RU2555174C1 - Marine gravity platform with embedded foundation - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: platform comprises a body, a foundation part with a bottom slab equipped with ribs embedded into the foundation soil. At the same time the foundation in its lower part along the entire perimeter at the outer side is equipped with ploughshares with depth of submersion and distance between them determined on the basis of the given expression. The ploughshare width is also made from the mathematical expression.

EFFECT: reduced material intensity in development of a marine gravity platform, reduced volume of ballast for provision of ribs embedding into the foundation soil, increased stability and bearing capacity of the soil foundation, increased reliability and reduced risk of loss of gravity platform stability during the period of operation under action of combined external impact of loads.

4 cl, 6 dwg

Description

The invention relates to the field of hydraulic engineering and can be used to create and operate marine gravity platforms for the development of hydrocarbon resources on the continental shelf.

Known platform gravity type, containing a housing that serves as a support for the placement of surface operational technological equipment (US patent No. 3824795). The lower part of the platform body - the foundation in the form of a flat plate rests directly on the bottom of the reservoir or artificial foundation (bed) and supports the surface structure of the upper structure of the platform, where operational technological equipment for preparing hydrocarbon for transport is located.

The disadvantage of a gravity platform with a foundation in the form of a flat plate is its low resistance to horizontal shear loads, in particular ice, and high local contact stresses at the bottom of the flat plate. In addition, careful planning of the natural or artificial foundation is required to ensure the necessary contact between the foundation and the foundation.

Known gravity platform containing a housing, a base part with a bottom plate equipped with ribs that are buried in the soil of the seabed. The space between the slab and the seabed is filled with cement mortar (French patent No. 2,335,133). This platform has several advantages, in particular, higher stability and uniform contact stresses. Moreover, the construction of the foundation part allows you to refuse to perform preliminary planning work of the bottom of the reservoir or the construction of an artificial base (bed).

However, the disadvantage of this platform, equipped with ribs, is the need to create significant efforts to crush them into the soil of the base, which leads either to a limitation of the depth of crushing and not to reach the ribs of solid layers of soil and, as a result, a decrease in the bearing capacity of the base, or to an increase in the size of ballast capacities. As practice and calculations show, at water depths in the water area of less than 15-20 meters, it is not possible to push the ribs to a given depth in strong soil layers due to the low installation weight of the platform (weight of the support block plus weight of the ballast).

The aim of the invention is to reduce the material consumption by reducing the resistance to crushing the ribs by immersing them to a shallower depth (only to the depth of soft soils) created by the weight of the platform and ballast (installation weight), and by immersion by clogging (immersing) additional coulters in strong soil layers.

This goal is achieved due to the fact that in the well-known gravity platform containing a housing, a foundation part with a bottom plate equipped with ribs, openers are installed in the lower part along the perimeter of the foundation with the height necessary to achieve the installation of strong layers of soil, with the distance between the openers determined from expression

$$B\le 2H\tan \alpha \tan \varphi (\mathrm{one})$$

where B is the distance between the coulters, m;

H is the depth of immersion of the opener, m;

φ is the angle of internal friction of the soil, deg;

α is the bulging angle, degrees, determined from the equation (see S.N. Levachev, V.G. Fedorovsky, Yu.M. Kolesnikov, S.V. Kurillo. Calculation of pile foundations of hydraulic structures. M., Energoatomizdat, 1986, pg. 61).

Moreover, the opener width is assigned in accordance with the formula

where b is the opener width, m;

k is an empirical coefficient, k≥1.0.

The value of the empirical coefficient k is established on the basis of the analysis of the initial data (geotechnical conditions of the platform installation site, loads acting on the platform, conditions for the possibility of erosion of the soil base of the platform) so as to provide the greatest bearing capacity of the soil base (stability of the platform) under the combined effect of external loads .

In addition, in difficult geological conditions, experimental studies are carried out to clarify the coulter width at which the maximum bearing capacity of the soil base (platform stability) is achieved.

The openers in the horizontal section are made rectangular, and in the vertical plane are flat, usually rectangular or trapezoidal and triangular in shape with a metal thickness, which provides the coulter flexural strength when immersed in the ground and in the working position when operating the platform (usually the opener metal thickness - 20-40 mm). In the upper part of the coulter a support headgear is installed.

The technical results that are provided by the implementation of the invention are as follows:

- reduction of material consumption when creating a marine gravity platform by reducing the resistance to crushing;

- increasing the stability and bearing capacity of the soil base by immersing the coulters in strong soil layers and transferring loads from the gravity platform to these strong soil layers of the base;

- improving the reliability and reducing the risk of loss of stability of the gravity platform during operation under the action of the combined external impact of loads by increasing the stability of the structure;

- reducing the risk of emergencies, environmental pollution due to the loss of stability of the gravity platform and the violation in this regard of the normal operation of downhole and technological equipment, pipeline systems.

The problem is solved in that in the technical solution of the design of the marine gravity platform, comprising a body, a base part with a bottom plate equipped with ribs, according to the invention, openers with a height H necessary to achieve strong layers of soil with distance are installed at the bottom along the perimeter of the foundation between the coulters B. A support cap is mounted in the upper part of the coulter. The opener width b is assigned at least the distance between the openers B. The openers in a horizontal section are rectangular in shape and in the vertical plane are generally rectangular, trapezoidal or triangular in shape with a metal thickness that ensures the opener flexural strength when immersed in the ground and working position during operation of the platform.

The combination of new significant distinguishing features with other essential features allows us to solve a new problem, namely, to reduce material consumption by reducing resistance to crushing forces, to increase the stability and bearing capacity of the soil base of the marine gravity platform by immersing the coulters in strong layers of the soil, which ultimately leads to an increase reliability, durability, risk reduction of emergency situations.

The invention is illustrated by drawings, in which Fig. 1 shows the main components and elements of a marine gravitational platform, ensuring the implementation of the proposed technical solution, afloat in a transport position, Fig. 2 - marine gravitational platform mounted on a natural base with flat strip crushed into the ground base ribs (if any) in relatively weak base soils, in Fig.3 - a gravity platform with submersible coulters in strong layers of the soil base by any known method bom (e.g., piling equipment), 4 - a longitudinal sectional view of a platform submerged in a durable soil openers seabed 5 - immersion of the coulter in the soil foundation, 6 - platform foundation plan openers.

The marine gravity platform with a deepened foundation (Fig. 1) contains a supporting body 1. On the supporting body there is a top structure 2. In the lower part, the supporting body is equipped with a foundation 3 with a bottom plate 4, provided with gaps 5 around the perimeter of the foundation for installing openers 6. In the lower parts along the perimeter of the foundation are equipped with openers 6, in the upper part of which are mounted head restraints 7 with a pin lock 8. The openers 6 are installed in the gap between the foundation 3 and the limiting straps 9, which are attached to the foundation 3 cut kerchief 10, a thickness not less than the thickness of the coulters. In the transport position, the coulters 6 are fixed by any known method, for example, using a metal retainer that has low strength characteristics compared to the coulter 6. In addition, a soil base is shown, consisting of a weak layer 11 and a strong layer 12 of soil.

The bulging angle α is indicated in FIG. 4, and the angle of internal friction φ is shown in FIG. 6. In addition, figure 3, 4, 6 shows the designation of the immersion depth of the coulter H, the height of the ribs h, the distance between the coulters B and its width b.

The invention is implemented as follows.

In stationary factory conditions (for example, a dry dock), the support building 1, the upper structure 2, the base part 3 with the bottom plate 4, to which the ribs are mounted, are constructed (the option without flat strip ribs is possible). Around the perimeter from the outside, limit bars 9 are installed through the scarves 10 to form a gap 5 according to the size of the cross section of the opener 6. The height of the opener is selected based on the engineering and geological conditions of the site so that the openers are immersed in strong layers of soil 12 to ensure a given platform stability . A weak soil layer 11 must be traversed by the coulters 6. The height of the ribs (if any) is also assigned on the basis of engineering and geological conditions so that they pass a weak soil layer 11 and reach a strong soil layer 12. The coulters 6 are placed at such a distance apart from each other, so that the prism of the head in a solid soil layer formed by the coulters 6 upon loss of stability of the structure, are within the soil layer 12. Based on this condition, the distance between the coulters 6 is determined by the expression (1). The coulters, as a rule, are made rectangular or trapezoidal and triangular in their lower part, which is immersed in a strong soil layer 12, which allows to reduce the resistance of immersion (driving) of the coulters 6 into a strong soil layer 12. The thickness of the coulters 6 is determined based on the strength calculation loads acting on the coulter during immersion and operation of the platform, and usually it is 20-40 mm. The opener width 6 is assigned in accordance with the expression (3). In difficult geological conditions, the coulter width and the gap length are determined on the basis of experimental studies from the condition of achieving the maximum bearing capacity of the soil base (maximum stability of the structure). The made openers 6 together with the supporting headgear 7 and the pin retainer 8 are installed in the gap between the base part and the limiting straps 9, which are made of at least two. The openers 6 are installed so that the lower end of the opener 6 does not go beyond the dimensions of the foundation plate 4, which is achieved by installing clamps of any design, for example, a soft metal key is installed, which is cut off when the opener 6 is clogged.

After carrying out routine maintenance in a dry dock, the platform is taken out of the dock and transported to the installation site. Upon arrival at the installation site, partial casing 1 of the platform is made, and as a result the platform lowers, and then touches the weak soil layer 11 with the ribs. The platform is positioned and further ballasting is carried out with the ribs crushed into a weak soil layer 11 until they reach a solid soil layer 12 and the crushing resistance forces increase sharply. At this point, further ballasting is stopped and the installation weight of the platform (platform weight plus ballast weight) reaches its maximum. After checking the verticality of the platform, work begins on the immersion of the coulters 6 using underwater hammers or vibration absorbers, fixing them on the support headgear 7 using the pins of the latches 8. Monitoring of the coulters 6 in the ground of the base 12 is carried out using underwater video cameras and transmitted to the operator on the vessel. After the coulter reaches the design position, the clogging of this coulter 6 is stopped and the next coulter 6 is immersed. Moreover, it is advisable to drive alternately on the diametrically opposite sides of the foundation 3 of the platform body 1. After completing the clogging of the coulters 6, if necessary, grout is pumped into intercostal spaces between stove 4 and a layer of soil 11 of the seabed.

In general, the described technical solution allows, in addition to the main goals achieved, to increase the reliability of protection of the base from erosion.

Thus, the application of the proposed technical solution allows you to expand the range of depths (in the direction of a significant reduction in their value) at which it is possible to effectively use gravity structures with a deep foundation.

The analysis of the prior art showed that the claimed combination of essential features set forth in the claims is unknown. This allows us to conclude that it meets the criterion of "novelty."

To verify the conformity of the claimed invention with the criterion of "inventive step", an additional search was carried out for known technical solutions in order to identify features that match the distinctive features of the claimed technical solution from the prototype. It is established that the claimed technical solution does not follow explicitly from the prior art. Therefore, the claimed invention meets the criterion of "inventive step".

The new, industrially applicable technical solution described above represents a single inventive concept, which, in our opinion, meets the criterion of inventive step, and therefore, a patent for an invention is proposed for legal protection.

Claims (4)

1. Marine gravity platform with a buried foundation, comprising a hull, a foundation part with a bottom plate equipped with ribs buried in the ground of the base, characterized in that, in order to reduce the material consumption while increasing the stability of the platform, the foundation in its lower part along the entire perimeter with the outer side is equipped with openers with immersion depth and distance between them, determined from the expression
B≤2H tanα tanφ,
where B is the distance between the coulters, m;
H is the depth of immersion of the opener, m;
φ is the angle of internal friction of the soil, deg;
α - bulging angle, degrees, determined from the equation

moreover, the coulter is made of a width determined from the expression
b≥kB,
where b is the opener width, m;
k is an empirical coefficient, k≥1.0, determined on the basis of experimental studies. 2. The platform according to claim 1, characterized in that the coulter is made rectangular in the area of immersion in strong layers of soil. 3. The platform according to claim 1, characterized in that the coulter is trapezoidal in the area of immersion in strong layers of soil. 4. The platform according to claim 1, characterized in that the coulter is made triangular in the area of immersion in the strong layers of the pound.

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