Research On Microscopic Expansion And Contraction Mechanism And Engineering Characteristics Of Expansive Rock Based On Xicheng Line

The total length of Xining to Chengdu railway is about 570 km,of which the part of the Xining to the Xiahe section,whose length of which is about 180 km,passes through the third series of strata and it is mainly mudstone of Guide formation and Linxia formation.According to the experimental data in the preliminary stage,this mudstone is generally expansive and has great influence on tunnel,subgrade and bridge engineering.At present,many researches on expansion and contraction mechanism of expansive rock have been carried out at home and abroad.But the previous research usually studies the macroscopic law of expansive rock from the angle of geotechnical engineering,for example,considering the volume change of the expansive rock and soil to make modeling analysis,making equation derivation for the infiltration and consolidation of the remolded expansive rock(soil),and making formula deduction and physical modeling for expansion and contraction of swelling rock and soil and so on,while there are not only few studies on the intrinsic micro expansion and contraction mechanism of expansive rock,but also few studies on the upwarp and deformation of the strata caused by no or weak expansive rock in practical engineering.:This paper aims at carrying out research work in this aspect.Through reading a large number of documents and consulting relevant geological data,combining with the investigation work of the Chengdu railway in Xining,from the angle of Geology and minerals,this paper analyzes the basic engineering geological characteristics of two research areas in Pingan and Jianzha,and analyses the time distribution,lithologic features and types of the strata in this area.In this paper,the basic characteristics of the original samples,such as physical properties,water properties,expansion characteristics and strength characteristics are obtained through laboratory tests.By using X ray diffractometer,electron scanning microscope and chemical method,the origin of weak swelling rock,mineral composition,mineral microstructure,mineral cementation and ion types are studied from microscopic angle,and the deformation and disintegration characteristics of this kind of swelling rock after immersion are observed to study the relationship between the intrinsic micro expansion and contraction mechanism and its engineering characteristics.According to the requirements and standards for the formation deformation of the high speed railway,this paper puts forward the evaluation standard of the expansibility of the mudstone which is in line with this section,and makes a quantitative classification of the mudstone in the test area.In this paper,the test of the in-situ expansion and deformation of the typical section of the site is carried out to determine the bearing capacity of the mudstone foundation in this stratum,and to analyze the deformation law of the mudstone after the immersion of the mudstone,as well as the lawof the expansion and deformation of the soaked mudstone under the same overburden condition with the different strata,and provide reference and train of thought for the treatment scheme of the expansive rock.