Research On Sliding Soil Reinforced By Ionic Soil Stabilizer

China, as one of the nations which have been mostly suffered from landslide hazards, has very complicated geological conditions and intense tectonic movements. Landslide plays a significant role of natural disasters in our country according to the statistic data during the past years. The economic loss directly due to landslide takes 80 percent among all the paroxysmal geological disasters, which brought serious harm to the economic constructions as well as people's property, and Innumerable amount of money has been paid for landslide controlling. Thus, to find the Countermeasures to reduce the harm of such disaster and new landslide controlling methods has always been one of the major tasks of geological disasters prevention and treatment for Chinese government in such situation. Besides,it is the key issue of the annual international conference of landslide hazard as well as an important component of international project on landslide.At present there are many engineering measures in landslide controlling projects including four major categories which are 1. the modification of slope geometric primitivity; 2. Drainage engineering; 3. Using the reinforcement structure; 4. The reinforcement of the inner part of the slope. The first three measures are widely used and all have been well developed theoretically, designing and construction methods. The last one, however, is seldom used or researched. The reinforcement of the inner part of the slope includes the reinforcement of sliding body, sliding surface and sliding bed. Generally speaking, the mechanism of the landslide is that it will happen when the shear force in the sliding area is larger than the shear strength of the sliding surface. It means the geotechnical property of the sliding soil often controls the stability of the slope and the shear strength is the key factor considering the scale and the investment for the treatment of landslide.There are several ways to reinforce the soil, such as electroosmosis method, roasting method and grouting method. The advantages of all the methods above are straight-forward and high efficiency along with environmental benefits, avoiding the excavation or changing of the present slope. On the other hand their disadvantages are also, such as poor operability and low grouting feasibility, these energy—consuming and expensive methods are hard to put into practice or need to be further researched.However, the landslide control is a complex systematic engineering and different measures are selected and applied comprehensively according to the specific conditions and to save energy and budget. In this article a new physicochemical method, i.e, the Ionic Soil Stabilizer (ISS for short) for improving the shear strength of sliding soil and the stability of the slope as one of the controlling methods is introduced. It can largely reduce the cost of engineering and make the landslide treatment more effective.ISS as a dark brown liquid at normal temperature is a new electrochemical Soil Stabilizer which is slightly more viscous than water and easily soluble in water. It ionizes in water in a short time and the solution becomes more conductive afterwards. This method is suitable for soils in which the percentage of clay fraction is higher than 25%. Since 1970s, ISS method has been widely used in road stabilization and field-hydraulic engineering seepage control domains in more than dozens of nations and regions. In this research project ISS is injected into sliding zone to enhance the shear strength of the sliding soil by reducing the thickness of adsorbed water and creating some new components after a series of ion exchange reactions.The most important issue in this method is to have an in-depth understanding of reinforcement mechanism about the Ionic Soil Stabilizer and the reinforcement effect evaluation. Meanwhile it also need to be further investigated on the reinforcement method, seepage and diffusion of the ISS as they all have significant effects on the shear strength of the sliding soil as well as the design and construction. The safety and cost of the landslide treatment engineering can also be determined on the basis of these factors subsequently.In this work, we took Dayantang land-slide, in the area of Shibuya hydroelectric station of Qingjiang river, as the research platform, compared with many other methods of landslide preventing examples, and introduced a method of using Ionic Soil Stabilizer (ISS for short) to improve the shear strength of sliding soil according to the engineering characters of the sliding soil is saturated clay. This method, in coordination with other methods, can be an economical, environmental friendly and effective method of preventing landslide. According to field survey and indoor analysis, the analysis of theoretic & experimental data, qualitative & quantitative, relations of macroscopic mechanics, microstructure and microscopic substance, we analyzed the action mechanism, consolidation effect and feasibility of the methods. The conclusions are summarized below:1. As the sliding soil often locates 25-40 m underground, and can't be removed from underground, insufflated or mixed with ISS, the in-situ reinforce method should be adopted. For the special characters of these sliding soil, high viscosity, tight structure and weak permeability, the method of high pressure injecting can be an economical and efficient choice, so the in this work, infiltration experiment using "Nan-55" instruments to solidify the clay is conducted and the standard experiment process is established. In order to keep the uniformity of each samples, it is suggested that the samples of the remolded sliding soil should be consolidated under a pressure of 12.5KP.2. During the process of infiltration experiment, the samples infiltrated by distilled water and ISS solution were investigated in parallel,. The sharp decrease of the permeability of the sliding soil after the reaction started (the soil infiltrated by ISS solution) was observed, it is mainly caused by the different permeabilities of consolidating solutions and the viscosity coefficient of ISS infiltrating solutions. The higher viscosity coefficient, the lower k (permeability coefficient). The permeability of solidified soil is calculated to be 1/3 of that before solidification. The possible reasons behind this phenomenon can be explained by a) the function of condensation, b) the hydration with soil matrix, c) the reduction of the size of big pores and the thickness of adsorbed water,d) the channels of the water are jammed, e) the density of soil is increased and f) the permeability is decreased.3. The experimental results achieved previously was investigated. According to the conclusion of "For some high density clays with the permeability coefficient K is lower than 10-6 cm/s, their parameter of quick and direct shear test is close to the shear strength parameter of unconsolidated and undrained triaxial shear test", it can be summarized that, the premeabilities of clays before and after solidification are both smaller than 10—6cm/s and the plastic index is 24, the previously concluded conditions are basically achieved, therefore, quick and direct shear test is adopted to test the change of share strength before and after the reaction between SIS and soil. The result shows that the cohesion force is largely increased 256%, and the angle of internal friction increased 122%. The strength of soil increases with reaction time. This demonstrates that the solidification of the slide soil by infiltration using SIS solution can increase the strength of the soil and therefore is a feasible and effective method.4 Based on the macroscopic physical mechanics experiment, using microcosmic analysis, we evaluated the changes of microstructure by Scanning Electronic Microscope (SEM for short), in different multiple and qualitively analysed the result of solidification from microscale. The amplificatory picture of SEM, magnified 2000 to 12000 times, were analyzed, the grain of clay, big soil aggregates and the relation between single grain and pore were observed. The difference among the microstructures of solidified soil before and after the reaction is obvious. Before reaction, it appears that the soil aggregates assembled loosely, display honeycomb structure, single grain appears conglobation with visible impracticable structure; After the reaction, the grains of soil are connected with borders and faces, especially no no obvious interspaces were vibible along the connection in the wedge-inlay style , Single grains are contacted with each other face to face, no granular material and with few pores, display a condensed platelet structure.5. Based on the fractal theory, the 8000 times scanning picture is treated with Binarization, by GIS, the fractal dimension of different slide soil can be calculated to describe the poros characteristic quantitatively. Porosity distribution dimension and porosity edge shape dimension are decreased after soliditication, it indicates that the distribution area diminished and the edge of porosity turn smoothly, the effect of consolidation reaction is very well The fractal dimension reflect different diameter porosity distribution, the porosity fractal dimension in one special diameter after reaction, increased from 1.185 to 2.043, this can reflect the changes of porosity diameter aren't uniform, the distance of two pores are different. The P-A model is used to measure the scrambling of the porous shape. It is concluded that the soil pores after reaction is more scrambling, this observation agrees with the situation of single grain' pores edge shape.6 As the X-ray diffraction test is a half-quantitative evaluating method with error about 5%, the XRD result can indicate that there's no new clay mineral formed during the reaction and the change is mainly caused by the Ion-exchange of a series of physiochemical reactions. Through the composition analysis of the leachates of solidification process, the rule of leachate ion concentration changes over time is researched, the result indicates that the soluble cations leached out from slide soil are mainly Ca²⁺,Na⁺ and Mg²⁺ and They are dissolved from the beginning of the experiment. The cation concentration changes of Ca²⁺/Na⁺,Mg²⁺/Na⁺ shows that Ca²⁺ is the main cation in the reaction, it's concentration and charge directly depend on with the reaction.7 The effect of solidification is greatly affected with the change of the double electrical layer structured clay, due to the ion absorption and exchange and finally impact the inter-particle force of soil grains are influenced by the thickness of the absorbed water and the double charged layer structure. The soil grains aggregated tightly or loosely are determined by the inter-particle force, the sizes of pores also affect the strength and permeability of soil. Based on this point of view, we believe that the reaction between ISS and soil enhances the shear strength of slide soil,. The mechanism can be explained as follow: the thicknesses of the absorbed water and the double charged layer structure are reduced by the reaction of caion exchange, mainly the Ca²⁺ and the inter-particle force of soil grain is strengthened.Summary all discussed above, through the experiment on ionic soil stabilizer reinforced sliding soil using in situ infiltrating method, the mechanism and effect of the solidification reaction are analyzed qualitatively, this method can be applied to strengthen the slide soil, as one of methods to prevent land-slide. The mathematic method of fractals can be used to describe the complex distribution characteristic of soil pore and the fractal dimension can be used to describe abundance information of viscosity slide soil in solidification and forecasted the degree of consolidation.