Optimization of design solutions for main pipeline projects in conditions of island and intermittent permafrost

The results of numerical experimental studies on optimization of construction of main pipelines in areas of intermittent and seasonally melting permafrost are presented. The paper is devoted to inexpediency of an above-ground method of laying the pipeline on supports in small areas of island permafrost zones characterized by solid ice lenses and heaving mounds. Alternatively. the method of underground anchoring of sections using specially designed anchor supports on flexible rods is proposed. The design of these supports takes into account the features of alternating seasonal loads that occur in various variants of thawing trenches in frozen rocks under the influence of ambient temperatures and the pipeline itself. In order to assess the stress-strain state of underground sections that deviated from the design position, a multi-factor finite element model was developed that allows to calculate the permissible loads and determine the places of dangerous cross-sections for selecting the maximum step of placement of supports. As a result of calculations performed using the developed mathematical model in ANSYS. it was confirmed that it is not practical to use thermal insulation. the weight of which repeatedly increases the level of tension at dangerous sections. both when surfacing and when sagging sections in a thawed trench. For a pipeline with a diameter of 1200 mm, the permissible values of spans are defined - the maximum step of placement of underground supports. Using the developed model, optimization calculations were performed for various combinations of constant and variable loads, during which the possibility of reducing the number of support structures by eliminating thermal insulation, limiting the installation temperature and laying the underground section with an elastic bend in the direction opposite to the predicted deflection of the pipeline axis during thawing of the soil was confirmed.