Experimental Study On Permeability Characteristics Of Microexpansive Mudstone In Ballastless Track Of High-speed Railway

With the continuous development of China's high-speed railway construction,the line inevitably passes through some unfavorable geological areas,and the high-speed railway construction requires high smoothness,comfort and safety of the line.Therefore,new requirements are put forward on how to better adapt to the high-speed railway construction standards for different foundation soils.The mudstone with weak expansibility in the foundation of Lanxin Railway has caused many roadbed archs in the construction and operation,which brings challenges to the normal operation of high-speed railway.Taking the mudstone of Lanxin Railway foundation as the research object,this paper systematically studies the swelling deformation and permeability characteristics of the mudstone of low clay mineral of high-speed railway by field investigation,laboratory test,large-scale model test,in-situ immersion test and numerical simulation calculation.The main research work is as follows:(1)Based on the field investigation of typical upper arch section of Lanxin Railway,the causes of subgrade arch are analyzed from the aspects of topography,hydrogeology and core drilling sampling.It is concluded that mudstone is the possible cause of subgrade arch.(2)Taking low clay mineral mudstone as the research object,the basic characteristics of mineral composition analysis,free expansion rate,liquid limit and cation exchange capacity were tested.It was found that there were a small amount of expansive minerals such as montmorillonite,and the results of free expansion rate and cation exchange capacity showed that it had expansibility.(3)In order to further determine the macro-expansive deformation characteristics of mudstone with low clay minerals,indoor expansive deformation test and expansive force test were carried out.The influence laws of thickness,overlying load and water content on expansive deformation,expansive characteristics of soil and water content on expansive force were analyzed.(4)Saturated permeability test and unsaturated permeability test of mudstone were carried out to determine the saturated permeability coefficient of undisturbed mudstone in situ,and the difference of permeability coefficient between undisturbed and remolded soil was compared.Based on the factors affecting soil permeability,the influence of overlying load and dry density on saturated permeability of mudstone is studied.The correlation between soil permeability and pore structure is analyzed by mercury injection test results.The permeability model tests of unsaturated soils under different overlying loads were carried out using self-made infiltration cylinders.The attenuation law of soil moisture transfer rate with infiltration distance and overlying loads was obtained.(5)Expansion tests under different overlying loads were carried out in situ.The development law of expansive deformation,the relationship between overlying load and expansive deformation and soil moisture content were analyzed,and the attenuation law of soil moisture growth rate with overlying load and infiltration distance was analyzed.(6)Combined with laboratory and in-situ tests,the causes and influencing factors of subgrade arch are analyzed.The main causes of subgrade swelling are low clay mineral mudstone and water,and the measures of subgrade arch treatment are discussed.