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Geological Hazard Characteristics And Analysis Of Freezing And Thawing Of Loess Collapse In Linfen City Shanxi Province

Posted on:2018-08-23Degree:MasterType:Thesis
Country:ChinaCandidate:J ZhaoFull Text:PDF
GTID:2310330536965925Subject:Civil engineering
Abstract/Summary:PDF Full Text Request
The loess collapse disasters is one of the most common and relatively serious geological disasters in loess plateau region.Deal to the change of climate,deterioration of the climatope and the increasing of human activities in Loess Area,the loess landform and loess structure has been deeply affected,together with its special properties such as macropore,Vertical joint development,collapsible deformation,it is more likely to induce the Loess geological disasters,Under the influence of the external environment changes or human factors.According to investigation and statistics,The Loess Plateau Region in the northwest of China is an area with many geological disasters,In this paper,the Linfen city of Shanxi province is in this range,And this region is prone to collapse.Loess is a kind of soil sediment formed by the action of wind,mainly lied In arid and semi-arid regions,Small particle,Loose texture,it can exhibit vertical characteristics in dry conditions,hard soil,high cohesive force,collapsibledeformation and easy to soften when meeting water.In addition to the special nature of the soil to induce the loess collapse,There are also rainfall,freeze-thaw cycle,river erosion,biological activities of animals and plants and human engineering intervention.Getting rid of the intervention of human factors,In the natural environment,rainfall and freeze-thaw cycle factors are the most important causes of loess collapse,The destruction of rainfall is the sudden increase of soil water content,pore-water pressure increases among the particles,effective stress reduce,With the increase of soil weight,The shear strength of soil is not enough to support the increase of soil mass,finally cause the collapse disaster;the destruction of freeze-thaw cycle is pore-water among the particles will turn in ice and volume expansion when suffering the cold weather,and thaw settlement deformation will appear when temperature rising.With repeated ablation and frost heave,The original stable order of soil particles will be broken,Shear strength wil be decreased and the stress balance condition of the soil will change continuously,Finally,under the influence of human activities or environmental changes,collapse appear.In view of the causes of loess collapse,by field sampling in collapse disaster area,wrapping the soil samples with plastic film,put them in low temperature test chamber to simulating the freezing and thawing cycles under closed system.using shear strength test of the samples,The physical and mechanical indexes such as shear strength,cohesion,internal friction angle and moisture content were compared after the text.Through comparison we found inclosed system the moisture content of soil and the cohesive force is decreased by freeze-thaw action,In the direct shear test,when the confining pressure is lower,the internal friction angle is larger than that of the original soil,with the increase of confining pressure,the internal friction angle of the soil comes to inverse;When the confining pressure increases to the next level the shear strength of soil will increase accordingly,When the initial confining pressure is small,the increase of shear strength of the original is greater than that of the frozen one,With the increase of confining pressure,the growth of frozen soil's strength is larger than that of original soil.The most important factor of freeze-thaw cycle damage is the content of pore water among the particles,when the content is large the ice volume expansion and thaw settlement deformation will greater,All these factors affect the structure of the original soil itself,reduce the strength of soil,while the content is small the structural effect on the original soil is also small.
Keywords/Search Tags:the loess plateau, undisturbed loess, loess collapse, hazard, freezing-thawing cycle, causal factors
PDF Full Text Request
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