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.

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 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. 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 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 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 there are more than 20 companies in the world producing about 200 models of such soil compaction rollers various standard sizes, differing from each other in total weight (from 3.3–3.5 to 25.5–25.8 tons), the weight of the vibrating roller module (from 1.6–2 to 17–18 tons) and their 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:

• vibrations (oscillations, shocks, 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 denser 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 1.2–1.5 g.

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 in iron and steel embankments with pneumatic rollers highways and airfields in the oil and gas 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 of the road and distorting the overall longitudinal profile of the railway to a “sawtooth” shape with a high accident rate. road surface BAM.

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 with 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 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. Kharhuta has shown that when compacting practically pure sands 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 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. 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 at different speeds changes in the stressed 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 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 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, 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 vibration theory, elasticity theory, 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 fairly simple analytical relationship was obtained for determining contact pressures under any operating pressure roller body of a wheeled or roller type (pneumatic tire wheel, smooth hard, rubber-coated, 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 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).

Vibrate mode The soil is loose, K y = 0.85–0.87 h = 60 cm; E 0 = 60 kgf/cm 2 a = 1.1 Kd 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 Kd 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;
• 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 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 the same pattern (dashed curve in the graph of Fig. 2) and 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 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.

Crushed stone is a common construction material, which is obtained by crushing rock hard rock. Raw materials are extracted by blasting during quarrying. The rock is divided into appropriate fractions. In this case, the special compaction coefficient of crushed stone is important.

Granite is the most common, as its frost resistance is high and water absorption is low, which is so important for any building structure. The abrasion and strength of granite crushed stone meets the standards. Among the main fractions of crushed stone we can note: 5-15 mm, 5-20 mm, 5-40 mm, 20-40 mm, 40-70 mm. The most popular is crushed stone with a fraction of 5-20 mm; it can be used for various works:

• construction of foundations;
• production of ballast layers for highways and railway tracks;
• additive to construction mixtures.

The compaction of crushed stone depends on many indicators, including its characteristics. Should be considered:

1. The average density is 1.4-3 g/cm³ (when compaction is calculated, this parameter is taken as one of the main ones).
2. Flakiness determines the level of plane of the material.
3. All material is sorted into fractions.
4. Frost resistance.
5. Radioactivity level. For all work, you can use crushed stone of the 1st class, but the 2nd class can only be used for road work.

Based on such characteristics, a decision is made which material is suitable for certain type works

Types of crushed stone and technical characteristics

Various crushed stones can be used for construction. Manufacturers offer different types of it, the properties of which differ from each other. Today, based on the type of raw material, crushed stone is usually divided into 4 large groups:

• gravel;
• granite;
• dolomite, i.e. limestone;
• secondary.

To make granite material, the appropriate rock is used. This is a non-metallic material that is obtained from hard rock. Granite is solidified magma that is very hard and difficult to process. Crushed stone of this type is manufactured in accordance with GOST 8267-93. The most popular is crushed stone having a fraction of 5/20 mm, as it can be used for a variety of works, including the manufacture of foundations, roads, platforms and other things.

Crushed gravel is a bulk construction material that is obtained by crushing stony rock or rock in quarries. The strength of the material is not as high as that of crushed granite, but its cost is lower, as is the background radiation. Today it is common to distinguish between two types of gravel:

• crushed type of crushed stone;
• gravel of river and sea origin.

According to the fraction, gravel is classified into 4 large groups: 3/10, 5/40, 5/20, 20/40 mm. The material is used to prepare various building mixtures As a filler, it is considered indispensable for mixing concrete, building foundations, and paths.

Crushed limestone is made from sedimentary rock. As the name implies, the raw material is limestone. The main component is calcium carbonate, the cost of the material is one of the lowest.

The fractions of this crushed stone are divided into 3 large groups: 20/40, 5/20, 40/70 mm.

It is applicable to the glass industry, in the manufacture of small reinforced concrete structures, in the preparation of cement.

Recycled crushed stone has the lowest cost. They make it out of construction waste, for example, asphalt, concrete, brick.

The advantage of crushed stone is its low cost, but in terms of its main characteristics it is much inferior to the other three types, so it is rarely used and only in cases where strength is not of great importance.

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Compaction factor: purpose

The compaction coefficient is a special standard number determined by SNiP and GOST. This value shows how many times crushed stone can be compacted, i.e. reduce its external volume during compaction or transportation. The value is usually 1.05-1.52. According to existing standards, the compaction coefficient can be as follows:

• sand and gravel mixture - 1.2;
• construction sand - 1.15;
• expanded clay - 1.15;
• crushed gravel - 1.1;
• soil - 1.1 (1.4).

An example of determining the compaction coefficient of crushed stone or gravel can be given as follows:

1. It can be assumed that the mass density is 1.95 g/cm³; after compaction was carried out, the value became 1.88 g/cm³.
2. To determine the value, you need to divide the actual density level by the maximum, which will give a crushed stone compaction coefficient of 1.88/1.95=0.96.

It is necessary to take into account that the design data usually does not indicate the degree of compaction, but the so-called skeleton density, i.e. During calculations, it is necessary to take into account the level of humidity and other parameters of the building mixture.

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.

Wide practical use did not find due to the inaccessibility of equipment for weighing large volumes of material or the lack of sufficient accurate indicators. Alternative option coefficient output – volumetric accounting.

Its only drawback is the need to determine the seal on 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 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 change physical properties pit after digging out the sand.

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.

The cement is 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 quantity required material, and accordingly 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 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. 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.

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.

The high pace of construction, the accelerated development of residential areas and office buildings makes us think about quality characteristics concrete. Solid, strong foundation without concrete mortar impossible to create. Concrete is the main connecting and structural material in construction. The quality of concrete directly affects the strength and service life of structures. The solution can be prepared from sand and gravel mixtures, paying attention to the source of origin and observing the required ratio of components.

Purpose of PGS

The sand-gravel mixture, or in other words ASG, consists of gravel. The composition is prepared in two ways:

• natural;
• artificial.

The resulting mixture is in great demand and is used in industrial, road, and housing construction:

• For ;
• for the manufacture of monolithic, reinforced concrete structures;
• as a drainage layer of the road surface;
• landscape leveling.

Types, mixture structure

Gravel in the mixture should be up to 75% by weight.

The proportional content of sand and gravel in the mixture is the main criterion for gravel mass. Gravel should not be more than 75% of total mass. Great importance is paid to the size of components, and they are also checked for compliance with standards. Based on the proportional content of components, two types of sand and gravel are distinguished:

• Natural (pgs). The ratio of gravel as a percentage relative to the total mass is no less than 10 and no more than 95 - 1/5 of the total composition. Additional processing the classic composition is not exposed. The gravel mass is extracted from a quarry and immediately shipped to the buyer. Basically, the gravel content is 10-20% of the bulk. The percentage can rise to 30 if the mixture was mined in reservoirs. The size of the elements reaches from 10 to 70 mm. By separate agreement with the buyer, the size may be larger than stated, the maximum value is 10 cm.
• Enriched (OPGS). The proportions of the components are as follows: sand 30%, gravel up to 70%. 3/4 of the entire enriched mass is gravel.

The enriched composition can be obtained through special preparation. Observing certain proportions, mix necessary components. The result is opgs. Considering percentage gravel, five groups of enriched mixture are distinguished.

• 1 group. The percentage of gravel from the total mass is 15-25%.
• 2nd group. The amount of gravel is 25-30%.
• 3rd group. The component content is from 35 to 50%.
• 4th group. The percentage of gravel is 50-65%.
• 5 group. Gravel in quantities from 65 to 75%.

The greater the percentage of gravel contained in the solution, the harder the mass is. The technical characteristics of the solution and operating parameters depend on the amount of gravel. The final cost of concentrated gravel compounds is influenced by the amount and percentage of natural stone content.

Based on the deposit and initial source of formation, natural gravel mixtures are divided into:

• Gully (mountain) are characterized by an admixture of rocks, the shape of the natural stone is acute-angled, the size is different. The heterogeneity of the structure of this type does not allow the use of the ravine-mountain type for the production of concrete. The mixture is widely used as drainage during the repair of highways, filling pits and pits.
• River (lake) A small amount of clay and shell rock is observed. The shape of the elements is rolled.
• Marine. Impurities are contained in small quantities or absent. The shape of the stones is round and dense.

Lake-river and sea gravel mixtures are used to make concrete mortar, necessary for buildings of special strength, and for pouring foundations.

Features of mass selection

The enriched sand and gravel mixture should have the largest grains of gravel.

In all branches of construction: preparation of structures, pouring any type of foundation, concrete is required. A responsible approach to the production of concrete mortar ensures reliability and strength of structures. Important role V technological process plays the ratio of components.

The main point is to buy the right one high quality products, it's not worth saving. The concrete reflects the method of extraction of the material. Pay attention to various impurities; the structure of the mass should not contain them. The absence of foreign components increases the adhesion between the gravitational mass and other components of the solution.

To work with the foundation, enriched mixtures are used, since the amount of gravel in them exceeds the sand content, which increases the density and reduces the looseness of the solution.

Compaction degree

Transportation of a bulk substance leads to its compaction. Compression is controlled by regulations building standards. The exponential value that determines the amount of reduced volume is called the compaction coefficient. Compaction standards are set at the state level.

Compacting the material is a natural process; the coefficient depends on the mass of the batch. Important points are the quality of the material and the method of transportation. The average compaction index is 1.2, according to the standards. For example, for sand the compaction index is 1.15, for crushed stone - 1.1.

Compression Rate - important point in construction. At the beginning of work it is carried out preparatory stage, during which the thickness, level, quantity and other indicators necessary for subsequent work are determined. The acceptance of the final result is influenced by the compaction factor.

Tamping sand and gravel mixture.

When compacting soil using the tamping method, the main rules are followed. Differences in the depth of the dug trench are leveled out by compaction from the highest elevations, gradually moving to lower ones. Compaction is carried out until the density required by the standards is achieved. When working with the mixture, freezing of materials is not allowed; humidity is normal. The process is considered complete when the number of strikes does not exceed the established limits. The so-called “two control strikes” rule.

Concrete preparation process

During individual construction, the mixture is prepared with your own hands. For small construction volumes, there is no need to hire expensive construction equipment. Before starting work, it is worth determining the structure, calculating the mass, and preparing the appropriate components.

To mix it yourself you will need the following: consumables and tools:

• stock of cement of the required brand;
• clean warm water;
• opgs;
• kneading container;
• (concrete mixer);
• bucket.

Correctly matched components affect the quality result. For an enriched look, it is worth making the ratio of parts 8 to 1, where the first is the mixture, the second is cement. This coefficient was determined by trial and error and is still actively used today. experienced craftsmen. How much water to add is an individual matter. It is worth focusing on the dryness of the components, gradually adding liquid until the desired consistency of the solution is achieved.

Portland cement is a hydraulic binder that hardens in water and air.

Cement for mortar is used of those brands that provide the required strength. These are M300, M500, M600. Recently, Portland cement has become popular because it has excellent astringent properties. For a small amount of work, M400 concrete is used, taking into account the fact that the finished mixture should be used within two hours.

High-quality concrete made from PGS is influenced by the size of natural stone. The solution acquires the required strength when the gravel size is 8 cm. Cured required proportions: 6 - mixture, 1 - cement.

The need to know the exact density of bulk building materials arises when transporting them, compacting them, filling containers and pits, and selecting proportions when preparing mortars. One of the indicators taken into account is the compaction coefficient, which characterizes the compliance of the laid layers with regulatory requirements or the degree of reduction in the volume of sand during transportation. The recommended value is indicated in project documentation and depends on the type of structure being built or type of work.

The compaction coefficient is a standard number that takes into account the degree of reduction in the external volume during the process of delivery and laying followed by compaction (you can find information on compacting crushed stone). In a simplified version, it is found as the ratio of the mass of a certain volume taken during sampling to the reference parameter obtained in laboratory conditions. Its value depends on the type and size of filler fractions and varies from 1.05 to 1.52. In the case of sand construction work it is 1.15, it is used as a starting point when calculating building materials.

As a result, the actual volume of sand supplied is determined by multiplying the measurement results by the compaction rate during transportation. The maximum permissible value must be specified in the purchase agreement. The opposite situations are also possible - to check the integrity of suppliers, the volume is found at the end of delivery, its quantity in m 3 is divided by the sand compaction coefficient and compared with the delivered one. For example, when transporting 50 m 3 after compaction in the back of a car or wagons, no more than 43.5 will be brought to the site.

Factors influencing the coefficient

The given number is a statistical average; in practice, it depends on many different criteria. These include:

• Sand grain sizes, purity and other physical and Chemical properties, determined by the place and method of extraction. The characteristics of the source may change over time; as the material is removed from the quarries, the looseness of the remaining layers increases; to eliminate errors, the bulk density and related parameters are periodically checked in laboratory conditions.
• Conditions of transportation (distance to the facility, climatic and seasonal factors, type of transport used). The stronger and longer the vibration affects the material, the more efficiently the sand is compacted; maximum compaction is achieved when it is moved by vehicles, slightly less - during rail transportation, and minimal - during sea transportation. At the right conditions transportation exposure to humidity and subzero temperatures reduced to a minimum.

These factors should be checked immediately; the values ​​of the indicators are acceptable natural humidity and bulk density are specified in the passport. Additional volumes of bulk solids due to losses during transportation depend on the delivery distance and are taken equal to 0.5% within 1 km, 1% beyond this parameter.

Using the coefficient in the preparation of sand cushions and road construction

A characteristic feature of any bulk building materials is a change in volume when unloading into a free area or compacting it. In the first case, the sand or soil becomes loose; during storage, the particles settle and adhere to each other with virtually no voids, but still do not meet the standards. On last stage– when laying and distributing compositions at the bottom of the pit, the coefficient of relative sand compaction is taken into account. It is a criterion for the quality of work carried out during the preparation of trenches and construction sites and varies from 0.95 to 1, the exact value depends on intended purpose layer and method of backfilling and compaction. It is determined by calculation and must be indicated in the design documentation.

The compaction of the soil backfilled is considered the same mandatory action, as when bookmarking sand cushion under the foundations of buildings or when constructing roads. To achieve the desired effect, use special equipment– rollers, vibrating plates and vibrating stamps; in its absence, tamping is carried out hand tools or feet. The maximum permissible thickness of the treated layer and the required number of passes refer to the table values, the same applies to the recommended minimum of bedding on top of pipes or communications.

During the process of compacting sand or soil, their bulk density increases, and the volumetric area inevitably decreases. This must be taken into account when calculating the amount of material purchased, along with the total losses due to weathering or the amount of stock. When choosing a compaction method, it is important to remember that any external mechanical influences affect only the upper layers; vibration equipment is required to obtain a coating with the required quality.