Heating the soil with solid fuel. Methods for heating concrete mortar in winter
The labor intensity 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 inability to use certain types of earthmoving and earthmoving-transport machines, reduced productivity and accelerated wear of the working parts of the equipment. And yet one advantage frozen ground has - you can dig pits in it without installing slopes.
There are four main ways to carry out excavation during the cold season:
- protection land plot works against freezing with the further use of conventional earth-moving machines;
- preliminary loosening and excavation of frozen soil;
- direct development of soil in a frozen state, i.e. without any preparation;
- bringing to a thawed state and subsequent removal.
Let's look at each of the above methods in detail.
Protecting soils from freezing
Protection from low temperatures is provided to the soil by loosening the top layer, covering insulating materials and pouring aqueous salt solutions.
Plowing and harrowing of the land plot is carried out in the sector of further work on soil extraction. The result of such loosening is the input large quantity 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 with rippers or factor plows, its depth is 200-350 mm. Next, harrowing is carried out in one or two directions (crosswise) 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 insulation when covering the site of future work is performed by cheap local materials - dry moss, sawdust and shavings, fallen tree leaves, slag and straw mats, you can use PVC film. Bulk materials are placed on the surface in a 200-400 mm layer. Insulation of the soil surface is most often carried out on small plots of land.
Frozen soil - loosening and excavation
To reduce the mechanical strength of winter soil, methods of mechanical and explosive processing are used. The extraction of the soil loosened in this way is then carried out in the usual way - using earthmoving machines.
Mechanical loosening. During its implementation, the soil is cut, chipped and split due to static or dynamic loads.
Static loads on frozen soil are carried out metal tool cutting type - tooth. A special hydraulically driven design, equipped with one tooth or more, is carried out along the work site while being placed on a crawler excavator. This method allows you to remove soil layer by layer to a depth of up to 400 mm for each pass. During the loosening process, the installation equipped with a tooth is first pulled parallel to the previous passes with a distance of 500 mm from them, then it is carried transversely to them at an angle of 60 to 90 degrees. The volume of frozen soil excavation reaches 20 cubic meters per hour. Layer-by-layer static development of frozen soil ensures the use of loosening installations at any depth of soil freezing.
Impact loads on unpaved areas allow you to reduce the mechanical strength of frozen ground due to dynamic effects. Hammers are used free fall, providing splitting and loosening, or hammers with a directed action for loosening by splitting. In the first case, a hammer is used in the form of a ball or cone with a maximum mass of 5 tons - it is secured with a rope to the boom of an excavator and, after being lifted to a height of five to eight meters, it is dropped onto the work site. Ball hammers are best suited for sandstones and sandy loams, clay soils Conical hammers are effective, provided that the freezing depth does not exceed 700 mm.
Directed action on frozen soil is carried out by diesel hammers mounted on a tractor or excavator. They are used on any soil provided the freezing depth is no more than 1300 mm.
Reducing the strength of frozen ground by explosion is most effective - this method allows for winter excavation at a depth of 500 mm and when significant volumes need to be extracted. In undeveloped areas, open blasting is carried out, and in partially built-up areas, it is necessary to first install shelters and explosion limiters - massive slabs of metal or reinforced concrete. The explosive is placed in a crack or hole (with a loosening depth of up to 1500 mm), and if it is necessary to excavate soil at greater depths, in cracks and wells. Drilling or milling machines are used to cut slots; the slots are made at a distance of 900-1200 mm from each other.
The explosive is placed in the middle (central) slot, and the slots located nearby will provide compensation for the explosive shift of frozen soil and dampen the shock wave, thereby preventing destruction outside the work area. An elongated charge or several short charges at once are placed in the gap, 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 the excavation, will remain intact.
Development of frozen soil without its preparation
There are two methods of direct soil development in low temperature conditions - mechanical and block.
The technology for mechanical development of frozen soils is based on force, in some cases including shock and vibration. During its implementation, both conventional earthmoving machines and those equipped with special tools are used.
At shallow freezing depths, conventional earth-moving machines are used to extract soil: excavators with a direct or reverse bucket; draglines; scrapers; bulldozers. Single-bucket excavators can be equipped with special attachments - buckets with gripping jaws and vibration-impact teeth. Such equipment allows you to influence frozen soil through excessive cutting force and carry out its layer-by-layer development, combining loosening and excavation in one working operation. 
Layer-by-layer soil extraction is carried out with a special earth-moving and milling installation, which cuts off layers 2600 mm wide and up to 300 mm deep from the work site. The design of this machine includes bulldozer equipment that ensures the movement of cut soil.
The essence of block mining is cutting frozen soil into blocks and then removing them using a tractor, excavator or construction crane. The 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 remove the blocks it is enough to make cuts along the area. 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 maintaining a positive temperature will not interfere with the separation of soil blocks. The distance between the slits should be approximately 12% less than the edge width of the excavator bucket. Extraction of soil blocks is carried out using backhoe excavators, because... It is quite difficult to unload them from the bucket of a straight shovel.
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 top supply of heat to the ground is the least effective - the source of thermal energy is located in the air space and is actively cooled by air, i.e. Substantial part 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 costs energy, as heat spreads under a strong 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 using thermal elements vertically recessed into the ground. The effectiveness of radial thawing is between the results of upper and lower soil heating. To implement this method, somewhat smaller, but still quite high amounts of work on preparing the heating are required.
Defrosting the soil in winter is carried out using fire, electric thermoelements and hot steam.
The fire technique is applicable for digging relatively narrow and shallow trenches. A group of metal boxes is placed on the surface of the work site, 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 ignited. The gallery of boxes becomes a horizontal exhaust pipe - the exhaust comes from the last box, and combustion products move along the gallery and heat the ground. To reduce heat loss from contact of the box body with air, they are covered with slag or melted soil from the area where work was carried out previously. The strip of defrosted soil formed at the end of heating must be covered with sawdust or covered with PVC film so that the accumulated heat contributes to further thawing.
Electrical 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 using 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 the electrodes placed on it is covered with sawdust (layer thickness - 150-200 mm), pre-moistened with a saline solution (salt concentration - 0.2-0.5%) in an amount equal to the initial mass of sawdust. The task of sawdust soaked in saline solution is to conduct current, since frozen soil will not conduct current at the initial stage of work. The top layer of sawdust is closed PVC film. As it warms up, the upper ground layer becomes a current conductor between the electrodes and the intensity of thawing increases significantly - first the middle layer of soil is thawed, and then those located below. As the layers of soil are included in the conduction of electric current, the layer of sawdust begins to perform a secondary task - the conservation of thermal energy in the work area, for which it is necessary to cover the sawdust wooden shields or roofing felt. Thawing of frozen soil with horizontal electrodes is carried out to a freezing depth of up to 700 mm, the energy consumption when heating a cubic meter of earth is 150-300 MJ, the sawdust layer is heated to 90 o C, no more. 
Vertical electrode defrosting is carried out using rods made of reinforcing steel and having one sharp end. If the freezing depth of the soil is 700 mm, the rods are first driven in to a depth of 200-250 mm in a checkerboard pattern, and after the top layer has thawed, they are sunk to a greater depth. In the process of vertical defrosting of the soil, it is necessary to remove the snow that has accumulated on the surface of the site and cover it with sawdust soaked in saline solution. The heating process proceeds in the same way as with horizontal thawing using strip electrodes - as it thaws upper layers 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 defrost on their own thanks to the accumulated thermal energy. Electricity costs for vertical defrosting are slightly lower than for horizontal defrosting.
For electrode heating of the soil in the direction from bottom to top, it is necessary preliminary preparation wells - they are drilled 150-200 mm deeper than the freezing depth. The wells are located in a checkerboard pattern. This method characterized by lower energy costs - about 50-150 MJ per cubic meter of soil.
The electrode rods are inserted into the prepared wells, reaching the unfrozen layer of the earth, the surface of the area is covered with sawings soaked in saline solution, and laid on top plastic film. As a result, the thawing process occurs in two directions - from top to bottom and from bottom to top. This method Thawing of frozen soil is carried out rarely and only when it is necessary to urgently defrost an area for excavation.
Steam defrosting 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, wells are drilled in the ground (checkerboard pattern, distance 1000-1500 mm) with a length of 70% of the required thawing depth. Metal caps equipped with seals are placed on the holes of the well, 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 area 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 compared to heating with buried electrodes.
The method of thawing frozen soil using contact electric heaters is externally similar to steam defrosting. Heating elements with insulation from the metal body of the needle are installed in hollow metal needles, about 1000 mm long and no more than 60 mm in diameter. When connecting power a heating element transfers thermal energy to the body of the needle-pipe, and it to the layers of the soil. Thermal energy during heating it spreads radially.
There is one a big problem by doing construction work ah 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 weak sides. 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
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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.
How less distance between 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 plastic film overlap 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.
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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
- Laying the hose in free form, no restrictions on terrain
- Ease of operation, control, assembly, storage exceptional flexibility maneuverability and maintainability
- Does not affect or destroy nearby communications and the 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 (bridges, 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 a construction site during the “cold” period
- Heating of residential and non-residential premises
Surface heating devices from Wacker Neuson are 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.
A significant part of Russia's territory is located in areas with long and severe winters. However, construction is carried out year-round, in this regard, about 15% of the total volume earthworks must be performed 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, and almost always for 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, a thermal insulation cover with the development of soil in a thawed state. Protection is carried out before the onset of stable negative temperatures, with advance removal of surface water from the insulated area. Apply following methods thermal insulation coating devices: 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, practically does not require preparatory work, it is most often applicable 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. It has the lowest temperature, so it requires a lot 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. The main disadvantage of this method is the need to perform labor-intensive preparatory operations, which limits the scope of its 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 operation, significant preparatory work.
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 number of truncated metal boxes, from which a gallery of the required length is easily assembled; in the first of them, a combustion chamber for solid or liquid fuel is installed (a fire made of wood, liquid and gaseous fuel 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 its 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 The essence of this method is to pass 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 warms up and the thawed water begins to conduct electricity, the process goes deeper into the soil over time, the 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 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 with high frequency currents. 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 hot water and steam, at 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 high-power construction machines is becoming increasingly widespread. In accordance with environmental requirements, before winter excavation it is necessary to autumn period Use a bulldozer to remove a layer of plant soil from the area planned for development. 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 with 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 is used as an attachment 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 the initial period of winter, 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)
For winter conditions, special equipment has been developed 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, a special cutting tool is used 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 earthmoving 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.
Our country is located in northern latitudes. Winter period with negative temperatures takes a lot of time from builders. However, you can’t stop capital construction, if you warm up the soil. This procedure is becoming increasingly popular. In this article we will talk about the main methods of heating the soil.
Why is soil heating needed in winter?
When construction is carried out within the city, it becomes dangerous to remove frozen soil using demolition equipment. You can easily damage underground communications, of which there are so many in the city: cable lines, water pipes, gas pipelines. In such places, soil often has to be removed manually. In winter, frozen soil cannot be removed from the trench with shovels. Therefore, soil heating is ordered immediately before the start of construction work. At the same time, heating of the concrete after pouring the foundation is ordered to ensure its hydration and proper hardening.
What are the different ways to warm up the soil?
There are many ways to warm the ground at a construction site. They differ not only in costs, but also in efficiency. We list the main ones:- Warming up with hot water. This method is suitable for defrosting small areas of land. Labyrinths of flexible hoses are laid over the area, which are covered with polyethylene or any heat insulator. Water heated to 70-90 degrees Celsius is released through the sleeves. For this, a heat generator or pyrolysis boiler is used. The defrosting speed is no more than 60 cm per day. Disadvantages: high cost of equipment and low warm-up speed.
- Warming up with steam and steam needles. Wells from one and a half to two meters deep are drilled at the site for special metal pipes with a diameter of up to 50 mm. These so-called needles have holes at the ends no larger than 3 mm. The pipes are staggered every 1-1.5 meters. Saturated water vapor is supplied to the needles (temperature - more than 100 degrees Celsius, pressure - 7 atmospheres). This method is used only for deep pits - more than 1.5 meters. Disadvantages are complex preparatory work, the release of large volumes of condensate and the need for constant monitoring of the process.
- Warming up with heating elements. This method is similar to the steam needles used as a tool. Pipes with a length of 1 meter and a diameter of up to 60 mm are also used. They are installed in drilled wells at the same distance. Inside the pipes there is a liquid dielectric with high thermal conductivity. The heating elements are connected to the electrical network. Electricity consumption per 1 cubic meter meter of land - 42 kWh. Disadvantages: high costs.
- Warming up with electric mats. The method involves the use of infrared mats, which work on the principle of similar mats for “warm floors”. Electromats heat the soil to a temperature of 70 degrees. The heating depth is no more than 80 cm in 32 hours. Electricity consumption - 0.5 kWh per 1 square meter. Disadvantages - fragile material, need for constant monitoring.
- Heating with ethylene glycol using a Waker Neuson unit. The equipment runs on diesel fuel. From this point of view, it is autonomous and does not depend on communications (electricity). A hose is laid out like a snake across the area of the site, through which heated ethylene glycol will circulate. This liquid has the highest thermal conductivity and a higher boiling point than water. The hoses are covered with thermal insulation mats. One installation allows you to defrost 400 square meters to a depth of 1.5 meters in 8 days.
Our company offers soil and concrete heating services using the Waker Neuson installation. This method is considered the most effective in terms of cost per area and defrosting time.