Experimental Study On Air Permeability And Microcosmic Mechanism Of Malan Loess

As a natural foundation and fill material for the construction of loess area,Malan loess has a direct impact on the stability of the engineering construction due to its water and air permeation characteristics.In this study,a series of tests air permeability on dry intact loess and remoulded loess are accomplished by using improved ZC-2015 air permeameter and TST-55 permeameter,samples are exhumed from Heifangtai,Yan'an,Chan river profile.combining with the microscopic electron micrographs test to discuss the water and air permeability and microscopic mechanism of typical Ma Lan loess.Studying on the relationship between air permeability k_a and saturated permeability coefficient K_w.Finally,the mathematical model is established between macroscopic and microscopic pore parameters and permeability parameters.The results of gas permeability test show that the air permeability increases with the increase of the soil volume due to the size effect of different volume soil samples.With the increase of dry density,air permeability of remolded loess decreases,the higher content of clay particles in loess,effective gas permeability pore decreases and air permeability of remolded loess decreases.Structural differences of remolded loess under different moisture content is larger due to the static pressure method,and the aggregate,particle softening,the effect of matric suction effect,the air permeability increases with initial moisture content increases.While in the whole humidification and dehumidification process,no structural differences in loess samples,soil water affects its air permeability by affecting the size of the air passage,air permeability drops with the increase of water content.During the humidification process,when water content is less than 20%,air permeability significantly drops with the increase of water content,and the air permeability in the dehumidification process is always greater than air permeability of the humidification process in the same water content.The air permeability of dry intact loess loess decreases with the depth of loess sample increases,while the air permeability of remolded loess decreases with the increase of soil depth.Air permeability k_a not only describes the pore and structural characteristics of unsaturated soils,but also can be used to predict the K_w.k_a decreases with the increase of permeability diameter,and ultimately this trend becomes stabilized,the stable permeability of the undistured and remolded loess is 8cm.There is a significant double-logarithmic linear relationship between k_a and K_w,The correlation between the lgk_a and lgK_w of the remolded loess with different grain composition and undistured loess in different depths are obvious,but the fitting formula between the undisturbed soil and the remolded soil is very different.In addition,when the content of clay particles is high,the slope?and intercept?of the remoulded sample is obviously increased.Under the different water content,the formula of the remolded soil is very different,when the water content is high,the chage of k_a is more than K_w with the increase of the dry density,and the slope?and the intercept?of fitting line are obviously reduced.With the increase dry density of remolded soils increases,the number of particles per-unit volume increase,The fractal dimension of large and medium pores increases,circularity decreases,and the number of pores decreases.The buried depth of undisturbed dry soil samples increase,soil pore size and pore number,the average pore diameter significantly decrease of macropores and mesopore in loess.The semi-logarithmic linear model can eliminate the magnitude difference between K_w,k_a and the pore structure parameters,and the fitting results is better.lgK_w,lgk_a with e,e₀ show a good linear relationships.When the water content changes,The regulation of slope and intercept about the gas permeability fit lines change obviously.Due to uniform sample preparation,fitting curves of remolded soils show the high fitting degree.Comparing with the remolded loess,fitting degree of undisturbed loess in different depth is low because of structural differences of deposition process.