The Experimental Study On Engineering Characteristics Of The Soil With High Saturated Degree After Dynamic Consolidation And The Soil's Constitutive Model

After high-saturated soil of a foundation is processed by dynamic consolidation, most deformation of the soil is eliminated under construction loading; the strength of the soil is the factor controlling the stability of the foundation. However, as most projects are time-limited, tamped soil needs to be examined immediately, which leads to the value of indices lower than normal value. At present, the quality of tamped soil is usually evaluated by techno-clerks in-situ according to their experience. Therefore, the criterion of soil improvement needs to be improved. In fact, tamped soil is compacted unsaturated silt. The traditional theory of saturated soil mechanics cannot satisfy the necessity of improved soil research. The theory of unsaturated soil mechanics provides the theoretical evidence for the research of engineering characteristics of the soil. The study of the characteristics and the constitutive model of the tamped soil is the key to solution of the stability problems concerning evaluation and prediction of bearing capacity.Based on the theory of modern foundation soil science and unsaturated soil mechanics, the author has tried to combine microstructure properties with macro-mechanical behavior of soil consistently. The strength and deformation properties of high-saturated soil have been investigated, and the constitutive model of the tamped soil has been built. These have not been reported in related literatures available, and thus are the innovation of this paper. As for the case of the project of Century Garden phase II in ShiJiazhuang, the following conclusions can be drawn after the analysis of a great deal of lab test data.(1) The soil from Century Garden is an alluvial and diluvia soil in an alkalescent medium. And it should be ascribed to silt according to the view of its mineral composition, particles distribution, physical and mechanical indices. Not only is the content of cla> relatively high, but also the exchange capacity of ion, chiefly high-electronvalent calcareous ion, is great. Due to aggregations filled with pore among inter-particles, the soil has the engineering properties of silty clay.(2) Tamped soil with an attenuated phenomenon has been found for the first time through lab microstructure research and particle distribution test. Observed through SEM, grain edge of Clastic feldspar was broken into pieces because of dynamic consolidation. Compared with samples of the same layer and location before and after tamping, grain diameter of tamped soil was attenuated. This may be due to the phase contact between inter-particles.(3) The mechanism of improved soil deformation has been discussed from the view of the soil microstructure for the first time. Because of the clay and aggregation in the soil, which induces the permeability to be bad, excessive pore water pressure produced in the process of dynamic consolidation does not dissipate quickly; it will lead to the deformation and the failure of the soil. However, for its thin thickness of bound water membrane for the surface of tamped soil particles, its small expulsive force between grains and fast resumption of the strength, tamped soil shows a good thixotropy.(3) The analysis results of granularity distribution and pore distribution indicate that the soil from Century Garden has fractal distribution feature by linear regression. The granularity distribution of the soil before dynamic consolidation has double peaks, the dimension value is greater, and the average value is;2.51. In contrast, the granularity distribution of tamped soil has single peak, the dimension value is smaller, and the average value is 2.39. In the scope of different pore diameter, the pore surface dimension has different distribution rules. The value of pore dimension is smaller in the bigger pore section; however, the value is bigger in the smaller poresection. Therefore, the size of the dimension value may be used to reflect the soil engineering property. Fractal theory is an effective means to study unsaturated soils property.(4)...