Research On Uplift Calculation Method And Track Structure Response Of High-speed Railway Caused By Micro-expansion Mudstone Foundation

Ballastless tracks for high-speed railways have been widely applied due to their significant rigidity,high durability,excellent safety.My country’s high-speed rail has developed rapidly in recent years with the guidance of the country’s "transportation power" policy.However,the problem of uplift deformation for the ballastless track subgrade caused by the micro-expansion mudstone has become increasingly prominent.There is no suitable theory and calculation method for calculation of the heave of micro-expansion mudstone in foundation for high-speed railway at present.And more empirical formulas are obtained by laboratory tests or field tests.Due to the different emphasis of these formulas,the calculation results of the swelling amount are often quite different.Therefore,the basic research was carried out by indoor experiment,field test,theoretical derivation and numerical simulation methods in this article.The expansion mechanism was revealed,the micro expansive mudstone dilatability quantitative assessment method was established,and the heave mechanism of ballastless track subgrade on micro-expansion mudstone foundation was illustrated,as well as the multi-factor coupling micro expansive mudstone foundation under the action of frantic jumble track subgrade on arch calculation method was proposed.The effect of micro-expansion mudstone deformation on track structure was further analyzed.The research results can provide theoretical basis for the design,construction and maintenance of ballastless track in micro-expansion mudstone area.The main research work of this paper is as follows:The non-expansive mudstone judged by the existing railway code was divided into four expansion grades Ⅰ,Ⅱ,Ⅲ,and Ⅳ.NMR tests and SEM tests of different micro-swelling mudstones under different water content were carried out.The particle morphology and pore structure changes of micro-swelling mudstones after immersion swelling deformation were analyzed,and the expansion and deformation mechanism of micro-swelling mudstones were revealed.The equivalent montmorillonite content,cation exchange capacity,free expansion rate and liquid limit are selected as the indexes of swelling property of mudstone based on a passenger dedicated line in the west of China.The grading standard for swelling expansion potential of mudstone is proposed based on a large number of field measured data of mudstone borehole.The combined weights of discriminant indexes are determined by the improved analytic hierarchy process,gini coefficient method and relative entropy theory.A quantitative evaluation model for the swelling property of mudstone is established based on the linear comprehensive evaluation method.The applicability of the evaluation method and classification standard to the micro-expansive mudstone for Lanzhou to Xinjiang Railway was verified by laboratory test of expansive force.The in-situ test of weakly expansive mudstone foundation under different overburden loads was carried out by artificial flooding method in the heave for a passenger dedicated line in the west of China.And the overall swelling deformation characteristics of micro-expansive mudstone foundation were studied under overburden loads of 0,15,30 and 45 k Pa.The development process of swelling deformation and the law of the swelling change with the amount of water and the overlying load were analyzed.And the uplift deformation mechanism for the ballastless track subgrade of the micro-swelling mudstone foundation was revealed.Based on the expansion mechanism of montmorillonite,a method for calculating vertical and transverse expansion forces of micro-expansive mudstone considering water content and expansibility was established.By introducing the classical viscoelastic theory and the elastic solution of Mindlin’s half-space action concentration force,the calculation method of subgrade heave under the coupling action of expansion-water-content-thickness-overburden load of micro-expansion mudstone foundation with high iron was derived theoretically.The correctness of the calculation method compared with the results of numerical simulation and field test was verified,which provides a theoretical basis for the design and construction of ballastless track in micro-expansive mudstone area.The expansion-force calculation formula proposed in this paper was embedded into ANSYS finite element model.And the micro-expansion mudstone foundation for high-speed railway ballastless track subgrade structure model was established.The track structure response caused by the upward arch of the micro-expansion mudstone foundation was studied.The variation law of rail vertical displacement,rail axial stress,equivalent stress of rail plate and equivalent stress of base plate was analyzed under different moisture content,swelling and water absorption thickness of micro-expansive mudstone foundation.The influence law of uneven uplift deformation of micro-expansive mudstone foundation on the stress of structural layers and smoothness of track surface for ballastless track was revealed.