Experimental Study On Micro-nano-scale Microstructure Characteristics Of Loess

With the implementation and development of the Western Development Strategy of China,the 13 th Five-Year Plan and the “Belt and Road” policy,environmental geology and engineering geology problems have become increasingly prominent in the loess distribution areas in central and northwest of China.After the accumulation of quantitative changes to a certain extent,the microscopic structure of the soil breaks through a certain critical state,which is manifested as macroscopic deformation and destruction.It is one of the main directions of loess research to study the structure of loess from the microstructure characteristics of loess,and to explain and predict the macro-mechanical characteristics of loess at present.Although there have been many studies on the microstructure of loess,the research on the structure of loess,especially the microstructure,must be further studied.The microstructure of the loess includes the composition of the soil,the pore structure and the connection characteristics between soil particles.Particles or Grain is the core and soul of loess structure.The mineral particles that makeup loess include millimeter,micron,submicron and nanoscale particle combinations,and spanning 6 orders of magnitude from macro to micro.However,previous studies on loess particles focused on clay particles have mostly stopped at clay particles.In this paper,the occurrence of submicron-nano-scale particles formed in loess below the clay grade in loess microstructure was studied.Using the process and method of sieving-dispersing-settling-air drying,the particle size separation test was carried out on the loess,and the soil samples of two components,silt and fine,were obtained.Using an intelligent ultra-depth microscope and scanning electron microscope,the loess was observed under the microscope.On the one hand,from the perspective of particles,the occurrence form of submicron-nano-scale particles in loess was observed,and it was found that the loess particles were mostly combined with other particles to form an "aggregate" structure.Or it can be coated on the surface of particles and aggregates to form a "particle core-particle coating" structure.On the other hand,from the perspective of pores,the occurrence of submicron-nano-scale particles in loess is mainly composed of two different types of pores,namely intergranular pores and intragranular pores.And it was found that the intergranular pores and intragranular pores together formed the double pore structure of loess.The method of sectioning and slicing loess samples using a scanning electron microscope with a mapping surface scanning function is mainly described.At the same time,the composition and occurrence of loess particles are understood from the surface and inside.And the particle size composition of loess and its fine particles are preliminarily discussed the role of substances in the loess structure.Finally,the hydro-mechanical properties of the loess modified by nano-silica were tested for the particle size,permeability,collapsibility and centrifugal dehydration of the undisturbed and reshaped soil samples under the conditions of natural moisture and dry density.The experimental results show that adding nano-silica to loess can improve and enhance the hydraulic properties of loess.