Effect Of Particle Size Composition And Density On Engineering Characteristics Of Loess And Response Of Filling Slope Infiltration Process

The geomorphology of the gully in the loess area has greatly restricted the development space of the city.“Digging the mountain and filling the ditch” has solved the dead knot of the city without development space,but the construction of large-scale projects in the loess area has triggered a series of new disaster hazards.The loess fill slope is easily destabilized under the influence of external factors such as rainfall,posing a serious threat to industrial and agricultural production and people’s lives in the loess area.The catastrophic problem of loess fill slope has become a new research hotspot in the field of geotechnical engineering.From the northwest to the southeast,the loess shows a rule that the particles are tapered,the sand grains are reduced,and the clay is increased.According to Liu Dongsheng et al.(1985),the loess plateau can be divided into three zones: Ⅰ with sand loess,Ⅱ with typical loess,and Ⅲ with sticky loess.As an important filler for the fill slope of loess area,loess is directly affected by the composition of the particles,which affects the stability of the fill slope.Based on the regional distribution characteristics of loess,this paper selects the typical loess area,conducts field investigation and sampling,conducts indoor experiments on loess samples in different areas,and studies its basic physical and mechanical properties and its variation in the region.On this basis,select Yan’an loess,with different granularity composition and dry density of loess samples,focusing on the influence of grain size composition and density on the microstructure,soil-water characteristics and strength characteristics of loess,and then studying the rainfall of loess fill slope considering the difference in particle size composition and density.The mechanical response law provides a scientific theoretical basis for the practice of filling engineering and disaster prevention in the loess area.The main research results are as follows:(1)The loess particle size composition has a large difference in the horizontal area.The Ⅰ belt is adjacent to the Mu Us Desert,with coarse loess particles and a fine sand content of 52%.The zone Ⅱ has a lower content of fine sand and a higher content of clay.The zone Ⅲ has fine loess particles,the content of fine sand is very low,and the content of clay is the highest.The grain composition of loess samples in the central zone is gradually thinner from north to south.The composition of loess particles is not obvious from west to east.The variation of the grain size composition of the loess in the vertical direction is generally shown that except for the difference in grain size composition of the paleosol layer and the weathering layer,the grain size composition of the loess has a small fluctuation and exhibits a certain rhythm.(2)From the Ⅰ belt to the Ⅲ belt,as the sand content decreases,the clay content increases,the optimum moisture content of the loess gradually increases,and the variation of the maximum dry density is not obvious.The cohesion between the maximum dry density and the optimum moisture content was positively correlated with the fine particle content,and the internal friction angle was negatively correlated with the fine particle content.(3)For different particle size composition of loess,with the increase of sand content,the content of fine particles decreased,the uniformity of particle size gradually became worse,the area of large and medium pores of the scaffold gradually increased,the area of inlaid pores gradually decreased,and the pores of the cement and the area of intragranular pores gradually decreased.With the decrease of dry density,the pore structure of loess gradually transitions from the relatively stable small pores to the relatively unstable medium-large overhead pores.The large and medium pore areas of the supports gradually increase,and the mosaic pore area gradually decreases.The porosity of the cement and the pore area within the granule gradually decrease,the surface void ratio gradually increases,and the pore connectivity gradually becomes better.(4)The unsaturated soil water characteristic curve is mainly affected by the particle size composition and dry density.The smaller the sand content,the more the clay content,the higher the dry density,the better the water retention of the soil,the higher the intake value and the residual moisture content,and the smaller the dehumidification rate.The effect of dry density on the intake value is significantly greater than the effect of the change in loess particles on the intake value.The change of grain size composition of loess is the main controlling factor affecting the residual water content.With the increase of matrix suction,the effect of dry density on the soil water characteristic curve is gradually weakened.When the matrix suction exceeds 100 kPa,the difference of dry density has little effect on the soil water characteristic curve.(5)The consolidated undrained shear strength characteristics of loess samples vary with particle size composition,dry density and consolidation confining pressure.Under the same dry density,the cohesive force decreases with the increase of sand content,and the internal friction angle increases with the increase of sand content.Under the same particle size composition,the peak strength,cohesion and internal friction angle of loess are both The dry density is positively correlated.(6)Under the effect of rainfall infiltration on the slope of loess fill,the more the sand content,the smaller the clay content,the smaller the dry density,and the faster the pore water pressure increases with time.Different dry density and particle size composition of the loess fill slope are affected by the depth of the rain.The larger the sand content and the smaller the dry density,the greater the depth of rainfall below the slope.(7)During the rainfall period,the stability coefficient of loess fill slopes continued to decrease.The more loess sand content,the smaller the clay content,the smaller the dry density,the better the permeability and the shorter the critical time.