Baryshev, Vladislav N. (Far Eastern Federal University) | Sabodash, Olga A. (Far Eastern Federal University) | Tsimbelman, Nikita Ya. (Far Eastern Federal University) | Bekker, Alexander T. (Far Eastern Federal University)
An attempt has been undertaken to design an ice-resistant exploration platform for operations in the shallow waters in the Arctic seas on weak foundation soils. The platform is sufficiently mobile and able to resist significant horizontal loads while installed on weak foundation soils.
The proposed ice-resistant exploration platform is a combination of jack-up drilling platform and monopod. The monopod base is a steel pontoon, equipped with cylindrical columns. The columns are immersed into the ground in the operational position to ensure the perception of large horizontal load from the ice. This design can adapt to a range of depths, typical of the shallow shelf areas of the Arctic and enables extension of the drilling operations outside the navigation season.
In the article on the example of conditions in the Kara Sea, Ob’ and Tazov Bays the feasibility of the proposed design of exploration drilling platform is examined.
The following problems have been taken into consideration arising while discovering and developing hydrocarbon deposits in the arctic offshore: short navigation season; small depths in shallow waters; complicated wind and wave conditions; lack of coastal infrastructure
The discovery of large hydrocarbon deposits in the Arctic offshore area has given an impetus for the development of new projects of offshore oil and gas facilities. World experience shows that there is a necessity to create new engineering solutions for the development of hard-to-reach challenging water areas.
Oil and gas development in the area of interest using current mobile drilling platforms presents considerable difficulty due to severe hydro-meteorological conditions, with navigation season of about two months, as well as very complicated ice conditions. Besides, the water areas of Ob’ and Tazov Bays are characterized by prevailing soils with low bearing capacity such as silt and loams which forms difficulties while creating fail-safe and stable structures, especially in shallow water areas (Bekker AT, 2004).
The most well-known method of determining specific energy fracture of ice is the falling hard spheres method (Drop Ball Test -DBT), when the value of this magnitude is calculated as the ratio of the spent on fracture of ice energy of sphere after it struck on to ice surface to volume of the fractured ice in a sphere imprint in the ice. Earlier studies have shown that the ice crumbling layer by layer in such experiments, and specific energy fracture of ice is fairly stable, with the expressed the temperature dependence of ice only and not dependent on mass and velocity of indenter. But localization processes fracture the ice in the array is different from development fracture in the edge of ice field limited thickness, when ice sheet dissected by the vertical radial cracks and splitting by horizontal cracks on the trapezoidal and wedge-shaped blocks, which not separated from ice cover array in the distance from the contact zone. In this study adopted a form of ice samples trapezoidal beams such as in nature, as well as the scheme of deformation and fracture of samples like the fracture of the edges of these blocks in contact with the surface of penetration into the ice cover of the leg of structure. The objective of the laboratory experiments is the approbation of the testing method axial compression samples of ice trapezoidal and wedge-shaped to determine the specific energy of mechanical fracture of ice.
The methodology of identification of ice load acting upon structure is considered as a complex process for setting of actual problems. This complex process is based upon the ice destruction mechanism providing the transfer of a kinetic energy of drifting ice field upon the structure. Besides, in order to obtain the results of ice load calculation subject to the adequate processes related to real structures, it is essential to consider four procedures that shall be agreed during the investigation and designing process. At this, firstly, it is important to agree the calculation method of contact force resulting in ice destruction with applied criterion of its destruction. Secondly, the form and the size of sample shall correspond to real blocks destructed subject to compression due to the contact of ice field and structural support. Thirdly, in order to define the critical values of ice destruction criterion, the method and parameters of samples loading at the laboratory shall correspond to ice blocks loading parameters subject to field conditions, inclusive of its phenomenological particulars.
Sea ice is a very complicated natural material that consists of separate various shape and size crystals, inclusive of brine areas, air impurities and mechanical fractions. So, during the investigation of sea ice strength, the integral strength properties shall be mentioned inclusive of structural strength (links between its components) and fresh ice crystal lattice strength. The mechanical properties of ice depend upon its composition, physical state and temperature. The essence of mechanical and physical processes of ice destruction subject to contact with penetrated surface of structure support is the object of ten years investigation.
Introduction to the practice of new criteria designing of ice strength is a complex task, because one or another criterion of equivalence can be the basis for practical calculations of durability only subject to it empirical testing and the experiment results are reasonably close to the results of theoretical calculation. There are new results in determining of ice strength in massive (the method of logging tool tests) and in the mechanisms of destruction of ice field edge (consideration of vertical and horizontal radial and the circular cracks). Besides according to practical research in the field of mechanics of solid deformable body was defined that the energetical hypothesis of the strength is suitable for solution of ice fracture task. Subject to specific fracture energy of ice, the mathematical expressions for calculation of ice load are simplified, they become simple and clear. Investigations of the specific energy of mechanical fracture of ice via DBT method both in laboratory and in-situ were previously performed has shown the complete invariant nature of this criterion of ice strength, inclusive of high predictability and reproducing of results. Taking into account the laws of ice plate edges fracture, the methodological approach for calculation of ice load on vertical support of structure subject to specific energy of mechanical fracture of ice was considered herein.
Subject to the calculation of ice load acting upon a particular sea structure the third Newton's law was used during all the time of investigation of ice effects. Earlier the structure was considered as an rigid and in compliance with the ISO/FDIS 19906 (2010) and SP 38.13330.2012 (2013), ice breaking strength obtained via testing of small prismatic samples for uniaxial compression shall be assumed as a basic strength property of ice for calculation of load. The huge amount of studies has revealed the broad differentiation of ice fracture mechanism at the ice-structure interface.
Such differentiation appeared as a discrepancy of ice strength diagram from almost stable level per time up to cyclic variations (Peyton, 1968; Afanasyev et al., 1971; Schwarz, 1971; Kopajgorodskiy and Vershinin, 1973; Hyrayama et al.,1975; Korenkov 1976; Croasdale et al., 1977; Khrapaty and Tsuprik, 1979; Jordaan and Timco, 1988; Bekker et al., 1993, Kamesaki et al., 1996; Bjerkås and Skiple, 2005; Bjerkås, 2007; Karulin et. al., 2014; etc.). These mechanisms can be presented by ice fracture via crushing along the entire height of ice field edge; breaking; chipping of "wedges" adjacent to the upper and lower surfaces of the ice plate; as well as the alternation of ice fracture mechanisms depending on ice temperature, speed of ice field drifting, and relative size of structure s and ice thickness (Tsuprik, 1992).
The present article is devoted to the experimental research of strength and crack resistance of reinforced concrete eccentric compacted elements with high excentricity, armored with rhombic basalt-plastic reinforcement. All samples were fabricated and tested in compliance with a specially developed project. This project involves the investigation of two series of reinforced concrete samples. The first series of samples included armored with basalt-plastic non-metal reinforcement; the second series of samples included armored with steel reinforcement. The strength, crack resistance and stress-strain behavior of these samples were investigated. The comparative analysis of eccentric compacted elements armored with steel and basalt-plastic reinforcement under load was performed. The present article contains the results of obtained experimental data analysis.
The application of non-metal reinforcement in construction projects has the potential to increase significantly in the future. The mechanical properties of such reinforcement are notably increased; new technologies and new materials are being developed for its production. The technology of fabrication of basalt fiber was developed in Russia. (Osnos et al, 2010). This fact has prompted interest in its application However, this is subject to the production of basalt-plastic reinforcement that is close to steel in terms of its properties.
Basalt-plastic bars consist of a polymer matrix and reinforcing elements. Reinforcing elements consist of continuous strong basalt fibers combined into a rod. The distinctive feature of this reinforcement is the high resistance to corrosive and hostile environments, in particular, chloride salts, carbon dioxide sulphur dioxide, nitrogen oxides and others. Exposure to such environments significantly increases the need for repair of reinforced concrete structures.
Composite basalt-plastic reinforcement is a dielectric with a low coefficient of thermal conductivity. It is also radiotransparent, and magnetically indifferent, and as a result, in some cases, it can provide non-magnetic and dielectric properties to structures. The enhanced corrosion resistance of basalt reinforcement means that the risk of corrosion of the reinforcement is minimal. The life expectancy of structures reinforced with basalt-plastic reinforcement when exposed to corrosive environments such as sea water is approximately 80 years (STO 2.6.90-2013).
The problem of the offshore engineering constructions ice loads estimating now becomes more important due to the necessity of developing continental shelf oil and gas freezing waters of the northern seas and the Far East. Ice loads field measuring is time-consuming and expensive. Therefore, it is efficient for solving this problem to use methods of half field measuring and laboratory researches, which allow checking up scientific hypothesis in controlled conditions in comparison with field measuring.
The results of theoretical and experimental studies of the ice load formation in the ice plate cylindrical indenter cutting process regularities are given. Experimental studies were carried out for testing theoretical model of the ice plate structure destruction process before constructing. Specific features of study have been identified by theoretical model, i.e. determining the amount of construction loading cycles depending on the load (Bekker, AT, 1998). That is why carried out half field measuring studies showed definite range of changing boundary conditions covered by theoretical model.
Bekker, Alexander T. (Far Eastern Federal University) | Tsimbelman, Nikita Ya. (Far Eastern Federal University) | Chernova, Tatiana I. (Far Eastern Federal University) | Bruss, Vadim D. (Far Eastern Federal University) | Bilgin, Ömer (University of Dayton, School of Engineering)
Thin metal or reinforced concrete shells with granular infill structures are considered in this article. These structures are massive and they are used as support for the construction of berthing quays, piers, artificial islands, shore protection, and other structures of coastal infrastructure. It is more convenient to use the thin shell structures during the development of the Arctic shelf, because it is possible to install them from the ice side. In addition, it is possible to enhance the technology and install thin shells with infill on deeper solid foundation layers. A mathematical model for the stresses on a compressible foundation soil in front of a thin cylindrical shell with infill due to the eccentric loading is developed. A modeling and experimental determination of the interface strength of the contact surface between the infill and the inner surface of the shell is proposed. The details of the construction stages and testing of the physical model used for the experiments are discussed. The effects of the interface friction on the shell behavior and on the foundation stresses in front of the wall are investigated. The influence of parameters affecting the interaction between the soil infill and the inner surface of the shell material is determined. It is based on a comparison of experimental results with calculations performed using the proposed mathematical model. The obtained parameters and proposed methods can be used in numerical simulations using the finite element method to analyze and design the thin shell structures with soil infill. The findings of the study and proposed methods can also be applied to the thin shell structures used in other facilities such as hydraulic, industrial, civil, and transportation.
Bekker, Alexander T. (Far Eastern Federal University) | Umansky, Andrey M. (Far Eastern Federal University) | Pogodaev, Anton (Far Eastern Federal University) | Ivanov, Egor S. (Far Eastern Federal University)
The article is devoted to the experimental behavioral research of concrete elements with basalt-plastic reinforcement of rhombic relief under flexure with failure along the oblique section from the action of lateral force. The plan of the experiment provides for testing two types of concrete beams; the first type is with basalt-plastic nonmetallic reinforcement, the second type is with steel reinforcement. The samples were tested for durability, fracture strength and stress-strain behavior. Comparative analysis of the behavior of flexural elements with steel and basalt-plastic reinforcement under load was conducted. The article describes the results of experimental data analysis.
Bekker, Alexander T. (Far Eastern Federal University) | Sabodash, Olga A. (Far Eastern Federal University) | Shpagin, Konstantin D. (Far Eastern Federal University) | Krikunova, Yulia A. (Far Eastern Federal University)
Development of oil and gas fields in the Russian arctic seas located few hundred miles from shoreline is according to experts’ opinion the most challenging project in the world.
Russian Arctic is believed to be an area with the highest unexplored hydrocarbons potential in the world. About 60% of planned oil and gas production in 2035 will be from fields, not yet discovered and developed. Current production facilities are mostly gravity based structures – steel/concrete, and artificial islands – gravel/concrete blocks. These structures are used in general in deepwater offshore zones. Hence, it is necessary to develop advanced technical solutions of exploration and production mobile platforms for specific Arctic shallow water conditions where water depths are about 4-17m.
In the paper the analysis of technical solutions of exploration platforms in shallow waters for year-round production in the Russian Arctic on weak soils has been made. In this study the review of design solutions of offshore structures in shallow waters of freezing seas has been made. Analysis of ice conditions of the Kara Sea has been carried out. General solutions of exploration platforms in a shallow water zone have been offered. Detailed calculations of stability of platform and foundation under the external loads on the basis of PLAXIS 7.0 software have been fulfilled.
Bekker, Alexander T. (Far Eastern Federal University) | Tsimbelman, Nikita Ya. (Far Eastern Federal University) | Potyanikhin, Dimitriy A. (Far Eastern Federal University) | Mamontov, Andrey I. (Far Eastern Federal University) | Bilgin, ?mer (University of Dayton) | Chernova, Tatiana I (University of Dayton)
A description of finite element model and analysis of a shell with an infill is performed. A large diameter thin cylindrical shell structure with the edge leaning against compressible foundation soil is analyzed. Different materials are considered individually for the models of each structure shell and infill component (metal or reinforced concrete shell, and granular or elastic infill in a shell and foundation soil loaded by the structure). Contact conditions between 1) the infill and the shell’s inner surface and 2) between the foundation material and the shell edge are analyzed. An example of calculating strain conditions in the shell according to the proposed finite element model and tasks of its development process and specification are provided in this paper.
Bekker, Alexander T. (Far Eastern Federal University) | Umansky, Andrey M. (Far Eastern Federal University) | Zavgorodnev, Alexey V. (Far Eastern Federal University) | Ivanov, Egor S. (Far Eastern Federal University)
This paper presents the study of the flexural concrete elements behavior with modified basalt FRP bars "ANK-BM" with rhomboid relief (non-spinneret technology) “Plaintrusion”. The comparative analysis of the flexural elements behavior strengthened by steel and composite reinforcement was carried out. The resistance of flexural composite-concrete elements in standard cross-sections was studied within the area of a peak bending moment at all stress and strain states down to rapture. The comparison was made of test and theoretical results.