When a section of soil is switched on with the help of cathodes, a heating current with a voltage of 120, 220 and 380 V can be passed through it through it.
The electrical conductivity of the soil depends on its moisture content (Fig. 3, a), the state and temperature of moisture, the concentrations of solutions of salts and acids in the soil (Fig. 3, b), the structure and temperature of the soil (Fig. 3, c), etc. .
The complexity of the structure of the soil, the physical phenomena occurring in it and the changes associated with power processes, significantly complicates the theoretical side of the electrical heating of the soil, which is still under development.
Rice. 1. Installation of horizontal (string) electrodes on frozen ground with sawdust backfill
1 - frozen soil; 2 - horizontal (jet) electrodes with a diameter of 12-16 mm; 3 - wires supplying current; 4 - sawdust moistened with a salt solution; 5 - top insulation (roofing, wooden shields, mats, etc.)
Rice. 2. Installation of vertical (rod) electrodes in frozen ground with sawdust backfill
1 - vertical electrodes; 2 - wires supplying current; 3 - sawdust moistened with a salt solution, 4-top insulation (roofing, wooden sheets, mats, etc.)
Soil thawing is carried out using horizontal (lined) and vertical (rod and deep) electrodes. When thawing with horizontal electrodes (Fig. 1), the surface of the heated soil area is covered with a 15–25 cm layer moistened with an aqueous solution of salt (sodium chloride, calcium, blue vitriol etc.) having the purpose only to bring current and warm upper layer frozen ground, since the latter, even at a voltage of 380 V, practically does not pass current.
With horizontal electrodes, heat is initially transferred to the soil only from the heating layer of sawdust. Only the top layer of soil, of insignificant thickness, adjacent to the electrodes, is included in the electrical circuit and is a resistance in which heat is generated.
The distance between the rows of electrodes included in different phases is 40–50 cm at a voltage of 220 V and 70–80 cm at a voltage of 380 V. The use of horizontal electrodes is advisable when thawing frozen bases and a small (up to 0.5-0.7 m) freezing depth, as well as in cases where vertical (rod) electrodes cannot be used due to the low electrical conductivity of the soil or the impossibility of driving them into the ground.
When thawing with vertical rod electrodes, wet sawdust first serves as an incentive to warm up the upper layer of soil, which, as it thaws, is included in the electrical circuit, after which the sawdust only reduces the heat loss of the thawed soil. Instead of sawdust, salt solutions poured into grooves in the soil, pierced with a chisel between all electrodes to a depth of 6 cm, can serve as an incentive.
When covering the surface of the heated soil with a layer of dry sawdust, as practice shows, the arrangement of such grooves gives nice results.
The use of vertical electrodes is more effective when the depth of the frozen ground is more than 0.7 m, and also when it is impossible to ensure proper contact between the horizontal electrodes and the ground. In solid (clay and sandy soils with a moisture content of more than 15-20%), the electrodes are hammered to a depth of 20-25 cm, and then immersed deeper as the soil thaws (approximately every 4-5 hours).
The distance between the electrodes is assigned from 40 to 70 cm, depending on the voltage, the nature and temperature of the soil. When thawing to a depth of 1.5 m, it is recommended to have two sets of electrodes - short and long; when the soil thaws to a depth of short electrodes, they are replaced by long ones. Soil heating to a depth of 2 m or more should be carried out in several steps, layer by layer with periodic removal of thawed layers with the current turned off. In order to save energy and maximize the use of power, one should strive to ensure that by the end of thawing, the average soil temperature does not exceed +5 ° and maximum +20 °, and heating should be carried out in sections, periodically turning off the current.
Rice. 3. Change in soil resistivity depending on
a - on the moisture content of soil from red clay, b - on the content of NaCi in clay soil at 30% of its moisture content (by weight), 8 - on soil temperature at a moisture content of 18.6%
The soil thawing plant consists of shields and spotlights (4-5 for each switchboard) for connecting electrodes to the network.
When using deep electrodes, thawing of frozen soil is carried out from the bottom up to its day surface. To do this, electrodes made of round steel with a diameter of 12-19 mm (depending on their length and hardness of the soil) are hammered in a checkerboard pattern through the entire thickness of the frozen layer by 15-20 cm into the thawed soil. At the start of defrosting electricity, passing in the thawed soil, heats it and thaws the part of the frozen layer located directly next to it. Thus, the heat flow, gradually increasing in thickness from bottom to top, sequentially warms the frozen soil, and almost all the heat released by the current is used to thaw the frozen layer.
This method of defrosting, in addition to reducing heat loss, provides a number of other benefits.
As you know, excavators can develop a frozen crust of soil up to 25-40 cm thick without preliminary loosening, which makes it possible to correspondingly reduce the depth of the thawed soil. Since the upper layers of the soil are usually the most complex and energy-intensive, their development in a non-thawed state reduces energy consumption and speeds up the work.
The use of a higher voltage makes it possible to increase the distance between the electrodes. The latter at a voltage of 220 V is taken at 0.5 m, and at 380 V it is already 0.7 m.
The lower end of the electrode is sharpened, and drilled in the upper through hole with a diameter of 3-4 mm, through which a bare copper wire 25-30 cm long is passed; one end of the wire is welded to the electrode, and the other is connected to the mains, followed by phase sequence.
If it is difficult to drive the electrodes, wells with a diameter that is 1-2 mm less than the accepted electrode diameter are preliminarily passed.
According to experimental data, loams with a moisture content of 18% at a freezing depth of 1.5 m and a voltage of 220 V thaw for about 16 hours.
The heated area is allocated with a portable fence and multiplied by warning signals with a categorical prohibition of entry to it.
When using any method of heating the soil, it is necessary to strictly follow the rules set forth in the special “Instructions for the use of electric heating in construction”.
Defrosting by high frequency currents. Frozen soil is permeable to high-frequency currents, and its warming occurs due to the heat released in the soil when it is placed and alternating electric field high frequency.
The high frequency generator consists of a step-up transformer, a rectifier, generator lamps, capacitors and an oscillatory circuit. The mobile unit is mounted in a trailer and is powered by a 220-380 V network or from a mobile power station.
This method is possible with a small amount of work, the development of trenches, and especially during emergency work, when the deadline for their implementation is a decisive factor.
There is one a big problem while 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, which makes it impossible to carry out earthworks without additional time.
There are several ways to thaw the soil:
- 1. Brute force. mechanical destruction.
- 2. Thawing with heat guns.
- 3. Burn. Oxygen free combustion.
- 4. Defrost with a steam generator.
- 5. Thawing with hot sand.
- 6. Defrosting with chemicals.
- 7. Soil heating with thermoelectric mats or electric heating cable.
Each of the above methods has its own weak sides. Long, expensive, poor quality, dangerous, etc.
The optimal way, however, can be recognized as the method using the Installation for warming up the soil and concrete. The earth is heated by a liquid circulating through hoses spread over a large surface.
Advantages over other methods:
- Minimal surface preparation
- Independence and autonomy
- The heating hose is not energized
- The hose is completely sealed, not afraid of water
- The hose and thermal insulation cover are resistant to mechanical impact. Hose reinforced synthetic fiber and have exceptional flexibility and tensile strength.
- The serviceability and readiness of the equipment for operation is controlled by built-in sensors. 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.
- Hose can be laid arbitrarily
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Stages of work using the installation for heating surfaces Wacker Neuson HSH 700 G:
Site preparation.
Clear the heated surface from snow.
Thorough cleaning will reduce the defrosting time by 30%, save fuel, get rid of dirt and excess melt water that makes further work difficult.
Heating hose installation.
The smaller the distance between the turns, the less time it takes to warm up the surface. In the HSH 700G unit, the hose is sufficient to heat up an area of up to 400 m2. Depending on the inter-hose distance, the desired area and heating rate can be achieved.
Vapor barrier of the heated area.
The use of a vapor barrier is mandatory. The laid out hose is covered plastic wrap overlap. The film will not allow heated water to evaporate. Melt water will instantly melt the ice in the lower layers of the soil.
Laying of thermal insulation material.
A heater is laid on the vapor barrier. The more carefully the heated surface is insulated, the less time it will take to warm the soil. The equipment does not require specific knowledge of skills and long-term staff training. The laying, steam and thermal insulation procedure takes from 20 to 40 minutes.
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Advantages of technology using a surface heating installation
- Heat transfer 94%
- Predictable result, complete autonomy
- Preheating time 30 minutes
- No danger of electric shock, does not create magnetic fields and interference with control devices
- Hose laying in free form, no terrain restrictions
- Ease of operation, control, assembly, storage exceptional flexibility maneuverability and maintainability
- Does not affect and destroy nearby communications and the environment
- The HSH 700 G is certified in Russia and does not require special permits for the operator
Possible uses for the Wacker Neuson HSH 700 G
- Soil thawing
- Laying communications
- Concrete heating
- Warming up complex structures(column bridges, etc.)
- Heating of reinforcing structures
- Thawing gravel for laying pavers
- Warming up teams formwork structures
- Prevention of icing of surfaces (roofing, football fields, etc.)
- Gardening (greenhouses and flower beds)
- Finishing work at the 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 you to hand over projects on time.
In autumn and spring, they also make an invaluable contribution to the workload of your company: after all, these devices speed up many technological processes.
UPGO SPECT are designed to solve a number of tasks: warming up inert materials in winter, water heating and space heating.
We offer steam-gas heating plants that produce heating of inert materials on BSU (sand, crushed stone, gravel, limestone):
|
type of instalation |
Thermal power, |
RBU performance cubic meters in a mixture per hour |
price, rub. |
| UPGO SPECT-400 | 400 | 10-30 | from 1 100 000 |
| UPGO SPECT-800 | 800 | 30-60 | from 1 800 000 |
| UPGO SPECT-1200 | 1200 | 60-90 | from 2 400 000 |
| UPGO SPECT-1600 | 1600 | 90-120 | from 2 900 000 |
The numbers indicate the nominal thermal power units in kilowatts.
The equipment is manufactured in accordance with the patent and certificate of conformity obtained by us.
How do inert ones warm?
(Selection guide).
The technology for producing concrete mixtures in winter is somewhat different from the technology for producing concrete in summer.
At low temperatures environment from -5°C and below, there are several additional problems:
- The temperature of inert materials (sand, gravel) is such that conditions arise for water to freeze during mixing, and the mixture does not work.
- indoors concrete plant heating is required for comfortable operation of personnel and units.
- Ready-mixed concrete must be delivered to construction site with a temperature not lower than 15°C. Mixers transporting concrete are also filled with water at a temperature not lower than 40°C.
The first problem in mild frosts is partially solved by using antifreeze additives and heated water. The second is the use of electric heaters. The third problem is not solved without the use of special tools.
What is required for the production of concrete in winter?
- Heating of inert (sand and gravel) to a temperature of 5°C to 20°C.
- Water heating up to temperature from 40°С to 70°С.
- Use of an economical space heating system.
What energy sources are available for inert and water heating?
Let's not consider exotic energy sources like wind turbines, solar panels, thermal springs etc. Let's formulate the problem as follows:
Required to work at low temperatures;
There is no central heating system;
The use of electricity is too expensive.
How to heat inert?
The most common energy sources are gas and diesel, and they work well with automation systems. It is possible to use fuel oil and heating oil. Firewood and coal are used less often due to the complexity of automation.
What equipment is used for heating inert materials?
The industry produces installations for heating sand, gravel, water, operating on various physical principles. The advantages and disadvantages of the installations are given below:
1. Heating of inert materials with hot air.
Fuel: diesel.
Advantages:
Air temperature up to 400 °С
Small dimensions;
Flaws:
Low efficiency (high energy consumption during operation, since air does not efficiently transfer heat to materials, most of heat is released into the atmosphere).
Slow heating of inert materials (30-60 minutes);
Low air pressure does not blow fine fractions and sand;
No process water heating;
Not used for space heating.
2. Heating of inert materials with steam.
Fuel: diesel.
Advantages:
High efficiency;
High efficiency of heating of inert materials;
Rapid heating of inert materials (10-20 minutes);
Average cost;
Can heat water
Small dimensions;
Electric power up to 2 kW.
Flaws:
They create high humidity of inert materials (due to steam condensation from 500 to 1000 kg per hour;
High-efficiency steam boilers with temperatures above 115 °C and pressures above 0.7 kg/cm² are supervised;
It is difficult to use for space heating (turns off when the concrete plant is idle).
3. Heating of inert materials with registers hot water or ferry.
Fuel: diesel or central heating.
Advantages:
High efficiency;
Not complicated, cheap equipment;
Technical supervision permit is not required;
Can heat water
Can be used for space heating;
Very small dimensions;
Electric power up to 0.5 kW.
Flaws:
Often requires repair and maintenance of registers;
Low efficiency of heating of inert materials;
The heating process takes several hours.
4. Turbomatics (heating of inert steam-air mixture with heat exchangers).
Fuel: diesel.
Advantages:
High efficiency;
Technical supervision permit is not required;
No registers;
You can heat water.
Flaws:
Complex, expensive equipment;
Not applicable for space heating;
Large dimensions;
Electric power up to 18-36 kW (cyclically).
5. Steam-gas-air plants.
Heating of inert materials with flue gases.
Fuel: diesel.
Advantages:
High efficiency;
High efficiency of heating of inert materials (10-20 minutes);
Not sophisticated equipment with an average cost;
Technical supervision permit is not required;
No registers;
The temperature of the mixture is up to 400 °C.
Can be used for space heating (there is a standby mode);
There is water heating for technological needs and refueling of mixers;
Small dimensions.
Flaws:
Electric power up to 18 kW (cyclically).
All five types of installations can be fueled with low or medium pressure natural gas if available in the equipment gas burners. Coordination with technical supervisory authorities, the availability of a project and expertise are required.A significant part of the territory of Russia is located in zones with a long and harsh winter. However, construction is carried out year-round, in this regard, about 15% of the total earthworks have to be performed in winter conditions and in the frozen state of the soil. A feature of soil development 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 excavation 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 performed without slopes. Water, with which there are many troubles in the warm season, in a frozen state becomes an ally of the builders. Sometimes there is no need for sheet piling, almost always in the drainage system. Depending on the specific local conditions, the following soil development methods are used:
■ protection of soil from freezing followed by development by conventional methods;
■ thawing of soil with its development in a thawed state;
■ development of soil in a frozen state 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 scheduled for development in winter, a thermal insulation cover with the development of soil in a thawed state. Protection is carried out until the onset of stable negative temperatures, with early removal from the insulated area surface water. The following methods of thermal insulation coating are used: preliminary loosening of the soil, plowing and harrowing of the soil, cross loosening, covering the soil surface with heaters, 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 on the site intended for development in winter conditions. When loosening the soil surface, the upper layer acquires a loose structure with air-filled closed voids that have 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. the total freezing depth is approximately 73. Snow cover can be increased by moving snow to the site with bulldozers or motor graders or by installing several rows of snow protection fences from lattice shields measuring 2 X 2 m at a distance of 20 ... 30 m row from row perpendicular to the direction of the prevailing winds.
Deep loosening is carried out by excavators to a depth of 1.3. ..1.5 m by transferring the developed soil to the site where the earthwork will be located in the future.
Cross loosening of the surface to a depth of 30 ... 40 cm, the second layer of which is located at an angle of 60 ... .3.5 months, the total freezing depth sharply decreases.
Pre-treatment of the soil surface by mechanical loosening is especially effective in warming these areas of the earth.
Shelter of the soil surface with heaters. For this, cheap local materials are used - tree leaves, dry moss, peat, straw mats, shavings, sawdust, snow. The easiest way is to lay these heaters with a layer thickness of 20 ... 40 cm directly on the ground. Such surface insulation is used mainly for small recesses.
Shelter with air gap. More effective is the use of local materials in combination with an air gap. To do this, beds 8 ... .10 cm thick are laid out on the surface of the soil, slabs or other improvised material - branches, rods, reeds - are laid out on them; a layer of sawdust is poured over them or wood shavings 15...20 cm thick with protection from blowing 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 shelter (insulation) on each side by 2 ... 3 m, which will protect the soil from freezing not only from above, but also from the side.
With the beginning of the development of the soil, it must be carried out at a rapid pace, immediately to the entire required depth and small areas. In this case, the insulating layer must be removed only on the developed area, otherwise, in severe frosts, a frozen soil crust will quickly form, making it difficult to carry out work.
5.11.2. Soil thawing method with its development in a thawed state
Defrosting 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.
Defrosting methods are classified according to the direction of heat propagation in the ground and according to the heat carrier used (fuel combustion, steam, hot water, electricity). In the direction of thawing, all methods are divided into three groups.
Soil thawing from top to bottom. Heat propagates in the vertical direction from the day surface deep into the ground. The method is the simplest, practically does not require preparatory work, is most often applicable in practice, although from the point of view of economical consumption energy is the most imperfect, since the heat source is located in the zone of cold air, therefore, significant energy losses into the surrounding space are inevitable.
Soil thawing from bottom to top. Heat spreads from the lower boundary of the frozen ground to the day surface. The method is the most economical, since soldering takes place under the protection of the frozen crust of the soil and heat loss into space is practically excluded. The required thermal energy can be partly saved by leaving the upper crust of the soil in a frozen state. It has the lowest temperature, so it requires a lot of energy for soldering. But this thin layer of soil of 10...15 cm will be freely developed by an excavator, for this the power of the machine will be enough. The main disadvantage of this method is the need to perform labor-intensive preparatory operations, which limits its scope.
Radial thawing of soil occupies an intermediate position between the two previous methods in terms of thermal energy consumption. Heat is distributed radially in the ground from vertically installed heating elements, but in order to install and connect them to work, significant preparatory work is required.
To perform soil thawing 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 overmoisten the soil.
Depending on the heat carrier used, there are several methods of defrosting.
Defrosting by direct combustion of fuel. If in winter it is necessary to dig 1 ... 2 holes, the simplest solution is to get by with a simple fire. Maintaining the fire during the shift will lead to thawing of the soil under it by 30 ... you can kindle a fire again or develop thawed soil and make 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 extracting small trenches; a link structure is used (Fig. 5.41) from a series metal boxes truncated type, from which a gallery of the required length is easily assembled, in the first of them they arrange a combustion chamber for solid or liquid fuel (firewood, liquid and gaseous fuels 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 desirable to insulate the top of the box, often thawed soil is used as a heater. After the change, the unit is removed, the strip of thawed soil is covered with sawdust, 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. Use horizontal and vertical electrodes in the form of rods or strip steel. For the initial movement of electric current between the rods, it is necessary to create a conductive medium. Such an environment can be thawed soil, if the electrodes are hammered into the soil to the thawed soil, or on the surface of the soil, cleared of snow, pour a layer of sawdust 15 ... 20 cm thick, moistened with a saline solution with a concentration of 0.2-0.5%. Initially, wetted sawdust is a conductive element. Under the influence of heat generated in the layer of sawdust, the top layer of soil heats up, soldering and itself becomes a current conductor from one electrode to another. Under the influence of heat, the underlying layers of the soil are thawed. Subsequently, the distribution of thermal energy is carried out mainly in the thickness of the soil, the sawdust layer only protects the heated area from heat loss to the atmosphere, for which 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 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. Plant for thawing soil with liquid fuel:
a - general form; b - box insulation scheme; 1 - nozzle; 2 - insulation (sprinkling with thawed soil); 3 - boxes; four - exhaust pipe; 5 - cavity of thawed soil
Soil thawing with strip electrodes laid on the soil surface, cleared of snow and debris, as level as possible. The ends of the strip iron are bent upwards 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 the ground in the frozen state is not a conductor, at the first stage the current moves through the sawdust moistened with the solution. Further, the upper layer of the soil warms up and the thawed water begins to conduct an electric current, the process eventually goes deep into the soil, sawdust begins to act as a thermal protection of the heated area from heat loss to the atmosphere. Sawdust from above is usually covered with roofing paper, 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 less intensively put into operation, they heat up much more slowly. In addition, they are sufficiently saturated with water since autumn, which requires more energy to go into a thawed state. Energy consumption ranges from 50-85 kWh per 1 m3 of soil.
Soil thawing with rod electrodes (Fig. 5.42). This method carried out from top to bottom, from bottom to top and combined methods. When the soil is thawed with vertical electrodes, reinforcing iron rods with a pointed lower end are driven into the soil in a checkerboard pattern, usually using a 4x4 m frame with crosswise tensioned wires; the distance between the electrodes is in the range of 0.5-0.8 m.
Rice. 5.42. Soil thawing with deep electrodes:
a - from bottom to top; b - from top to bottom; 1 - thawed soil; 2 - frozen ground; 3- electrical wire; 4 - electrode, 5 - layer waterproofing material; 6 - a layer of sawdust; I-IV - defrosting layers
When warming up from top to bottom, the surface is preliminarily cleaned of snow and ice, the rods are driven into the ground by 20 ... 25 cm, 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 depth of heating will be within 0.7 ... 1.5 m. The duration of thawing of the soil by the influence of electric current is approximately 1.5 ... ...2 days The distance between the electrodes is 40...80 cm, the energy consumption is reduced by 15...20% compared to strip electrodes and amounts to 40...75 kWh per 1 m3 of soil.
When warming up from the bottom, 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.
Third, combined method, will take place when the electrodes are buried in the underlying thawed soil and a sawdust filling impregnated with saline is placed on the day surface. The electrical circuit will be closed at the top and bottom, the thawing of the soil will occur from top to bottom and from bottom to top at the same time. Since the complexity of the preparatory work with this method is the highest, its use can be justified only in exceptional cases when accelerated thawing of the soil is required.
Defrosting by high frequency currents. This method allows you to drastically reduce preparatory work, since the frozen soil retains conductivity to high-frequency currents, so there is no need for a large depth of electrodes in the soil and for sawdust backfilling. The distance between the electrodes can be increased to 1.2 m, i.e., their number is almost halved. The process of thawing the soil proceeds relatively quickly. The limited use of the method is associated with insufficient production of high frequency current generators.
One of the methods that have now lost their effectiveness and have been superseded by more modern ones is the thawing of the soil with steam or water needles. For this day it is necessary to have sources hot water and steam, at a small, up to 0.8 m depth of soil freezing. Steam needles are metal pipe up to 2 m long and 25...50 mm in diameter. On the lower part pipes are fitted with a tip with holes with a diameter of 2 ... 3 mm. The needles are connected to the steam pipeline with flexible rubber hoses with taps on them. The needles are inserted into wells previously drilled to a depth approximately equal to 70% of the thaw depth. The wells are closed with protective caps, equipped with glands to pass the steam needle. Steam is supplied under pressure of 0.06...0.07 MPa. After installing the accumulated caps, the heated surface is covered with a layer of thermal insulation material, most often sawdust. The needles are staggered 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, the heating of the soil is especially intensive. This method requires about 2 times more thermal energy than the vertical electrode method.
Soil thawing by thermal electric heaters. This method is based on the transfer of heat to frozen soil by contact. As the main technical means electric mats are used, made of a special heat-conducting material through which an electric current is passed. Rectangular mats, the dimensions of which can cover the surface from 4 ... 8 m2, are laid on the thawed area and connected to a 220 V power source. 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 on the depth of soil freezing and averages 15-20 hours.
5.11.3. Development of soil in a frozen state with preliminary loosening
Loosening of frozen soil with subsequent development by earth-moving and earth-moving machines is carried out by a mechanical or explosive method.
Mechanical loosening of frozen soil using modern construction machines with increased power is becoming more common. In accordance with the requirements of the environment, before the winter development of the soil, it is necessary to remove a layer of vegetable soil from the site planned for development in the autumn with a bulldozer. Mechanical loosening is based on cutting, splitting or chipping frozen soil by static (Fig. 5.43) or dynamic action.
Rice. 5.43. Loosening of frozen soil by static impact:
a - bulldozer with active teeth, b - excavator-ripper, 1 - direction of loosening
With a dynamic impact on the soil, it is split or chipped by hammers free fall and directional action (Fig. 5.44). In this way, soil loosening is carried out by free-fall hammers (ball and wedge hammers) suspended on ropes on excavator booms, or by directional hammers, when loosening is carried out by chipping the soil. Mechanical loosening allows its development by earth-moving and earth-moving machines. Hammers weighing up to 5 tons are dropped from a height of 5 ... 8 m: a ball-shaped hammer is recommended for loosening sandy and sandy loamy soils, wedge hammers - for clay (with a freezing depth of 0.5 ... 0.7 m). As a directional hammer, diesel hammers on excavators or tractors are widely used; they allow destroying frozen soil to a depth of up to 1.3 m (Fig. 5.45).
The static effect is based on the continuous cutting force in the frozen ground 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 means 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. Soil loosening is carried out by parallel layer-by-layer penetrations every 0.5 m followed by transverse penetrations at an angle of 60...900 to the previous ones. The movement of loosened soil into the dump is carried out by bulldozers. It is advisable to attach attachments directly to the bulldozer and use it to independently move loosened soil (see Fig. 5.21). Ripper capacity 15...20 m3/h.
The ability of static rippers to develop frozen soil in layers 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, find wide application in construction. This is due to their high economic efficiency. So, the cost of soil development with the use of rippers compared to the explosive method of loosening is 2...3 times lower. The depth of loosening by these machines is 700...1400 mm.
Fig.5.45. The scheme of joint operation of a diesel hammer and a straight shovel excavator
Explosion loosening of frozen soils is effective in case of significant volumes of frozen soil development. The method is used mainly in undeveloped areas, and in limited built-up areas - using shelters and explosion localizers (heavy loading plates).
Depending on the depth of soil freezing, blasting is performed (Fig. 5.46):
■ the method of blast-hole and slot charges at a depth of soil freezing up to 2 m;
■ using borehole and slot charges at a freezing depth of more than 2 m.
Holes are drilled with a diameter of 22 ... 50 mm, wells - 900 ... 1100 mm, the distance between rows is taken from 1 to 1.5 m. Vymi myaptnyami milling type or bar machines. Of the three adjacent slots, the explosive is placed only in the middle, outer and intermediate slots to compensate for the shift of the frozen ground during the explosion and to reduce the seismic effect. The slots are charged with elongated or concentrated charges, after which they are covered with melted sand from above. With high-quality performance of preparatory work in the process of blasting, 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, downhole; in - the same, boiler; g - the same, small-chambered; e, f - the same, chamber; g - the same, slotted; 1 - explosive charge; 2 - stemming; 3 - face chest; 4 - sleeve; 5 - pit; b - adit; 7 - working slot; 8 - compensation gap
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 mining method is applicable for large areas and is based on the fact that the solidity of the frozen soil is broken by cutting it into blocks. With the help of 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). With a shallow freezing depth (up to 0.6 m), it is enough to make only longitudinal cuts.
Bar machines that cut slots have one, two or three cutting chains mounted on tractors or trench excavators. Bar machines make it possible to cut slits 1.2 ... 2.5 m deep in frozen soil. They use steel teeth with a cutting edge made of a durable alloy, which prolongs their service life, and when worn or abraded, allows them to be quickly replaced. The distance between the bars is taken, depending on the soil, after 60 ... 100 cm. The development is carried out by backhoe excavators with a large bucket or blocks of soil are dragged from the developed site to the dump by bulldozers or grantors.
Fig.5.47. Scheme of block development of soil:
a - cutting slots with a bar machine; b - the same, with the extraction of blocks by a tractor; c - development of a pit with the extraction of blocks of frozen soil with a crane; I - layer of frozen soil; 2 - cutting chains (bars); 3 - excavator; 4 - cracks in frozen ground; 5 - chopped blocks of soil; 6 - blocks moved from the site; 7 - crane tables; eight - vehicle; 9 - tick grip; 10 - construction crane; 11 - tractor
The mechanical method is based on a force, and more often in combination with a shock or vibration effect on an array of frozen soil. The method is implemented using conventional earth-moving and earth-moving machines and machines with working bodies specially designed for winter conditions (Fig. 5.48).
Conventional serial machines are used in initial period winters, when the depth of soil freezing is negligible. A forward and backhoe can develop 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 m3; 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 way direct development of the soil:
a - excavator bucket with active teeth; b - excavation of the soil with a backhoe excavator and a gripping tongs device; c - earth-moving and milling machine; 1 - bucket; 2 - bucket tooth; 3 - drummer; 4 - vibrator; 5 - gripping device; b - bulldozer blade; 7 - hydraulic cylinder for raising and lowering the working body; 8 - working body (cutter)
For winter conditions, special equipment has been developed for single-bucket excavators - buckets with vibro-impact active teeth and buckets with a gripping tongs device. The energy consumption for cutting the soil is about 10 times greater than for chipping. Mounting in cutting edge excavator bucket vibro-impact mechanisms, similar in operation to a jackhammer, bring good results. Due to the excessive cutting force, such single-bucket excavators can develop an array of frozen soil in layers. The process of loosening and excavating the soil is the same.
Soil development is also carried out by bucket-wheel excavators specially designed for trenching in frozen soil. For this purpose, a special cutting tool in the form of fangs, teeth or crowns with inserts of hard metal, mounted on buckets. On fig. 5.48, a shows the working body of a bucket-wheel excavator with active teeth for the development of rocky and frozen soils.
Layer-by-layer soil development can be carried out with a specialized earth-moving and milling machine that removes chips up to 0.3 m deep and 2.6 m wide. The movement of the developed frozen soil is carried out by bulldozer equipment included in the machine kit.
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