Penetration resistance prediction method and system for suction bucket foundation in sand

Abstract

The present invention discloses a method and system for predicting the penetration resistance of a suction-type barrel foundation in sand, which belongs to the field of offshore wind power suction-type barrel foundation soil sinking construction. The method and system include: based on a suction-type barrel foundation in sand, by evaluating drainage conditions, clarifying the penetration characteristics of the suction-type barrel foundation, obtaining the outer friction resistance, inner friction resistance and end bearing capacity of the suction-type barrel foundation, and predicting the drainage penetration resistance of the suction-type barrel foundation. The present invention is based on the limit equilibrium theory, takes into account the enhancement of the effective stress of the barrel end soil caused by side wall friction, and is more accurate in predicting the deadweight penetration depth; at the same time, it takes into account the seepage characteristics caused by sand drainage during the barrel foundation sinking process, takes into account the reduction of the effective stress of the soil inside and at the barrel end due to seepage, and the increase of the effective stress of the soil outside the barrel. The force analysis conforms to the actual situation of the barrel foundation, and the prediction of the penetration resistance during the suction penetration process is closer to the actual situation.

Description

Technical Field

[0001] The present invention relates to the field of soil sinking construction of offshore wind power suction-type barrel foundations, and in particular to a method and system for predicting the penetration resistance of suction-type barrel foundations in sandy soil. Background Art

[0002] Suction-type bucket foundations are a widely used structure in the offshore wind power industry. Their rapid installation, low cost, and reusability have made them a mainstream foundation for offshore wind farm construction. Technological advancements have led to continuous innovation in bucket foundation design, evolving from the initial single-bucket foundation to single-bucket multi-chamber, triple-bucket, quad-bucket, pile-bucket composite, and five-chamber structures to accommodate diverse environments and power requirements. While bucket foundations are widely used in clay soils, their application in sandy soils is relatively limited due to installation challenges.

[0003] When sinking a bucket foundation in sand, complex seepage and soil heave phenomena occur, increasing the difficulty of calculating the penetration resistance. Currently, there are three main methods for calculating the penetration resistance of bucket foundations in sand: strength-based methods, static penetration testing, and a combination of different methods. However, existing methods have limitations. For example, strength-based methods are based on limit equilibrium theory and do not consider the influence of suction seepage. The accuracy of static penetration testing methods is affected by empirical coefficients, making existing prediction methods overly conservative.

[0004] Therefore, there is an urgent need for an accurate prediction method for the penetration resistance of bucket foundations in sand. This method should take into account the changes in the loading state of the bucket foundation to improve the accuracy of the calculation and the reliability of engineering applications. Summary of the Invention

[0005] In order to solve the problems of low calculation accuracy and overly conservative results in the penetration resistance of existing offshore wind power suction barrel foundations, the purpose of the present invention is to provide a penetration resistance prediction technology suitable for suction barrel foundations in sandy soil, so as to more accurately calculate the suction penetration resistance of the barrel foundation, which is more consistent with the measured value.

[0006] To achieve the above technical objectives, the present application provides a method for predicting the penetration resistance of a suction barrel foundation in sand, comprising the following steps:

[0007] Based on the suction bucket foundation in sand, the drainage conditions are evaluated, the penetration characteristics of the suction bucket foundation are clarified, the outer friction resistance, inner friction resistance and end bearing capacity of the suction bucket foundation are obtained, and the drainage penetration resistance of the suction bucket foundation is predicted.

[0008] Preferably, in the process of evaluating the drainage condition, the dimensionless parameter V is used to evaluate the drainage condition of the soil:

[0009]

[0010] Where v is the penetration rate of the barrel foundation, t is the thickness of the barrel wall, and c is the penetration rate of the barrel foundation. v is the consolidation coefficient of the surrounding soil. For sand, when V < 0.01, it corresponds to the drainage state of the soil.

[0011] Preferably, in the process of determining the penetration characteristics, the penetration characteristics of the bucket foundation are determined to include undrained penetration and drained penetration based on the penetration speed of the bucket foundation and the drainage conditions of the surrounding soil. Among them, when the permeability of the soil layer is low and there is no obvious dissipation of pore water pressure during the penetration process, then the penetration characteristic is undrained penetration.

[0012] Preferably, in the process of predicting the drainage penetration resistance, based on the positive pressure penetration characteristics of the barrel foundation in sand, the theory of limit equilibrium is used to analyze the force on the barrel during the deadweight penetration process to predict the penetration resistance of the barrel foundation.

[0013] Preferably, in the process of analyzing the force on the cylinder during the self-weight penetration process, the equilibrium equation of the penetration resistance of the cylinder foundation in sand without suction is constructed:

[0014]

[0015] Where R is the penetration resistance of the bucket foundation soil during the sinking process; F i 、F o are the inner and outer friction resistances respectively; Q tip is the end resistance; A i 、A o are the inner and outer circumferences of the cylinder wall respectively; A tip is the area of ​​the tube end; h is the penetration depth of the tube foundation; z is the vertical depth below the seabed; t is the wall thickness of the tube; γ' is the effective bulk density of the soil; K is the horizontal earth pressure coefficient of the soil; σ vi '、σ vo ' is the vertical effective stress of the soil inside and outside the bucket foundation; q is the effective overburden pressure of the soil; N q 、N γ is the bearing capacity coefficient, where N q =e πtanφ tan 2 (45+φ / 2), N γ =1.5(N q -1)tanφ; φ is the internal friction angle of soil drainage; δ is the friction angle between the cylinder wall and the sand (δ=rφ); r is the relationship coefficient between the internal and external friction angles.

[0016] Preferably, in the process of obtaining the end bearing capacity, the end bearing capacity is obtained based on the end resistance caused by the overlying load and the end resistance caused by the deadweight.

[0017] Preferably, in the process of predicting the drainage penetration resistance of the suction bucket foundation, the drainage penetration resistance is expressed as:

[0018]

[0019] Where W′ is the self-weight stress, F o is the outer friction resistance, F i is the inner friction resistance, Q q is the end resistance caused by the overburden load, Q γ is the end resistance caused by deadweight, a is the pore pressure factor, A in Indicates the top cover area of ​​the barrel foundation.

[0020] The present invention discloses a penetration resistance prediction system for a suction barrel foundation in sand, comprising:

[0021] A data analysis module is used to determine the penetration characteristics of suction bucket foundations in sandy soils by evaluating drainage conditions;

[0022] The data prediction module is used to predict the drainage penetration resistance of the suction bucket foundation based on the penetration characteristics by obtaining the outer friction resistance, inner friction resistance and end bearing capacity of the suction bucket foundation.

[0023] Preferably, the data analysis module is further configured to evaluate the drainage condition of the soil using a dimensionless parameter V:

[0024]

[0025] Where v is the penetration rate of the barrel foundation, t is the thickness of the barrel wall, and c is the penetration rate of the barrel foundation. v is the consolidation coefficient of the surrounding soil. For sand, when V < 0.01, it corresponds to the drainage state of the soil.

[0026] Preferably, the data analysis module is also used to determine the penetration characteristics of the bucket foundation, including undrained penetration and drained penetration, based on the penetration speed of the bucket foundation and the drainage conditions of the surrounding soil. When the permeability of the soil layer is low and there is no obvious dissipation of pore water pressure during the penetration process, the penetration characteristic is undrained penetration.

[0027] The present invention discloses the following technical effects:

[0028] (1) Based on the limit equilibrium theory, the enhancement of the effective stress in the soil at the end of the cylinder caused by the side wall friction is taken into account, which makes the prediction of the self-weight penetration depth more accurate.

[0029] (2) The seepage characteristics caused by sand drainage during the penetration of the bucket foundation are taken into account. The reduction of the effective stress of the soil inside and at the ends of the bucket and the increase of the effective stress of the soil outside the bucket due to seepage are considered. The force analysis is consistent with the actual situation of the bucket foundation, and the prediction of the penetration resistance during the suction penetration process is closer to the actual situation.

[0030] (3) The parameters required for calculation are few and easy to obtain, the calculation method is simple, in line with engineering practice, and the calculation results of penetration resistance are more accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0032] Figure 1 It is a schematic diagram of the forces acting on the barrel foundation of the present invention during the sinking process in sand;

[0033] Figure 2 This is a comparison chart of the calculated value and the measured value of the self-weight sinking depth described in the present invention;

[0034] Figure 3 This is a comparison chart of the calculated penetration resistance of the single-tube composite tube foundation described in the present invention and the measured value from the model test;

[0035] Figure 4 This is a comparison chart of the calculated penetration resistance of the five-tube foundation described in the present invention and the actual measurement in the model test;

[0036] Figure 5 This is a comparison chart of the calculated and measured values ​​of the single-tube in two different regions described in the present invention. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of this application.

[0038] like Figure 1-5 As shown, the present invention provides a penetration resistance prediction technology applicable to suction bucket foundations in sandy soils, and the calculation is performed using the following steps:

[0039] Assess drainage conditions and clarify the bucket foundation's penetration characteristics. Before conducting a bucket foundation installation test, first assess the bucket foundation's penetration rate and the surrounding soil's drainage conditions. This helps determine whether the penetration is drained or undrained. If the soil layer has low permeability and there is no significant dissipation of pore water pressure during the penetration, then the penetration is undrained, and it is difficult for the soil to form a seepage field.

[0040] Calculate the drainage penetration situation. During drainage penetration, the water in the cabin is extracted, forming suction (pressure difference) inside and outside the cylinder. The suction will cause the soil inside and outside the cylinder to form a seepage field, affecting the stress state of the soil layer. The applied suction causes the seepage to develop from outside the cylinder to inside the cylinder, and the degree of influence inside the cylinder is greater than outside the cylinder, which reduces the vertical effective stress inside the cylinder and reduces the internal cylinder-soil friction; at the same time, the high hydraulic gradient around the cylinder wall will also reduce the end resistance; the vertical effective stress outside the cylinder increases, which enhances the friction between the outer wall of the cylinder and the soil. The reduction in resistance inside the cylinder and the end of the cylinder is significantly greater than the increase in the effective stress of the soil outside the cylinder, which is comprehensively manifested as a significant reduction in penetration resistance. The present invention is suitable for the calculation of drainage penetration resistance.

[0041] The dimensionless parameter V is used to evaluate the drainage condition of the soil:

[0042]

[0043] Where: v is the penetration rate of the barrel foundation; t is the thickness of the barrel wall; c v is the consolidation coefficient of the surrounding soil. For sandy soil, when V < 0.01, it corresponds to the drainage state of the soil.

[0044] Based on the characteristics of bucket foundations sinking under positive pressure in sand, the theory of limit equilibrium is used to analyze the forces acting on the bucket during the self-weight penetration process. The penetration resistance of the bucket foundation is divided into three parts: inner wall friction resistance, outer wall friction resistance, and end bearing capacity. The equilibrium equation for the penetration resistance of the bucket foundation in sand without suction is established:

[0045]

[0046] Where: R is the penetration resistance of the bucket foundation soil during the sinking process; F i 、F o are the inner and outer friction resistances respectively; Q tip is the end resistance; A i 、A o are the inner and outer circumferences of the cylinder wall respectively; A tipis the area of ​​the tube end; h is the penetration depth of the tube foundation; z is the vertical depth below the seabed; t is the wall thickness of the tube; γ' is the effective bulk density of the soil; K is the horizontal earth pressure coefficient of the soil; σ vi '、σ vo ' is the vertical effective stress of the soil inside and outside the bucket foundation; q is the effective overburden pressure of the soil; N q 、N γ is the bearing capacity coefficient, where N q =e πtanφ tan 2 (45+φ / 2), N γ =1.5(N q -1)tanφ; φ is the internal friction angle of soil drainage; δ is the friction angle between the cylinder wall and the sand (δ=rφ); r is the relationship coefficient between the internal and external friction angles.

[0047] The effective overburden pressure of the soil is q = γ'h. However, when the wall length is large relative to the wall thickness, the friction of the cylinder wall will generate additional vertical stress around the cylinder wall. Considering that the friction of the cylinder wall will generate an additional vertical stress at the cylinder end, the stress at the cylinder end will be enhanced. The effective stress of the soil at the cylinder end can be expressed as:

[0048] q=γ′h+α f f tip =γh(1+α f K tanδ) (3)

[0049] Where: α f —Ratio of the vertical normal stress increment at the cylinder end to the friction force of the cylinder wall, it is recommended to take 1; f tip —Cylinder wall friction at the cylinder end.

[0050] During the suction penetration process, the magnitude of the suction will continuously change the seepage of the soil. Considering the effect of the seepage force on the stress of the soil inside and outside the cylinder, the stress change caused by the seepage is proportional to the average hydraulic gradient i inside and outside the cylinder:

[0051]

[0052] Where: a is the pore pressure factor, which is the ratio of the excess pore pressure on the soil surface inside the cylinder to the excess pore pressure at the cylinder end. The theoretical value of a is less than 0.5. Due to the large upward seepage in the cylinder, when the seepage caused by suction does not change the permeability of the soil, that is, the permeability coefficient of the soil inside and outside the cylinder is k f =1, the pressure factor a can be approximated as:

[0053]

[0054] When k f ≠1,

[0055]

[0056] Where: k f is the soil permeability coefficient k in the cylinder during suction penetration i The permeability coefficient k of the soil outside the cylinder o The ratio of k f If the number is unknown, you can choose 2 or 3.

[0057] Assume that the pore pressure inside and outside the cylinder is linearly distributed with depth, and the vertical stress solution inside and outside the cylinder is exactly the same as the original solution, except that the effective bulk density γ' of the soil inside and outside the cylinder is replaced by:

[0058]

[0059] Substituting formula (7) into formula (1) yields the formula for calculating the negative pressure penetration resistance:

[0060]

[0061] Where: W' is the deadweight stress, s is the suction required for penetration.

[0062] From Equation (8), it can be seen that suction not only plays a driving role, but also has a significant effect on reducing the stress at the tube ends and inner wall. Because the reduction in soil resistance inside and at the tube ends is greater than the increase in resistance on the outer wall, the penetration resistance of the tube foundation is significantly reduced.

[0063] From formula (8), we can get the expression of s:

[0064]

[0065] The expression in the brackets in the numerator of formula (9) corresponds to the force required for self-weight penetration (F i +F o +Q q +Q γ ). The numerator and denominator are multiplied by γ'h at the same time, and F also appears in the denominator. i , F o , Q q , Q γ , further simplifying the calculation formula of suction force:

[0066]

[0067] Where: F o is the outer friction resistance, F o =0.5γ'h 2 (Ktanδ) o A o ; F i is the inner friction resistance, F i =0.5γ'h 2 (Ktanδ)i A i ;Q q is the end resistance caused by the overburden load, Q q =γ'h(1+α f Ktanδ)N q A tip ;Q γ is the end resistance caused by its own weight, Q γ =0.5γ'tN γ A tip , A in Indicates the top cover area of ​​the barrel foundation.

[0068] Example: The present invention discloses a penetration resistance prediction technology suitable for suction-type barrel foundations in sand. The example calculates cases of five structural types located in three regions, two of which are model tests: a seven-compartment barrel and a five-compartment barrel installed in a laboratory; three field tests: a single barrel installed in the first region, and a single barrel installed in the second region. The single barrel has an open bottom, a closed top, and a middle cavity, and its appearance is similar to an inverted barrel; the seven-compartment barrel is a single barrel that uses steel structure compartments to divide the space inside the barrel into seven compartments, and is a type of offshore wind power foundation; the five-compartment barrel is a five-compartment barrel foundation that connects four independent single-barrel wind power foundations with an arc-shaped transition section, forming a five-compartment barrel foundation with an intermediate barrel connecting four single barrels. It is suitable for wind power barrel foundations in deep and deep sea areas. The dimensions of the model barrel are shown in Table 1, and the physical and mechanical parameters of the soil are shown in Table 2:

[0069] Table 1

[0070]

[0071] Table 2

[0072]

[0073]

[0074] The specific calculation steps are as follows:

[0075] (1) Calculate the drainage conditions during the sinking process of the bucket foundation according to formula (1). According to actual engineering experience, the sinking rate of the bucket foundation is generally 0.5-1.0 m / h. In order to conservatively evaluate the drainage conditions, the smaller sinking rate of 0.5 m / h is selected to evaluate the drainage conditions during the sinking process. According to the soil consolidation coefficient cv and the wall thickness t of the bucket foundation, the dimensionless parameters V of the five bucket foundations are: seven-compartment bucket V = 8.2 × 10 -6 , Five-barrel V=8.2×10 -6 Tenby monocular V = 9.3 × 10 -7 、Sandy Haven monocular V=2.3×10 -6、Draupner E monocular V=3.15×10 -6 , are all less than 0.01, which shows that the sinking process of the bucket foundation in sand is a complete drainage process.

[0076] (2) Determine the structural type, diameter, wall thickness, height and weight of the barrel foundation, which will be used to calculate the area of ​​the inner wall, outer wall and end of the barrel during the sinking process of the barrel foundation.

[0077] (3) Determine the conditions for submerged foundation soil, soil permeability coefficient k and consolidation coefficient c v , used to determine the conditions for the drainage of bucket foundations. Buoyant density γ', internal friction angle φ, external friction angle δ, horizontal earth pressure coefficient K, according to formula (2), the self-weight penetration depth of the bucket foundation is calculated. The self-weight penetration depths of the five types of bucket foundations are shown in Table 3 and Figure 2 .

[0078] Table 3

[0079]

[0080] Determine the permeability coefficient ratio k of the soil inside and outside the cylinder f , Substitute into formula (5) or formula (6) to obtain the pore pressure factor a. Substitute the calculated result of the pore pressure factor a into formula (4) to obtain the change of the seepage force of the soil inside and outside the cylinder caused by suction, that is, the magnitude of the hydraulic gradient i in formula (4) is reflected. Substitute the calculated result of the hydraulic gradient i into formula (7) to obtain the change of the vertical effective stress of the soil inside and outside the cylinder caused by seepage. Substitute formula (7) into the suction required for penetration formula (10) to obtain the suction required for the suction penetration of the cylinder foundation, which is used to guide the construction of sinking in the soil. The suction required for the penetration of the five types of foundations is shown in Figure 3-Figure 5 , the required suction force can be substituted into formula (10) to obtain the penetration resistance; the prediction process of the present invention requires few parameters and is easy to obtain, and the method is simple, in line with engineering practice, and the calculation result of the penetration resistance is more accurate.

[0081] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0082] In the description of the present invention, it should be understood that the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0083] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

Claims

1. A method for predicting the penetration resistance of a suction bucket foundation in sand, characterized in that: The following steps are involved: Based on a suction bucket foundation in sand, by evaluating drainage conditions, clarifying the penetration characteristics of the suction bucket foundation, obtaining the outer friction resistance, inner friction resistance and end bearing capacity of the suction bucket foundation, and predicting the drainage penetration resistance of the suction bucket foundation; In the process of evaluating drainage conditions, the dimensionless parameter V is used to evaluate the drainage conditions of the soil: Where v is the penetration rate of the barrel foundation, t is the thickness of the barrel wall, and c is the penetration rate of the barrel foundation. v is the consolidation coefficient of the surrounding soil. For sandy soil, when V < 0.01, it corresponds to the drainage state of the soil; In the process of determining the penetration characteristics, according to the penetration speed of the bucket foundation and the drainage conditions of the surrounding soil, the bucket foundation penetration characteristics are determined to include undrained penetration and drained penetration. Among them, when the soil permeability is low and there is no obvious pore water pressure dissipation during the penetration process, the penetration characteristics are undrained penetration. In the process of predicting the drainage penetration resistance, based on the positive pressure penetration characteristics of the barrel foundation in sand, the limit equilibrium theory is used to analyze the force on the barrel during the self-weight penetration process, and the penetration resistance of the barrel foundation is predicted; In the process of analyzing the force on the cylinder during the self-weight penetration process, the equilibrium equation of the penetration resistance of the cylinder foundation in sand without suction is constructed: Where R is the penetration resistance of the bucket foundation soil during the sinking process; F i 、F o are the inner and outer friction resistances respectively; Q tip is the end resistance; A i 、A o are the inner and outer circumferences of the cylinder wall respectively; A tip is the area of ​​the tube end; h is the penetration depth of the tube foundation; z is the vertical depth below the seabed; t is the thickness of the tube wall; γ' is the effective bulk density of the soil; K is the horizontal earth pressure coefficient of the soil; 、 are the vertical effective stresses of the soil inside and outside the bucket foundation respectively; q is the effective overburden pressure of the soil; N q 、N γ is the bearing capacity coefficient, where N q =e πtanφ tan 2 (45+φ / 2), N γ =1.5(N q -1)tanφ; φ is the internal friction angle of soil drainage; δ is the friction angle between the cylinder wall and the sand: δ=rφ; r is the relationship coefficient between the internal and external friction angles; In the process of obtaining the end bearing capacity, the end bearing capacity is obtained based on the end resistance caused by the overlying load and the end resistance caused by the deadweight; In the process of predicting the drainage penetration resistance of the suction bucket foundation, the drainage penetration resistance is expressed as: Where, is the self-weight stress, F o is the outer friction resistance, F i is the inner friction resistance, Q q is the end resistance caused by the overburden load, Q γ is the end resistance caused by its own weight, is the pore pressure factor, A in Indicates the top cover area of ​​the barrel foundation; ; F i =0.5γ'h 2 (Ktanδ) i A i ; ; , It represents the ratio of the vertical normal stress increment at the cylinder end to the cylinder wall friction.

2. A system for predicting the penetration resistance of a suction bucket foundation in sand, for implementing the method for predicting the penetration resistance of a suction bucket foundation in sand as claimed in claim 1, characterized in that: include: A data analysis module for determining the penetration characteristics of a suction bucket foundation in sand by evaluating drainage conditions; a data prediction module for predicting the drainage penetration resistance of the suction bucket foundation based on the penetration characteristics by obtaining the outer friction resistance, inner friction resistance, and end bearing capacity of the suction bucket foundation; The data analysis module is also used to evaluate the drainage condition of the soil using the dimensionless parameter V: Where v is the penetration rate of the barrel foundation, t is the thickness of the barrel wall, and c is the penetration rate of the barrel foundation. v is the consolidation coefficient of the surrounding soil. For sandy soil, when V < 0.01, it corresponds to the drainage state of the soil; The data analysis module is also used to determine the penetration characteristics of the bucket foundation, including undrained penetration and drained penetration, based on the penetration speed of the bucket foundation and the drainage conditions of the surrounding soil. Among them, when the permeability of the soil layer is low and there is no obvious dissipation of pore water pressure during the penetration process, the penetration characteristic is undrained penetration.

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