RU2057845C1 - Method for installation of marine stationary platform with flat bottom and marine stationary platform - Google Patents

Abstract

FIELD: hydraulic structures. SUBSTANCE: method for installation of marine platform includes leveling out sea floor in the point where the platform is placed. Concurrently with platform immersion platform braking is carried out using rotary panels installed on platform bottom by deviating them at 0 - 90 to its bottom. Deviation angle is decreased from 90 to 0 when the panels come in touch with the bed. The platform is fastened to sea floor by anchor piles. Marine stationary platform includes braking panels fastened with their edges to platform bottom and foundation plate mounted flush with platform bottom. Deviation of panels is carried out by hydraulic jack connected to hydraulic damp. Foundation plate has cantilever ledges with vertical openings. Piles with hydraulic damps or vibration devices are installed flush in the openings. EFFECT: increased accuracy in descending marine stationary platform onto the sea floor using development of stationary marine platform providing self-adjustment of platform braking concurrently with its immersion, compacting and leveling off the bed, keeping intact bed and continental soil, reliable fastening the platform to the sea floor by anchor piles, increased strength, improved resistance to cracks and durability of foundation slab and platform. 8 cl, 9 dwg

Description

 The invention relates to hydraulic structures of foundations and foundations, and in particular to the installation of offshore stationary platforms at the bottom and their structures.

 Known offshore platforms installed in the North Sea, in particular, they include a stationary platform type "BERIL A" with a stepped surface of the bottom of the foundation slab, as well as "ECOFISK".

 The disadvantage of these platforms is the presence of a protrusion on the lower surface of the foundation slab, as a result of which, when lowering to the seabed, the structure loosens it when it touches the bed, and also destroys the mainland soil, as a result of which caverns with voids are formed under the lower part of the structure, which require installation of the platform additional work on filling with cement-sand mortar.

 Platforms such as "FRIG TR1", "STATFORD A", "NAYNIEN", as well as domestic ones installed in the North Sea, are also known. The indicated platforms for increasing braking forces have around the perimeter a “skirt” of a metal sheet pile 4.5 m high four corners of hollow piles with a diameter of 600.1200 mm and a height of 6.7 m.

 The purpose of the "skirt" and piles is to quench the horizontal speed of the structure before landing on the bed and alert about the proximity of the ground. A common drawback of these platforms is the same violations of the bed and the structure of the natural occurrence of the soil, and this usually leads to cementation of caverns and uneven settlement of the structure as a whole due to additional influences in the form of lateral undercurrent or ice pressure.

 In the design solutions of the platforms, there is also the danger of a part of the platform freezing due to the fact that, in one corner, the supporting pile may not reach the bedrock when planting on the bed, but stopped in the area with the sink, which is the main danger, since this leads to a redistribution of efforts, to a change in the design scheme of the base plate and the formation of cracks with destruction along the hover line. In addition, in these platforms, the installation of piles involves swiveling them with a foundation plate and a "skirt", which is less durable, since the first contact of the bed and soil occurs with a pile, and then with a "skirt", therefore, with significant effects when braking can significantly deviate from the design position due to the less rigid design of the "skirt", which will lead to the destruction of the site or damage to the pile.

 A common drawback for these platforms is also an unsatisfactory adjustment of the speed of the construction approach to the design dive point. So the BERIL A platform, when approaching the calculated position at a wave height of 0.8 m and a wind of 2 points on the BORORT scale, had a miss of 84 m.

The Brent B platform with a 2-point wind had a miss of 25 m. The calculated phase of braking of the BERIL A platform was 54 m when the pile was deepened at the moment of stopping 1.62 m. The indicated data are given in the studies:
1) Hafner T. Rohrleitunger und Bahaltеr im Meer-mit Jnst Wasserbau Uniw Stuttgart, 1987, N 51230;
2) Chari TR Geotechnical aspects of icebery scour on ocean floors, Canadian geotechnical, 1979, N 16.

 The purpose of the invention is to increase the accuracy of lowering the marine stationary platform to a selected bottom section by creating a stationary marine platform that provides independent regulation of the platform braking simultaneously with its immersion, compaction and leveling of the bed, preservation of the indestructibility of the bed and mainland soil, reliable fixing of the platform to the bottom of the sea with anchor piles, increase strength, crack resistance and durability of the base plate and platform.

This goal is achieved by the fact that the method of installing an offshore stationary platform with a flat bottom, including transporting the platform by tugboats afloat to the place of its placement and diving the platform to the bottom of the sea by filling the ballast compartments, includes a certain sequence of operations; with the formation of a bed, simultaneously with the immersion of the platform, the platform is braked by rotary panels mounted on the bottom of the platform, rejecting them gradually at an angle of 0 to 90 ^on its bottom, and in contact with a bed of panels angle of deflection decreased from 90 ^to 0, and after installation of the platform in the design position produce its fastening to the bottom of the sea anchor piles.

Additionally, the fixed offshore platforms, comprising a hollow floor slab with an upper structure, ballast compartments and a flat bottom, further provided with a swivel brake panels hinged one edge to the bottom of the foundation plate rotatably relative thereto at an angle of ^90, and hydraulic jacks, the rod each of which is pivotally connected to the free edge of one of the panels, while the panels are installed horizontally flush with the bottom of the base plate and each hydrod the mkrat is equipped with a hydraulic shock absorber made with a spring, while the panels are located at a distance of 0.15 L from each other along a line perpendicular to the axis of the hinges and are equipped with bed contact sensors attached to the face of each panel along its height at a distance of 0.1 l from friend, where L is the length of the panel, m, l the height of the panel, m, and the base plate has cantilevered protrusions with vertical holes in which piles flush with the bottom of the plate are installed with hydraulic jacks or vibration devices connected to the top of the pile.

 In FIG. 1 shows a general view of the platform during transportation to the destination; in FIG. 2 plan of the platform with the location of the supporting piles; in FIG. 3 first stage of immersion loading of ballast tanks and the beginning of braking by brake panels; in FIG. 4 second stage of immersion, the brake panels are in contact with the bed, friction forces arise; in FIG. 5 the third stage, the base plate has approached the theoretical immersion point, the base plate is anchored by pressing anchor piles into the ground; in FIG. 6 node I in FIG. 3; in FIG. 7 node II in FIG. 3; in FIG. 8 the position of the piles in the node of the platform after entering the ground; in FIG. 9 a way of fixing the "skirt" and piles to the slab in existing platforms.

 Fixed offshore platform includes foundation plate 1, anchor piles 2, niches for pivot panels 3, pivot panels 4, first contact sensors 5, guide holes 6 for piling, hydraulic jack or vibration loader 7, rod 8, hydraulic jack 9, hydraulic shock absorber 10 s spring 11, movable diaphragm 12, fixed diaphragm 13, valves 14 and 15, pump station 16, bed 17, piston 18, rod 19, holder 20, console 21, head of pile 22, embedded part 23, hinges 24 and 25, secondary console 26 and the "skirt" 27.

 The installation method of the offshore stationary platform includes a number of activities and is carried out in stages.

 Preparatory stage.

 According to the data of geological, meteorological, hydrological studies, as well as parameters that take into account design solutions for the proposed method of installing the platform, several design schemes are created and the theoretical design phase of the platform braking is determined on a computer basis. Simultaneously, modeling is carried out on the model of the task of immersing and braking the platform also taking into account the recommendations of the proposed solution in order to determine the experimental phase of braking of the platform. The design value of braking is defined as the average value of the calculated and experimental phases. The preparatory phase also includes the alignment of the bottom of the sea at the location of the platform with the formation of a bed.

 Transportation of the offshore stationary platform is carried out in accordance with the known technological scheme by tugboats, as shown in FIG. 1. The transportation of the platform ends, not reaching the coordinate point of immersion by the value of the constructive phase of braking. After this, the first stage of immersion begins, platform braking occurs simultaneously with the loading of ballast tanks and the operation of the brake devices in two stages.

 In the first stage (FIG. 3), before contact with the bed, the brake devices shown in FIG. 6, and as a result of this, the rotary panels 4 located in the niches 3 are turned off by an angle α.

As a result, we have
W q ₁ + q ₂ , where W is the towing force;
q ₁ platform water resistance;
q ₂ variable resistance (pressure) on the brake panels, depending on the angle of inclination α
The brake device operates as follows.

 The pump station 16 is turned on. The valve 14 is closed. The valve 15 is turned on. As a result, the energy damper 10 is turned off and the rod 8 of the hydraulic jack 9 is lowered and all synchronously connected brake panels deviate. It is hereby foreseen that the platform moves from the right side to the left, as shown by the arrow in FIG. 3.

 By increasing or decreasing the deflection angle of the panels 4, it is possible to adjust the amount of braking due to the friction forces and the pressure of the water on the brake panels. The braking phase is controlled from one control panel.

 The moment of contact of the panels 4 with the bed of soil 16 is fixed by sensors 5 from this begins the second stage of the second stage of immersion of the platform (Fig. 4). Data from the sensors 5 is transmitted to a central point and from there a command is received in automatic mode to turn off the pump station 16 and valve 15 and open the valve 14. Under pressure of the ground, the rod 8 of the cylinder 9 deviates upward, as a result of braking, the fluid flows through the valve 14 into the chamber of the hydraulic shock absorber 10, presses on the piston 18 and then through the rod 19 to the diaphragm 20 and further to the spring 11. In this case, the rod 19 has free movement inside the spring 11 by Δ.

 Under the action of the vertical force of the platform weight with the phased loading of ballast tanks, the panel 4 is smoothly pressed to the bed 17 with its alignment and compaction, while energy is extinguished during horizontal movement of the platform by the braking devices. As a result of this, the rod 8 enters the cylinder 9, which allows the brake panel 4 to enter the niche 3 and take its original position. As a result of this, the platform will lower to the coordinate point of the base of the platform.

 After installing the platform on the bed in the design position, the foundation plate of the platform begins to be fixed to the bottom of the sea with anchor piles (Fig. 2 and 7). This is carried out as follows: in the cantilever part of the foundation plate 1, through holes 6 with a diameter greater than the diameter of piles by 30.40 mm are provided, into which hollow reinforced concrete piles 2 with a diameter of 3.6 m are inserted before the platform is immersed and secured in a vertical position by the holder 20, console 21. On the head end 22, a vibrating loader or hydraulic jack is attached 7. After that, the holders 4 are released, the vibrators or jacks are turned on and the piles 2 freely pass into the hole 6 and then goes deeper into the mainland the length of the anchoring zone. The final fastening of the piles in the vertical plane is carried out by the secondary console 28 attached to the part 25, with emphasis on the top of the piles after removing the vibrator. After that, fine-grained concrete is laid in the space between the pile along the outer perimeter and the inner perimeter of the opening of the foundation slab.

 Using the proposed method for installing an offshore stationary platform and an offshore stationary platform provides the following advantages compared to existing methods and offshore stationary platforms: it improves the accuracy of installing the platform on the seabed by independently adjusting the speed of the construction approach by damping the energy of the structural elements of the platform; makes it possible to level and compact the bed; preserves the natural structure of the soil without the formation of cavities and voids under the foundation slab due to the absence of hanging supporting piles and a "skirt" on the bottom surface of the foundation slab; rejection of the cost of cementing caverns and voids under the foundation slab; reliable anchoring of the foundation plate with anchor piles to the bottom of the sea; increase in strength, crack resistance and durability of the foundation plate and platform due to the absence of freezing of one of the corners of the foundation plate; profitability by reducing the use of tug times and more accurate lowering of the platform to a selected section of the seabed.

Claims (8)

1. A method of installing a stationary flat-bottom offshore platform, including transporting the platform by tugboats afloat to its location and diving the platform to the bottom of the sea by filling in the ballast compartments, characterized in that the sea bottom is first aligned at the platform location to form a bed, simultaneously when the platform is immersed, the platform is braked by turning panels mounted on the bottom of the platform, gradually deflecting them at an angle of 0 - 90 ^o to its bottom, and when the panel touches th with the bed, their deviation angle is reduced from 90 to 0 ^o .

 2. The method according to p. 1, characterized in that after installing the platform in the design position, it is secured to the bottom of the sea by anchor piles.

3. Offshore stationary platform, including a hollow base plate with a top structure, ballast compartments and a flat bottom, characterized in that it is equipped with rotary brake panels pivotally attached by one edge to the bottom of the base plate with the possibility of rotation relative to it at an angle of up to 90 ^o , and hydraulic jacks, the rod of each of which is pivotally connected to the free edge of one of the panels.

 4. The platform according to claim 3, characterized in that the panels in a horizontal position are installed flush with the bottom of the base plate.

 5. Platform according to claims 3 and 4, characterized in that each hydraulic jack is equipped with a hydraulic shock absorber.

 6. The platform according to claim 5, characterized in that the hydraulic shock absorber is made with a spring.

 7. The platform according to claims 3 and 4, characterized in that the panels are located at a distance of 0.15 L from one another along a line perpendicular to the axis of the hinges, and are equipped with bed contact sensors attached to the face of each panel by its height at a distance of 0.1 l from each other, where L is the panel length, m, l panel height, m

 8. The platform according to PP.3 to 7, characterized in that the base plate has cantilevered protrusions with vertical holes in which piles are installed flush with the bottom of the plate, and hydraulic jacks or vibration devices connected to the upper parts of the pile.

Images