Effect Of Freeze-thaw Cycle And Dry-wet Alternation On Mechanical Properties Of Loess And Its Application In Slope Engineering

Unsaturated loess is widely distributed in the seasonal frozen soil region of Northwest China.Roadbeds,slopes and other projects are mostly located in the unsaturated zone,and are exposed to the atmosphere in a large area.Due to the impact of seasonal climate changes,the physical and mechanical properties of the shallow soil are in the dynamic variety for a long time.Especially under the repeated freeze-thaw and dry wet alternation,the microstructure of soil is changed,and water is redistributed.It is reflected on some aspects,such as the particle size and its spacing,array and the connection,which result in the decrease of the cohesive force between in soil particles,and strength attenuation.Eventually,that causes engineering entities to produce diseases.In view of that,this paper carries on the related research about mechanism of mechanical behavior of loess under freeze-thaw cycle and dry-wet alternation and their applications in slope engineering,and the research results are expected to provide reference values for the constructions of seasonal frozen soil area.In this paper,the typical high slope loess along the BAOLAN high-speed railway is selected as the research object.After the operation of the freeze-thaw cycle,dry and wet alternation and their interactions,the direct shear and the consolidation tests were carried out to study the mechanical properties of loess.Moreover,using the geotechnical analysis software Geo-Studio to simulate the effect of different slope gradients should be studied about temperature field,seepage field,and their changes in stability of different slope gradients under the effect of freeze-thaw cycle and dry-wet alternation.Our research work includes the following four aspects:(1)At the given dry density,with the increase of water content,no matter what kinds of soil samples,the cohesion,internal friction angle and compressive modulus 1-2E gradually decrease,while the porosity increment and the compression coefficient1-2a increase gradually.In addition,the effect of the freeze-thaw cycle,dry-wet alternation and their interactions on the destruction of the soil increases in turn.(2)At the given moisture content,with the increase of dry density,no matter what kinds of soil samples,the cohesion,internal friction angle and compressive modulus 1-2E gradually increase,while the porosity increment and the compression coefficient 1-2a decrease gradually.However,the response of the internal friction angle,pore ratio increment,compression modulus1-2E and so on subjected to freeze-thaw cycle are closely related to the initial dry density.(3)At the given moisture content and dry density,with the increase in the number of cycles,the cohesion and compressive modulus 1-2E gradually decrease,while the porosity increment and the compression coefficient 1-2a increase gradually.But for the internal friction angle,the freeze-thaw cycle makes it increase,and dry-wet alternation and their interaction makes it decrease.(4)With the freeze-thaw cycle,and dry-wet alternation occurring,the slope safety factor continues to decrease,especially in the early period.In addition,the slope gradient is negatively correlated with the safety factor for freeze-thaw slopes,but this is not comprehensive for dry-wet slopes,which is related to seepage strength and slope grade.