Ways to warm the soil in winter. Frozen soil and methods of its development

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The development of soil associated with digging a trench in winter conditions is complicated by the need for preliminary preparation and heating of frozen soil. The depth of seasonal freezing of the soil is determined according to the data of meteorological stations.
In urban conditions, in the presence of a large number of existing cable lines and other underground utilities, the use of impact 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 ​​​​operating cable lines, must be pre-warmed so that earthworks can be carried out with shovels without the use of impact tools.
Soil heating can be carried out with electric reflex furnaces, electric horizontal and vertical steel electrodes, electric three-phase heaters, gas burners, steam and water needles, hot sand, fires, etc. Methods of soil heating, in which heating needles are introduced into the frozen ground by drilling wells or their driving, have not been used, since this method is effective and its use can be economically justified at a digging depth of more than 0.8 m, i.e. at a depth that is not used for cable work. Soil heating can also be carried out with 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 cleared of snow, ice and the top covers of the base (asphalt, concrete).

Soil heating by electric currents of industrial frequency using steel electrodes laid horizontally on frozen ground, is to create an electric current circuit, where the frozen ground is used as 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 frozen soil conducts electricity poorly, 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, under the influence of an electric current, intense heating occurs. As the soil warms up, its conductivity increases and the electric current passing through the soil, the intensity of soil heating increases.
In order to reduce heat loss from dispersion, a layer of sawdust is compacted and covered with wooden shields, mats, roofing paper, etc.
The consumption of electrical energy for heating the soil using steel electrodes is largely determined by soil moisture and ranges from 42 to 60 kWh per 1 m 3 of frozen soil with a heating duration of 24 to 30 hours.
Work on defrosting the soil with electric current must 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 implementation, of course, limit the application of this method. The best and safer method is to apply voltages up to 12 V.

Rice. 15. The design of three-phase heaters for heating the soil

a - heater; b - switching circuit; 1 - steel rod with a diameter of 19 mm, 2 - steel pipe with a diameter of 25 mm, 3 - steel bushing with a diameter of 19-25 mm, 4 - copper contacts with a cross 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 strip of steel welded to them, forming a neutral point of the heater star. The three ends of the pipes located in the B-B plane, with the help of copper clamps fixed to them, are connected through a special step-down transformer with a power of 15 kV-A to the electrical network. The heater is laid directly on the ground and covered with 200 mm thick melted sand. To reduce heat loss, the heated area is additionally covered with fiberglass mats on top.
The consumption of electrical energy for heating 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 fast 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 with electric reflex furnaces. As a heater in the furnace, a nichrome or fechral wire with a diameter of 3.5 mm is used, wound in a spiral onto a steel pipe insulated with asbestos (Fig. 16).
The furnace reflector is made from an axially bent parabola with a distance from the reflecting reflector to the spiral (focus) of 60 mm aluminum, duralumin or chrome-plated steel sheet 1 mm thick. The reflector reflects the thermal energy of the oven, directing it to the area of ​​the warmed ice cream soil. To protect the reflector from mechanical damage, the furnace is closed with a steel casing. There is an air gap between the casing and the reflector, which reduces heat loss from dissipation.
The reflex oven is connected to the electrical network with a voltage of 380/220/127 V.
When heating the soil, a set of three single-phase reflex furnaces is assembled, which are connected into a star or a triangle, according to the mains voltage. The heating area of ​​one furnace is 0.4X1.5 m 2; power of a set of furnaces is 18 kW.


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

Heating frozen soil with fire. For this purpose, both liquid and gaseous fuels are used. Solar oil is used as liquid fuel. Its consumption is 4-5 kg ​​per 1 m 3 of warmed soil. The installation consists of boxes and nozzles. With a length of boxes 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 thawing of the soil occurs due to the accumulated heat by its surface layer.
A more efficient and economical fuel for heating the soil is gaseous.
The gas burner used for this purpose is a piece of steel tube with a diameter of 18 mm with an oblate cone. Hemispherical boxes are made of sheet steel with a thickness of 1.5-2.5 mm. To save (heat loss), 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 is on average 0.2-0.3 rub / m 3.
Warming the soil with fires is used for a small amount of work (digging pits and trenches for insertion). A fire is lit after clearing the place of snow and ice. For greater heating efficiency, the fire is covered with iron sheets 1.5-2 mm thick. After the soil is warmed to a depth of 200-250 mm, which is set 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 depression, a fire is again made, repeating this operation until the frozen soil is selected to the full depth. In the course of work on warming the soil, it is necessary to ensure that water from melting snow and ice does not flood the fire.
In the process of ground warming, the existing cables can be damaged as a result of the impact of the heater. As experience has shown, for proper protection of existing cables during soil heating, it is necessary that a layer of earth with a thickness of at least 200 mm be maintained between the heater and the cable during the entire heating period.

The complexity of extracting frozen soil is extremely high due to its significant mechanical strength. In addition, the frozen state of the soil complicates the task of excavating it due to the impossibility of using some types of earth-moving and earth-moving machines, reducing productivity and accelerated wear of the working parts of the equipment. And yet, frozen soil has one advantage - it is possible to dig pits in it without slopes.

There are four main ways to excavate during the cold season:

• protection of the land plot of work from freezing with the further use of conventional earth-moving machines;
• preliminary loosening and excavation of frozen soil;
• direct mining in a frozen state, i.e. without any preparation;
• bringing to a thawed state and subsequent excavation.

Let's take a closer look at each of these methods.

Protection of soils from freezing

Protection from low temperatures is provided to the soil by loosening the top layer, covering with insulating materials and pouring aqueous salt solutions.

Plowing and harrowing of the land plot is carried out in the sector of further work on the extraction of soil. The result of such loosening is the introduction of a large amount of air into the soil layers, the formation of closed air voids that prevent heat transfer and maintain a positive temperature in the soil. Plowing is carried out by rippers or factor plows, its depth is 200-350 mm. Next, harrowing is carried out in one or two directions (cross) to a depth of 150-200 mm, which ultimately increases the thermal insulation properties of the soil by at least 18-20%.
The role of a heater when covering the site of future work is performed by cheap local materials - dry moss, sawdust and shavings, fallen leaves of trees, slag and straw mats, you can use PVC film. Bulk materials are placed on the surface in a 200-400 mm layer. Warming of the soil surface is carried out most often on small plots of land.

Frozen soil - loosening and excavation

To reduce the mechanical strength of winter soil, methods of its mechanical and explosive processing are used. The extraction of the earth loosened in this way is then carried out in the usual way - with the help of earthmoving machines.

Mechanical loosening. In the process of its implementation, the soil is cut, chipped and split due to loads of a static or dynamic nature.

Static loads on frozen soil are produced by a metal tool of a cutting type - a tooth. A special hydraulically driven design, equipped with one or more teeth, is driven around the job site while placed on a crawler excavator. This method allows you to remove the soil in layers to a depth of 400 mm for each pass. In the process of loosening, the installation equipped with a tooth is first pulled parallel to the previous passes with an indent of 500 mm from them, then it is carried out transversely to them at an angle of 60 to 90 °. The volumes of excavation of frozen soil at the same time reach 20 cubic meters per hour. Layer-by-layer static development of frozen ground ensures the use of loosening installations at any depth of soil freezing.

Impact loads on soil areas can reduce the mechanical strength of the frozen earth due to dynamic impact. Free-fall hammers are used for splitting and loosening, or directional hammers for split loosening. In the first case, a hammer is used in the form of a ball or cone with the largest mass of 5 tons - it is fixed with a rope on the excavator boom and, after lifting to a height of five to eight meters, is dropped to the work site. Ball-shaped hammers are best suited for sandstone and sandy loam, conical hammers are effective on clay soils - provided that the freezing depth does not exceed 700 mm.

Directed action on frozen ground is carried out by diesel hammers mounted on a tractor or excavator. They are used on any soil, subject to a freezing depth of not more than 1300 mm.

Reducing the strength of frozen ground by means of an explosion is most effective - this method allows you to perform winter excavation at a depth of 500 mm and, if significant volumes are required. In undeveloped areas, an open explosion is carried out, and in partially built-up areas, it is necessary to first set up shelters and explosion limiters - massive slabs of metal or reinforced concrete. The explosive is placed in a slot or borehole (with a loosening depth of up to 1500 mm), and if excavation is required at a greater depth, in slots and wells. Drilling or milling machines are used to cut slots, slots are made at a distance of 900-1200 mm from each other.

Explosives are placed in the middle (central) slot, and adjacent slots will provide compensation for the explosive shift of frozen soil and dampen the shock wave, thereby preventing damage outside the work area. An elongated charge or several short charges at once is placed in the slot, then it is filled with sand and compacted. After the explosion, the frozen soil in the work sector will be completely crushed, while the walls of the trench or pit, the creation of which was the purpose of excavation, will remain intact.

Development of frozen soil without its preparation

There are two methods of direct soil development at low temperatures - mechanical and block.

The technology of mechanical development of frozen soils is based on force action, in some cases including shock and vibration. In the course of its implementation, both conventional earth-moving machines and those equipped with special tools are used.

At shallow depths of freezing, conventional earth-moving machines are used to excavate the soil: excavators with a direct or reverse bucket; draglines; scrapers; bulldozers. Single-bucket excavators can be equipped with special attachments - buckets with gripping tongs and vibro-impact teeth. Such equipment makes it possible to act on frozen soil by means of excessive cutting force and to carry out its layer-by-layer development, combining loosening and excavation in one working operation.

Layer-by-layer extraction of soil is carried out by a special earthmoving and milling unit, which cuts layers 2600 mm wide and up to 300 mm deep from the work site. The design of this machine provides for bulldozer equipment that ensures the movement of cut soil.

The essence of block development of soils is cutting frozen soil into blocks with their subsequent extraction using a tractor, excavator or construction crane. Blocks are cut by sawing through the soil with cuts perpendicular to each other. If the ground is frozen shallow - up to 600 mm - then to extract the blocks, it is enough to make cuts along the site. Slots are cut to 80% of the depth to which the soil is frozen. This is quite sufficient, since a layer with weak mechanical strength, located between the frozen soil zone and the zone that maintains a positive temperature, will not interfere with the separation of soil blocks. The distance between the slots-slots should be approximately 12% less than the edge width of the excavator bucket. Extraction of soil blocks is carried out using backhoes, because. unloading them from a straight shovel bucket is quite difficult.

Methods for thawing frozen soil

They are classified according to the direction of heat supply to the ground and the type of coolant used. Depending on the direction of supply of thermal energy, there are three ways to defrost the soil - upper, lower and radial.

The upper heat supply to the ground is the least efficient - the source of thermal energy is located in the air space and is actively cooled by air, i.e. much of the energy is wasted. However, this method of thawing is the easiest to organize and this is its advantage.

The thawing procedure, carried out from underground, is accompanied by minimal energy costs, since heat is distributed under a solid layer of ice on the ground surface. The main disadvantage of this method is the need to perform complex preparatory measures, so it is rarely used.

The radial distribution of thermal energy in the soil is carried out with the help of thermal elements vertically recessed into the ground. The efficiency of radial thawing is between the results of the upper and lower heating of the soil. To implement this method, somewhat smaller, but still quite high volumes of work on the preparation of heating are required.

Soil defrosting in winter is carried out using fire, electric thermoelements and hot steam.
The firing technique is applicable to digging relatively narrow and shallow trenches. On the surface of the work site, a group of metal boxes is exposed, each of which is a truncated cone cut in half. They are placed with the cut side on the ground close to each other and form a gallery. Fuel is placed in the first box, which is then set on fire. The gallery of boxes becomes a horizontal chimney - the hood comes from the last box, and the combustion products move along the gallery and heat the soil. To reduce heat loss from the contact of the duct body with air, they are covered with slag or thawed soil from the site where work was carried out earlier. The strip of defrosted soil formed at the end of warming up must be covered with sawdust or covered with PVC film so that the accumulated heat contributes to further thawing.

Electric heating of frozen soil is based on the ability to heat materials when an electric current is passed through them. For this purpose, vertically and horizontally oriented electrodes are used.

Horizontal thawing is carried out by electrodes made of round or strip steel laid on the ground - in order to connect electrical wires to them, the opposite ends of the steel elements are bent by 150-200 mm. The heated area with electrodes placed on it is covered with sawdust (layer thickness - 150-200 mm), pre-moistened with saline solution (salt concentration - 0.2-0.5%) in an amount equal to the initial mass of sawdust. The task of sawdust impregnated with saline is to conduct current, since frozen soil will not conduct current at the initial stage of work. From above, a layer of sawdust is covered with a pvc film. As the upper soil layer warms up, it becomes a current conductor between the electrodes and the thawing intensity increases significantly - first the middle soil layer is defrosted, and then those located below. As the layers of soil are included in the conduction of electric current, the sawdust layer begins to perform a secondary task - the preservation of thermal energy in the work area, for which it is necessary to cover the sawdust with wooden shields or roofing paper. Thawing of frozen soil with horizontal electrodes is carried out to a freezing depth of up to 700 mm, the cost of electricity for heating a cubic meter of earth is 150-300 MJ, the sawdust layer warms up to 90 ° C, no more.

Vertical electrode thawing is carried out using rods made of reinforcing steel and having one sharp end. If the depth of soil freezing is 700 mm, the rods are first driven in to a depth of 200-250 mm in a checkerboard pattern, and after thawing the top layer, they are sunk to a greater depth. In the process of vertical defrosting of the soil, it is required to remove the snow accumulated on the surface of the site, cover it with sawdust moistened with saline. The heating process proceeds in the same way as with horizontal thawing using strip electrodes - as the upper layers are thawed, it is important to periodically immerse the electrodes further into the ground to a depth of 1300-1500 mm. At the end of the vertical thawing of the frozen soil, the electrodes are removed, but the entire site remains under a layer of sawdust - for another 24-48 hours, the soil layers will thaw on their own due to the accumulated thermal energy. The energy costs for vertical defrost work are slightly lower than for horizontal defrost.

For electrode heating of the soil in the upward direction, preliminary preparation of wells is necessary - they are drilled 150-200 mm deeper than the freezing depth. The wells are arranged in a checkerboard pattern. This method is characterized by lower energy costs - about 50-150 MJ per cubic meter of soil.

The rods of the electrodes are inserted into the prepared wells, reaching the unfrozen layer of the earth, the surface of the site is covered with sawdust moistened with saline, a plastic film is laid on top. As a result, the thawing process goes in two directions - from top to bottom and from bottom to top. This method of thawing frozen soil is rarely carried out and only if it is urgently necessary to unfreeze a site for excavation.

Steam thawing is carried out using special devices - steam needles made of metal pipes with a diameter of 250-500 mm, through which hot steam is introduced into the soil. The lower part of the steam needle is equipped with a metal tip containing many 2-3 mm holes. A rubber hose equipped with a tap is connected to the upper (hollow) part of the needle pipe. To install steam needles in the ground, wells are drilled (staggered order, distance 1000-1500 mm) with a length of 70% of the required thawing depth. Metal caps are put on the holes of the well, equipped with glands, through which a steam needle will be passed.

After installing the needles through the hose, steam is supplied to them under a pressure of 0.06-0.07 MPa. The surface of the thawed piece of land is covered with a layer of sawdust. Steam consumption for heating a cubic meter of soil is 50-100 kg, in terms of thermal energy consumption, this method is 1.5-2 times more expensive than heating with buried electrodes.

The method of thawing frozen soil using contact electric heaters is outwardly similar to steam defrosting. In metal hollow needles with a length of about 1000 mm and a diameter of not more than 60 mm, heating elements are installed with insulation from the metal body of the needle. When the power supply is connected, the heating element imparts thermal energy to the body of the needle-pipe, and it to the soil layers. Thermal energy in the process of heating is distributed radially.

A significant part of the territory of Russia is located in areas with long and severe winters. However, construction is carried out here all year round, and therefore, approximately 20% of the total volume of earthworks has to be carried out when the ground is frozen.

Frozen soils are characterized by a significant increase in the complexity of their development due to increased mechanical strength. In addition, the frozen state of the soil complicates the technology, limits the use of certain types of earth-moving (excavators) and earth-moving (bulldozers, scrapers, faders) machines, reduces the productivity of vehicles, and contributes to the rapid wear of machine parts, especially their working bodies. At the same time, temporary excavations in frozen ground can be developed without slopes.

Depending on the specific local conditions, soil development in winter conditions is carried out by the following methods: 1) soil protection from freezing and subsequent development by conventional methods, 2) soil development in a frozen state with preliminary loosening, 3) direct development of frozen soil, 4) thawing of the pound and its development in a thawed state.

The protection of the soil from freezing is carried out by loosening the surface layers, covering the surface with various heaters, impregnating the pound with saline solutions.

Soil loosening by plowing and harrowing is carried out on a site intended for development in winter conditions. As a result, the top layer of the pound acquires a loose structure with closed voids filled with air, which has sufficient thermal insulation properties. Plowing is carried out by factor 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%.

The soil surface is covered with thermal insulation materials, preferably from cheap local materials: tree leaves, dry moss, peat litter, straw mats, slag, flasks and sawdust, laid in a layer of 20 ... 40 cm directly on the pound. Surface insulation of the pound is used mainly for small recesses.

Loosening of frozen soil with subsequent development by earth-moving or earth-moving-fansport machines is carried out by a mechanical or explosive method.

Mechanical loosening is based on cutting, splitting or chipping a layer of frozen soil by static or dynamic action.

Static action is based on the action of a continuous cutting force in frozen soil by a special working body - a tooth. For this, special equipment is used, in which the continuous cutting force of the tooth is created due to the traction force of the tractor-tractor. Machines of this type perform layer-by-layer penetration of frozen soil, providing for each penetration a loosening depth of the order of 0.3 ... 0.4 m. ° to the previous ones. Ripper capacity 15...20 m3/h. As static rippers, hydraulic excavators with a working body - a ripper tooth are used.

The possibility of layer-by-layer development of the frozen ground makes static rippers applicable regardless of the depth of freezing.

The dynamic effect is based on the creation of shock loads on the open surface of the frozen ground. In this way, the pound is destroyed by free-fall hammers (split loosening) or directional hammers (split loosening). A free-fall hammer can be in the form of a ball or a wedge weighing up to 5 tons, suspended on a rope to an excavator boom and dropped from a height of 5 ... 8 m. .5 ... 0.7 m).

As a directional hammer, diesel hammers are widely used as attachments to an excavator or tractor. Diesel hammers allow you to destroy the pound to a depth of 1.3 m.

Explosion loosening is effective at freezing depths of 0.4 ... 1.5 m or more and with significant volumes of frozen ground development. It is used mainly in undeveloped areas, and in built-up areas - with the use of shelters and explosion localizers (heavy slabs). When loosening to a depth of up to 1.5 m, blast hole and slot methods are used, and at greater depths, borehole or slot methods. Slots at a distance of 0.9 ... 1.2 m from one another are cut with slot-cutting machines of the milling type or bar machines. Of the three adjacent slots, one middle slot is charged, the outer and intermediate slots serve to compensate for the shift of the frozen ground during the explosion and to reduce the seismic effect. The slots are charged with elongated or concentrated charges, after which they are clogged with sand. When blasting, the frozen pound is completely crushed without damaging the walls of the pit or trench.

The direct development of frozen soil (without preliminary loosening) is carried out by two methods: block and mechanical.

The block method is based on the fact that the solidity of the frozen soil is broken by cutting it into blocks, which are then removed by an excavator, construction crane or tractor. Cutting into blocks is performed in mutually perpendicular directions. With a shallow freezing depth (up to 0.6 m), it is enough to make only longitudinal cuts. The depth of the slots cut in the frozen layer should be approximately 80% of the freezing depth, since the weakened layer at the border of the frozen and thawed zones is not an obstacle to detaching blocks from the massif. The distance between the cut slots depends on the size of the excavator bucket edge (the dimensions of the blocks should be 10 ... 15% less than the width of the excavator bucket mouth). For the shipment of blocks, excavators with buckets with a capacity of 0.5 m3 or more are used, equipped mainly with a backhoe, since unloading blocks from the bucket with a straight shovel is very difficult.

The mechanical method is based on force (sometimes in combination with shock or vibration) action on the frozen ground massif. It is implemented using both conventional earth-moving and earth-moving machines, and machines equipped with special working bodies.

Conventional machines are used at a shallow freezing depth of a pound: straight and backhoe excavators with a bucket with a capacity of up to 0.65 m3 - 0.25 m, the same, with a bucket with a capacity of up to 1.6 m3 - 0.4 m, dragline excavators - up to 0.15 m, bulldozers and scrapers - 0.05 ... 0.1 m.

In order to expand the field of application of single-bucket excavators in winter, the use of special equipment has begun: buckets with vibro-impact active teeth and buckets with a gripping tongs device. Due to the excessive cutting force, such single-bucket excavators can develop an array of frozen ground in layers, combining the processes of loosening and excavation into a single one.

Layer-by-layer development of the soil is carried out by a specialized earth-moving and milling machine that removes "chips" up to 0.3 m thick and 2.6 m wide. The movement of the developed frozen soil is carried out by bulldozer equipment included in the machine kit.

The thawing of frozen soil is carried out by thermal methods, which are characterized by significant labor intensity and energy intensity. Therefore, thermal methods are used only in cases where other effective methods are unacceptable or unacceptable, namely: near existing underground utilities and cables, if it is necessary to thaw a frozen base, during emergency and repair work, in cramped conditions (especially in conditions of technical re-equipment and reconstruction enterprises).

Methods for thawing frozen soil are classified both according to the direction of heat propagation in the soil and according to the type of coolant used.

According to the direction of heat propagation into the soil, the following three methods of soil thawing can be distinguished.

The method of thawing the soil from top to bottom is inefficient, since the heat source 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, since it requires minimal preparatory work.

The bottom-up soil thawing method requires minimal energy consumption, since thawing occurs under the protection of the ice-earth crust and heat loss is practically eliminated. The main disadvantage of this method is the need to perform labor-intensive preparatory operations, which limits its scope.

When the soil is thawed in the radial direction, heat spreads in pounds radially from vertically installed hewing elements, fed in pounds. This method, in terms of its economic indicators, occupies an intermediate position between the two previously described, and for its implementation it also requires significant preparatory work.

According to the type of coolant, the following main methods of thawing frozen soils are distinguished.

The fire method is used to excavate small trenches in winter. To do this, it is economical to use a link assembly 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 draft, thanks to which the combustion products pass along the gallery and warm up the soil located under it. To reduce heat loss, the gallery is sprinkled with a layer of thawed soil or slag. A strip of thawed soil is covered with sawdust, and further thawing in depth continues due to the heat accumulated in the soil.

The method of electrical heating is based on the passage of current through the heated material, as a result of which it acquires a positive temperature. The main technical means are horizontal or vertical electrodes.

When thawing the soil with horizontal electrodes, electrodes made of strip or round steel are laid on the soil surface, the ends of which are bent by 15 ... 20 cm to connect to the wires. The surface of the heated area is covered with a layer of sawdust 15–20 cm thick, which are 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 of sawdust. Initially, wetted sawdust is a conductive element, since the frozen ground is not a conductor. Under the influence of heat generated in the layer of sawdust, the top layer of soil thaws, which turns into a current conductor from electrode to electrode. After that, under the influence of heat, the next layer of soil begins to thaw, and then the underlying layers. In the future, the sawdust layer protects the heated area from heat loss to the atmosphere, for which the sawdust layer is covered with roofing paper or shields. This method is used when the freezing depth of a pound is up to 0.7 m, the power consumption for heating 1 m3 of soil ranges from 150 to 300 MJ, the temperature in the sawdust does not exceed 80 ... 90 ° C.

Soil thawing with vertical electrodes is carried out using reinforcing steel rods with pointed lower ends. With a freezing depth of 0.7 m, they are driven into the ground 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 snow and arrange sawdust backfill moistened with saline. The heating mode for rod electrodes is the same as for strip electrodes, and during a power outage, the electrodes should be successively deepened as the soil warms up to 1.3 ... 1.5 m. After a power outage for 1 ... 2 days, the depth thawing continues to increase due to the heat accumulated in the soil under the protection of the sawdust layer. The energy consumption in this method is somewhat lower than in the horizontal electrode method.

Applying heating from the bottom up, before the start of heating, it is necessary to drill wells arranged in a checkerboard pattern to a depth exceeding the thickness of the frozen ground by 15 ... 20 cm. Energy consumption during pound cutting from bottom to top is significantly reduced, amounting to 50 ... 150 MJ per 1 m3, and a layer of sawdust is not required.

When the rod electrodes are deepened into the underlying thawed pound and at the same time a sawdust filling impregnated with saline is placed on the day surface, thawing occurs both in the direction from top to bottom and from bottom to top. At the same time, the food intensity of preparatory work is much higher than in the first two options. This method is used only in exceptional cases, when it is necessary to exfoliate the pound thaw.

Steam thawing is based on the inlet of steam per pound, for which special technical means are used - steam needles, which are a metal tube up to 2 m long, 25 ... 50 mm in diameter. 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 by flexible rubber hoses with taps. The needles are buried in wells, previously drilled to a depth equal to 70% of the thaw depth. The wells are closed with protective caps equipped with glands to pass the steam needle. Steam is supplied under pressure of 0.06...0.07 MPa. After installing the accumulated caps, the heated surface is covered with a layer of thermally insulating material (for example, sawdust). The needles are staggered with a distance between centers of 1 ... 1.5 m. The steam consumption per 1 m3 of a pound is 50 ... 100 kg. This method requires about 2 times more heat consumption than the deep electrode method.

The main purpose of warming up concrete is to comply with the correct conditions for the removal of moisture during work in winter or during their limited periods. The principle of operation of the technology is to maintain an elevated temperature inside or around the thickness of the solution (within 50-60 ° C), implementation methods depend on the type and size of structures, the strength grade of the mixture, budget and environmental conditions. To achieve the desired effect, heating must be uniform and economically justified, the best results are observed when combined.

Overview of heating methods

1. Electrodes.

A simple and reliable method of electrical heating, which consists in placing reinforcement or wire rod 0.8-1 cm thick in a wet solution, forming a single conductor with it. Heat is released evenly, the impact zone reaches half the distance from one electrode to another. The recommended interval between them varies from 0.6 to 1 m. To start the circuit, the ends are connected to a power supply with a low voltage of 60 to 127 V, exceeding this range is possible only when concreting unreinforced systems.

The scope of application includes structures with any volume, but the maximum effect is achieved by heating walls and columns. The power consumption in this case is significant - 1 electrode requires at least 45 A, the number of rods connected to the step-down transformer is limited. As the solution dries, the applied voltage and costs increase. When pouring reinforced concrete products, the technology of heating with electrodes requires coordination with specialists (a project is drawn up for their placement, excluding contact with the metal frame). At the end of the process, the rods remain inside, re-exploitation is excluded.

2. Bookmark wires.

The essence of the method lies in the location in the thickness of the solution of an electric wire (in contrast to the electrodes - insulated), heated by the passage of current and evenly giving off heat. One of the following types is used as work items:

• PNSV - steel cable insulated with polyvinyl chloride.
• Self-regulating sectional varieties: KDBS or VET.

The use of wires is considered the most effective when it is necessary to fill floors or foundations in winter, they convert electrical energy into thermal energy with virtually no loss and ensure its uniform distribution.

PNSV is cheaper, if necessary, it is laid over the entire area of ​​\u200b\u200bthe structure (the length is limited only by the power of the step-down transformer), a cross section from 1.2 to 3 mm is suitable for these purposes. The heating technology features include the need to use installation wires with an aluminum core in open areas. APV cable has suitable characteristics. The PNSV 1.2 scheme excludes overlaps, the recommended step between adjacent rings and lines is 15 cm.

Self-regulating sections (KDBS or VET) are effective for heating in winter without the possibility of using a transformer or supplying 380 V. Their insulation is better than that of PNSV, but they are more expensive. The wire laying scheme is generally similar to the previous one, but its length is limited, it is selected taking into account the dimensions of the structure, it cannot be cut. With the addition of a current control device, heating is carried out more smoothly and economically. In general, both options are considered effective when concreting in winter, the disadvantages include only the complexity of laying and the impossibility of re-use.

3. Heat guns.

The essence of the technology is to increase the air temperature using electric, gas, diesel and other heaters. The processed elements are covered from the cold with a tarpaulin, the creation of such a tent allows you to reach conditions inside from +35 to 70 ° C. Heating is carried out by an external source, which is easily transferred to another place without the need for wires or special equipment. Due to the difficulty of closing large objects and only affecting the outer layers, this method is more often used with small volumes of concrete or with a sharp drop in temperature. Energy consumption in comparison with electrodes or PNSV is acceptable, when diesel guns are used, heating is possible at objects without power supply.

4. Thermomats.

The principle of operation of this technology is based on the coating of a freshly poured solution with polyethylene and infrared film sheets in a moisture-resistant shell. Thermomats are connected to a regular network, the amount of energy consumption varies between 400-800 W / m2, when the limit is reached at +55 ° C, they turn off, which reduces the cost of electrical heating of concrete. The maximum effect of the application is achieved in winter, including when combined with chemical additives.

The risk of moisture freezing inside the concrete products is eliminated after 12 hours, the process is completely autonomous. Unlike PNSV wires, thermomats are in contact with open air and moisture without any problems; in addition to concrete structures, they are successfully used to warm the soil.

With proper care (no overlaps, bending strictly along the allotted lines, protection with polyethylene), IR films can withstand at least 1 year of active operation. But with all the advantages, the technology is poorly suited for heating massive monoliths, the effect of the mats is local.

5. Heating formwork.

The principle of operation is similar to the previous one: an infrared film or asbestos-insulated wires are placed between two sheets of moisture-resistant plywood, which generate heat when connected to the network. This method provides heating in winter to a depth of 60 mm, due to local action, the risk of cracking or overstressing is eliminated. By analogy with mats, these heating elements have thermal protection (bimetallic sensors with auto-return). The scope of application includes structures with any slope, the best results are observed when pouring monolithic objects, including those with limited construction time, but a simple technology cannot be called. When concreting the foundation, a mortar with a temperature of at least +15 ° C is poured into the heating formwork, the soil needs to be preheated.

6. Induction method.

The principle of operation is based on the formation of thermal energy under the influence of eddy currents, the method is well suited for columns, beams, supports and other elongated elements. The induction winding is placed on top of the metal formwork and creates an electromagnetic field, which in turn affects the reinforcing bars of the frame. Heating of concrete is carried out evenly and efficiently with an average energy consumption. Also suitable for pre-preparation of formwork panels in winter.

7. Steaming.

An industrial version, the implementation of this method requires a double-walled formwork, which not only withstands the mass of the solution, but also brings hot steam to the surface. The processing quality is more than high, unlike other methods, steaming provides the most suitable conditions for cement hydration, namely, a humid hot environment. But due to its complexity, this technique is rarely used.

Comparison of advantages and limitations of heating technologies

UPGO SPECT are designed to solve a number of tasks: heating of inert materials in winter, water heating and space heating.

We offer steam-gas heating plants that produce heating of inert materials on BSU (sand, crushed stone, gravel, limestone):

The numbers indicate the rated thermal power of the installation in kilowatts.

The equipment is manufactured in accordance with the patent and certificate of conformity obtained by us.

How do inert ones warm?

(Selection guide).

The technology for producing concrete mixtures in winter is somewhat different from the technology for producing concrete in summer.

At low ambient temperatures of -5°C and below, several additional problems arise:

1. The temperature of inert materials (sand, gravel) is such that conditions arise for freezing of water during mixing, and the mixture does not work.
2. In the premises of a concrete plant, heating is required for the comfortable operation of personnel and units.
3. Ready-mixed concrete must be delivered to the construction site with a temperature of at least 15°C. Mixers transporting concrete are also filled with water at a temperature not lower than 40°C.

The first problem in mild frosts is partially solved by the use of antifreeze additives and heated water. The second is the use of electric heaters. The third problem is not solved without the use of special tools.

What is required for the production of concrete in winter?

1. Heating of inert (sand and gravel) to a temperature of 5°C to 20°C.
2. Water heating up to temperature from 40°С to 70°С.
3. Use of an economical space heating system.

What energy sources are available for inert and water heating?

We will not consider exotic energy sources like wind turbines, solar panels, thermal springs, etc. Let's formulate the problem as follows:

Required to work at low temperatures;

There is no central heating system;

The use of electricity is too expensive.

How to heat inert?

The most common energy sources are gas and diesel, and they work well with automation systems. It is possible to use fuel oil and heating oil. Firewood and coal are used less often due to the complexity of automation.

What equipment is used for heating inert materials?

The industry produces installations for heating sand, gravel, water, operating on various physical principles. The advantages and disadvantages of the installations are given below:

1. Heating of inert materials with hot air.

Fuel: diesel.

Advantages:

Air temperature up to 400 °C

Small dimensions;

Disadvantages:

Low efficiency (high energy consumption during operation, since the air does not efficiently transfer heat to materials, most of the heat goes into the atmosphere);

Slow heating of inert materials (30-60 minutes);

Low air pressure does not blow through fines and sand;

No process water heating;

Not used for space heating.

2. Heating of inert materials with steam.

Fuel: diesel.

Advantages:

High efficiency;

High efficiency of heating of inert materials;

Rapid heating of inert materials (10-20 minutes);

Average cost;

Can heat water

Small dimensions;

Electric power up to 2 kW.

Disadvantages:

They create high humidity of inert materials (due to steam condensation from 500 to 1000 kg per hour;

High-efficiency steam boilers with temperatures above 115 °C and pressures above 0.7 kg/cm² are supervised;

It is difficult to use for space heating (turns off when the concrete plant is idle).

3. Heating of inert materials with hot water or steam registers.

Fuel: diesel or central heating.

Advantages:

High efficiency;

Not complicated, cheap equipment;

Technical supervision permit is not required;

Can heat water

Can be used for space heating;

Very small dimensions;

Electric power up to 0.5 kW.

Disadvantages:

Often requires repair and maintenance of registers;

Low efficiency of heating of inert materials;

The heating process takes several hours.

4. Turbomatics (heating of inert steam-air mixture with heat exchangers).

Fuel: diesel.

Advantages:

High efficiency;

Technical supervision permit is not required;

No registers;

You can heat water.

Disadvantages:

Complex, expensive equipment;

Not applicable for space heating;

Large dimensions;

Electric power up to 18-36 kW (cyclically).

5. Steam-gas-air plants.

Heating of inert materials with flue gases.

Fuel: diesel.

Advantages:

High efficiency;

High efficiency of heating of inert materials (10-20 minutes);

Not complex equipment with an average cost;

Technical supervision permit is not required;

No registers;

The temperature of the mixture is up to 400 °C.

Can be used for space heating (there is a standby mode);

There is water heating for technological needs and refueling of mixers;

Small dimensions.

Disadvantages:

Electric power up to 18 kW (cyclically).