Sinusoidal Buckling Behaviour of Surface Casing with Negative Friction in Thawing Permafrost

During the development of oil fields in permafrost regions, once the surface casing buckling occurs under the formation thawing and subsidence, it will cause great economic losses. In this paper, sinusoidal buckling of surface casing under negative friction is studied and preliminarily discussed. Based on the Winkler foundation theory and considering the different distribution forms of negative friction and soil resistance, the elastic stability model of casing is established. Combining dimensionless and Rayleigh-Ritz method, the critical slenderness ratio of sinusoidal buckling is obtained. The influence of boundary conditions, soil resistance and negative friction distribution on casing stability is quantitatively analysed on the basis of sufficient data calculation. It is found that the product of the critical slenderness ratio and the square root of the strain at the lower boundary is a fixed value which only depends on the boundary conditions and the value of soil resistance parameter, and the negative friction of different distribution forms can be superimposed according to the principle of ‘inverse square’ of the critical slenderness ratio. On this basis, the approximate calculation formula of the critical slenderness ratio is obtained by fitting, and the average error is less than 0.4%. The numerical example shows that the increase of soil resistance will weaken the influence of negative friction distribution on the critical slenderness ratio significantly. The ability to resist sinusoidal buckling can be improved by increasing the constraint of the lower casing section and increasing the casing thickness.