unit is mounted in a trailer and is powered from a 220-380 V mains or from a mobile power station.
This method is possible with a small amount of work, the development of trenches, and especially during emergency work, when the timing of their implementation is a decisive factor.

Winter is traditionally considered an unfavorable period for work in the construction industry. However, the use of thermoelectric devices will help you achieve an advantage over your competitors by switching to a year-round work schedule, regardless of weather conditions and the presence of wind, you can avoid downtime and send your workers on forced leave. We will help you become the strongest company in the market!

Flexible heating mats are installed on areas subject to defrosting, heating or frost protection. Installation and removal of mats takes very little time! The heating element of the thermomats gives off heat directly to the ground.

Heating temperature thermoelectromat 70 o C. Thanks to the built-in reflective material, the heat flow is directed only to the heating zone,
for maximum heat transfer and to reduce heat loss. The thermomat heats up and effectively thaws the soil to a depth of 30 - 40 cm per day, depending on the condition of the soil.

The thermomat functions independently of the operator until the task is completed.

Using a mat with our heating and defrosting concept will help you achieve a competitive advantage over other players in the market. You can continue
work while the rest will wait for the natural thawing of the frozen soil. The thermomat has already generated a lot of interest in the construction industry.

Efficient and easy to use, low maintenance mats have set a new standard in heating concrete and defrosting frozen soil in cold climates.

This is the future!

The area of \u200b\u200bapplication is intended for consumers in need of frost-free materials or soil, for year-round performance of work in accordance with established specifications and quality requirements. In addition to defrosting, preventing freezing and increasing frost resistance, the thermomat can also be used for heating concrete, heating pipelines, tanks, sand masses, masonry and other non-standard heating tasks.

Examples of equipment applications

Thawing of soil and territories:

• Water supply and sewerage systems
• Cable trenches
• Shafts, plinths and floor areas
• Roofs and coverings
• Removing ice and snow

When freezing:

• Areas intended for cladding
• Sand masses, jig sand
• Bulk masses
• Pipeline lines
• Railroad switches
• Floating marinas

Pre-heating of soil or concrete:

• Foundations before laying the foundation
• Formwork and equipment for concrete work
• Increasing the degree of hardening of concrete and lightweight concrete slabs

Development of soil in winter conditions.

AT construction of the total volume of earthworks from 20 to 25% is carried out in winter conditions, while the proportion of soil developed in a frozen state remains constant -10-15% with an increase from year to year in the absolute value of this volume.

AT in the practice of construction, it becomes necessary to develop soils that are in a frozen state only in the winter season, i.e. soils of seasonal freezing, or throughout the year, i.e. permafrost soils.

Development of permafrost soils can be carried out in the same ways as for frozen soils of seasonal freezing. However, when erecting earthen structures in permafrost conditions, it is necessary to take into account the specific features of the geothermal regime of permafrost soils and the change in soil properties when it is disturbed.

At negative temperatures, the freezing of water contained in the pores of the soil significantly changes the construction and technological properties of non-rocky soils. In frozen soils, the mechanical strength increases significantly, and therefore, their development with earth-moving machines is difficult or even impossible without preparation.

The depth of freezing depends on the air temperature, the duration of exposure to negative temperatures, the type of soil, etc.

Earthwork in winter is carried out by the following three methods. The first method involves preliminary preparation of soils with their subsequent development by conventional methods; in the second case, frozen soils are pre-cut into blocks; in the third method, soils are developed without preliminary preparation. Preliminary preparation of soil for development in winter consists in protecting it from freezing, thawing frozen soil, and preliminary loosening of frozen soil.

Preservation of soil from freezing... It is known that the availability on the daytime

the surface of the thermal insulation layer reduces both the period and the depth of freezing. After removing surface water, you can arrange a thermal insulation layer in one of the following ways.

Loosening the soil. When plowing and harrowing the soil in the area intended for development in winter, its upper layer acquires a loose structure with closed voids filled with air, which has sufficient thermal insulation properties. Plowing is carried out with tractor plows or rippers to a depth of 20 ... 35 cm, followed by harrowing to a depth of 15 ... 20 cm in one direction (or in cross directions), which increases the thermal insulation effect by 18 ... 30%. Snow cover in the area to be insulated, it can be artificially increased by shoveling snow with bulldozers, motor graders or by means of snow retention using shields. Most often, mechanical loosening is used to insulate large areas of land, Protection of the soil surface with thermal insulation materials. The insulating layer can also be made from cheap local materials: wood leaves, dry moss, peat, straw mats, slag, shavings and sawdust. Surface insulation of soil is used mainly for excavations of small area.

Soil impregnation with saline solutionslead as follows. On the surface

the specified amount of salt (calcium chloride 0.5 kg / m2, sodium chloride 1 kg / m2) is poured into the sandy and sandy loam soil, after which the soil is plowed. In soils with low filtration capacity (clay, heavy loams), wells are drilled into which a salt solution is injected under pressure. Due to the high labor intensity and cost of such works, they are, as a rule, insufficiently effective.

Methods for thawing frozen soilcan be classified both by the direction of heat propagation in the soil and by the type of heat carrier used. On the first basis, the following three methods of soil thawing can be distinguished.

Thawing soil from top to bottom... This method is the least effective, since the heat source in this case is located in the cold air zone, which causes large heat losses. At the same time, this method is quite easy and simple to implement, it requires minimal preparatory work, and therefore, it is often used in practice.

Thawing soil from bottom to toprequires minimal energy consumption, since it occurs under the protection of an earth crust and heat loss is practically excluded. The main disadvantage of this method is the need to perform labor-intensive preparatory operations, which limits the scope of its application.

When thawing the soil in the radial direction heat spreads in the ground radially from vertically installed heating elements immersed in the ground. In terms of economic indicators, this method occupies an intermediate position between the two previously described, and for its implementation it also requires significant preparatory work.

By the type of coolant, the following methods of thawing frozen soil are distinguished

Fire method. For small trenches in winter, an installation is used (Fig. 1a), consisting of a number of metal boxes in the form of truncated cones cut along the longitudinal axis, from which a continuous gallery is assembled. The first of the boxes is a combustion chamber in which solid or liquid fuel is burned. The exhaust pipe of the last box provides traction, thanks to which the combustion products pass along the gallery and heat the soil located under it. To reduce heat loss, the gallery is sprinkled with a layer of thawed soil or slag. The strip of thawed soil is covered with sawdust, and further thawing in depth continues due to the heat accumulated in the soil.

Figure 1. Schemes of soil thawing by fire method and steam needles: a

By firing method; b - steam needles; 1 - combustion chamber; 2 - exhaust pipe; 3 - sprinkling with thawed soil: 4 - steam line; 5 - steam valve; 6 - steam needle; 7 - drilled well; 8 - cap.

Thawing in hothouses and reverberatory ovens ... Teplyaki are open-bottom boxes with insulated walls and a roof, inside which are placed incandescent coils, water or steam batteries, suspended from the box lid. Reflective ovens have a curved surface on top, in the focus of which there is an incandescent spiral or an infrared emitter, while energy is consumed more economically, and the soil thaws more intensively. Heat houses and reverberatory furnaces are powered by 220 or 380 V. Power consumption per 1 m3 thawed soil (depending on its type, humidity and temperature) fluctuates within 100 ... 300 MJ, while a temperature of 50 ... 60 ° С is maintained inside the greenhouse.

When thawing the ground with horizontal electrodes on the surface of the ground

that is, electrodes of strip or round steel are placed, the ends of which are bent 15 ... 20 cm to connect to the wires (Fig. 2a). The surface of the heated area is covered with a layer of sawdust 15 ... 20 cm thick, which is moistened with a saline solution with a concentration of 0.2 ... 0.5% so that the mass of the solution is not less than the mass

sawdust. Initially, the wetted sawdust is a conductive element, since the freezing soil is not a conductor. Under the influence of heat generated in the layer of sawdust, the top layer of the soil thaws, which turns into a current conductor from electrode to electrode. After that, under the influence of heat, the upper layer of the soil begins to thaw, and then the lower layers. Subsequently, the sawdust layer protects the heated area from heat loss into the atmosphere, for which the sawdust layer is covered with plastic wrap or shields.

Figure 2. Scheme of soil thawing by electric heating: a - horizontal electrodes; b - vertical electrodes; 1 - three-phase electrical network; 2 - horizontal strip electrodes; 3

A layer of sawdust moistened with salt water; 4 - a layer of roofing or roofing felt; 5 - rod electrode.

This method is used at a depth of soil freezing up to 0.7 m, the power consumption for heating 1 m3 of soil ranges from 150 to 300 MJ, the temperature in sawdust does not exceed 80 ... 90 ° C.

Thawing soil with vertical electrodes ... The electrodes are reinforcing steel rods with pointed lower ends. With a freezing depth of more than 0.7 m, they are driven into the soil in a checkerboard pattern to a depth of 20 ... 25 cm, and as the upper layers of the soil thaw, they are immersed to a greater depth. When thawing from top to bottom, it is necessary to systematically remove the snow and arrange a sawdust backfill moistened with saline. The heating mode with rod electrodes is the same as with strip electrodes, and during a power outage, the electrodes should be further deepened by 1.3 ... 1.5 m.After a power outage for 1 ... 2 days, the thawing depth continues to increase for due to the heat accumulated in the ground under the protection of the sawdust layer. The energy consumption with this method is slightly lower than with the method of horizontal electrodes.

Applying heating from the bottom up, before the start of heating, it is necessary to drill wells in a checkerboard pattern to a depth exceeding the thickness of the frozen soil by 15 ... 20 cm. Energy consumption when warming up the soil from bottom to top is significantly reduced (50 ... 150 MJ per 1 m3), the use of a layer of sawdust is not required. When the rod electrodes are deepened into the underlying thawed soil, while the saline-soaked sawdust backfill is installed on the day surface, thawing occurs from top to bottom and from bottom to top. Moreover, the complexity of the preparatory work is much higher than in the first two options. This method is used only when it is necessary to urgently thaw the soil.

Thawing soil from top to bottom using steam or water registers. Reg-

the strips are laid directly on the surface of the heated area cleared of snow and covered with a heat-insulating layer of sawdust, sand or thawed soil to reduce heat loss in space. The registers thaw the soil with a frozen crust thickness of up to 0.8 m. This method is advisable in the presence of sources of steam or hot water, since the installation of a special boiler plant for this purpose is usually too expensive.

Thawing soil with steam needlesis one of the most effective means, but it causes excessive soil moisture and increased heat consumption. The steam needle is a metal pipe 1.5 ... 2 m long, with a diameter of 25 ... 50 mm. A tip with holes of 2 ... 3 mm in diameter is mounted on the lower part of the pipe. The needles are connected to the steam line

flexible rubber hoses with cranes (Fig. 1b). The needles are buried in wells previously drilled to a depth of 0.7 thawing depth. The wells are closed with protective caps made of wood, sheathed with roofing steel with an opening equipped with a gland for the passage of a steam needle. Steam is supplied at a pressure of 0.06 ... 0.07 MPa. After installing the storage caps, the heated surface is covered with a layer of thermal insulating material (for example, sawdust). To save steam, the heating mode with needles should be intermittent (for example, 1 hour - steam supply, 1 hour - break) with alternating steam supply to parallel groups of needles. The needles are staggered with a distance between their centers of 1 ... 1.5 m. Steam consumption per 1 m3 of soil is 50 ... 100 kg. This method requires more heat consumption than the method of deep electrodes, approximately 2 times.

When thawing the soil with water circulation needles as a heat

the media use water heated to 50 ... 60 ° C and circulating in a closed system "boiler - distribution pipes - water needles - return pipes - boiler". This scheme ensures the most complete use of thermal energy. The needles are installed in the wells drilled for them. The water needle consists of two coaxial pipes, of which the inner one has an open at the bottom, and the outer one has a pointed ends. Hot water enters the needle through the inner pipe, and through its lower hole enters the outer pipe, through which it rises to the outlet pipe, from where it goes through the connecting pipe to the next needle. The needles are connected in series, several pieces in groups, which are connected in parallel between the distributing and return pipelines. The thawing of the soil with needles in which hot water circulates is much slower than around steam needles. After continuous operation of the water needles for 1.5 ... 2.5 days, they are removed from the soil, the surface is insulated, after which for 1 ...

The thawed zones expand due to accumulated heat for 1.5 days. The needles are staggered at a distance of 0.75 ... 1.25 m between themselves and are used at depths of freezing from 1 meter or more.

Thawing of soil by heating elements (electric needles) ... Heating elements are steel

pipes with a length of about 1 m with a diameter of up to 50 ... 60 mm, which are inserted into the wells previously drilled in a checkerboard pattern.

A heating element is mounted inside the needles, isolated from the pipe body. The space between the heating element and the walls of the needle is filled with liquid or solid materials that are dielectrics, but at the same time transfer and retain heat well. The intensity of thawing of the soil depends on the surface temperature of the electric needles, and therefore the most economical temperature is 60 ... 80 ° C, but the heat consumption is higher in comparison with the deep electrodes by 1.6 ...

1.8 times.

When thawing the soil with saline solutions wells are pre-drilled on the surface to a depth to be thawed. Wells with a diameter of 0.3 ... 0.4 m are staggered with a step of about 1 m. A saline solution heated to 80 ... 100 ° C is poured into them, with which the wells are replenished within 3 ... 5 days. In sandy soils, a well with a depth of 15 ... 20 cm is sufficient, since the solution penetrates deeply due to the dispersion of the soil. Soils thawed in this way do not freeze again after their development.

Method of layer-by-layer thawing of permafrost soils it is most appropriate in the spring, when the warm air of the surrounding atmosphere, warm rainwater, and solar radiation can be used for these purposes. The upper thawed soil layer can be removed with anyearthmoving or leveling machines, exposing the underlying frozen layer, which, in turn, thaws under the influence of the above factors. The soil is cut at the border between the frozen and thawed layers, where the soil has a weakened structure, which creates favorable conditions for the operation of machines. In permafrost regions, this method is one of the most economical

common and common for excavation when planning excavations, trenches, etc.

Method of layer-by-layer freezing of aquifers provides for the development

booting before the onset of frost of the upper layer of the soil lying above the groundwater horizon. When, under the influence of cold atmospheric air, the calculated freezing depth reaches 40 ... 50 cm, they begin to develop the soil in the excavation in a frozen state. Development is carried out in separate sections, between which are left bridges of frozen soil with a thickness of about 0.5 m to a depth of about 50% of the thickness of the frozen soil. Bulkheads are designed to isolate individual areas from adjacent ones in case of groundwater breakthrough. The development front moves from one section to another, while in the already developed sections the freezing depth increases, after which the development is repeated. Alternate freezing and development of sites is repeated until the design level is reached, after which the protective bridges are removed. This method makes it possible to develop excavations in the frozen state of the soil (without fastening and drainage), which significantly exceed in their depth the thickness of the seasonal freezing of the soil.

Preliminary loosening of frozen soil by means of small-scale mechanization

change with a small amount of work. For large volumes of work, it is advisable to use mechanical and permafrost machines.

Explosive method of looseningsoil is most economical for large volumes of work, significant depth of freezing, especially if the energy of the explosion is used not only for loosening, but also for throwing earth masses into the dump. But this method can only be used in areas located away from residential buildings and industrial buildings. When using localizers, the explosive method of loosening the soil can be used near buildings.

Figure 3. Schemes of loosening and cutting frozen soil: a - loosening with a wedge-hammer; b - loosening with a diesel hammer; c - cutting cracks in frozen ground with a multi-bucket excavator equipped with cutting chains - bars; 1 - hammer wedge; 2 - excavator; 3 - frozen soil layer; 4- guide bar; 5 - diesel hammer; 6 - cutting chains (bars); 7 - bucket excavator; 8 - cracks in frozen ground.

Mechanical loosening of frozen soils used for a fragment of small pits and trenches. In these cases, the frozen soil is loosened to a depth of 0.5 ... 0.7 mwedge-hammer (fig. 3a) suspended from the boom of an excavator (dragline) - the so-called splitting loosening. When working with such a hammer, the boom is set at an angle of at least 60 °, which ensures a sufficient drop height of the hammer. When using free fall hammersdue to dynamic overload quickly wear out the steel rope, trolley and individual machine units; in addition, from impact on the ground, its vibrations can adversely affect nearby structures. Mechanical rippers loosen the soil at a freezing depth of more than 0.4 m. In this case, the soil is loosened by chipping or cutting blocks, and the laboriousness of breaking the soil with a chip is several times less than when loosening the soil by cutting. Number of beats

a ditch along one track depends on the depth of freezing, the group of soil, the mass of the hammer (2250 ... 3000 kg), the height of the rise, it is determined by the drummer of the DORNII design.

Diesel hammers (Fig. 3b) can loosen the soil at a freezing depth of up to 1.3 m and, along with wedges, are attachments to an excavator, a tractor loader and a tractor. It is possible to loosen frozen soil with a diesel hammer according to two technological schemes. According to the first scheme, the diesel hammer loosens the frozen layer, moving in a zigzag along the points located in a checkerboard pattern with a step of 0.8 m. At the same time, the crushing spheres from each working station merge with each other, forming a continuous loosened layer prepared for subsequent development. The second scheme requires preliminary preparation of the open face wall developed by the excavator, after which the diesel hammer is installed at a distance of about 1 m from the face edge and hitting them in one place until a chunk of frozen soil occurs. Then the diesel hammer is moved along the edge, repeating this operation.

Impact permafrost rippers (Fig. 4b) work well at low soil temperatures, when it is characterized not by plastic, but by brittle deformations that contribute to its splitting under the impact of an impact.

Loosening the soil with tractor rippers. This group includes equipment in which the continuous cutting force of the knife is created due to the pulling force of the tractor-tractor. Machines of this type pass through the frozen soil layer by layer, providing for each penetration a loosening depth of 0.3 ... 0.4 m: Therefore, they develop a frozen layer, previously loosened by such machines as bulldozers. In contrast to impact rippers, static rippers work well at high soil temperatures when soil has significant plastic deformation and mechanical strength is reduced. Static rippers can be trailed or mounted (on the rear axle of the tractor). Very often they are used in conjunction with a bulldozer, which in this case can alternately loosen or develop the soil. At the same time, the trailed ripper is unhooked, and the mounted ripper is raised. Depending on the engine power and the mechanical properties of the frozen soil, the number of ripper teeth ranges from 1 to 5, and most often one tooth is used. For efficient operation of the tractor ripper on frozen ground, it is necessary that the engine has sufficient power (100 ... 180 kW). The soil is loosened by parallel (after about 0.5 m) penetrations, followed by transverse penetrations at an angle of 60 ... 90 ° to the previous ones.

Figure 4. Schemes of development of frozen soils with preliminary loosening: a - loosening with a wedge-hammer; b - a tractor vibro-wedge ripper; 1 - dump truck; 2 - excavator; 3 - hammer wedge; 4 - vibrocline.

Frozen soil loosened by cross-penetration by a single shank ripper can be successfully developed with a tractor scraper, and this method is considered very economical and successfully competes with the drilling and blasting method.

When developing frozen soils with preliminary cutting in blocks, slots are cut in the frozen layer (Fig. 5), dividing the soil into separate blocks, which are then removed by an excavator or construction cranes. The depth of the slots cut in the frozen layer should be approximately 0.8 of the freezing depth, since the weakened layer at the border of the frozen and thawed zones is not an obstacle for excavation. In areas with permafrost soils, where the underlying layer is absent, the block mining method is not used.

Figure 5. Schemes for the development of frozen soils by the block method: a, b - by the small block method; c, d - large-block; 1 - removal of snow cover; 2, 3 - cutting blocks of frozen soil with a bar machine; 4 - development of small blocks with an excavator or bulldozer; 5 - development of thawed soil; 6 - development of large blocks of frozen soil with a tractor; 7 - the same, with a crane.

The distances between the cut slots depend on the dimensions of the excavator bucket (the dimensions of the blocks should be 10 ... 15% less than the width of the mouth of the excavator bucket). Blocks are shipped by excavators with buckets with a capacity of 0.5 m and more, equipped mainly with a backhoe, since unloading blocks from the bucket with a straight shovel is very difficult. Various equipment installed on excavators and tractors is used to cut cracks in the ground.

It is possible to cut cracks in frozen ground using rotary excavators, in which the bucket rotor is replaced by milling discs equipped with teeth. For the same purpose, disc milling machines are used (Fig. 6), which are attachments to the tractor.

Figure 6. Disk-milling earth-moving machine: 1 - tractor; 2 - system of transmission and control of the working body; 3 - working body of the machine (cutter).

It is most effective to cut cracks in frozen soil with bar machines (Fig. 5), the working body of which consists of a cut-in chain mounted on the basis of a tractor or a trench excavator. Bar machines cut slots 1.3 ... 1.7 m deep. The advantage of chain machines compared to disc machines is the relative ease of replacing the most quickly wearing parts of the working body - replaceable teeth inserted into the cut chain.