Warming up the soil in winter with fire. Laying power cable lines - methods for heating frozen soil

There is one a big problem by doing construction work during the cold season. Many builders are familiar with this problem and constantly face it.
The surface of the earth, gravel, clay, sand freezes, and the fractions freeze together, which makes it impossible to carry out excavation work without additional time.

There are several ways to thaw soil:

• 1. Brute force. Mechanical destruction.
• 2. Thawing using heat guns.
• 3. Burning. Oxygen-free combustion.
• 4. Defrosting using a steam generator.
• 5. Thawing with hot sand.
• 6. Thawing with chemical reagents.
• 7. Heating the soil with thermoelectric mats or a heating electric cable.

Each of the above methods has its own weaknesses. Long, expensive, poor quality, dangerous, etc.
The optimal method can be considered a method using an installation for heating soil and concrete. The earth is warmed by liquid circulating through hoses laid out on a large surface.

Advantages over other methods:

• Minimal preparation of the heated surface
• Independence and autonomy
• The heating hose is not energized
• The hose is completely sealed and is not afraid of water
• The hose and heat-insulating blanket are resistant to mechanical stress. The hose is reinforced synthetic fiber and have exceptional flexibility and tensile strength.
• The serviceability and readiness of the equipment for operation is monitored by built-in sensors. A puncture or rupture of the hose is visible visually. The problem can be fixed in 3 minutes.
• There are no restrictions on the heated surface.
• The hose can be laid as desired

Stages of work using the Wacker Neuson HSH 700 G surface heating unit:

Site preparation.
Clear the heated surface of snow.
Thorough cleaning will reduce the defrosting time by 30%, save fuel, and get rid of dirt and excess melt water that complicates further work.

Laying a hose with coolant.
The smaller the distance between the turns, the less time it will take to warm up the surface. The HSH 700G unit has enough hose to heat an area of ​​up to 400 m2. Depending on the inter-hose distance, the required area and heating rate can be achieved.

Vapor barrier of the heated area.
The use of a vapor barrier is mandatory. The unfolded hose is covered with an overlap of plastic wrap. The film will not allow the heated water to evaporate. Melt water will instantly melt the ice in the lower layers of the soil.

Laying thermal insulation material.
Insulation is laid over the vapor barrier. The more thoroughly the heated surface is insulated, the less time it will take to warm up the soil. The equipment does not require specific knowledge of skills and long-term training of personnel. The installation, steam and thermal insulation procedure takes from 20 to 40 minutes.

Advantages of technology using an installation for heating surfaces

• Heat transfer 94%
• Predictable result, complete autonomy
• Preheating time 30 minutes
• No risk of electric shock, does not create magnetic fields or interfere with control devices
• Hose laying in any shape, no restrictions on terrain
• Ease of operation, control, assembly, storage exceptional flexibility maneuverability and maintainability
• Does not affect or destroy nearby communications and environment
• The HSH 700 G unit is certified in Russia and does not require special permits for the operator

Possible applications for the Wacker Neuson HSH 700 G

• Soil thawing
• Laying communications
• Warming up the concrete
• Warming up complex structures(bridge columns, etc.)
• Warming up reinforcement structures
• Thawing gravel for laying paving stones
• Warming up prefabricated formwork structures
• Prevention of icing of surfaces (roofing, football fields, etc.
• Gardening (greenhouses and flower beds)
• Finishing work on construction site during the cold period
• Heating of residential and non-residential premises

Surface heating devices from Wacker Neuson are an economical and effective solution for the winter period, allowing projects to be completed on time.
In autumn and spring, they also make an invaluable contribution to the workload of your enterprise: after all, these devices speed up many technological processes.

Winter time is traditionally considered an unfavorable period for work in the construction industry. However, the use of thermoelectromatic 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 will be able to avoid downtime and sending your workers on forced leave. We will help you become the strongest company on the market!

Flexible heating mats are installed in areas that need to be defrosted, heated, or require frost protection. Installation and dismantling of mats takes very little time! The heating element of thermomats releases heat directly into 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 competitive advantage before other players in the market. You will be able to continue
work while others wait for the frozen ground to naturally thaw. The thermomat has already attracted great interest in the construction industry.

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

This is the future!

The scope of application is intended for consumers requiring frost-resistant 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 application

Defrosting soil and territories:

• Water supply and sewerage systems
• Cable trenches
• Shafts, plinths and areas for flooring
• Roofs and coverings
• Ice and snow removal

When freezing:

• Areas intended for cladding
• Sand masses, jigging sand
• Bulk masses
• Pipeline lines
• Turnout switches
• Floating piers

Pre-heating of soil or concrete:

• Grounds before foundation is laid
• Formwork and equipment for concrete work
• Increasing the degree of hardening of concrete and lightweight concrete slabs

A significant part of the territory of Russia is located in zones with long and harsh winter. However, construction is carried out year-round, in this regard, about 15% of the total volume of earthworks has to be carried out in winter conditions and when the soil is frozen. The peculiarity of developing soil in a frozen state is that when the soil freezes mechanical strength it increases, and development becomes more difficult. In winter, the labor intensity of soil development increases significantly ( handmade 4...7 times, mechanized 3...5 times), the use of some mechanisms is limited - excavators, bulldozers, scrapers, graders, at the same time, excavations in winter can be carried out without slopes. Water, which causes many problems in the warm season, becomes an ally of builders when frozen. Sometimes there is no need for sheet piling, almost always in drainage. Depending on specific local conditions, the following soil development methods are used:

■ protection of soil from freezing with subsequent development using conventional methods;

■ thawing of soil with its development in a thawed state;

■ development of frozen soil with preliminary loosening;

■ direct development of frozen soil.

5.11.1. Protecting the soil from freezing

This method is based on artificial creation on the surface of the site planned for development in winter time, thermal insulation cover with soil development in a thawed state. Prevention is carried out until the onset of stable negative temperatures, with advance removal from the insulated area surface waters. The following methods of installing a thermal insulation coating are used: preliminary loosening of the soil, plowing and harrowing of the soil, cross-loosening, covering the soil surface with insulation, etc.

Preliminary loosening of the soil, as well as plowing and harrowing is carried out on the eve of the onset of the winter period in the area intended for development in winter conditions. When loosening the soil surface upper layer acquires a loose structure with air-filled closed voids with sufficient thermal insulation properties. Plowing is carried out with tractor plows or rippers to a depth of 30...35 cm, followed by harrowing to a depth of 15...20 cm. This treatment, in combination with the naturally formed snow cover, delays the onset of soil freezing by 1.5 months, and for the subsequent period reduces the total freezing depth is approximately 73. Snow cover can be increased by moving snow onto the site with bulldozers or motor graders, or by installing several rows of snow fences made of lattice panels measuring 2 X 2 m perpendicular to the direction of the prevailing winds at a distance of 20...30 m row from row.

Deep loosening is carried out with excavators to a depth of 1.3. ..1.5 m by transferring the excavated soil to the area where the earthen structure will subsequently be located.

Cross loosening of the surface to a depth of 30...40 cm, the second layer of which is located at an angle of 60...900, and each subsequent penetration is carried out with an overlap of 20 cm. Such treatment, including snow cover, delays the onset of soil freezing by 2.5.. .3.5 months, the total freezing depth decreases sharply.

Preliminary treatment of the soil surface by mechanical loosening is especially effective in insulating these areas of the ground.

Covering the soil surface with insulation. For this, cheap local materials are used - tree leaves, dry moss, peat fines, straw mats, shavings, sawdust, snow. The simplest way is to lay these insulation materials with a layer thickness of 20...40 cm directly on the ground. Such surface insulation is used mainly for small-area recesses.

Shelter with air gap. It is more effective to use local materials in combination with an air gap. To do this, lay beds 8...10 cm thick on the surface of the ground, on them are slabs or other available material - branches, twigs, reeds; a layer of sawdust or wood shavings 15...20 cm thick, protecting them from being blown away by the wind. Such a shelter is extremely effective in the conditions of central Russia; it actually protects the soil from freezing throughout the winter. It is advisable to increase the area of ​​the shelter (insulation) on each side by 2...3 m, which will protect the soil from freezing not only from above, but also from the sides.

Once soil development begins, it must be carried out at a rapid pace, immediately to the entire required depth and in small areas. In this case, the insulating layer must be removed only in the area being developed, otherwise, during severe frosts, a frozen crust of soil will quickly form, making work difficult.

5.11.2. Method of thawing soil with its development in a thawed state

Thawing occurs due to thermal effects and is characterized by significant labor intensity and energy costs. It is used in rare cases when other methods are unacceptable or unacceptable - near existing communications and cables, in cramped conditions, during emergency and repair work.

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

Thawing of the soil from top to bottom. Heat spreads in the vertical direction from the day surface deep into the soil. The method is the simplest and requires virtually no preparatory work, is most often used in practice, although from the point of view of economical energy consumption it is the most imperfect, since the heat source is located in the cold air zone, therefore significant energy losses into the surrounding space are inevitable.

Thawing of soil from bottom to top. Heat spreads from the lower boundary of the frozen soil to the day surface. The method is the most economical, since soldering occurs under the protection of the frozen crust of the soil and heat loss into the space is practically eliminated. The required thermal energy can be partially saved by leaving the top crust of the soil in a frozen state. She has the most low temperature, therefore requiring large amounts of energy for soldering. But this one thin layer 10...15 cm of soil will be easily excavated by an excavator; the machine’s power is quite enough for this. Main disadvantage This method requires labor-intensive preparatory operations, which limits its scope of application.

Radial soil thawing occupies an intermediate position between the two previous methods in terms of thermal energy consumption. Heat spreads radially in the ground from vertically installed heating elements, but in order to install them and connect them to work, significant preparatory work is required.

To carry out thawing of the soil using any of these three methods, it is necessary to first clear the area of ​​snow, so as not to waste thermal energy on thawing it and it is unacceptable to over-wet the soil.

Depending on the coolant used, there are several defrosting methods.

Defrosting by direct combustion of fuel. If in winter you need to dig 1...2 holes, the simplest solution is to make do with a simple fire. Maintaining a fire during a shift will lead to thawing of the soil underneath it by 30...40 cm. Having extinguished the fire and well insulating the heating area with sawdust, thawing of the soil inward will continue due to the accumulated energy and during a shift can reach a total depth of up to 1 m. If necessary, You can light the fire again or develop thawed soil and build a fire at the bottom of the pit. The method is used extremely rarely, since only a small part of the thermal energy is spent productively.

The fire method is applicable for excavating small trenches; a link structure is used (Fig. 5.41) from a series of truncated metal boxes, from which a gallery is easily assembled required length, in the first of them there is a combustion chamber for solid or liquid fuel (wood fire, liquid and gaseous fuel with combustion through a nozzle). Thermal energy moves to the exhaust pipe of the last box, which creates the necessary draft, thanks to which hot gases pass along the entire gallery and the soil under the boxes warms up along the entire length. It is advisable to insulate the top of the box; thawed soil is often used as insulation. After the change, the unit is removed, the strip of thawed soil is covered with sawdust, and further soldering continues due to the heat accumulated in the soil.

Electric heating Essence this method consists of passing an electric current through the soil, as a result of which it acquires a positive temperature. Horizontal and vertical electrodes in the form of rods or strip steel are used. For the initial movement of electric current between the rods, it is necessary to create a conductive environment. Such a medium can be thawed soil, if the electrodes are driven into the ground until the soil thaws, or on the surface of the soil, cleared of snow, a layer of sawdust 15...20 cm thick, moistened with a saline solution with a concentration of 0.2-0.5%, is poured. Initially, the wetted sawdust acts as a conductive element. Under the influence of heat generated in the sawdust layer, the top layer of soil heats up, melts and itself becomes a conductor of current from one electrode to another. Under the influence of heat, the underlying layers of soil thaw. Subsequently, the distribution of thermal energy occurs mainly in the soil thickness; the sawdust layer only protects the heated area from heat loss into the atmosphere, for which purpose it is advisable to cover the sawdust layer roll materials or shields. This method is quite effective at a depth of soil freezing or thawing of up to 0.7 m. Electricity consumption for heating 1 m3 of soil ranges from 150...300 kWh, the temperature of heated sawdust does not exceed 80...90 °C.

Rice. 5.41. Installation for thawing soil with liquid fuel:

A - general form; b - diagram of the insulation of the box; 1 - nozzle; 2 - insulation (sprinkling with thawed soil); 3 - boxes; 4 - exhaust pipe; 5 - cavity of thawed soil

Thawing of soil with strip electrodes placed on the soil surface, cleared of snow and debris, leveled if possible. The ends of the strip iron are bent upward by 15...20 cm for connection to electrical wires. The surface of the heated area is covered with a layer of sawdust 15...20 cm thick, moistened with a solution of sodium chloride or calcium with a consistency of 0.2...0.5%. Since soil in a frozen state is not a conductor, at the first stage the current moves through sawdust moistened with the solution. Next, the top layer of soil is heated and the thawed water begins to conduct electric current, a process with time goes by deep into the soil, sawdust begins to act as a thermal protection for the heated area from heat loss into the atmosphere. Sawdust is usually covered with roofing felt, glassine, shields, and other protective materials. The method is applicable at a heating depth of up to 0.6...0.7 m, since at greater depths the voltage drops, the soils are put into operation less intensively and heat up much more slowly. In addition, they are sufficiently saturated with water in the fall, which requires more energy to transition to a thawed state. Energy consumption ranges from 50-85 kWh per 1 m3 of soil.

Thawing of soil using rod electrodes (Fig. 5.42). This method is carried out top-down, bottom-up and combined methods. When thawing the soil with vertical electrodes, reinforcing iron rods with a pointed lower end are driven into the ground in a checkerboard pattern, usually using a 4x4 m frame with cross-tensioned wires; the distance between the electrodes is within 0.5-0.8 m.

Rice. 5.42. Thawing of soil with deep electrodes:

a - from bottom to top; b - from top to bottom; 1 - thawed soil; 2 - frozen soil; 3 - electrical wire; 4 - electrode, 5 - layer of waterproofing material; 6 - layer of sawdust; I-IV - thawing layers

When warming up from top to bottom, the surface is first cleared of snow and ice, the rods are driven into the ground 20...25 cm, and a layer of sawdust soaked in a salt solution is laid. As the soil warms up, the electrodes are driven deeper into the soil. The optimal heating depth will be within 0.7...1.5 m. The duration of soil thawing under the influence of electric current is approximately 1.5...2.0 days, after which the increase in thawing depth will occur due to accumulated heat for another 1 ...2 days. The distance between the electrodes is 40...80 cm, energy consumption compared to strip electrodes is reduced by 15...20% and amounts to 40...75 kWh per 1 m3 of soil.

When heating from bottom to top, wells are drilled and electrodes are inserted to a depth exceeding the depth of the frozen soil by 15...20 cm. The current between the electrodes flows through the thawed soil below the freezing level; when heated, the soil warms the overlying layers, which are also included in the work. With this method, a layer of sawdust is not required. Energy consumption is 15...40 kW/h per 1 m3 of soil.

The third, combined method will take place when the electrodes are buried in the underlying thawed soil and a sawdust backfill impregnated with a saline solution is placed on the day surface. The electrical circuit will close at the top and bottom, and the soil will thaw from top to bottom and bottom to top at the same time. Since the labor intensity of preparatory work with this method is the highest, its use can be justified only in exceptional cases when accelerated thawing of the soil is required.

Defrosting by currents high frequency. This method makes it possible to sharply reduce preparatory work, since the frozen soil remains conductive to high-frequency currents, so there is no need for large penetration of electrodes into the soil and for the installation of sawdust backfill. The distance between the electrodes can be increased to 1.2 m, i.e. their number is reduced by almost half. The process of soil thawing proceeds relatively quickly. The limited use of the method is due to the insufficient production of high-frequency current generators.

One of the methods that has now lost its effectiveness and has been replaced by more modern ones is thawing the soil with steam or water needles. On this day, it is necessary to have sources of hot water and steam, with a shallow freezing depth of up to 0.8 m. Steam needles are a metal pipe up to 2 m long and 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 with flexible rubber hoses if they have taps. The needles are buried in wells that have been previously drilled to a depth approximately equal to 70% of the thaw depth. The wells are closed with protective caps equipped with seals for the passage of a 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 thermal insulation material, most often sawdust. The needles are placed in a checkerboard pattern with a distance between centers of 1-1.5 m.

Steam consumption per 1 m3 of soil is 50... 100 kg. Due to the release of latent heat of vaporization by steam in the soil, heating of the soil is especially intense. This method requires approximately 2 times more thermal energy consumption than the vertical electrode method.

Thawing of soil using thermal electric heaters. This method is based on the transfer of heat to frozen soil by contact method. As main technical means Electrical mats are used, made of a special heat-conducting material through which electric current is passed. Rectangular mats, the dimensions of which can cover a surface of 4...8 m2, are laid on the thawed area and connected to a 220 V source of electricity. In this case, the generated heat effectively spreads from top to bottom into the thickness of the frozen soil, which leads to its thawing. The time required for thawing depends on the ambient temperature and the depth of soil freezing and averages 15-20 hours.

5.11.3. Development of frozen soil with preliminary loosening

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

Mechanical loosening of frozen soil using modern construction machines increased power is becoming increasingly widespread. In accordance with environmental requirements, before winter development of soil, it is necessary to remove a layer of plant soil from the site intended for development with a bulldozer in the autumn. Mechanical loosening is based on cutting, splitting or chipping frozen soil by static (Fig. 5.43) or dynamic action.

Rice. 5.43. Loosening frozen soil by static action:

a - a bulldozer with active teeth, b - an excavator-ripper, 1 - direction of loosening

With dynamic impact on the soil, it is split or chipped by free-fall and directional action hammers (Fig. 5.44). In this method, loosening of the soil is carried out using free-fall hammers (ball and wedge hammers), suspended on ropes on the booms of excavators, or with directional hammers, when loosening is carried out by chipping the soil. Loosening mechanically allows for its development by earth-moving and earth-moving and transport machines. Hammers weighing up to 5 tons are dropped from a height of 5...8 m: a ball-shaped hammer is recommended to be used when loosening sandy and sandy loam soils, wedge hammers - for clayey ones (with a freezing depth of 0.5...0.7 m). Diesel hammers on excavators or tractors are widely used as directional hammers; they allow the destruction of frozen soil to a depth of up to 1.3 m (Fig. 5.45).

The static impact is based on the continuous cutting force in the frozen soil of a special working body - a ripper tooth, which can be the working equipment of a hydraulic backhoe excavator or be an attachment on powerful tractors.

Loosening with tractor-based static rippers involves quality attachments a special knife (tooth), the cutting force of which is created due to the traction force of the tractor.

Machines of this type are designed for layer-by-layer loosening of soil to a depth of 0.3...0.4 m. The number of teeth depends on the power of the tractor, with a minimum tractor power of 250 hp. one tooth is used. Loosening of the soil is carried out by parallel layer-by-layer penetrations every 0.5 m with subsequent transverse penetrations at an angle of 60...900 to the previous ones. Loose soil is moved to the dump using bulldozers. It is advisable to attach attachments directly to the bulldozer and use it to independently move loosened soil (see Fig. 5.21). Ripper productivity is 15...20 m3/h.

The ability of static rippers to develop frozen soil layer by layer makes it possible to use them regardless of the depth of soil freezing. Modern rippers based on tractors with bulldozer equipment, due to their wide technological capabilities, are widely used in construction. This is due to their high efficiency. Thus, the cost of developing soil using rippers is 2...3 times lower compared to the explosive method of loosening. The loosening depth of these machines is 700...1400 mm.

Fig.5.45. Scheme of joint operation of a diesel hammer and a straight shovel excavator

Explosion loosening of frozen soils is effective for significant volumes of frozen soil development. The method is used mainly in undeveloped areas, and in limited areas - with the use of shelters and explosion localizers (heavy loading plates).

Depending on the depth of soil freezing, blasting operations are performed (Fig. 5.46):

■ using the method of hole and slot charges at a soil freezing depth of up to 2 m;

■ by the method of borehole and slot charges at a freezing depth of over 2 m.

Holes are drilled with a diameter of 22...50 mm, holes - 900...1100 mm, the distance between the rows is taken from 1 to 1.5 m. Slots at a distance of 0.9... 1.2 m from one another are cut with a slitting machine. Milling-type molds or bar machines. Of the three adjacent slits, explosive is placed only in the middle one; the outer and intermediate slits serve to compensate for the displacement of frozen soil during an explosion and to reduce the seismic effect. The cracks are charged with elongated or concentrated charges, after which they are covered with melted sand on top. If the preparatory work is carried out with high quality during the blasting process, the frozen soil is completely crushed without damaging the walls of the pit or trench.

Rice. 5.46. Methods for loosening frozen soil by explosion:

a - blasthole charges; b - the same, well; c - the same, boiler; g - the same, small-chambered; d, f - the same, chamber; g - the same, slotted; 1 - explosive charge; 2 - stope; 3 - face chest; 4 - sleeve; 5 - pit; b - adit; 7 - working slot; 8 - compensation slot

The soil loosened by explosions is developed by excavators or earth-moving machines.

5.11.4. Direct development of frozen soil

Development (without preliminary loosening) can be carried out by two methods - block and mechanical.

The block development method is applicable for large areas and is based on the fact that the solidity of frozen soil is broken by cutting it into blocks. Using attachments on a tractor - a bar machine - the soil is cut with mutually perpendicular penetrations into blocks 0.6...1.0 m wide (Fig. 5.47). For shallow freezing depths (up to 0.6 m), it is enough to make only longitudinal cuts.

Bar machines that cut slits have one, two or three cutting chains mounted on tractors or trench excavators. Bar machines allow you to cut cracks 1.2...2.5 m deep in frozen soil. They use steel teeth with a cutting edge made of a durable alloy, which extends their service life, and when worn or abraded, allows you to quickly replace them. The distance between the bars is taken depending on the soil at 60... 100 cm. Development is carried out using backhoe excavators with a large-capacity bucket, or blocks of soil are dragged from the excavated site to a dump using bulldozers or grantors.

Fig.5.47. Scheme of block soil development:

a - cutting slots with a bar machine; b - the same, with the blocks being removed by a tractor; c - development of a pit with the removal of blocks of frozen soil using a crane; I - layer of frozen soil; 2 - cutting chains (bars); 3 - excavator; 4 - cracks in frozen soil; 5 - chopped soil blocks; 6 - blocks moved from the site; 7 - crane tables; 8 - vehicle; 9 - pincer grip; 10 - Construction crane; 11 - tractor

The mechanical method is based on force, and more often in combination with shock or vibration effects on frozen soil. The method is implemented using conventional earthmoving and earthmoving-transport machines and machines with working parts specially designed for winter conditions (Fig. 5.48).

Conventional production machines are used in initial period winters, when the depth of soil freezing is insignificant. A forward and backhoe can excavate soil at a freezing depth of 0.25...0.3 m; with a bucket with a capacity of more than 0.65 m3-0.4 m; dragline excavator - up to 0.15 m; bulldozers and scrapers are able to develop frozen soil to a depth of 15 cm.

Rice. 5.48. Mechanical method direct soil development:

a - excavator bucket with active teeth; b - development of soil with a backhoe excavator and a gripping and pincer device; c - earth-moving and milling machine; 1 - ladle; 2 - bucket tooth; 3 - drummer; 4 - vibrator; 5 - gripping and pincer device; b - bulldozer blade; 7 - hydraulic cylinder for raising and lowering the working body; 8 - working body (mill)

Designed for winter conditions special equipment for single-bucket excavators - buckets with vibro-impact active teeth and buckets with a gripping-pincer device. Energy consumption for cutting soil is approximately 10 times more than for chipping. Installing vibration-impact mechanisms, similar in operation to a jackhammer, into the cutting edge of an excavator bucket brings good results. Due to the excessive cutting force, such single-bucket excavators can develop frozen soil layer by layer. The process of loosening and excavating the soil turns out to be one and the same.

Soil development is also carried out using multi-bucket excavators, specially designed for digging trenches in frozen soil. For this purpose there is a special cutting tool in the form of fangs, teeth or crowns with hard metal inserts, mounted on buckets. In Fig. 5.48, and shows the working body of a multi-bucket excavator with active teeth for the development of rocky and frozen soils.

Layer-by-layer development of soil can be carried out with a specialized earth-moving and milling machine, which removes shavings up to 0.3 m deep and 2.6 m wide. The developed frozen soil is moved using bulldozer equipment included in the machine.

The main purpose of heating concrete is to maintain the right conditions removal of moisture when carrying out work in winter or for 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, grade of strength of the mixture, budget and environmental conditions. To achieve the desired effect, heating must be uniform and economically feasible, top scores observed when combined.

Overview of heating methods

1. Electrodes.

Simple and reliable way electrical heating, which consists of placing reinforcement or wire rod 0.8-1 cm thick in a wet solution, forming a single conductor with it. Heat release occurs 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 reduced voltage from 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 when heating walls and columns. Electricity 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 agreement with specialists (a design for their placement is drawn up, excluding contact with metal frame). At the end of the process, the rods remain inside and re-use is excluded.

2. Laying wires.

The essence of the method is to place an electric wire (in contrast to electrodes - insulated) in the thickness of the solution, heated by passing current and uniformly releasing heat. One of the following types is used as work items:

• PNSV – polyvinyl chloride insulated steel cable.
• 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 heat with virtually no losses and ensure its uniform distribution.

PNSV is cheaper; if necessary, it is laid over the entire area of ​​the structure (the length is limited only by the power of the step-down transformer); for these purposes, a cross-section from 1.2 to 3 mm is suitable. Features of the heating technology include the need to use installation wires with an aluminum core on open areas. The automatic reclosure 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, and it cannot be cut. When adding a current control device to it, heating is carried out more smoothly and economically. In general, both options are considered effective when concreting in winter; the only disadvantages include the complexity of installation 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 elements being processed are covered from the cold with a tarpaulin; creating such a tent allows you to achieve indoor conditions from +35 to 70 °C. Heating is carried out from an external source, which can be easily transferred to another place without the need for wire consumption or special equipment. Due to the difficulty of covering large objects and affecting only the outer layers, this method is more often used for small volumes of concreting or when there is a sharp drop in temperature. Energy consumption in comparison with electrodes or PNSV is acceptable, when activated diesel guns Heating is possible in facilities without power supply.

4. Thermal mats.

The operating principle of this technology is based on covering the freshly poured solution with polyethylene and infrared film sheets in a moisture-resistant shell. Thermal mats are connected to a regular network, the energy consumption varies between 400-800 W/m2, when the limit reaches +55 ° C they are turned off, which reduces the cost of electrical heating of concrete. The maximum effect of use 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 come into contact with open air and moisture without problems, in addition to concrete structures they are successfully used to warm the soil.

At proper care(no overlaps, bends strictly along designated lines, protection with polyethylene) IR films can withstand at least 1 year of active use. But despite 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: between two sheets of moisture-resistant plywood an infrared film or asbestos-insulated wires are placed, which generate heat when connected to the network. This method provides heating in winter to a depth of up to 60 mm; thanks to local exposure, the risk of cracking or overstrain 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 the technology cannot be called simple. When concreting the foundation, a solution with a temperature of at least +15 °C is poured into the heating formwork; the soil needs to be preheated.

6. Induction method.

The operating principle is based on the generation 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 average energy consumption. Also suitable for preliminary preparation formwork panels in winter.

7. Steaming.

An industrial version, to implement this method, a double-walled formwork is required, which not only can withstand the mass of the solution, but also supply hot steam to the surface. The quality of processing is more than high; unlike other methods, steaming ensures maximum suitable conditions for cement hydration, namely a moist hot environment. But due to its complexity, this technique is rarely used.

Comparison of advantages and limitations of heating technologies

Way	Optimal scope of application	Advantages	Disadvantages, limitations
Electrodes	Pouring vertical structures	Quick installation and warm-up, just place the electrode in the concrete and connect it to an alternating current source	Significant energy consumption - from 1000 kW per 3-5 m3
PNSV	Foundations and floors when concreting in winter	High efficiency, uniformity. Heating with wire allows you to achieve 70% strength in a few days	Need for step-down transformer and wire for cold ends
VET or KDBS		The same, plus operation from a simple network	High cable cost, limited section lengths
Thermal emitters	Designs with low thickness	Possibility of temperature control, use during sudden cold snaps, minimum wires, relatively low energy consumption	The impact is carried out locally, high-quality heating occurs only in the outer layers
Thermomat	Soil before pouring mortar, floors	Repeated use, the ability to control the temperature of the sweep, achieving 30% of brand strength within 24 hours	High cost of mats, presence of fakes
Heating formwork	Rapid construction objects (combination with sliding formwork technology)	Ensuring uniform heating, the possibility of high-quality grouting of joints	Standard sizes high price, average efficiency
Induction winding	Columns, crossbars, beams, supports	Uniformity	Not suitable for floors and monoliths
Steaming	Industrial construction objects	Good quality of heating	Complexity, high cost

Earthworks in winter period complicated by the need for preliminary soil preparation. The use of jackhammers or other mechanical action is not always justified, and sometimes is simply impossible. There is a possibility of damaging underground utilities or causing damage standing nearby buildings. Therefore, thermal methods of exposure have become widespread.

Traditional types of heating frozen soil

Many technologies have been developed based on various thermal principles. Each of them has advantages and disadvantages.

Reflex oven

Fast, convenient and mobile method well suited for working in urban areas. Nichrome wire 3.5 mm thick serves as a heat generator. The direction of thermal radiation is corrected by a reflector made of chrome plated sheet about 1 mm thick.


The reflector itself is protected by a metal casing. Between the walls of two metals there is air bag, which plays the role of thermal protection. The stove operates from a 127/220/380V network and is capable of heating 1.5 m2 of soil. For warming up cubic meter soil requires about 50 kW/hour electrical energy and 10 hours time. Significant flaws of the method:

1. high probability of electric shock to unauthorized persons. Fencing and security are required while the installation is operating;
2. small coverage area;
3. an energy supply system with a capacity of about 20 kW/hour is needed to operate a complex of three units.

Electrodes

They are made from round or strip steel, driven into the ground and connected to a power source. The surface of the soil is covered with sawdust and soaked in saline solution. This layer serves both as a conductor and as insulation.


Electricity consumption for thawing a cubic meter of soil is 40-60 kW, and the process takes 24-30 hours. Among the disadvantages of the method it should be noted:

1. high probability of electric shock to unauthorized persons;
2. requires a constant supply of electricity;
3. defrosting of the soil takes a very long time;

Open flame

The method is based on the combustion of liquid or solid fuel in a special device consisting of open tanks. The design provides that the first box serves as a combustion chamber, and the last is equipped with an exhaust pipe. Users note the disadvantages of the technology:

1. significant losses of thermal energy;
2. You must first complete a set of preparatory work;
3. harmful emissions and the need for constant monitoring.

Chemical method

To defrost the soil using chemical reagents holes are drilled in the soil. Sodium chloride is then poured into the holes to dissolve the ice. The entire process lasts from six to eight days. Disadvantages of the chemical method:

1. defrosting takes a long time;
2. the need for arrangement of pits;
3. the environmental friendliness of the process raises many questions;
4. materials cannot be reused.

Steam needles

Actually, a pipe two meters long and up to 50 mm in diameter can hardly be called a needle. Water vapor is supplied through it into the soil. To install the needles, you first need to drill holes to a depth of at least 70% of the height of the thawing layer. After connecting to the steam supply system, the wells themselves are closed with caps and covered with a layer of thermal insulating material.


The main disadvantages of the method are:

1. need for training;
2. the need for a steam generator;
3. formation and further freezing of condensate;
4. careful control over the process is required.

Hot coolant

The soil is heated by the hot mineral (100-200 degrees Celsius) that covers the surface of the earth. Road waste is often used - defective asphalt or concrete chips. Defrosting time is at least 20-30 hours. Among the shortcomings this method it should be noted:

1. dependence on a subcontractor;
2. heat loss during coolant delivery;
3. the need to clean up the coolant after the ground freezes;
4. long thawing period.

Tubular electric heaters

The technology involves the transfer of thermal energy by contact method. The working elements are electric needles. They are meter-long pipes with a diameter of 50-60 mm. Electric heating elements are installed inside.
The heating elements are located horizontally in the ground and connected to the circuit in series. The disadvantages of this method are:

1. the need for constant monitoring;
2. possibility of electric shock;
3. small thawing area;
4. need for preparatory work.

Heating the soil with thermoelectromatic devices

A great alternative existing methods warming up the soil is heating it using thermomats. They ensure uniform heating of the soil throughout its depth and maintain the set temperature automatically.
The equipment is manufactured on the basis of heat-emitting films. They are produced in various sizes and configurations. The panel thickness is about 10 mm. It operates from a single-phase network and can generate temperatures up to 70 0C. The directional action of infrared radiation determines high efficiency device operation.


Advantages of using FlexiHit thermoelectromats.