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A Study of Impact Factors and Stability on the Sediment Aggregates in Yellow River Delta

Author: WangJunPeng
Tutor: ChenYouZuo
School: Ocean University of China
Course: Environmental Engineering
Keywords: the Yellow River Estuary sediment Micro-aggregate Stability
CLC: P343.5
Type: Master's thesis
Year: 2010
Downloads: 89
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Abstract

The stability of soil is actually a comprehensive expression of soil structural units’characters, which mainly depend on the characters of soil particles aggregate, even on single-particle minerals. The research on soil microstructure can help us study the basic structural unit of soil, and understand the stability of soil essentially. Through a series of lab experiments and tests, this paper analyzes the basic compositions of sediment aggregates in yellow river estuary, and studies the pHysical stability and water stability of aggregates. The effect of some factors,such as organic and inorganic substances and clay particle, on aggregate composition and stability is analyzed in this paper. To a certain extent, the conclusions can explain the formation mechanism of aggregates, and offers a kind of reference to the research of stability of sediments. The research has a certain degree of theoretical and practical value to the coastal protection, and also supplies some references to study the sediment characteristics.1、The research on the stability of the sediment aggregates in Yellow River delta shows that sediment particles are mostly less than 0.75mm, in which the most part is between 0.05mm and 0.01mm; Because of the salty seawater, the intertidal sediments of the Yellow River Delta contain a large number of soluble salt ions, of which the main cations are Ca2+, Mg2+, Na+, anions are Cl-, SO42-, HCO3-. And therefore the Soluble salt in the intertidal sediments of the Yellow River Delta is ten times more than that in loess of Malan, north of Shaanxi Prevence. But the number of binding material in both regions is at the same level. The average content of organic matter in the sediments of the Yellow River Delta is about 0.4%, which has no significant effect on sediments aggregates. The microstructure observation shows that, in natural state, soil particles are not single but aggregate together. Therefore the soil seems have less Clay and colloidal particles, have more silt. That also induce the silt character enhanced. 2、Except for sodium humate, clay, inorganic ions (Ca2+, Na+), there are mang factors which can affect the aggregation of sediments, such as glucose, calcium carbonate, ferric and aluminum oxides. Moreover the inertial cross-coupling effects of two factors has greater aggregation effect than one alone. The researches show that glucose, belongs to monosaccharide, has simpler structure. It does not have much stronger effect on sediments aggregation; Because of large specific surface, colloidal and clay particles can bond with each other, which has stronger effect on sediments aggregation; The connection between the particles is enhanced because of calcium carbonate, which belongs to non-soluble secondary mineral. Therefore the sediments aggregation is also enhaced. Trivalent aluminum has stronger effect on sediments aggregation than divalent magnesium; The inertial cross-coupling effects of clay and calcium carbonate or glucose has much greater effect on sediments aggregation than one alone.3、By speaking of sediment aggregates water stability, disintegration experiments shows that sodium humate has stronger effect on sediments aggregates water stability than glucose, because there are many functional groups in the structure of sodium humate, which can take negatively charged species. These functional groups can cemente Ca2+、Mg2+ of sediments. While the structure of glucose is much simpler, it has limited effect on aggregate water stability. Ferric oxides has the same effect as sodium humate, but less obvious. The "bridges" between ferric oxides and clay particles can enhance sediments aggregates water stablity.4、By speaking of sediment aggregates mechanical stability, it would effect sediment aggregates mechanical stability more or less by adding glucose, clay or ferric oxide. When adding glucose into sediments, the maximum axial stress would first increase then reduce. It do not help a lot to aggregates mechanical stability. While adding clay or ferric oxides to sediments, the maximum axial stress increases with the increase of clay or ferric oxides. The plasticity of sediments also improves.5、Through the researches above we find that the formation of sediment aggregates in Yellow River delta accord with aggregates mode by Edwards and Bremner based on organic-inorganic complex. The essence of aggregates formation is clay particles adsorb polar organic molecules through Multivalent cations. Different factors have the same effect to aggregates formation and stability. Take example for glucose, it dose not have great effect on both mechanical and water stability of sediment aggregates, which have a positive relationship with ferric oxides quantity.

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