A quasi-static calculation method suitable for simulating the impact of pile driving operations on adjacent structures

Abstract

The present invention discloses a quasi-static calculation method suitable for simulating the influence of pile driving operation on adjacent structures. The present invention takes into account the excavation process of underwater structures, divides the soil into three areas: column hole area caused by pile shoe downward pressure, excavation area of ​​underwater structures, and influence area for analysis. According to the column hole expansion theory, the force of the pile shoe penetration process on the surrounding soil is simplified to the base pressure acting at the depth of pile shoe downward pressure and the hole expansion tension acting on the side wall of the soil, so as to accurately calculate the influence of pile driving operation on the deformation and stress of adjacent structures in actual engineering. The present invention uses ABAQUS finite element software and adopts static analysis steps, which has high calculation efficiency, short time consumption, reliable numerical calculation of underwater structure deformation and stress, and the calculation results are consistent with the centrifuge test results, which can effectively solve the problems in actual engineering. The present invention is in line with engineering practice, the method is simple and clear, and it is easy to calculate.

Description

Technical Field

[0001] The invention belongs to the technical field of numerical simulation, and in particular relates to a pseudo-static calculation method suitable for simulating the influence of a pile driving operation on an adjacent structure. Background Art

[0002] Rapid economic development is often accompanied by a large consumption of energy. However, the development level of onshore oil and gas resources is very high, and the proven exploitable oil and gas resources are becoming less and less. In contrast, offshore oil and gas resources are relatively abundant, so large-scale development of offshore oil and gas resources has become an inevitable trend. Self-elevating drilling platforms are marine mobile platforms with the advantages of strong positioning capabilities and good operating stability. They are increasingly widely used in the field of offshore oil and gas resource exploration and development. The diameter of the pile shoe of a self-elevating drilling platform is generally between 10 and 20 meters. During drilling operations, the insertion and extraction of the pile shoe will displace a large amount of soil. The movement of the soil will inevitably have an adverse effect on the surrounding platform foundations or underwater protective structures, endangering the safety of facilities. How to evaluate the impact of the insertion and extraction of piles on self-elevating drilling platforms on adjacent structures has become a research focus in recent years.

[0003] At present, the commonly used numerical analysis method for studying the influence of pile shoe insertion and extraction on adjacent structures is mainly based on the coupled Euler-Lagrangian (CEL) method of ABAQUS numerical analysis software. The CEL method is mainly used for fluid-solid coupling simulation or large deformation simulation. When solving the problem of the influence of pile shoe insertion and extraction on adjacent structures, it has three defects: ① It cannot accurately deal with the influence of pile insertion on the surrounding excavation pits and other hole structures. In the existing CEL method, holes are generally set within 10m above the Euler soil body to provide space for the soil body to bulge upward during the pile shoe insertion and extraction process. The soil body continuously flows to the upper hole during the pile insertion operation. However, if there is an excavation structure in the soil body, the Euler soil body needs to be set as a hole at the excavation site. At this time, the flow mechanism of the soil body changes, and even time effects will occur, affecting the stress and deformation of the adjacent structures. ② Since the principle of the CEL method is that the shape, size and position of the spatial grid remain unchanged during the calculation process, and the soil body continuously flows between the grids, the bearing capacity curve calculated using the CEL large deformation algorithm is unstable, and the deformation results of the adjacent structures are too large. ③The CEL algorithm has low computational efficiency and takes a long time.

[0004] In view of the above problems, based on the column hole expansion theory and the static analysis in ABAQUS, a finite element analysis method for analyzing the impact of pile driving on adjacent structures is proposed. This method can consider the impact of pile shoe insertion and extraction on the surrounding soil and structures when there are holes such as excavated pits, and the static analysis method is used, which shortens the calculation time and effectively solves the problem of low calculation efficiency. Summary of the invention

[0005] The purpose of the present invention is to provide a quasi-static calculation method suitable for simulating the influence of pile driving operation on adjacent structures. The method simplifies the force exerted by the pile shoe penetration process on the surrounding soil into the base pressure acting at the pile shoe downward pressure depth and the hole expansion tension acting on the side wall of the soil based on the column hole expansion theory. The unit life and death function in ABAQUS is used to realize the static method to simulate the continuous penetration process of the pile shoe, thereby accurately evaluating the influence of the pile shoe insertion and extraction action on the underwater structure in the actual project.

[0006] The technical solution adopted by the present invention is:

[0007] A pseudo-static calculation method suitable for simulating the impact of pile driving operations on adjacent structures, the specific calculation steps are as follows:

[0008] S1. According to the analysis conditions, the corresponding finite element analysis model is established, which specifically includes: soil model and underwater structure model. The soil model is divided into three areas, including: column hole area caused by pile shoe pressure, excavation area and influence area of ​​underwater structure. The diameter of the pile shoe, that is, the diameter of the column hole area, is D1, the penetration depth of the pile shoe, that is, the depth of the column hole area, is d, the diameter of the excavation area is D2, the depth of the excavation area is h, the width of the influence area is ≥10D1, and the depth of the influence area is ≥10d; the outer diameter of the underwater structure model is D2, the height of the underwater structure model is H, and the wall thickness of the underwater structure model is t.

[0009] S2. Establish soil material properties and underwater structure material properties, and assign them to the soil model and underwater structure model respectively.

[0010] S3. According to the calculation conditions, the underwater structure model and the soil model are assembled together to form an assembly. The parameters to be set include: the distance between the pile shoe and the underwater structure model and the burial depth of the underwater structure model.

[0011] S4. Establish the calculation analysis step of the numerical analysis model. A total of 5 analysis steps are established, including: ground stress analysis step, underwater structure placement analysis step, underwater structure excavation analysis step, column hole area formation analysis step and column hole area expansion analysis step.

[0012] S5. Establish interaction. First, establish the contact properties between the underwater structure and the soil, generally using surface-to-surface contact. Then use the unit life and death function in the interaction to simulate the placement of the underwater structure and the excavation of the internal soil, as well as the process of the pile shoe pressing down to produce the column hole area. The specific steps are: use the unit life and death function to set the underwater structure to invalid in the ground stress analysis step, and set it to reactivate in the underwater structure placement analysis step; set the underwater structure excavation area to invalid in the excavation analysis step to simulate the excavation of the soil in this area; set the column hole area to invalid in the column hole formation analysis step to simulate the formation of the column hole area in the soil in this area due to the pressure of the pile shoe.

[0013] S6. Establish the boundary conditions of the model. Set reasonable displacement boundaries for the soil model, including: full constraints at the bottom of the soil, release of displacement along the depth direction on the sides of the soil, and full constraints on the rest, and displacement along the depth direction on the top of the soil.

[0014] S7. Establish load conditions. Including: ① Apply gravity to all soils in the geostress analysis step. ② Apply gravity to underwater structures in the underwater structure placement analysis step. ③ Apply a pressure equal to the base pressure to the bottom soil surface in the column hole area expansion analysis step. ④ Apply a pressure equal to the expansion force to the lateral soil surface in the column hole area expansion analysis step.

[0015] S8. Apply geostress field to the soil.

[0016] S9. Grid the soil model and the underwater structure model.

[0017] S10. Submit the job for calculation.

[0018] The advantages and positive effects of the present invention are:

[0019] 1. Considering the excavation process of underwater structure, the soil is divided into three areas: column hole area caused by pile shoe pressure, excavation area of ​​underwater structure, and influence area for analysis. According to the column hole expansion theory, the force exerted by the pile shoe penetration process on the surrounding soil is simplified to the base pressure acting at the pile shoe pressure depth and the hole expansion tension acting on the side wall of the soil, so as to accurately calculate the influence of pile driving operation on the deformation and stress of adjacent structures in actual engineering.

[0020] 2. Using ABAQUS finite element software and static analysis step, the calculation efficiency is high, the time consumption is short, the calculation of underwater structure deformation and stress is reliable, the calculation results are consistent with the centrifuge test results, and can effectively solve problems in actual engineering.

[0021] 3. In summary, the present invention is in line with engineering practice, the method is simple and clear, and it is easy to calculate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of soil model area division.

[0023] Figure 2 It is a schematic diagram of column hole expansion.

[0024] Figure 3 It is a schematic diagram of the relative position of the ring ribs.

[0025] Figure 4 It is a schematic diagram of finite element mesh division.

[0026] Figure 5 This is the centrifugal test steel cylinder displacement and strain gauge measurement point arrangement diagram.

[0027] Figure 6 This is a comparison chart between the steel cylinder body strain centrifugal test and numerical model results.

[0028] Figure 7 It is a numerical calculation cloud diagram of the displacement of the steel cylinder body.

[0029] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0030] In order to further illustrate the content and calculation effect of the present invention, the following examples are listed in conjunction with the accompanying drawings for illustration:

[0031] Example 1

[0032] S1. According to the analysis conditions, the corresponding finite element analysis model is established, including: soil model and steel cylinder model. The soil model is divided into three areas, including: column hole area caused by the downward pressure of the pile shoe, the excavation area inside the steel cylinder and the influence area. The diameter of the pile shoe, that is, the diameter of the column hole area, is D1, the penetration depth of the pile shoe, that is, the depth of the column hole area, is d, the diameter of the excavation area is D2, the depth of the excavation area is h, the width of the influence area is ≥10D1, and the depth of the influence area is ≥10d; the outer diameter of the underwater structure model is D2, the height of the underwater structure model is H, and the wall thickness of the underwater structure model is t.

[0033] In this step, the calculation parameters are as follows: the diameter of the pile shoe D1 = 18m, the penetration depth of the pile shoe d = 3m; the adjacent underwater structure is a large-diameter thin-walled steel cylinder with a diameter of D2 = 28m and a height of H = 18m. The cylinder wall and transverse ribs are made of Q345B steel. The thickness of the ring rib on the steel cylinder is 25mm, the width of the ring rib is 260mm, and the relative position of the ring rib is shown in the figure. Figure 3 As shown in the figure, the distance between the edge of the steel cylinder and the edge of the pile shoe is 0.8D1; the soil is homogeneous clay, and the excavation depth of the soil inside the steel cylinder is h=9.2m. The specific parameters of the steel cylinder and soil are shown in Table 1.

[0034] Table 1 Calculation parameters

[0035]

[0036] S2. Establish soil material properties and steel cylinder material properties, and assign them to the soil model and steel cylinder model respectively.

[0037] S3. According to the calculation conditions, the distance between the pile shoe and the steel cylinder is determined to be 0.8D1, the buried depth H of the steel cylinder is determined to be 18m, and the steel cylinder model is assembled together with the soil model to form an assembly.

[0038] S4. Establish corresponding calculation and analysis steps (static, general), including: ground stress analysis step, steel cylinder placement analysis step, steel cylinder excavation analysis step, column hole area formation analysis step, column hole area expansion analysis step.

[0039] S5. Establish interaction. First, establish the contact properties between the steel cylinder and the soil, using surface-to-surface contact, with the normal behavior set to "hard" contact and the tangential behavior penalty function set to 0.4. Then use the unit life and death function in the interaction to simulate the placement of the steel cylinder, the excavation of the internal soil, and the process of the pile shoe pressing down to form a column hole area. The specific steps are: use the unit life and death function to set the steel cylinder to invalid in the ground stress analysis step, and set it to reactivate in the steel cylinder placement analysis step; set the internal excavation area of ​​the steel cylinder to invalid in the excavation analysis step to simulate the excavation of the soil in this area; set the column hole area to invalid in the column hole formation analysis step to simulate the formation of a column hole area in the soil in this area due to the pressure of the pile shoe.

[0040] S6. Establish the boundary conditions of the model. Set reasonable displacement boundaries for the soil model, including: set displacement constraints on the sides of the soil, set directions 1 and 2 to 0; set displacement constraints on the bottom of the soil, set directions 1, 2, and 3 to 0; set displacement constraints on the top of the soil, set direction 3 to 0.

[0041] S7. Establish load conditions. Including: ① In the ground stress analysis step, gravity is applied to all soils, and the vertical component is set to 10. ② In the steel cylinder placement analysis step, gravity is applied to the steel cylinder, and the vertical component is set to 10. ③ In the column hole area expansion analysis step, a pressure equal to the base pressure is applied to the bottom soil surface in the area, and the specific value is 220kPa. ④ In the column hole area expansion analysis step, a pressure equal to the expansion force is applied to the lateral soil surface in the area. The load distribution form is rectangular along the depth direction, and the maximum value is determined by Figure 2 The column hole expansion theory is derived. According to the column hole expansion theory solution, the soil satisfies the following equilibrium differential equation:

[0042]

[0043] The penetration process of the pile shoe in clay is an undrained process, and the soil material obeys the Tresca yield criterion, that is:

[0044] σ r -σ θ =2K (2)

[0045] Where: K is Tresca constant, K = s u .

[0046] Combining equations (1) and (2), and substituting the corresponding boundary conditions into the integral, we can obtain:

[0047]

[0048] Where: I r is the stiffness index, and its expression is G is the shear modulus of the soil, s u is the undrained strength of the soil; p u is the hole expansion tension, and after substituting it into the hole expansion tension p in this example, u It is 280kPa.

[0049] S8. Apply a geostress field to the soil to balance the geostress. Since the soil height is 40m, the geostress value at the bottom of the soil is -380kPa.

[0050] S9. Grid the soil model and the steel cylinder model. Both the soil model and the steel cylinder model are simulated using solid units, the grid attribute is hexahedral unit C3D8R, and the grid size in the grid encryption area is 0.05D1. The area outside the range of one diameter of the pile shoe is less affected, so the grid is selected with single precision and the grid size is 0.05D1-0.2D1. The specific grid division method is shown in Figure 4 .

[0051] S10. Submit the job for calculation.

[0052] Example 2

[0053] This embodiment carries out a centrifuge model test on the influence of pile shoe penetration on the adjacent steel cylinder structure when the pile shoe spacing is 0.8D1 for the example working condition. The centrifuge used in the test is a TK-C500 geotechnical centrifuge. In the test, the pile shoe and steel cylinder models were established with reference to the example working condition at a scale of 1:100. The centrifuge test can measure the strain and displacement of the cylinder wall more accurately. During the test, in order to measure the deformation of the steel cylinder, four displacement measuring points F1-F4 were arranged on the top surface of the steel cylinder. The measuring point data was collected by a laser displacement sensor. The specific arrangement is as follows: Figure 5 (a) As shown; a group of strain gauges are set at intervals of 45° along the circumferential direction on the outer wall of the steel cylinder, numbered 1-8 in sequence, and the strain gauges are BX120-2AA type. The specific arrangement is shown in the diagram Figure 5 (b) As shown. For the specific soil preparation method and test loading process, please refer to the literature: Zhang Haiyang, Liu Run, Jia Zhaolin. Study on the influence of pile insertion of self-elevating platform on the pile foundation of adjacent platform[J]. Chinese Journal of Geotechnical Engineering, 2021, 43(05): 867-876.

[0054] Figure 6 The following is a comparison chart of the strain results of the adjacent steel cylinder body affected by the insertion and removal of the pile shoe calculated using this method and the centrifuge test results. Figure 6It can be seen that the method proposed in this invention is in good agreement with the centrifuge test results and can more accurately consider the influence of the insertion and extraction of the pile shoe on the stress and strain of the adjacent structure. Figure 7 As shown in the figure, the displacement reaches the maximum at the position of the pile shoe connection line at the top of the steel cylinder, and the displacement deformation mode is the same as the centrifuge test result. The specific numerical values ​​and the centrifuge test results are compared in Table 2. As can be seen from Table 2, the numerical calculation displacement result differs from the centrifuge test displacement result by 1.70%, which shows that the method proposed in the present invention can better simulate the influence of pile shoe insertion and extraction on the displacement of adjacent structures.

[0055] Table 2 Comparison of displacement of steel cylinder

[0056]

[0057] The present invention is described above by way of example. It should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacement that can be made by those skilled in the art without inventive effort falls within the protection scope of the present invention.

Claims

1. A pseudo-static calculation method suitable for simulating the impact of pile driving operations on adjacent structures, characterized in that: S1. According to the analysis conditions, a corresponding finite element analysis model is established, which specifically includes: a soil model and an underwater structure model. The soil model is divided into three areas, including: a column hole area caused by the downward pressure of the pile shoe, an excavation area of ​​the underwater structure, and an influence area. The diameter of the pile shoe, i.e., the diameter of the column hole area, is D1, the penetration depth of the pile shoe, i.e., the depth of the column hole area, is d, the diameter of the excavation area is D2, the depth of the excavation area is h, the width of the influence area is ≥10D1, and the depth of the influence area is ≥10d; the outer diameter of the underwater structure model is D2, the height of the underwater structure model is H, and the wall thickness of the underwater structure model is t; S2, establishing soil material properties and underwater structure material properties, and assigning them to the soil model and the underwater structure model respectively; S3. According to the calculation conditions, the underwater structure model and the soil model are assembled together to form an assembly; S4, calculation and analysis step of establishing a numerical analysis model; S5. Establish the interaction. First, establish the contact properties between the underwater structure and the soil. Then, use the unit life and death function in the interaction to simulate the placement of the underwater structure, the excavation of the internal soil, and the process of the pile shoe pressing down to produce the column hole area. S6. Establish the boundary conditions of the model and set reasonable displacement boundaries for the soil model; S7. Establish load conditions, including: ① applying gravity to all soils in the geostress analysis step, ② applying gravity to the underwater structure in the underwater structure placement analysis step, ③ applying a pressure equal to the base pressure to the bottom soil surface in the column hole area expansion analysis step, and ④ applying a pressure equal to the expansion force to the lateral soil surface in the column hole area expansion analysis step; S8. Apply geostress field to soil; S9. Meshing the soil model and the underwater structure model; S10. Submit the job for calculation.

2. A pseudo-static calculation method suitable for simulating the impact of pile driving operation on adjacent structures according to claim 1, characterized in that: In S3, the parameters to be set include: the distance between the pile shoe and the underwater structure model and the burial depth of the underwater structure model.

3. A pseudo-static calculation method suitable for simulating the impact of pile driving operation on adjacent structures according to claim 1, characterized in that: In S4, a total of 5 analysis steps are constructed, including: ground stress analysis step, underwater structure placement analysis step, underwater structure excavation analysis step, column hole area formation analysis step and column hole area expansion analysis step.

4. A pseudo-static calculation method suitable for simulating the impact of pile driving operation on adjacent structures according to claim 1, characterized in that: In S5, the specific steps are: use the unit life and death function to set the underwater structure to invalid in the ground stress analysis step, and set it to reactivate in the underwater structure placement analysis step; set the underwater structure excavation area to invalid in the excavation analysis step to simulate the excavation of the soil in this area; set the column hole area to invalid in the column hole formation analysis step to simulate the formation of the column hole area in the soil in this area due to the downward pressure of the pile shoe.

5. A pseudo-static calculation method suitable for simulating the impact of pile driving operation on adjacent structures according to claim 1, characterized in that: In S6, the displacement boundaries include: full constraint at the bottom of the soil, release of displacement along the depth direction on the sides of the soil, and full constraint on the rest, and displacement along the depth direction on the top of the soil.

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