The device of crushed stone pavement (base) of highways by the method of impregnation with bitumen. Crushed stone base and asphalt concrete pavement device Gravel base device
When constructing a crushed stone base, treated in the upper part with a sand-cement mixture, the following operations are performed:
Transportation and distribution of crushed stone;
Preparation of crushed stone for processing with a sand-cement mixture;
Treatment of crushed stone with a sand-cement mixture according to the method of impregnation;
Base seal;
Foundation maintenance;
Figure 1.5 Scheme of a crushed stone base treated in the upper part with a sand-cement mixture according to the impregnation method
Before building a base made of crushed stone treated with a sand-cement mixture, it is necessary to perform
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Ensure the readiness of the subgrade (underlying layer of pavement) in accordance with the requirements of the current building codes and rules;
Prepare temporary access roads for the supply of materials to the work site;
Make a planned and high-altitude breakdown of the base, ensuring compliance with its design thickness, width and transverse slopes;
Provide drainage;
Work on the construction of a crushed stone base, treated in the upper part with a sand-cement mixture, is carried out in the developed technological sequence on three grips 200 m long each.
On the first grip, the following operations are performed:
Delivery of crushed stone of fraction 40-70 mm for the device of the basis;
Distribution and leveling of crushed stone with a motor grader;
Profiling a layer of crushed stone with a motor grader;
In this flow chart, crushed stone is delivered to the site by KamAZ-55118 dump trucks in the amount necessary for constructing a structural layer of a given thickness, taking into account the safety factor for compaction of 1.25-1.3, and unloaded onto the prepared underlying underlying or frost-protective layer. Crushed stone is unloaded in two rows parallel to the longitudinal axis of the base. Leveling and leveling of crushed stone is carried out by a motor grader DZ-122 in 4 passes along one track, performing passes according to a shuttle scheme with a working stroke in one direction.
During the first and second passes along one track, the distribution and rough leveling of crushed stone is performed, during the third pass, the final leveling. During the fourth pass, the final profiling and planning of the crushed stone layer is carried out according to the design marks, taking into account the settlement of the layer during compaction. The first, second and third passes of the motor grader along one track start from the edges of the base, moving along the roadsides and orienting themselves along the heights of the breakdown, with a gradual movement
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During the first and second passes along one track: grip angle 40-50°, cutting angle up to 40°, tilt angle 3-5°;
During the third pass: grip angle 55-60°, cutting angle 45-60°, angle of inclination along the design transverse slope of the base;
At the fourth pass: start leveling with a blade grip angle of 90°, then the grip angle is set to 60-65°, and the cutting angle to 40°, the angle of inclination corresponding to the transverse slope of the base;
On the second grip, the following technological operations are performed:
Moisturizing the crushed stone layer with a watering machine;
Rolling up the crushed stone layer with a light roller;
To identify irregularities in the crushed stone layer and to ensure the passage of construction vehicles, crushed stone is rolled up with a light roller roller in 2-4 passes along one track. The map is based on rolling by a self-propelled smooth-roller roller DU-96. The first pass of the roller is carried out with the capture of the shoulders to ensure the support of the base. After compaction, the base is moistened with a watering machine at the rate of 3-10 l / . MD 433-03 was adopted as a watering machine.
On the third grip, the following technological operations are performed:
Delivery of sand-cement mixture to the site by dump trucks;
Distribution of sand-cement mixture by motor grader;
Pressing the sand-cement mixture into the crushed stone layer with pneumatic rollers;
Consolidation of the base with a roller on pneumatic tires;
final compaction
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Applying a film-forming material to the surface of the base layer;
Care of the finished base layer;
The sand-cement mixture is delivered to required quantity dump trucks (adopted by KAMAZ 55118) and unloaded onto the crushed stone layer in two rows. After unloading onto the surface of the base, the sand-cement mixture is leveled with a DZ-122 motor grader in 3-4 passes along one track. The sand-cement mixture, distributed in an even layer over the surface of the crushed stone, is pressed into the voids of the upper part of the crushed stone layer in 2-3 passes of the pneumatic roller in one track according to the shuttle scheme.
The indentation of the mixture is carried out immediately after its distribution in order to prevent the thin layer of the mixture from drying out. This operation is performed by a self-propelled skating rink on pneumatic tires DU-100. The indentation of the sand-cement mixture starts from the edges of the base with a gradual shift of the skating rink passages to the middle of the base and overlapping the previous track by 0.25-0.40 m. In this case, the speed of the rink should be 1.5 -2 km / h and the movement should be smooth, without jerks.
To achieve the standard density of the base, it is compacted with a roller DU-100 (on pneumatic tires) in 12-16 passes along one track and additionally compacted with a light smooth-roller roller DU-96. To create a persistent part along the edges of the base, make 2 more passes along one track. Rolling of crushed stone also begins from the edges of the base with a gradual shift to the middle according to the shuttle scheme, overlapping the previous track by 0.25-0.4 m.
During the first 4-5 passes, the roller moves at a speed of 2-4 km/h. Subsequent passes are performed at a speed of 8-10 km/h. At the same time, the air pressure in the tires must be constant (0.6-0.8 MPa). The final number of passes is specified by trial rolling. The absence of a track from the rink and a wave on the base in front of it indicates the required layer density.
For additional compaction of the upper part of the base and elimination of irregularities from the wheels of the pneumatic roller, final compaction is carried out with a self-propelled smooth-roller roller in 3-5 passes along one track according to the shuttle scheme. Should be considered,
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Immediately after compaction of the base, film-forming materials are applied to the surface - marol, lacquer-ethinol or bituminous emulsion at a filling rate of 0.6-0.8 l /
For the device of crushed stone layers (bases and coatings), the following work is performed: removal of crushed stone for the lower layer and its distribution by self-propelled distributors (as an exception, crushed stone distribution by a bulldozer or motor graders can be allowed); crushed stone compaction with simultaneous watering; removal of crushed stone for the top layer and its distribution; crushed stone compaction with watering; removal of crushed stone for cutting and its distribution by mounted distributors with sweeping with mechanical brushes; sealing with watering; removal of crushed stone for the final wedging of coatings, its distribution and final compaction with watering.
In the lower and middle layers of crushed stone bases, crushed stone of fractions 40-70 and 70-420 mm is used; in the upper layers of bases and coatings - 40-70 mm; for wedges - 5-10, 10-20 and 20-40 mm.
For bases laid by the “spell” method, fractionated crushed stone of natural rocks, crushed stone from mining waste and low-active crushed stone from ferrous metallurgy slag. Cast slag crushed stone is also used chemical industry(phosphoric), containing predominantly oxides of calcium (CaO) and silica (SiO2), the content of oxides (Al2O3, FeO, MnO, MgO) is lower than in ferrous metallurgy slags. Distinctive feature of these slags is the presence of CaF2 and P2O5 compounds. The strength of crushed stone must comply with the current SNiPs.
Requirements for strength and frost resistance of standard (up to 70 mm) and large (70-120 mm) fractions of crushed stone from natural rocks and from slag for foundations, depending on the category of roads and climatic conditions are listed in Table. fifty.
The removal and distribution of crushed stone is carried out taking into account the compaction coefficient of 1.25-1.30. The maximum thickness of the compacted layer should not exceed 18-20 cm.
Two types of self-propelled crushed stone pavers can be used to distribute crushed stone: I - for laying crushed stone or gravel layers on a sandy layer (the paver is loaded by dump trucks moving along the roadside); II - for laying crushed stone or gravel layers on a solid base (material is loaded from the side of the base).
Crushed stone from a dump truck usually enters the hopper of the crusher spreader, the exit from which is controlled by dampers. The thickness of the leveled layer is regulated by the leveling bar, and the width is fixed by the side limiters. The leveled layer of crushed stone (gravel) is compacted by vibrating plates with vibrators installed on them.
At sandy base and in the absence of self-propelled spreaders, crushed stone can be unloaded at the edge of the compacted crushed stone layer and then moved onto it by a bulldozer. In the trough, crushed stone is leveled with a motor grader or bulldozer.
When rolling crushed stone in a trough, it is necessary to create a reliable side stop, for which a strip of side stones is laid along the edges of the trough until the crushed stone is scattered or temporary thrust boards 5-6 cm thick are placed on the edge along the edges of the roadway. with careful tamping.
Compaction of crushed stone is the most important part of the work on the device of a crushed stone layer. In the process of compaction, crushed stones move, approach and mutual jamming, and significant vertical and horizontal forces occur. Compaction is carried out by motor rollers with metal rollers, rollers on pneumatic tires, vibratory rollers and vibrating plates. The entire compaction cycle can be divided into three periods: crushed stone sedimentation, compaction, and the creation of a dense surface crust.
The first period is characterized by the compaction of the placer, the movement of individual gravel, which continues until they take the most stable position. This period is characterized by the presence of mainly residual deformations, which significantly decrease by the end of the period.
The second period is characterized by complete approach and mutual jamming of gravel with gaps filled with broken particles; as a result of this process, a rigid, stable skeleton with a spongy (porous) surface is obtained. By the end of the second period, residual deformation should be practically absent.
In the third period, the formation of a dense crust in the upper part of the layer should be achieved by wedging its surface with fine gravel.
To obtain a dense and durable crushed stone layer, it is very important to provide correct mode watering during compaction. The initial compaction of crushed stone of ordinary sizes does not require watering, since in a loose placer individual crushed stones are relatively easily distributed and mutually moved. In the first period, watering is carried out only when crushed stone of low-strength rocks larger than 70 mm in size is compacted. When the initial settlement of the layer is reached, further compaction requires overcoming the friction between the gravel. Water in this case facilitates compaction, and partly also goes to the formation of a cementing paste from the fines resulting from the breaking of the edges of the crushed stone. During the formation of a dense surface crust, the cementing dough from the screenings can stick to the rollers of the rink and contribute to the tearing of gravel from the coating, so watering is stopped at the last stage of coating formation. On average, 15-25 liters of water per 1 m2 are required in the second period and about 10-12 liters per 1 m2 of coverage in the third rolling period.
Watering is carried out immediately before compaction from tank trucks equipped with a distribution system. With a lack of water, the compaction time is extended, and with an excess, the underlying layer may become waterlogged.
Compaction begins with light rollers from the edges to the middle of the coating. The compaction of crushed stone with rollers with metal rollers begins from the shoulders in three or four passes along one track, followed by the approach of the passages of the rollers to the axis of the road, overlapping the previous tracks by 1/3 of the width and reducing the number of passes along the axis of the road to one. Having reached the axis, the roller again goes to the edge and moves from the edge to the axis.
Roll with a light roller until it leaves a noticeable mark. Then the compaction is continued with heavier rollers with mandatory watering to reduce friction during mutual jamming of gravel. In the event of the formation of subsidence, it is necessary to immediately level them by adding fresh gravel.
When rolling the upper layer, the first passes compact the area, the axis of which is the curb (edge of the placer) with partial captures of the shoulders, which are poured from stable soils in the process of laying the foundation in layers and over the entire width. This creates a stop that prevents the spread of crushed stone during rolling. With subsequent passes, the skating rink, alternately moving from one side to the other, approaches from the edges to the middle.
The compaction of crushed stone in the second period requires the largest number of passes of the roller along one track, and it is very important to establish the end of rolling, since overconsolidation can lead to rounding and crushing of crushed stones and to the breakdown of the rolled layer,
Before the third rolling period, to fill the voids in the upper layer of the crushed stone skeleton, crushed stone is distributed over the surface for wedging by mounted distributors at the rate of 1.5-2 m3 per 100 m2 of coverage, depending on the size of the crushed stone. The signs of the end of the compaction of the upper layer in the second and third periods are: the absence of a trace - precipitation from the passage of a 12-ton skating rink, the immobility of the crushed stone, the disappearance of the wave, crushing the crushed stone thrown under the rink.
When arranging crushed stone pavements, it is also necessary to spread stone fines (1 m3 per 100 m2 of pavement) with its spreading over the surface and rolling with a heavy roller. Before rolling the wedge and stone chips, the coating is watered.
The number of passes of the rink along one track depends on the quality of the crushed stone and is approximately 3-6 for the first period of compaction; the second - 10-35; third - 10-15 passes. In each case, the number of passes should be determined by the experimental compaction of the site.
When compacting a crushed stone coating, it is necessary to periodically check the longitudinal and transverse profiles. In the event of the formation of individual irregularities and waves during rolling, the crushed stone in these places must be loosened and the excess moved to lower places, or the subsidence should be leveled with crushed stone of the same size, followed by rolling with light rollers.
At the end of rolling, the top layer should be even and uniform; a heavy roller leaves no trace on such a layer. It is advisable to control the evenness of the coating with a mobile double-support folding rail PKP-5 designed by Soyuzdornia.
To receive flat surface the bases of the mixture should be laid with special laying machines or motor graders with a tracking system.
Altitude evenness of layers road structures is achieved by using tracking systems to ensure evenness: stabilizing (according to the grader scheme DS-515), tracking (D-699, D-700), software.
The basis of stabilizing systems is the principle of providing a gap, not more than permissible, under a rail of a certain length. An effective remedy to reduce the amplitude of the unevenness of the leveled surface and expand the range of leveled wavelengths, the long-base leveler DS-515, made according to the grader scheme with a reduced ratio of the distance from the axis of the rear support to the working body to the base of the planner, can serve.
Tracking systems installed on pavers and motor graders provide a given evenness due to the movement of the working body in accordance with the change in vertical marks of a real reference longitudinal profile, called a copier.
The following can be used as a copier: a compacted and profiled base or an adjacent coating strip; rigid metal copier made of rails 1.5-4.0 m long; a wire or cable stretched along the coating with supports installed every 5-15 m; a beam (light, laser, etc.) with an arrangement of radiation sources every 10-400 m, depending on the longitudinal profile of the road.
The domestic industry produces asphalt pavers D-699, D-700, concrete paver DS-510 with a tracking system, as well as systems. "Profile-1" and "Profile-2" to the motor grader.
Software systems set the vertical marks of the surface of the base or cover by means of the appropriate setting of the working body, and the control variable software system is a program or record of commands to change the position of the working body.
The moment of the end of rolling can be precisely set using Ya. A. Kaluga's dynamometer. This device is installed on a motorized roller and records the value of the rolling resistance coefficient (the ratio of traction force to the mass of the roller). After the disappearance of residual deformations, the value of the coefficient becomes minimal and stabilizes. This shows that further compaction with this roller is impractical.
Of great importance for the efficiency of rolling is the speed of the roller. Especially carefully should be rolled at the beginning, with a significant wave in front of the rollers of the rink. In this case, the speed should not exceed 1.5-2.0 km/h (for rollers with metal rollers).
When choosing types of rollers, it is necessary to take into account not only the rolling period, but also the strength of the stone material being rolled. For low strength stone materials lighter rollers should be used (Table 51).
When working on three-roller two-axle rollers, it should be borne in mind that they compact mainly with the rear rollers, which give a large amount of pressure, and therefore the roller passes must be taken into account in strips corresponding to the width of these rollers.
If it is impossible to achieve the required compaction (or it is necessary to open traffic on a crushed stone base), the following measures can be taken: wedging the base with fine crushed stone or sand treated in installations with organic binders; pouring bitumen or tar (2-3 kg / m2) before scattering crushed stone or distributing a wet mixture of cement with sand (1: 4) at the rate of 7-10 kg of cement per 1 m2; replacement of wedging small crushed stone with another one with good cementing properties (limestone); replacement of strongly rounded crushed stone with sharp-edged.
Crushed stone, crushed stone-sand or cement-sand mixtures for splitting are distributed by mounted distributors at the rate of 2-3 m3 per 100 m2 of base, depending on the size and compactibility of crushed stone.
In the first 10-15 days of operation of the crushed stone coating, it is necessary to organize care for its formation: correct partial minor damage and baste the scattered trifles. On fig. 43 shown technology system crushed stone layer devices.
Road bases from large crushed stone. Crushed stone materials maximum size up to 120 mm are used for the device of the lower crushed stone layers, pieces with a height of about 16 cm of the appropriate shape can, in some cases, be used for the device of packing bases or bridges.
The arrangement of bases from coarse crushed stone of low-strength limestones and sandstones has the appearance of features. Careful work is required to ensure the purity of crushed stone and its minimum crushability during movement, planning and, most importantly, during compaction. It is advisable to bring very large crushed stone into piles placed perpendicular to the axis of the road. Crushed stone is leveled and planned by a bulldozer or motor grader equipped with a special blade. When moving forward, the blade moves the crushed stone into required space, and then after setting it to a given height, this layer aligns in reverse. Bulldozers should be used with low or medium power (preferably on pneumatic tires), as heavy machines crush the rubble and press it into the sand layer.
With a design thickness of up to 20 cm, it is advisable to arrange the bases in one layer of crushed stone 40-120 mm in size, and use crushed stone 25-40 mm in size for the wedging. With a base thickness of more than 20 cm, it is arranged in two layers, and crushed stone 70-120 mm in size is used for the lower layer.
In view of the fact that the bulldozer performs only rough leveling, in order to obtain the required profile on a layer of large crushed stone, it is advisable to lay crushed stone with fractions of 40-70 or 25-70 mm; This gravel can be leveled with a motor grader.
If the base surface is too porous, crushed stone with a particle size of 15-25 mm can be used. This crushed stone is distributed by trailed crushed stone spreaders. The scattering of each fraction must be compacted.
To compact layers of low-strength crushed stone, machines that do not destroy crushed stone (planar vibrators, self-propelled rollers on pneumatic niches) should be used. When compacting coarse crushed stone of low strength, the forces required to move the crushed stone exceed the efforts spent on breaking off the edges.
This can explain the significant crushability of crushed stone already in the first period of compaction. To reduce crushability, large crushed stone must be watered from the very beginning of compaction. The amount of water should be such that it does not cause severe weakening and crushing of crushed stone. When vibrocompacting, the crushed stone must be dry.
The technological scheme of the construction of foundations made of coarse gravel on a draining sandy layer consists of the following operations.
- removal of crushed stone fractions of 70-120 mm by dump trucks and unloading it into heaps at the edge of the placer; leveling rubble with bulldozers;
- compaction of crushed stone with rollers on pneumatic tires (with watering) or vibration machines (without watering);
- removal of crushed stone with a particle size of 40-70 mm by dump trucks and its distribution by self-propelled crushed stone distributors;
- compaction of crushed stone with light rollers on pneumatic tires (with watering) or vibration machines (without watering), removal by dump trucks and distribution by trailed distributors of crushed stone with a particle size of 15-40 or 25-40 mm in case of a porous surface;
- compaction of crushed stone with light rollers on pneumatic tires (with watering) or plane vibrating machines (without watering).
The given technological scheme can be modified depending on the thickness of the base, size and class of crushed stone, the presence of sealing agents and crushed stone distributors.
landscaping
Composition of operations and controls
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controlledoperations | Control (method, volume) | Documentation |
| Preparatory work | Check: Availability of passports for materials; Compliance of slopes and marks of the pound base with the project; Callout of center axes and reliability of their fastening; Implementation of drainage measures; Soil moisture content. |
Visual Measuring Technical inspection of the entire surface |
Passports (certificates), general work log |
| Control: Humidity of crushed stone; Width and thickness of the laid layer; The quality of the compaction and compliance with the care regimen; Temperature of hot and warm asphalt mix; Surface evenness; The quality of the longitudinal and transverse joints of the laid strips; Elevation marks and transverse slope of the canvas. |
Measuring, at least once a shift Measuring Visual Measuring, in each dump truck Measuring, rail 3 m long Visual Measuring |
General work log | |
| Acceptance of work performed | Check: Compliance of the work performed with the requirements of the project. |
Technical inspection, comprehensive assessment of the quality of work performed |
Act of acceptance of work performed |
| Control and measuring tool: level, tape measure, theodolite, three-meter rail. | |||
| Operational control is carried out by: foreman (foreman), surveyor --during works. Acceptance control is carried out; quality service workers, foreman (foreman), surveyor, representatives of the technical supervision of the customer. |
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Technical requirements
SNiP Z.06.0Z-85 p. 7.1, 10.16
Limit deviations:
- the smallest thickness of the distributed layer of crushed stone should be at least 10 cm when laying on a solid foundation and at least 15 cm when laying on sand;
- maximum thickness crushed stone layer should not exceed the values \u200b\u200bspecified in the table;
- the thickness of the layer of asphalt concrete mixture to be arranged must be at least 4 cm.
Coatings and bases made of asphalt concrete mixtures should be arranged in dry weather. Laying of hot and cold mixes should be carried out in spring and summer at an ambient temperature of at least 5 ° C, in autumn - at least 10 ° C; warm mixtures - at a temperature not lower than 10 "C.
GOST 8736-93*. Sand for construction work. Specifications. GOST 9128-97. Mixes asphalt concrete road, airfield and asphalt concrete. Specifications.
The manufacturer accompanies each batch of crushed stone and sand with a quality document, which indicates:
Name and address of the manufacturer;
Number, date of issue of the document;
Product name and quantity;
Fraction size;
Density (true and average);
Porosity;
Voidness (volume of intergranular voids);
Water absorption.
Asphalt concrete mixtures are characterized by the following indicators:
The nature of the mixture depending on its temperature;
Density of asphalt concrete;
The largest size of the filler mixture.
The temperature of hot mixtures when they are discharged from the mixer must be at least 140 °C.
Quality control of asphalt concrete mixtures is carried out at asphalt concrete plants during their manufacture, as well as during laying. To control the quality of the mixture, one sample from each batch is taken and tested.
Each batch of the mixture must be accompanied by a quality document to the consumer.
Work instructions
SNiP 3.06.03-85 paragraphs. 1.7, 1.8, 1.12, 7.1, 73-7.4, 7.8, 10.18
Work on the arrangement of layers of pavement should be carried out only on a ready-made and accepted in the prescribed manner, not waterlogged and not deformed subgrade.
Coating and base with binder materials should be arranged on a dry and clean underlying layer, and when using organic binder materials, in addition, on an unfrozen layer.
Prior to the beginning of the construction of each layer of the base and coating, it is necessary to carry out layout work to fix the position of the edges and elevations of the layers. When using machines equipped with automatic tracking systems, fixing the edges and height marks is carried out by installing copy strings on one or both sides of the layer to be laid. Stakeout works and their control should be carried out using geodetic instruments.
Compaction of subgrade layers, bases and coatings with rollers must be carried out from the edges to the middle, with each trace from
of the previous pass of the rink must overlap with the next pass by at least 1/3.
The number of passes of the roller and the thickness of the compacted layer, taking into account the safety factor for the compaction of materials, should be established based on the results of a trial compaction. The results of the trial compaction must be recorded in the general work log.
The smallest thickness of the spreading layer should be 1.5 times the size of the largest particles and be at least 10 cm when laying on a solid base and at least 15 cm when laying on sand.
It is allowed to take out crushed stone and gravel and stack them on a subgrade or intermediate storage for subsequent use in the construction of pavement.
Work on the device of crushed stone bases and coatings by the wedge method should be carried out in two stages:
Distribution of the main fraction of crushed stone and its preliminary compaction (compression and interlocking);
Distribution of wedging rubble (double-, three-time wedging) with compaction of each fraction. For bases, one-time wedging is allowed. When using crushed stone of sedimentary rocks of a strength grade of less than 600, when arranging the foundations, work can be performed in one stage.
After the compaction of the coating is completed, fine stone from igneous rocks of a grade of strength not lower than 800 (from sedimentary rocks - not lower than 600) should be distributed over its surface in the amount of 1 cubic meter. m per 100 sq. m and compact in approximately 4-6 passes of the roller.
It is allowed to carry out work using hot asphalt mixes at an air temperature of at least 0 °C, subject to the following requirements:
The thickness of the arranged layer must be at least 4 cm;
It is necessary to use asphalt mixes with surfactants or activated mineral powders;
As a rule, only the bottom layer of a two-layer asphalt concrete pavement; if in winter or spring vehicles will move along this layer,
It should be arranged from dense asphalt-concrete mixtures;
The top layer is allowed to be arranged only on the freshly laid bottom layer until it cools down (while maintaining the temperature of the bottom layer at least 20 ° C).
The laying of cold asphalt mixes should be completed approximately 15 days before the beginning of the autumn rainy season, except for mixes with activated mineral materials.
TYPICAL TECHNOLOGICAL CHART (TTK)
The device of the crushed stone basis and coverings
General provisions
General provisions
1. Quality control and acceptance of work on the installation of crushed stone, gravel, slag bases and coatings of roads and bridges must be carried out in accordance with the requirements of SNiP 3.06.03-85.
2. Prior to the installation of these bases and coatings, the subgrade and drainage must be prepared.
3. During the installation of bases and coatings, the controlled operations include:
- delivery and layer-by-layer distribution of materials used;
- pre-compaction, profiling and final compaction.
4. When importing and distributing materials, the margin for shrinkage during compaction should be taken into account:
- for sand and gravel (crushed stone) mixtures of optimal grain composition and crushed stone of fractions 40-70 and 70-120 mm, strength grade 800 or more - 25-30%;
- for crushed stone of strength grades 300-600 and slag - 30-50%.
5. The smallest thickness of the distributed layer should be 1.5 times the size of the largest particles and be at least 10 cm when laying on a solid base and at least 15 cm when laying on sand. The maximum layer thickness should not exceed the values given in Table 1.
Table 1
(SNiP 3.06.03-85, table 5)
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Material type |
Maximum thickness of the compacted layer, cm, when using rollers |
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with smooth rollers weighing 10 tons or more |
lattice and pneumatic tires weighing 15 tons or more |
vibration and combined mass, t |
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16 or more |
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1. Difficult to compact (from igneous and metamorphic rocks of a strength grade of 1000 or more, gravel is strong, well rounded, vitrified structure slags) |
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2. Easily compacted (from igneous and metamorphic rocks of grade less than 1000 in strength, sedimentary, unrounded gravel, slags with a porous structure) |
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1 AREA OF USE
A typical technological map has been developed for the installation of crushed stone bases and coatings.
CONSTRUCTION OF TRANSITION TYPE COATINGS
The pavements are called transitional because as the intensity of traffic increases, they serve as the basis for improved types of pavements. The latter are economical even with a traffic intensity of more than 200 vehicles per day.
The disadvantages of transitional type coatings include strong dustiness in the dry season, lack of evenness, especially in cobblestone pavements, and a quick loss of original evenness.
The inefficiency of transition type coatings is explained by their relatively rapid wear, which requires frequent and expensive repairs, as well as the high cost of road transport.
In the construction of transitional coatings, mainly mineral materials with soil binders are used: mineral grains are held together by silt-clay particles, which acquire astringent properties when moistened. The transitional type also includes coatings from soils and low-strength mineral materials treated with organic binders. Such coatings generate less dust, but have lower strength and disadvantages common to all coatings of this group. Transitional pavements also include gravel and crushed stone pavements, cobblestone pavements.
Peculiarities of subgrade preparation for pavements with transitional type pavements
For pavements with transitional pavements, the subgrade is backfilled a year before the construction of the pavement so that it is additionally compacted under the influence of cars and precipitation. The subgrade suit mainly trough profile.
The trough profile is created in two ways. In the first one (Fig. 1), the subgrade is backfilled to a level corresponding to the bottom of the pavement, i.e. to the surface on which the base will be located.
Fig.1. Subgrade prepared for pavement with an additional base layer for the entire width of the subgrade:
B- width roadbed, B- the width of the subgrade, L- the width of the carriageway, a- curb width, i- slopes
In the second method, the subgrade is erected to the mark H, shown in Fig. 2. With the first method, the subgrade will be with powdered shoulders. Simultaneously with the backfilling of the subgrade, in the same year, the roadsides are backfilled from the soil imported or pushed up from the road reserves by bulldozers. The soil is backfilled and compacted in layers to form a trough of the required depth for placing the pavement (Fig. 3).
Fig.2. The subgrade with a semi-trough profile:
B- the width of the roadway, B- the width of the subgrade, L- the width of the carriageway, a- curb width, i- slopes
Fig.3. Road bed with powdered shoulders
During the construction of a subgrade with powdered shoulders, a year before the construction of the pavement, water can accumulate in the trough, waterlogging the subgrade. To avoid this, slots are arranged in the roadsides and in the lowered places of the longitudinal profile for the release of water from the trough. To avoid waterlogging of the subgrade with water from the trough, roadsides are sprinkled immediately before the construction of the pavement. In this case, backfilling is carried out from imported soil or by grader-elevators from roadside reserves. In the second method, the subgrade is called a semi-trough profile.
The trough in the subgrade is cut out mainly by motor graders, which move in a circular pattern, cutting and moving the soil towards the shoulders.
After the formation of the trough in front of the foundation device, the bottom of the trough is compacted with a 6-8-ton roller in two or three passes along one track.
Gravel and other pavements made of similar fine-grained materials (slag, shell, etc.) on roads of category V are built of a crescent type on a subgrade (Fig. 4, a), erected with a gable profile with slopes of 40-60+, and sometimes with a half-trough profile if it is necessary to thicken the coating along the width of the carriageway (Fig. 4, b).
Fig.4. Cross profile of the V category road with crescent-shaped pavement
If it is necessary to have a trough deeper than 0.3-0.4 m in non-cohesive soil, its walls are made with slopes with a steepness of 1: 1, and the soil for subsequent backfilling of the sinus is stored on the side of the road along the trough or shifted over the edge to the slope.
Instructions for the arrangement of work on soil compaction
The degree of soil compaction depends on the method of embankment construction. When filling the soil with a grader-elevator or a dragline excavator, the initial compaction reaches 0.65-0.7 of the optimal density (1.0). Bulldozers give 0.7-0.8, cars and scrapers 0.8-0.85. With soil moisture close to optimal, compaction can reach 0.85-0.9. Thus, in order to achieve a soil density of 0.95-1.0, its artificial compaction is required.
The main factors affecting the conditions and quality of compaction are soil moisture (dry material is compacted in layers of smaller thickness) and the type of compacting machine (mechanism). Accordingly, the choice of compaction machines depends on the type and moisture of the soil, the required compaction, the required thickness of the compacted layer, the productivity and maneuverability of the machines. The greater the compaction value, the heavier the soil and the lower its moisture content compared to the optimum, the more powerful and heavier the machines and the number of their passes along one track are required. The length of time the soil is in contact with the compacting machine matters. A number of very efficient compacting machines (heavy self-propelled rollers and mechanical rammers) require pre-compaction with light machines.
For operational control, it is possible to establish the "tensile strength" of the soil at its compaction by rolling, which characterizes the conditions for the transition of the soil from the compaction stage to the stage of bulging out from under the working body of the machine.
For soil compaction during the construction of embankments, heavy rollers (trailed or self-propelled), cam, lattice and ribbed rollers, rollers on pneumatic tires, mechanical rammers (electric or pneumatic), tamping plates, tamping and vibro-compacting machines, vibro-impact machines are used.
Compaction of the soil on the embankment is carried out in the same sequence as its filling. The soil is compacted by successive circular penetrations of the roller over the entire area of the embankment, and each subsequent penetration should overlap the previous one by 0.2 ... 0.3 m. .
Rollers smooth and with ribbed rollers compact the soil to a depth of 10 cm. Cam rollers are used to compact loamy and clay soils to a depth of up to 30 cm, in sandy soils, the compaction captures the soil to a depth of 35 ... 50 cm. The mass of such rollers is different - from 5 to 30 tons.
Figure 5 shows a diagram of a static roller with pneumatic tires and a working body with smooth (Fig. 5, a) and cam (Fig. 5, b) rollers.
Fig.5. Soil compaction rollers:
a- smooth roller; b- cam roller; in- tandem articulated roller
The main parameter of soil-compacting machines is the mass together with the ballast. Main technological parameters: compaction strip width, compacted layer thickness. Rollers on pneumatic tires are produced with a mass of 10 to 100 tons together with ballast. Self-propelled vibratory rollers have a mass of up to 8 tons. Rollers with smooth rollers on pneumatic wheels can compact soils in layers of 0.4 m. soil ranges from 8 to 12.
In the presence of water for sandy soils, sealing with excessive moisture is sometimes used. In this case, water is supplied from below the compacted layers (by heating).
Smooth rollers, although inefficient, are most suitable for cohesive and poorly cohesive soils. Their disadvantages are that they can compact thin layers (no more than 0.2 m), require relatively a large number passages at low speeds and a large scope of work. All this creates significant difficulties in the organization of high-speed construction of the subgrade and prevents the full compaction of embankments.
Cam rollers are intended mainly for cohesive and slightly cohesive soils. With the same mass as smooth rollers, they provide almost twice the compaction depth and require fewer passes. Cam rollers work more efficiently in loose and lumpy soils and are completely unsuitable in waterlogged ones. Trailer rollers usually work in several pieces with one tractor. The peculiarity of the operation of cam rollers is that they compact the soil below the level of penetration of the cams. The drums of the rollers are hollow, for loading them with ballast. The efficiency of rolling with cam rollers is increased when used in conjunction with rollers on pneumatic tires. First, rolling is carried out by cam rollers, and the required density of the upper layer is achieved by rolling with rollers on pneumatic tires.
Rollers on pneumatic tires can compact cohesive and non-cohesive soils (Fig. 6). These rollers are much more efficient than smooth rigid rollers by reducing the number of passes. Self-propelled rollers on pneumatic tires are mainly used for compacting bases and coatings.
Fig.6. Scheme of operation of a trailed roller on pneumatic tires during embankment compaction:
L- the length of the capture, 1-10 - the sequence of penetrations
Tamper plates are used as attachments on cranes or excavators (Fig. 7). They are one of the most effective means of compacting embankments to a depth of 0.6-1.5 m, suitable for work in cohesive and non-cohesive soils. The area of the plates is 0.6-1.5 m, the mass is 1.5-2.5 tons. The height of the fall of the plate is 1-2 m.
Fig.7. Scheme of operation of a heavy rammer during soil compaction
For compaction of weakly water-resistant fine-grained or gravelly soils, including loamy and clayey gravel-sand mixtures, mixtures with organic impurities, the water content is very important, especially when vibrocompacting. Such soils can be compacted by machines of any type. If the water content is less than optimal, it is preferable to use pneumatic and vibratory rollers.
Rocky and clastic soils are compacted with both pneumatic and vibratory rollers with a layer thickness of 30 to 80 cm. If the size of the stones exceeds 80 mm, the layer thickness for vibratory rollers is reduced to 30-40 cm.
Pure gravel-sand mixtures with grains less than 50 mm, compacted by vibratory rollers and rollers on pneumatic tires, are water-resistant, and therefore the degree of compaction of these mixtures may be less than that of other materials. Cam rollers are not used to compact clean sands. Vibrating machines can be used to compact loose soils (sands, sandy loam). When vibrating, movements of soil particles occur due to oscillatory movements reported by the vibrator. The increase in soil density is achieved by the fact that the soil particles move, taking a more stable position.
Pneumatic and electric rammers can be light 0.1-0.2 tons and heavy - 0.5-1.5 tons and compacting to a depth of 20-30 cm and 40-90 cm, respectively.
Self-propelled tamping machines are equipped with a number of hammers weighing from 0.3 to 1.5 tons, falling from a height of 50-250 cm. productivity 200-500 m/h.
Table 1.1
Basic data on the production of work by various machines