Method for calculating ultimate shear strength of diaphragm wall

Abstract

To provide a calculation method for ultimate sheer capacity of an underground continuous wall allowing a secondary design for the underground continuous wall.SOLUTION: A calculation method for ultimate sheer capacity of an underground continuous wall is provided to adjacently construct a precedingly constructed preceding element 2 and a following element 3 constructed after the preceding element 2. A corrugated steel plate 41 is arranged on a vertical joint part 6 which joints the preceding element 2 and the following element 3 over a whole height direction of the wall along an end part on the following element 3 side for a preceding concrete part 21. For the corrugated steel plate 41, a surface of the preceding element 2 side is fixed on the preceding concrete part 21, and a surface on the following element 3 side is fixed on a following concrete part 31. Ultimate sheer capacity of an underground continuous wall 1 is calculated through the following formula (1). Q=0.95 N (1) where Q is ultimate sheer capacity of the underground continuous wall, and N is force acting in a wall length direction of the underground continuous wall to go over the corrugated steel plate when pulling out force acts on the underground continuous wall.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for calculating the ultimate shear strength of a diaphragm wall using a corrugated steel plate for a vertical joint part.

Background Art

[0002] A method for constructing a diaphragm wall by constructing a diaphragm wall made of reinforced concrete using a bucket-type or rotary horizontal multi-axis excavator is known. As such a method for constructing a diaphragm wall, there is a method of constructing a diaphragm wall by providing leading elements at intervals in the ground and connecting a trailing element between the previously provided leading elements to the leading elements.

[0003] Regarding the structure of the vertical joint part between adjacent leading elements and trailing elements, there are structures in which a partition plate is provided in the vertical joint part and the horizontal bars of the leading element and the horizontal bars of the trailing element are rigidly joined as an overlapping joint, and there are types with or without a partition plate in the vertical joint part. However, there is a structure in which horizontal bars are not passed through the vertical joint part and stress transmission (joint strength) is not expected. In addition, as the structure of the vertical joint part, there is also known a semi-rigid joint structure in which horizontal bars are not passed through the vertical joint part, but a corrugated steel plate with a continuous waveform in the vertical direction is provided as a vertical joint member, and the corrugated steel plate becomes a shear key (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the design of diaphragm walls, allowable stress design has been followed so far, but recently, secondary design has also been required for diaphragm walls.

[0006] Therefore, an object of the present invention is to provide a method for calculating the ultimate shear strength of a diaphragm wall that enables secondary design of the diaphragm wall.

Means for Solving the Problems

[0007] To achieve the above object, a method for calculating the ultimate shear strength of a diaphragm wall according to the present invention includes a preceding element constructed in advance and a succeeding element constructed after the preceding element, which are In the wall length direction a method for calculating the ultimate shear strength of a diaphragm wall constructed adjacent to the ground, wherein a vertical joint portion joining the preceding element and the succeeding element has, in the concrete portion of the preceding element, In the wall length direction a corrugated steel plate is provided over the entire wall height direction along the end portion on the succeeding element side, The corrugated steel sheet has unevenness forming a waveform when viewed from the wall thickness direction, and the unevenness is arranged in the wall height direction, and the surfaces on both sides in the wall length direction are uneven surfaces. the corrugated steel plate has, on the preceding element side, Unevenness a surface fixed to the concrete portion of the preceding element and, on the succeeding element side, Unevenness a surface fixed to the concrete portion of the succeeding element, The ultimate shear resistance of the diaphragm wall is the shear resistance against the shear force acting in the wall height direction. the ultimate shear strength of the diaphragm wall is calculated by the following formula (1) And Equation (2) as follows. Q = 0.95N ···(1) N = 0.1F c ·B·L ···(2) Q: Ultimate shear strength of the diaphragm wall F c : Design standard strength of concrete in the concrete part (N / mm 2 ) B: Wall thickness dimension of the diaphragm wall (mm) L: Wall height dimension of the diaphragm wall (mm)

[0008] In the present invention, by calculating the ultimate shear strength of the diaphragm wall using the above formula (1), the ultimate shear strength of the diaphragm wall can be evaluated on the safe side. Thereby, secondary design of the diaphragm wall becomes possible.

Effects of the Invention

[0009] According to the present invention, it is possible to realize a diaphragm wall that enables secondary design.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Embodiments for Carrying Out the Invention

[0011] Hereinafter, a method for calculating the ultimate shear strength of a diaphragm wall according to an embodiment of the present invention will be described with reference to FIGS. 1-10. The method for calculating the ultimate shear strength of the diaphragm wall according to the present embodiment is a method for calculating the ultimate shear strength of the elements in the diaphragm wall 1 having a plurality of wall-like elements 2 and 3 arranged in the wall length direction as shown in FIGS. 1 and 2. The plurality of elements 2 and 3 are all constructed by excavating the ground 11 (see FIG. 1). The excavation of the ground is performed, for example, by a bucket-type or rotary horizontal multi-axis type excavator. The wall length direction indicates the horizontal direction along the wall surface of the diaphragm wall 1. The horizontal direction orthogonal to the wall length direction is defined as the wall thickness direction, and the vertical direction (perpendicular to both the wall length direction and the wall thickness direction) is defined as the wall height direction. In FIGS. 1 and 2, the wall length direction is indicated by arrow X, the wall thickness direction is indicated by arrow Y, and the wall height direction is indicated by arrow Z.

[0012] The plurality of elements 2 and 3 constituting the diaphragm wall 1 are composed of a preceding element 2 constructed first and a succeeding element 3 constructed after the preceding element 2, and the preceding element 2 and the succeeding element 3 are alternately arranged in the wall length direction.

[0013] The preceding element 2 and the succeeding element 3 are set to have the same dimensions in the wall thickness direction and the wall height direction, and are arranged so that their respective wall cores coincide. The preceding element 2 and the succeeding element 3 are arranged such that their respective end portions in the wall length direction abut against each other. In the following description, the side where the succeeding element 3 is arranged with respect to the preceding element 2 in the wall length direction is referred to as the front side, the side where the preceding element 2 is arranged with respect to the succeeding element 3 is referred to as the rear side, and the wall length direction may be denoted as the front-rear direction. Also, the wall height direction may be denoted as the vertical direction.

[0014] The diaphragm wall according to the present embodiment is constructed as follows. First, the entire area where the preceding element 2 is to be constructed and the area near the end portion in the wall length direction of the succeeding element 3 are excavated in advance. Then, after constructing the preceding element 2, the remaining area of the area where the succeeding element 3 is to be constructed (the area other than the area near the end portion in the wall length direction of the succeeding element 3) is excavated to construct the succeeding element 3.

[0015] Hereinafter, the area excavated in advance is denoted as the preceding excavation part 12, and the area excavated after constructing the preceding element 2 is denoted as the succeeding excavation part 13. The area where the vicinity of the end portion in the wall length direction of the succeeding element 3 (the vicinity of the end portion on the side of the preceding element 2) in the preceding excavation part 12 is constructed is denoted as the front end area 14.

[0016] As shown in FIGS. 1 and 2, the preceding element 2 includes a wall-shaped preceding concrete part 21 of RC construction in which reinforcing bars 24 are arranged in concrete 23, and a vertical joint member 4 provided at the front end in the wall length direction of the preceding concrete part 21 (the end on the side of the succeeding element 3). The vertical joint member 4 is provided so as to extend over the entire wall height direction of the preceding concrete part 21.

[0017] The succeeding element 3 includes a wall-shaped succeeding concrete part 31 of RC construction in which reinforcing bars 34 are arranged in concrete 33. The dimension of the succeeding element 3 in the wall height direction is substantially the same as the dimension of the preceding element 2 in the wall height direction. The preceding element 2 and the succeeding element 3 are joined via the vertical joint member 4 of the preceding element 2. The joint part between the preceding element 2 and the succeeding element 3, that is, the front end part of the concrete 23 of the preceding concrete part 21, the vertical joint member 4, and the rear end part of the succeeding concrete part 31 are defined as a vertical joint 6.

[0018] As shown in FIGS. 1 and 2, the vertical joint member 4 includes a corrugated steel plate 41, a pair of side members 42 and 43 attached to both ends in the wall thickness direction of the corrugated steel plate 41 and extending rearward, a strength addition member 44 attached between the pair of side members 42 and 43 and arranged to overlap the rear side of the corrugated steel plate 41, and a protruding part 45 attached to the front side of the corrugated steel plate 41 and protruding forward.

[0019] The corrugated steel plate 41 is a steel plate processed to have a cross-sectional shape that is corrugated and has a surface with unevenness arranged in a corrugated shape. The corrugated steel plate 41 is arranged such that the surface forming the corrugated shape faces the wall length direction. That is, the shape of the corrugated steel plate 41 as viewed from the wall thickness direction is corrugated. The waveform of the cross-sectional shape of the corrugated steel plate 41 in the present embodiment is in the form of a trapezoidal wave in which trapezoids are connected.

[0020] In this embodiment, two corrugated steel plates 41 are arranged side by side in the wall thickness direction, and a protruding portion 45 is joined between the two corrugated steel plates 41. Hereinafter, the two corrugated steel plates 41 are collectively referred to as the corrugated steel plate 41. The dimension of the corrugated steel plate 41 in the wall height direction is the same as that of the preceding element 2 in the wall height direction. The dimension of the corrugated steel plate 41 in the wall thickness direction is set to be smaller than the dimensions of the preceding element 2 and the succeeding element 3 in the wall thickness direction.

[0021] The protruding portion 45 is provided as a member that engages with a protective member (not shown) installed in the front end region 14 of the preceding excavation portion 12 when constructing the preceding element 2, or guides a cleaning machine (not shown) when cleaning the front end portion (vertical joint member 4) of the constructed preceding element 2. The protruding portion 45 is a shaped material with a T-shaped cross section and is arranged in a direction extending in the wall height direction. The protruding portion 45 is arranged between the two corrugated steel plates 41 arranged side by side in the wall thickness direction and is joined to each of the two corrugated steel plates 41.

[0022] As shown in FIGS. 1 and 3, a pair of side members 42, 43 are provided to be symmetric with respect to the wall thickness direction. The pair of side members 42, 43 are each long shaped materials with an L-shaped cross section and are arranged in a direction extending in the wall height direction. The pair of side members 42, 43 are set to have the same length dimension as the length dimension of the corrugated steel plate 41 in the wall height direction. Two pieces that are orthogonally connected to form the L-shaped cross section of the pair of side members 42, 43 are defined as front plate portions 421, 431 and side plate portions 422, 432.

[0023] One of the side members 42 is arranged such that the front plate portion 421 is along the vertical plane facing the wall length direction, and the side plate portion 422 protrudes rearward from the end portion on the other side in the wall thickness direction of the front plate portion 421 (the end portion on the corrugated steel plate 41 side). The other side member 43 is arranged such that the front plate portion 431 is along the vertical plane facing the wall length direction, and the side plate portion 432 protrudes rearward from the end portion on one side in the wall thickness direction of the front plate portion 431 (the end portion on the corrugated steel plate 41 side).

[0024] The front plate portions 421 and 431 of the pair of side members 42 and 43 are arranged such that their front surfaces are at substantially the same position as the position of the front end portion of the corrugated steel plate 41. The side plate portions 422 and 432 of the pair of side members 42 and 43 are in contact with the side portions of the corrugated steel plate 41 on the side of the corrugated steel plate 41 and are joined to the corrugated steel plate 41. The side plate portions 422 and 432 of the pair of side members 42 and 43 and the corrugated steel plate 41 are joined via, for example, an L-shaped angle member and bolts and nuts. The side plate portions 422 and 432 are formed to be longer than the dimension of the corrugated steel plate 41 in the front-rear direction (wall length direction), and the rear end portions are arranged on the rear side of the rear end portion of the corrugated steel plate 41. Both end portions of the corrugated steel plate 41 in the wall thickness direction are closed by the pair of side members 42 and 43.

[0025] The strength adding member 44 is a long-shaped member with a U-shaped (C-shaped) cross-sectional shape and is arranged in a direction extending in the wall thickness direction. A plurality of strength adding members 44 are provided at intervals in the wall height direction. One end portion in the length direction (one end portion in the wall thickness direction) of the strength adding member 44 is joined near the rear end portion of the side plate portion 422 of one side member 42, and the other end portion in the length direction (the other end portion in the wall thickness direction) is joined near the rear end portion of the side plate portion 432 of the other side member 43. By providing the strength adding member 44 in the preceding element 2, the rigidity and strength of the vertical joint portion 6 can be increased, and the rigidity and strength required during lifting at the time of construction can be ensured.

[0026] In the diaphragm wall 1 of the present embodiment, the concrete 23 of the preceding concrete portion 21 is placed behind the main body portion 412 of the corrugated steel plate 41 and in front of the front plate portions 421 and 431 of the pair of side members 42 and 43, and the concrete 33 of the subsequent concrete portion 31 is placed in front. The side plate portions 422 and 432 of the pair of side members 42 and 43 and the strength adding member 44 are embedded in the preceding concrete portion 21. The protruding portion 45 joined to the corrugated steel plate 41 is embedded in the subsequent concrete portion 31.

[0027] The concrete 23 of the preceding concrete part 21 and the concrete 33 of the succeeding concrete part 31 also fill the concave portions of the corrugations of the corrugated steel plate 41. The preceding concrete part 21 and the succeeding concrete part 31 have a meshed shape via the corrugated steel plate 41, and a shear key is formed at the joint portion between the preceding element 2 and the succeeding element 3. Therefore, the preceding element 2 and the succeeding element 3 are configured to be able to transmit in-plane shear forces to each other.

[0028] As shown in FIG. 1, in the present embodiment, the pair of side members 42, 43 are provided with a sheet member 51 that prevents the concrete 23 from flowing out to the succeeding element 3 side (front side) during the placement of the concrete 23 of the preceding element 2, and a rod-shaped pressing member 52 (such as a stud) that suppresses the sheet member 51 from approaching the side members 42, 43 and keeps it along the side surface of the preceding excavation part 12.

[0029] Subsequently, a method for calculating the ultimate shear strength of the underground continuous wall according to the present embodiment will be described. The ultimate shear strength calculation formula of the underground continuous wall is shown in Equation (1). Q =0.95N ···(1) Here, Q: Ultimate shear strength of the underground continuous wall F c : Design standard strength of concrete (N / mm 2 ) B: Thickness dimension of the underground continuous wall (mm) (see FIGS. 4 and 5) L: Height dimension of the underground continuous wall (mm) (see FIGS. 3 and 4 )

[0030] Regarding the above N, when evaluating the results of the tests conducted in 2020 using five test specimens with the concrete compressive strength as a parameter on the safe side, it can be calculated by the following formula (2). N = 0.1Fc·B·L···(2) The symbols in Equation (2) are the same as those used in Equation (1).

[0031] The validity of the above formula (1) was confirmed by a structural experiment. The outline of the structural experiment is shown below. The shapes and dimensions of the test specimens are shown in Figs. 3 - 5, and the shape and dimensions of the shear key (corrugated steel plate 41, hereinafter referred to as shear key 41) are shown in Fig. 6. The test specimens 101 - 105 are partial models obtained by extracting the vertical joint part 6 (around the vertical joint member 4) of the diaphragm wall, and the concrete strength is used as the test parameter (No. 1: Fc18 (Fc = 18 N / mm 2 ), No. 2: Fc30 (Fc = 30 N / mm 2 ), No. 3: Fc45 (Fc = 45 N / mm 2 ), No. 4: Fc60 (Fc = 60 N / mm 2 ), No. 5: Fc80 (Fc = 80 N / mm 2 )) for a total of 5 specimens. In the drawings, test specimen No. 1 is indicated by the symbol "101", test specimen No. 2 is indicated by the symbol "102", test specimen No. 3 is indicated by the symbol "103", test specimen No. 4 is indicated by the symbol "104", and test specimen No. 5 is indicated by the symbol "105". The design standard strength of the concrete for test specimens No. 1 - No. 5 is 18 N / mm 2 or more and 80 N / mm 2 or less. The shape, dimensions, and material of the shear key 41 provided at the vertical joint part 6 of each of the test specimens No. 1 - No. 5 were the same for all test specimens. The shear key 41 was fabricated from PL - 2.3 (SS400). The concrete placement direction for each of the test specimens No. 1 - No. 5 was in the direction of arrow C in Fig. 3, and for all test specimens, it was placed vertically in accordance with the actual construction.

[0032] The test apparatus 8 is shown in Fig. 7. The test specimens No. 1 - No. 5 were installed in the test apparatus such that the wall height direction of the vertical joint part 6 was horizontal, and the upper and lower stubs were fastened to the loading frame 81 with PC steel bars 82. With the axial force set to 0, and with the initial vertical displacement kept constant by two 2 MN vertical jacks 83, in accordance with the loading cycle shown in Fig. 8 (the long - term allowable shear force of the concrete L Pa (= L τa·As, the long - term allowable shear stress of the concreteL τa = min(σ B / 30, 0.49 + σ B / 100)) level and repeated twice, then the same short-term allowable shear force S Pa (= S τa·As = 1.5· L τa·As) level and repeated twice), and alternating positive and negative cyclic loading was applied by a 3MN horizontal jack 84.

[0033] The displacement measurement positions are shown in Fig. 9. During the test, the horizontal load (shear force) was measured by a 3MN load cell, and the slip deformations DHN and DHS of the vertical joint part 6 and the control vertical displacements DVN and DVS were measured by a high-sensitivity displacement meter CDP-100.

[0034] The Q / (Fc·B·L) - N / (Fc·B·L) relationship of each test specimen is shown in Fig. 10. In addition, only the experimental data on the positive loading side were adopted for the evaluation. Equation (1) is shown in Fig. 10. From the above bearing capacity calculation results and structural experiments, in the ultimate shear bearing capacity calculation method of the diaphragm wall according to this embodiment, the ultimate shear bearing capacity of the diaphragm wall using corrugated steel plates in the vertical joint part can be evaluated on the safe side. Thereby, it can contribute to the secondary design of the diaphragm wall.

[0035] The applicant of this application has previously filed a patent application (Japanese Patent Application No. 2021-086826) for the ultimate shear bearing capacity calculation method of the diaphragm wall. In Japanese Patent Application No. 2021-086826, the ultimate shear bearing capacity calculation formula of the diaphragm wall is shown in the following formula (2). τ = Q / (B·L) = 0.1Fc Q = 0.1FcBL ···(2) Here, Q: Ultimate shear bearing capacity of the diaphragm wall Fc: Design standard strength of concrete (N / mm 2 ) B: Thickness dimension of the diaphragm wall (mm) L: Height dimension of the diaphragm wall (mm)

[0036] Formula (2) is also shown in Fig. 10. As can be seen from Fig. 10, in formula (1), the ultimate shear strength can be evaluated with higher accuracy than in formula (2).

[0037] As described above, the embodiments of the method for calculating the ultimate shear strength of the diaphragm wall according to the present invention have been described. However, the present invention is not limited to the above embodiments and can be appropriately modified without departing from the spirit thereof. For example, in the above embodiment, the design standard strength of the concrete is 18 N / mm 2 or more and 80 N / mm 2 or less. However, it may be outside this range. The cross-sectional shape of the corrugated steel sheet may be other than the above.

Explanation of symbols

[0038] 1 Diaphragm wall 2 Leading element 3 Trailing element 4 Vertical joint member 6 Vertical joint 11 Ground 21 Leading concrete part 31 Trailing concrete part 41 Corrugated steel sheet

Claims

【Claim 1】 A method for calculating the ultimate shear strength of a diaphragm wall constructed in the ground with an antecedent element constructed first and a subsequent element constructed after the antecedent element adjacent to each other in the wall length direction, comprising: In a vertical joint portion joining the antecedent element and the subsequent element, a corrugated steel plate is provided over the entire wall height direction along an end portion on the subsequent element side in the wall length direction of the concrete portion of the antecedent element. The corrugated steel plate has unevenness forming a waveform arranged in the wall height direction when viewed from the wall thickness direction, and both surfaces on both sides in the wall length direction are uneven surfaces. The corrugated steel plate has the uneven surface on the antecedent element side fixed to the concrete portion of the antecedent element and the uneven surface on the subsequent element side fixed to the concrete portion of the subsequent element. The ultimate shear strength of the diaphragm wall is the shear strength against the shear force acting in the wall height direction. The method for calculating the ultimate shear strength of the diaphragm wall is a method for calculating the ultimate shear strength of the diaphragm wall according to the following formulas (1) and (2). Q = 0.95N... (1) N = 0.1Fc・B・L... (2) Q: Ultimate shear strength of the diaphragm wall Fc: Design standard strength of concrete in the concrete portion (N / mm2) B: Wall thickness dimension of the diaphragm wall (mm) L: Wall height dimension of the diaphragm wall (mm)

Images