Introduction and development of soil thermal stabilization technologies at the objects of oil pumping station-2 (OPS-2) of "Kuyumba - Tayshet" trunk oil pipeline

The article deals with the questions of designing the foundations for the Oil Pumping Station-2 site of "Kuyumba - Tayshet" trunk oil pipeline. The problems of choice and grounds for technical solutions are considered basing on the results of complex thermotechnical calculations. The construction territory of OPS-2 site of "Kuyumba - Tayshet" trunk oil pipeline is characterized by complex engineering and geocryological conditions: 1) presence of permafrost soil on 80 % of the site area; 2) absence of sufficiently widespread rocky soils under designed buildings and constructions; 3) transition of loamy grounds into yield during thawing. The buildings and facilities are designed on the basis of pile foundation type with high rigid foundation grill. The piles’ diameter is 325 mm and 426 mm, the total length of piles is 9-12 m. The full designed vertical loading, transferred to the pile, is ranging from 10.6 to 50.4 tf. According to the results of the calculations, in order to provide the necessary bearing capacity of piles, securing the perception of transmitted designed loadings, the equivalent temperature of the soil along the side surface of piles ( e) should not be higher than -0,5 °C. Taking into account that the soil temperatures on the projected site mainly range from -0.1 to -0.3 °C, in order to lower their temperatures to the calculated values ventilated underground areas are arranged under the buildings and facilities and seasonally active cooling devices (soil thermal stabilizers) are installed. Assembly technique and construction of ventilated underground areas with application of soil thermal stabilizers were developed earlier while designing the pipeline system "Zapolyarye - Oil Pumping Station Purpe". For confirmation of the accepted decisions forecasting thermotechnical calculations were performed with the use of a special computer program TermoStab 67-87, which allows simulating the changes of temperature regimes of the permafrost in the process of construction and operation of the facility. As a result of thermo-technical calculations, in case of operation of ventilated underground areas only, in the foundation of the facilities at the OPS-2 site (without the application of thermal stabilizers) a reduction in temperature of frozen soils is predicted, however, the required design temperatures, necessary for providing the bearing capacity of piles (-0,5 °C on their side surfaces and below), in one cold season cannot be achieved. For the areas of the distribution of the confluent type of the permafrost the necessary temperatures are achieved only by the 5th year of operation, and for the areas of distribution of non-confluent type of permafrost such temperatures are not achieved even by the 10th year of operation. A joint operation of the ventilated underground areas and soil thermal stabilization systems is conductive to the reduction of soil temperature of the buildings and facilities’ foundations up to the required values, which secure the load-bearing capacity of piles for one cold season