Fractal Study on Consolidation of Soft Soil Foundation under Vacuum Preloading

The research on nonlinear system of soft soil provides new ideas. Aiming at the problems existing in the consolidation of soft soil foundations under vacuum preloading and some fractal phenomena in soil research, the prospects of the research were discussed using the fractal theory. The vacuum preloading was demonstrated from both macro and micro perspectives. It is feasible that the fractal consolidation of soft soil foundation is effected.

China's soft soils are widely distributed. The characteristics of soft soils such as high water content, high compressibility, and low strength are difficult to meet the needs of engineering construction under natural conditions. However, with the development of the national economy, many engineering projects have to be carried out on soft soils. Therefore, the treatment of soft soils is particularly important. In the soft ground treatment method, the vacuum preloading method is a very effective new method that has just been developed in recent years. However, the theory of consolidation deformation of soft soil under vacuum preloading has not been perfected so far, and the calculation of consolidation deformation of soft soil foundation is very different from the actual engineering. This is due to the characteristics of soil itself. It is determined that, for example, the mechanical properties of soils are far from being elastic or plastic, but they are very complex and non-linear feature systems, which makes it difficult to express them using traditional methods based on linear analysis.

Fractal theory was proposed by French-American scientist Mandelbrot RB (Mandelbrot RB) 13 in the 1960s and 1970s. Its generation deepened people's understanding of the irregular geometry of nature and enabled people to use the internals of things. Self-similarity provides insights into the fine structure hidden in the chaos. It provides people with a partial understanding of the whole and provides a completely new way of thinking and describing tools from a limited understanding of infinity. Fractal theory has been widely used in many disciplines including geotechnical engineering. In this paper, we summarize a large number of related researches on the fractal theory in soft soil consolidation and microstructure, and consider that it is feasible to use fractal theory to study the consolidation of soft soil foundation under vacuum preloading.

1 Structure Fractals of Soils Many researches on the microstructure of soils show that the microstructure parameters used to describe soils are characterized by complexity, irregularity, and disorder from the surface morphology. For example, soil particles and pores are geometric bodies with no characteristic length and self-similarity. These characteristics of the microstructure system are precisely suitable for the study by fractal theory.

1.1 Pores in soil pores are one of the important properties of soil. No matter whether the soil deformation, soil slope stability, or bearing capacity of foundations are directly or indirectly represented by the pores of the soil.

The mercury porosimetry method was used to determine the porosity of loess. Using the concept of fractal-free geometric theory, combined with the actual distribution of soil pores, the boundaries of the pore separation of cohesive soils were determined and clearly discussed in the scale-free interval. The characteristics of the pores provide a theoretical basis for solving the current disorder of the pore size distribution in the pore study. 1.2 Particles of soft soils in soil The particle morphology generally includes particle size, particle shape, port 1 cat work, etc. The base S1蹦r is the distribution of soil particles measured by the densitometer method. From (a), it can be seen that the distribution of soil particles measured after addition of dispersant is basically the same, and the distribution is linear, indicating that the fractal distribution of the debris formed by rock fragmentation is the same. (b) The fractal dimension measured with no dispersant is somewhat different, indicating that as time passes, interactions between soil particles and interactions with bound water cause the original soil particles to change and change. The composition of the original soil particles, the corresponding distribution of soil particles are also different. As can be seen from (b), the distribution of soil particles measured with no dispersant has multifractal characteristics 1111. It is the relationship between particle size fractal dimension and time in soil consolidation process, and its fractal dimension tends to be constant with time. The value, which is determined by the consolidation properties of the soil itself.

Partial body deviation, the maximum top deviation from the design value of 2m so quickly eliminate the impact of excessive static pore water pressure on the body become the focus of the project, to take measures for the cloth plastic drainage board, set the depth of 20m, spacing L0m In the square layout, some of the more serious sites accelerate the dissipation of excess pore water pressure by vacuuming, and further consolidate the soil. The following is an information fractal curve of some measured data in soft soil consolidation process. It is the relationship between fractal dimension and time of soil particle distribution. Li Xiangquan 1131 proposes that the consolidation process is a kind of aggregation-crushing and re-aggregation-re-crushing from the perspective of microstructure. the process of. At the later stage, it shows the adjustment behavior of the particles under the effect of constant effective stress.

2 Fractal information of soils in the field - Analysis of engineering examples The following describes the fractal curves of field measured data through an engineering example. The site is the main building of a power plant due to improper handling and 21 pore water pressure is the fractal curve of the dissipated rate distribution of the excess pore water pressure after the water body is driven into the drainage body. The statistical data in the figure is measured by the pore water pressure for 4 months. Based on the value, the x-axis represents the rate of dissipation, and the y-axis represents the number of days less than this dissipation rate. The curve is obtained through a certain transformation using the principle of data statistics. It can be seen at least that the dissipated velocity of the pore water pressure has obvious fractal characteristics in the scale interval in the figure, in which the P3 and P4 measuring points are under vacuum preloading. Under the fractal curve, apparently the slope, that is, the fractal dimension, is larger than P1 and P2, which means that the dissipation rate is increasing more than normal, which is exactly the same as the actual situation. Vacuum preloading acts on soil consolidation. It is consistent with shorter time.

This is the fractal curve of deep horizontal displacement of the soil under the condition of the excess pore water pressure dissipated in the main powerhouse of the power plant. The figure shows the locations of -0.5m, -2.5m, and -4.5m below the ground. The statistical data is based on a 2-month deep horizontal displacement measurement, with the x-axis representing the amount of displacement and the j-axis representing the number of days less than this amount. It can be seen from the figure that the deep horizontal displacement distribution also has obvious fractal characteristics in the scale interval of the figure, in which the slope at 2.5m below the ground is larger than that at 0.5m and 4.5m, which indicates that the slope is 2.5m. The displacement at the point is a sudden change, both decreasing upward and downward.

At present, many scholars have used fractal theory for on-site monitoring, point 114~171, and have applied the concept of fractal to some of the data actually measured in the field to process it. Although this is an exploration, the result is very promising for researchers. Encourage and believe that if we take a deep layer of mathematical probability statistical analysis on more measured data, then we can use fractal theory to show its changing graph and determine the layered fractal dimension, so we will get more regular information and various parameters. The intrinsic link between changes provides the basis for predicting the further development of soil consolidation and deformation.

3 Methodological implications of fractal theory on consolidation of soils under vacuum preloading The establishment of fractal theory has drawn attention to the study of irregular geometries that cannot be represented or described by the usual measures of length, area, and volume. Nature enables people to describe nature in a more natural language. Fractal theory is mainly used to study the self-similarity of complex systems. With it, we can reproduce the original research objects with a small amount of information. It not only has the characteristics of less specified information and easy calculation, but also it has a similarity to the whole and part of the system. Research, trying to find a new order between orderly, disorderly, macroscopic, microscopic, and overall, so as to deepen the understanding of such relations in the system and the unified understanding of the diversity of the material world 1181. The establishment of fractal theory, It not only improves the soil consolidation theory under vacuum preloading, but also has important methodological significance for deepening scientific research.

From a theoretical perspective, fractal theory takes advantage of the self-similar nature of things to provide insights into the fine structure hidden in chaos. It provides a new way for people to learn from things, from the limited cognitive cognition to local cognition. From the point of view of the problem-solving approach, the fractal theory establishes the nature of the whole by proceeding from the part, and examines the correlation between the part and the whole from the microscopic to the macroscopic perspective. The systematic theory emphasizes the nature of the partial dependence on the whole, reflecting the From the overall point of view to understand some of the ideas 13181, and the fractal theory emphasizes the overall dependence on the part of the nature, reflects the method of understanding the whole starting from the part, to provide a microscopic to macroscopic study for the consolidation of vacuum preloaded soil consolidation. Ideas.

4 Conclusion Fractal theory to study the consolidation of soil under vacuum preloading is still at an exploratory stage. The above data show that many of the microstructure parameters of soil have fractal features, and the measured displacement of soil deformation is also very Good fractal characteristics, and this feature provides a basis for predicting further deformations. Many field monitoring data of soft soils under vacuum preloading indicate that pore water pressure in soil, stratified settlement, deep horizontal displacement, surface Solid slopes such as settlement and surface horizontal displacement are expected to have strong soil and water strength. The bHsh test has a discrete nature with git, but the change trend is basically stable. According to the self-similarity of objects in nature, the soil is an open, disordered, and complex system. All the external forms obtained by reflecting the changes in their characteristics with different methods have a degree of similarity.

Fractal theory is currently used to study the consolidation deformation of soft soil during vacuum preloading. It is believed that this will not only link the microscopic and macroscopic consolidation of soft soil organically, but also lay the foundation for the establishment of the structural model 111131 of soft soil, and it also has a certain degree of theoretical complement to study the consolidation of soft soil under vacuum preloading. significance.

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