The compaction coefficient of crushed stone is a dimensionless indicator that characterizes the degree of change in the volume of the material during compaction, shrinkage and transportation. It is taken into account when calculating the required amount of filler, checking the mass of products delivered to order and when preparing foundations for load-bearing structures, along with bulk density and other characteristics. The standard number for a specific brand is determined in laboratory conditions; the real one is not a static value and also depends on a number of inherent properties and external conditions.

The compaction coefficient is used when working with bulk building materials. Their standard number varies from 1.05 to 1.52. The average value for gravel and granite crushed stone is 1.1, expanded clay - 1.15, sand-gravel mixtures - 1.2 (read about the degree of sand compaction). The actual figure depends on the following factors:

• Size: the smaller the grain, the more efficient the compaction.
• Flakiness: Needle-shaped and irregularly shaped crushed stone compacts less well than cube-shaped aggregate.
• Duration of transportation and type of transport used. The maximum value is achieved when delivering gravel and granite stone in dump truck bodies and railway cars, the minimum is in sea ​​containers.
• Conditions for filling into a car.
• Method: manually achieving the desired parameter is more difficult than using vibration equipment.

In the construction industry, the compaction coefficient is taken into account primarily when checking the mass of purchased bulk material and backfilling foundations. The design data indicates the density of the structure skeleton. The indicator is taken into account in conjunction with other parameters of building mixtures; humidity plays an important role. The degree of compaction is calculated for crushed stone with a limited volume of walls; in reality, such conditions are not always created. A striking example is a backfilled foundation or drainage cushion (fractions extend beyond the boundaries of the layer), an error in the calculation is inevitable. To neutralize it, crushed stone is purchased with a reserve.

Ignoring this coefficient when drawing up a project and carrying out construction work leads to the purchase of incomplete volumes and deterioration performance characteristics constructed structures. With the correct degree of compaction selected and implemented, concrete monoliths, building and road foundations can withstand the expected loads.

Degree of compaction on site and during transportation

Deviation in the volume of crushed stone loaded and delivered to the final point – known fact, the stronger the vibration during transportation and the further the distance, the higher its degree of compaction. To check the compliance of the amount of material brought, a regular tape measure is most often used. After measuring the body, the resulting volume is divided by a coefficient and checked with the value indicated in the accompanying documentation. Regardless of the size of the fractions, this indicator cannot be less than 1.1; if there are high requirements for delivery accuracy, it is negotiated and specified in the contract separately.

If this point is ignored, claims against the supplier are unfounded; according to GOST 8267-93, the parameter does not apply to mandatory characteristics. The default value for crushed stone is 1.1; the delivered volume is checked at the receiving point; after unloading, the material takes up a little more space, but over time it shrinks.

The required degree of compaction when preparing the foundations of buildings and roads is indicated in project documentation and depends on the expected weight loads. In practice, it can reach 1.52, the deviation should be minimal (no more than 10%). Tamping is carried out in layers with a thickness limit of 15-20 cm and the use of different fractions.

Road surface or foundation pads are poured onto prepared sites, namely with leveled and compacted soil, without significant level deviations. The first layer is formed from coarse gravel or granite crushed stone; the use of dolomite rocks must be permitted by the project. After preliminary compaction, the pieces are separated into smaller fractions, if necessary, even to the point of filling with sand or sand-gravel mixtures. The quality of work is checked separately on each layer.

The compliance of the obtained tamping result with the design one is assessed using special equipment - a density meter. The measurement is carried out provided that there is no more than 15% grains with a size of up to 10 mm. The tool is immersed 150 mm strictly vertically, maintaining the required pressure, the level is calculated by the deflection of the arrow on the device. To eliminate errors, measurements are taken at 3-5 points in different places.

Bulk density of crushed stone of different fractions

In addition to the compaction coefficient, to determine the exact amount of material required, you need to know the dimensions of the structure being filled and the specific gravity of the filler. The latter is the ratio of the mass of crushed stone or gravel to the volume it occupies and depends primarily on the strength of the original rock and size.

Type	Bulk density (kg/m3) with fraction sizes:
	0-5	5-10	5-20	20-40	40-70
Granite	1500	1430	1400	1380	1350
Gravel		1410	1390	1370	1340
			1320	1280	1120

Specific gravity must be indicated in the product certificate; in the absence of accurate data, it can be found independently experimentally. To do this, you will need a cylindrical container and a scale; the material is poured without compaction and weighed before and after filling. The quantity is found by multiplying the volume of the structure or base by the obtained value and by the degree of compaction specified in the design documentation.

For example, to fill 1 m2 of a 15 cm thick cushion of gravel with a fraction size in the range of 20-40 cm, you will need 1370 × 0.15 × 1.1 = 226 kg. Knowing the area of ​​the base being formed, it is easy to find the total volume of filler.

Density indicators are also relevant when selecting proportions when preparing concrete mixtures. For foundation structures, it is recommended to use granite crushed stone with a fraction size in the range of 20-40 mm and a specific gravity of at least 1400 kg/m3. Seal in in this case is not carried out, but attention is paid to flakiness - for the manufacture of reinforced concrete products, a cube-shaped filler with a low content of grains of irregular shape is required. Bulk density is used when converting volumetric proportions to mass proportions and vice versa.

What is the compaction coefficient of bulk materials? Sand and gravel mixture compaction coefficient

Compaction coefficient of sand-gravel mixture

All building materials, especially mixtures, have a number of indicators, the value of which plays an important role in the construction process and largely determines the final result. For bulk materials, such indicators are the fraction size and compaction coefficient. This indicator records how much the external volume of the material decreases when it is compacted (compacted). This coefficient is most often taken into account when working with construction sand, however, sand-gravel mixtures and just gravel itself can also change their value during compaction.

Why do you need to know the compaction coefficient of a sand-gravel mixture?

Any bulk mixture, even in the absence of mechanical action, changes its density. This is easy to understand by remembering how a mountain of sand that has just been dug changes over time. The sand becomes denser, then, when processed again, it returns to a more free-flowing form, changing the volume of the occupied area. How much this volume increases or decreases is the density coefficient.

This compaction coefficient of a sand-gravel mixture does not record the volume lost during artificial compaction (for example, during the construction of a foundation substrate, when the mixture is compacted with a special mechanism), but the natural changes that occur with the material during transportation, loading and unloading. This allows you to determine losses incurred during transportation and more accurately calculate the required volume of supply of sand and gravel mixture. It should be noted that the size of the compaction coefficient of a sand-gravel mixture is influenced by many indicators, such as batch size, transportation method, and the initial quality of the sand itself.

In construction work, information about the volume of compaction is used when making calculations and preparing for construction. In particular, based on this parameter, certain indicators are established for the depth of the trench, the thickness of the backfill for the future cushion of sand and gravel mixture, the intensity of compaction, and much more. Among other things, the season is taken into account, as well as climatic indicators.

The size of the compaction coefficient of a sand-gravel mixture may vary for different materials, each type of bulk mixture has its own standard indicators that guarantee its quality. It is believed that the average size The compaction coefficient for a sand-gravel mixture is about 1.2 (these data are indicated in GOST). It should be borne in mind that the same indicator, but separately for sand and gravel, will be different, from 1.1 to 1.4 depending on the type and size of the fractions.

When carrying out construction work, purchase materials with the required ratio, otherwise the quality of construction may suffer.

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vyborgstroy.com

Compaction factors for bulk materials for construction

The essence of determining the compaction coefficient of gravel, sand, crushed stone and expanded clay can be briefly described as follows. This is a value equal to the ratio of the density of bulk building material to its maximum density.

This coefficient is different for all bulk solids. For ease of use, its average value is fixed in regulations, compliance with which is mandatory for all construction work. Therefore, if you need, for example, to find out what the compaction coefficient of sand is, it will be enough to just look at GOST and find the required value. Important note: all values ​​given in the regulations are averaged and may vary depending on the conditions of transportation and storage of the material.

The need to take into account the compaction coefficient is due to a simple physical phenomenon that is familiar to almost all of us. In order to understand the essence of this phenomenon, it is enough to remember how the dug up earth behaves. At first it is loose and quite voluminous. But if you look at this land after a few days, you will already notice that the soil has “settled” and become compacted.

The same thing happens with building materials. First, they lie at the supplier's place in compacted own weight condition, then during loading there is “loosening” and an increase in volume, and then, after unloading at the site, natural compaction by its own weight occurs again. In addition to mass, the material will be affected by the atmosphere, or more precisely, its humidity. All these factors are taken into account in the relevant GOSTs.

Crushed stone delivered by road or rail is weighed on scales. When delivered by water transport, the weight is calculated based on the vessel's draft.

How to use the coefficient correctly

An important step Any construction work requires the preparation of all estimates with mandatory consideration of the compaction coefficients of bulk materials. This must be done in order to include the correct and necessary amount of building materials in the project and avoid their excess or shortage.

How to use the coefficient correctly? Nothing could be simpler. For example, in order to find out what volume of material will be obtained after shaking in the back of a dump truck or in a carriage, you need to find in the table the required compaction coefficient of soil, sand or crushed stone and divide the purchased volume of products by it. And if you need to know the volume of materials before transportation, then you will need to do not divide, but multiply by the appropriate coefficient. Let’s say that if you purchased 40 cubic meters of crushed stone from a supplier, then during transportation this amount will turn into the following: 40 / 1.15 = 34.4 cubic meters.

Work related to the complete chain of movement of sand masses from the bottom of the quarry to the construction site must be carried out taking into account the relative reserve factor of sand and soil for compaction. This is a value that shows the ratio of the weight density of the solid structure of the sand to its weight density at the supplier's shipping area. To determine the required amount of sand to ensure the planned volume, you need to multiply this volume by the relative compaction coefficient.

In addition to knowing the relative coefficient given in the table, correct use GOST implies mandatory consideration of the following factors for the delivery of sand to the construction site:

• physical properties and chemical composition of the material inherent in a particular area;
• conditions of transportation;
• taking into account climatic factors during the delivery period;
• obtaining in laboratory conditions the values ​​of maximum density and optimal humidity.

Compaction of sandy bases

This type of work is necessary when backfilling. For example, this is necessary after the foundation has been installed and now it is necessary to fill the gap formed between the outer contour of the structure and the walls of the pit with soil or sand. The process is carried out using special tamping devices. The compaction coefficient of the sand base is approximately 0.98.

Coefficient for concrete mixtures

Concrete mixture, like any other building material installed by pouring or pouring, requires further compaction to obtain the required density, and therefore the reliability of the structure. Concrete is compacted using vibrators. The compaction coefficient of the concrete mixture is taken in the range from 0.98 to 1.

taxi-pesok.ru

Coefficient for compaction and loss of ASG

When carrying out the construction of energy complex facilities and guided by design data, the construction of embankments, backfilling of trenches, pits, pit cavities, filling under floors must be done with imported soil (sand, crushed stone, ASG, etc.) with a compaction coefficient of up to 0.95.

When drawing up local estimates for these types of work, we use the following prices: EP 01-01-034 "Filling trenches and pits with bulldozers", EP 01-02-005 "Soil compaction with pneumatic compactors" - when filling with a bulldozer and EP 01-02-061 " Manually backfilling trenches, pit cavities and pits" - when backfilling by hand.

Since backfilling is carried out with imported soil (sand, crushed stone, ASG, etc.), in addition to the prices, we take into account its cost. Since the prices take into account compact soil, when calculating the volume of imported soil required for work and delivered to the construction site in a loosened state, we apply a compaction coefficient of 1.18 in accordance with clause 2.1.13 of the Technical Part of the GESN-2001- 01 (ed. 2008-2009).

In addition, when backfilling trenches and pit cavities with a bulldozer, we take into account the loss of ASG in accordance with clause 1.1.9 of the Technical Part of the Collection GESN-2001-01 (ed. 2008-2009):

• in the amount of 1.5% - when moving soil with a bulldozer over a foundation composed of another type of soil,
• in the amount of 1% - when transporting by road over a distance of more than 1 km.

Please confirm the legality of our actions, since the Customer requires a compaction coefficient (1.18) and the loss of ASG (1.5% and 1%) to be excluded from the estimates.

The provisions of paragraph 2.1.13 of Section II “Calculation of the scope of work” of the state estimate standards GESN (FER) - 2001, approved by order of the Ministry of Regional Development of Russia dated November 17, 2008 No. 253 (hereinafter referred to as the Standards), are applicable when determining the estimated cost of work on filling iron embankments and highways.

Based on the data presented in the appeal on the performance of work on backfilling trenches, excavation cavities and pits, the use of a compaction coefficient of 1.18 specified in paragraph 2.1.13 of the Standards appears to be unjustified.

In accordance with clause 1.1.9 of section I " General provisions"Regulations, the volume of soil to be transported by motor transport to the site for backfilling trenches and pits, when transported by motor transport over a distance of more than 1 km - 1.0%; when moving soil by bulldozers along a base composed of another type of soil, it is calculated according to the design dimensions of the embankment with adding 1.5% for losses.

In accordance with clause 7.30 of the set of rules "SP 45.13330.2012. Code of rules. Earthworks, foundations and foundations. Updated edition of SNiP 3.02.01-87",

approved by order of the Ministry of Regional Development of Russia dated December 29, 2011 No. 635/2, it is allowed to accept a higher percentage of losses with sufficient justification, by a joint decision of the customer and the contractor.

smetnoedelo.ru

table snip, for tamping, for backfilling and GOST 7394 85

The compaction coefficient must be determined and taken into account not only in narrowly focused areas of construction. Professionals and ordinary workers performing standard procedures for using sand are constantly faced with the need to determine the coefficient.

The compaction coefficient is actively used to determine the volume of bulk materials, in particular sand, but also applies to gravel and soil. Most exact method Determining compaction is a weight method.

It has not found wide practical application due to the inaccessibility of equipment for weighing large volumes of material or the lack of sufficiently accurate indicators. Alternative option coefficient output – volumetric accounting.

Its only drawback is the need to determine compaction at different stages. This is how the coefficient is calculated immediately after production, during warehousing, during transportation (relevant for road deliveries) and directly at the end consumer.

Factors and properties

The compaction coefficient is the dependence of the density, that is, the mass of a certain volume, of a controlled sample to the reference standard.

Density reference values ​​are derived in laboratory conditions. The characteristics are necessary for carrying out assessment work on the quality of the completed order and compliance with the requirements.

To determine the quality of a material, regulatory documents are used that specify reference values. Most regulations can be found in GOST 8736-93, GOST 7394-85 and 25100-95 and SNiP 2.05.02-85. Additionally, it may be specified in the design documentation.

In most cases, the compaction coefficient is 0.95-0.98 of the standard value.

The “skeleton” is a solid structure that has some parameters of looseness and moisture. Volumetric gravity is usually calculated based on the relationship between the mass of solid particles in the sand and what the mixture would acquire if water occupied the entire soil space.

The best way to determine the density of quarry, river, and construction sand is to conduct laboratory tests based on several samples taken from the sand. During the inspection, the soil is gradually compacted and moisture is added, this continues until the normalized moisture level is reached.

After reaching the maximum density, the coefficient is determined.

Relative compaction coefficient

Carrying out numerous procedures for extraction, transportation, and storage, it is obvious that the bulk density changes somewhat. This is due to the compaction of sand during transportation, long-term storage in the warehouse, absorption of moisture, changes in the level of looseness of the material, and grain size.

In most cases, it is easier to use a relative coefficient - this is the ratio between the density of the “skeleton” after mining or being in a warehouse to the one it acquires when reaching the final consumer.

Knowing the standard that characterizes the density during mining, indicated by the manufacturer, it is possible to determine the final coefficient of the soil without conducting constant surveys.

Information about this parameter must be indicated in the technical and design documentation. Determined by calculations and the ratio of initial and final indicators.

This method assumes regular deliveries from one manufacturer and no changes in any variables. That is, transportation occurs using the same method, the quarry has not changed its quality indicators, the duration of stay in the warehouse is approximately the same, etc.

To perform calculations, it is necessary to take into account the following parameters:

• characteristics of sand, the main ones are the compressive strength of the particles, grain size, caking ability;
• determination of the maximum density of the material in laboratory conditions when adding the required amount of moisture;
• bulk weight of the material, that is, density in the natural environment of location;
• type and conditions of transportation. The worst impact is on road and rail transport. Sand is less subject to compaction during sea deliveries;
• weather conditions when transporting soil. It is necessary to take into account humidity and the likelihood of exposure to sub-zero temperatures.

During mining

Depending on the type of pit, the level of sand extraction, its density also changes. In this case, it is important climate zone, in which resource extraction work is carried out. The documents define the following coefficients depending on the layer and region of sand production.

In the future, on this basis, you can calculate the density, but you need to take into account all the effects on the soil that change its density in one direction or another.

When compacting and backfilling

Backfilling is the process of filling a previously dug pit after the construction of the necessary buildings or carrying out certain work. Usually covered with soil, but quartz sand is also often used.

Tamping is considered a necessary process for this action, as it allows you to restore the strength of the coating.

To perform the procedure, you must have special equipment. Typically, impact mechanisms or those that create pressure are used.

Vibrating stamps and vibrating plates of varying weights and power are actively used in construction.

The compaction coefficient also depends on the compaction and is expressed as a proportion. This must be taken into account, since as compaction increases, the volumetric area of ​​sand simultaneously decreases.

It is worth considering that all types of mechanical, external seals can only affect upper layer material.

The main types and methods of compaction and their effect on the upper layers of soil are presented in the table.

To determine the volume of backfill material, the relative compaction coefficient must be taken into account. This is due to changes in the physical properties of the pit after sand is pulled out.

When pouring a foundation you need to know correct proportions sand and cement. By clicking on the link, you will become familiar with the proportions of cement and sand for the foundation.

Cement is a special bulk material, which in its composition is a mineral powder. Here is about the different brands of cement and their applications.

With the help of plaster, the thickness of the walls is increased, which increases their strength. Here you will find out how long it takes for plaster to dry.

By extracting quarry sand, the quarry body becomes looser and gradually the density may decrease slightly. Periodic density tests should be carried out by a laboratory, especially when the composition or location of the sand changes.

For more information about sand compaction during backfilling, watch the video:

During transportation

Transportation of bulk materials has some peculiarities, since the weight is quite large and a change in the density of resources is observed.

Basically, sand is transported using road and rail transport, and they cause shaking of the load.

Transportation by car

Constant vibration shocks to materials act on it in a similar way to compaction from a vibrating plate. Thus, constant shaking of the load, possible exposure to rain, snow or sub-zero temperatures, increased pressure on the lower layer of sand - all this leads to compaction of the material.

Moreover, the length of the delivery route is directly proportional to compaction until the sand reaches the maximum possible density.

Sea deliveries are less affected by vibrations, so the sand retains a greater level of looseness, but some slight shrinkage is still observed.

To calculate the amount of building material, it is necessary to multiply the relative compaction coefficient, which is calculated individually and depends on the density at the starting and ending points, by the required volume included in the project.

In a laboratory setting

It is necessary to take sand from the analytical stock, about 30 g. Sift through a sieve with a 5 mm mesh and dry the material until it reaches a constant weight. Bring the sand to room temperature. Dry sand should be mixed and divided into 2 equal parts.

Next, you need to weigh the pycnometer and fill 2 samples with sand. Next, add distilled water in the same amount to a separate pycnometer, approximately 2/3 of the total volume, and weigh again. The contents are mixed and placed in a sand bath with a slight slope.

To remove air, boil the contents for 15-20 minutes. Now you need to cool the pycnometer to room temperature and wipe it off. Next, add distilled water to the mark and weigh.

P = ((m – m1)*Pв) / m-m1+m2-m3, where:

• m – mass of the pycnometer when filled with sand, g;
• m1 – weight of an empty pycnometer, g;
• m2 – mass with distilled water, g;
• m3 – weight of the pycnometer with the addition of distilled water and sand, after getting rid of air bubbles
• Pv – water density

In this case, several measurements are taken based on the number of samples provided for testing. The results should not differ by more than 0.02 g/cm3. When high flow rate the average of the received data is displayed arithmetic number.

Estimates and calculations of materials and their coefficients are the main component of the construction of any objects, as it helps to understand the amount of material needed, and, accordingly, the costs.

To correctly draw up an estimate, you need to know the density of the sand; for this, information provided by the manufacturer is used, based on surveys and the relative compaction coefficient upon delivery.

What causes the compaction level to change?

The sand passes through a tamper, not necessarily a special one, perhaps during the moving process. It is quite difficult to calculate the amount of material obtained at the output, taking into account all the variable indicators. For an accurate calculation, it is necessary to know all the effects and manipulations carried out with sand.

The final compaction ratio depends on various factors:

• method of transportation, the more mechanical contact with irregularities, the stronger the compaction;
• route duration, information available to the consumer;
• presence of damage from mechanical influences;
• amount of impurities. In any case, foreign components in the sand give it more or less weight. The purer the sand, the closer the density value is to the reference value;
• the amount of moisture that has entered.

Immediately after purchasing a batch of sand, it should be checked.

You need to take samples:

• for a batch of less than 350 tons - 10 samples;
• for a batch of 350-700 tons – 10-15 samples;
• when ordering above 700 tons - 20 samples.

Take the resulting samples to a research institution for examination and comparison of quality with regulatory documents.

Conclusion

The required density depends greatly on the type of work. Basically, compaction is necessary to form a foundation, backfill trenches, create a cushion for roadbed etc. It is necessary to take into account the quality of compaction; each type of work has different requirements to compaction.

In the construction of highways, a roller is often used; in places difficult to reach for transport, a vibrating plate of various capacities is used.

So, to determine the final amount of material, you need to set the compaction coefficient on the surface during compaction; this ratio is indicated by the manufacturer of the compaction equipment.

The relative indicator of the density coefficient is always taken into account, since soil and sand tend to change their indicators based on the level of humidity, type of sand, fraction and other indicators.

strmaterials.com

Compaction coefficient of crushed stone: gravel, granite and dolomite

The compaction coefficient of crushed stone is a dimensionless indicator that characterizes the degree of change in the volume of the material during compaction, shrinkage and transportation. It is taken into account when calculating the required amount of filler, checking the mass of products delivered to order and when preparing foundations for load-bearing structures, along with bulk density and other characteristics. The standard number for a specific brand is determined in laboratory conditions; the real one is not a static value and also depends on a number of inherent properties and external conditions.

1. Determination of the coefficient
2. Tamping during transportation and on site
3. Bulk density for different fractions

Functional value of the indicator

The compaction coefficient is used when working with bulk building materials. Their standard number varies from 1.05 to 1.52. The average value for gravel and crushed granite is 1.1, expanded clay – 1.15, sand-gravel mixtures – 1.2 (read about the degree of sand compaction here). The actual figure depends on the following factors:

• Size: the smaller the grain, the more efficient the compaction.
• Flakiness: Needle-shaped and irregularly shaped crushed stone compacts less well than cube-shaped aggregate.
• Duration of transportation and type of transport used. The maximum value is achieved when gravel and granite stone is delivered in dump truck bodies and railway cars, the minimum value is achieved in sea containers.
• Conditions for filling into a car.
• Method: manually achieving the desired parameter is more difficult than using vibration equipment.

In the construction industry, the compaction coefficient is taken into account primarily when checking the mass of purchased bulk material and backfilling foundations. The design data indicates the density of the structure skeleton. The indicator is taken into account in conjunction with other parameters of building mixtures; humidity plays an important role. The degree of compaction is calculated for crushed stone with a limited volume of walls; in reality, such conditions are not always created. A striking example is a backfilled foundation or drainage cushion (fractions extend beyond the boundaries of the layer), an error in the calculation is inevitable. To neutralize it, crushed stone is purchased with a reserve.

Ignoring this coefficient when drawing up a project and carrying out construction work leads to the purchase of an incomplete volume and a deterioration in the performance characteristics of the structures being built. With the correct degree of compaction selected and implemented, concrete monoliths, building and road foundations can withstand the expected loads.

Degree of compaction on site and during transportation

The deviation in the volume of crushed stone loaded and delivered to the final point is a known fact; the stronger the vibration during transportation and the further the distance, the higher its degree of compaction. To check the compliance of the amount of material brought, a regular tape measure is most often used. After measuring the body, the resulting volume is divided by a coefficient and checked with the value indicated in the accompanying documentation. Regardless of the size of the fractions, this indicator cannot be less than 1.1; if there are high requirements for delivery accuracy, it is negotiated and specified in the contract separately.

If this point is ignored, claims against the supplier are unfounded; according to GOST 8267-93, the parameter does not apply to mandatory characteristics. The default value for crushed stone is 1.1; the delivered volume is checked at the receiving point; after unloading, the material takes up a little more space, but over time it shrinks.

The required degree of compaction when preparing the foundations of buildings and roads is indicated in the design documentation and depends on the expected weight loads. In practice, it can reach 1.52, the deviation should be minimal (no more than 10%). Tamping is carried out in layers with a thickness limit of 15-20 cm and the use of different fractions.

The road surface or foundation pads are poured onto prepared sites, namely with leveled and compacted soil, without significant level deviations. The first layer is formed from coarse gravel or granite crushed stone; the use of dolomite rocks must be permitted by the project. After preliminary compaction, the pieces are separated into smaller fractions, if necessary, even to the point of filling with sand or sand-gravel mixtures. The quality of work is checked separately on each layer.

The compliance of the obtained tamping result with the design one is assessed using special equipment - a density meter. The measurement is carried out provided that there is no more than 15% grains with a size of up to 10 mm. The tool is immersed 150 mm strictly vertically, maintaining the required pressure, the level is calculated by the deflection of the arrow on the device. To eliminate errors, measurements are taken at 3-5 points in different places.

Bulk density of crushed stone of different fractions

In addition to the compaction coefficient, to determine the exact amount of material required, you need to know the dimensions of the structure being filled and the specific gravity of the filler. The latter is the ratio of the mass of crushed stone or gravel to the volume it occupies and depends primarily on the strength of the original rock and size.

The specific gravity must be indicated in the product certificate; in the absence of accurate data, it can be found independently experimentally. To do this, you will need a cylindrical container and a scale; the material is poured without compaction and weighed before and after filling. The quantity is found by multiplying the volume of the structure or base by the obtained value and by the degree of compaction specified in the design documentation.

For example, to fill 1 m2 of a 15 cm thick cushion of gravel with a fraction size in the range of 20-40 cm, you will need 1370 × 0.15 × 1.1 = 226 kg. Knowing the area of ​​the base being formed, it is easy to find the total volume of filler.

Density indicators are also relevant when selecting proportions when preparing concrete mixtures. For foundation structures, it is recommended to use granite crushed stone with a fraction size in the range of 20-40 mm and a specific gravity of at least 1400 kg/m3. In this case, compaction is not carried out, but attention is paid to the flakiness - for the manufacture of reinforced concrete products, a cube-shaped filler with a low content of irregularly shaped grains is required. Bulk density is used when converting volumetric proportions to mass proportions and vice versa.

stroitel-lab.ru

table, snip, according to GOST fractions 40-70

Crushed stone today is the most practical, cheap, effective, and, accordingly, widespread materials. It is mined by crushing rock, most often the raw material is obtained by blasting in quarries.

In this case, the rock is destroyed into pieces of different sizes, and the compaction coefficient strongly depends on the fraction.

Fraction

Granite crushed stone is the most common option because it has high level resistance to temperature influences and practically does not absorb water. The durability of granite matches all technical requirements. The most popular fractions of granite:

• fine-grained - 5-15 mm;

• small – 5-20 mm;

• average small – 5-40 mm;

• average – 20-40 mm;

• large – 40-70 mm.

Each type has different areas of application; the fine fraction of slag is mainly used for:

• preparation of ballast layers that are necessary for railway tracks and roads;

• added to building mixtures.

Based on what to choose a seal

The compaction coefficient strongly depends on various indicators and characteristics of the material; the following must be taken into account:

• average density, usually set by the manufacturer, but generally ranges from 1.4 to 3 g/cm³. This is one of the key parameters used in the calculations;
• flakiness to predict the plane of crushed stone;
• fractional sorting, smaller size grains - more density;
• resistance of the material to frost depends on the breed;
• radioactivity of rubble. The first class can be used everywhere, and the second only for country roads.

Varieties and characteristics

Can be used for construction different kinds crushed stone, the range today is quite large, but the properties also differ significantly.

Depending on the type of rock, the following main raw material groups are distinguished:

• gravel;
• limestone;
• granite;
• secondary.

Granite rock is the strongest because it is the material that remains after the magma cools. Due to the high strength of the rock, it is difficult to process. Produced on the basis of GOST 8267-93.

Crushed stone 5-20 mm has become widespread, as it can be used for almost all types of construction.

The gravel variety is more free-flowing, and accordingly the compaction coefficient of crushed stone is higher. It is mined by grinding rocks, because of this it is more cheap material, but also less durable.

In preparation for construction, they carry out special studies and tests that determine the suitability of the site for the upcoming work: they take soil samples, calculate the level of groundwater and examine other soil features that help determine the possibility (or lack thereof) of construction.

Carrying out such activities helps to improve technical performance, as a result of which a number of problems that arise during the construction process are solved, for example, soil subsidence under the weight of the structure with all the ensuing consequences. Its first external manifestation looks like the appearance of cracks on the walls, and in combination with other factors it leads to partial or complete destruction of the object.

Compaction factor: what is it?

By soil compaction coefficient we mean a dimensionless indicator, which, in fact, is a calculation from the ratio of soil density/soil density max. The soil compaction coefficient is calculated taking into account geological indicators. Any of them, regardless of the breed, is porous. It is permeated with microscopic voids that are filled with moisture or air. When the soil is excavated, the volume of these voids increases significantly, which leads to an increase in the looseness of the rock.

Important! The density of bulk rock is much less than the same characteristics of compacted soil.

It is the soil compaction coefficient that determines the need to prepare the site for construction. Based on these indicators, we prepare sand pillows under the foundation and its base, additionally compacting the soil. If this detail is missed, it may cake and begin to sag under the weight of the structure.

Soil compaction indicators

The soil compaction coefficient shows the level of soil compaction. Its value varies from 0 to 1. For the base of a concrete strip foundation, a score of >0.98 points is considered the norm.

Specifics of determining the compaction coefficient

The density of the soil skeleton, when the subgrade is subjected to standard compaction, is calculated in laboratory conditions. Schematic diagram The study consists of placing a soil sample in a steel cylinder, which is compressed under the influence of external brute mechanical force - the impact of a falling weight.

Important! The highest soil density values ​​are observed in rocks with moisture content slightly above normal. This relationship is depicted in the graph below.

Each subgrade has its own optimal moisture content, at which the maximum level of compaction is achieved. This indicator is also studied in laboratory conditions, giving the rock different moisture content and comparing compaction rates.

Real data is the final result of research, measured at the end of all laboratory work.

Methods for compaction and coefficient calculation

Geographical location determines high-quality composition soils, each of which has its own characteristics: density, humidity, ability to subsidence. That is why it is so important to develop a set of measures aimed at qualitatively improving the characteristics for each type of soil.

You already know the concept of compaction coefficient, the subject of which is studied strictly in laboratory conditions. This work is carried out by the relevant services. The soil compaction indicator determines the method of influencing the soil, as a result of which it will receive new strength characteristics. When carrying out such actions, it is important to consider the percentage of gain applied to obtain the desired result. Based on this, the soil compaction coefficient is calculated (table below).

Typology of soil compaction methods

There is a conventional system for subdividing compaction methods, groups of which are formed based on the method of achieving the goal - the process of removing oxygen from soil layers at a certain depth. Thus, a distinction is made between superficial and in-depth research. Based on the type of research, specialists select an equipment system and determine the method of its use. Soil research methods are:

• static;
• vibration;
• percussion;
• combined.

Each type of equipment displays a method of applying force, such as a pneumatic roller.

Partially, such methods are used in small private construction, others exclusively in the construction of large-scale objects, the construction of which is agreed with the local authorities, since some of such buildings can affect not only a given site, but also surrounding objects.

Compaction coefficients and SNiP standards

All construction-related operations are clearly regulated by law and are therefore strictly controlled by relevant organizations.

Soil compaction coefficients are determined by SNiP clause 3.02.01-87 and SP 45.13330.2012. The actions described in the regulatory documents were updated and updated in 2013-2014. They describe compactions for different types of soil and ground pillows, used in the construction of foundations and buildings of various configurations, including underground.

How is the compaction coefficient determined?

The easiest way to determine the coefficient of soil compaction is by the cutting ring method: a metal ring of a selected diameter and a certain length is driven into the soil, during which the rock is tightly fixed inside a steel cylinder. After this, the mass of the device is measured on a scale, and at the end of weighing, the weight of the ring is subtracted, obtaining the net mass of the soil. This number is divided by the volume of the cylinder and the final density of the soil is obtained. After which it is divided by the indicator of the maximum possible density and a calculated value is obtained - the compaction coefficient for a given area.

Examples of calculating the compaction factor

Let's consider determining the soil compaction coefficient using an example:

• the value of the maximum soil density is 1.95 g/cm 3 ;
• cutting ring diameter - 5 cm;
• cutting ring height - 3 cm.

It is necessary to determine the soil compaction coefficient.

With such practical task It's much easier to deal with than it might seem.

To begin with, drive the cylinder completely into the ground, after which it is removed from the soil so that the internal space remains filled with earth, but no accumulation of soil is noted outside.

Using a knife, the soil is removed from the steel ring and weighed.

For example, the mass of the soil is 450 grams, the volume of the cylinder is 235.5 cm 3. Calculating using the formula, we obtain the number 1.91 g/cm 3 - soil density, from which the soil compaction coefficient is 1.91/1.95 = 0.979.

The construction of any building or structure is a responsible process, which is preceded by the even more important moment of preparing the site to be built, designing the proposed buildings, and calculating the total load on the ground. This applies to all buildings without exception that are intended for long-term use, the duration of which is measured in tens or even hundreds of years.

The compaction coefficient must be determined and taken into account not only in narrowly focused areas of construction. Professionals and ordinary workers performing standard procedures for using sand are constantly faced with the need to determine the coefficient.

The compaction coefficient is actively used to determine the volume of bulk materials, in particular sand,
but also applies to gravel and soil. The most accurate method for determining compaction is the weight method.

It has not found wide practical application due to the inaccessibility of equipment for weighing large volumes of material or the lack of sufficiently accurate indicators. An alternative option for deriving the coefficient is volumetric accounting.

Its only drawback is the need to determine compaction at different stages. This is how the coefficient is calculated immediately after production, during warehousing, during transportation (relevant for road deliveries) and directly at the end consumer.

Factors and properties of construction sand

The compaction coefficient is the dependence of the density, that is, the mass of a certain volume, of a controlled sample to the reference standard.

It is worth considering that all types of mechanical, external compaction can only affect the top layer of the material.

The main types and methods of compaction and their effect on the upper layers of soil are presented in the table.

To determine the volume of backfill material, the relative compaction coefficient must be taken into account. This is due to changes in the physical properties of the pit after sand is pulled out.

When pouring a foundation, you need to know the correct proportions of sand and cement. By going through, familiarize yourself with the proportions of cement and sand for the foundation.

Cement is a special bulk material, which in its composition is a mineral powder. about different grades of cement and their application.

With the help of plaster, the thickness of the walls is increased, which increases their strength. find out how long it takes for the plaster to dry.

P = ((m – m1)*Pв) / m-m1+m2-m3, Where:

• m – mass of the pycnometer when filled with sand, g;
• m1 – weight of an empty pycnometer, g;
• m2 – mass with distilled water, g;
• m3 – weight of the pycnometer with the addition of distilled water and sand, after getting rid of air bubbles
• Pv – water density

In this case, several measurements are taken based on the number of samples provided for testing. The results should not differ by more than 0.02 g/cm3. If the received data is large, the arithmetic average is displayed.

Estimates and calculations of materials and their coefficients are the main component of the construction of any objects, as it helps to understand the amount of material needed, and, accordingly, the costs.

To correctly draw up an estimate, you need to know the density of the sand; for this, information provided by the manufacturer is used, based on surveys and the relative compaction coefficient upon delivery.

What causes the level of the bulk mixture and the degree of compaction to change?

The sand passes through a tamper, not necessarily a special one, perhaps during the moving process. It is quite difficult to calculate the amount of material obtained at the output, taking into account all the variable indicators. For an accurate calculation it is necessary to know all the effects and manipulations carried out with sand.

The final coefficient and degree of compaction depends on various factors:

• method of transportation, the more mechanical contact with irregularities, the stronger the compaction;
• route duration, information available to the consumer;
• presence of damage from mechanical influences;
• amount of impurities. In any case, foreign components in the sand give it more or less weight. The purer the sand, the closer the density value is to the reference value;
• the amount of moisture that has entered.

Immediately after purchasing a batch of sand, it should be checked.

What samples are taken to determine the bulk density of sand for construction?

You need to take samples:

• for a batch of less than 350 tons - 10 samples;
• for a batch of 350-700 tons – 10-15 samples;
• when ordering above 700 tons - 20 samples.

Take the resulting samples to a research institution for examination and comparison of quality with regulatory documents.

Conclusion

The required density depends greatly on the type of work. Basically, compaction is necessary to form a foundation, backfill trenches, create a cushion under the road surface, etc. The quality of the compaction must be taken into account, each type of work has different compaction requirements.

In the construction of highways, a roller is often used; in places difficult to reach for transport, a vibrating plate of various capacities is used.

So, to determine the final amount of material, you need to set the compaction coefficient on the surface during compaction; this ratio is indicated by the manufacturer of the compaction equipment.

Always the relative density coefficient is taken into account, since soil and sand tend to change their indicators based on the level of humidity, type of sand, fraction and other indicators.

Mandatory compaction of soil, crushed stone and asphalt concrete in the road industry is not only integral part technological process of constructing the subgrade, base and coating, but also serves as the main operation to ensure their strength, stability and durability.

Previously (until the 30s of the last century), the implementation of the indicated indicators of soil embankments was also carried out by compaction, but not by mechanical or artificial means, but due to the natural self-settlement of the soil under the influence, mainly, of its own weight and, partly, traffic. The constructed embankment was usually left for one or two, and in some cases even three years, and only after that the base and surface of the road were built.

However, the rapid motorization of Europe and America that began in those years required the accelerated construction of an extensive network of roads and a revision of the methods of their construction. The technology of roadbed construction that existed at that time did not meet the new challenges that arose and became a hindrance in solving them. Therefore, there is a need to develop the scientific and practical foundations of the theory of mechanical compaction of earthen structures, taking into account the achievements of soil mechanics, and to create new effective soil compaction means.

In those years they began to study and take into account physical and mechanical properties soils, assess their compaction taking into account the granulometric and moisture conditions (the Proctor method, in Russia - the standard compaction method), the first classifications of soils and standards for the quality of their compaction were developed, and methods of field and laboratory monitoring of this quality began to be introduced.

Before this period, the main soil-compacting agent was a smooth drum static roller of a trailed or self-propelled type, suitable only for rolling and leveling the near-surface zone (up to 15 cm) of the poured soil layer, and even manual tamper, used mainly for compacting surfaces, repairing potholes and for compacting roadsides and slopes.

These simplest and ineffective (in terms of quality, thickness of the layer being worked and productivity) compacting means began to be replaced by such new means as plate, ribbed and cam (remember the invention of 1905 by the American engineer Fitzgerald) rollers, tamping plates on excavators, multi-hammer tamping machines on a caterpillar tractor and smooth roller, manual explosion-rammers (“jumping frogs”) light (50–70 kg), medium (100–200 kg) and heavy (500 and 1000 kg).

At the same time, the first soil-compacting vibrating plates appeared, one of which from Lozenhausen (later Vibromax) was quite large and heavy (24–25 tons including the base crawler tractor). Its vibrating plate with an area of ​​7.5 m2 was located between the tracks, and its engine had a power of 100 hp. allowed the vibration exciter to rotate at a frequency of 1500 kol/min (25 Hz) and move the machine at a speed of about 0.6–0.8 m/min (no more than 50 m/h), providing a productivity of approximately 80–90 m2/h or not more than 50 m 3 / h with a thickness of the compacted layer of about 0.5 m.

More universal, i.e. capable of compacting Various types soils, including cohesive, non-cohesive and mixed, the compaction method has proven itself.

In addition, during compaction, it was easy and simple to regulate the force compacting effect on the soil by changing the height of the fall of the tamping plate or the tamping hammer. Due to these two advantages, the impact compaction method became the most popular and widespread in those years. Therefore, the number of tamping machines and devices multiplied.

It is appropriate to note that in Russia (then the USSR) they also understood the importance and necessity of the transition to mechanical (artificial) compaction road materials and establishing the production of compaction equipment. In May 1931, the first domestic self-propelled road roller was produced in the workshops of Rybinsk (today ZAO Raskat).

After the end of the Second World War, the improvement of equipment and technology for compacting soil objects proceeded with no less enthusiasm and effectiveness than in pre-war times. Trailed, semi-trailer and self-propelled pneumatic rollers appeared, which for a certain period of time became the main soil-compacting means in many countries of the world. Their weight, including single copies, varied over a fairly wide range - from 10 to 50–100 tons, but most of the pneumatic roller models produced had a tire load of 3–5 tons (weight 15–25 tons) and the thickness of the compacted layer, depending from the required compaction coefficient, from 20–25 cm (cohesive soil) to 35–40 cm (non-cohesive and poorly cohesive) after 8–10 passes along the track.

Simultaneously with pneumatic rollers, vibrating soil compactors - vibratory plates, smooth roller and cam vibratory rollers - developed, improved and became increasingly popular, especially in the 50s. Moreover, over time, trailed models of vibratory rollers were replaced by more convenient and technologically advanced ones for performing linear earthworks self-propelled articulated models or, as the Germans called them, “Walzen-zug” (push-pull).

Smooth vibratory roller CA 402
from DYNAPAC

Each modern model The soil compacting vibratory roller, as a rule, has two versions - with a smooth and a cam drum. At the same time, some companies make two separate interchangeable rollers for the same single-axle pneumatic-wheeled tractor, while others offer the buyer of the roller, instead of a whole cam roller, just a “shell attachment” with cams, which is easily and quickly fixed on top of a smooth roller. There are also companies that have developed similar smooth roller “shell attachments” for mounting on top of a padded roller.

It should be especially noted that the cams themselves on vibratory rollers, especially after the start of their practical operation in 1960, underwent significant changes in their geometry and dimensions, which had a beneficial effect on the quality and thickness of the compacted layer and reduced the depth of loosening of the near-surface soil zone.

If earlier “shipfoot” cams were thin (supporting area 40–50 cm 2) and long (up to 180–200 mm or more), then their modern counterparts “padfoot” have become shorter (height is mainly 100 mm, sometimes 120–150 mm) and thick (supporting area about 135–140 cm 2 with a side size of a square or rectangle about 110–130 mm).

According to the laws and dependencies of soil mechanics, an increase in the size and area of ​​the contact surface of the cam contributes to an increase in the depth of effective deformation of the soil (for cohesive soil it is 1.6–1.8 side sizes support platform cam). Therefore, the layer of compaction of loam and clay with a vibrating roller with padfoot cams, when creating the appropriate dynamic pressures and taking into account the 5–7 cm depth of immersion of the cam into the soil, began to be 25–28 cm, which is confirmed by practical measurements. This thickness of the compaction layer is comparable to the compacting ability of pneumatic rollers weighing at least 25–30 tons.

If we add to this the significantly greater thickness of the compacted layer of non-cohesive soils using vibratory rollers and their higher operational productivity, it becomes clear why trailed and semi-trailed pneumatic wheel rollers for soil compaction began to gradually disappear and are now practically not produced or are rarely and rarely produced.

Thus, in modern conditions The main soil-compacting means in the road industry of the vast majority of countries in the world has become a self-propelled single-drum vibratory roller, articulated with a single-axle pneumatic-wheeled tractor and having a smooth (for non-cohesive and poorly cohesive fine-grained and coarse-grained soils, including rocky-coarse-grained soils) or a cam roller ( cohesive soils).

Today in the world there are more than 20 companies producing about 200 models of such soil compaction rollers of various sizes, differing from each other in total weight (from 3.3–3.5 to 25.5–25.8 tons), the weight of the vibrating drum module (from 1 ,6–2 to 17–18 t) and its dimensions. There are also some differences in the design of the vibration exciter, in the vibration parameters (amplitude, frequency, centrifugal force) and in the principles of their regulation. And of course, at least two questions may arise before a road builder: how to choose the right suitable model of a similar roller and how to most effectively use it to carry out high-quality soil compaction at a specific practical site and at the lowest cost.

When resolving such issues, it is necessary to first, but quite accurately, establish those predominant types of soils and their condition (particle size distribution and moisture content), for the compaction of which a vibratory roller is selected. Especially, or first of all, you should pay attention to the presence of dusty (0.05–0.005 mm) and clayey (less than 0.005 mm) particles in the soil, as well as its relative humidity (in fractions of its optimal value). These data will give the first ideas about soil compaction, possible way its seals (pure vibration or power vibration-impact) will allow you to choose a vibratory roller with a smooth or padded drum. Soil moisture and the amount of dust and clay particles significantly affect its strength and deformation properties, and, consequently, the necessary compacting ability of the selected roller, i.e. its ability to provide the required compaction coefficient (0.95 or 0.98) in the soil backfill layer specified by the roadbed construction technology.

Most modern vibratory rollers operate in a certain vibration-impact mode, expressed to a greater or lesser extent depending on their static pressure and vibration parameters. Therefore, soil compaction, as a rule, occurs under the influence of two factors:

• vibrations (oscillations, tremors, movements) causing a decrease or even destruction of the forces of internal friction and small adhesion and engagement between soil particles and creating favorable conditions for effective displacement and more dense repacking of these particles under the influence of their own weight and external forces;
• dynamic compressive and shear forces and stresses created in the soil by short-term but frequent impact loads.

In the compaction of loose, non-cohesive soils, the main role belongs to the first factor, the second serves only as a positive addition to it. In cohesive soils, in which the forces of internal friction are insignificant, and the physical-mechanical, electrochemical and water-colloidal adhesion between small particles is significantly higher and predominant, the main acting factor is the force of pressure or compressive and shear stress, and the role of the first factor becomes secondary.

Research by Russian specialists in soil mechanics and dynamics at one time (1962–64) showed that compaction of dry or almost dry sand in the absence of external loading begins, as a rule, with any weak vibrations with vibration accelerations of at least 0.2g (g – earth acceleration) and ends with almost complete compaction at accelerations of about 1.2–1.5g.

For the same optimally wet and water-saturated sands, the range of effective accelerations is slightly higher - from 0.5g to 2g. In the presence of an external load from the surface or when the sand is in a clamped state inside the soil mass, its compaction begins only with a certain critical acceleration equal to 0.3–0.4 g, above which the compaction process develops more intensively.

At about the same time and almost exactly the same results on sand and gravel were obtained in experiments by the Dynapac company, in which, using a bladed impeller, it was also shown that the shear resistance of these materials when vibrating can be reduced by 80–98% .

Based on such data, two curves can be constructed - changes in critical accelerations and attenuation of soil particle accelerations acting from a vibrating plate or vibrating drum with distance from the surface where the source of vibrations is located. The intersection point of these curves will give the effective compaction depth of interest for the sand or gravel.

Rice. 1. Damping curves of vibration acceleration
sand particles during compaction with a DU-14 roller

In Fig. Figure 1 shows two decay curves of the acceleration of oscillations of sand particles, recorded by special sensors, during its compaction with a trailed vibratory roller DU-14(D-480) at two operating speeds. If we accept a critical acceleration of 0.4–0.5 g for sand inside a soil mass, then it follows from the graph that the thickness of the layer being processed with such a light vibratory roller is 35–45 cm, which has been repeatedly confirmed by field density monitoring.

Insufficiently or poorly compacted loose non-cohesive fine-grained (sand, sand-gravel) and even coarse-grained (rock-coarse-clastic, gravel-pebble) soils laid in the roadbed of transport structures quite quickly reveal their low strength and stability under conditions of various types of shocks and impacts , vibrations that can occur during the movement of heavy trucks, road and rail transport, during the operation of various impact and vibration machines for driving, for example, piles or vibration compaction of layers of road pavements, etc.

The frequency of vertical vibrations of road structure elements when a truck passes at a speed of 40–80 km/h is 7–17 Hz, and a single impact of a tamping slab weighing 1–2 tons on the surface of a soil embankment excites vertical vibrations in it with a frequency of 7–10 to 20–23 Hz, and horizontal vibrations with a frequency of about 60% of vertical ones.

In soils that are not sufficiently stable and sensitive to vibrations and shaking, such vibrations can cause deformations and noticeable precipitation. Therefore, it is not only advisable, but also necessary to compact them by vibration or any other dynamic influences, creating vibrations, shaking and movement of particles in them. And it is completely pointless to compact such soils by static rolling, which could quite often be observed at serious and large road, railway and even hydraulic facilities.

Numerous attempts to compact low-moisture, one-dimensional sands with pneumatic rollers in embankments of railways, highways and airfields in oil and gas regions Western Siberia, on the Belarusian section of the Brest-Minsk-Moscow highway and at other sites in the Baltic states, the Volga region, the Komi Republic and the Leningrad region. did not give the required density results. Only the appearance of trailed vibratory rollers at these construction sites A-4, A-8 And A-12 helped to cope with this acute problem at the time.

The situation with the compaction of loose coarse-grained rock-coarse-block and gravel-pebble soils may be even more obvious and more acute in its unpleasant consequences. The construction of embankments, including those with a height of 3–5 m or even more, from such soils that are strong and resistant to any weather and climatic conditions with their conscientious rolling with heavy pneumatic rollers (25 tons), it would seem, did not give serious reasons for concern to the builders, for example, one of the Karelian sections of the federal highway"Kola" (St. Petersburg-Murmansk) or the "famous" Baikal-Amur Mainline (BAM) railway in the USSR.

However, immediately after they were put into operation, uneven local subsidence of improperly compacted embankments began to develop, amounting to 30–40 cm in some places of the road and distorting the general longitudinal profile of the BAM railway track to a “sawtooth” with a high accident rate.

Despite the similarities general properties and the behavior of fine-grained and coarse-grained loose soils in embankments, their dynamic compaction should be carried out using vibrating rollers of different weights, dimensions and intensity of vibration effects.

Single-sized sands without dust and clay impurities are very easily and quickly repacked even with minor shocks and vibrations, but they have insignificant shear resistance and very low permeability of wheeled or roller machines. Therefore, they should be compacted using light-weight and large-sized vibratory rollers and vibrating plates with low contact static pressure and medium-intensity vibration impact, so that the thickness of the compacted layer does not decrease.

The use of trailed vibratory rollers on single-size sands of medium A-8 (weight 8 tons) and heavy A-12 (11.8 tons) led to excessive immersion of the drum into the embankment and squeezing out sand from under the roller with the formation in front of it of not only a bank of soil, but and a shear wave moving due to the “bulldozer effect”, visible to the eye at a distance of up to 0.5–1.0 m. As a result, the near-surface zone of the embankment to a depth of 15–20 cm turned out to be loosened, although the density of the underlying layers had a compaction coefficient of 0.95 and even higher. With light vibratory rollers, the loosened surface zone can decrease to 5–10 cm.

Obviously, it is possible, and in some cases advisable, to use medium and heavy vibratory rollers on such same-sized sands, but with an intermittent roller surface (cam or lattice), which will improve the roller’s permeability, reduce sand shear and reduce the loosening zone to 7–10 cm. This is evidenced by the author’s successful experience in compacting embankments of such sands in winter and summer in Latvia and the Leningrad region. even a static trailed roller with a lattice drum (weight 25 t), which ensured the thickness of the embankment layer compacted to 0.95 was up to 50–55 cm, as well as positive results compaction with the same roller of one-size dune (fine and completely dry) sands in Central Asia.

Coarse-grained rock-coarse-clastic and gravel-pebble soils, as practical experience shows, are also successfully compacted with vibratory rollers. But due to the fact that in their composition there are, and sometimes predominate, large pieces and blocks measuring up to 1.0–1.5 m or more, it is not possible to move, stir and move them, thereby ensuring the required density and stability of the entire embankment. -easy and simple.

Therefore, on such soils, large, heavy, durable smooth roller vibratory rollers with sufficient intensity of vibration impact should be used, weighing a trailed model or a vibrating roller module for an articulated version of at least 12–13 tons.

The thickness of the layer of such soils processed by such rollers can reach 1–2 m. This kind of filling is practiced mainly at large hydraulic engineering and airfield construction sites. They are rare in the road industry, and therefore there is no particular need or advisability for road workers to purchase smooth rollers with a working vibratory roller module weighing more than 12–13 tons.

Much more important and serious for the Russian road industry is the task of compacting fine-grained mixed (sand with varying amounts of dust and clay), simply silty and cohesive soils, which are more often encountered in everyday practice than rocky-coarse-clastic soils and their varieties.

Particularly a lot of trouble and trouble arises for contractors with silty sands and purely silty soils, which are quite widespread in many places in Russia.

The specificity of these non-plastic, low-cohesion soils is that when their humidity is high, and the North-Western region is primarily “sinned” by such waterlogging, under the influence of vehicle traffic or the compacting effect of vibratory rollers, they pass into a “liquefied” state due to their low filtration capacity and the resulting increase in pore pressure with excess moisture.

With a decrease in humidity to the optimum, such soils are relatively easily and well compacted by medium and heavy smooth-roller vibratory rollers with a vibratory-roller module weight of 8–13 tons, for which the layers of filling compacted to the required standards can be 50–80 cm (in a waterlogged state, the thickness of the layers is reduced to 30– 60 cm).

If a noticeable amount of clay impurities (at least 8–10%) appears in sandy and silty soils, they begin to exhibit significant cohesion and plasticity and, in their ability to compact, approach clayey soils, which are very poorly or not at all susceptible to deformation by purely vibrational methods.

Research by Professor N. Ya. Kharkhuta has shown that when almost pure sands are compacted in this way (impurities of dust and clay less than 1%) optimal thickness layer compacted to a coefficient of 0.95 can reach up to 180–200% of the minimum size of the contact area of ​​the working body of the vibrating machine (vibrating plate, vibrating drum with sufficient contact static pressures). With an increase in the content of these particles in the sand to 4–6%, the optimal thickness of the layer being worked is reduced by 2.5–3 times, and at 8–10% or more it is generally impossible to achieve a compaction coefficient of 0.95.

Obviously, in such cases it is advisable or even necessary to switch to a force compaction method, i.e. for the use of modern heavy vibratory rollers operating in vibro-impact mode and capable of creating 2–3 times more high pressure than, for example, static pneumatic rollers with a ground pressure of 6–8 kgf/cm 2.

In order for the expected force deformation and corresponding compaction of the soil to occur, the static or dynamic pressures created by the working body of the compaction machine must be as close as possible to the compressive and shear strength limits of the soil (about 90–95%), but not exceed it. Otherwise, shear cracks, bulges and other traces of soil destruction will appear on the contact surface, which will also worsen the conditions for transmitting the pressures necessary for compaction to the underlying layers of the embankment.

The strength of cohesive soils depends on four factors, three of which relate directly to the soils themselves (grain size distribution, moisture and density), and the fourth (the nature or dynamism of the applied load and estimated by the rate of change in the stressed state of the soil or, with some inaccuracy, the time of action of this load ) refers to the effect of the compaction machine and the rheological properties of the soil.

Cam vibratory roller
BOMAG

With an increase in the content of clay particles, the strength of the soil increases up to 1.5–2 times compared to sandy soils. The actual moisture content of cohesive soils is very important indicator, affecting not only strength, but also their compactability. The best way Such soils are compacted at the so-called optimal moisture content. As the actual humidity exceeds this optimum, the strength of the soil decreases (up to 2 times) and the limit and degree of its possible compaction significantly decreases. On the contrary, with a decrease in humidity below the optimal level, the tensile strength increases sharply (at 85% of the optimum - 1.5 times, and at 75% - up to 2 times). This is why it is so difficult to compact low-moisture cohesive soils.

As the soil compacts, its strength also increases. In particular, when the compaction coefficient in the embankment reaches 0.95, the strength of cohesive soil increases by 1.5–1.6 times, and at 1.0 – by 2.2–2.3 times compared to the strength at the initial moment of compaction ( compaction coefficient 0.80–0.85).

In clayey soils that have pronounced rheological properties due to their viscosity, the dynamic compressive strength can increase by 1.5–2 times with a loading time of 20 ms (0.020 sec), which corresponds to a frequency of application of a vibration-impact load of 25–30 Hz, and for shear – even up to 2.5 times compared to static strength. In this case, the dynamic modulus of deformation of such soils increases up to 3–5 times or more.

This indicates the need to apply higher dynamic compaction pressures to cohesive soils than static ones in order to obtain the same deformation and compaction result. Obviously, therefore, some cohesive soils could be effectively compacted with static pressures of 6–7 kgf/cm 2 (pneumatic rollers), and when switching to their compaction, dynamic pressures of the order of 15–20 kgf/cm 2 were required.

This difference is due to the different rate of change in the stress state of cohesive soil, with an increase of 10 times its strength increases by 1.5–1.6 times, and by 100 times – up to 2.5 times. For a pneumatic roller, the rate of change in contact pressure over time is 30–50 kgf/cm 2 *sec, for rammers and vibratory rollers – about 3000–3500 kgf/cm 2 *sec, i.e. the increase is 70–100 times.

For correct purpose functional parameters of vibratory rollers at the time of their creation and to control the technological process of these vibratory rollers performing the very operation of compacting cohesive and other types of soils is extremely important and it is necessary to know not only the qualitative influence and trends in changes in the strength limits and deformation moduli of these soils depending on their granular composition, humidity, density and dynamic load, but also have specific values ​​of these indicators.

Such indicative data on the strength limits of soils with a density coefficient of 0.95 under static and dynamic loading were established by Professor N. Ya. Kharkhuta (Table 1).

Table 1
Strength limits (kgf/cm2) of soils with a compaction coefficient of 0.95
and optimal humidity

It is appropriate to note that with an increase in density to 1.0 (100%), the dynamic compressive strength of some highly cohesive clays of optimal moisture will increase to 35–38 kgf/cm2. When humidity decreases to 80% of the optimum, which can be in warm, hot or dry places in a number of countries, their strength can reach even large values– 35–45 kgf/cm2 (density 95%) and even 60–70 kgf/cm2 (100%).

Of course, such high-strength soils can only be compacted with heavy vibro-impact pad rollers. The contact pressures of smooth drum vibratory rollers, even for ordinary loams of optimal moisture, will be clearly insufficient to obtain the compaction result required by the standards.

Until recently, the assessment or calculation of contact pressures under a smooth or padded roller of a static and vibrating roller was carried out very simply and approximately using indirect and not very substantiated indicators and criteria.

Based on the theory of vibrations, the theory of elasticity, theoretical mechanics, mechanics and dynamics of soils, the theory of dimensions and similarity, the theory of cross-country ability of wheeled vehicles and the study of the interaction of a roller die with the surface of a compacted linearly deformable layer of asphalt concrete mixture, crushed stone base and subgrade soil, a universal and quite a simple analytical relationship for determining the contact pressures under any working part of a wheeled or roller-type roller (pneumatic tire wheel, smooth hard, rubberized, cam, lattice or ribbed drum):

σ o – maximum static or dynamic pressure of the drum;
Q in – weight load of the roller module;
R o is the total impact force of the roller under vibrodynamic loading;
R o = Q in K d
E o – static or dynamic modulus of deformation of the compacted material;
h – thickness of the compacted layer of material;
B, D – width and diameter of the roller;
σ p – ultimate strength (fracture) of the compacted material;
K d – dynamic coefficient

A more detailed methodology and explanations for it are presented in a similar collection-catalog “Road Equipment and Technology” for 2003. Here it is only appropriate to point out that, unlike smooth drum rollers, when determining the total settlement of the surface of the material δ 0, the maximum dynamic force R 0 and the contact pressure σ 0 for cam, lattice and ribbed rollers, the width of their rollers is equivalent to a smooth drum roller, and for pneumatic and rubber-coated rollers, an equivalent diameter is used.

In table 2 presents the results of calculations according to the specified methodology and analytical dependencies of the main indicators of dynamic impact, including contact pressures, smooth drum and cam vibratory rollers from a number of companies in order to analyze their compacting ability when pouring one of the possible types fine-grained soils with a layer of 60 cm (in loose and dense states, the compaction coefficient is 0.85–0.87 and 0.95–0.96, respectively, the deformation modulus E 0 = 60 and 240 kgf/cm 2, and the value of the real amplitude of vibration of the drum also respectively a = A 0 /A ∞ = 1.1 and 2.0), i.e. all rollers have the same conditions for the manifestation of their compacting abilities, which gives the calculation results and their comparison the necessary correctness.

JSC "VAD" has in its fleet a whole range of properly and efficiently working soil-compacting smooth drum vibratory rollers from Dynapac, starting from the lightest ( CA152D) and ending with the heaviest ( CA602D). Therefore, it was useful to obtain calculated data for one of these skating rinks ( CA302D) and compare with data from three Hamm models similar and similar in weight, created according to a unique principle (by increasing the load of the oscillating roller without changing its weight and other vibration indicators).

In table 2 also shows some of the largest vibratory rollers from two companies ( Bomag, Orenstein and Koppel), including their cam analogues, and models of trailed vibratory rollers (A-8, A-12, PVK-70EA).

Vibrate mode The soil is loose, K y = 0.85–0.87 h = 60 cm; E 0 = 60 kgf/cm 2 a = 1.1 K d R 0 , tf p kd , kgf/cm 2 σ od, kgf/cm 2 Dynapac, CA 302D, smooth, Q вm = 8.1t Р 0 = 14.6/24.9 tf weak 1,85 15 3,17 4,8 strong 2,12 17,2 3,48 5,2 Hamm 3412, smooth, Q вm = 6.7t Р 0 = 21.5/25.6 tf weak 2,45 16,4 3,4 5,1 strong 3 20,1 3,9 5,9 Hamm 3414, smooth, Q вm = 8.2t P 0m = 21.5/25.6 tf weak 1,94 15,9 3,32 5 strong 2,13 17,5 3,54 5,3 Hamm 3516, smooth, Q inm = 9.3t P 0m = 21.5/25.6 tf weak 2,16 20,1 3,87 5,8 strong 2,32 21,6 4,06 6,1 Bomag, BW 225D-3, smooth, Q inm = 17.04t P 0m = 18.2/33.0 tf weak 1,43 24,4 4,24 6,4 strong 1,69 28,6 4,72 7,1 Q inm = 16.44t P 0m = 18.2/33.0 tf weak 1,34 22 12,46 18,7 strong 1,75 28,8 14,9 22,4 Q вm = 17.57t P 0m = 34/46 tf weak 1,8 31,8 5 7,5 strong 2,07 36,4 5,37 8,1 Q вm = 17.64t P 0m = 34/46 tf weak 1,74 30,7 15,43 23,1 strong 2,14 37,7 17,73 26,6 Germany, A-8, smooth, Q вm = 8t P 0m = 18 tf one 1,75 14 3,14 4,7 Germany, A-12, smooth, Q вm = 11.8t P 0m = 36 tf one 2,07 24,4 4,21 6,3 Russia, PVK-70EA, smooth, Q вm = 22t P 0m = 53/75 tf weak 1,82 40,1 4,86 7,3 strong 2,52 55,5 6,01 9,1

Brand, vibratory roller model, drum type Vibrate mode The soil is dense, K y = 0.95–0.96 h = 60 cm; E 0 = 240 kgf/cm 2 a = 2 K d R 0 , tf p kd , kgf/cm 2 σ 0d, kgf/cm 2 Dynapac, CA 302D, smooth, Q вm = 8.1t P 0 = 14.6/24.9 tf weak 2,37 19,2 3,74 8,9 strong 3,11 25,2 4,5 10,7 Hamm 3412, smooth, Q вm = 6.7t P 0 = 21.5/25.6 tf weak 3,88 26 4,6 11 strong 4,8 32,1 5,3 12,6 Hamm 3414, smooth, Q вm = 8.2t P 0 = 21.5/25.6 tf weak 3,42 28 4,86 11,6 strong 3,63 29,8 5,05 12 Hamm 3516, smooth, Q вm = 9.3t P 0 = 21.5/25.6 tf weak 2,58 24 4,36 10,4 strong 3,02 28,1 4,84 11,5 Bomag, BW 225D-3, smooth, Q inm = 17.04t P 0 = 18.2/33.0 tf weak 1,78 30,3 4,92 11,7 strong 2,02 34,4 5,36 12,8 Bomag, BW 225РD-3, cam, Q inm = 16.44t P 0 = 18.2/33.0 tf weak 1,82 29,9 15,26 36,4 strong 2,21 36,3 17,36 41,4 Orenstein and Koppel, SR25S, smooth, Q вm = 17.57t P 0 = 34/46 tf weak 2,31 40,6 5,76 13,7 strong 2,99 52,5 6,86 16,4 Orenstein and Koppel, SR25D, cam, Q вm = 17.64t P 0 = 34/46 tf weak 2,22 39,2 18,16 43,3 strong 3 52,9 22,21 53 Germany, A-8, smooth, Q вm = 8t P 0 = 18 tf one 3,23 25,8 4,71 11,2 Germany, A-12, smooth, Q вm = 11.8t P 0 = 36 tf one 3,2 37,7 5,6 13,4 Russia, PVK-70EA, smooth, Q вm = 22t P 0 = 53/75 tf weak 2,58 56,7 6,11 14,6 strong 4,32 95,1 8,64 20,6

table 2

Data analysis table. 2 allows us to draw some conclusions and conclusions, including practical ones:

• created by Glakoval vibratory rollers, including medium weight (CA302D, Hamm 3412 And 3414 ), dynamic contact pressures significantly exceed (on sub-compacted soils by 2 times) the pressures of heavy static rollers (pneumatic wheel type weighing 25 tons or more), therefore they are capable of compacting non-cohesive, poorly cohesive and light cohesive soils quite effectively and with a layer thickness acceptable for road workers;
• Cam vibratory rollers, including the largest and heaviest ones, compared to their smooth drum counterparts, can create 3 times higher contact pressures (up to 45–55 kgf/cm2), and therefore they are suitable for the successful compaction of highly cohesive and fairly strong heavy loams and clays, including their varieties with low humidity; an analysis of the capabilities of these vibratory rollers in terms of contact pressures shows that there are certain prerequisites for slightly increasing these pressures and increasing the thickness of the layers of cohesive soils compacted by large and heavy models to 35–40 cm instead of today’s 25–30 cm;
• Hamm's experience in creating three various vibratory rollers(3412, 3414 and 3516) with the same vibration parameters (mass of the vibrating roller, amplitude, frequency, centrifugal force) and different total mass of the vibrating roller module due to the weight of the frame should be considered interesting and useful, but not 100%, and above all from the point seeing the slight difference in the dynamic pressures created by the rollers of the rollers, for example, in 3412 and 3516; but in 3516, the pause time between loading pulses is reduced by 25–30%, increasing the contact time of the drum with the soil and increasing the efficiency of energy transfer to the latter, which facilitates the penetration of higher density soil into the depths;
• based on a comparison of vibratory rollers according to their parameters or even based on the results of practical tests, it is incorrect, and hardly fair, to say that this roller is generally better and the other is bad; each model may be worse or, conversely, good and suitable for its specific conditions of use (type and condition of the soil, thickness of the compacted layer); One can only regret that samples of vibratory rollers with more universal and adjustable compaction parameters have not yet appeared for use in a wider range of types and conditions of soils and thicknesses of backfilled layers, which could save the road builder from the need to purchase a set of soil compacting agents different types in terms of weight, dimensions and compaction ability.

Some of the conclusions drawn may not seem so new and may even be already known from practical experience. Including the uselessness of using smooth vibratory rollers to compact cohesive soils, especially low-moisture ones.

The author at one time tested at a special testing ground in Tajikistan the technology of compacting Langar loam, placed in the body of one of the highest dams (300 m) of the now operating Nurek hydroelectric power station. The composition of the loam included from 1 to 11% sandy, 77–85% silty and 12–14% clay particles, the plasticity number was 10–14, the optimal humidity was about 15.3–15.5%, the natural humidity was only 7– 9%, i.e. did not exceed 0.6 from the optimal value.

The loam was compacted using various rollers, including a very large trailed vibratory roller specially created for this construction. PVK-70EA(22t, see Table 2), which had fairly high vibration parameters (amplitude 2.6 and 3.2 mm, frequency 17 and 25 Hz, centrifugal force 53 and 75 tf). However, due to the low soil moisture, the required compaction of 0.95 with this heavy roller was only achieved in a layer of no more than 19 cm.

More efficiently and successfully, this roller, as well as the A-8 and A-12, compacted loose gravel and pebble materials laid in layers up to 1.0–1.5 m.

Based on the measured stresses using special sensors placed in the embankment at various depths, a decay curve of these dynamic pressures along the depth of the soil compacted by the three indicated vibratory rollers was constructed (Fig. 2).

Rice. 2. Decay curve of experimental dynamic pressures

Despite quite significant differences in total weight, dimensions, vibration parameters and contact pressures (the difference reached 2–2.5 times), the values ​​of experimental pressures in the soil (in relative units) turned out to be close and obey one pattern (dashed curve in the graph of Fig. 2) and the analytical dependence shown in the same schedule.

It is interesting that exactly the same dependence is inherent in the experimental stress decay curves under purely shock loading of a soil mass (tamping slab with a diameter of 1 m and a weight of 0.5–2.0 t). In both cases, the exponent α remains unchanged and is equal to or close to 3/2. Only the coefficient K changes in accordance with the nature or “severity” (aggressiveness) of the dynamic load from 3.5 to 10. With more “sharp” soil loading it is greater, with “sluggish” loading it is less.

This coefficient K serves as a “regulator” for the degree of stress attenuation along the depth of the soil. When its value is high, the stresses decrease faster, and with distance from the loading surface, the thickness of the soil layer being worked decreases. With decreasing K, the nature of the attenuation becomes smoother and approaches the attenuation curve of static pressures (in Fig. 2, Boussinet has α = 3/2 and K = 2.5). In this case, higher pressures seem to “penetrate” deep into the soil and the thickness of the compaction layer increases.

The nature of the pulse effects of vibratory rollers does not vary very much, and it can be assumed that the K values ​​will be in the range of 5–6. And with a known and close to stable attenuation of relative dynamic pressures under vibratory rollers and certain values ​​of the required relative stresses (in fractions of the soil strength limit) inside the soil embankment, it is possible, with a reasonable degree of probability, to establish the thickness of the layer in which the pressures acting there will ensure the implementation of the coefficient seals, for example 0.95 or 0.98.

Through practice, trial compactions and numerous studies, the approximate values ​​of such intrasoil pressures have been established and presented in Table. 3.

Table 3

There is also a simplified method for determining the thickness of the compacted layer using a smooth roller vibratory roller, according to which each ton of weight of the vibratory roller module is capable of providing approximately the following layer thickness (with optimal soil moisture and the required parameters of the vibratory roller):

• sands are large, medium, AGS – 9–10 cm;
• fine sands, including those with dust – 6–7 cm;
• light and medium sandy loam – 4–5 cm;
• light loams – 2–3 cm.

Conclusion. Modern smooth drum and pad vibratory rollers are effective soil compactors that can ensure the required quality of the constructed subgrade. The task of the road engineer is to competently comprehend the capabilities and features of these means for correct orientation in their selection and practical application.