A cofferdam structure design method based on dynamic growth of boundary conditions

Abstract

The present invention discloses a cofferdam structure design method based on dynamic growth of boundary conditions, including: dividing the cofferdam structure construction process into multiple stages, and determining the boundary conditions of each stage; first determining the initial values ​​of various dimensional parameters of the cofferdam structure under the boundary conditions of the first stage; replacing the boundary conditions of the previous stage with the boundary conditions of the current stage in subsequent construction stages, and using the various dimensional parameters of the cofferdam structure obtained in the previous stage to calculate the stress value of the cofferdam structure under the boundary conditions of the current stage, and judging whether the ratio of the stress value of the cofferdam structure to the design strength of the cofferdam structure at this time reaches the expected value; if not, then correcting the various dimensional parameters of the cofferdam structure obtained in the previous stage until the requirements are met. The present invention can ensure that the stress level of the cofferdam structure in each construction stage is within the expected range, and the structural design is more economical and reasonable.

Description

Technical Field

[0001] The present invention relates to the field of cofferdam structure construction, and more specifically, to a cofferdam structure design method based on dynamic growth of boundary conditions. Background Art

[0002] There are various forms of bridge foundations in my country. For underwater foundations, it is usually necessary to construct a cofferdam first, pump out water to form a dry construction environment, and then construct the foundation. For structures similar to large cofferdams, static design methods based on the ultimate bearing capacity of unfavorable working conditions are often used. At the beginning of the design, the most unfavorable working conditions that may occur are often considered, and the bearing capacity of the temporary structure is calculated as the most unfavorable conditions, so as to determine and optimize the size and form of the structure. However, for some temporary structures, due to their long construction period, or foundation treatment before construction, and the effect of foundation treatment takes a long time to gradually appear, the external boundary conditions of the temporary structure are constantly changing during different construction stages or use stages. If the previous static design method is still used for design, there will inevitably be a situation where the boundary is weak in the early stage, the safety factor of the structure is particularly high, and the utilization rate of the structure is very low. Therefore, it is urgent to propose a large-scale temporary structure design method based on the dynamic growth of boundary conditions to solve this problem. Summary of the invention

[0003] An object of the present invention is to solve at least the above problems and to provide at least the advantages which will be described hereinafter.

[0004] In order to achieve these purposes and other advantages according to the present invention, a cofferdam structure design method based on dynamic growth of boundary conditions is provided, comprising: dividing the cofferdam structure construction process into multiple stages, and determining the boundary conditions of each stage; the cofferdam structure includes multiple dimensional parameters, and firstly determining the initial values ​​of the dimensional parameters of the cofferdam structure according to the boundary conditions of the first stage; in subsequent construction stages, the boundary conditions of the previous stage are replaced by the boundary conditions of the current stage, and the dimensional parameters of the cofferdam structure obtained in the previous stage are used to calculate the stress value of the cofferdam structure under the boundary conditions of the current stage, and it is judged whether the ratio of the stress value of the cofferdam structure to the design strength of the cofferdam structure at this time reaches the expected value; if not, the dimensional parameters of the cofferdam structure obtained in the previous stage are corrected until the ratio of the stress value of the cofferdam structure in the current stage to the design strength of the cofferdam structure reaches the expected value.

[0005] Preferably, it is characterized in that the estimated value of the ratio of the stress value of the cofferdam structure at the current stage to the design strength of the cofferdam structure is 50% to 70%.

[0006] Preferably, the cofferdam structure is a steel pipe pile cofferdam, and its dimensional parameters include the length, diameter and wall thickness of the steel pipe piles.

[0007] Preferably, the boundary condition includes soil spring stiffness of the soil where the cofferdam structure is located.

[0008] Preferably, in the first construction stage, the initial values ​​of the dimensional parameters of the cofferdam structure are calculated according to the following steps:

[0009] S1.1. In the case of no soil treatment, the maximum initial value of each dimension parameter of the cofferdam structure is calculated based on the principle that the ratio of the stress value of the cofferdam structure at the current stage to the design strength of the cofferdam structure reaches the expected value;

[0010] S1.2. When the soil is solidified, the minimum initial value of each dimension parameter of the cofferdam structure is calculated based on the principle that the ratio of the stress value of the cofferdam structure at the current stage to the design strength of the cofferdam structure reaches the expected value;

[0011] S1.3. Take the average of the maximum initial value and the minimum initial value of each size parameter of the cofferdam structure as the initial value of the corresponding size parameter;

[0012] S1.4. Calculate the stress value of the cofferdam structure according to the boundary conditions of the first stage. If the ratio of the stress value to the design strength of the cofferdam structure reaches the expected value, the current preliminary initial value is the initial value of each dimensional parameter of the cofferdam structure; otherwise, the dimensional parameters of the cofferdam structure are revised until the ratio of the calculated stress value to the design strength of the cofferdam structure reaches the expected value.

[0013] Preferably, when the dimensional parameters of the cofferdam structure need to be modified, the following principles are followed:

[0014] The difference between the maximum initial value and the minimum initial value of each dimension parameter of the cofferdam structure calculated in the first stage is divided into N equal parts, and each time a correction is made, the value of the current dimension parameter is increased by one equal part.

[0015] Preferably, when the difference between the maximum initial value and the minimum initial value of each dimensional parameter of the cofferdam structure calculated in the first stage is divided into N equal parts, the value of N corresponding to each dimensional parameter may be different.

[0016] The present invention has at least the following beneficial effects:

[0017] The cofferdam structure design method based on the dynamic growth of boundary conditions provided by the present invention firstly formulates the initial values ​​of the dimensional parameters of the cofferdam structure in the first stage, and then continuously replaces them according to the changes of boundary conditions in different stages, and repeatedly iterates the calculation to ensure that the stress level of the cofferdam structure in each construction stage is within the expected range. Compared with the structure directly calculated and designed according to the most unfavorable working conditions, the maximum utilization rate of the entire construction stage is achieved, and the structural design is more economical and reasonable.

[0018] Other advantages, objectives and features of the present invention will be embodied in part through the following description, and in part will be understood by those skilled in the art through study and practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a flow chart of the cofferdam structure design method based on dynamic growth of boundary conditions according to the present invention;

[0020] Figure 2 It is a schematic diagram of the implementation effect of the cofferdam structure design method based on dynamic growth of boundary conditions according to the present invention; DETAILED DESCRIPTION

[0021] The present invention will be further described in detail below in conjunction with the accompanying drawings so that those skilled in the art can implement the invention with reference to the description.

[0022] It should be noted that the experimental methods described in the following embodiments are conventional methods unless otherwise specified, and the reagents and materials are commercially available unless otherwise specified; in the description of the present invention, the terms "lateral", "longitudinal", "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0023] like Figure 1 As shown, the present invention provides a cofferdam structure design method based on dynamic growth of boundary conditions, including: dividing the cofferdam structure construction process into multiple stages, and determining the boundary conditions of each stage; the cofferdam structure includes multiple dimensional parameters, and firstly determining the initial values ​​of the dimensional parameters of the cofferdam structure according to the boundary conditions of the first stage; the boundary conditions of the previous stage are replaced by the boundary conditions of the current stage in the subsequent construction stages, and the stress value of the cofferdam structure under the boundary conditions of the current stage is calculated using the dimensional parameters of the cofferdam structure obtained in the previous stage, and judging whether the ratio of the stress value of the cofferdam structure to the design strength of the cofferdam structure at this time reaches the expected value; if not, correcting the dimensional parameters of the cofferdam structure obtained in the previous stage until the ratio of the stress value of the cofferdam structure in the current stage to the design strength of the cofferdam structure reaches the expected value.

[0024] In this technical solution, the initial values ​​of the dimensional parameters of the cofferdam structure in the first stage are first formulated, and then they are continuously replaced according to the changes in the boundary conditions of different stages, and the calculation is repeated iteratively to ensure that the stress level of the cofferdam structure in each construction stage is within the expected range; when all construction stages have completed the iterative calculation, the dimensional parameters of the cofferdam structure finally obtained are the final values ​​of the dimensional parameters of the cofferdam structure. The present invention determines whether the stress level of the cofferdam structure is within the prefabrication range by whether the dimensional parameters of the cofferdam structure in the current stage meet the ratio of the stress value of the cofferdam structure after the construction of the current stage to the design strength of the cofferdam structure to reach the expected value. Compared with the structure directly calculated and designed according to the most unfavorable working conditions, the maximum utilization rate of the entire construction stage is achieved, and the structural design is more economical and reasonable.

[0025] In another technical solution, the ratio of the stress value of the cofferdam structure at the current stage to the design strength of the cofferdam structure is estimated to be 50% to 70%. That is, when the stress value of the cofferdam structure accounts for 50% to 70% of the design strength of the cofferdam structure, it can be considered that the cofferdam structure meets the stress requirements.

[0026] In another technical solution, specifically, the cofferdam structure is a steel pipe pile cofferdam, and its dimensional parameters include the length, diameter and wall thickness of the steel pipe piles.

[0027] The boundary conditions include the soil spring stiffness of the soil where the cofferdam structure is located.

[0028] In another technical solution, in the first construction stage, the initial values ​​of the dimensional parameters of the cofferdam structure are calculated according to the following steps:

[0029] S1.1. In the case where the soil is not treated, the maximum initial value of each size parameter of the cofferdam structure is calculated based on the principle that the ratio of the stress value of the cofferdam structure at the current stage to the design strength of the cofferdam structure reaches the expected value;

[0030] S1.2. In the case of soil solidification, the minimum initial values ​​of the various dimensional parameters of the cofferdam structure are calculated based on the principle that the ratio of the stress value of the cofferdam structure at the current stage to the design strength of the cofferdam structure reaches the expected value;

[0031] S1.3. Take the average of the maximum initial value and the minimum initial value of each size parameter of the cofferdam structure as the initial value of the corresponding size parameter;

[0032] S1.4. Calculate the stress value of the cofferdam structure according to the boundary conditions of the first stage. If the ratio of the stress value to the design strength of the cofferdam structure reaches the expected value, the current preliminary initial value is the initial value of each dimensional parameter of the cofferdam structure; otherwise, the dimensional parameters of the cofferdam structure are revised until the ratio of the calculated stress value to the design strength of the cofferdam structure reaches the expected value.

[0033] Furthermore, when the dimensional parameters of the cofferdam structure need to be modified, the following principles shall be followed:

[0034] The difference between the maximum initial value and the minimum initial value of each dimension parameter of the cofferdam structure calculated in the first stage is divided into N equal parts, and each time a correction is made, the value of the current dimension parameter is increased by one equal part.

[0035] When the difference between the maximum initial value and the minimum initial value of each size parameter of the cofferdam structure calculated in the first stage is divided into N equal parts, the value of N of each size parameter can be different. The value of N is an empirical value and is selected according to actual conditions.

[0036] The design of a cofferdam structure for island construction is taken as an example to further illustrate the cofferdam structure design method based on the dynamic growth of boundary conditions described in the present invention. The geological conditions of this engineering project are deep silt geology, with extremely small internal friction angle and extremely weak shear resistance. The silt soil within a range of more than ten meters cannot consider its lateral spring stiffness in the calculation process. The overall construction process is that before the construction of the island cofferdam, the seabed silt is first treated with a plastic drainage board for foundation treatment. According to the actual situation on site and finite element simulation, as time goes by, within a period of nearly 90 days, the consolidation degree of the silt after drainage gradually increases to more than 90%, and the entire cofferdam island construction cycle is also close to 90 days. During this period, the island cofferdam construction is experienced, the island is backfilled with medium and coarse sand for the first, second, and third time, and the membrane bag concrete is constructed outside the cofferdam. The external load increases continuously at different construction stages. According to the above content, the cofferdam structure construction of the project is divided into four stages, and the boundary conditions of the four stages are determined. The finite element model of the entire cofferdam structure is established using finite element analysis software. The constraint conditions are that the bottom of the steel pipe pile is consolidated, and a spring that only transmits axial force is used to constrain the hoop and the steel pipe pile. The lateral stiffness of the soil is converted according to the soil strength of the steel pipe pile, and soil spring constraints are applied. The input of the material properties of the steel pipe pile includes the steel properties, length, diameter and wall thickness of the steel pipe pile.

[0037] (1) According to the condition of untreated sludge, the maximum initial length L of the steel pipe pile is calculated based on the principle that the stress level of the cofferdam structure is controlled at 50%~70% of the design strength of the cofferdam structure. max , maximum initial diameter D max , Maximum initial wall thickness C max ;

[0038] (2) According to the situation of sludge treatment, the minimum initial length L of the steel pipe pile is calculated based on the principle that the stress level of the cofferdam structure is controlled at 50%~70% of the design strength of the cofferdam structure. min , minimum initial diameter D min , minimum initial wall thickness C min ;

[0039] The maximum and minimum initial values ​​of the dimensional parameters of the above-mentioned cofferdam structure are obtained by bringing the stress of the cofferdam structure into the finite element model and adjusting the stiffness of the soil spring.

[0040] (3) Determine the initial length L of the steel pipe pile according to the dichotomy method ′ 1. Initial diameter D ′ 1. Initial wall thickness C ′ 1.L ′ 1=(L max +L min ) / 2, D ′ 1=(L max +L min ) / 2, C ′ 1=(L max +L min ) / 2;

[0041] (4) In the first construction stage, the boundary conditions of the first stage (i.e., the soil spring stiffness when the sludge is not treated) are introduced into the finite element model to perform structural calculations. At this time, the stress value σ1 of the steel pipe pile is obtained. If σ1 is between 50% and 70% of the design strength of the cofferdam structure, the next stage of calculation is performed. If the calculated stress value of the steel pipe pile does not meet the requirements, the initial length L1, initial diameter D1, and initial wall thickness C1 of the steel pipe pile are corrected. The correction amplitude △L= (L max -L min ) / N L , △D=(D max -D min ) / N D , △C = (C max -C min ) / N C , N L 、N D 、N C The value of is selected according to the actual situation, and can be the same or different; for example, if the length difference is 10m, it can be increased by 0.1m, if the diameter difference is 0.5m, it can be increased by 0.05m, and if the wall thickness difference is 10cm, it can be increased by 0.1cm; and the initial values ​​of various dimensional parameters of the first-stage cofferdam structure are determined, namely, the initial length L1, initial diameter D1, and initial wall thickness C1.

[0042] (5) Perform the second stage analysis (the first backfill of medium-coarse sand on the island), bring the boundary conditions of the second stage into the finite element model (the soil spring stiffness corresponding to the silt strength after 20 days of silt treatment), and perform structural calculations. At this time, the stress value σ2 of the steel pipe pile is obtained. If σ2 is between 50% and 70% of the design strength of the cofferdam structure, proceed to the next stage of calculation; if σ2 does not meet the requirements, continue to modify the dimensional parameters of the steel pipe pile according to △L, △D and △C obtained in step (4) until the calculated σ2 meets the requirements, and use the dimensional parameters of the cofferdam structure corresponding to the stress value that meets the requirements as the dimensional parameters of the cofferdam structure in the current stage.

[0043] (6) Repeat step (5) until the fourth construction stage is completed. If σ1~σ4 are all between 50% and 70% of the design strength of the cofferdam structure, Figure 2 As shown, the structural design is completed, and the final dimensional parameter values ​​of the cofferdam structure are the final values ​​of the dimensional parameters of the determined cofferdam structure. Figure 2 The dynamic design marked in the figure is the cofferdam structure design method based on dynamic growth of boundary conditions provided by the present invention.

[0044] Compared with the static design theory, the cofferdam structure design method based on the dynamic growth of boundary conditions provided by the present invention can control the design indicators such as stress within the expected range at each construction stage, and the structure is reasonably stressed at each stage and the performance is fully utilized. If the static design is designed according to the initial boundary conditions and the most unfavorable load in order to achieve the final design level, the utilization rate of the early structure is only 20% to 30%.

[0045] Although the embodiments of the present invention have been disclosed as above, they are not limited to the applications listed in the specification and the implementation modes, and they can be fully applied to various fields suitable for the present invention. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present invention is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A cofferdam structure design method based on dynamic growth of boundary conditions, characterized in that: include: Divide the cofferdam structure construction process into multiple stages and determine the boundary conditions for each stage; The cofferdam structure contains multiple size parameters. First, the initial values ​​of the size parameters of the cofferdam structure are determined according to the boundary conditions of the first stage. In the subsequent construction stages, the boundary conditions of the previous stage are replaced by the boundary conditions of the current stage, and the size parameters of the cofferdam structure obtained in the previous stage are used to calculate the stress value of the cofferdam structure under the boundary conditions of the current stage, and it is judged whether the ratio of the stress value of the cofferdam structure to the design strength of the cofferdam structure at this time reaches the expected value. If not, the dimensional parameters of the cofferdam structure obtained in the previous stage are corrected until the ratio of the stress value of the cofferdam structure in the current stage to the design strength of the cofferdam structure reaches the expected value.

2. The cofferdam structure design method based on dynamic growth of boundary conditions according to claim 1 is characterized in that: At the current stage, the estimated value of the ratio of the stress value of the cofferdam structure to the design strength of the cofferdam structure is 50%~70%.

3. The cofferdam structure design method based on dynamic growth of boundary conditions according to claim 1 is characterized in that: The cofferdam structure is a steel pipe pile cofferdam, and its size parameters include the length, diameter and wall thickness of the steel pipe piles.

4. The cofferdam structure design method based on dynamic growth of boundary conditions according to claim 1, characterized in that: The boundary conditions include the soil spring stiffness of the soil where the cofferdam structure is located.

5. The cofferdam structure design method based on dynamic growth of boundary conditions according to claim 1, characterized in that: In the first construction stage, the initial values ​​of the dimensional parameters of the cofferdam structure are calculated according to the following steps: S1.

1. In the case of no soil treatment, the maximum initial value of each dimension parameter of the cofferdam structure is calculated based on the principle that the ratio of the stress value of the cofferdam structure at the current stage to the design strength of the cofferdam structure reaches the expected value; S1.

2. When the soil is solidified, the minimum initial value of each dimension parameter of the cofferdam structure is calculated based on the principle that the ratio of the stress value of the cofferdam structure at the current stage to the design strength of the cofferdam structure reaches the expected value; S1.

3. Take the average of the maximum initial value and the minimum initial value of each size parameter of the cofferdam structure as the initial value of the corresponding size parameter; S1.

4. Calculate the stress value of the cofferdam structure according to the boundary conditions of the first stage. If the ratio of the stress value to the design strength of the cofferdam structure reaches the expected value, the current preliminary initial value is the initial value of each dimensional parameter of the cofferdam structure; otherwise, the dimensional parameters of the cofferdam structure are revised until the ratio of the calculated stress value to the design strength of the cofferdam structure reaches the expected value.

6. The cofferdam structure design method based on dynamic growth of boundary conditions according to claim 5, characterized in that: When it is necessary to modify the size parameters of the cofferdam structure, follow the following principles: The difference between the maximum initial value and the minimum initial value of each dimension parameter of the cofferdam structure calculated in the first stage is divided into N equal parts, and each time a correction is made, the value of the current dimension parameter is increased by one equal part.

7. The cofferdam structure design method based on dynamic growth of boundary conditions according to claim 6, characterized in that: When the difference between the maximum initial value and the minimum initial value of each size parameter of the cofferdam structure calculated in the first stage is divided into N equal parts, the value of N corresponding to each size parameter is different.

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