Досвід та перспективи використання інноваційних технологій по стабілізації грунтів

Asmatulaev B. A. Doctor of Technical Sciences, Professor, Tursumuratov M. T., Candidate of Technical Sciences, Asmatulaev R. B., Candidate of Technical Sciences, KazNIiPI Dortrans Institute 

Zherebitsky M. I., Hobe Associates LLC, (USA) 

Currently, heavy-duty vehicles with single-axle tires, which create an axle load of 13 tons or more, are moving on the republic's roads, while the total mass of vehicles reaches up to 40-80 tons and above.The appearance of similar transport loads in Western Europe in the 1990s led to a radical revision of the materials of road structures, including asphalt-concrete road surfaces, due to the appearance of premature deformations and ruts on them [1]. 

The main reasons that lead to premature track formation on coatings are residual deformations that arise from the impact of dynamic transport and temperature and climatic loads on the road, which accumulate over the years in the layers of road structures. In addition, the low quality of bitumen supplied for the production of asphalt concrete should be added, which also leads to premature deformation and cracking. In addition, in Kazakhstan, in summer, asphalt concrete coatings are heated to 65-75 ° C [2], which is not taken into account by the current interstate standard for asphalt concrete (GOST 9128), asphalt concrete at such temperatures completely loses its load-bearing capacity. The latter also contributes to the premature formation of ruts on highways, with the appearance of cracks and other deformations in the future. At the same time, the track extends not only to the thickness of the coating, but also captures layers of crushed stone and sand materials of the base and upper part of the ground of the roadbed. It should be noted that according to the test results of Professor Smirnov A.V. (SIBADI), it is established that in the absence of monolithic layers in road structures, asphalt concrete coatings are deformed and transfer at least 90% of the total transport load to the ground of the working layer of the roadbed. This indicates that in road structures with asphalt-concrete surfaces, in order to prevent the occurrence and accumulation of residual deformations in the ground, it is necessary to strengthen the soils of the working layer of the roadbed. In the southern hot regions of Kazakhstan, asphalt-concrete coatings lose their elastic-plastic properties when heated above 50oC. Then the entire load is transferred to the weakest structural layer-the ground of the roadbed. If the ground is waterlogged or the permissible transport load is exceeded, first of all, residual deformations will accumulate on the ground, which is unacceptable on highways with heavy and heavy traffic. 

Long-term monitoring of the technical condition of Kazakhstan's highways, carried out by our institute, has shown that the main cause of deformations on roads is the decompression of the soil of the working layer of the roadbed and the non-reinforced lower layers of road structures. A similar conclusion was made in the 90s by Professor N. V. Gorelyshev, after a survey of Kazakhstan's roads by specialists of the Soyuzdornii Institute, carried out on the instructions of the Minister of Roads L. B. Goncharov. Therefore, the current "Instructions for designing non-rigid road coverings" in Kazakhstan recommend the mandatory presence of monolithic layers of temperature-resistant materials in road structures: concrete or stone materials and soils treated with inorganic binders and stabilizers. A clear example of the long-term operation of such structures is the Alma-Ata-Kapchagai highway, which was built in the 70s with a cement-concrete surface, and then in the 90s was covered with an asphalt concrete surface, which has been in operation for more than 40 years. There is an experience of long-term operation of roads built in 1976-87, with bases made of reinforced stone materials with slag, slurry and ash binders [3]. In this regard, the most promising road structures that allow modern heavy-duty vehicles to pass through without compromising the road structure are cement-concrete coatings or asphalt-concrete coatings of the SHMA type on solid monolithic bases. However, it should not be forgotten that not only asphalt-concrete pavements, but also cement-concrete pavements require the installation of stronger bases. It is well known that the inevitable annual heaving of the entire road structure, which occurs during the winter period of operation of highways, allows the asphalt concrete surface to rise up to 30 mm, then the cement concrete surface should not exceed 10 mm. Hence, the requirements for the grounds must be appropriate. Currently, the first six-lane Kazakhstan highway "Astana-Shchuchinsk" with a length of 215 km is successfully operating, of which 96 km are made with cement-concrete coating. On the construction site of the company "K-Dorstroy", for the first time in Kazakhstan, ash-mineral material with a stabilizing additive "Dorzin" was used as the base material (photos 1 and 2). The stabilizing additive "Dorzin" is widely used in road construction abroad and in Kazakhstan [4]. The effectiveness of using the soil stabilizer "Dorzin" in combination with ash – mineral material is felt on the perfect evenness of the cement-concrete pavement of the Astana-Shchuchinsk railway station. 

The Western Europe - Western China highway, which is under construction and has a length of more than 2,700 km, is also planned to be paved with cement. In some sections of this international corridor, the ground of the working layer of the roadbed is treated with small doses of cement with the addition of the stabilizer "Dorzin" (photos 3 and 4) . The domestic company "K-Dorstroy" continues to use the stabilizer "Dorzin" on the construction of 58 km of the highway "Western Europe-Western China" on the section "border of Southern Kazakhstan-Taraz", road category-1b and confirms the effectiveness of its use in combination with the addition of 2% cement. The strength characteristics of such reinforced soils are similar when using reinforced soils with 5 % cement, but without the addition of the stabilizer "Dorzin" (Table. 1 and fig. 1) 

Physical and mechanical characteristics of samples from reinforced soils at the design age of 90 days 

Table 1 

Fig. 1. Strength characteristics of water-saturated samples of reinforced clay soil with a design age of 90 days. 

According to the degree of water permeability according to the conditions of GOST 25100-95, samples from the initial and reinforced (at the design age of 90 days) clay soil - light sandy loam, are divided as follows: compositions -1, 2 and 3 are classified as waterproof, composition -4 is poorly permeable, the initial soil without strengthening is permeable. This indicates the mandatory need to strengthen the soil of the working layer of the roadbed and the effectiveness of the stabilizer "Dorzin". The mechanism of interaction between the stabilizer and the ground is explained as follows [4]. As a result of dissolving the stabilizer in water, the latter is activated by ionization (H+, OH, H3O). The stabilizer solution actively affects the condition, first of all, of clay and colloidal soil particles. It changes the charge of clay-colloidal particles due to the exchange of electric charges between ionized water and soil particles, which is confirmed by studies of the pH of the stabilizer solution medium and the pH of the water extract of the soil. By exchanging charges with ionized water, natural connections with capillary and film water are disrupted between ground particles. It is easily separated from soil particles, thereby creating favorable conditions for high compaction of the soil during compression. In addition to the exchange between the electric charges of the aqueous stabilizer solution and ground particles, an ion exchange process occurs between the stabilizer components and the absorbing complex of the clay - colloidal fraction. This leads to an increase in the density and load-bearing properties of the soil, while saving moisture by 15-25% and reducing cement consumption by 50-60%, which is very important in arid regions of the construction of the Western Europe - Western China highway (Fig. 

Figure 2. Map of the highway "Western Europe - Western China", indicating that the main route lies in the arid regions of Kazakhstan 

Photo 1 Checking the compaction of the ash-mineral layer with a dynamic density meter at the Astana-Shchuchinsk railway station, employees of the K-Dorstroy and KazNIiPI Dortrans laboratories at the acceptance of works . 

Photo 2. Ready-made ash-mineral base on the Astana-Shchuchinsk highway km 7-57, contractor "K-Dorstroy" 

Reconstruction of the section km 536-593 of the Almaty –Kordai - Blagoveshchenka - Merke - Tashkent – Termez railway station under category 1 was also carried out by K-Dorstroy (photo-3, 4, 5, 6), taking into account its positive experience, foreign companies began to use the Dorzin stabilizer in combination with small doses of cement. On the sections of km 1398-1578 of the highway "Border of the Russian Federation ( to Samara) -Shymkent", Kyzylorda Region, the Italian company JSC " Salini Kostruttori S. P. A. "(photos 7, 8, 9), reinforced the working layer of the roadbed with the use of the enzyme preparation "Dorzin" in combination with 3% cement. When using this technology of soil strengthening, mandatory strict operational quality control is carried out, both by the stabilizer manufacturer and the technology developer of the KazNIiPI Dortrans Institute. Positive reviews from domestic contractors and foreign companies, as well as engineering services, indicate the effectiveness of such joint work, so high quality is guaranteed. 

Photo 3. Loading of cement into the "cement distributor", which is used as a crushed stone distributor 

Photo 4. Introduction of an aqueous solution of Dorzin in the soil mixture 

Photo 5.Mixing of the soil-cement mixture after applying an aqueous solution of Dorzin with a soil mixer 

Photo 6. Compaction of reinforced ground with air rollers on the section km 536-593 of the Almaty –Kordai-Blagoveshchenka - Merke-Tashkent –Termez railway station, contractor K-Dorstroy company 

Photo 7. Distribution of cement by a cement distributor over the prepared and profiled surface of the roadbed. 

Photo 8. Milling with a recycler, mixing soil with cement with simultaneous delivery of an aqueous solution with Dorzin 

Photo 9. Finished section of road with stabilized ground of the roadbed "Border of the Russian Federation (to Samara) - Shymkent", Kyzylorda Region, contractor Italian company JSC "Salini Kostruttori S. P. A." 

The highway "Western Europe - Western China" runs through arid regions of Kazakhstan, with a high temperature of heating of surfaces, especially asphalt concrete (Fig. 1). The main technical problem of asphalt-concrete road surfaces is the progressive loss of their load-bearing capacity during the movement of heavy-duty vehicles, especially at high operating temperatures, with the formation of ruts and temperature cracks. To eliminate the causes of rutting, taking into account the world experience [4,5,6], in the lower layers of the SHMA coating, it is necessary to arrange not porous layers of asphalt concrete, but dense ones with a frame structure. Some designers believe that if they have provided for a third layer of bitumen-mineral material, then the remaining layers may be made of non-cohesive stone materials. This is a fundamentally wrong decision. As the crushed-sand and crushed-stone bases which are still used without strengthening by binders cannot perform functions of the bearing layer at temperatures of heating of an asphalt concrete covering over 50°C. Such layers are well resistant to compressive loads, but do not have tensile strength, and even more so when bending. Examples of practical engineering failures are evident in some sections of the newly built Almaty - Astana and Almaty – Bishkek highways that have premature defects. Such design errors are also present in the new projects of the highways "Border of the Russian Federation (to Omsk) - Maykapshagai (exit to China) through Pavlodar, Semey "km792-828 and" Omsk-Pavlodar_maykapshagai " km 324-408, in which three layers of asphalt concrete are designed, including porous and highly porous mixtures in coatings. Our attempts to change and include a monolithic layer using bauxite sludge in the structure, or to replace porous asphalt-concrete mixes with frame ones, were not accepted. Although there is many years of practical experience in operating such a structure with a bauxite sludge base, the smoothness and strength of the structures ensures the passage of intensive heavy-duty transport. One of the disadvantages is the appearance of reflected temperature cracks, which can be eliminated by technological or constructive methods. 

Main conclusions and suggestions: 

Analysis of global trends that have emerged in the last decade in transport-developed countries: the United States, Western Europe, as well as in Russia, China and Kazakhstan shows a significant increase in traffic loads on highways. Traditional construction of low-cost roads with a 20-year perspective is becoming inefficient, and such roads are prematurely subjected to rutting and other deformations. The construction of cement-concrete pavements, as well as crushed-mastic asphalt-concrete pavements on monolithic bases, is increasing to allow modern traffic to pass through the roads of foreign countries. We believe that in order to increase the profitability of construction costs and their payback, it is necessary to design roads for a longer term of their operation up to 40-50 years. For this purpose, it is necessary not only to build expensive cement-concrete coatings, but also to widely use monolithic conglomerates made of local materials, secondary raw materials and soils, obtained on the basis of the use of new innovative resource-saving technologies and materials. Make greater use of resource-saving and energy-saving cold chemical technologies, which make it possible to utilize various cheap multi-million-dollar dumps of man-made waste from the energy, chemical, metallurgical and non-ferrous industries for road construction instead of traditional expensive technologies.

All the above-mentioned effective developments and directions, along with their readiness for use in road construction, require further detailed scientific research and pilot tests in order to clarify and expand the scope of their use. This requires the resumption of R & D funding. For example, the lack of an interstate regulatory and technical document for road concretes based on non-traditional cements hinders their widespread use in road construction. 

When using the proposed resource-saving technologies and materials, in almost all regions of the country, it is possible to abandon the use of traditional cost-effective technologies, while simultaneously solving the following state tasks:: 

The possibility of reducing the loan for investment financing from foreign Banks for the construction of new highways, through the use of resource-saving and energy-saving innovative technologies and materials developed by domestic scientists and tested in Kazakhstan.
Re-dispose of the construction materials of existing roads. Millions of tons of " old " asphalt and crushed stone remain in the lower layers of road and airfield surfaces around the country as useless ballast every year, and then are covered with new layers. It is established that when they are reused, it is possible to fully restore and improve their construction properties, due to their strengthening with mineral binders based on man-made industrial waste in Kazakhstan.
To cover the required huge deficit in road construction materials, it is possible to use man-made waste and industrial by-products, which will cover the need for new road construction materials and will contribute to environmental protection in many regions of the country. The volume of accumulated various slags and slurries in the republic exceeds 1 billion tons, and the fly ash of hydraulic removal is up to 2 billion tons. The volume of this waste continues to increase every year.

References: 

1. Development and justification of new technologies for road construction and repair works, including the stabilization of soils, materials and new road structures, including the use of man-made waste from the road construction industry. Scientific and technical report vol. I. Ministry of Transport of the Republic of Kazakhstan, KAD and SIC, Almaty, 2003, p. 210. 
   
   Teltaev B. B. et al. Zoning of the territory of Kazakhstan based on the estimated summer temperature of asphalt-concrete road surfaces //Strength of materials and structures in transport/ Volume III, Almaty: KAZATK Publ., 1996, pp. 134-139. 
   
   
2. Asmatulaev B. A. Construction of road coverings with repeated use of materials of reconstructed roads. Evero, Almaty, 1999, P. 210.
3. Asmatulaev B. A., Tursumuratov M. T., Asmatulaev R. B. et al. Recommendations for the use of "Dorzin" in the construction and repair of highways. //PR RK 218-67-2008, MTK RK KAD, Astana, 2008, p. 21
4. Iliopolov S. N. Koleya: Novye aspekty, problemy [Track gauge: New aspects, problems]. // Zh
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5. Miroshnichenko S. I. Strategic material.Highways. No. 04 (953), Moscow, 2011, pp. 47-52. 
   
6. Finnish standards for asphalt. / / PANK, Helsinki, 1995. p. 70