Earthworks in winter. Earthworks in winter. To ensure these requirements, the soil to be used for backfilling the pit is laid in dumps, while the necessary measures must be taken to exclude it.

Pile classification

Modern construction allows buildings to be erected various designs on almost any soil. Pile classification It is produced according to the method of transferring loads from structures to the ground, the shape of the trunk, cross-section, material and methods of work.

According to the production method, piles are divided into hammered and stuffed. Production driven piles is carried out in the factory, after which they are transported to the construction site and immersed in the ground by shock or non-impact methods. Howling turn stuffed piles are formed directly on the construction site in the soil itself.

According to the material, piles are divided into reinforced concrete and concrete, wood and metal. According to their shape, piles are round, square and prismatic in section. In the longitudinal section, the piles can be of the same width, tapering towards the end or, conversely, expanding.

Features of the earthworks in winter time 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 should be compensated. Soils are protected from freezing as follows:
before the onset of frost, soils to be developed in winter are protected from freezing by laying a layer of material with low thermal conductivity, loosening (plowing) or treating with salts that lower the freezing point of water;
in the course of work, the sealing layer is removed only in an area sufficient in size for the operation of the SCM during the shift, in such a way that the open ground does not have time to freeze before its development;
soil should be developed on the most compressed front of work.

Method of soil protection from freezing and technology its developments are chosen by means of a technical and economic comparison of various options that are possible under given conditions. The simplest and most economical way to prevent deep freezing of soils is their preliminary loosening before the onset of frost, carried out by cross-plowing with tractor plows or trailed rippers to a depth of 25-35 cm. After plowing, harrowing is carried out to a depth of 10-15 cm. Pores of loosened soil filled with air, reduce its thermal conductivity.

The freezing of loosened soil occurs more slowly than the surrounding dense soil. The frozen layer of loosened soil has low strength and is relatively easy to develop with excavators or bulldozers. The warming effect of loosened soil is enhanced by the accumulation of snow on it. Soil warming by loosening is usually used in areas scheduled for development during the first third of winter.

One of the ways to protect the soil from freezing is to treat it chemical additives lowering the freezing point of water. Most often, CaCl2 and NaCl salts are used for this purpose. Soil treatment consists in pouring solutions of these salts on its surface. Penetrating into the soil, saline solutions reduce the freezing point of the moisture in the soil, and thus protect it from freezing. Soil layer impregnated salt solutions, in turn, protects the underlying layers from freezing.

Loosening of frozen soils by this method should be used when the soil freezing depth h is more than 0.4 m (mainly in undeveloped areas, and in built-up areas - using shelters and explosion localizers).

14 In construction, from 20 to 25% of the total excavation work is carried out in winter conditions.

At negative temperatures ah, the freezing of water contained in the pores of the soil significantly changes the construction and technological properties of non-rocky soils. In frozen soils, it increases significantly mechanical strength, in connection with which the development of their earth-moving machines is difficult or even impossible without preparation. The depth of freezing depends on the air temperature, the duration of exposure to negative temperatures, the type of soil, etc. frozen ground, thawing of frozen ground. The direct development of frozen soils can be carried out in a block way or by earth-moving machines with working equipment that destroys frozen soil in its natural occurrence. It is allowed to develop frozen soil with single-bucket excavators, depending on the bucket capacity, with a frozen layer thickness of 0.25 to 0.4 m. Explosive loosening is one of the main methods for preparing frozen soils for excavation. This method is very effective at a freezing depth of more than 1 m and large volumes works performed in newly developed territories or far from buildings and structures.

The essence of the explosive method of loosening consists in crushing frozen soil with the energy of an explosion of charges placed in cavities previously created in the soil (holes, wells, sleeves, boilers, slots).

Mechanical loosening of frozen soil is used at a freezing depth of 0.4 to 1.5 m and small excavations of trenches or pits.

The essence of mechanical loosening consists in crushing or chipping the frozen layer by dynamic or static action, which is carried out by replaceable working equipment installed on the base machine (excavator, tractor, etc.). Dynamic impact is produced by shock, vibration and vibro-impact methods.

At shock method use a hammer ball or wedge hammer, diesel hammer, wedge tractor rippers, etc.

The destruction of frozen soil by static action is carried out continuously by a working body, consisting of one or several (up to 5) teeth, which are introduced into the soil when the tractor (tractor) is moving.

The thawing of frozen soils is used for small amounts of work, in cramped conditions, hard-to-reach places, and in cases where it is impossible to use more economical and less energy-intensive methods. The essence of the thawing method lies in the fact that the heat transferred to the layer of frozen soil melts the ice in its pores and turns the soil into a thawed state.

15. In this technological map, the following composition of mechanisms is taken as an example: a DZ-34S bulldozer with DP-9S ripping equipment and an EO-4124 backhoe equipped with a bucket with teeth with a capacity of 0.65 m 3, designed for the development of loose and cohesive soils I-IV groups and pre-loosened rocky and frozen soils with pieces no larger than 400 mm in size.

2.5 Along the marked route of the trench and the territory adjacent to it, in the places of storage and laying out of pipes, snow is cleared with a bulldozer if necessary.

2.6 After that, they start loosening the frozen soil with a DP-9S mounted ripper along the width of the trench, adopted in accordance with clause 3.3 of SNiP3.02.01-87. Loosening of the soil is carried out in layers for two penetrations. To ensure the work front for the excavator, the upper layer is initially loosened to a depth of 0.4 m and completely removed by the bulldozer into the dump in the parts remote from the bottom. During the second penetration, the soil is loosened to the remaining freezing depth in the trench section about 50 m long and (as necessary) a rough layout of the loosened section is made with the movement of large blocks of soil to the dump.

The excavator EO-4124, moving along the leveled surface of loosened soil along the axis of the trench, develops the soil to a mark of minus 2.1 m with loading the soil into dump trucks. The trench is developed by an excavator from low elevations of the longitudinal profile towards the slope. The soil development scheme in the trench is shown in Figure 1.

1 - excavator EO-4124; 2 - bulldozer DZ-34S with mounted ripper DP-9S; 3 - dump truck KAMAZ-55111; 4 - inventory fence; 5 - pole

Figure 1 - Scheme of excavation in a trench

2.7 Further loosening of the second layer of frozen soil is carried out each time for the volume of soil that ensures the operation of the excavator for 2 shifts.

2.8 Cleaning the bottom of the trench to the design mark is carried out by the same excavator using a leveling plow. The shortfall remaining after mechanized cleaning should not exceed 0.05 m.

2.9 Need to fulfill handmade for cleaning up the shortfall is determined when linking the map to specific conditions, depending on the purpose of the trench and the type of communications.

2.10 The soil is transported by KAMAZ-55111 dump trucks and others along a planned dirt road for a distance of up to 1 km. Dump trucks approaching for loading are installed at pre-set milestones at a distance of at least 2 m from the bottom of the excavation slope.

2.11 A DZ-34S bulldozer is used for the construction and maintenance of roads, soil leveling.

2.12 The method of restoring the foundations, broken as a result of freezing, is agreed with the design organization.

21. Drainage and lowering of the level ground water. When arranging excavations located below the groundwater level, it is necessary to drain the water-saturated soil and ensure its development in normal conditions. In addition, it is necessary to prevent the ingress of groundwater into pits, trenches and workings and the period of work in them.

efficient technological method The solution to such problems is the pumping of groundwater. Ditches and trenches with a small influx of groundwater are developed using open drainage, and if the inflow of water is significant and big thickness saturated layer to be developed, then before the start of work, the groundwater level is artificially lowered using various methods of closed drainage, called dewatering.

Open drainage is used to pump out the flowing hearth directly from the pits or trenches with pumps. With open drainage, groundwater seeps through the slopes and the bottom of the pit and is directed along dug drainage ditches or trays to pits specially arranged in the lower part of the pit, called sumps, from where water is pumped out by diaphragm or centrifugal pumps of appropriate capacity.

Pumps are selected depending on the debit (inflow) of water, and the debit itself is calculated according to the formulas for the steady movement of groundwater.

Drainage ditches are arranged with a bottom width of 0.3 ... 0.6 m and a depth of 1 ... 2 m with a slope of 0.01 ... 0.02 m towards the pits. The pits themselves stable soils fixed in the form wooden frame without a bottom, and in floating soils also with a sheet pile wall.

Open drainage is simple and accessible way groundwater control, but has a serious technological disadvantage. Ascending flows of groundwater flowing through the walls and bottom of pits and trenches liquefy the soil and carry it out to the surface small particles. As a result of such washing out, this method has a number of significant disadvantages:

■ the natural strength of the excavation base decreases due to its erosion by running water;

■ presence of water at the bottom of the excavation hinders excavation;

■ fastening of the walls of the excavations is required, since the movement of water to the sumps also sets in motion the soil;

■ The inflow of water to the catchment ditch can cause weakening of the foundations of buildings and structures located next to the facility under construction.

In cases where drainage is inappropriate, three change the artificial lowering of the groundwater level (water drawdown).

24 . Equipment used in piling

Driving piles into the ground is complex process and is carried out in two main ways: 1) using pile drivers impact action; 2) using vibrators. In addition to these methods, for driving piles, machines of pressing and screwing action are used, as well as aggregates of mixed action - vibro-impact hammers and vibro-pressing machines.

Percussion pile drivers include pile hammers, which are divided according to the type of drive into hammers with an internal combustion diesel engine (diesel hammers), single and double-acting steam-air hammers and mechanical hammers (27.1).

Diesel hammers work on the principle of diesel engines; steam-air hammers are powered by steam or compressed air, directly acting on the impact part of the hammer, and mechanical hammers are driven by a winch connected by ropes through a system of blocks with the impact part of the hammer.

For pulling and installing piles at the place of deepening, for installing a hammer on a pile, for directing a hammer to a pile when driving, as well as for moving a pile driving unit at a construction site, pile drivers are used. Depending on the purpose, the pile drivers are divided into pile drivers for driving vertical piles, rotary pile drivers for various types of immersion, and pile driver mounted on a crawler crane or on a single-bucket excavator.

When piles are located in clusters in weakly compressible soils, piles are driven in a spiral pattern, starting from the middle of the row in a spiral towards the outer rows of the site. On the large areas and dense soils, piles are driven according to a sectional scheme, i.e. they are immersed in sections through a row. Before driving piles, the main axes of the building or structure are preliminarily outlined and the shape and dimensions of the pile field are determined to draw up a layout drawing, from which the distances between the axes of the piles and from the walls of the building are transferred to the area.

As a rule, piles for the foundation under the foundations are driven one at a time using pile drivers.

Sheet pile driving is carried out with hammers of all types using pile drivers and shooting cranes. To hold the sheet piles and prevent their deviation from the vertical during driving, a guide frame is arranged, consisting of lighthouse piles and guide bouts attached to it. For immersion of steel sheet piles, guide templates are used, the shape of which is determined by the project

31. . Construction of stone structures in winter conditions

Negative temperatures have a strong influence on the physical and mechanical processes occurring in freshly laid masonry. The hardening of the mortar in the masonry stops due to the transition of the water of the solution into ice, and the cement hydration reaction, which began with the laying of the mortar, fades and stops as the temperature of the mortar decreases. The solution, when frozen, turns into a strong mechanical mixture of cement (lime), sand and ice. Water, passing into ice, increases in volume, which leads to an increase in the volume of the solution, as a result of which it loosens, the bonds between its particles are broken, and the strength decreases sharply. An ice film forms on the surface of the stones, and this further reduces the adhesion strength of the solution to the stone. As a result, with early freezing of masonry, its final strength at the age of 28 days. is significantly lower than the strength of normally hardened masonry.

In lime mortar, when frozen, the hardening process also stops, but unlike cement mortar, after thawing, the hydration process does not resume.

To perform masonry in winter conditions, the freezing method is used. His distinctive features are as follows:

■ at a positive temperature after thawing, the masonry will continue to gain its strength if the mortar has gained critical strength, which is usually more than 20% of brand strength;

■ the freezing method is not applicable to eccentrically compressed structures with significant eccentricity and structures subjected to vibration, as well as in rubble masonry, in walls made of rubble concrete, in vaults;

■ only cement and complex mortars are used, since lime and lime-clay mortars do not retain their ability to harden after thawing;

■ vehicles, in which the solution is delivered to the construction site, they must be insulated, a portion of the solution is supplied to the place of work only for 20 ... 30 minutes of work and at a temperature of the solution not lower than + 20 ° C;

■ a log of control over the execution of brickwork and its defrosting is mandatory, since due to the uneven density of the mortar during thawing, uneven precipitation is possible.

34. Depending on the type of stone products, their physical and mechanical properties and design requirements masonry can be solid, hollow, layered and large-block. Solid brickwork is made of bricks of all types. The solidity of the masonry is ensured by overlapping vertical seams. Along the wall, the masonry is tied up in each row, and in its thickness, after several rows, but not less than 50 cm. increased strength. When laying by freezing, as well as when erecting pillars and narrow piers, a single-row dressing system is recommended. With any system for dressing the seams of solid masonry, it is necessary to lay bonded rows in the lower (first) and upper (last) rows of the structure, as well as at the levels of the edges of walls, pillars and protruding rows (cornices, corbels, etc.). Concrete masonry and natural stones must have at least one bonding row for every three rows of masonry.

Brickwork with multi-row (a) and single-row (b) dressing system, hollow masonry from light concrete (c) and ceramic stones(d), layered lightweight (e) and facing (f) masonry: 1-insulation; 2-face brick; 3-metal brackets; 4-lightweight concrete.

Brick pillars, pilasters and piers up to 64 cm wide as the most important stone structures should be built only from a whole brick. For the walls of damp and wet rooms, in all cases, solid masonry should be used, primarily from ordinary clay bricks of plastic pressing. Hollow masonry made of lightweight concrete and ceramic stones with slit-like voids should be performed using a single-row dressing system. Hollow masonry is very effective. It allows you to increase productivity and reduce the mass of walls by 30...40%.

Laminated lightweight masonry consists of structural and heat-insulating layers connected by rigid or flexible ties. Thickness carrier layers determined by the requirements of masonry strength. The heat-insulating layer of the wall can be located both inside the masonry and at its inner surface. Its thickness is selected taking into account the results of heat engineering and economic calculations. The connections of the layers are rigid only if the distance between the axes of the vertical diaphragms is not more than 120 cm. Flexible connections consist of corrosion-resistant steels, the total cross-sectional area of which is not less than 0.4 sq. see 1 sq. m. wall surface.

Lightweight masonry is used for bearing walls buildings up to five stories high and self-supporting walls up to nine stories high. However, in all cases, layered masonry cannot be used if the premises have a high moisture content. Layered are also walls consisting of face brick or stone and embedded or flat facing slabs. External cladding tied with a stone and performed simultaneously with the construction of walls and pillars. The leaning thin cladding is attached to the wall with mortar or special mastic and connected to the masonry with corrosion-protected steel anchors. If the masonry is plastered, then the seams on its surface are not filled with mortar to a depth of 15 mm in walls and up to 10 mm in pillars and narrow piers. In rooms with wet processes production must be protected internal surfaces walls facing tiles, waterproof film coatings, etc. In this case, arrange external plaster Not recommended.

38. Conducted marketing research market construction products and analysis of literary sources made it possible to identify the following groups of properties, which are reflected in the quality indicators of construction:

social properties;
functional properties;
reliability;
aesthetic properties;
regional properties;
durability;
ease of use;
manufacturability;
maintainability;
environmental friendliness;
economic properties.

39 Determining the scope of earthworks

When a pound freezes, its mechanical strength increases significantly and, as a result, the time spent on its development increases dramatically. At the same time, temporary excavations in the frozen ground can be built without slopes, which reduces the cost of its development. The development of frozen soil with single-bucket excavators (forward and backhoes) without preliminary loosening is allowed with a frozen layer thickness of up to 0.25 m using a bucket with a capacity of 0.5-0.65 m; 0.4 m - bucket with a capacity of 1 - 1.25 m 3.

The pound to be developed, when it freezes to a great depth, must be preliminarily prepared in one of the following ways: protecting the soil from freezing; thawing of frozen soil; loosening of frozen soil.

The method of preparation should be selected and justified in the project, depending on the scope and conditions of work, the timing of their implementation and the availability of equipment. Pound protection from freezing should be carried out:

preliminary loosening until the soil freezes (plowing, harrowing, shoveling with an excavator);
coating the surface of the pound with heat-insulating materials with the retention of snow cover.

It is necessary to protect the soil from freezing before the onset of stable negative temperatures. When planning the development of soil in the first third of the winter period, it is necessary to provide for plowing the pound, followed by harrowing and keeping the snow cover, and for the rest of the winter time, deep loosening (shoveling) or warming the soil with heat-insulating materials.

Soil insulation is carried out with straw, sawdust, dry peat or slag, as well as synthetic coatings on the area in the contour of the trenches of the pit or excavation with a broadening on each side to the freezing depth. The thickness of the insulation layer is determined by calculation.

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 melts and the soil becomes thawed.

Methods for thawing frozen soil are classified according to the direction of heat propagation and the type of coolant used. According to the first sign, there are three ways to thaw a pound: from top to bottom (surface); from bottom to top (deep); in the radial direction. According to the type of coolant, the following main methods of thawing frozen pounds are distinguished: fire, in greenhouses with horizontal and vertical electrodes connected to power sources (electroprofessional); using steam or water registers, water circulation needles; salt solutions; pre-heated sand or slag.

Preparation for the development of frozen pounds by thawing should be used in cramped conditions, inaccessible places and with small amounts of work (up to 50 m 3), as well as when it is impossible to use other, more economical methods. With a freezing depth of a pound of more than 0.4 m, it is better to thaw it using the radial (deep) method, installing the heaters in the thickness of the frozen pound. Profit fun-ta is produced using heating appliances in the form of needles installed in wells drilled in the frozen layer. Needles can be electric, water circulating and steam. Electric needles are made from 1.5 m long tubs, inside which electric resistance winding elements are placed nichrome wire. Install needles in drilled wells.

Water needles require 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 smaller freezing depth, it is allowed to use the method of surface thawing.

Soil thawing needles

a - water circulation; b - electric; 1 - flange; 2 - inner tube;
3 - pipe; 4 - tip; 5 - nichrome spiral: 6 - asbestos powder

The work of earth-moving machines with soil prepared for development should be carried out continuously and around the clock with a narrow front to avoid freezing of the soil during breaks.

To prevent soil freezing in open trenches and secondary freezing of loosened soil, it is necessary: not to open soil areas covered with heat-insulating materials or snow before the start of work; to protect from freezing the soil of open parts of pits, trenches, subject to development during subsequent penetrations.

Backfilling of pits and trenches should be carried out, fulfilling the following requirements: the number of frozen clods in the soil, which fills the sinuses between the walls of the pits or trenches, should not exceed 15% of the total backfill volume. Winter trenches should be backfilled immediately after laying and testing the pipes to prevent damage to their insulation.

In construction, from 20 to 25% of the total excavation work is carried out in winter conditions, while the share of soil developed in a frozen state remains constant - 10-15% with an increase in the absolute value of this volume from year to year. Consequently, the optimization of excavation technology in winter conditions is a significant reserve for increasing the efficiency of construction production.

In construction practice, it becomes necessary to develop soils that are in a frozen state only in the winter season, i.e. soils of seasonal freezing, or throughout the year, i.e. permafrost soils.

The development of permafrost soils can be carried out in the same ways as frozen soils of seasonal freezing. However, when erecting earthworks in permafrost conditions, it is necessary to take into account the specific features of the geothermal regime of permafrost soils and changes in soil properties when it is disturbed.

At negative temperatures, the freezing of water contained in the pores of the soil significantly changes the construction and technological properties of non-rocky soils. In frozen soils, mechanical strength increases significantly, and therefore their development by earth-moving machines is difficult or even impossible without preparation.

The depth of freezing depends on the air temperature, the duration of exposure to negative temperatures, the type of soil, etc.

In technological design, for preliminary calculations, the freezing depth is taken according to the data of the nearest meteorological station or

climate guide. In winter conditions, earthworks can be carried out: with preliminary preparation of frozen soil for development; with the direct development of frozen soils in their natural state by machines specially equipped for this purpose.

Preliminary preparation of the soil for development is carried out in one of the following ways: by protecting the soil from freezing, by loosening the frozen soil, and by thawing the frozen soil. The direct development of frozen soils can be carried out in a block way or by earth-moving machines with working equipment that destroys frozen soil in its natural occurrence. It is allowed to develop frozen soil with single-bucket excavators, depending on the capacity of the bucket, with a frozen layer thickness of 0.25 to 0.4 m.

Reducing the freezing depth makes it possible to reduce the additional costs associated with earthworks in winter, and is achieved by creating thermal insulation at the development site or by chemically impregnating the soil with saline solutions that lower the freezing point of water in the soil pores. The soil is protected from freezing if the location of the excavation is known in advance.

Explosive loosening is one of the main methods of preparing frozen soils for excavation. This method is very effective at a freezing depth of more than 1 m and large volumes of work performed in newly developed territories or far from buildings and structures.

The explosive charge for loosening frozen soil can be determined by calculation (see formulas 1 and 2).

Mechanical loosening of frozen soil is used at a freezing depth of 0.4 to 1.5 m and small excavations of trenches or pits.

In the percussion method, a hammer ball or wedge hammer, diesel hammer, wedge tractor rippers, etc. are used.

When loosening by static impact, the cost and labor costs per 1 m of developed soil are lower than with impact.

Defrosting methods are classified: by type of energy - into thermal, electrical, energy chemical reactions; by type of heat carrier - for air, steam, water; in the direction of heat propagation in the soil.

The fire method is the least economical, but due to its simplicity, it is used in emergency repair work.

Chemical thawing of frozen soils is carried out by introducing a sodium chloride solution into the soil, under the action of which ice crystals dissolve in the pores of frozen soil, and it can be developed with conventional earth-moving machines.

The block development method provides for the development of frozen soil, the solidity of which is broken by cutting it into blocks (strips). Slots 5 to 15 cm wide are cut with specialized machines or attachments in parallel and intersecting penetrations, and individual blocks are then removed by an excavator, bulldozer or crane.

Excavation work with preliminary preparation of frozen soil for development causes significant complications and additional costs. In this regard, an intensive search is underway for mining methods and mechanization tools that allow the development of frozen soil in natural occurrence.

For the development of frozen soil without pre-training earth-moving and milling machines, multi-bucket and single-bucket excavators with special working equipment are used to ensure the destruction of frozen soil during its excavation (Fig. 1).

Fig.1. Technical means for the development of frozen soils without preliminary preparation:

a - earth-moving machine: 1 - tractor; 2 - system of transmission and control of the working body; 3 - working body of the machine (cutter); b - excavator bucket with active teeth: 4 - bucket; 5 - bucket tooth; 6 - drummer; 7 - vibrator

Excavation work in winter conditions is associated with additional costs of material, technical and energy resources, an increase in the cost and labor intensity of work, therefore, careful development of this section in the work design (PPR) is necessary.

During technological design, the sequence and scope of different kind operations for the preparation and development of soil on the basis of complex mechanization of the entire process, ensuring the minimum terms of work, labor intensity and resource costs. When developing soil in winter conditions, various technological schemes and sets of machines can be applied. Rational schemes and sets are chosen for a specific object and time of work and are performed on the basis of a comprehensive analysis of technical and economic indicators.

Technological schemes of soil development at various combinations machines in the set depend on the type of earthen structure, the type of soil, the depth of freezing, the availability of material and technical resources, etc. Some of the most common technological schemes in construction practice in winter conditions are shown in Fig. 2-4.

Fig. 2 Schemes for the development of frozen soils with preliminary loosening:

a - loosening with a wedge hammer; b - tractor vibro-wedge ripper; 1 - dump truck; 2 - excavator; 3 - wedge-hammer; 4 - vibrowedge

Fig.3. Schemes for the development of frozen soils in a block way:

a, b - small-block method; c, d - large-block; 1 - removal of snow cover; 2, 3 - cutting blocks of frozen soil with a bar machine; 4 - development of small blocks with an excavator or bulldozer; 5 - development of thawed soil; 6 - development of large blocks of frozen soil by a tractor; 7 - the same, with a crane

Fig.4. Development schemes with chemical soil thawing:

a - using a liquid chemical reagent: 1 - removal of snow cover; 2 - drilling holes; 3 - spilling a solution of a chemical reagent; 4 - soil development; b - with preliminary "salinization" of the soil: 5 - removal of the vegetation layer; 6 - spilling salt; 7 - soil harrowing; eight - excavation

The efficiency of the development of frozen soils depends on the choice of the development method, which, in turn, depends on the scope of work, the parameters of the earthwork, the type of soil, local meteorological and hydrogeological conditions, the availability of material, technical and energy resources, etc.

The decision to use one or another method is made on the basis of a comparison of a number of technically feasible options for excavation and an analysis of their technical and economic indicators. Depending on the specific conditions of construction, the optimization of the solution of this problem can be carried out according to the minimum of one or a combination of several parameters: cost, energy consumption, terms of work, etc.

Frozen soils, with the exception of rocky ones, greatly complicate the excavation work and significantly increase their cost, therefore, it is necessary to outline in advance those sections of excavation work, the development of which in the winter period will cause the least rise in price. Winter conditions do not cause an increase in the cost of work in the development of rocky soils, closed penetrations, such as shield penetrations, etc. Relatively little rises in price in winter.

The soil to be developed in winter conditions must be prepared in advance. Preparation consists in protecting it from freezing, loosening or thawing already frozen soil.

Protecting the soil from freezing. To reduce the depth of freezing before the onset of frost, a series of preparatory work: withdrawal from the site surface water, deep plowing of the surface layer (up to 30-35 cm) with obligatory harrowing, covering the surface of the earth with cheap local thermal insulation materials(sawdust, moss, peat, leaves, etc.).

The most effective is loosening the soil with a tractor multi-column ripper to a depth of at least 0.35 m, which, taking into account the snow cover, provides middle lane for the period of winter time, the thawed state of the soil under the loosened layer.

Soil protection from freezing great importance in the regions of Siberia, where big construction and where the soil freezes by 3-4 m. To reduce the depth of freezing, the areas are covered with polymer foams obtained from carbamide resin on solution nodes foaming. Loosening and warming of the soil should be carried out within the working contours of the excavations with widening to a double freezing depth.

Mechanical loosening of frozen soil. The applied methods of loosening frozen soil depend on the depth of its freezing. A layer of frozen soil up to 0.25 m thick is destroyed by an excavator with a bucket with a capacity of 0.5 m 3, and with a layer of up to 0.4 m - by an excavator with a bucket with a capacity of 1-1.25 m 3. Therefore, for the development of pits and trenches in winter conditions, at the specified freezing depth and the use of appropriate excavators, it is not necessary to first loosen the frozen soil.

With a freezing depth of more than 0.8 m, it is advisable to loosen the soil in an explosive way. If it is impossible to use the explosive method, mechanical loosening of the soil is carried out using diesel hammers with wedges, three-wedge tractor rippers and by cutting the soil into blocks using cutting machines (cutting or disk). Diesel hammers can be equipped with single-bucket excavators or tractors; cutting and disk machines are equipped with tractors or trench excavators.

Loosening frozen soil with pneumatic and electric jackhammers is inefficient, expensive and therefore cannot be recommended. Jackhammers are usually used for emergency work and small amounts of work.

Thawing of frozen soils. With small volumes of earthworks, to facilitate the development of the soil, they use various ways its thawing: fire, steam, hot water or electric current. The defrosting method is determined based on technical capabilities, economic considerations and local conditions.

The fire method of thawing soil with open fires is not recommended as ineffective and uneconomical. For the development of trenches in urban areas in the presence of an underground gas network, thawing of the soil is carried out by supplying gas to a burner installed at one end of a metal box, which is assembled from semicircular segments (half-pipes) overlapped along the axis of the trench. Installed at the other end of the box chimney. To reduce the loss of heat escaping into the atmosphere, the box is sprinkled with soil with a layer of 10-15 cm.

In the absence of a gas network, liquid fuel (solar oil) can be used. Liquid fuel is sent to the nozzle, where compressed air is supplied from a cylinder or a small compressor. Under the action of a jet of compressed air, liquid fuel is sprayed, forming a large torch.

If the depth of soil freezing exceeds 1 m, it is thawed with steam using steam needles. Steam needles are installed in pre-drilled wells. To prevent steam from leaking through the wells, they are covered with caps in which heat is accumulated. Steam needles are used in the development of trenches and small pits.

Soils have low thermal conductivity, they can receive and transfer to the thawing zone only a certain amount of heat, so it is advisable to supply steam to the needles intermittently. The most acceptable temperature for warming the soil is 40-50°C. Under this condition, it is more economical to thaw the soil with hot water using water circulation needles installed at a distance of 0.75-1.5 m from each other in pre-drilled wells. Hot water from the boiler passes first through the outer pipe of the water needle, and then through the inner one; after passing sequentially a battery of installed needles, it enters centrifugal pump and returns to the boiler under pressure.

If there is free electricity at the construction site, thawing of the soil can be carried out with an alternating current of 220 and 380 V. At a freezing depth of up to 0.7 m, horizontal electrodes are used, laid on the soil surface with backfilling them with a 15-20 cm layer of sawdust moistened with sodium chloride solution. Heating in this case will go from top to bottom.

When the depth of soil freezing is more than 0.7 m, it is advisable to use vertical deep electrodes for its thawing, which are steel rods with a diameter of 12-19 mm with a pointed end. The electrodes are clogged below the freezing depth by 8-10 cm. In this case, the current flows through the thawed soil. The released heat warms up the layer of frozen soil lying above, and the thawing process occurs in the direction from bottom to top. With this method, it is not required to clear the heating area from snow and cover it with sawdust; there will be no heat loss to the air, and the power consumption will be less, since the current is turned off before the entire soil thaws.

When electrically heating the soil, it is necessary to strictly comply with all the requirements for electrical safety in the conditions of the construction site.

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 tools 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, heat of water from natural reservoirs, and artificial - due to the combustion of solid, liquid or gaseous fuel, using 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 by impact, vibration or their combined impact 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 excavate 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 the development of frozen soil without its preliminary preparation (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.

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