JPH0651971B2 - Continuous underground wall - Google Patents

Description

TECHNICAL FIELD The present invention relates to a continuous underground wall, and more particularly to improvement of strength of a concrete joint surface.

<< Prior Art >> A conventionally known continuous underground wall has a structure shown in FIG.

In this underground wall, as shown in FIG. 1A, a reinforcing bar cage 3 having a hollow joint box 2 attached to one end is inserted into a preceding excavation hole 1a excavated from the ground, and the inside of the joint box 2 is inserted. Except for this, concrete is placed in the excavation hole 1a to form the leading wall 4.

The joint box 2 is composed of a pair of side plates 2a, 2a, a partition plate 2b, a drawing plate 2c and a bottom plate (not shown). The horizontal main bar 3a of the reinforcing bar cage 3 penetrates the partition plate 2b and projects into the box 2. Then, after the concrete of the preceding wall 4 has been cast, as shown in FIG. 2B, the trailing excavation hole 1b is excavated to the side of the drawing plate 2c, and the drawing plate 2c is removed. The trailing rebar cage 5 with the same structure as the rebar cage 3 and the joint box 2
After the end portions of the rebar cages 3 and 5 are inserted in the overlapped state, concrete is placed in the trailing excavation hole 1b to form the trailing wall 6, and the same process is repeated to obtain the desired shape. Build an underground wall.

<< Problems to be Solved by the Invention >> According to the above method, an integrally joined wall body is obtained,
For example, if a pier foundation is constructed using this method, it is superior to the conventional pneumatic caisson method in terms of construction safety, easiness, shortening of construction period, economy, etc., but the partition plate 2b of the joint box 2 is Since it is made of flat steel plate, it has the following problems.

That is, the partition plate 2b serves as a connecting surface between the leading and trailing walls 4 and 6, and since this is a flat surface, sufficient out-of-plane shear resistance cannot be obtained.

For this reason, it has been proposed to interpose a shear connector orthogonal to the partition plate 2b to reinforce the out-of-plane shear resistance, but the out-of-plane shear resistance does not increase as expected due to the flat connecting surface. .

Therefore, it is disclosed in Japanese Patent Laid-Open No. 55-72514 that the partition plate 2b is provided with unevenness in the vertical or horizontal direction. Resistance increases but sufficient strength cannot be obtained.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to improve the out-of-plane shear resistance of the connecting surface of the continuous underground wall.

<< Means for Solving the Problems >> In order to achieve the above object, the present invention uses a rebar cage having a hollow joint box at one end, and the end portions of the rebar cage are overlaid within the joint box. In a continuous underground wall that is sequentially formed by wrapping, the horizontal section of the partition plate of the joint box located at the joint of the underground wall has a sinusoidal waveform and the wavelength / height ratio of the waveform. Is set in the range of 3 to 5.

<< Embodiment and Action >> Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a perspective view showing a reinforcing bar cage 10 for an underground wall according to the present invention, and FIGS. 2 (a), (b) and (c) are steps of a continuous underground wall construction method using the reinforcing bar cage 10. It is a horizontal sectional view showing order.

In the drawings, a reinforcing bar cage 10 used in an embodiment of the present invention
The horizontal main bar 101 and the vertical bar 102 are combined and welded in a grid pattern, and a hollow joint box 12 is attached to one end.

The ends of the horizontal main bars 101 are integrated in a state of protruding into the joint box 12.

The joint box 12 includes a partition plate 121 penetrating the horizontal main bar 101, a pair of side plates 122, and a bottom plate 123.
And a pull-out plate 124 which is located at the end of the joint box 12 and which can be inserted and removed in the vertical direction. Further, as shown in FIGS. 2A and 2B, the partition plate 121 is integrally provided with a pair of shear connectors 126 in a penetrating state. The partition plate 121 is made of a corrugated steel plate and is arranged so that the wave direction of the corrugated plate is horizontal.

Next, a continuous underground wall construction method using the rebar cage 10 having the above configuration will be described.

First, as shown in FIG. 2 (a), in the preceding construction section [I],
The preceding drill hole 14 is formed, and then the rebar cage 1 having the above-mentioned configuration is formed.
0 is inserted into the excavation hole 14 and concrete is poured into the excavation hole 14 except the joint box 12 to form the leading wall 16.

Next, after the trailing excavation hole 18 is excavated in the trailing work section [II] on the side end side of the joint box 12 and the extraction plate 124 is extracted, as shown in FIG. Similar to the above, the rebar cage 10 having a joint box (not shown) at one end is inserted. An auxiliary reinforcing bar cage 110 for joining is integrally provided at the rear end of the reinforcing bar cage 10.

The auxiliary reinforcing bar cage 110 is formed narrower than the width between the horizontal main bars 101 in the joint box 12, and is inserted in the joint box 12 so as to overlap the horizontal main bars 101.

In this state, as shown in FIG.
When concrete is placed inside, the trailing wall 20 having the partition plate 121 as a joining surface is formed.

Thereafter, the same process is repeated to form a continuous, integral underground wall.

In the formed underground wall, a partition plate 121 that constitutes a connecting surface
Has a corrugated shape with respect to the shearing direction.
With respect to the external force such as earth water pressure acting on the leading and trailing walls 16 and 20 sandwiching 21, it has a different aspect from that of the conventional flat steel plate.

FIG. 3 shows an underground wall model M having a partition plate 121 as a connecting surface.
FIG. 3 is an explanatory view showing a pressurized state of No. 2, where pressure P is applied from both sides of the partition plate 121, the model M is supported at point A, and the shear force is measured.

FIG. 4 is a graph of measurement results in which the vertical axis represents the shear force and the horizontal axis represents the relative slip amount according to the applied pressure.

In the figure, the characteristics shown in (a) and (b) are respectively obtained by using a conventional flat steel plate, (a) shows a single flat steel plate, and (b) shows a case where a shear connector is added to the flat steel plate.
Further, (C) and (D) show the case where the partition plate made of the corrugated steel plate of the present invention is used, (C) shows the case without a shear connector, and (D) shows the shear connector. It shows the case where it is attached.

In this test, the thickness and overlap length of the horizontal main bars and vertical bars are set to the same, the shear connectors are made of the same material and have the same length, and the height of the corrugated steel plate is 50 m.
m, wavelength is 150 mm (wavelength / height = 150/50 =
3), the one having a thickness of 4.5 mm was used.

The results are in any case, and the partition plate using the corrugated steel sheet according to the present invention has higher out-of-plane shear resistance than the conventional one, and is improved by 2 to 2.5 times as compared with the conventional one. .

Further, FIG. 5 shows the cracked state of the conventional underground wall model M ′ used for the above-mentioned measurement and the underground wall model M of the present invention. It was found that the crack connecting P and the partition wall is clearly generated, whereas the underground wall model M according to the present invention has only a crack extending obliquely from the partition wall.

In the examples, as a representative example, 1 (wavelength) / h of the test piece is used.
(Height) = 3 was used, but when l / h was changed other than that, the following tendency is shown.

(A) l / h ≧ 5 Since the wave height is smaller than the wave height distance, the bearing area that resists the wave front is small, and the bearing strength locally increases, resulting in the same shape as the flat steel sheet and the effect of the waveform. Fades.

(B) 5> l / h ≧ 3 There is no sudden shear fracture, the bearing pressure is dispersed on the wave front, and the shearing force of the joint surface is effectively transmitted through the corrugated steel sheet, and the plastic deformability is improved.

(C) When 3> l / h 5> l / h, the fracture property near the corrugated surface shifts from bearing failure to shear fracture, but when 3> l / h, it extends between the corrugated convex portions. The shear fracture of concrete becomes remarkable, and the effect of corrugation diminishes.

Reasonable waveforms that can be concluded from the results of (a), (b), and (c) above are that there is no shear fracture across the convex portions of the waveform, and there is a local pressure breakdown due to the local pressure acting by the wave front. That is not the case. This balanced state is 5
If it is in the range of> l / h ≧ 3, shear cracks will occur from the fracture surface in the direction of about 45 ° to the joint surface, the bearing force acting on the wave front will be dispersed over the entire joint surface, and the bearing capacity will be improved. The plastic deformability will be greatly improved.

The above-mentioned waveform may be a sinusoidal waveform as shown in each figure, or a waveform similar to a sinusoidal waveform.

<< Effects of the Invention >> As is clear from the above conclusion, according to the present invention, the horizontal cross section of the partition plate is corrugated, and the wavelength / height ratio of the corrugation is set in the range of 3 to 5 so far. The out-of-plane shear resistance on the joint surface can be greatly improved as compared with the structure of the joint using the flat steel plate.

[Brief description of drawings]

FIG. 1 is a perspective view showing a reinforcing bar portion of the underground wall according to the present invention, and FIGS. 2 (a), (b) and (c) show a process sequence of a continuous underground wall construction method using the reinforcing bar portion. FIG. 3 is a horizontal sectional view, FIG. 3 is an explanatory view showing the applied state of the underground wall model, and FIG. 4 is a relationship between the shear force and the relative slip amount of the conventional underground wall model and the underground wall model of the present invention. A graph comparing FIG. 5 (a),
(B) is a schematic plan view showing a cracked state of the conventional underground wall model used for the measurement and the underground wall model of the present invention,
FIG. 6 is a horizontal sectional view showing a conventional method of constructing a continuous underground wall. 1a, 1b ... Drilling hole, 10 ... Reinforcing box 12 ... Joint box 121 ... Partition plate, 122 ... Side plate 123 ... Bottom plate, 124 ... Extraction plate [I] ... Preceding section, [II] ... … Subsequent work zone

Continuation of front page (56) Reference JP-A-55-72514 (JP, A) JP-A-52-38723 (JP, A) JP-A-49-132808 (JP, A) JP-A-59-88533 (JP , A)

Claims (1)

[Claims] 1. A continuous underground wall in which a rebar cage having a hollow joint box provided at one end is used, and end portions of the rebar cage are overlapped in the joint box so as to be sequentially connected to each other. The horizontal section of the partition plate of the joint box located at the joint portion of the inner wall has a sinusoidal waveform, and the wavelength / height ratio of the sinusoidal waveform is set in the range of 3 to 5. Continuous underground wall.