The main purpose of the report is analysis of stability of an artificial island for gas field development. The stability analysis is made in 3D on the basis of analyzing the stress-strain state of the structure - foundation system, with account for staged load application (own weight, equipment weight and ice load). Coulomb-Mohr model is used for foundation soils, strengthening soil model with account for relationship of soil stiffness on stress for filled sands of the artificial island.
The artificial island is constructed for development of a gas field in the sea 10–12 m deep (Fig. 1). The island has a protective contour consisting of separate floating pontoons connected with each other. In the horizontal plane, the protective contour is a regular octagon which consists of 8 submersible welded metallic pontoons, each 80 m long. To secure the pontoon to the soil, it has a skirt 1.5 m high, made as crossing plates. The pontoon body material is steel. The thickness of the casing is 0.022 m. The inner space of the protective contour is filled with sand. The resulting territory is used for processing equipment accommodation. The artificial island is subjected to wind, wave and ice loading of all directions. To protect from ice and waves, the site of processing equipment is made 2.5 m higher than the water surface. The geological engineering conditions of the planned site of the artificial island are of medium complexity because there are weak sandy-clayey formations of marine alluvial, alluvial, lake alluvial genesis, represented by mud, silty clay and fine sands, in a significant part of the soil foundation (first 10 meters). The clayey deposits are yield and plastic.
The stability (bearing capacity) of the structure - foundation system is ensured if the following criterion is met.