As the soil freezes, the mechanical strength of the soil increases sharply, which leads to an increase in the cost of machine time and labor for its development, and, consequently, to an increase in the cost of work. In this regard, if it is necessary to carry out earthworks in winter, measures are taken to protect the soil from freezing, and it is developed only after thawing or loosening.

Protecting the soil from freezing. Provide by creating a thermal insulation layer on its surface; loosening the top soil layer; covering the ground with various thermal insulation materials.

Loosen the soil until it freezes by plowing and harrowing, having previously provided drainage surface water. processed in this way upper layer soil acquires a loose structure with closed voids filled with air, and has sufficient thermal insulation properties. Plowing is carried out by tractor plows to a depth of 200...350 mm, followed by harrowing to a depth of 150...200 mm. Artificial increase in snow cover by raking snow with bulldozers, motor graders or by snow retention using shields can increase the thermal insulation effect. Mechanical loosening of the soil is most often used to insulate large areas.

Protecting the soil surface with thermal insulation materials is effective in small areas and in the presence of local cheap materials, tree foliage, sawdust and shavings, moss, peat, straw, and slag. Thermal insulation materials are laid in a layer of 200 ... 400 mm directly on the ground

Thawing of frozen soil. It is the most expensive and time-consuming method, so it is used when not large volumes works.

The following methods of thawing frozen soil have found the greatest distribution in construction practice: fire, electric heating, steam heating and water heating (Fig. 16).

fire method based on the combustion of various fuels on the ground surface under the cover of a metal box with an exhaust pipe (Fig. 6.16.a). To reduce heat loss, the box is covered with slag or thawed soil. A strip of thawed soil is covered with sawdust, and the underlying layer thaws due to the heat accumulated by the upper layer.

excavation soil excavator bulldozer

Rice. 16. Scheme of thawing frozen soil: a - fire method; b - electrical heating using horizontal electrodes; in the same way, using vertical electrodes; g - steam heating; 1 - box section; 2 - insulation; 3-- exhaust pipe; 4 - thawed soil; 5--three-phase electrical network; 6 - horizontal strip electrodes; 7 - a layer of sawdust; 8 - a layer of roofing or roofing felt; 9 - rod electrode; 10 - pipeline; 11 - steam needle; 12 - drilled well; 13 - cap.

Electrical heating soil is carried out using electrodes located on the surface or immersed vertically in frozen soil.

When using horizontal electrodes, the soil surface is covered with a layer of sawdust 150 ... 200 mm thick (Fig. 6.16.6). Sawdust is moistened with an aqueous saline solution with a concentration of 0.2 ... 0.5% to increase electrical conductivity in the initial period of thawing, since frozen soil is not a conductor. After the soil of the upper layer thaws, it becomes a conductor itself, and the sawdust layer acts as a heat-protective layer. Surface electrical heating is used at a depth of soil freezing up to 0.7 m.

With a greater depth of freezing, vertical electrodes are used. Defrosting is carried out from top to bottom or from bottom to top (Fig. 16, c).

When thawing from top to bottom, electrodes in the form of pins are driven into the ground in a checkerboard pattern to a depth of 200 ... 250 mm and covered with sawdust soaked in concentrated saline. As you thaw upper layers the electrodes are periodically immersed deeper and deeper. The energy consumption with this method is somewhat lower than with the horizontal arrangement of the electrodes.

Heating from the bottom up requires the electrodes to be immersed 150-200 mm below the freezing depth of the soil, for which wells are pre-drilled in the soil. The surface of the thawed soil is not covered with sawdust. Energy consumption when heating the soil from the bottom up is significantly reduced compared to heating from the top down.

Steam heating soil is carried out using steam needles installed in pre-drilled wells to a depth of 0.7 of the thawing depth (Fig. 16, d).

The steam needle is a pipe 1.5 ... 2 m long, 25..50 mm in diameter. On the lower part of the pipe there is a tip with holes of 2...3 mm for steam outlet. The needles are connected at the top with a steam line. For the most efficient use of steam and reduction of its losses, the wells are covered from above with protective caps having holes for passing a steam needle.

After installing the storage caps, the heated surface is covered with a layer of sawdust or other thermal insulation material. The needles are placed in a checkerboard pattern at a distance of 1 ... 1.5 m from each other.

Ground water heating lead with the use of water circulation needles, the installation of which is similar to steam needles. The heat carrier here is water heated to 50...60 °C, which circulates in a closed circuit "boiler - distributing pipes - water needles - return pipes - boiler". Such a scheme provides the most complete use of thermal energy.

The water needle consists of inner and outer tubes. The outer tube has a pointed deaf lower end, and the inner one is open. Hot water is supplied to the inner pipe, which enters the outer pipe through the lower hole, rises up to the outlet pipe and flows through the connecting pipe to the next needle or to the return pipe. The needles are staggered at a distance of 0.75 ... 1.25 m from each other

Preliminary loosening of frozen soils. Carried out by mechanical and explosive methods.

Mechanical loosening used for small amounts of work and relatively small freezing depths (up to 1.3 m). For loosening, wedge hammers, diesel hammers and tractor rippers, bucket-wheel excavators equipped with bur chains are used (Fig. 17).

The wedge hammer is suspended from the crane boom, and the diesel hammer is attachments to the crane, tractor loader and tractor.

Tractor rippers are mounted on the basis of caterpillar tractors with an engine power of more than 110 kW or use attachments for them. The working body of the ripper is a comb with teeth, the number of which is 1 ... 5.

Frozen soils can be developed with preliminary cutting into blocks. With this method, mutually perpendicular cuts are made in an array of frozen soil with the help of bar, disc milling and other machines to a depth of 0.8 of the freezing depth. The resulting blocks are removed with an excavator bucket or pushed back by a bulldozer.

Rice. 17. Scheme of loosening soils: a - wedge-hammer; b - diesel hammer; in - a bucket-wheel excavator equipped with cutting bar chains; 1 - wedge-hammer; 2 - excavator; 3 - guide rod; 4 - diesel hammer; 5 - cutting chains (bars); 6 - bucket-wheel excavator; 7 - cracks in frozen ground

Explosive loosening of frozen soil used for large volumes of work and a significant depth of freezing. This method is economical, especially when, in addition to loosening, it is required to move the soil to the dump. The blasting technique has been described previously.

A significant part of the territory of Russia is located in areas with long and severe winters. However, construction is carried out year-round, in this regard, about 15% of the total earthworks have to be carried out in winter conditions and in frozen ground. A feature of soil development in a frozen state is that when the soil freezes, its mechanical strength 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 for drainage. Depending on specific local conditions The following soil development methods are used:

■ protection of soil from freezing with subsequent development 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 the artificial creation of a thermal insulation cover on the surface of the area scheduled for development in winter, with the development of soil in a thawed state. Protection is carried out until the onset of stable negative temperatures, with early removal of surface water from the insulated area. 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 closed voids filled with air, which 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 an air layer. 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 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.

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 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 (Fig. 5.41) is used from a number of metal boxes of a 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 fuel with combustion through the 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 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 view; b - box insulation scheme; 1 - nozzle; 2 - insulation (sprinkling with thawed soil); 3 - boxes; 4 - 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. Next, the top layer of soil warms up and the thawed water begins to conduct electric current, the process time goes by deep into the ground, sawdust begins to play the role of 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 included in the work, 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 is 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 cleared 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.

The 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. 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 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 autumn period to remove a layer of vegetable soil with a bulldozer from the site 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 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 free-fall and directional hammers (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. loosening mechanically allows to carry out 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 implies a special knife (tooth) as an attachment, 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, are widely used 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 gap; 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 allow you to cut slots 1.2 ... 2.5 m deep in frozen soil. Use steel teeth with cutting edge from a durable alloy, which prolongs their service life, and when worn or abraded, it 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 the initial period of winter, when the depth of soil freezing is insignificant. 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 method of direct excavation of 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 the cutting edge of the excavator bucket of vibro-impact mechanisms, similar in operation to a jackhammer, brings 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 is used in the form of fangs, teeth or crowns with hard metal inserts, 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.

Frozen soils are equal in hardness to rocky ones.. If possible, you should prepare in advance in the pre-winter time the places planned for digging in winter period.

To do this, the soil is plowed or shoveled and insulated. However, in cities and settlements such preparation of soils for excavation is extremely limited, therefore, frozen soils have to be loosened or thawed (thawed) before their development.

When soils freeze to a depth of 0.25-0.4 m, they can be developed with an excavator without preliminary loosening or thawing. If the soil is frozen to a great depth, it should be loosened in one of the following ways:

mechanized- a wedge of a diesel hammer mounted on an excavator, tractor or tractor loader, tractors equipped with bars with cutters, earth-moving and milling machines, as well as jackhammers powered by a compressor, or electric hammers;

manually- crowbars, sledgehammers using wedges;

explosive, if possible.

The mechanized method of soil loosening is the most efficient and economical. However, the possibility of using this method in cities and towns is limited, since pieces of frozen soil, asphalt and concrete scatter over considerable distances (up to 50 m). By installing protective nets, this method can also be used in places with relatively heavy traffic and people.

The method associated with the use of percussion machines (diesel hammer) is used if ground shaking is allowed near houses and above underground structures and communications.

Manual soil development is safe, but inefficient, so it is used only in exceptional cases (with small amounts of soil loosening).

Warming (thawing) of the soil is not one of the economical ways and is used for small amounts of work or when working in cramped conditions, when other methods of preparing frozen soil for development are not possible.

Thawing can be superficial or deep..

For surface defrosting on the open surface of the soil, liquid, solid or gaseous fuels are burned under special devices (metal boxes). In other cases, hot sand with a temperature of at least 180 ° C, covered with a heat-insulating material, is laid on the heated soil. Heat spreads from the surface of the earth to the depth of thawing.

For deep thawing heaters (electrodes heated by electric current, steam, water or electric needles) are immersed in the thickness of the frozen soil. In this case, heat is distributed in the soil simultaneously over the entire thawing depth.

With a large depth of soil freezing, thawing using ducts heated by flue gases is carried out in several stages. The boxes are installed in one or several rows, depending on the required heating width, sprinkled with soil and fuel is burned under them. After thawing the upper freezing zone, the boxes are removed and the warmed soil is selected. Then the boxes are re-installed to warm the remaining frozen layer.

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GPOU "Krasnokamensk Industrial and Technological College"

abstract

on the subject "Road construction"

on the topic " Features of earthworks in low temperatures and during hot weather"

Fulfilled

3rd year student of group TD-38

Strelnikov Ivan Vladimirovich

Krasnokamensk - 2016

• Introduction
• 1. Earthworks at low temperatures
• 1.1 Soil features in winter
• 1.2 Protecting the soil from freezing
• 1.3 Method of soil protection
• 1.4 Soil loosening methods
• 1.4.1 Explosive way
• 1.4.2 Mechanized method
• 1.5 Soil thawing
• 1.6 Requirements for thawing and loosening of soil
• 1.7 Methods for constructing embankments from cohesive soils
• 2. Excavation during hot weather
• 2.1 Features of excavation in hot weather
• 2.2 Rational method of soil development
• 2.3 Trenching with bulldozers
• Conclusion
• Used Books

Introduction

The topic of the abstract is "Peculiarities of excavation work in conditions of low temperatures and during hot weather."

This topic is of particular relevance in modern world, since earthworks have great value(interest) for the state and for the whole world as a whole, since the construction of buildings, various structures, roads and everything related to the development of soil is very important for people and for living on earth.

The purpose of the work: consideration of the features of earthworks in conditions of low temperatures and during hot weather.

To achieve the goal, the following tasks will be solved: find out the features of the soil in winter; learn how to protect the soil from freezing, what are the ways to protect and loosen the soil; find out what are the types and methods of thawing soils; what are the requirements for thawing and loosening; what are the uses for cohesive soil embankments. It is also necessary to clarify the issue of excavation during hot weather, its features, methods of excavation in summer time how the development of trenches with bulldozers is going on.

1. Earthworks at low temperatures

Excavation in winter conditions is allowed if it ensures the efficiency of all construction process and timely execution of construction and installation works. During this period, excavations and reserves are developed in dry sands, gravel-pebble and rocks, embankments are erected from concentrated reserves, dry excavations with a depth of more than 3 m from clay soils are developed, embankments are made of sandy soils in swamps, drainage slots are made, freeze-outs, etc. d.

The features of earthworks in winter are negative air temperature, the presence of snow and ice. Soil freezing complicates their development, transportation, laying and compaction. The rise in construction costs caused by winter work must be compensated.

Excavation work in winter makes it possible to extend the construction season and, at the same time, to increase the pace of construction and ensure the uniform use of working mechanization. At the same time, the performance of work in these conditions should not lead to a decrease in quality, stability and durability.

1.1 Soil features in winter

Excavation work in winter has features associated with a change in the physical and mechanical properties of the soil under the influence of low temperatures, and requires systematic monitoring of the quality of their implementation. At negative temperatures, moistened soils freeze and form a monolithic mass that is difficult to destroy.

The development of frozen soils is the most time-consuming process of winter construction work. It requires the implementation of preparatory measures and the use of the most advanced mechanisms and devices, as well as methods of work that ensure the technical and economic feasibility of earthworks in winter conditions.

The soil becomes permanently frozen after 5-20 days. on the onset of the winter period and retains this state for 30-15 days. after its completion. These tentative dates apply respectively to the northern and southern regions of the Soviet Union.

In cold weather, soils, especially clay ones, freeze due to the freezing of water contained in their pores. Frozen soil has a significant viscosity, which makes it difficult to develop it with impact tools. The viscosity of frozen soil increases with an increase in the percentage of unfrozen water content in it. The surface of the soil to be developed in winter conditions is protected from freezing before the onset of cold weather. The following methods are used: plowing and harrowing, deep loosening, bunding, snow cover retention, construction of an insulating layer made of cheap local materials (sawdust, peat, slag), etc. If these measures were not taken in a timely manner or turned out to be insufficient, then mechanical loosening or thawing of the frozen soil is used.

According to their condition, frozen soils are subdivided as follows: hard frozen, firmly cemented by ice, characterized by relatively brittle fracture; plastic-frozen, ice-cemented cohesive soils with viscoplastic properties due to the presence of unfrozen water in them; loose-frozen, non-cohesive soils not cemented by ice. The latter include sandy and gravel-pebble soils, the development of which is almost the same as the development of thawed soils.

The depth of soil freezing depends on its thermal properties, intensity and duration of exposure to negative temperatures. For clay soils, a coefficient of 0.8 should be entered, and for sands and sandy loams - a coefficient of 1.2. The mechanical strength of soils during freezing increases significantly. The resistance of frozen soil in compression is 3-4 times greater than in tension, so it is advisable to develop hard-frozen soils not by crushing, but by chipping.

With an increase in temperature, frozen cohesive soils lose their fragility and acquire plastic-frozen properties with a sharp drop in mechanical strength. Loose soil can freeze again when the temperature drops, while the time of the beginning of freezing of the soil (depending on the outside temperature) is: at -5 ° C - 90 minutes, at -10, -20, -30 ° C - respectively 60, 40 and 20 min.

1.2 Protecting the soil from freezing

Soil protection from freezing is carried out in late autumn after the end of the rainy period, but before the first snow falls and a stable negative temperature sets in. It is carried out by creating an insulating layer from pre-loosened soil or from cheap heat-insulating materials. Preliminary loosening of the soil is carried out by plows and rippers to a depth of at least 35 cm, followed by harrowing. Small areas (the bottom of the pit, trenches, etc.) are protected from freezing by covering the soil with a layer of insulation (sawdust, slag, leaves and other cheap heat-insulating materials). Soil protection from freezing over large areas of development is carried out by retaining snow.

1.3 Method of soil protection

The method of soil protection from freezing and the technology of its development are chosen by means of a technical and economic comparison of various options that are possible under given conditions.

The effectiveness of insulation layers depends on their thickness and the thermal conductivity of the materials used, air temperature, wind speed, the time during which it is necessary to protect the soil from freezing, etc.

The effectiveness of insulation increases when laying insulating layers in advance of the onset of negative temperatures. The higher the temperature of the soil at the time of insulation, the longer the process of its cooling will be and, therefore, it will remain in this state longer.

Insulating layers made of loose materials (sawdust, straw, moss, peat) must be protected from compaction caused by the movement of transport or construction vehicles, since with an increase in the density of these materials, their thermal insulation properties decrease.

1.4 Soil loosening methods

1.4.1 Explosive method

For loosening frozen soil, heavy rippers, impact devices that are equipped with excavators, as well as special machines and mechanisms are used. At deep freezing soil, its loosening is carried out in an explosive way. The method of mass ejection explosion is considered to be especially effective. Loosening of frozen soils by explosions is advisable to use for large volumes of work on sites located far from residential buildings and industrial buildings, and at a freezing depth of more than 0.6 m.

In the production of blasting, it is necessary to calculate in advance the magnitude of the charge, i.e., the amount of explosives laid in one place. The amount of explosive charge intended to explode a certain volume of soil depends on a number of factors:

the location of the charge in relation to the day (open surface) of the soil;

soil strength;

the type of explosives used and the form of charge;

given release (whether the explosion is set to release or only loosening);

the number or mutual arrangement of charges, etc.

It is very difficult to take into account the influence of all these factors in advance. Therefore, the magnitude of the charge is preliminarily calculated approximately according to empirical formulas, and then it is refined by trial explosions.

The value of the specific charge q of various explosives is preliminarily assigned according to reference books and then specified empirically.

The resistance of frozen soils to blasting varies significantly depending on their temperature and humidity during freezing. The specific consumption of explosives also depends on the depth and diameter of the hole. In most cases, with a decrease in the thickness of the frozen layer and, consequently, with a decrease in the value of a unit charge specific consumption VV increases.

The depth of the holes should be 0.8-0.9 of the thickness of the frozen layer, the diameter should be 40-70 mm. Boreholes of large diameters are used with a greater thickness of the frozen layer (Fig. 1)

Rice. 1. Scheme of the location of boreholes when loosening frozen pounds with explosions: H - depth of the face; L is the thickness of the frozen layer; I, - distance between holes; 12 - distance between rows of holes

1.4.2 Mechanized method

The development of frozen soil by excavators is possible at a small depth of freezing. So, excavators equipped with a straight shovel with a bucket with a capacity of 0.65 m³ can develop a frozen crust up to 25 cm thick, with a bucket of 0.35 m³ - up to 15 cm. bucket wheel excavator or trench chain excavator with special interchangeable equipment.

To deal with frost, buckets are equipped with electric heaters or vibrators.

Application construction equipment not designed to work in northern construction conditions, leads to rapid wear, frequent breakdowns and excessive repair costs. At low negative temperatures, there is a rapid failure of hydraulic systems and rubber tires of machines, increased fragility of parts. It is also inappropriate to use excavators as a base machine as a ripper. impact action due to the reduction of their service life. One D-652AC ripper is used more efficiently and productively than 20 mechanical hammers mounted on E-652 excavators.

Due to the high abrasiveness of frozen soils, the wear of the metal of the cutting bodies of earth-moving machines increases sharply, the specific energy intensity of the development of frozen soils increases by 4-6 times, therefore, in some cases (especially in extremely cramped areas) during repair and construction work, subject to safety precautions for loosening frozen soils, an explosive method is used. Promising direction development of frozen soils is the use of static rippers and disc milling machines. For loosening frozen soils before excavation, bar earth-moving machines and trench excavators converted for this purpose are used. The use of mechanized methods for the development of frozen soils makes it possible to reduce the proportion of the volume of work performed with the help of percussion bodies mounted on excavators (hammer ball, wedge-woman, "torpedo"), and to use excavators for their intended purpose - for excavation.

With limited volumes of earthworks in cramped conditions, frozen soil is destroyed with a mechanized tool (jackhammers, thermal drills, high-frequency electromechanical devices, explosive tools, etc.) or highly mobile small-sized working bodies are used on pneumatic wheel tractors (screw permafrost, spring-loaded wedge-hammer (Fig. 2) , impact machines, end mills with a torsional vibration vibrator, etc.).

Rice. 2. Loosening frozen soil with a diesel hammer with a wedge earthwork winter soil

With mechanical methods of developing frozen soil, the length of the grip is determined taking into account the hourly productivity of the rippers, air temperature and wind speed. In winter, dump trucks with metal bodies are used to transport soil. The lower the air temperature, the harder it is to unload their bodies due to the freezing of soils with metal. In areas with an average monthly temperature in January not lower than -10 °C, when transporting soils containing clay particles up to 10%, bodies should be heated with exhaust gases. Under lower air temperatures and especially with bulk materials with a humidity above the optimum value, in contact with a metal surface for up to 5 hours, the inner surface of the body must be lubricated with solutions of chloride salts, sprinkled with slag, molding sand or other bulk materials at each trip.

If the temperature approaches -50 ° C, then the body needs to be lubricated with oily prophylactic liquids (used by autol, nigrol and other antifreeze reagents) after 3-7 flights. At temperatures up to -20 °C, sodium nitrate, sodium or calcium nitrate, urea and many other reagents with a concentration of 30 to 50% can be used. When backfilling trenches or erecting the upper part of embankments in winter, as already mentioned, mainly sandy soils are used, which are easier to develop in winter than coherent ones, due to their lower moisture content.

Sands at a negative temperature, but not lower than -0.5 ° C, compact well. Thus, the technology of work is simplified when using sandy soils.

It is of interest to use a manual high-frequency electrothermomechanical device for the destruction of loose frozen soils, which is based on the combined use of high-frequency and mechanical energy. The manual high frequency knife is equipped with high frequency generator and a working body - a pair of flat electrodes converging at an acute angle. The electrodes perform a dual function: an emitter of electromagnetic energy and a mechanical wedge. The mass of the tool is 5 kg, the speed of penetration of slots is up to 40 cm/s.

In recent years, for the destruction of frozen and rocky soils, hydraulic hammers, which are hung on hydraulic excavators as replaceable working equipment, have found useful use. If the depth of soil freezing is not more than 1.3 m, then loosening is carried out in one pass, at a greater depth - in layers of 0.9-1.0 m with cleaning of the loosened layer. For layer-by-layer loosening of frozen and dense soils and rocky fissured rocks, mounted rippers of static and dynamic action, earth-moving milling machines, and vibratory roller rippers are used. Mass-produced mounted rippers have the highest productivity, especially during linear work, with a freezing depth of 0.6-1 m. There are also experimental samples of rippers with a working body - a steel shaft with replaceable wedge-shaped tips or attachments in the form of a set of pneumatic hammers.

1.5 Soil thawing

Thawing of frozen soils is carried out when the explosive or mechanical method of loosening is impossible and with small amounts of work. Soil thawing is carried out by heating it with steam, hot water, electric current or fire. Depending on the method of heat supply from the heaters to the ground, there are 3 types of thawing: surface, radial, deep.

The following methods of thermal thawing of the soil are possible:

fire, open fire, when burning solid, liquid or gaseous fuel;

radiation, using polymer film. Apply in spring time;

electric - high-frequency or low-frequency. Low-frequency, in turn, is high-voltage and low-voltage;

steam-water;

hydraulic.

Preparation for the development of frozen soils using thawing should be used in cramped conditions, hard-to-reach places and with small amounts of work (up to 50 m3), as well as when it is impossible to use other, more economical methods. If the soil freezing depth is more than 0.4 m, it is better to thaw it using the radial (deep) method, installing heaters in the thickness of the frozen soil.

The fire method is ineffective and is used only in the presence of fuel waste and small amounts of work. Fuel consumption is 3 kg of standard fuel per 1 m² of surface at a thawing depth of 0.6 m.

For electric thawing, surface, vertical and deep electrodes are used. The latter are the most efficient. The electrodes are made of rolled steel with a diameter of 10-25 mm, a length of 1 m or more. The step of the electrodes during thawing of the soil is 0.4-0.6 m. For deep electrical heating, perforated tubular electrodes are used, through which electrolyte is poured into the soil (4% solution of sodium chloride and calcium chloride).

Electricity consumption during surface thawing is 90-120, radial - 70-90, depending on the characteristics of the soil.

For areas with an average monthly outdoor temperature of -15 ° C and a freezing depth of up to 1.5 m, the duration of deep thawing is 10-12 hours.

Soil heating is carried out using heating appliances in the form of needles (Fig. 3) installed in wells drilled in the frozen layer. Needles can be electric, water circulating and steam. Electric needles are made from pipes 1.5 m long, inside which electric heating elements nichrome wire resistors. Install needles in drilled wells.

Water needles require the construction of a special boiler room, and heat pipes require constant supervision, since in severe frosts they may freeze. Water and steam needles are uneconomical and are used very rarely. With a shallower freezing depth, it is allowed to use the method of surface thawing.

Rice. 3. a - steam needle; b - water needle; c - electric needles; g - electrodes located horizontally; d - the same, vertically.

With this method, the soil is not moistened, but a large amount of heat is required.

However, with all methods of heating, one should not strive to thaw the entire volume of frozen soil. For example, the lower part of a layer of frozen soil 15-20 cm thick can be left in a frozen state and loosened when the soil is excavated by excavators. This speeds up excavation work and reduces heat consumption.

1.6 Requirements for thawing and loosening of soil

soil earthen trench bulldozer

The thawing and loosening of the soil is carried out sequentially, in sections, the dimensions of which are assigned based on the daily productivity of earth-moving machines. At the same time, it is necessary to organize earthworks in such a way that the development of the prepared soil is carried out around the clock in order to avoid freezing of the soil during breaks (transfer of shifts, repair of mechanisms and other operations).

In the process of backfilling pits, it is necessary to ensure that the volume of frozen clods in the soil, which fills the sinuses between the walls of the pit and the foundation erected in it, does not exceed 15% of the total backfill volume. Frozen soil should not be used when backfilling sinuses inside the building.

To ensure these requirements, the soil to be used for backfilling the pit is laid in dumps, while necessary measures, excluding its freezing.

When loosening frozen soil to a depth of up to 1.5 m, as well as when finalizing slopes and foundations of pits and trenches, borehole and slotted methods should be used, and for h> 1.5m, borehole or slotted methods.

Well drilling in non-rocky soils by the borehole method is carried out by screw-type drilling rigs. At a depth of loosening of frozen soil up to 2 m, concentrated charges are used, and at a large depth, dispersed ones.

Slots in frozen soil, in order to avoid oversized pieces, are usually cut at a distance of 0.9 m from one another when using excavators with buckets with a capacity of up to 0.65 m3; at a distance of up to 1-1.2 m - when using larger excavators. Slots are cut to the depth of soil freezing with slot-cutting machines of milling type or bar machines.

In winter, the construction of embankments from rocky, gravel and sandy low-moisture soils that retain their flowability when freezing is carried out in the same way as in summer, but without allowing the formation of layers of unremoved snow, ice and accumulations of frozen clods in the embankment. The number of penetrations of the means of soil compaction, as a rule, is specified empirically.

When choosing the grip length, in addition to air temperature, soil properties and the content of frozen clods, as well as the presence of earthmoving equipment, wind speed must also be taken into account: the higher the speed, the faster the soil aggregates freeze, therefore, the duration of soil compaction is prescribed taking into account the norms.

The greatest length of the capture l m, soil compaction is determined by the formula

l \u003d P (T-Ttr-Tr) 60bh

where P is the performance of a set of compacting machines, m/h;

T - the time during which the soil after development is still suitable for compaction, min;

Тtr - time of transportation of soil by one dump truck, min;

Tr is the duration of its unloading, min;

b and h are the width and thickness of the compacted layer, respectively.

The range of soil transportation is set from the condition of inevitable heat loss, but when it can still be compacted on a grip of minimum length.

Mounds of cohesive soils are erected taking into account their compaction and settlement after thawing at the rate of 5% of their height in severe natural conditions and 3% of height in years with mild winters.

1.7 Methods for constructing embankments from cohesive soils

When constructing embankments from cohesive soils in winter, several methods are used.

Putting soil into water. They are mainly used in the construction of dams. For laying in water, cohesive soils are used, which ensure the consolidation of the embankment within 5-6 months.

The soil is laid in special ponds in layers of 3 m or more. At temperatures below -10 ° C, the water in the pond is heated by special installations. To reduce the heat transfer of ponds, the surface of the water is covered with polystyrene foam plates.

Laying thawed soil "dry" with layer-by-layer compaction. In this way, any clay soil with optimal moisture in layers of 0.4-0.45 m in a loose body. Freshly laid and planned soil is treated with a concentrated solution of sodium chloride or calcium chloride at the rate of 1-3 l / m3, depending on the temperature of the external soil. The soil treated with saline is compacted with pneumatic rollers in 8-10 passes. Soil acceptance, its leveling, treatment with solutions and compaction occur continuously as the soil enters the laying area. There is no usual division of the laying area into separate cards (acceptance, leveling, compaction, etc.). The entire cycle of soil treatment at an outdoor temperature of -40 ° C lasts no more than 1.5-2 hours, at a temperature of -20 ° C - 5-6 hours. If necessary, the surface of the laid card and especially the base of the layer being laid is treated with heat.

An inclined method of backfilling the soil, which allows to reduce the size of the maps, and consequently, to reduce the cooling and freezing of the soil. Depending on the height of the embankment and its profile, filling is carried out by a scraper to the full height or in tiers. The dumping process is carried out continuously - in one area the soil is taken and leveled, in the other it is compacted. The recommended layer thickness is -0.2 m. The backfill map is covered with the next layer of soil before it freezes, so the dimensions of the map sections are assigned depending on the intensity of soil backfilling and air temperature.

With this method, it is recommended, if necessary, to apply soil treatment with chlorides at the rate of 0.5-2 l/m3 and heat.

In all cases of development of frozen soils, it is necessary to take into account its further use after loosening.

For loosened frozen soil, the size of the blocks is limited only by the size of the bucket of the excavator used. When laying the soil in the embankment, the dimensions of the pieces obtained during spalling should not exceed the dimensions allowed by the technical instructions from the conditions of compaction of the poured layers (15-30 cm).

2. Excavation during hot weather

2.1 Features of excavation in hot weather

High temperature, low humidity and strong winds(dry winds) lead to drying and hardening of the soil, during development, the dust content of the air increases, reducing productivity and deteriorating the performance of earth-moving machines. Therefore, when drawing up traffic patterns for earth-moving machines and vehicles, it is necessary to take into account the prevailing wind direction, organizing their working movement against the wind direction or at an angle to it.

2.2 Rational method of soil development

Most in a rational way soil development under these conditions is their preliminary moistening (if possible) to optimal values, which reduces the dust content of the air and facilitates the development of the soil. Moistening the soil to the optimum moisture content also gives a high effect when it is compacted.

2.3 Trenching with bulldozers

When developing trenches with bulldozers, it is recommended to use longitudinal-transverse and transverse-shuttle traffic patterns (Fig. 4). According to the first scheme, two bulldozers develop the soil: one develops the soil in the longitudinal direction, and the second moves it to the dump with transverse passages, while the soil is evenly laid along the entire edge of the trench, which facilitates backfill.

Rice. 4. Schemes of movement of bulldozers: a - longitudinal-transverse; b - cross-shuttle; No. 1, No. 2, No. 3 - bulldozers

According to the cross-shuttle scheme, the soil is developed by two bulldozers moving towards each other from the ends of the grip to the middle, and the third bulldozer moves it to the dump. The length of the capture is taken within 50 m. The disadvantage of this scheme is the concentration of the dump in the middle of the trench, which then makes it difficult to backfill.

Loose sand is recommended to be developed and moved in paired operation by several bulldozers, which at the same time move in parallel at the same speed at a distance of 0.3 to 0.5 m from each other, reducing lateral losses of soil.

A significant effect is achieved in the development of sandy loams and loams by self-propelled scrapers DZ-13 and DZ-15 using a pusher tractor, which doubles the filling of the bucket and reduces the loading path by the same amount.

Conclusion

So, summing up the results of the work, we conclude that the topic of the essay "Peculiarities of excavation work in conditions of low temperatures and during hot weather" is disclosed. It has been proven to be relevant. Excavation work in winter conditions is allowed if it ensures the efficiency of the entire construction process and the timely completion of construction and installation works.

The performance of earthworks during hot weather has its own characteristics, which must be taken into account when designing the production of works.

The purpose of the work was achieved, since the work considered the features of earthworks in conditions of low temperatures and during hot weather.

Upon reaching the goal, the following tasks were solved: to find out the features of the soil in winter; learn how to protect the soil from freezing, what are the ways to protect and loosen the soil; find out what are the types and methods of thawing soils; what are the requirements for thawing and loosening; what are the ways to use cohesive soils for embankments, find out the issue of excavation during hot weather, its features, methods of excavation of soils in the summer, how trenches are being developed with bulldozers.

Used Books

1. Kremneva E.G. Production of earthworks. Workshop. M.2008

2. Neklyudov M.K. Mechanization of soil compaction. M. Stroyizdat. 1985

3. Help Guide. Production of earthworks.

4. Cherkashin V.A. Development of frozen soils. Leningrad. Stroyizdat. 1986

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Features of earthworks in winter

In winter, when negative temperatures are established, the soil freezes due to heat loss and the transition of the water contained in its pores into ice, accompanied by a change in its physical and mechanical properties (strength, deformability, thermal conductivity, etc.).

Considering that during freezing, the mechanical strength of the soil and, consequently, the labor intensity of development, increase sharply, they try to carry out measures for the preliminary protection of the soil from freezing, ensuring its development in thawed form. Τᴀᴋᴎᴍ ᴏϬᴩᴀᴈᴏᴍ, the main methods of preparing and developing soils in winter are their protection from freezing, thermal and chemical thawing, loosening and mechanical development of frozen soils. The factors determining the choice of methods and methods of winter excavation are the scope of work, soil properties, type of earthwork and specific construction conditions.

Soil protection from freezing is carried out long before the onset of cold weather by plowing with harrowing, deep loosening, sheltering with insulating materials and chemical treatment.

For plowing the soil, various plows with a loosening depth of at least 35 cm and rippers with a loosening depth of 50 ... 70 cm are used. Then the soil is harrowed to a depth of 15 ... 20 cm. With deep loosening (to a depth of 1.3 ... 1 .5 m) use single-bucket excavators with a bucket with a capacity of 0.4 ... 0.65 m 3, while the soil is developed all over and laid in place of the adjacent (previous) penetration.

Local materials are used as insulating materials: dry leaves, peat, sawdust, straw, reeds, slag, etc.
Hosted on ref.rf
Can also be applied polymer materials, films, polystyrene, etc. Sometimes the soil is chemically treated before plowing, ᴛ.ᴇ. impregnation of the surface layer of the soil with calcium chloride and sodium, sodium nitrite-nitrate, which lower the freezing point of water in the soil (up to - 30 ° C). The soil protected from freezing is developed in the usual mechanized way.

At the same time, when the soil could not be protected from freezing in a timely manner and according to the work schedule, it is extremely important to develop the soil in winter, ᴛ.ᴇ. in a frozen state, then in this case it is necessary either to thaw them, or to develop them in a frozen form using special means and methods.

Methods for thawing frozen soils are based on the fact that due to the heat transferred to the layer of frozen soil, the ice in its pores is melted and the soil becomes thawed. Soil thawing is used for small volumes of work, in cramped conditions, hard-to-reach places and in cases where more economical and less energy-intensive methods cannot be used. Soil thawing is carried out both with the help of natural heat sources - solar heat, water heat from natural reservoirs, and artificial - due to the combustion of solid, liquid or gaseous fuels, the use of steam or electricity. According to the direction of heat propagation in the soil, the following three basic methods of thawing can be distinguished: from top to bottom (surface); bottom up (deep); in the radial direction.

Surface thawing is carried out either using natural heat sources or artificial ones - hot gases (fire method), in greenhouses, reverberatory furnaces, horizontal electrodes, by chemical means. Chemical thawing involves the introduction of a solution of sodium chloride into the soil, under the influence of which ice crystals dissolve in the pores of the frozen soil.

Deep and radial thawing is carried out with hydraulic, circulating water, steam and electric needles, as well as electrodes.

Loosening and development of soils in a frozen state, it is carried out by explosive or mechanical means.

Explosive (hole or slot) method is one of the basic ways of preparing frozen soils for excavation. It is especially effective at freezing depths of 0.4 ... 1.5 m or more and with significant volumes of frozen soil development. It is used mainly in undeveloped areas, and in built-up areas - using shelters and explosion localizers (heavy loading platforms). When loosening to a depth of 1.5 m, blast hole and slot methods are used, and at greater depths, borehole or slot methods. Slots at a distance of 0.9 ... 1.2 m from one another are cut with slot-cutting milling machines or bar machines. The slots are charged through one with elongated or concentrated charges, after which they are filled with sand from above. Holes and wells are staggered.

When loosening the soil in an explosive way (Fig. 4.22, a), the site is divided into grips, where holes are drilled on the first of them, charged and blown up; the second job is not performed due to safety conditions; on the third they are developing the soil. The dimensions of the grips are determined based on the variable capacity of the excavator (excavators).

Mechanical loosening of frozen soils is used at a freezing depth of 0.4 ... 1.5 m and small excavations of pits and trenches. At the same time, crushing or chipping of the frozen layer is carried out by dynamic or static action of special interchangeable working equipment installed on the base machine (tractor, excavator, etc.). Dynamic impact is provided due to shock, vibration or their combined effects using a ball or wedge hammer, diesel hammers, wedge tractor rippers, etc.
Hosted on ref.rf
Static impact during the destruction of frozen soil is provided by introducing into it a working body consisting of one or more (up to 5) teeth while the tractor (tractor) is moving.

For mechanical loosening of frozen soil (Fig. 4.28), when excavating pits and trenches, weightless rippers and earth-moving milling machines, as well as bar machines (for cutting frozen soil into blocks), are used, and for vertical site planning - mounted rippers. These machines are paired with excavators that develop both loosened frozen and non-frozen soil.

Rice. 4.28 - Loosening frozen soils when arranging pits

With a small depth of soil freezing, it is loosened by tractor rippers with longitudinal penetrations at an angle of 60 °. The loosened soil is moved by a bulldozer to the end of the pit and loaded onto dump trucks by an excavator. Subsequent layers of frozen soil can be developed with a ripper, first with transverse penetrations, then with longitudinal and diagonal ones. The ripper tooth, based on the properties of the soil and the power of the bulldozer, is buried by 0.5 ... 0.8 m.

With a large depth of freezing, block methods of developing frozen soils are often practiced, when their solidity is first broken by cutting into blocks (strips) using special machines equipped with circular saws or bars. Usually small- and large-block methods of soil development are used. small block method(Fig. 4.28, b) is used when digging small pits and trenches at a freezing depth of 0.6 ... 1.4 m. Longitudinal and transverse slots of a disc milling machine or bars cut the frozen layer into blocks ranging in size from 0.6 x 0 .8 to 1 x 1.1 m, and then with a front shovel excavator (bucket capacity 0.65 ... 1 m 3) frozen blocks are loaded and thawed soil is developed. Large block method used in the development of pits near buildings or structures, when soil shaking is not allowed, which is inevitable during shock and vibro-impact loosening. Frozen soils are cut into blocks weighing 4 ... 10 tons by their subsequent removal from the face with bulldozers (Fig. 4.28, c), cranes (Fig. 4.28, d) or electric winches. When using cranes, the blocks are torn off and moved away from the thawed base by bulldozers, and then, using a tong grip, they are loaded onto dump trucks with the tailgate removed (Fig. 4.28, d). At the same time, the recesses are divided into two grips; on the first one, blocks are cut, and on the second, they are removed with a crane and the base is cleaned.

The development of soils in a frozen state can only be carried out with the help of powerful earth-moving equipment, ĸᴏᴛᴏᴩᴏᴇ allows you to develop frozen soil without it pre-training(loosening). Hydraulic excavators are used as such equipment. They work especially effectively when using front and back shovels with buckets. active action, in the bottom of which pneumatic hammers with teeth are mounted, ensuring the destruction of frozen soil.

Trench Development Methods in winter, the following: development of a trench in reserve, with protection of the soil from freezing, without preliminary preparation, with preliminary loosening. The development of trenches in advance (ᴛ.ᴇ. in advance) for a full profile is carried out in the autumn period before the onset of frost. The disadvantage of this method is that the slopes of the trench partially collapse over time, and the soil dump freezes by the time the pipelines are backfilled, which requires its preliminary loosening before backfilling. Methods for developing trenches with soil protection from freezing are fundamentally similar to the methods discussed above. Trenches without preliminary preparation are developed in cases where the necessary technical conditions are available. With a freezing depth of up to 0.3 m, trenches can be developed with single-bucket excavators, and in soils with a freezing depth of up to 1.5 m, they can be torn off to a full profile with bucket-wheel excavators.

The method of developing a trench with preliminary loosening of the soil by explosive or mechanical means is used when the soil freezes to a depth of more than 0.4 m. Loosening is carried out with hole charges or using rippers. The loosened soil is planned by a bulldozer, and the development of the trench is carried out by a single-bucket excavator. It is extremely important to take the length of the loosened soil section equal to the excavator's shift productivity in order to avoid repeated freezing of the soil.

The pace of earthworks when digging trenches in winter is extremely important to strictly coordinate with the pace of insulating and laying work on the pipeline, since even 2 ... 3 days ahead of earthworks, there is a danger of soil dump freezing. This will require either preliminary loosening of the soil in the dump before backfilling the pipeline (which is not always easy to do), or powdering the pipes before backfilling.

When developing trenches in frozen soils, several types of machines are most often used, each of which prepares a work front for machines that perform subsequent operations. For example, clearing the soil surface from snow with a bulldozer allows you to start loosening or cutting through the frozen soil with rippers (bar machines), which, in turn, prepare the work area for the excavator, etc. With a freezing depth of up to 1.3 m trenches, narrow pits can be developed with backhoes with a bucket with a capacity of 0.65 m 3 and above, with preliminary cutting of slots through 0.4 ... 0.5 m with a bar machine. Moreover, with a trench width of up to 2 m, it is enough to make longitudinal cuts along the trenches, and with a width of more than 2 m, transverse cuts are also made at an angle of 30 °, while cutting blocks in the form of rhombuses. Wide trenches or pits (up to 8 m wide) are developed with two end penetrations of an excavator. When developing wide trenches for laying collectors in frozen soils with a significant freezing depth, bar machines, wedge-hammer excavators and backhoes are usually used.

Backfilling trenches with pipelines in winter conditions. If the construction of pipelines is carried out by the flow-combined method (the pipeline is laid in a trench immediately after its development), it is backfilled with thawed soil by a bulldozer, as in normal conditions. In the event of freezing of the soil in the dump, for example, in case of violation of the flow, the pipeline in the trench is sprinkled with thawed soil to a height of at least 0.2 m above the pipe in order to avoid damage to the insulation. Further backfilling of the pipeline with frozen soil that does not contain clods of more than 5 ... 10 cm is carried out by bulldozers.

1. SNB 5.01.01-99 Bases and foundations of buildings and structures. - Mn.: Ministry of Architecture and Construction of the Republic of Belarus, Mn., 1999. - 36 p.

2. SNiP 3.02.01-87. Earthworks, foundations and foundations / Gosstroy of the USSR - M .: CITP Gosstroy of the USSR, 1988. - 128 p.

3. Manual P11-01 to SNB 5.01.01-99. Geotechnical reconstruction of building foundations and foundations of structures. - Minsk: Ministry of Architecture and Construction of the Republic of Belarus, Minsk, 2001. - 120 p.

4. Manual P17-02 to SNB 5.01.01-99. Design and installation of retaining walls and foundations for foundation pits. - Mn.: Ministry of Architecture and Construction of the Republic of Belarus, Mn., 2003. - 95 p.

5. Earthworks (Builder's Handbook) / Ed. L.V. Grishpun. – M.: Stroyizdat, 1992. – 352 p.

Topic 5. Concrete and reinforced concrete work

Features of earthworks in winter - the concept and types. Classification and features of the category "Peculiarities of earthworks in winter" 2017, 2018.