Study On The Expansion Characteristics Of Neogene System In Xining Basin

The Xicheng railway passes through the Neogene mudstone area of the Xining Basin.The mudstone in this area encounters an increase in water volume,cracks,and loss of original strength,It has certain expansion characteristics,It has great influence on railway construction.So,It is very important for the railway construction to study whether the mudstone in this area has swelling ability and what kind of expansion characteristics.In order to obtain the specific characteristics of mudstone in this area,a series of rock basic characteristics experiments and expansion characteristics experiments are performed on the original sample.Through the analysis and analysis of the experimental data,it is found that the mudstone in this area is indeed inflated,and the swelling characteristics are related to the four indicators of clay mineral content,initial moisture content,initial dry density,and particle size of the crumb.In order to verify the correlation between the expansion characteristics and the four indicators in the original sample,we conduct a remodeling experiment.Through the analysis and analysis of experimental data of remodeling samples,the qualitative effect of each index on the expansion characteristics s verified.Based on the experimental data of the original sample and the remodeling sample,the quantitative formulas of the swelling characteristics with the clay mineral composition,initial dry density,and particle size of the detritus are proposed.Swelling characteristics with clay mineral composition,initial dry density fits formula y = kx + b,and it is linear changes;The expansion force rate is nonlinear with the change of the debris gradation.There are three different nonlinear formulas under different conditions.The swell force rate will exhibit an inflection point when the moisture content is about 12%.Before the inflection point,the swell force rate increases slowly with the moisture content.After the inflection point,the swell force rate decreases rapidly with the moisture content.Through the analysis of remodeling experimental data,it is found that the clay mineral content is about 20%,with a certain dry density of 1.7g/cm3,the particle size of the detritus is 0.4-0.8mm,and the criticality of expansion often occurs when the moisture content is above 12%.value;It is concluded that the impact of each index on the expansion characteristics is related to clay mineral content>water content>dry density>detritus particle size.Finally,the controlling factors for the swelling characteristics are clay mineral content and moisture content.