Dissertation
Dissertation > Transportation > Rail transport > Railway Line Project > Line constructed > Subgrade > Special areas roadbed

Study on Stability for Saline Soil Subgrade and Pile Foundation in Permafrost of Cold and Arid Region

Author LiuLu
Tutor WuYaPing
School Lanzhou Jiaotong University
Course Road and Railway Engineering
Keywords Cast-in-place Pile Group Hydration Heat Refreezing Rate Saturated FineSand Creep
CLC U213.14
Type Master's thesis
Year 2013
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With the pace of China’s western development progresses, more and more railways,highways and other transportation projects and facilities are built in the western region andput into use gradually. Such as the Qinghai-Tibet Railway line linking and put into operation,which greatly facilitates the Tibet region and the eastern part of the economic and culturalexchanges. At the same time, in order to accelerate the development of the local economy inQinghai and other western provinces and cities, many local railways are built to facilitate thedevelopment and utilization of regional resources with nearly the pace of large-scaledevelopment of the western region. However, special soil such as permafrost, saline soil isdifferent from the general soil due to the special geographical location and natural climaticconditions of the western, which bring difficulties and inconvenience to the construction ofrailways, roads and other engineering structures and safe use of them.In railway construction process of the permafrost regions, in order to ensure the smoothrailway construction and safe operation, the "Bridge-Instead-of-Embankment" dry bridgestructure to the principle of the protection of permafrost in the design of the Qinghai-TibetRailway construction has been a large number of applications. However, due to drillingfriction heat in the process of bored pile construction, concrete hydration heat, and moldingtemperature, it is inevitable to bring thermal disturbance to permafrost, which may causes soilmelts around the piles, so that the pile bearing capacity drops to affect the progress of theconstruction of the railway and safe operation. In this paper, with railway bridge engineeringexample in the permafrost area, consider the field hydrogeological conditions, atmospherictemperature changes, initial ground temperature field, concrete casting temperature andphase-change effect, deduced three-dimensional heat conduction equation of concretehydration heat within the pile foundation and permafrost, and given the initial conditions andboundary conditions at the same time. On this basis, geothermal field of finite element modelof pile in frozen is established, calculate and analysis impact on foundation permafrostrefreezing process between hydration heat of a common concrete with low temperature earlystrength and hydration heat of a new type of concrete with low hydration heat lowtemperature and early strength. Results obtained both the foundation permafrost temperaturefield is basically the same law. But due to the different hydration heat between the twoconcretes, refreezing time of permafrost which surrounding the ordinary concrete pile lagslightly in the same position at the new low hydration heat low temperature early strengthconcrete pile, while the former refreezing rate also smaller than the latter, and this differencestill can not be completely eliminated in five years after casting. The low hydration heat lowtemperature early strength concrete can significantly shorten the construction time. In order to make more effective development and utilization of the local domain salt lakenatural resources to promote the rapid development of the local economy, the railway isconstructed between Xitieshan and North Hob Johnson in North Hob Johnson Lakes region inQinghai Province. However, in North Hob Johnson Lakes railway subgrade foundationmemory in large tracts of the surface is covered with a salt crust with high salt saturated finesand due to the saline lake of cold and arid region the special engineering geologicalconditions, which causes difficulties in building of the railway in this region. To summarizethe settlement laws of high salt saturated fine sand subgrade, and evaluate the treatment effectof the foundation on this basis, in this paper three-parameter H-K model is selected tosimulation analysis the rheological deformation of the test subgrade, and gives constitutiveequation and creep equation. Using ANSYS finite element software to calculated settlementdeformation of high salt saturated fine sand subgrade model, combined with field settlementtest data, and verify reasonable ground treatment of the region. And at the same time, analysisand forecasting the seasonal frost heave deformation of the subgrade, combined with indoorfrost heaving test and field test. The results obtained that there may be frost heave disease inthis region and it is recommended to take certain anti-frost heave measures.

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