Buckling of vertical sandwich cylinders embedded in soil

Composite or sandwich materials have been used in the construction of pipelines for some time, but not for the construction of inspection cameras, which are buried vertical cylinders that connect the pipeline with the ground. This paper explores the buckling and post-buckling behavior of vertical sandwich shells under lateral pressure, considering typical dimensions of inspection cameras employed in the industry. The analysis is carried out using a finite element model including geometric nonlinearity, in which the shell and the soil are represented together with the contact zone between them. Parametric studies are reported to account for the influence of shell slenderness, imperfection amplitude and soil elasticity. Results are also compared with those obtained for a circular ring under similar lateral constraints. The results show that for a shell in rigid soil the critical loads are higher than in the case of elastic soil, but the sensitivity with respect to imperfections in the geometry is also high. Cylinders in an elastic soil, on the other hand, tend to have lower buckling loads and moderate imperfection sensitivity. Finally, a ring model leads to good approximations to buckling loads but does not adequately represent the post-buckling behavior of a shell in this problem.