The Study On The Deformation Low Of Subgrade In The Second Lanxin Railway In Permafrost Regions

The second new railway of Lan Xin goes through three provinces of Gansu, Qinghai andthe Xinjiang Uygur Autonomous Region, the main line is about1782kilometers long, thedesign speed is more than200km/hour, the permafrost which the Ganqing lines of the newsecond railway from Lanzhou to Urumqi use has the genotype of high thermal sensitivity andlow thermal stability. The change of seasons brings about the occurrence of freeze-thawcycling; the phase transition of the water in soil easily caused the roadbed deformation andcracking. This thesis is based on fundamental knowledge of the permafrost and the practicalexperiences in Qinghai Tibet Railway, making an analyses on the factors of deformation andthe deformation law on which the new second Lanxin Railway Subgrade in permafrostregions of Gansu to Qinghai DK366+021.00~DK366+089.44segment show.The main contents and results of the research:(1) Based on the understanding of the fundamental knowledge of permafrost and frozendamage mechanism, the thesis makes analyses on the new second Lanxin railway geologicaldistribution, the railway roadbed designing principles and construction methods. The result:the designing principle of Railway Roadbed in permafrost region of Qilian Mountainsincludes protecting permafrost, allowing melting and controlling melting rate.(2) By referring to relevant information on the new second Lan Xin railway and thedeformation influence factors about permafrost. The analysis result: Taking methods toreduce the solar radiation, heating conduction and thermal convection, which will do good toimprove the thermal stability of Subgrade in permafrost region of Qilian Mountains.(3)Combining with previous research on the control equation of the non steady statetemperature field and the basic stress-strain equations, the thesis deduces the thermal-stresscoupled equations, providing a theoretical basis for the research on Numerical Simulation ofSubgrade in permafrost region mathematic equations for roadbed deformation.(4)The thesis establishes a two-dimensional finite element model through the finiteelement software ANSYS to calculate the distribution when the trigonometric function oftemperature load is applied, and the stress field coupling of temperature andstress,deformation calculation and analysis of deformation of roadbed, the analysis show thatthe temperature field decreases gradually along the longitudinal with the changeabletemperature outside and melting state of the frost heaving force decreases, cause roadbedsubsidence deformation,during melting,The increase of temperature made frost heaving forcedecreased the ice of soil melt into water,soil is compcated under the gravity which land todeformation of roadbed.during freezing, the temperature is decreased in the winter,the waterof soil began frozen from top to bottom. Due to the affection of temperature gradient andcapillary theory, the water of soil is moving to ice surface gradually.The water became in toice,the volume of ice is expand.ice crystals produce frost heaving force until the volume of iceis lager than the gap between the soil grains.When frost heaving force is larger than cohesive force and gravity between the soil grains,frost heaving force increases quickly land to theupward expansion deformation of roadbed.(5) Combining the new second Lanxin railway on permafrost area and analyses on thefactors of deformation and deformation results, the thesis make a research on how to reducethe deformation of roadbed caused by changeable temperature. Analysis result: When theoutside temperature is high, the internal temperature of subgrade is higher as well, The frostheaving force of subgrade decreased,the roadbed produce deformation of subsidence. weshould choose large latent heat of freezing unit volume.we should adjust the embankmentheight in the construction according to the road properly. When the outside temperature is low,the internal temperature of subgrade is lower as well, that increase the frost heaving force ofsubgrade, when the ice volume is larger than the gap between the soil grains, frost heavingforce increases quickly land to the upward expansion deformation of roadbed. Usually, wetake some measures such as changing soil、thermal pipe embankment and the drainage ofSubgrade to decrease the deformation of Frost heaving force; The foot of the slope ofsubgrade is the main position of stress concentration, we should construct in accord with therequirements of the design specifications of subgrade strictly. Eliminate waste slopephenomenon, design the side slope and the height of embankment rationally, using thecomprehensive treatment scheme to protect permafrost.