Study On Engineering Characteristics And Application Of Slope Piedmont Facies Softclay

With the flourishing development of infrastructure construction in China,a kind of“soft soil on slope”which was obviously different from the general soft soil property is found in the mountainous area of southwest China.It has brought a lot of harm to the construction of railway and highway,but there are few studies on soft soil on slope.It is of great significance to study the engineering characteristics of soft soil in the southwest mountainous areas.Based on the construction of soft soil subgrade of slope piedmont facies of zhenxiong station of chengxian-guizhou railway,this paper systematically carried out the research on the engineering characteristics of soft soil on slope and the key technology of subgrade construction with the methods of indoor test,field test and theoretical analysis.The main conclusions are as follows:?1?According to the analysis of soil micro-test system results,the results show that Al₂O₃,CaO and MgO account for about 15%of the whole the gray soft soil on slope of zhenxiong station.These three components are active in chemical properties and easy to react with water,resulting in parent rock weathering and providing material conditions for the formation of soft soil on the slope.In addition,due to a small amount of montmorillonite and muscovite,it has weak expansibility.The original structure and remolded structure of the gray soft soil on slope are dominated by clay matrix structure,which is different from the general marine soft soil in structure.?2?The results of laboratory test show that the direct shear of undisturbed the gray soft soil on slope under low normal stress is obviously better than that under normal stress.The direct shear results of the gray soft soil on slope with remolded show that the soft soil is sensitive to water and the cohesion and internal friction angle decrease with the increase of water content.The unconfined peak compressive strength of the soft soil on slope after disturbance is only about 30%of that of the original soil.The sensitivity value of the gray soft soil on slope is 2.81,which belongs to the medium sensitivity,indicating that the soft soil on slope has a certain structural strength.With the increase of moisture content,the expansibility of the gray soft soil on slope decreases successively and has good correlation and the moisture content is lower,the expansion speed is faster.?3?The dynamic stress-strain relationship,dynamic elastic modulus,dynamic strength and dynamic strength parameters of undisturbed the gray soft soil on slope under different confining pressure and consolidation ratio were studied by laboratory dynamic triaxial test.The test results show that the dynamic stress-strain curve of the undisturbed soft soil on slope can be fitted by hyperbolic model,and the parameters of the hyperbolic model are obtained.With the increase of dynamic strain,the dynamic elastic modulus first decreases rapidly and then decreases slowly,showing obvious strain softening.When other conditions are constant,the confining pressure or consolidation ratio is larger,the dynamic strength will be greater under the same vibration number.The confining pressure or consolidation ratio is larger,the dynamic cohesion and internal friction angle will be larger under the same vibration level.However,with the increase of vibration level,the dynamic cohesion and internal friction angle will show a small linear trend.?4?Starting from the statistical analysis of the physical and mechanical properties of slope piedmont facies softclay,combined with the laboratory test results of representative the gray soft soil on slope,this paper expounds the reasons why it is difficult to form a single direction cement soil mixing pile,and puts forward the construction technology of forward and backward mixing pile with“no cement mixing”.By adding no cement mixing,the original structure of soft soil can be destroyed,its cohesion can be reduced,the difference in soil strength can be improved,and the purpose of soil strength homogenization can be achieved to ensure the evenness of cement slurry distribution in the later stage of shotcrete mixing pile and improve the quality of mixing pile.?5?Based on the settlement standard of railway subgrade and different foundation treatment methods,five suitable methods for foundation treatment of soft soil on slope subgrade section of high-speed railway are given.Proposed?grade level of railway and the following lines should be"against sliding is given priority to,drainage,soft both"as the design principles,and sums up the three different forms of soft foundation under the response.This paper puts forward that the design of high speed railway foundation should be based on the principle of"anti-slip,soft treatment and perfect drainage".