Research On Compaction Characteristics Of Fine-grained Soil And Compaction Control Technology In Wet Area

In the hot and rainy area of southern China, there is a wide distribution of fine-grained soil, such as sandy silt, ordinary silt, clay, high liquid limit of red clay and so on. And it will be difficult to compact these fine-grained soils in the highway construction period due to their high natural moisture contents. If the soil is turned over for basking to decrease its water content to meet the requirements of standard, then it is difficult to guarantee the construction period as well as the long-term stability of the subgrade. Besides, the strength of bearing ratio of some filler can hardly meet the requirements of modern standard due to high content of fine-grained soil. Based on one of the projects of the technological progress and innovation plan of Hunan Provincial Communications Department, that is "study on the compaction construction technology of fine-grained soil subgrade of highway", theoretical analysis and indoor and outdoor tests are conducted in this paper to present a thorough investigation of the engineering properties and the control technology of subgrade filling of fine-grained soil of the highway in moist area. And a series of technical difficulties about the subgrade filling have been solved. Specific work done in this paper is as follows:(1) Compaction characteristics of fine-grained soil and the complete compaction curve. Compared with the traditional compaction test, the compaction test conducted in this paper has a wider range of water contents, which aims to understand the important border characteristics of compaction curve which are ignored by previous researchers. The dry density versus water content in the compaction curve is transformed into saturation versus water content. And by defining four new parameters Sm,wm,p and n, a function of the complete compaction curve is developed and method of defining of the four parameters proposed. In addition, influences of the four parameters on the shape of compaction curve are analyzed as well as the correlation between these parameters and soil physical properties and the magnitude of compaction work. In the end, the developed function is verified through the results of a compaction test of a typical fine-grained soil.(2) Fine-grained soil classification and the engineering properties. Comparative analysis of the fine-grained soil classification standards in different countries at home and abroad is conducted. Specifically, the United States Edward EPC classification system is analyzed in detail, and the engineering suitability of typical fine-grained soil filler in Hunan province is evaluated by using the EPC system. Besides, the characteristics of strength and deformation of soil samples with the same range of water contents as in the complete compaction curve are studied and the relationship between the initial compaction state of filling soil and their engineering properties is also investigated. Based on the relationship between CBR and water contents under different compaction work, the intensity and deformation properties of fine-grained soil samples subjected to soaking in water are investigated through a series of tests.(3) Simplified analysis of the compaction mechanism of bumping vibration roller. Under the rolling of bumping vibration roller, large deformation will be initiated in clay. On the base of the non-linear strength criterion, the static and dynamic analysis models simulating the process of bumping vibration roller compacting the fine-grained clay are built by adopting large deformation, double scalar damage constitutive model and the plastic theory; the distribution law of stress and velocity in elastic area of the clay under static and dynamic pressure consolidation of the roller is obtained. Also obtained is the distribution solution of the stress and velocity in elastic zone, damage zone and plastic zone under the dynamic pressure consolidation of the roller. In addition, the calculated effective influence depth induced by the roller is in good agreement with that in practical engineering.(4) Field compaction tests of fine-grained soil and the technology of filling control in moist region. First of all, factors that affect the subgrade compaction are summed up; Secondly, large-scale field compaction tests were carried out on the high water content sandy silt and high liquid limit soil (red clay) of Hunan. Specifically, by setting different matsuura thickness, water contents at filling stage, rolling times and using different compaction machinery, fruitful test results are obtained. Finally, field compaction properties and construction technology of these two types of soils are summarized and the filling control standards put forward. the deficiency of compaction index and control standard are analyzed and the performance of these filling materials is evaluated and the assumption that take the porosity as the compaction control index of fine-grained soil in moist area is proposed. According to the requirements of specification in China, suggestions for compaction control standards in different filling parts of highway embankment are presented in this paper.