Buckling of Soil-Surrounded Tubes

A bifurcation buckling theory was derived for the case of a tube surrounded by soil with the postulate that outward buckling displacements are prohibited and the inward displacements are retarded by an elastic reduction in external soil pressure. A single wave form buckling mode results which matches experimental evidence qualitatively. The proper choice of apparent thickness of the tube to account for imperfections and empirically computing the spring constant of the soil permits a good correlation with published data on the buckling at soil-surrounded tubes. A graphical procedure is presented for solving for the buckling pressure, the subtended angle of the local buckle, and the mode numbers defining the buckled shape. It was found that the effective spring constant of the soil varies with the local effective stress of the soil and, to a lesser degree, the thickness of the surrounding soil cylinder.