How to check soil compaction coefficient. Everything about sand compaction: essence and goals, verification, coefficient calculation, standard values. Significant factors and properties
The application of vibration or static force to bulk material—sand compaction—has the goal of increasing the strength of each layer and preventing shrinkage during operation. This technique is most in demand in road construction, in the process of landscape and foundation work, and in the construction of dams and embankments.
The quality of soil compaction has a direct impact on the bearing capacity of the material and its level of water resistance. An increase in the intensity of exposure by 1% causes an increase in the strength of raw materials by 10-20%. Poor compaction can cause soil subsidence, which will cause expensive repairs to the structure and increase the cost of its maintenance.
Soil compaction can be vibrational or static. In the first case, vibration is formed due to the movement of an eccentric load: as a result of impacts, particles acquire the most dense state, the impact penetrates into the thickness of the material. This method is widely used due to the high quality of the result. Statistical compaction is carried out under its own weight; here the top layer prevents compaction of the lower ones, which is not always appropriate during construction work. This procedure involves rollers operating on pneumatic tires or smooth rollers.
Sand can reach its maximum density either completely saturated or completely dry. But this material exhibits high drainage properties, thanks to which sufficient compaction can be performed at any percentage of moisture content. But here it is necessary to take into account that impurities impair the ability to remove water, the material becomes more plastic, which also affects the ability to compact.
Areas of application for rammers
Most often, the technique is used in road work, during the construction of building foundations, during the laying of railways, and during the construction of ports and airports.
To optimize the bearing capacity of the roadway and extend its service life, compaction of all layers, starting with the embankment, is practiced. The base and bedding are responsible for the rigidity of the road “pie”, so special attention is paid to their compaction.
When constructing railways, it is important to ensure the roadbed is resistant to high loads; for this purpose, the most dense embankment is built.
The quality of the foundation determines the service life and stability of buildings; the conscientiousness of its execution is especially important in areas with unstable soils. Sand, together with other bulk materials, is used here to create a drainage cushion; special compaction equipment is necessarily involved in its formation.
Large infrastructure projects such as ports and airports place greater demands on the quality of materials used. In such conditions, ramming is used not only during the construction of buildings and infrastructure facilities, but also in the construction of runways and berths.
Checking the seal and its main purpose
Calculating and accounting for compaction intensity is justified not only in narrow branches of construction; accurate data is needed in all areas of economic and commercial activity related to the use of sand. The compaction coefficient is significant for all bulk materials, in particular for soil, sand, and gravel.
The most accurate method for checking compaction is by weight, but it is not widely used due to the lack of publicly available equipment capable of measuring the mass of large volumes of raw materials. An alternative option is volumetric accounting, but in this case there is a need to calculate compaction at all stages of sand use: after extraction, during storage, during transportation, at the end user’s site.
Compaction coefficient value
The need to determine the exact density of sand appears during its transportation, filling containers and pits, compacting, and calculating proportions for mixing mortars. The compaction coefficient is a basic indicator taken into account; it illustrates:
- reduction of material volumes based on transportation results;
- the degree of compliance of the laid layers with industry standards.
The sand compaction coefficient looks like a standard number that reflects the degree of reduction in the total volume of material during transportation and placement, accompanied by compaction. If you use a simplified formula, it is calculated as the ratio of the mass characteristic of a specific volume (meaning indicators based on the results of sampling) to the laboratory reference parameter. The latter depends on the size of the fractions and the type of fillers; it is in the range of 1.05-1.52. In relation to construction sand, the coefficient value is 1.15; it is important when drawing up estimates of materials.
The actual volume of brought sand is found by multiplying the compaction rate during transportation by the measurement results obtained. The range of acceptable limits must be specified in the contract regulating the purchase of the material.
The opposite situations are common when, to check the supplier, the planned volume of delivered sand is divided by the compaction coefficient and compared with real indicators. In particular, 50 cubic meters of sand are compacted in the body so that in fact 43.5 cubic meters will be delivered to the site.
Standard values
The sand compaction coefficient is the dependence of the mass characteristic of a certain volume of a control sample (otherwise known as density) to the accepted reference standard.
Laboratory studies make it possible to obtain standard density parameters; these characteristics form the basis of assessment work, the purpose of which is to determine the quality of the delivered order and its adherence to industry requirements. Regulatory documents that set out generally accepted reference frameworks are considered to be:
- GOST 8736-93,
- GOST 25100-95,
- GOST 7394-85,
- SNiP 2.05.02-85.
Additional information and restrictions are indicated in the design documentation. As can be seen from the table data, the compaction coefficient is within 0.95-0.98 of the standard value.
Standards for typical types of work
| The essence of manipulation | Accepted compaction factor |
| Restoration of road trenches in the utility zone | 0,98-1 |
| Backfilling the trench | 0,98 |
| Sinus filling | 0,98 |
| Secondary filling of the pit | 0,95 |
A solid structure with known moisture and friability values is used as a denomination. Volumetric weight is defined as the relationship between the mass of solid particles contained in sand and the potential mass of the mixture in which water could occupy the entire volume of soil.
To calculate the density of river, quarry, and construction raw materials, samples of the substance are taken and sent for laboratory testing. During surveys, sand is compacted with water until it reaches the moisture level specified in the standards.
Factors affecting compaction level
Sand is not always purposefully compacted; it often occurs during transportation. Taking into account variable indicators, it becomes difficult to calculate the amount of material at the output, since it is necessary to rely on all the manipulations and influences to which the raw material was subjected.
The compaction coefficient depends on the following factors:
- duration of the travel route;
- method of transportation (the number of physical contacts with uneven surfaces, the more of them, the more the material is compacted);
- volume of impurities - foreign components can reduce or increase the weight of the batch, the density of pure sand is closest to the standard values;
- volume of moisture absorbed.
The sand is checked immediately upon receipt. If the batch weighs less than 350 tons, 10 samples are enough, 350-700 tons - up to 15 samples are taken, from 700 tons - 20 samples are taken. They are sent to research laboratories: this measure makes it possible to monitor the quality of raw materials according to regulatory documents.
Relative compaction coefficient
This is the ratio of the density of particles after storage or extraction to the density characteristic of the raw material that was brought to the final consumer. Knowing the rate specified by the manufacturer, you can calculate the final coefficient without organizing additional research.
At the time of production
The density of raw materials here depends on the depth of the deposits being developed, the type of pit, and the climatic zone. The bases indicated in the table make it possible to calculate the final parameters of the material, taking into account the accompanying impact on the soil.
During the process of compaction and secondary backfilling
Backfilling (or secondary backfilling) is the procedure for filling an already dug pit after work has been completed or construction has been completed. As a rule, soil is used to fill the pit; quartz sand also has optimal characteristics for this purpose. A related action is tamping, which is necessary to enhance the strength of the coating. Vibrating plates and vibrating stamps, which differ in performance and weight, are used to compact the filled raw materials.
The table above illustrates the proportional relationship between compaction and compaction method. All types of mechanical impact affect primarily the upper layers. When sand is extracted, the structure of the quarry becomes looser, so the density of the raw material may decrease; laboratory tests are regularly organized to monitor changes.
During transportation
Moving bulk materials presents a number of challenges, as the density of resources changes during the transportation of large quantities. As a rule, delivery is carried out by road or rail, and is accompanied by intense shaking of the cargo (transportation by ship, in turn, has a gentle effect). In such conditions, the density will also be affected by precipitation, temperature changes, and increased pressure on the lower layers.
In laboratory conditions
For the study, 30 g of raw material from the analytical stock is used, it is sifted and thoroughly dried to obtain a constant weight value. The material brought to room temperature is mixed and divided into 2 parts.
The samples are weighed, combined with distilled water, boiled to remove air, and cooled. All operations are accompanied by measurements; based on the data obtained, the relative compaction coefficient is calculated.
Regardless of the conditions for changing the characteristics of raw materials, a number of circumstances are taken into account during testing:
- initial properties of sand - size of fractions, compressive strength, caking ability;
- bulk density - density characteristic of the natural environment of origin;
- weather conditions accompanying transportation;
- the maximum possible density detected in laboratory conditions;
- type of transport used - road, rail, sea, river.
All data related to the relative compaction coefficient is recorded in the design and technical documentation. This method of comparing material qualities implies the use of regular deliveries: the information will be correct only when ordering sand from one manufacturer; changes in variables are not allowed here. It is important that transportation is carried out in the same way, the technical characteristics of the quarry are preserved, and at least approximately the same duration of storage of raw materials in the warehouse is practiced.
The compaction coefficient is an indicator that demonstrates how much the volume of a loose material changes after compaction or transportation. It is determined by the ratio of total and maximum density.
Any bulk material consists of individual elements – grains. There are always voids or pores between them. The higher the percentage of these voids, the larger the volume the substance will occupy.
Let's try to explain this in simple language: remember a children's snowball fight. To get a good snowball, you need to scoop up a larger handful from the snowdrift and squeeze it harder. In this way we reduce the number of voids between the snowflakes, that is, we compact them. At the same time, the volume decreases.
The same thing will happen if you pour a little cereal into a glass and then shake it or compact it with your fingers. The grains will become compacted.
In other words, the compaction coefficient is the difference between the material in its normal state and the compacted one.
Why do you need to know the compaction coefficient?
It is necessary to know the compaction coefficient for bulk materials in order to:
- Check whether the ordered quantity of material was actually delivered to you
- Buy the right amount of sand, crushed stone, screenings for backfilling pits, pits or ditches
- Calculate the probable shrinkage of soil when laying a foundation, laying a road or paving slabs
- Correctly calculate the amount of concrete mixture for pouring foundations or floors
Transport compaction factor
Imagine that a dump truck is carrying 6 m³ of crushed stone from a quarry to a customer site. On the way he comes across holes and potholes. Under the influence of vibration, the crushed stone grains are compacted, the volume is reduced to 5.45 m³. This is called shaking the material.
How can you be sure that the quantity of goods indicated in the documents has been delivered to the site? To do this, you need to know the final volume of the material (5.45 m³) and the compaction coefficient (for crushed stone it is 1.1). These two numbers are multiplied, and the initial volume is obtained - 6 cubic meters. If it does not coincide with what is written in the documents, then we are not dealing with rubble shaking, but with an unscrupulous seller.
Compaction coefficient when filling holes
In construction there is such a thing as shrinkage. Soil or any other bulk material is compacted and reduced in volume under the influence of its own weight or pressure from various structures (foundation, paving slabs). The shrinkage process must be taken into account when backfilling ditches and pits. If this is not done, after a while a new hole will form.
To order the required amount of material for backfilling, you need to know the volume of the hole. If you know its shape, depth and width, you can use our calculator to calculate it. After this, the resulting figure must be multiplied by the bulk density of the material and its compaction coefficient.
When filling correctly calculated material into a hole, a mound may result. The fact is that under natural conditions shrinkage occurs over a certain period of time. You can speed up the process by using a tamper. It is carried out manually or using special mechanisms.
Compaction factor in construction
You probably know cases where cracks appeared in buildings immediately after construction. What about potholes on new roads or fallen paving slabs on paths and in courtyards? This happens if you incorrectly calculate soil shrinkage and do not take appropriate measures to eliminate it.
To know the shrinkage, the compaction factor is used. It helps to understand how compacted a particular soil is under certain conditions. For example, under the pressure of the weight of a building, tiles or asphalt.
Some soils shrink so much that they have to be replaced. Other types are specially compacted before construction.
How to find out the compaction factor
The easiest way is to take data on the compaction coefficient from GOSTs. They are designed for different types of material.
| Name of material | Compaction factor |
| PGS | 1,2 |
| PShchS | 1,2 |
| Sand | 1,15 |
| Expanded clay | 1,15 |
| Crushed stone | 1,1 |
| Multicomponent soil mixture | 1,5 |
In laboratory conditions, the compaction coefficient is determined as follows:
- The total or bulk density of the material is measured. To do this, measure the mass and volume of the sample and calculate their ratio
- The sample is then shaken or pressed, the mass and volume are measured, and then the maximum density is determined
- Based on the ratio of two indicators, the coefficient is calculated
The documents indicate average values of the compaction coefficient. The indicator may vary depending on various factors. The numbers given in the table are quite arbitrary, but they allow you to calculate the shrinkage of large volumes of material.
The value of the compaction coefficient is affected by:
- Features of transport and method of transportation
If the material is transported over potholes or railways, it is more compacted than when transported on a flat road or sea - Granulometric composition (sizes, shapes of grains, their ratio)
If the composition of the material is heterogeneous and the presence of flaky particles (flat or needle-shaped), the coefficient will be lower. And in the presence of a large number of small particles - higher - Humidity
The higher the humidity, the lower the compaction coefficient - Tamping method
If the material is compacted manually, it is less compacted than after using vibrating mechanisms - Bulk Density
The compaction coefficient is directly related to the bulk density. As we have already said, during the process of compaction or transportation, the density of the material changes, as there are fewer voids between the particles. Therefore, the bulk density during shipment to the vehicle at the quarry and after arrival at the customer is different. This difference can be calculated and verified precisely thanks to the compaction coefficient.
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In preparation for construction, they conduct special studies and tests to determine the suitability of the site for the upcoming work: they take soil samples, calculate the groundwater level 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, sand cushions are prepared for the foundation and its base, further 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. The basic design of the study involves placing a soil sample in a steel cylinder, which is compressed under the influence of an 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 the qualitative composition of soils, each of which has its own characteristics: density, humidity, and 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 various types of soil and soil cushions used in the construction of foundations and buildings of various configurations, including underground ones.
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.
This practical task is much easier to cope 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 soil compaction coefficient is a dimensionless indicator, calculated as the ratio of soil density to its maximum density. Any soil has pores - microscopic voids filled with air or moisture; when the soil is excavated, there are too many of these pores, it becomes loose, much less than the density of compacted soil. Therefore, when preparing foundation bases or when preparing the soil, it is necessary to further compact it, otherwise over time the soil will cake and will sag under its own weight and the weight of the building.
Required compaction ratio
The soil compaction coefficient shows how well the soil is compacted and can take values from 0 to 1. For foundation foundations, the required compaction coefficient is 0.98 or higher.
Determination of compaction factor
The maximum density - the density of the soil skeleton - is determined in laboratory conditions using the standard compaction method. It consists of placing soil in a cylinder and compressing it, striking it with a falling load. The maximum density depends on soil moisture, the nature of this dependence is shown in the graph:
For each soil there is a temperature at which maximum compaction can be achieved. This humidity is also determined in laboratory tests of soil at different humidity levels.
The actual density of the soil during foundation preparation is measured after compaction work. The simplest method is the cutting ring method: a metal ring of a certain diameter and known length is driven into the soil, the soil is fixed inside the ring, then its mass is measured on a scale. After weighing the soil, subtract the mass of the ring to obtain the mass of the soil. Divide it by the volume of the ring - we get the density of the soil. Then we divide the density of the soil by its maximum density and calculate the soil compaction coefficient.
What is the soil compaction coefficient?
For example, the maximum density of the soil skeleton is known - 1.95 g/cm3, the cutting ring has a diameter of 5 cm and a height of 3 cm, let us determine the coefficient of soil compaction. The first step is to hammer the ring completely into the ground, then remove the soil around the ring, use a knife to separate the ring with the soil inside from the soil under the base and remove the ring, holding the soil from below so that nothing falls out. Then, also using a knife, the soil can be removed from the ring cavity and weighed. For example, the mass of the soil was 450 g. The volume of our ring is 235.5 cm3, which means the density of the soil is 1.91 g/cm3, and the soil compaction coefficient is 1.91/1.95 = 0.979.
- 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.
- 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 of them to 35–40 cm instead of today’s 25–30 cm;
- The experience of the Hamm company in creating three different vibratory rollers (3412, 3414 and 3516) with the same vibration parameters (mass of the oscillating roller, amplitude, frequency, centrifugal force) and different total mass of the vibratory roller module due to the weight of the frame should be considered interesting and useful, but not 100% and primarily from the point of view of 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 compactors of different types by weight, dimensions and sealing ability.
- 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.
Mandatory compaction of soil, crushed stone and asphalt concrete in the road industry is not only an integral part of the 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.
It was in those years that the physical and mechanical properties of soils began to be studied and taken into account, their compactability was assessed 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 began to be introduced field and laboratory control of this quality.
Before this period, the main soil-compacting means was a smooth-roller 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 also a manual tamper, which was used mainly for compacting coatings, when repairing potholes and for compaction curbs 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 slabs 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. The compaction method has proven itself capable of compacting various types of soils, including cohesive, non-cohesive and mixed.
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 of road materials and the establishment of 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 produced models of pneumatic rollers 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 (loose and poorly cohesive) after 8–10 passes along the track.
Simultaneously with pneumatic rollers, vibratory 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 self-propelled articulated models for performing linear excavation work, or, as the Germans called them, “Walzen-zug” (push-pull).
Smooth vibratory roller CA 402
from DYNAPAC
Each modern model of soil compaction vibratory roller, as a rule, has two versions - with a smooth and cam drum. At the same time, some companies make two separate interchangeable rollers for the same single-axle pneumatic wheel tractor, while others offer the buyer of the roller, instead of a whole cam roller, only 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 cm2) and long (up to 180–200 mm or more), then their modern analogs “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 times the size of the side of the cam support pad). 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 working body (for non-cohesive and poorly cohesive fine-grained and coarse-grained soils, including rocky soils). coarse clastic) or pad 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), 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 for a road worker: how to choose the right model of such a 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 idea about the compactability of the soil, the possible method of its compaction (pure vibration or power vibration-impact) and 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:
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 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 the embankments of railways, highways and airfields in the oil and gas-bearing regions of 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 and distorting the general longitudinal profile of the BAM railway track to a “sawtooth” shape with a high accident rate.
Despite the similarity of the general properties and 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 tons), which ensured the thickness of the embankment layer compacted to 0.95 was up to 50–55 cm, as well as positive results of compaction with the same roller of one-size dune (fine and completely dry) sands in Central Asia.
Coarse-grained rocky-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 (dust and clay impurities less than 1%), the optimal thickness of the layer compacted to a coefficient of 0.95 can reach 180–200% of the minimum size of the worker’s contact area vibrating machine organ (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 higher pressures than, for example, static pneumatic wheel 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 a very important indicator that affects not only their strength, but also their compactability. Such soils are best 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 the correct assignment of the functional parameters of vibratory rollers at the time of their creation and for controlling the technological process of these vibratory rollers performing the very operation of compacting cohesive and other types of soils, it is extremely important and 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 load dynamics, but also have specific values for 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 the humidity decreases to 80% of the optimum, which can happen in warm, hot or dry places in a number of countries, their strength can reach even greater values - 35–45 kgf/cm 2 (density 95%) and even 60–70 kgf/ cm 2 (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 content, 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 material being compacted;
K d – dynamic coefficient
A more detailed methodology and explanations for it are presented in a similar collection-catalog “Road Engineering 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 Figure 2 presents the results of calculations using the specified method 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 compaction ability when pouring into the roadbed one of the possible types of fine-grained soils with a layer of 60 cm (in loose and in a dense state, the compaction coefficient is equal to 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 roller is 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).
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Table 2
Data analysis table. 2 allows us to draw some conclusions and conclusions, including practical ones:
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 compaction of the loam was carried out 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 different 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 the total weight, dimensions, vibration parameters and contact pressures (the difference reached 2–2.5 times), the values of the experimental pressures in the soil (in relative units) turned out to be close and obey the same pattern (the dotted curve in the graph of Fig. 2) and the analytical dependence shown on the same graph.
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 nature of the 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):
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.
