Characteristics And Mechanism Analysis Of Freeze-Thaw Disease Of Loess Road Cutting Slope In Northern Shaanxi

The loess region of Northern Shaanxi is located in the seasonally frozen soil area.The physical and mechanical properties of soil will deteriorate under the action of freeze-thaw cycle,which is one of the important reasons for the freeze-thaw disease of loess cutting slope.Therefore,this paper takes the problem of freeze-thaw disease of loess cutting slope in Northern Shaanxi as the starting point,through the physical and mechanical property test of remolded loess in Northern Shaanxi under different freeze-thaw cycles,obtains the variation law of basic physical parameters,mesoscopic pore structure and shear strength index of soil,so as to explore the influencing factors and disaster mechanism of freeze-thaw disease of loess cutting slope in Northern Shaanxi.Through field investigation and field test,the occurrence environment characteristics and particle size distribution characteristics of loess in the study area are preliminarily mastered.At the same time,the phenomenon of freeze-thaw disease of loess cutting slope is summarized into two types:freeze-thaw spalling failure of Manually Excavated Slope and shallow freeze-thaw instability of natural slope.Among them,freeze-thaw spalling failure can be divided into four forms:skin,layer,fragment and mixed.Taking the remolded loess in different areas of Northern Shaanxi as the research object,the physical and mechanical properties tests under different freeze-thaw cycles are carried out.It is found that the increase of sample pore ratio gradually decreases after a sharp increase,and the initial pore structure is mainly micro and small pores,which is in a dynamic change process in the process of freezing and thawing.The cohesion and internal friction angle first decrease significantly and then tend to be stable in the process of freezing and thawing.The stress-strain curve will transition from weak softening type to weak hardening type with the increase of confining pressure.At the same time,the freezing and thawing damage model of loess in Northern Shaanxi under the triaxial stress state of equal confining pressure is also constructed.It is found that when the soil reaches the same damage degree,the strain of soil will increase with the increase of confining pressure,and the freeze-thaw damage rate decreases with the increase of freeze-thaw cycle times.After discussing the occurrence mechanism of freeze-thaw disease of loess cutting slope in Northern Shaanxi,it is finally considered that the main causes of freeze-thaw spalling failure of manually excavated slope are the mutual connection of macro cracks generated in the process of freeze-thaw and the separation of soil particles from the slope after freeze-thaw disintegration.The reason for the shallow freeze-thaw instability of natural slope is that the water will change the migration direction along the freeze-thaw interface during the infiltration process,and the interlayer cement will hydrolyze,resulting in the significant reduction of the shear strength of the soil at the interface,thus inducing the bedding instability of shallow soil.This paper uses the research methods of field investigation,field test,laboratory test and theoretical analysis to deeply analyze the physical and mechanical properties and the occurrence mechanism of freeze-thaw diseases of remolded loess in different areas of Northern Shaanxi under the action of freeze-thaw cycle.The research results obtained not only provide a theoretical reference for the follow-up exploration of the freeze-thaw disaster mechanism of loess cutting slope in Northern Shaanxi,but also have a certain guiding significance for the prevention and control of freeze-thaw diseases.