| With the rapid development of China's national economy, Quaternary red clay, which is widely distributed in the southern region, has been used extensively as construction materials and foundation engineering to use. Due to the physical nature of poor expansion and contraction, the red clay often lead to many engineering hazards, such as roads cracking, uneven ground settlement, slope instability and deformation of foundation pit destruction. During the long-term work on soil stabilization, we gradually recognize that there is a remarkable lack of curing with the use of cement, lime, fly ash and other traditional materials, which can not meet the construction and social development needs.In order to improve the red clay's undesirable physical properties, improve its strength and reduce deformation, use a new type of electrochemical reinforcement imported from Australia—Ionic Soil Stabilizer (English name of the Ionic Soil Stabilizer, referred as ISS, domestic commonly known as "solid roadbed"), to make reinforcement on the red clay in Wuhan. ISS is a surface active agent type soil stabilizer, which was firstly developed into success by Professor Reynolds of chemistry of the United States. ISS contains active ingredient suffocated oil—dark brown liquid under room temperature and soluble in water. Mainly through the physical chemical principles, it makes a series of physical and chemical reactions, improving the soil physical strength and enhancing water stability of the school role. With the advantage of low cost, easy construction, durable, protective to the ecological environment and a wide range of applicability, ISS has important practical significance for our country to establish an environmentally friendly, conservation-minded society and promote the building of the rural economy.Since ISS was introduced into China quite late, due to the lack of theoretical research support, ISS engineering in China is mostly applied in small-scale projects; large-scale project dare not use this new technology. For this issue, this paper combines the National Natural Science Fund (No.40972185) "Ionic Soil Stabilizer's Effects on Red Clay Bound Water" and the National Natural Science Foundation (No.40672188) "Ionic Soil Stabilizer Reinforced Landslide Zone Mechanism of Soil " making a large number laboratory testing from different aspects, carrying out deep research on the ISS reinforcing mechanism and reinforcing effect on the red clay.In this paper, research work is carried out as follows:(1) Using plasma emission spectrometry and ion chromatography, the ion composition contained in ionic soil stabilizer was studied. The results showed that:ISS is soluble in water with a high ion concentration. In water, it can be dissociated into a positively charged cation [X]n+and the negatively charged anion [Y]n-,cation mainly refers K+, Na+, Ca2+, Mg2+among which Na+ions have the highest concentration; anion mainly refers Cl-, NO3- and SO42-, and SO42-ions have the highest concentration; ISS do no harm on our human body, animals and nature, which help protect the ecological environment.(2)With the use of the maximum bubble pressure method, surface tension on the ISS solution was studied. The results showed that:after being dissolved in water, ISS can significantly reduce the surface tension, and with the increasing of its concentration, the surface tension shows a downward trend. As the ISS can be dissolved in water to significantly lower the surface tension of water, so it is easy ISS solution spreads on the soil particle surface, helps the rapid ion exchange reaction carry out and create the conditions for ISS solidified soil. So that ISS easily move into the diffusion layer to improve the clay particle surface charge properties.(3) Experimental research has been carried out on ISS solidified soil with different combinations for unconfined compressive strength and limits of water content. Study results show that:the optimal ratio of ISS reinforced red clay can be fixed down by plasticity index, or unconfined compressive strength changes. Due to the advantages of rapid plasticity index application---fficient, economic and applicable, a minimum plasticity index was recommended to determine the optimal ratio of ISS soil reinforcement. On the variation in intensity, ISS intensity of solidified soil increases with age. During 0-28 days of age, the growth rates of intensity are faster, on the arrival of 28th day and so on, the speed slows down.(4) Under the optimal water content ratio of ISS, shear tests were carried out for different density of ISS solidified soil, and the study results showed that:by adding the red clay to ISS, the cohesion of soil could be improved significantly, but not too much impact on internal friction angle; Moreover, in optimal water content and within a certain degree of compaction, the density of ISS solidified soil affect shear strength parameters at a certain way, which is shear strength parameters and degree of compaction (density) have a good linear relation. The concrete expression of cohesion increases with the density going up, while internal friction angle decreases with increasing density.(5) Testing about ISS reinforcement effect of the red clay was performed and results showed: engineering properties of red clay were improved after adding ISS, in terms of enhanced following parameters, which including strength, dry density, cohesion, water holding capacity and reduce the compression deformation, At the same time improve the soil plasticity, swelling, shrinkage and absorbency.(6) Home-made seegage test device was selected for one-dimensional vertical seepage test of water, ISS solution, and water, three-phase experiment based on the same soil columns. Following results were achieved:①in stable flow condition, the law of pure water seepage in the red clay, non-linear flow laws, does not comply with the law of Darcy's linear flow. The initial hydraulic gradient I0, when the hydraulic gradient in the lower range, the flow velocity is relatively low, it follows Darcy's law; but as the hydraulic gradient increases, I0 will deviate from the linear property of Darcy's law; the permeability coefficient of soil is no longer fixed.②No matter in the steady flow or unsteady flow, one-dimensional vertical seepage laws of ISS water solution in the red clay are not compatible with the linear Darcy's law, while there existing the initial hydraulic gradient.③In the steady flow condition, the red clay which under penetrating through ISS, seepage of pure water in soil does not meet the law of Darcy's linear flow law, which has an obvious initial hydraulic gradient, but water seepage speed in the soil body dropped an average of 43% when comparing with original sample, its permeability goes smaller obviously.(7) The dynamic triaxial tests of ISS modified soil were conducted under the Rating load, given that the confining pressure is varying. The results show that the red clay were greatly improved under the dynamic condition, the maximum dynamic shear modulus ratio acquired an incensement of 27.72% on average. It was concluded that the confining pressure influenced the dynamic shear modulus and damping ratio to a certain extent. Given the same strain conditions, with the incensement of confining pressure increases, the dynamic shear modulus increased and the damping ratio decreased. Moreover, when plotting the dynamic shear modulus versus the dynamic shear strain, the similar curve can be formed for both the natural soil and the modified one, the dynamic shear modulus monotonously decreased with the incensement of the dynamic shear strain. However, the value of dynamic shear modulus differed in the same shear strain between the natural soil and the soil modified by ISS.(8) The sample was prepared by the way of Freeze drying-vacuum sublimation, the scanning electron microscopy was applied to study the micro-structure of red clay reinforced by the ISS. The results showed that:for the natural clay, the main types of micro-structure is stacked structure accompanied by void structures based on the aggregate, structural elements are contacted in the form of point-face and line-plane, the void also well developed. After treated by the ISS, the main types of micro-structure changed to be the aggregate structure, however, aggregate apparently turned to be bigger and correspondingly void volume decrease with a denser structure. The structural elements were contacted mainly in the form of line-plane and plane-plane. It could be seen from the SEM photograph that the cements were greatly obvious on the surface of modified soil particles unit, and flaky of clay minerals in the form of particles to surface contacted with one side was very closely.(9)On the base of fractal theory, the 3000-times SEM photographs were vectored by ARCGIS, thereafter Aperture Tester was employed to determine and quantitatively analyze the change of soil porosity. After ISS reinforced, the numbers of pore distribution in unit region of red clay significantly decreased, and particles increased, the size ratio of pore to particle reduced from 1.390 to 1.031, which indicated that the porosity decreased and density increase. Under identical pressure conditions, the reduction of pore volumes were principally caused by those pore volumes whose sizes were lower than 3.006101 nm.(10) X-ray diffraction analysis showed that the main clay minerals of non-reinforced Wuhan red clay are kaolinite, illite and vermiculite, and the non-clay minerals are quartz, feldspar and hematite. It should be noted that no new mineral was found after ISS reinforced, but the slight reduction of the crystal plane spacing of clay minerals.(11) Using Zeta potential instrument, electric potential of the clay has been tested. The results showed:red clay joining the ISS, itsξ-potential decrease in varying degrees, reflecting the combination water film turned to thin, but different ratios had different magnitude of decrease. In the optimal ratio, theξ-potential reduced to minimum, from -31.02 mV to -17.62mV, the rate of reduction reached 43.2% and the variation ofξpotential and the ratio of ISS was basically the same to the plasticity index; the same time,ξ-potential tests showed, even though ISS can reduced theξpotential of the red clay, the value ofξpotential still existed, it showed that the surface of clay particles still had double-layer structure, only just the thickness of diffusion layer turned smaller.(12) through analyzing the components of leaching solution flow in different periods,it studied the variation laws of each ion concentration over time in the process of soil reinforcement with ISS. It found that the soluble salts of red clay mainly contained four kinds of cations:K+, Na+, Ca2+, Mg2+and three kinds of anions:Cl,NO3-,SO42+, and at the early stage of test, there had the phenomenon of dissolution. Through the value changes of Na+/Ca2+, Na+/ Mg2+, it can be drawn that the of the Na+ions in ISS solution had cation exchange reaction with the Ca2+, Mg2+ions of clay particle surface, its concentration directly related to the response degree.(13) ISS reduced the thickness of adsorbed water by the function of physics and chemistry. There are two main aspects:①rely on ISS "hydrophilic head" and the clay particles on the surface of metal cations by the formation of the role of the chemical chain, ISS elements occupy the red clay particles on the surface of part of the cation vacancy, get rid of the red clay particles adsorbed on the surface of the hydrophilic cation, ISS also be attracted to the clay mineral surface;②ISS "the hydrophobic tail" around the red clay surface, forming a greasy layer, "hydrophobic tail" on the red clay particles on the surface of certain marginalized the role of water and prevent water entering this system. It is more common role, ISS reduces the red clay surface, the combination of water film thickness.Due to ISS making the thickness of double electric layer to small and combined water film to thin, so reducing the mutual exclusion between the soil particles and increasing the attractiveness, particles to be close to each other, so that the soil becoming more dense, the intensity of soil also increasing. This is the ISS reaction mechanism in reinforcing the red clay.(14) Spectrum tests showed that after the red clay was treated by ISS, soil particles on the surface of the C elements had changed markedly, from scratch, confirmed the ISS elements combined with the role of soil particles, the role of the ISS is also the place with the soil Physical chemical reaction, improve the engineering properties of soil of the important reasons.(15)Integration of all the test results and analysis, it obtained the mechanism ISS reinforcing the red clay mainly affected by a combination of the following five factors:①When ISS is soluble in water, it significantly reduced the surface tension of water. It is conducive to adsorption of soil particles and ion exchange reaction, creating the conditions for ISS solidified soil. This role makes ISS easily fit into the diffusion layer, improving the surface charge properties of red clay particle.②ISS's "water head" with the surface of clay particles form a chemical chain of the role of metal ions to ISS elements combine with clay particles.③rely on ISS "hydrophilic head" and the clay particles formed by surface chemical chain cation role, ISS elements occupy the red clay particles on the surface of part of the cation vacancy, get rid of the red clay particles adsorbed on the surface of the hydrophilic cation, while ISS's "hydrophobic tail" on the red clay particles on the surface of certain marginalized the role of water and prevent water entering the system, so without much mechanical force can be discharged. Common role of the above, ISS so that the thickness of electric double layer of clay decreases, combined with thin water film, which reduces the repulsion between Soil Particles Ershi increase attractiveness, so that particles close to each other, changing soil more dense, soil strength increased.④It remains a "film effect" between clay-water interface, when the cation concentration in crystal layer of the clay mineral between and the cation concentration in the water is different, between of two will form a so-called "membrane effect", that is, a high concentration side will be absorbent, low-side will be water loss. The ISS is a high concentration solution, when it contacts with the crystal layer of clay minerals, it will affect the water loss in interlayer of clay minerals, so that clay Mineral crystal layer is closer.⑤the cation of ISS solution is an organic cation, which has functions as a positively charged inorganic cation, in additional, also through the carbon and hydrogen, it produces hydrogen key between oxygen with of underside crystal layer and so on. So it has a more powerful attraction to the mineral crystal layer with negatively charge, it makes crystal layer space more stable and not vulnerable to the impact of the characteristic change of pore fluid. The expansion and contraction crystal in red clay does not have clear changes expansion and contraction in the volume at this time, which diminished the red clay swell-shrink capacity. In the combined effect of above five factors, it achieve the purpose of enforcement the red clay after the actions between ISS with the red clay, as well as between their own physical, physical chemistry and chemical actions.The innovative of the studies in this paper reflected in:(1) Using home-made flow test device, it made pure water, ISS solution, and then pure water three-phase, one-dimensional vertical seepage test on the same soil column. By analyzing the relation between flow rate with the head gradient, it researched the seepage law of ISS solution and pure water in the red clay. (2) considering the different effect of confining pressure, imposing the dynamic load by levels, it carried out the dynamic triaxial tests on the ISS solidified soil, studied the dynamic properties of ISS solidified soil. (3) Through ionic composition test of seepage leaching solution with time of the same soil column in different periods, it analyzed the variation law of concentration of the ions with the time and the influence of the electric double layer structure during the progress of ISS reinforcement soil, and researched the reaction mechanism of ISS.
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