The Study On Stability Of Typical Structure Embankment Of The Qinghai-tibet Railroad At The Permafrost Regions Under Train Dynamic Load

The Golmud-Lhasa section of the Qinghai-Tibet railway (QTR) is1,142kilometers in length，of which546.41kilometers crosses large areas of continuouspermafrost regions (the talik region of the permafrost area is101.68kilometers). Theproportion of distance embankment is about72.3%of the total length in thepermafrost regions in. Since QTR opened for operation on July lst，2006, thelong-time stability of the QRT has been concerned, because the problem ofpermafrost engineering. The Thermal condition of the embankments along theQinghai-Tibet Railroad and the permafrost underground is a key factor whichinfluences the stability of roadbed in the permafrost areas.With the purpose of protecting the permafrost effectively and maintaining thestability of embankment in the permafrost areas，positively protective engineeringmeasures were taken in constructing the railway.Especially at the Beilu Riversegment, different embankments are presented, such as crushed/blocked rockembankments, ventilated railway embankment, thermal insulation material,thermosyphon, embankment with crushed-rock slope protection, reasonable heightembankment, shadow shield embankment, assembled culvert, et al. The protectiveeffect on protection the permafrost is obvious. However，during the completion andoperation of the railway, some diseases have been appeared at some sections inpermafrost regions, which affect strain speed and safe operation. Therefore, studyingon embankment stuation in permafrost after operation of the railway is the key ofassurance of its long-term, safe and reliable operation in permafrost regions.That the methods of field survey and related data collection and analysis, thereal time vibrating tests, theoretical analysis and calculation have been adopted forstudy the dynamic response characteristics of different structure embankmentsunder train vibration load at the Beilu River segment of the Qinghai-Tibet Railroad.The train vibration attenuation rule of the railroad embankment at permafrostregions has been obtained. Based on the real time vibrating tests in-situ, the dynamic finite element analysis method of two dimensions linearly equivalent was appliedfor dynamic response numerical calculation on the typical embankments. Moreover,based on the laboratory triaxial compression creep test, time hardening powerfunction rule and Druker—Prager yield and failure criterion coupled creep model ofthe ABAQUS FEMA program were utilized to simulate the creep effect of the plainfill embankment at the permafrost area of Qing-Tibet Railway. Some innovativeconclusions are presented as follows:（1）In permafrost regions, the vibration effect on the surface of the plain fillembankment during the transfer process from road shoulder to slope toe is strong,and this kind of structure is not conducive to maintain the dynamic stability of theembankment.（2）During the transfer process from road shoulder to slope toe, the vibrationresponse of same components of the embankment excellencies intensive. Thedifferent components of the embankment are absorbed. The natural frequency ofcrushed/blocked rock embankment, plain fill embankment is during30-40Hz, andventilated railway embankment is40~50Hz respectively.（3）There is an obvious attenuation effect during the transfer process fromroad shoulder to slope toe, the value of vibration attenuation in warm season isgreater than that in cold season. The vibration attenuation in plain fill embankmentis greater than that in crushed rock embankment.（4）The maximum settlement at both plain fill embankment and blocked rockembankment occurs at the top of these two embankments, The maximaldisplacement reaches0.018and0.020mm respectively. However, as for the purposeof vibration settlement control, the effect of blocked rock embankment is better.（5）The time hardening power function rule and creep model simulate the timeeffect during operation of the railway embankment accurately, vertical displacementdecreases gradually from center of embankment top to inside and both sides of theplain fill embankment. The maximal displacement reaches14mm in one year, andthis value coincides with the result of deformation observation in-situ.（6）The creep strain value of center is greater than that of top and naturalground of the embankment, and the center of embankment is mostly influenced by dynamic vibration of trains. And the creep strain value of slope declines from thecenter in the same height, and the strain value increases along the embankmentheight.