Study On Soil-water Chemical Mechanical Effect Of Clay Particles

Shear strength is a key index to evaluate the stability of soil slope,and aqueous solution is an active medium to induce the attenuation of shear strength.In practical engineering geology,clay minerals have low mechanical strength and are often distributed in the landslide slip zone and adjacent surface soil.It is inevitable that chemical reactions will occur after contact with water,which will affect the stability of soil and eventually induce landslide formation.This process is an objective existence in the stage of soil landslide development.The chemical and mechanical effects of water and soil play a very key role in the process of affecting the strength attenuation of slope soil.If the mechanism and law of water and soil chemistry can be correctly understood,and the situation can be improved and transformed,it will undoubtedly have a profound impact on the prediction,early warning and prevention of soil landslide.In order to explore the influence of acid and alkali on the mechanical effect of clay particles,this thesis simulates the field landslide incubation environment,and takes typical clay minerals-kaolinite and illite as the main research objects.The prepared remolded soil is placed in different aqueous solutions for soaking test.Through many direct shear tests,combined with the analysis of water chemical parameters of soaking solution,electron microscope scanning analysis,X-ray diffraction experiment analysis and other indoor test methods,the variation law and mechanism of cohesive force and internal friction angle of clay minerals under acid and alkali conditions were systematically analyzed.The quantitative calculation model and change calculation model of cohesive force of clay mineral remolded soil were established,and this calculation model was used to study the mechanism of Daping landslide.This thesis mainly draws the following conclusions:（1）Under the same temperature and time conditions,the variation characteristics of cohesion c of two different types of clay minerals,kaolinite and illite,are basically the same.Under acidic conditions,the cohesion showed a decreasing trend.Under alkaline conditions,the cohesion c value shows a trend of decreasing first and then increasing.（2）The shear strength of remolded soil is mainly determined by the strength of clay minerals as cementing materials,and is strongly controlled by the acidity and alkalinity of aqueous solution.Under acidic conditions,the clay minerals are dissolved,the cementation between particles is reduced,the overall structure becomes loose and porous.Under alkaline conditions,due to the formation of new cementing materials,compared with acidic conditions,the structure of remolded soil is closer.（3）Kaolinite and illite remolded soil samples were dissolved in nitric acid solution,and no obvious new characteristic peaks were generated.The soil cohesion showed a downward trend on the macro level.Strong alkali also causes loss of each component in the remolded soil sample,and the strength of the characteristic peak corresponding to the clay mineral decreases or offset obviously.Through the interpretation of jade software,it is considered that there are new substances such as zeolite minerals,albite and hydrated calcium silicate CSH in the kaolinite remolded soil samples at the later stage of soaking.At the same time,the quartz sand in the two remolded soils will react with alkali to form NaAlO₂（sodium aluminate）and Na₂SiO₃（water glass）,and the shear strength of the remolded soil will rebound in the middle and later stages of soaking.（4）In this thesis,the microscopic cementation nature of clay minerals and the effect of aqueous solution are comprehensively considered.Taking kaolin as an example,a quantitative calculation model of cohesion of saturated kaolinite-quartz sand remolded soil is constructed.Furthermore,combined with chemical reaction kinetics and cohesion change mechanism,a calculation model of cohesion change of kaolinite remolded soil under the action of water and soil chemistry was constructed,and the change trend of cohesion under acidic conditions was simulated,which was in good agreement with the measured values.（5）Taking the Daping landslide in the Three Gorges Reservoir area as an example,the effect of shear strength attenuation of clay minerals on the development of landslide under the action of water and soil chemistry was analyzed by Midas GTS NX software.