Numerical analysis of pipeline uplift resistance in a frozen clay soil subjected to temperature changes

Frozen clay soils comprise a large portion of permafrost in Canada. Long-term records indicate an on-going global warming has resulted in the thawing of portions of the permafrost area, which leads to extensive settlement of the ground surface and causing damage to infrastructures such as pipelines. The design of buried pipelines in permafrost region or artificially frozen grounds requires knowledge of the uplift resistance. The uplift resistance of a frozen soil is dependent on soil mechanical properties such as tensile strength, shear strength, and deformation modulus, and those properties are critical for characterizing the plastic yielding zones in the frozen soil around the pipe. Due to the existence of a large amount of unfrozen water, frozen clay soil displays complex mechanical properties which vary with temperatures. Previously, extensive experimental and simulation work has been done on the soil pipe interactions at normal temperatures, but less attention is given to the frozen soil pipe interactions. There are limited researches on frozen clay pipe interactions with the consideration of temperature changes. In this study, the finite element analysis is conducted to investigate frozen clay soil-pipe interactions at varying temperatures, where a pipe is simulated as being subjected to vertical load-controlled or vertical displacement-controlled stress path conditions. The temperature-dependent mechanical properties of frozen clay soil are obtained from the literature. Both tensile yielding and shear yielding behavior are included in the modeling and the temperature-dependent yielding surfaces are included in an explicit way. Modeled stress paths in several soil monitoring points are collected and analyzed. A comparison of results from the Mohr-Coulomb model with tensile cut off and the hyperbolic Drucker-Prager model is presented. The results indicate that hyperbolic Drucker-Prager model is an effective model for analyzing the plastic zones. Under a plane strain condition, the applied hyperbolic Drucker-Prager model gives more conservative uplift resistance-displacement relation when compared with the result from the Mohr-Coulomb model