| Marine soft soil is common in the pearl river delta, the Yangtze river delta, the beijing-tianjin-hebei coastal area and inland lake which is of high porosity, high natural water content, low permeability and high compression characteristics ect. The most representative is silt and muddy soil. These characteristics make the foundation soil as low intensity,big settlement and difficulty in drainage. And it also impact on the cost of the project progress and security. The formation of these properties closely related to its specific historical situation. It is proved by lots of researches and practices that the soft soil’s engineering properties not only related to material composition, particle size and the depth of the drainage condition of the loading state, but also to micro pore, characteristics of particles,the composition and connection of the particles and the cementation of the particles. This paper introduces the engineering properties of marine soft soil by series of experimentations. And it analyzes soft soil of all aspects of engineering properties from macroscopic and microcosmic.The mainly research work and theoretical results of this paper are as follows:(1)Summarize and analyze the macro and micro aspects about the soil research situation of domestic and international. And it also introduces the methods of macro and micro observation and data processing analysis.(2)Research on material composition. It is found that the marine soft soil in Zhuhai region is primarily comprised by clay and silt. And it has high content of clay mineral. The clay mineral of Zhuhai soft soil is primarily comprised by kaolinite,followed by illite and the montmorillonite has the least content. Because of the high content of clay mineral, the soil is presented as small particle size, large specific surface and poor engineering stability.(3)The compression and rebound test on soil and research on secondary consolidation properties. The unloading-rebound curve of the soft soil can be roughly divided into two stages, initial rebound stage and snapback stage. When the consolidation pressure is greater than the overlaying soil pressure, the soil is in the first stage, the curves’shape is cliffy which means the void ratio is growing fast. The proportion of secondary consolidation is larger, so it can’t ignore the impact of the secondary consolidation in the calculation of consolidation settlement. In the same pressure condition of different depths, the primary and secondary consolidation characteristics has no significant correlation to the depth change.(4)Research on micro pore characteristic of soil. Along with the increase of consolidation pressure, the pore diameter of the sampler change from400nm-2500nm into30nm-400nm. It means that the larger pore is changed into smaller pore in the process of consolidation. Along with the increase of consolidation pressure, the void ratio and average pore size decrease sharply in100kPa<p<200kPa interval. When the consolidation pressure p>200kPa,the void ratio and average pore size still decrease. The curve has slowed down.(5)Research on the development of micro structure in the process of consolidation. Most of the big pores are crushed into small pores in the process of consolidation,and the small particles fill in the big pore that make the soil more compacted and the particle with no obvious directionality. The particle element combination changed from side-surface and side-side into surface-surface. Particles converge into groups and closely contacted with each other. Showing that in the same time of increasing load,the water in the pore is decreasing,the membrane of bound water become thinner, and then the particles converge into groups. |
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