Research On The Growth And Water Transfer Mechanism Of Ice Lens Based On The Electrical Characteristics Of Saturated Clay

The area of permafrost in the cold region of China ranks third in the world,and it is the country that uses artificial freezing method to construct the most underground projects in water-rich strata such as mines,transportation and municipal administration.For a long time,the natural nature of frost heave and thaw settlement of permafrost poses a serious threat to the stability of roads and structures in cold regions,as well as the safety of artificial freezing method,and its frost heave and thaw settlement mechanism has always been the focus and research frontier of academic and engineering circles.Clay is widely distributed in central China.When the deep shaft passes through the deep clay layer,the frozen pipe fracture and shaft wall damage accidents occur from time to time due to the action of frost heave force.Clay has a specific mineral composition,and its frost heave mechanism is not only related to water-thermal-mechanical coupling,but also related to the electrical properties of its particle surface.Therefore,considering the surface electrical characteristics of clay,the study of ice lens growth and water transport mechanism of saturated clay has important theoretical significance to solve the problem of frost heave control of frozen clay.Therefore,based on the theory of diffusion double layer and interface premelting,using the research methods of theoretical analysis and laboratory tests,taking the special electrical properties of clay particles as the starting point,the electrical properties of soil and the interaction between pore ice and soil-water interface are studied,and the formation of ice lens and the migration mechanism of unfrozen water considering the electrical characteristics of clay surface are revealed.The main research work and conclusions of this paper are as follows:（1）Taking the deeply buried sandy clay in Lianghuai Pan Xie Gu Mining Area in Anhui Province as the test matrix,the physical properties such as particle size,mineral composition,microstructure,cation exchange capacity,freezing temperature and unfrozen water content were obtained by means of particle size analysis,XRD,SEM,N₂adsorption and low field nuclear magnetic resonance（NMR）;in order to study the effect of cation exchange capacity and type on the freezing characteristics of soil,16 kinds of cation adsorbed clay without changing the basic physical properties of soil were obtained by cation exchange adsorption method.（2）Based on the existing triaxial compression test platform of low temperature rock,the tensile test device of high temperature frozen soil was obtained after self-modification,and the tensile strength tests of frozen remolded sandy clay with different temperature（1.0～-2.0℃）,particle size and cation adsorption type were carried out,and the effects of the above factors on the tensile strength are analyzed.The results show that when the freezing temperature is between-1.5～-0.6℃,fine network cracks will appear on the surface of fractured soil samples,and eventually form a slight axial crack in the middle of the tensile strength soil sample,the lower the temperature and the smaller the particle size,the more obvious the brittle deformation;the load-displacement curve of the sample is parabola in the process of fracturing;at the same temperature level,the larger the particle size,the smaller the tensile strength of the soil sample;the effect of cation adsorption type on the tensile strength of soil depends not only on the hydration radius of cations but also on the mineral composition of soil.（3）Based on the influence of clay electrical characteristics on structural stability,the generalized colloid stability theory is adopted,and the expression of disjoining pressure between adjacent clay particles during freezing is established through the relationship between pore throat radius and freezing temperature.the internal relationship between the cracks in the frozen edge soil and the formation of the new ice lens is revealed and verified by experiments.The results show that the distance between adjacent clay particles is a single function of the disjoining pressure,and the temperature is the main factor affecting the disjoining pressure between frozen clay particles.the effect of surface force on the disjoining pressure between clay particles is proportional to the surface charge density of clay minerals.（4）Based on the electrical characteristics of clay and the interfacial premelting theory,the distribution of solid-liquid interface disjoining pressure is discussed,and the theoretical model of solid-liquid interface disjoining pressure of clay particles is constructed,the influence mechanism of solid-liquid interface disjoining pressure on water migration during freezing is revealed and verified by experiments.The results show that the disjoining pressure at the solid-liquid interface is a single-valued function of the thickness of the unfrozen water layer d,which can be expressed by the free energy on the surface of the charged body.When the electrostatic force is dominant,the thickness of the unfrozen water film is negatively correlated with the solution concentration;at the same temperature gradient,the tangential component of the disjoining pressure at the solid-liquid interface and the solution concentration gradient are the main driving forces of water migration;the effect of the disjoining pressure of the solid-liquid interface on the growth and water migration of the ice lens during freezing is mainly as follows:the tangent component of the disjoining pressure can cause the unfrozen water to move parallel to the tangent line of the clay surface,which provides the necessary conditions for the growth of the ice lens,and the thermal molecular forces generated by the disjoining pressure at the solid-liquid interface in the unfrozen water layer drive clay particles to move towards the warmer side,providing growth space for ice lenses.（5）Based on the criteria of the growth of old ice lenses and the formation of new lenses in saturated clay and the electrical characteristics of saturated clay,the deformation and fracture mechanism of clay skeleton caused by ice crystal growth during freezing are discussed by means of linear elastic fracture mechanics and colloid interface mechanics.A theoretical model of the whole process of ice crystal growth considering the effect of surface charge is proposed.The results show that when the sum of the radius of the ice cap and the thickness of the unfrozen water film is greater than the radius of the soil crack,ice crystals can penetrate the crack and induce the crack to continue to expand.The lateral extension of the crack promotes the formation of a strip shaped lens,and the formation of a new lens should be the result of the growth of the old lens along the vertical crack rather than secondary nucleation.Figure[74]Table[11]Reference[226]...