JP2014006797A - Analysis method and design method of marine structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an analysis method of a marine structure capable of analyzing its behavior with high accuracy.SOLUTION: Since contact definition of a contact part 12b between an impervious sheet material 10 and a covering layer 11, for example, includes a contact determination step and a relative displacement step, an analysis method of a marine structure 1 can recognize tensile force acting on the detailed behavior of the marine structure 1 and the impervious sheet material, with higher accuracy compared to a conventional analysis method using a finite element method.

Description

  The present invention relates to a marine structure analysis method for analyzing behavior when an external force is applied to a marine structure including a soil layer made of a soil material and a sheet material in contact with the soil layer, and the analysis thereof. The present invention relates to a design method for offshore structures based on the analysis results.

Conventionally, for example, a sheet material, for example, a water shielding sheet material, is laid on a foundation mound (soil layer) made of a soil material, and a covering layer (soil layer) is formed with the soil material on the surface of the water shielding sheet material. As the design method for offshore structures, the upper layer and lower layer of the cover layer are considered as one rigid body, and the sliding load that the upper layer slides on the water shielding sheet material is compared with the supporting resistance load of the lower layer. The structure of the coating layer was designed and evaluated to obtain a static stable state.
However, with this design method, when an external force is applied to the offshore structure, it is not possible to grasp the detailed behavior of the offshore structure, especially the covering layer, such as a part of the covering layer collapsing. As a design method that can be grasped, numerical analysis (FEM analysis) using a finite element method as disclosed in Non-Patent Document 1 has been proposed.

Nozomi Kotake et al., “FEM Analysis on Slope Slip in Surface Impregnation of Managed Sea Surface Disposal Site”, Geosynthetics Proceedings, Japan Branch of International Geosynthetics Society, December 2002, Volume 17, p. 87-94

  However, with the analysis method disclosed in Non-Patent Document 1, it has been difficult to analyze a behavior that is substantially equivalent to an actual behavior such as a stress acting on the water shielding sheet material. The main factors include, for example, the condition for the contact between the water-impervious sheet material and the soil layer when setting the mesh as an analysis model, and the condition for sharing the mesh points of both mesh elements. Since the sliding resistance force between the soil layer and the water-impervious sheet material was reproduced by giving the internal friction angle of the material set to the element, the analysis results differed from the actual behavior. Therefore, it was necessary to examine the contact conditions.

  That is, when the load F acts on the soil layer 11 from the state of FIG. 4A in the contact condition of the contact portion of the analysis method according to the conventional finite element method, the soil layer 11 and the water shielding sheet material 10 include a plurality of locations. Since it is a condition for sharing the nodes, the soil layer 11 and the water shielding sheet material 10 as a whole are analyzed to be deformed to the state of FIG. 4B, and the behavior of the soil layer 11 sliding on the water shielding sheet material 10 is analyzed. The tensile force on the water shielding sheet material 10 and the like are not accurately taken into account, and the analysis result is different from the actual one, and it is necessary to examine the contact condition.

  This invention is made in view of this point, and it aims at providing the design method of the offshore structure which employ | adopted the analysis method of the offshore structure which can analyze a behavior with high precision, and its analysis method. .

As a means for solving the above-mentioned problems, the present invention provides a marine structure analysis method according to claim 1 comprising a soil layer made of a soil material and a sheet material in contact with the soil layer. A marine structure analysis method for analyzing the behavior when an external force including its own weight is applied to an offshore structure, wherein the contact definition of the contact portion between the soil layer and the sheet material is A contact determining step for determining contact; and a relative displacement step for relatively displacing both against the sliding resistance force between the two when it is determined that both are in contact in the contact determining step. It is characterized by including.
In the invention of claim 1, since the contact definition of the contact portion between the soil layer and the sheet material includes a contact determination step and a relative displacement step, the details of the marine structure are compared with the conventional analysis method by the finite element method. The displacement behavior and tensile force acting on the behavior and the sheet material can be grasped with high accuracy.

  Here, it supplements about a contact determination step. When the distance between the soil layer (the upper side of the contact surface) and the sheet material (the lower side of the contact surface) are far apart (if they are not in contact), the weight or external force acting on the soil layer Analysis is performed so that the load is not transmitted to the sheet material. On the other hand, when the distance between the two is zero (when they are in contact with each other), analysis is performed so as to transmit the load due to the own weight or external force acting on the soil layer to the sheet material. In addition, when it is determined that the soil layer is in contact with the sheet material, the analyst can arbitrarily set the indentation distance that can actually occur, so that the excessive indentation state is not analyzed. It can be set as follows. These determinations are incorporated in the program, and can greatly contribute to the ability to reproduce actual phenomena with high accuracy.

  Next, the relative displacement step will be supplemented. In the conventional method, the sliding resistance force (friction resistance force) between the two is reproduced as the internal friction angle φ of the material set in the element of the aerial mesh set between the two. For example, when the friction coefficient μ between the soil layer and the sheet material is 0.4, the element of the aerial mesh set between the two is regarded as a soil material having an internal friction angle φ = 21.8 °. On the other hand, the sliding resistance force between the two at the relative displacement step in the first aspect of the present invention is set based on the friction coefficient μ. That is, the force obtained by multiplying the load due to the self-weight or external force acting on the soil layer by the friction coefficient μ is analyzed as the sliding resistance force between them. As a result, the displacement behavior between them and the tensile force acting on the sheet material can be reproduced with high accuracy.

The invention of the marine structure analysis method described in claim 2 is characterized in that, in the invention described in claim 1, the sheet material is arranged on the slope of the soil layer.
The invention of the offshore structure analysis method according to claim 3 is the watertight insulation according to claim 1 or 2, wherein the offshore structure is the sheet material on a slope of a foundation mound made of a soil material. A sheet material is laid, and a covering layer made of a soil material is disposed on the water-impervious sheet material.
The inventions according to claims 2 and 3 are particularly effective in grasping the behavior of the water-impervious sheet material disposed between the soil layer of the offshore structure, for example, the slope of the foundation mound and the covering layer.

The invention of the method for designing an offshore structure according to claim 4 is configured by laying a sheet material on a slope of a foundation mound made of a soil material, and disposing a covering layer made of the soil material on the sheet material. The offshore structure design method is characterized in that the offshore structure is designed by adopting the analysis method according to claim 1.
The invention of the design method of the offshore structure described in claim 5 is the invention of claim 4, wherein the offshore structure is provided with a counter material for stabilizing the offshore structure at the bottom of the covering layer. Are arranged.
In the inventions according to claims 4 and 5, it is possible to appropriately design the legal gradient of the foundation mound, which is the structure of the offshore structure, and the size of the counter material that shares the sliding load on the legal bottom portion of the covering layer and handles it. The material constituting the counter material can be appropriately selected and set, and the optimum sheet material can be designed and adopted in consideration of the friction coefficient between the foundation mound and the coating layer. This is particularly effective for the whole design.

According to the analysis method of the marine structure of the present invention, the detailed behavior of the marine structure, the displacement behavior between the materials, and the tensile force acting on the sheet material can be grasped with higher accuracy than the analysis method by the conventional finite element method. be able to.
In addition, according to the design method of the offshore structure of the present invention, it is possible to perform the optimum design by suppressing the overdesign of the offshore structure as compared with the conventional design method, thereby reducing the cost of the entire offshore structure. Can contribute.

FIG. 1 is a schematic view of an offshore structure in which an analysis method and a design method according to an embodiment of the present invention are employed. FIG. 2 is a schematic diagram for explaining the contact definition of the contact portion between the coating layer and the water-impervious sheet material employed in the present analysis method. FIG. 3 shows the tensile force acting on the water-impervious sheet material analyzed by this analysis method. FIG. 4 is a schematic diagram for explaining a problem in the conventional analysis method.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to FIGS.
An offshore structure 1 to which an analysis method according to an embodiment of the present invention is applied will be described with reference to FIG.
The offshore structure 1 includes a foundation mound 2 (soil layer) extending in a direction perpendicular to the wave direction, and a plurality of dam bodies 3 arranged on the foundation mound 2 at intervals. The foundation mound 2 is formed in a trapezoidal cross section by laminating a large number of rubble as a soil material. Each bank 3 is configured by arranging a plurality of block blocks 4 along a direction perpendicular to the wave direction. Each rectangular block 4 is arranged outside the bank on the upper surface of the foundation mound 2. An upper work 5 is arranged outside the bank on the upper surface of each block block 4. On the upper surface of the foundation mound 2, a backing layer 6 is formed by laminating a number of calculus stones, which are soil materials, from each block block 4 to the inside of the bank. The inner surface of the back layer 6 is formed in a slope that is continuous with the slope of the foundation mound 2. A covering layer 7 in which a large number of crushed stones are laminated is formed along the upper slope of the foundation mound 2 outside the bank.

The water shielding sheet material 10 is disposed so as to be continuous from the upper surface of the back layer 6 to the slope inside the bank of the back layer 6 and the slope inside the bank of the foundation mound 2. On the water-impervious sheet material 10, a covering layer 11 (soil layer) is formed by laminating a large number of crushed stones which are soil materials. The surface opposite to the foundation mound 2 of the covering layer 11 is a slope, and a counter member 13 for stabilizing the entire marine structure 1 is disposed on the slope of the covering layer 11. The counter material 13 is made of a soil material such as stone or sand. The water shielding sheet material 10 is formed by, for example, laminating a protective mat (non-woven fabric with long fiber, basis weight 850 g / m ² , t = 8 mm) on both sides of linear low density polyethylene (LLDPE, high specific gravity type, t = 3 mm). An integrated three-layer structure is employed.

And in the offshore structure 1 mentioned above, in order to grasp | ascertain the detailed behavior at the time of external force acting from the dead weight of the coating layer 11, and upper direction, the finite element method (FEM analysis) is employ | adopted.
In this analysis method, first, a mesh model is created by dividing and setting constituent members such as the foundation mound 2, the covering layer 11, and the water shielding sheet material 10 of the marine structure 1 into a predetermined number of elements. Subsequently, the physical property values (unit volume weight, internal friction angle, adhesive force, Young's modulus, Poisson's ratio, etc.) of each constituent member 2, 6, 10, 11 are set.

Next, the contact part 12a between the foundation mound 2 and the backing layer 6 and the water shielding sheet material 10 and the contact part 12b between the coating layer 11 and the water shielding sheet material 10 are analyzed according to this embodiment. Set contact definition, which is a feature of the method.
Next, as a contact definition condition, a friction coefficient μ between the contact portions 12a and 12b and a relative allowable amount of interference between the two are set. Further, as the boundary condition, setting is made such as whether the end is fixed or free.
Finally, the range and the size of the load F that acts as an external force are set.
The number of elements is appropriately set by the person in charge of design based on the desired analysis time and analysis accuracy.

Next, the contact definition employed in the analysis method according to the present embodiment will be described in detail. For example, the contact definition in the contact part 12b of the coating layer 11 which is a soil layer and the water-impervious sheet material 10 will be described.
In this contact definition, when it is determined in the contact determination step that determines whether or not both the coating layer 11 and the water-impervious sheet material 10 are in contact, and in the contact determination step, both are in contact, And a relative displacement step for relatively displacing the two against the sliding resistance force between them.

  Specifically, in the contact determination step, as shown in FIG. 2A, both of the contact portions 12 b, that is, arbitrary sides of each element set in the covering layer 11, and each element set in the water shielding sheet material 10. The distance L of the vertical component between the sides is calculated. As a result, if the distance L between the side of each element on the coating layer 11 side and the side of each element on the water shielding sheet material 10 side is a distance L> 0, the water shielding sheet material 10 and the coating layer 11 Is not contacted, and the weight F of the coating layer 11 and the load F acting on the coating layer 11 are not transmitted to the water shielding sheet 10, and the coating layer 11 is independently based on the weight and the load F. Displace. Then, it returns to a contact determination step again, and it is determined whether both 10 and 11 are contacting.

On the other hand, when the distance L between the side of each element on the covering layer 11 side and the side of each element on the water shielding sheet material 10 side is calculated as distance L = 0, the water shielding sheet material 10 and the covering It is determined that the layer 11 is in contact, and the process proceeds to the next relative displacement step.
Next, in the relative displacement step, as shown in FIG. 2B, the weight of the coating layer 11 and the load F acting on the coating layer 11 are transmitted from the coating layer 11 to the water shielding sheet 10, and The coating layer 11 and the water-impervious sheet material 10 are relatively displaced against the sliding resistance force (friction resistance force) between the two by the dead weight and the load F. In addition, the sliding resistance force between the coating layer 11 and the water-impervious sheet material 10 is analyzed as a force obtained by multiplying the load F caused by the weight or the external force of the coating layer 11 acting on the water-impervious sheet material 10 by the friction coefficient μ. .

By the way, when the distance L between the side of each element on the covering layer 11 side and the side of each element on the water shielding sheet material 10 side is calculated as a distance L <0 in the contact determination step described above. The impermeable sheet material 10 and the coating layer 11 are determined to be in contact with each other so as to be relatively indented, and the process proceeds to the relative displacement step. However, the analyst determines the allowable amount of indentation within a range that does not affect the analysis result. By setting it arbitrarily, it is set so as not to analyze an excessive sinking state.
And as a contact definition of the contact part 12b of the water-impervious sheet material 10 and the coating layer 11, a contact determination step and a relative displacement step are repeated and analyzed.

  As a result, the detailed behavior of the marine structure 1, for example, the behavior of the covering layer 11 sliding on the water shielding sheet material 10 and the tensile force acting on the water shielding sheet material 10 can be grasped with high accuracy. . For example, FIG. 3 shows the tensile force acting on the water shielding sheet material 10. Considering this simply, the tensile force acting on the water-impervious sheet material 10 (legal gradient 1: 1.5) in contact with the foundation mound 2 once increases in the vicinity of the shoulder and then reaches a certain ratio toward the butt. It increases in the vicinity, rapidly increasing in the vicinity of the buttocks and is responsible for the sliding load in a relatively short section. By confirming whether or not the analyzed tensile force is within the range of the elastic region of the water-impervious sheet material 10, the soundness of the water-impervious sheet material 10 employed in the marine structure 1 is appropriately determined. Judgment can be made.

  As described above, in the analysis method of the offshore structure 1 according to the embodiment of the present invention, for example, the contact portion 12a between the foundation mound 2 and the back layer 6 and the water shielding sheet material 10, and the covering layer 11 and the water shielding sheet material 10 are set to include the contact determination step and the relative displacement step described above as the contact definition according to the present embodiment. As a result, the detailed behavior of the offshore structure 1 and the displacement behavior of the water-impervious sheet material 10 and the applied tensile force can be grasped with higher precision than the conventional analysis method using the finite element method. The result can be reflected in the overall design of the offshore structure 1. Thereby, it becomes possible to suppress the excessive design of the offshore structure 1, construction cost, etc.

  Further, in the analysis result of the offshore structure 1 according to the embodiment of the present invention, when the friction coefficient μ on both surfaces of the water shielding sheet material 10 is changed from 0.5 to 0.4 (other detailed analysis data is omitted). ), The load transmitted to the inner bottom edge of the offshore structure 1 is about 1.3 times, and when the friction coefficient μ is 0.03, it slides on the water shielding sheet 10 and the revetment is unstable. Result. Therefore, it is possible to study an effective cross-section design and countermeasure method for revetment stabilization using the analysis method according to the embodiment of the present invention.

  Thus, in the analysis method according to the present embodiment, the water shielding sheet material 10 is laid on the slope of the basic mound 2 shown in FIG. 1, the covering layer 11 is disposed on the water shielding sheet material 10, and It is most effective when optimally designing the offshore structure 1 including the counter member 13 disposed on the method bottom of the covering layer 11. That is, the legal gradient of the foundation mound 2 can be appropriately designed based on the analysis result of the present analysis method, and the cross-sectional size of the counter member 13 that shares the sliding load on the legal bottom portion of the covering layer 11 and handles it. The material constituting the counter member 13, that is, a stone material, a sand material, a concrete material, or the like can be appropriately selected and designed. Furthermore, as described above, by adopting this analysis method, it is possible to immediately grasp that the variation of the friction coefficient μ on both surfaces of the water shielding sheet material 10 greatly affects the design of the entire marine structure. In short, by adopting this analysis method, it is possible to suppress the excessive design of the entire marine structure 1 and to carry out an optimal design taking into consideration the safety aspect (safety factor) for the revetment stability, and consequently the marine structure It becomes possible to reduce the overall cost of the object 1.

  Furthermore, in order to obtain a stable analytical solution in the conventional finite element method (analysis diverges and does not stop in the middle), the size ratio (aspect ratio) of adjacent meshes cannot be changed extremely, and therefore the element The number increases and the analysis time becomes relatively long. By adopting the contact definition of this analysis method on both sides of the thin sheet material, it is possible to arbitrarily set the mesh size near the sheet, so the analysis time compared to the conventional analysis method Can be shortened.

  In addition, although this embodiment demonstrated the analysis method and design method of the marine structure 1 which has arrange | positioned the water-impervious sheet | seat material 10 to the slope of the foundation mound 2, it coat | covers with the sheet | seat material which does not aim at water-impervious. This analysis method and design method can also be adopted for other offshore structures.

  DESCRIPTION OF SYMBOLS 1 Offshore structure, 2 Foundation mound (soil layer), 7 Cover layer (soil layer), 10 Water-proof sheet material (sheet material), 12a, 12b Contact part, 13 Counter material

Claims (5)

A marine structure analysis method for analyzing the behavior when an external force including its own weight is applied to a marine structure including a soil layer made of a soil material and a sheet material in contact with the soil layer,
The contact definition of the contact portion between the soil layer and the sheet material is
A contact determination step for determining contact of both in the contact portion;
A relative displacement step of relatively displacing both against the sliding resistance force between the two when it is determined in the contact determination step that both are in contact;
The analysis method of the offshore structure characterized by including.   The marine structure analysis method according to claim 1, wherein the sheet material is disposed on a slope of the soil layer.   The offshore structure is constructed by laying a water shielding sheet material, which is the sheet material, on a slope of a foundation mound made of a soil material, and disposing a covering layer made of a soil material on the water shielding sheet material. The marine structure analysis method according to claim 1, wherein the marine structure is analyzed. A design method for an offshore structure configured by laying a sheet material on a slope of a foundation mound made of a soil material and arranging a covering layer made of a soil material on the sheet material,
The marine structure is designed by adopting the analysis method according to claim 1.   The marine structure design method according to claim 4, wherein a counter material for stabilizing the marine structure is arranged at a bottom of the covering layer.

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