X Международная студенческая научная конференция
«Студенческий научный форум» - 2018
НОВЫЕ ТЕХНОЛОГИИ В ДОРОЖНОМ СТРОИТЕЛЬСТВЕ
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Transition to a new type of road concrete - fibro-basalt slag-alkaline concrete.
The use of such concrete allows solving two problems: fibers (basalt fibers) increase strength, and alkali increases resistance to acidic media.
The technology of concrete production has its own characteristics. The preparation of vibro-reinforced concrete mixture can be achieved provided that the fibrous reinforcement is fed uniformly and gradually into the concrete mixer while mixing the components of the concrete mix.
Geogrids prevent the displacement of the bulk ground used in the construction of the railway track. Thus, geogrids provide warranty, long-lasting, without additional maintenance of road functioning even in places with intensive traffic.
Local and inter-farm roads generally have transitional coverings. The exploitation of such roads is greatly complicated during the mudslides.
Geogrids are widely used in civil engineering throughout the world. Manufactured on the basis of high-strength polyethylene and polypropylene. The principle of operation is the cohesion of granular material with lattice cells. This jamming allows the grate to resist the horizontal shear of the embankment, thereby mobilizing the carrying capacity of soft ground. Geogrids are used as a reinforcement material on loose heterogeneous soils for roads and railways, in parking areas, on landing areas, as well as for reinforcing the foundations of the bridge, slopes and earthen dams.
Load sharing mechanism:
The application of the geogrid is a method of reinforcing the soil and leads to the formation of plates on its surface with a thickness corresponding to the height of the geogrid: 100 mm, 150 mm, 200 mm. The mechanism of transfer of loads caused by the movement of vehicles on the layers of soil underlying the slab are as follows:
• the voltage transmitted from the wheels of transport leads to an increase in the vertical stress in the soil, which fills the cell of the geogrid, resulting in increased pressure on the rough walls of the cell;
• the elastic band of the geogrid takes over some of these forces, and the remaining load is transferred to neighboring cells;
• cells connected to each other in the spatial structure of the geogrid will eventually distribute the load to large soil surfaces, resulting in a decrease in the magnitude of the vertical stress. This is of great importance for weak soil, which, after strengthening, can be used for construction;
• mutual blocking of cells practically does not allow the cells to move and limits the uneven subsidence of the geogrid.
Fixation of a pillow of various kinds of a road covering:
Geogrid with filling from rubble provides horizontal stability of a pillow of a road covering (fixing of rubble under a covering from a horizontal sprawl). The use of a geogrid makes it possible to use crushed stone of various types. When designing pavement structures, conditions must be fulfilled with respect to the required load capacity of the soil. Strengthening of the soil occurs by replacing the earth covering. Instead of soil with low load capacity, soil with a higher load capacity is used. As a result, the cost of construction increases. One way to strengthen the soil is to use the geogrid and fill it with earth material. The thickness of this design can be 50% less than the thickness of the standard replacement, which avoids costly substitution of the soil.
Sometimes when building a roadway, it becomes necessary to lay a separation layer from geotextiles. This happens when it is necessary to lay a geo-frame directly on an earthen cloth from fine-grained or cohesive soil. Usually, we recommend using a non-woven geotextile to separate the soil and granular filler (topsoil, a mixture of various granular aggregates, quartz sand, concrete, etc.) can be used as a filler. This separation is necessary to prevent the aggregate from being mixed with the ground in the subgrade, which reduces the thickness of the aggregate and maintains its strength relative to the horizontal shear.
Strengthening slopes and fixing slopes of increased steepness:
The geogrid also performs the function of preserving slopes and slopes, strengthening bulk embankments, strengthening slopes of earth dams, arranging river moorings, piers, river embankments, strengthening coastal lines, strengthening the foundations of bridges, strengthening the surfaces of slopes, embankments, gullies and drainage structures. Filling it with permeable materials, leads to the fact that the stability of the slopes increases to surface erosion, the shear forces directed along the slope in the contact zone with the filler decrease.
The typical structure of the slope reinforcement includes a geogrid, a geotextile separation layer, mounting and bearing anchors, a cell aggregate (vegetative soil, gravel, etc.), additional elements (stops - installed in places of possible erosion of the slope, drainage troughs - for tapping surface water). Separating interlayer of non-woven geotextile is arranged only on the submerged part of the slope. Non-woven geotextile is a kind of armature for the root system of plants. Geotextiles rolls are usually rolled from the edge of the slope to its sole. Backfilling of the upper edge of the geotextile in the excavated trench on the edge prevents the penetration of surface water under the structure of the slope. Between adjacent geotextile sections, it is necessary to ensure overlap and support it by installing in the seam of the pins or staples down the slope. Mounting of geogrids on a slope is carried out with the help of L-shaped anchors, and if necessary - polymer cables.
It should be noted that this method of fixing the slopes provides a reliable and immediate anchoring of the soil on the slope to the formation of a stable turf cover, and also prevents the removal of soil particles by wind and water.
2. Geotextile (dornite)
It is a non-woven material made from endless polypropylene fibers. In the world practice of construction, now steel, nonwoven materials are used, based on synthetic polymer fibers.
Composition: polyester fiber - 100% (at the request of the customer, the composition of raw materials can be changed).
The material is not susceptible to putrefaction, the effects of fungi and mold, rodents and insects, the germination of the roots. Used as a cushion layer for road construction (preventing mixing of pavement layers between each other (soil with gravel, crushed stone and sand), thereby yielding significant savings in sand and gravel), oil and gas pipelines, laying of pond film on the ground, for drainage, strengthening slopes, Operating temperature range: - 60 С + 150 С. The structure of the material provides good strength and filtering properties.
Geotextile canvas (Dornit) - the solution of any construction tasks, is an environmentally friendly nonwoven fabric made from endless polypropylene fibers with a needle-punched method, which ensures its high chemical resistance, resistance to thermal and oxidative aging. The material is not susceptible to putrefaction, the effects of fungi and mold, rodents and insects, the germination of the roots. Operating temperature range: - 60 С + 100 С. The structure of the material provides good strength and filtering properties.
Areas of application:
road construction, construction of tunnels, construction of garbage dumps, hydraulic structures, construction of railways, construction of pipelines, production of hydro-drainage systems, reinforcement of slopes and many others.
In the process of laying the material, there are no special difficulties, this is due to the following features: the rolls of the material are not large, thereby reducing transport and storage costs, as well as labor costs; the material does not absorb water, when used in damp conditions, the weight of the rolls remains unchanged; does not germinate roots, protection from rodents, resistance to natural acids and alkalis, etc. When laying it is necessary to make an overlap (10-12 cm).
Geotextile performs the function of layer separation and allows to redistribute the stress at the base of the embankment, to increase the bearing capacity of the base, the stability of slopes, and to improve the conditions for sealing the roadbed. Also in this application of the material, the reinforcement function is performed in the design of embankments from the soil of high humidity. A layer of geotextile is rolled in the longitudinal direction along the entire width of the roadbed. The webs are joined together by gluing or stitching. The ground is poured onto the geotextile canopy above the peat by 0.5 m. There is no mixing of soil with peat, the peat sediment is uniform. Replacement of sand drains by drains from geotextile allows to reduce the consumption of sand, to increase the rate of construction, to reduce labor intensity of work.
At present, one of the most promising technologies that simplify the construction of roads in difficult conditions and prolong their service life, due to the increase in strength, is the technology of reinforcing asphalt-concrete coatings and weak bases with geosynthetic materials, namely geo-networks.
Reinforcement of asphalt-concrete coverings by geo-grids allows to increase the between-repair periods of operation of motor roads by 2-3 times. In regions where fiberglass geogrids are used actively, road maintenance costs, due to a reduction in the volume of patch repairs, are reduced to 40%.
Advantages of use:
1. The service life of asphalt concrete pavements significantly increases.
2. The formation of cracks is substantially reduced.
3. The rut is reduced in areas with high traffic intensity.
4. The optimum connection of the geogrid with asphalt concrete is ensured.
5. The white color of the product serves as an indicator of the uniformity of the impregnation of the material with the bitumen emulsion.
5. The melting point of the material is 220 ° C.
6. Low material damage during laying.
7. The material is easy to lay and does not require additional fixation with the help of anchor fasteners.
8. The working diagram of the bituminous mixture is identical to the polyester operating diagram.
9. The similarity of the characteristics of the geocomposition material and the bituminous mixture contributes to their structural effects.
1. Reinforcement of road sections without leveling layer. The geogrid is laid on the old layer of asphalt concrete on flat parts of the road, but with increased cracking. The effect of preservation of old cracks is achieved due to the fact that the grid takes on horizontal stresses, and, thereby, prevents penetration of cracks from the old coating into the new one.
2. Strengthening of the existing pavement construction.
Over the road sections with a rut and potholes are laid leveling layer of asphalt concrete. Then, on the leveling layer, the geonet is stacked. The effect of eliminating or significantly reducing the rut and potholes is achieved due to the fact that the grid redistributes vertical local loads over a large surface area.
3. Reinforcement of the asphalt-concrete cover. The geogrid bridges the asphalt-concrete cover.
4. Prevention of cracks when the road is broadened. When the road sections are broadened, longitudinal cracks often appear at the interfaces between the old and new sections. Laying the mesh on these areas helps prevent cracking.
5. Pairing of road clothes of different types. When mating with road clothes made of cement concrete, an equalizing layer is required above the cement-concrete coating.
6. Pitch repair. When performing patching, the damaged sections of the road are milled with overlap along the perimeter of the damage zone by at least 50 cm. Then the mesh and asphalt concrete are laid.
7. Restoration of the road section after repair of underground communications. Cracks and potholes often occur on sections of roads passing over engineering communications. Mesh reinforcement eliminates or significantly slows down the destruction of these road sections.
The leveling is done with a bulldozer, the seal with a smooth-rolled roller with a mass of 10-12 tons without switching on the vibrator, and the layout with an autograder. The number of passes of the roller is set by a test seal, approximately 6-10 on one track. The movement of vehicles directly on geosynthetics is not allowed. The weight of the roller is adjustable depending on the condition of the soil.
Currently, in our country, the problems of finding better and more cost-effective technologies for road construction are still not solved, and, of course, no less important is the repair and restoration of the coverage of all types of motor roads. The point is that the technologies of road construction and repair that are used today simply do not provide the required service life of roads and cause the appearance of cracks and defects in the coating already in the first year of active operation.
If we talk about the situation in the field of road construction abroad, then there is obvious technological progress, which is expressed not only in the development, but also in the active application in practice of modern and effective methods of road construction and repair.
Road construction requires increased measures to prevent deterioration and strengthen the roadway. Climatic, geological difficulties, significant loads can damage the surface very quickly, and the introduction of new reinforcement technologies in road construction is the most reliable way of the industry development.
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