Numerical Calculation For The Temperature Coupled With Moisture And Stress Of Soil Around A Buried Pipeline In Permafrost Regions

Frozen soil also known as ice contained soil, it is the composite soil that composed of porous media skeleton, ice crystals and unfrozen water. According to the frozen time, it can be divided into short-term frozen soil, seasonally frozen soil and permafrost. The frozen soil is extremely sensitive to temperature. The frost heave and the thawing settlement are two big disasters in frozen soil construction that was caused by the property of long-term strength far lower than the instantaneous intensity. The common security problem is freezing damage with the buried pipeline that crossing the seasonal frozen soil and permafrost soil. As the moisture-heat sensitivity of the frozen soil environment that make a certain lag on the destruction of the underlying frozen soil, so that the adverse effect of the frozen soil on the pipe is often gradually appear only after a certain time of the production. So to make sure that the pipeline could operate securely and steadily, we should study the problems of the frost heave and thawing settlement deeply. The consideration of the mutual constraints among the three fields of frozen soil temperature field, water field, stress field would have practical significance to formulate the scientific and effective injury prevention methods, and it can help to master the process of the frost heave and the thawing settlement and make proper predictions of the freezing-thawing damage.As the soil is a kind of natural porous media, coupling water and heat in frozen soil porous media mathematical model is established in this paper. Starting from flow mechanics and heat transfer principles, numerical calculation on the temperature field coupling of moisture and heat of the soil around the buried pipeline in permafrost regions is done by the finite volume method. The frost heave stress and strain of the after calculated coupling of moisture and heat temperature load vector is analyzed by the finite element methodThe main work of this paper:(1)The effect of moisture migration, ice phase transition on frozen soil temperature.Models of porous medium coupling of moisture-heat and heat conduction are established. Numerical calculation of two critical state of saturated water contained frozen soil and none water frozen soil is respectively done. The effect of moisture on frozen soil temperature field and buried pipelines unsteady heat transfer is analyzed.(2)The mathematical model of unsaturated frozen soil (porous medium) coupling of moisture and heat is established.Multiphase porous media (water phase-gas phase) mass transfer mechanism is expatiated. The mathematical model of unsaturated frozen soil coupling of water, gas and heat is established. The effect of different water content rate on the temperature field of frozen soil is analyzed.(3)Take the frozen soil engineering of China-Russia crude oil pipeline for example, the numerical calculation of coupling of moisture, heat and stress is done.There is nearly 50km swamp frozen soil along the China-Russia crude oil pipeline. It can be regarded as saturated water contained tundra. Numerical calculation on this region coupling of moisture and heat of the soil around the buried pipeline is done by the software. And the frost heave stress and strain of the after calculated coupling of moisture and heat temperature field is analyzed by the software. (4)The mathematical model of porous media temperature coupled with moisture and stress in frozen soil is original explored.The mathematical model of (porous media) temperature coupled with moisture and stress in frozen soil is originally established by summarizing results of previous studies and combining of filtration, heat and mass transfer, engineering thermal physics, engineering mechanics.