Gubashova V. Substantiation of rational technological parameters of jet grouting in difficult geotechnical conditions

The dissertation is devoted to substantiation of rational technological parameters of jet grouting in difficult geotechnical conditions. Analysis of previous studies of jet grouting technology has shown that despite the fact that the technology began its development in the 70s of last century, there are still many issues to be explored: the relationship of technological parameters with the characteristics of the soil-cement array, the impact of technological processes on the soil environment, etc. In the course of work the current state of the normative base concerning designing and execution of soil-cement elements on jet technology is analyzed. It is noted that today on the territory of Ukraine there are almost no regulations that determine the procedure for calculation, design and implementation of jet-grouted elements. Based on the experimental data the relationship between the technological parameters of jet grouting and the diameter of the soil-cement column in different types of soils is investigated and established. The experimental data are divided according to the type of soils - incoherent and cohesive: sand and gravel, sandy loam and loam. The dependences of the lifting speed on the diameter of the soil-cement column were obtained, which not only generalize the relationship between the geometric characteristics of the soil-cement column and the technological parameter, but also facilitate the approach to choosing the operating parameters of the drilling tool. The next obtained dependence is the exponential dependence of the jet energy on the obtained column diameter, on the basis of which a method of determining the column diameter depending on soil type, jet pressure, lifting speed of the hydromonitor and cement solution consumption was developed. Comparative calculations were performed on the basis of completed construction projects, which, in turn, made it possible to introduce correction factors for soil conditions in Ukraine. The change of physical and mechanical properties of the soil surrounding the jet-grouted element and the presence of a zone of improved soil have been experimentally proved. Experimental data allowed us to investigate the change in the stress-strain state of the soil mass with reinforcement elements made by jet technology with the inclusion of improved soil zones in the calculation. Based on experimental data of soil-cement elements in different engineering and geological conditions on the territory of Ukraine, a comparative analysis of the results of compressive strength of soil-cement material and a graph with ranges of strength values for different soil conditions. The obtained values of strength can be used in the design of structures using soil-cement elements. It is proved experimentally and by modeling that in different soil conditions the soil zone with improved physical and mechanical characteristics varies from 10 to 30 cm. The calculated model of strengthening the soil base of the existing building shows the improving effect of the introduction of the zone of improved soil, which allowed to reduce the design number of soil-cement columns by 15%. Accordingly, the materials for the execution of jet-grouted elements will be reduced by 15%. For complex engineering-geological conditions (semi-rocky soils) a method of soil foundation reinforcement with complex-component systems consisting of elements of two geotechnologies - anchor elements of Ischebeck Titan type and soil-cement columns made by jet technology has been developed. Numerical modeling was performed with the help of Plaxis 3D Foundation high-rise building made of monolithic reinforced concrete, based on a layer of semi-rocky soil - limestone. The paper shows the joint work of reinforcement elements made by two different technologies, where the work of reinforcement elements includes a layer of limestone located in the base. The combination of the two technologies made it possible to create a complex-component element of amplification. When performing calculations, not only the loads from the structure were applied to the building model, but also the loads simulating shifting forces under seismic influences, which allowed to fully assess the positive aspects of combining the two technologies. On the example of the completed project to strengthen the soil base of a particular object, a comparative analysis of standard cost items in accordance with the estimate for construction work using the developed method of taking into account the area of improved soil when performing soil-cement columns by jet technology. On the basis of the analysis the economic efficiency from application of a technique is proved.