Ninth International Conference on Permafrost ... - IARC Research

Studies of the Freezing Soil Process at the Railway Contact System Supports toProvide Safe Transportation and Operation of FacilitiesS.A. Kudryavtsev, D.G.TsvigunovFar Eastern State Transport University (FESTU), Khabarovsk, RussiaIntroductionMaintenance and efficient operation of railway powerengineering facilities in regions with seasonal freezing andpermafrost soils are faced with serious difficulties connectedwith the bulging of contact system supports. Seasonal soilfreezing is one of the major factors taken into considerationfor contact system support foundations.The problem of frost heaving is characterized not onlyby the number of repaired contact system supports, but alsoby safe transportation, too. On sections of the Far Easternrailway, which pass through a permafrost area, a large numberof contact system supports has to be restored annually. Todevelop a reliable and stable foundation structure, an exactestimation of thermophysical and stress-deformed conditionsof heave-probable soils both at freezing and thawing isrequired.Studies of freezing, frost heaving, and thawing of soilsand their effect on contact system supports are complicatedprocesses and require further development. Their complexityis first of all explained by a great number of interactivefactors, changing in time and space. Studying these processesin natural conditions requires observations for a long periodof time, because the data of short-term observations may beaccidental.depth (m)temperature (C)-15 -10 -5 0 5 10 15 20 250-0,5-1-1,5-2-2,5Figure 1. Thermometric observation data.septemberoctobernovemberdecemberjanuaryfebruaryThermometric ObservationsTo check correctness of foundation designs used and searchfor new decisions in the field of construction, calculations,the utilization of structures, as well as establishing thecharacter of their interaction must be considered. Withseasonal freezing soils, monthly thermometric observationshave been organized on the Khabarovsk Section of the FarEastern Railway (8540 km.).They are:1. Thermal regime of the soil at the contact systemsupport.2. Geodesic control of the contact system supportposition.To watch the thermal regime, a temperature monitoringsystem, Thermoscan, had been used. It is designed to dowork for measuring temperature in continuous and singleregimes.The Thermoscan set includes a measuring block with acontroller, a measuring bus duct with temperature “sensors,”a pocket PC, a storage battery, and Thermoscan software.Numerical Modeling of the Freezing ProcessMeasurements of the thermo-moisture regime weremade with the help of numerical modeling. By analyzingFigure 2. The Thermoscan temperature monitoring system.the existent models of freezing and thawing of soils, amathematical model of numerical modeling of freezing, frostheaving, and thawing in an annual cycle has been developedby the method of finite elements in the space set, being acomponent of the programmed complex “FEM-models.”This complicated geotechnical task is done in two stages:The first stage solves the thermo technical task of definingtemperature and moisture fields for each period of time. Thesecond stage solves the task of defining stress-deformedconditions of fundamental soils in the process of freezingand thawing.We have simulated the process of freezing and heaving ofthe railway trial sector. Monthly calculations were made foryearly changes of the monthly average temperature in theregion. The maximum depth of soil freezing in the contactsystem support, without principally the thermal insulationlayer, was 2.0 m in March.Deformation of the principal area of the railway bedcaused by frost penetration is equal to 6 cm, and horizontaldeformation of the contact system support, about 3.5 cm.Use of expanded polystyrene thermal insulation materialslowers the freezing front (zero isotherm) to 1.4 m under the155