The Characteristics Research Of Specific Gravity And Particle Composition Of Soil Developed From Volcanic Ejecta

When systematically catagorizing the andosols which is a kind of soil developed by volcanic ejecta,it need to do the judgment on the soil sample.The ash properties is a series of feature set.Under certain conditions,it need to determine 2～0.02 mm grain content to decide whether the soil is of the ash properties.However,the identification standard of the ash properties has not clearly pointed out the measurement method of soil particle composition.The these studys on the soil which is developed by the volcanic ejecta of basaltic quality and rough rock which are cenozoic and not in the same period on the northeast of China,the specific gravity of soil particles in two kinds of lithologic soils with less than 0.1mm and less than 1mm was determined.Comparing and studying the measurement method of soil particle composition,the aims to provide scientific basis for revising and improving the characteristics of the identification of volcanic ash.The study shows that:(1)The diamater of the soil,developed by volcanic ejecta of basaltic qulity which is at a relativiety higher level of development,is less than 0.1 mm,the specific gravity of soil particle which is less than 1 mm is 2.78 g cm-3 and 2.62 g cm-3 respectively.The diamater of the soil,developed by volcanic ejecta of basaltic qulity which is at a relativiety low degree of development,is less than 0.1 mm,the specific gravity of soil particle which is less than 1 mm is 2.62 g cm-3 and 2.55 g cm-3 respectively.The diamater of the soil,developed by vocanic ejecta of basaltic quality which is at a relatively lower level of development,is less than 0.1 mm,the specific gravity of soil particle which is less than 1 mm is 2.56 g cm-3 and 2.50 g cm-3 respectively.The same king of lithology developed soil,the specific gravity of soil diamater which is less than 0.1 mm is larger than that of the soil diamater which is less than 1 mm.No matter what the soil diamater is,the specific gravity of the soil developed by vocanic ejecta of basaltic quality is large than that of the soil developed by vocanic ejecta of rough rock.The specific gravity is bigger when the development degree of soil is stronger.(2)When measuring the particle of soil developed by vocanic ejecta by hydrostatic sedimentation method,it is necessary to measure the specific gravity of soil particles,the diamater of which is less than 0.1 mm and calculate the precipitation time of soil particles pf each fraction.The experimental data shows:accordin to Stoke’s Law,with other conditions unchanged,when the specific gravity increases 0.01,the precipitation of coarse particle stortens 1～2 s;the precipitation time of cosmid stortens 5 min.When the water temperature increases every 1 ℃,the precipitation time shortens about 9～12 min.(3)The difference between sand,silt,clay content which is based on the gravity test of the particle diameter which is less than 1 mm and that based on the proportion value of 2.65 g cm-3 is 17.9 g kg-1,15.9 g kg-1,14.1 g kg-1.The difference between sand,silt,clay content which is based on the gravity test of the particle diameter which is less than 0.1 mm and that based on the proportion value of 2.65 g cm-3 is 15.3 g kg-1,13.8 g kg-1,13.2 g kg-1.The influence the soil gravity test has on each fraction content soil respectively is:sand>silt>clay.And it also has influence on the naming of soil geology.When the soil specific gravity value changes 0.01units,it may affect the soil geology of the name.(4)The content of grain size determined by hydrostatic sedimentation method based on the specific gravity of particle size less than 0.1 mm is larger than that of sieving method.Most soil samples are thicker than those measured by hydrostatic sedimentation method.the absolute error of big particle size(0.5～0.05 mm)is relatively large,and the absolute error of small particle size(0.05～0.02 mm)is relatively small.Because of the differences in the grain size determined by the different methods,the determination of the soil particle content is required in the volcanic ash characteristics.