Study On Microstructure And Swelling Charactristics Of Mudstones In Xining Region

With the rapid development of high-speed railway in China,the harm of expansive rock to railway is becoming more and more serious.In the construction of BOLN passenger dedicated line and Lanxin second line high-speed railway,there have been engineering problems such as cracking of the inverted arch of the tunnel and subgrade arch due to weak swelling mudstone.Therefore,the study of microcosmic expansion mechanism of mudstone can enhance the theoretical knowledge of rock expansion properties.And it also has great significance to engineering geological hazards.Taking the mudstones of the Guide Formation,the Xianshuihe Formation,the Zhongzhuang Formation and the Minhe Formation in the Xining area as the research objects,we had obtained the drilling samples.Around the physical properties,mineral composition,microscopic characteristics and expansion characteristics,the mineral composition,micro characteristics and pores of the mudstone in different geological times are made.The relationship between microstructure characteristics and expansion characteristics is analyzed,and the relationship between micro characteristics and macro mechanical effects is expounded.Through the research,the major achievements and conclusions are summarized as follows:(1)The mineral composition and microstructure of mudstone in Xining area are studied by X ray diffraction(XRD)and scanning electron microscopy(SEM).The results show that clay minerals in Xining area are mainly illite,chlorite and kaolinite,and montmorillonite is only localized in part,and the non-clay minerals are mainly quartz and sodium.The main micro spatial features are flat,dense,surface to surface connecting the peace film and opening and surface to surface connection.The main pore type is interparticle pore,and the Image-Pro Plus software shows that the face rate,the pore diameter,the fractal dimension of the mudstone of the Minhe Formation are the smallest,and the degree of roundness is the most,and the same land is in the same place.In the same layer,the face rate,pore diameter,fractal dimension and roundness all increase with the increase of embedment depth.(2)Through the free expansion rate test,lateral confinement expansion test,expansion test and expansion process monitoring test,it is found that the expansion process of mudstone can be divided into three stages.In other word,rapid expansion stage,slow expansion stage and expansion stability stage,and conductivity can be used as an index of ion concentration change during the process of antireflection expansion.The relationship between expansion force and rate is also divided into three stages,namely,rapid growth stage,slow increase stage and stable stage.(3)Through regression analysis,there is a certain correlation between clay mineral content,face rate,roundness,fractal dimension,average diameter and expansion force(rate),of which the correlation between clay mineral content and expansion force(rate)is weak,and structural factors(face rate,roundness,fractal dimension,average diameter)and swelling force(rate)is strong.It is indicated that the structural factors of mudstone in Xining region play a major role in the expansion characteristics.