Analysis Of The Effect Of Frost Heave On Soil-buried Pipeline In Permafrost Regions

Frozen soils are widely distributed in the northeast and western regions of China,which can be simply divided into short-term frozen soil,seasonal frozen soil and permafrost in terms of their durations.Due to needs of infrastructure construction,it is necessary to build the oil and gas pipelines in frozen soil areas.Damages to the oil and gas pipelines induced from frost heaves occur frequently every year.Therefore,in order to reduce losses caused by frozen heaves,in-depth researches on pipeline damages in frozen soil areas are required,according to which effective technical support for pipeline design,construction and maintenance can be provided.Based on the existing studies,an improved model on the calculation of internal forces and displacements of pipelines under the action of soil frost heaves is developed,by which the influence of frozen soil frost heave on pipeline in frozen soil area is analyzed.The conclusions are presented as follows:1)On the basis of the mechanism on the formation of frozen soil,moisture migration and phase transformation triggered by the change of temperature field will lead to frost heave and thaw collapse of frozen soil,and finally cause the vertical displacement of a buried pipe,which can generate stress in pipe.When the stress is greater than the yield strength of pipe,damage will happen.2)Based on the controlling factors of the lateral resistance exerted on pipe by soil frost heave,the formula for calculating internal force and displacement of pipe under the action of soil frost heave is accomplished by using the simplified description on the relationship between lateral resistance pipe displacement and the analysis of pipe deformation.With the use of the result given by the above-mentioned formula,it can be found that the dangerous section of the pipeline is located near the interface between the frost heave sensitive soil area and the stable frozen soil area.3)The model for calculating the temperature field around the pipe is established.Accordingly,through adopting the concept of flocculation potential with respect to the change of temperature,it is analyzed that the effect of soil freezing depth and frost heave displacement on both of lateral resistance and pipeline displacement.