Recently offshore pipelines are under active construction in the Russian Federation. The main advantages are their operating reliability, cost effectiveness, high efficiency and simplicity of operation. Offshore pipelines require differentiated approach to adopted technical and technological decisions depending on the natural and climatic characteristics of the region. Stability plays an important role for reliable and safe operation of offshore pipelines. One of the main conditions for stability is the strict adherence to standards and rules of calculation and design. But the standards cannot include all factors and force impacts to be taken into account. There are only general requirements to calculation and design of pipeline systems. Whereas the technical feasibility of all basic parameters necessary for reliability of offshore pipelines must be chosen and substantiated on early stages of design.

Stability of a pipeline depends on environmental loads and the trench (seabed) profile [1]. When calculating stability it is assumed that pipeline must preserve stable position on the seabed even in maximum possible seabed deformations in places where no soil layer is designed above the pipeline. Where there is no current influencing the trench of pipeline filled with the transported product buoyant force equal to the float displacement will be acting. Float displacement depends on the water-mass density: increase of density results in increase of buoyant force and reduction of pipeline stability on the bottom of the watered trench.

Works for development of hydrocarbon offshore fields (offshore pipeline lay, dumping) lead to concentration of suspended matter that manifold exceeds the natural level (figure 1). Time of existence and extent of suspended matter cloud can be determined by factors, the most significant of which are as follows: method of dredging (implementation of machines - dredging machines, sand suckers, hydraulic monitors, etc.); method and scope of disposal; current speed and depth at the disposal point; granulometric composition of suspended matter.

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