Method for constructing diaphragm walls

Abstract

To provide a method capable of smoothly performing excavation of an excavation pit for a following element, without performing filling work of gravel and crushed rock.SOLUTION: A construction method of an underground continuous wall comprises the steps of: forming a preceding excavation pit 4 by excavating natural ground; installing, on a side of constructing following elements 3 of the preceding excavation pit 4, partition plates 10 having a dimension in a depth direction of the preceding excavation pit 4 shorter than the depth dimension of the preceding excavation pit 4; constructing preceding elements 2 by placing concrete to the preceding excavation pit 4; removing the partition plates 10; forming a following excavation pit 5 by excavating the natural ground between the preceding elements 2, 2 from which the partition plates 10 are removed; and constructing the following elements 3 integrally with the preceding elements 2, by placing concrete to the following excavation pit 5. After constructing the multiple preceding elements 2 as wall bodies in the ground, the following elements are constructed between the preceding elements 2 to construct a continuous wall 1 in the ground.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for constructing a diaphragm wall.

Background Art

[0002] Conventionally, as a method for constructing a diaphragm wall, after constructing a preceding element by placing concrete in an excavation pit formed by excavating the ground, a succeeding element is constructed integrally with the preceding element adjacent to the preceding element (see, for example, Patent Document 1). By the way, when constructing the succeeding element, it is common to cut a concrete cutting portion, which is an end face in the joint direction of the preceding element, until the excavator enters the ground (to a depth of about 5 m) to excavate an excavation pit for the succeeding element. However, in this case, since concrete is excavated at a location close to the ground, there are problems such as high noise and vibration. In addition, at the initial stage of excavation, the drill of the excavator may not properly bite into the upper end portion of the preceding element, resulting in a so-called escape. Therefore, in Patent Document 1, the width of the upper part of the reinforcing cage is made smaller than the width of the excavation pit, partition plates made of steel plates with a thickness of 6 to 12 mm are attached to both end portions in the width direction, and when the concrete of the preceding element reaches the lower end of the partition plate, gravel or crushed stone is filled into the space between the partition plate and the excavation pit. Accordingly, at the initial stage of excavation, since the excavator excavates gravel or crushed stone that is easy to excavate, it is said that the excavation pit for constructing the succeeding element can be performed smoothly.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the method described in Reference 1 above requires not only filling the space between the partition plate and the excavated hole with gravel or crushed stone, but also, since the partition plates attached to the reinforcing cage are embedded in concrete, it was necessary to prepare as many partition plates as there were preceding elements.

[0005] This invention has been made in view of the problems of the prior art, and aims to provide a method for smoothly excavating a borehole for a trailing element without having to fill it with gravel or crushed stone. [Means for solving the problem]

[0006] The present invention relates to a method for constructing a continuous underground wall by constructing a plurality of preceding elements as a wall in the ground, and then constructing succeeding elements between the preceding elements, comprising the steps of: excavating the ground to form a borehole for constructing the preceding elements; installing a partition plate on the wall surface of the borehole on the side where the succeeding elements are to be constructed, and on the upper part of both ends in the construction direction which are concrete cutting portions of the preceding elements, the depth dimension of the borehole is shorter than the depth dimension of the borehole for the preceding elements; pouring concrete into the borehole to construct the preceding elements; removing the partition plate; and constructing a succeeding element adjacent to the preceding elements and integrally with the preceding elements. The continuous wall is a regular polygonal wall in plan view, consisting of a leading element which is isosceles trapezoidal in plan view and a trailing element which is rectangular in plan view and constructed adjacent to the leading element and integrally with the leading element, the leading elements are constructed at intervals of one element along the circumferential direction of the regular polygon, and the trailing elements are constructed between two adjacent leading elements, the partition plate comprises a partition plate body, a contact member provided on the upper part of the partition plate body, and a mounting member provided on the upper side of the partition plate body, the partition plate body is composed of a frame made by assembling steel plates into a right-angled trapezoid in plan view, and in the process of installing the partition plate, the mounting member is placed on a hydraulic jack installed on the ground which is the surface of the ground, , by adjusting the height of the hydraulic jack until the contact member contacts the ground, the partition plate body is installed on the wall surface of the excavation pit on the side where the trailing element is constructed, and at the upper part of both ends in the construction direction which are the concrete cutting portions of the leading element, such that the steel plates forming the legs perpendicular to the upper and lower bases of the right-angled trapezoid in plan view are located on the wall side of the excavation pit. In the process of constructing the leading element, the height of the hydraulic jack is raised and lowered before the concrete poured into the excavation pit has completely hardened, thereby separating the partition plate from the concrete poured into the excavation pit in advance. In the process of removing the partition plate, after a predetermined time has elapsed since the separation, the partition plate is lifted and removed. It is characterized by the following. This allows for the excavation of the borehole for the trailing element without the need for filling with gravel or crushed stone. It also has the advantage of allowing for the reuse of the partition plates. 。 [Brief explanation of the drawing]

[0007] [Figure 1] This figure shows an embodiment of the present invention. [Figure 2] These are a front view and a vertical cross-sectional view showing the partition plate according to this embodiment. [Figure 3] These are a cross-sectional view, a plan view, and a perspective view of the main part of the partition plate according to this embodiment. [Figure 4] This diagram shows the method for constructing a continuous underground wall (construction of the preceding elements). [Figure 5] This diagram shows the method for constructing a continuous underground wall (construction of the trailing element). [Figure 6] This figure shows another example of a method for constructing a continuous underground wall. [Modes for carrying out the invention]

[0008] Figures 1(a) to 1(c) illustrate this embodiment. (a) As shown in the figure, the underground continuous wall 1 is a wall body with a regular polygonal shape in plan view, consisting of a leading element 2 which is isosceles trapezoidal in plan view and a trailing element 3 which is rectangular in plan view and constructed adjacent to the leading element 2 and integrally with the leading element 2. The leading element 2 is constructed at one-element intervals along the circumferential direction of the regular polygon, and the trailing element 3 is constructed between two adjacent leading elements 2,2. The direction perpendicular to the circumferential direction of the regular polygon is hereafter referred to as the radial direction. In this example, as shown in Figure (b), when pouring the lead element 2, the concrete for the lead element 2 is poured with the partition plate 10 installed on the upper part of the lead excavation pit 4, which is the excavation pit for the lead element 2, on the side where the trailing element 3 is to be constructed. After the initial element 2 is cast, the partition plate 10 is removed, and the subsequent excavation pit 5, which is the excavation pit for the subsequent element 3, is excavated as shown in Figure (c). The initial excavation pit 4 described above corresponds to the excavation pit described in the claims. Reference numeral 6 in the figure indicates an excavator.

[0009] Figures 2(a) and 2(b) show examples of partition plates 10, with (a) being a front view and (b) being a cross-sectional view of (a) at section AA. Additionally, Figure 3(a) is a cross-sectional view of Figure 2(a) at section BB, Figure 3(b) is a plan view, and Figure 3(c) is a perspective view of the main part. The partition plate 10 comprises a partition plate body 11, an H-shaped steel beam 12 as a mounting member, a lifting device receiving member 13, member reinforcing and connecting members 14a to 14c, a rubber sheet 15, connecting concrete 16, reinforcing concrete 17, and abutment member 18. The partition plate 10 is placed on top of the pre-excavated pit 4 via hydraulic jacks 20 installed on the ground 8, which is the surface of the natural ground 7 radially outside the pre-excavated pit 4, at both ends of the H-shaped steel beam 12. The partition plate body 11 is a frame made by assembling four steel plates 11a to 11d into a right-angled trapezoidal shape in plan view, and reinforcing and connecting members 14a to 14c are attached inside the frame. Steel plates 11a and 11b form the upper and lower bases of the right-angled trapezoid, respectively, steel plate 11c forms the leg perpendicular to the upper and lower bases of the right-angled trapezoid, and steel plate 11d forms the other leg of the right-angled trapezoid. The partition plate body 11 is housed in the pre-drilled pit 4 such that the steel plate 11d is located on the interior side of the pre-drilled pit 4 and the steel plate 11c is located on the circumferential wall side of the pre-drilled pit 4. In other words, the partition plate body 11 is housed in the pre-drilled pit 4 such that the shorter steel plate 11a, which forms the upper base of the right-angled trapezoid, is located radially outward, and the longer steel plate 11b, which forms the lower base of the right-angled trapezoid, is located radially inward. Hereinafter, the steel plate 11a located radially outward of the pre-drilled pit 4 will be referred to as the outer steel plate, the steel plate 11b located radially inward will be referred to as the inner steel plate, the steel plate 11c will be referred to as the trailing element side steel plate (trailing side steel plate), and the steel plate 11d will be referred to as the pre-element side steel plate (pre-element side steel plate). In this example, to facilitate the retrieval of the partition plate 10, which will be described later, a slope section 11k is provided in which the length of the leading edge of the steel plates 11a to 11d in the depth direction becomes shorter as it goes further into the pre-excavated tunnel 4.

[0010] The H-shaped steel beams 12 are positioned such that the longitudinal directions of the upper and lower flanges 12a and 12b are perpendicular to the upper and lower bases (radial direction) of the right-angled trapezoidal frame that constitutes the partition plate body 11. The length of the H-shaped steel beam 12 is set to be longer than the radial length of the preceding element 2. Specifically, both ends of the H-shaped steel beam 12 in the longitudinal direction should extend radially outward beyond the positions of the hydraulic jacks 20 installed on the radially outer and inner sides of the preceding excavated hole 4. In this example, reinforcing plates 12k are provided between the upper and lower flanges 12a and 12b, extending in a direction perpendicular to the thickness direction of the web 12c. Two reinforcing plates 12k are provided on each end of the partition plate body 11, slightly inward from both ends. The suspension device receiving member 13 comprises a suspension device receiving portion 13a and a reinforcing piece 13b. The lifting device receiving portion 13a is a plate-shaped member whose plate surface protrudes from the upper side of the reinforcing plate 12k on the upper flange 12a of the H-shaped steel 12 and is perpendicular to the width direction of the H-shaped steel 12. A through hole 13s for hanging lifting devices such as crane hooks (not shown) is provided at the center of the plate surface. The lifting device receiving portions 13a are provided at two locations equidistant from the longitudinal center of the H-shaped steel 12. The reinforcing piece 13b extends from both ends in the width direction (length direction of the H-shaped steel 12) of the suspension support portion 13a to the width direction end of the upper flange 12a. When viewed from the length direction of the H-shaped steel 12, it is a right-angled triangular member in which one side forming a right angle is attached to the suspension support portion 13a and the other side is attached to the upper flange 12a. Four pieces are provided for each suspension support portion 13a.

[0011] The reinforcing and connecting member 14a comprises an angle 141 with an L-shaped cross-section, one side of which is attached to the trailing steel plate 11c and the other side which protrudes toward the leading steel plate 11d, and a reinforcing plate 142 whose plate surface abuts against the other side of the angle 141 and whose ends are attached to the trailing steel plate 11c and the leading steel plate 11d, and is attached to the inner steel plate 11b which forms the lower base of the right-angled trapezoid. The reinforcing and connecting member 14b, like the reinforcing and connecting member 14a, comprises an angle 143 with an L-shaped cross-section, one side of which is attached to the trailing steel plate 11c and the other side of which protrudes toward the leading steel plate 11d, and a reinforcing plate 144 whose plate surface abuts against the other side of the angle 143 and whose ends are attached to the trailing steel plate 11c and the leading steel plate 11d, and is installed approximately midway between the outer steel plate 11a and the inner steel plate 11b. The reinforcing and connecting member 14c is formed of an angle with an L-shaped cross section where one side is attached to the trailing-side steel plate 11c and the other side protrudes toward the leading steel plate 11d side, and can be attached to the outer steel plate 11a side of the right trapezoid. The upper ends of the reinforcing and connecting members 14a to 14c are connected to the lower flange 12b of the H-shaped steel 12 which is a placement member and extends to the upper part of the partition plate body 11. Further, a slanted surface is provided at the lower end in the same manner as the steel plates 11a to 11d.

[0012] The rubber sheet 15 is a rubber plate provided at both ends in the width direction of the trailing-side steel plate 11c of the partition plate body 11 and extending downward to prevent the outflow of concrete during the concrete placement of the leading element 2, and is screwed to both ends in the width direction of the trailing-side steel plate 11c. The rubber sheet 15 is installed so as to be wound into the leading excavation pit 4 side when the partition plate 10 is installed. That is, the tip side of the rubber sheet 15 abuts against the circumferential wall surface of the leading excavation pit 4 and the radial outer and inner wall surfaces of the leading excavation pit 4. The connecting concrete 16 is placed between the partition plate body 11 and the H-shaped steel 12 to firmly connect the partition plate body 11 to the H-shaped steel 12 which is a placement member. <000009 >The reinforcing concrete 17 is filled in the space between the steel plates 11a to 11d and the reinforcing and connecting members 14a to 14c. Thereby, the rigidity of the partition plate body 11 can be further increased, and the deformation of the partition plate body 11 during the concrete placement of the leading element 2 can be suppressed. <00000 >The connecting concrete 16 and the reinforcing concrete 17 are integrally formed by providing a formwork between the partition plate body 11 and the H-shaped steel 12 and placing concrete in this formwork The abutting member 18 is provided at the upper part of the trailing-side steel plate 11c of the partition plate body 11 and is formed of an angle with an L-shaped cross section extending in the extending direction of the H-shaped steel 12. The vertical piece is attached to the reinforcing concrete 17, and both ends of the horizontal piece abut against the ground 8 on the radial outer side and the radial inner side of the leading excavation pit 4. After the partition plate 10 is transported to the upper part of the prior excavation pit 4 by a crane (not shown), it is installed in the prior excavation pit 4. Specifically, the hook of the crane is hung on the sling receiving member 13, and after the partition plate 10 is held at the upper part of the prior excavation pit 4, the partition plate 10 is gradually lowered into the excavation pit 4, and both end portions in the longitudinal direction of the H-shaped steel 12 are placed on the hydraulic jacks 20 installed on the ground on both outer sides in the radial direction of the prior excavation pit 4, thereby installing the partition plate 10 in the prior excavation pit 4. In this example, after the H-shaped steel 12 is placed on the hydraulic jack 20, the height of the hydraulic jack 20 is adjusted (lowered) until the contact member 18 contacts the ground 8, so as to install the partition plate 10 at a predetermined position in the prior excavation pit 4. After the partition plate 10 is installed, as described above, concrete is placed in the prior excavation pit 4 where the partition plate 10 is installed to construct the prior element 2. Note that the subsequent element 3 is also made of reinforced concrete in the same manner as the prior element 2.

[0013] Next, a method for constructing the diaphragm wall 1 will be described. First, as shown in Fig. 4(a), a prior excavation pit 4 is excavated in the ground 7 using an excavator 6. In this example, a predetermined number of prior excavation pits 4 are excavated at an interval of one element. Next, as shown in Fig. 4(b), partition plates 10 having depth dimensions in the depth direction measured from the ground 8, which is the surface of the ground 7, (hereinafter referred to as partition depths) shorter than the depth dimension of the excavation pit 4 are installed at both circumferential end portions of the prior excavation pit 4. In this example, the depth of the prior excavation pit 4 is 80 m and the partition depth is 5 m. The partition depth only needs to be greater than or equal to the depth at which the excavator 6 enters the ground 7. If it is made longer than necessary, the recovery operation of the partition plate 10 will become difficult, so it is preferably 3 m to 7 m. After the partition plate 10 is transported to the upper part of the prior excavation pit 4 by a crane (not shown), it is installed in the prior excavation pit 4. Specifically, the partition plate 10 suspended by the crane is gradually lowered into the prior excavation pit 4 to install the partition plate 10 in the prior excavation pit 4. Specifically, it is installed at both upper ends 2k in the joint direction, which is the wall surface on the side of the subsequent element 3 of the prior excavation pit 4 and is the part of the conventional concrete cutting. Next, as shown in Figure 4(c), concrete is poured into the pre-excavated pit 4 where the partition plate 10 is installed to construct the pre-element 2. In this example, the preceding element 2 is made of reinforced concrete by installing a reinforcing cage (not shown) in the preceding excavation pit 4 and then pouring concrete.

[0014] After the construction of the preceding element 2, the partition plate 10 is lifted and recovered by a crane, as shown in Figure 5(a). Specifically, after the poured concrete has hardened to some extent, the height of a hydraulic jack 20 (not shown) is raised and lowered to pre-separate the partition plate 10 from the concrete in the preceding excavation hole 4. Then, after a predetermined time (for example, 4 to 5 hours) has elapsed and the concrete has hardened to some extent, the partition plate 10 is lifted, allowing it to be smoothly separated from the concrete and recovered. Next, as shown in Figure 5(b), a trailing excavation hole 5 is excavated in the ground 7 between adjacent trailing elements 2, 2 using an excavator 6. The constructed trailing element 2 has a space from the ground 8, where the recovered partition plate 10 was located, down to a depth of 5 m. In other words, the excavator 6 does not need to cut concrete from the ground 8 down to a depth of 5 m, and only needs to excavate the ground 7. Therefore, the excavator 6 can be easily lowered vertically, and the trailing excavation hole 5, which is the excavation hole for the trailing element 3, can be excavated smoothly. Furthermore, since the excavator 6 only begins excavating concrete after it has descended to a depth of 5m or more from the ground 8, noise and vibration during concrete excavation can be reduced, and dust can be prevented from being scattered onto the ground. After the excavation of the trailing borehole 5, concrete is poured into the trailing borehole 5, as shown in Figure 5(c), and the trailing element 3 is constructed adjacent to the trailing element 2, integrated with the trailing element 2.

[0015] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the embodiments. It will be apparent to those skilled in the art that various modifications or improvements can be made to the embodiments. It will be clear from the claims that such modified or improved forms may also be included in the technical scope of the present invention.

[0016] For example, in the above embodiment, the leading elements 2 were constructed with one element intervals, but as shown in Figure 6(a), the leading elements 2 may be composed of multiple elements. In short, when casting the leading elements 2, a partition plate 10 is installed on the side of the leading excavation hole 4 where the trailing elements 3 will be constructed, and after casting the leading elements 2, the partition plate 10 is removed to excavate the excavation hole for the trailing elements 3. Furthermore, in the above embodiment, the partition plate 10 was constructed from a frame equipped with a rubber sheet 15, but it may also be made from a concrete plate. Furthermore, in the above embodiment, the underground continuous wall 1 is a regular polygon in plan view, but it may be a polygon with sides of different lengths. Also, as shown in Figure 6(b), when constructing an underground continuous wall 1 with long straight sections such as a rectangle or square, it goes without saying that the partition plate 10 should be rectangular in plan view. [Explanation of symbols]

[0017] 1. Continuous underground wall, 2. Leading element, 3. Trailing element, 4. Leading drilled hole, 5. Trailing drilling shaft, 6. Excavator, 7. Natural ground, 8. Ground surface, 10 Partition plate, 11 Partition plate body, 12 H-beam, 13 Hanging device support member, 14a~14c Reinforcement and connecting members, 15 Rubber sheet, 16 Connecting concrete, 17 Reinforcing concrete, 18 Contact members, 20. Hydraulic jacks.

Claims

[Claim 1] A method for constructing a continuous wall underground by first constructing multiple preceding elements as a wall structure underground, and then constructing subsequent elements between the preceding elements, The process of excavating the ground to form a borehole for constructing the preceding element, A step of installing a partition plate on the wall surface of the excavation pit on the side where the trailing element is constructed, and on the upper part of both ends in the construction joint direction which are the concrete cutting portions of the leading element, the dimension of the excavation pit in the depth direction is shorter than the depth dimension of the excavation pit for the leading element, The process of constructing a preliminary element by pouring concrete into the aforementioned excavated hole, The process of removing the aforementioned partition plate, A step of constructing a successor element adjacent to the preceding element and integrally with the preceding element, Equipped with, The continuous wall is a regular polygonal wall in plan view, consisting of a leading element that is isosceles trapezoidal in plan view and a trailing element that is rectangular in plan view and constructed adjacent to the leading element and integrally with the leading element, wherein the leading element is constructed at one-element intervals along the circumferential direction of the regular polygon, and the trailing element is constructed between two adjacent leading elements. The partition plate comprises a partition plate body, a contact member provided on the upper part of the partition plate body, and a mounting member provided on the upper side of the partition plate body. The partition plate body is composed of a frame made by assembling steel plates into a right-angled trapezoidal shape in plan view. In the process of installing the partition plate, after the aforementioned mounting member is placed on a hydraulic jack installed on the ground which is the surface of the natural ground, the height of the hydraulic jack is adjusted until the contact member contacts the ground, so that the partition plate body is installed on the wall surface of the excavation pit on the side where the trailing element is constructed, and at the upper part of both ends in the construction direction which are the concrete cutting portions of the preceding element, the steel plates that constitute the legs perpendicular to the upper and lower bases of the right-angled trapezoid in plan view are located on the wall side of the excavation pit. In the process of constructing the preceding element, the height of the hydraulic jack is raised and lowered before the concrete poured into the excavation hole has completely hardened, thereby pre-separating the partition plate from the concrete poured into the excavation hole. A method for constructing a continuous underground wall, characterized in that, in the step of removing the partition plate, the partition plate is lifted up and removed after a predetermined time has elapsed since the separation of the boundary.

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