BACKFILL STRUCTURE AND BACKFILL CONSTRUCTION METHOD

Abstract

An object of the invention is to realize a backfill structure suitable for relatively small-scaled land improvement without causing such a problem that a retaining wall after construction is unstable. A backfill structure for constructing an underground structure is composed of a plurality of wall face panels 1 vertically provided on a front face of a ground portion, coupling members 2 which are inserted through through-holes provided in the wall face panels to be fastened on the front face side of the wall face panels, net-like sheets 3 fastened with the other ends of the coupling members 2, and backfill soil body which is filled on the net-like sheets 3 to bury and fix the net-like sheets 3, where the backfill soil body is filled between the wall face panels 1, the back face side of the wall face panels, and the ground portion.

Description

TECHNICAL FIELD

The present invention relates to a backfill structure and a backfill construction method for, when constructing a base portion of a structure or an underground structure, preventing a surrounding soil foundation from collapsing.

BACKGROUND ART

When a base portion of a structure or an underground structure such as a basement is constructed, it is a general construction method to first excavate a surrounding ground of the structure or the underground structure to secure a width required for the structure or the underground structure, provide a retaining wall, a base or the like on one side of slop faces, and perform backfill of an excavated soil on a back side of the retaining wall or the base, thereby constructing a backfill structure serving as a land retaining wall.

The conventional backfill structure and construction method will be described with reference to FIG. 10 to FIG. 12.

FIG. 10 is a plan view showing a configuration of the conventional backfill structure and FIG. 11 is a sectional view taken along line B-B in FIG. 10.

As shown in FIG. 10 and FIG. 11, in the conventional backfill structure, a wall face panel 101 is vertically provided on a boundary face of a backfill portion 6 via a runner 7, and a wire for stay 103 pulled from a crossbar 102 fixedly provided on the wall face panel 101 on the opposite side (hereinafter, simply called “front face side”) to the ground of the wall face panel 101 via a through-hole (not shown) provided on the wall face panel 1 is fastened to a supporting picket 104 such as an anchor piled in a ground portion 5, so that a soil pressure acting on the wall face panel 101 is supported by balance with a withdrawal resistance of the supporting picket 104.

A pulling direction of the wire for stay 103 is not limited to one direction necessarily, but the wire for stay may be pulled in a direction in which the soil pressure and the withdrawal resistance are easily balanced with each other as a whole, in a plurality of directions, if necessary.

FIGS. 12A, 12B and 12C are views showing construction steps of the conventional backfill structure.

In the construction, first, as shown in FIG. 12A, the wall face panel 101 is vertically provided in the backfill portion 6 formed by the excavating through the runner 7. The wire for stay 103 which has been stretched through the through-hole provided in the wall face panel 101 is pulled out of the crossbar 102 fixedly provided on the front face side of the wall face panel 101. Then, the supporting picket 104 is piled in the ground portion 5, and the wire for stay 103 is fastened to the supporting picket 104. Then, backfill soil is conveyed in to such an extent that the wire for stay 103 and the supporting picket 104 are buried to perform backfill. At this time, a surface compaction work is performed to the backfill soil so that the backfill soil is compacted.

As shown in FIG. 12B and FIG. 12C, the work is repeated from a bottom portion of the wall face panel 101 toward an upper portion thereof, and the backfill is performed until it reaches approximately the same height as the wall face panel 101, so that a backfill structure is constructed. The backfill structure thus constructed supports and stabilizes the wall face panel 101 by balance between the soil pressure of the backfill portion 6 and the withdrawal resistance of the supporting picket 104.

Now, an optimal construction method for piling the supporting picket 104 in such a case varies according to soil quality of the ground or the soil foundation or the condition of a construction environment. Therefore, a stable withdrawal resistance is not always obtained necessarily, so that the number or the construction positions of supporting pickets 104, the thickness of a reinforcing steel for stay or the number of twisted reinforcing steels, or the like must be changed according to the construction environment, especially, the construction position of the supporting picket easily deviates in the backfill soil portion after construction due to influence of fluctuation of the ground, rainwater, or the like, which results in such a problem that withdrawal resistance as intended cannot be obtained.

Further, by performing compaction by the surface compaction work, voids in the backfill portion 6 can be eliminated so that the backfill portion 6 can be made further dense. However, the wire for stay 103 is eventually pulled within the backfill portion 6 in a direction of the wall face panel 101 or in a direction of the ground 5 according to the work. Therefore, since such an event occurs that the wall face panel 101 is inclined or the supporting picket 104 is pulled out of the ground portion 5 due to pulling of the wire for stay 103, sufficient surface compaction work cannot be performed. Accordingly, a weak backfill structure is easily affected by fluctuation of the surrounding soil foundation or rainwater.

In order to solve such a problem, a lightweight fill structure where a grating crib is installed on a slope of the fill, a vegetation soil member and a fill body are provided inside the grating crib, and a net-like sheet burying and fixing the fill body is provided on a bottom portion of the grating crib has been reported (see Patent Literature 1).

PRIOR ART DOCUMENTS

Patent Document

Patent Document 1: Japanese Patent Application Laid-Open No. 2002-371559

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

As described above, in the backfill construction method using the conventional supporting pickets or anchors, such a case that withdrawal resistance as intended cannot be obtained occurs, and such a case that the retaining wall does not stabilize in such a manner that the retaining wall is pushed down by a side pressure of the backfill soil occurs.

Further, the invention described in Patent Document 1 requires preparation of a large-sized grating crib made of iron and is useful for a large-scale construction, but it is not intended to improve a soil foundation of a general construction site.

The present invention has solved such a problem and an object thereof is to realize a backfill structure and a backfill construction method which are suitable for a relatively small-scale land improvement without causing such a problem that a retaining wall after construction is unstable.

Means for Solving the Problem

In order to solve the above problem, a backfill structure according to the present invention is a backfill structure for constructing an underground structure by performing backfill of excavated soil, comprising: a plurality of wall face panels vertically provided at predetermined intervals on a slope of a ground portion; a plurality of sheet members attached along a height direction of the plurality of wall face panels; and coupling members for coupling the plurality of sheet members and the plurality of wall face panels, wherein backfill of the excavated soil is performed within the predetermined intervals, and the plurality of sheet members coupled to the plurality of wall face panels are laid and buried approximately in parallel with a ground face, respectively.

Further, in the backfill structure according to the present invention, the plurality of sheet members is formed in a mesh shape.

Further, in the backfill structure according to the present invention, the plurality of sheet members is made of steel, made of cloth, or made of resin.

Further, in the backfill structure according to the present invention, the plurality of sheet members has a length of about 1/3 or more of the lengths of the wall face panels 1 in a height direction thereof.

Further, a backfill construction method according to the present invention is a backfill construction method for constructing an underground structure by performing backfill of excavated soil comprising: an excavating step of excavating a ground face to be subjected to backfill; a panel-vertically-providing step of vertically providing a wall face panel on a front face of a ground portion; a step of attaching a plurality of sheet members to the wall face panel; a backfill step of performing backfill in a backfill portion positioned between the ground portion and the wall face panel up to laying levels of the plurality of sheet members; and a land-leveling step of leveling land after the backfill is repeated by the number of times corresponding to the number of the plurality of sheet members.

Further, a backfill construction method according to the present invention is a backfill construction method for constructing an underground structure by performing backfill of excavated soil comprising: an excavating step of excavating a ground face to be subjected to backfill; a panel-vertically providing step of vertically providing a wall face panel on a front face of a ground portion; a step of attaching a plurality of sheet members to the wall face panel; a backfill step of performing backfill in a backfill portion positioned between the ground portion and the wall face panel up to laying levels of the plurality of sheet members; a surface compaction step of, after the backfill is performed up to the laying levels of the plurality of sheet members, performing surface compaction to surfaces of the laying levels; and a land-leveling step of leveling land after the backfill step and the surface compaction step are repeatedly performed by the number of times corresponding to the number of the sheet members.

Advantageous Effect of the Invention

Since the present invention is configured and performs treatment in the above manner, it is suitable in construction at a small-scaled ground and makes construction matching with a site situation possible, so that a backfill structure and a backfill construction method which can maintain a wall face panel forming a retaining wall stably for a long period after construction can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a configuration of an embodiment of a backfill structure of the present invention;

FIG. 2 is a sectional view of the embodiment shown in FIG. 1 taken along line A-A;

FIG. 3 is a detailed view of a coupling member used in the embodiment shown in FIG. 1;

FIG. 4 is a flowchart diagram of a backfill construction method of the present invention;

FIG. 5 is a sectional view of a backfill structure according to a second embodiment;

FIG. 6 is a detailed view of a coupling member used in the second embodiment;

FIG. 7 is a flowchart showing a construction procedure of the backfill structure of the second embodiment;

FIGS. 8A to 8C are views showing a construction step of the backfill structure of the second embodiment;

FIGS. 9A to 9C are views showing a construction step of the backfill structure of the second embodiment;

FIG. 10 is a plan view showing a configuration of a conventional backfill structure;

FIG. 11 is a sectional view taken along line B-B in FIG. 10; and

FIGS. 12A to 12C are views showing a construction step of the conventional backfill structure.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First Embodiment

FIG. 1 to FIG. 3 are views showing a backfill structure according to a first embodiment.

Incidentally, in FIG. 1 to FIG. 3, reference numeral 1 denotes a wall face panel, reference numeral 2 denotes a coupling member, reference numeral 3 denotes a net-like sheet, reference numeral 4 denotes a backfill soil body, reference numeral 5 denotes a ground portion, reference numeral 6 denotes a backfill portion, reference numeral 21 denotes a JIS standard Number 3 washer, reference numeral 22 denotes a slab ring, reference numeral 23 denotes a nut, reference numeral 24 denotes a crossbar, and reference numeral 31 denotes a wire for stay. Explanation is made in detail with reference to FIG. 1 to FIG. 3.

FIG. 1 is a plan view of a backfill structure according to the first embodiment.

As shown in FIG. 1, a plurality of wall face panels 1 is vertically provided on a front face of the ground portion 5 at predetermined intervals on a slope of the ground portion 5, thereby configuring a front edge section of a backfill structure. Then, the net-like sheets 3 are buried between the front face of the ground portion 5 and the plurality of wall face panels 1. The net-like sheet 3 is fastened to the coupling member 2 via the wire for stay 31. One end of the coupling member 2 is inserted through a through-hole (not shown) provided in the wall face panel 1 and is connected with the wire for stay 31.

FIG. 2 is a sectional view taken along line A-A in FIG. 1.

As shown in FIG. 2, the wall face panel 1 is vertically provided on a runner 7 preliminarily installed on an excavated face. The net-like sheet 3 is laid on the lowermost portion of the wall face panel 1 so as to cover the ground face portion and is directly fixed to the wall face panel 1 by a screw 8 or the like in order to maintain stability of the wall face panel 1.

The net-like sheets 3 are fastened to the coupling members 2 via the respective wires for stay 31 at a plurality of sites of the wall face panel 1 in a height direction thereof except for the lowermost portion. The net-like sheets 3 are buried in the backfill portion 6 approximately in parallel with the ground face by the backfill soil 4, respectively. In FIG. 2, three net-like sheets 3 buried approximately in parallel with the ground face in a multi-layered manner are shown along the height direction.

By adopting such a configuration, soil pressures of the backfill soil 4 are imparted on the respective net-like sheets 3. By the soil pressures, the net-like sheets 3 can tether the ground portion 5 by the backfill portion 6 sufficiently even if supporting pickets are not piled unlike the conventional manner, and they can support the wall face panel 1 while being balanced with the soil pressure acting on the wall face panel 1.

Incidentally, as the wall face panel 1 used here, a steel form “E-PANET” (registered trademark) which has been applied with high corrosion resistance plating or the like can be used, and as the net-like sheet 3, a steel-made or resin-made one can be used.

FIG. 3 is a view showing details of the coupling member 2 used in the first embodiment.

As shown in FIG. 3, the coupling member 2 is composed of a combination of the JIS standard Number 3 washer 21, the slab ring 22, and the nut 23. At the use time of the coupling member 2, the slab ring 22 is inserted into the through-hole provided in the wall face panel 1 from the side of the ground portion 5 to extend through the JIS standard Number 3 washer 21 on the front face side of the wall face panel 1, and the slab ring 22 is fastened to the JIS standard Number 3 washer 21 by the nut 23. Then, crossbars 24 (reinforcing steels with a diameter of 10 mm are used here) are inserted into clearances formed between curved faces of a bracket of the JIS standard Number 3 washer 21 and the front face side of the wall face panel 1 and fastened. By fastening the crossbars 24, the wall face panel 1 is coupled to left and right wall face panels so that required strength can be obtained.

Incidentally, in order to fasten the net-like sheet 3 to the wall face panel 1, it is not required to use the coupling member 2 necessarily, but, for example, the net-like sheet 3 may be directly attached to the wall face panel 1.

In FIG. 1, the net-like sheets 3 are laid from each of three sets of wall face panels 1 approximately in parallel with the ground face and buried, but it is unnecessary to draw the net-like sheets 3 from all of the wall face panels 1 and if the wall face panels 1 are mutually coupled to one another, some of the net-like sheets can be omitted or some thereof may be replaced by fastening performed by supporting pickets shown in the conventional example.

FIG. 4 is a flowchart showing a backfill construction method in the first embodiment. The backfill construction method in the first embodiment will be described along the flowchart.

The backfill construction method of the present invention is a backfill construction method for constructing an underground structure in an excavated ground.

First of all, a predetermined piece of ground face is excavated (Step S1: excavating step). A wall face panel 1 is vertically provided at a predetermined position on the excavated face excavated (Step S2: panel-vertically-providing step).

Next, a net-like sheet 3 is fastened to the lowermost portion of the wall face panel 1 to be laid, and backfill soil 4 is conveyed in to perform backfill (Step S3: backfill step). Next, a net-like sheet 3 is laid on a laying level face in a height direction of the wall face panel 1 (Step S4: laying step). Then, whether or not laying of the net-like sheet 3 has been performed up to a predetermined height is determined (Step S5), and when the laying does not reach the predetermined height, the backfill step of Step S3 and the laying step of Step S4 are repeated.

After the repetition, the uppermost backfill portion 6 is subjected to land-leveling (Step S6: land-leveling step), so that backfill is completed.

By performing backfill in this manner, a plurality of layers composed of the backfill soil 4 and the net-like sheets 3 are stacked in the backfill portion 6 approximately in parallel with the ground face. Soil pressures of the backfill soil 4 are applied to the respective net-like sheets 3, and by the soil pressures, the net-like sheets 3 can tether the ground portion 5 by the backfill portion 6 sufficiently even if the supporting pickets are not piled unlike the conventional manner, and they can support the wall face panel 1 while being balanced with the soil pressure acting on the wall face panel 1.

Incidentally, as the wall face panel 1, an example of a steel form panel has been shown in the above, but the wall face panel 1 is not limited to this example and a panel made of resin or made of wood can be used.

As the material of the net-like sheet 3, a net-like sheet made of steel, made of cloth, made of resin, or the like corresponding to the material of the wall face panel 1 can be used. The net-like sheet 3 is not required to have mesh necessarily if it is a sheet-like member which can receive soil pressure. Further, the sheet-like members of the kinds described above can be selectively used according to the content rate of clay or sand contained in the soil.

Further, installation intervals of a plurality of net-like sheets 3 installed in the height direction of the wall face panel 1 can be similarly adjusted according to the scale of a structure to be constructed.

Furthermore, the net-like sheet 3 is installed on the lowermost portion of the backfill portion 6 in order to maintain stability of the wall face panel 1, but, for example, when blinding concrete is cast on the lowermost portion of the backfill portion 6, it is unnecessary to install the net-like sheet 3.

Second Embodiment

FIG. 5 and FIG. 6 are views showing a backfill structure according to a second embodiment of the present invention. Incidentally, since same configurations as those of the first embodiment have been attached with same reference numerals, repetitive explanation thereof will be omitted.

The backfill structure according to the second embodiment is for constructing an optimal backfill structure for a construction environment by changing the kind or the length of a net-like sheet drawn from a wall face panel.

FIG. 5 is a sectional view of the backfill structure according to the second embodiment.

As shown in FIG. 5, the backfill structure is similar to the first embodiment regarding such a point that a plurality of wall face panels 1 are vertically provided on the front face of the ground portion 5 to configure a front edge section of the backfill structure, such a point that the wall face panels 1 are vertically provided on a runner 7 preliminarily installed on an excavated face, such a point that the net-like sheets 3 are drawn from the wall face panels 1 via the coupling members 20 in the direction of the backfill portion 5, and such a point that the net-like sheets 3 are buried in the backfill portion 6 by the backfill soil 4, respectively, and a plurality of layers are stacked in the backfill portion 6 by the number corresponding to the number of net-like sheets 3.

The second embodiment is different from the first embodiment regarding the length of the net-like sheet 3 to be drawn from the wall face panel 1 and a coupling method using a coupling member.

As shown in FIG. 5, the length of the net-like sheet 3 to be drawn is not drawn up to the slope unlike the first embodiment, and it is about 1/3 of the height of the wall face panel 1 to be vertically provided. Since the length of the net-like sheet 3 is changed according to the soil property of the surrounding soil foundation, the soil property of the backfill soil 4, or the scale of the structure to be constructed, the length of the net-like sheet 3 is made adjustable. When the length is less than 1/3 of the height of the wall face panel 1, the force directed toward the front face side of the wall face panel 1 and the force directed toward the slope which are generated by the soil pressure are unbalanced, so that the wall face panel 1 cannot be supported. Accordingly, it is desirable that the length of the net-like sheet 3 to be drawn is about 1/3 or more of the height of the wall face panel 1.

FIG. 6 is a view showing a coupling member 20 used in the backfill structure according to the second embodiment.

As shown in FIG. 6, unlike the first embodiment, the net-like sheet 3 is directly fixed to the wall face panel 1 via the coupling member 20 as it is. The coupling member 20 is a member which is formed in an approximately U shape and is elongated in a widthwise direction of the wall face panel 1. When the net-like sheet 3 is fixed, one end of the net-like sheet 3 is sandwiched between the a back face of the coupling member 20 and the wall face panel 1 and the net-like sheet 3 is fixed to the wall face panel 1 in the sandwiched state using a screw 8.

By using the coupling member 20 with a simple shape in this manner, the net-like sheet 3 can be easily fixed regardless of the quality of material or the shape of the wall face panel 1

FIG. 7 is a flowchart showing a construction procedure of the backfill structure according to the second embodiment, and FIGS. 8A to 8C and FIGS. 9A to 9C are views showing a construction step of the backfill structure. The construction method of the backfill structure according to the second embodiment will be described below with reference to FIG. 7 to FIGS. 9A to 9C.

First of all, as shown in FIG. 8A, a predetermined piece of ground portion 5 is excavated in order to construct a backfill structure (Step S10 in FIG. 7). Next, as shown in FIG. 8B, a runner 7 is installed at a position where a width for forming a required backfill portion 6 has been secured from the slop 8 formed by the excavating step and wall face panels 1 are vertically provided on the runner 7 (Step S11 in FIG. 7). At this time, one end of a net-like sheet 3 is fixed near the runner 7 or the lowermost portion of the wall face panel 1 and the net-like sheet 3 is laid. Incidentally, when the wall face panel 1 is preliminarily vertically provided on blinding concrete or according to a construction environment, it is unnecessary to lay the net-like sheet 3 at the lowermost portion of the wall face panel 1. Next, backfill soil 4 is conveyed in to perform backfill up to a laying level of the net-like sheet 3 in the wall face panel 1 (Step S12 in FIG. 7), and a net-like sheet 3 is installed at a predetermined position in the height direction of the wall face panel 1 vertically provided via the coupling member 20 (Step S13 in FIG. 7).

Next, the net-like sheet 3 is laid on the backfill soil 4 so as to be approximately in parallel with the ground face. Further, as shown in FIG. 9A, the backfill soil 4 is conveyed in to such an extent that the net-like sheet 3 is buried and the backfill soil 4 is compacted by a surface compaction work (Step S14 in FIG. 7). Then, as shown in FIGS. 9B and 9C, the conveying-in and the surface compaction work of the backfill soil 4 are repeated by the number of times corresponding to the number of net-like sheets 3 installed (Step S15 in FIG. 7), and the uppermost backfill portion 6 is land-leveled (Step S16 in FIG. 7), so that the backfill is completed.

In the backfill structure constructed in this manner, since surface compaction is performed to the backfill soil 4 at the positions where the net-like sheets 3 have been laid, backfill soil 4 enters the mesh portions of the respective net-like sheets 3 so that frictional resistance between the net-like sheets 3 and the backfill soil 4 is improved. Thereby, the soil pressures acting on the net-like sheets 3 and the backfill soil, and the frictional resistance exceed the soil pressure of the backfill soil 4 acting on the wall face panel 1, so that support of the wall face panel 1 can be strengthened.

Further, since the lengths of the net-like sheets to be drawn from the wall face panel and the installation intervals thereof can be changed according to the height of the wall face panel, the net-like sheets can be used with the lengths or the number thereof matching the construction environment or the scale of the structure, so that a cost can be suppressed. Further, since the coupling member has a simple shape and it can securely fix the net-like sheet to the wall face panel easily, so that construction is made possible without requiring a special technique. Furthermore, a construction schedule can also be shortened.

Incidentally, it goes without saying that the surface compaction work performed in the second embodiment may be performed in the first embodiment.

INDUSTRIAL APPLICABILITY

The present invention is suitable for construction in a small-scale ground, makes construction matching a situation of a field site possible, and can maintain a wall face panel forming a retaining wall stable for a long period after the construction, it can be widely utilized in industrial field relating to construction and civil engineering.

REFERENCE NUMERALS

• 1: wall face panel
• 2, 20: coupling member
• 3: net-like sheet
• 4: backfill soil
• 5: ground portion
• 6: backfill portion
• 7: runner
• 8: screw
• 21: JIS standard Number 3 washer
• 22: slab ring
• 23: nut
• 24: crossbar
• 31: wire for stay

Claims

1. A backfill structure for constructing an underground structure by performing backfill of excavated soil, comprising:

a plurality of wall face panels vertically provided at predetermined intervals on a slope of a ground portion;

a plurality of sheet members attached along a height direction of the plurality of wall face panels; and

coupling members for coupling the plurality of sheet members and the plurality of wall face panels, wherein

backfill of the excavated soil is performed within the predetermined intervals, and the plurality of sheet members coupled to the plurality of wall face panels are laid and buried approximately in parallel with a ground face, respectively.

2. The backfill structure according to claim 1, wherein the plurality of sheet members are formed in a mesh shape.

3. The backfill structure according to claim 1, wherein the plurality of sheet members are made of steel, made of cloth, or made of resin.

4. The backfill structure according to claim 1, wherein the lengths of the plurality of sheet members are set to the lengths of about 1/3 or more of the lengths of the wall face panels 1 in a height direction thereof.

5. A backfill construction method for constructing an underground structure by performing backfill of excavated soil comprising:

an excavating step of excavating a ground face to be subjected to backfill;

a panel-vertically-providing step of vertically providing a wall face panel on a front face of a ground portion;

a step of attaching a plurality of sheet members to the wall face panel;

a backfill step of performing backfill in a backfill portion positioned between the ground portion and the wall face panel up to laying levels of the plurality of sheet members; and

a land-leveling step of leveling land after the backfill is repeated by the number of times corresponding to the number of the plurality of sheet members.

6. A backfill construction method for constructing an underground structure by performing backfill of excavated soil comprising:

an excavating step of excavating a ground face to be subjected to backfill;

a panel-vertically providing step of vertically providing a wall face panel on a front face of a ground portion;

a step of attaching a plurality of sheet members to the wall face panel;

a backfill step of performing backfill in a backfill portion positioned between the ground portion and the wall face panel up to laying levels of the plurality of sheet members;

a surface compaction step of, after the backfill is performed up to the laying levels of the plurality of sheet members, performing surface compaction to surfaces of the laying levels; and

a land-leveling step of leveling land after the backfill step and the surface compaction step are repeatedly performed by the number of times corresponding to the number of the sheet members.

7. The backfill structure according to claim 2, wherein the plurality of sheet members are made of steel, made of cloth, or made of resin.

8. The backfill structure according to claim 2, wherein the lengths of the plurality of sheet members are set to the lengths of about 1/3 or more of the lengths of the wall face panels 1 in a height direction thereof.

9. The backfill structure according to claim 3, wherein the lengths of the plurality of sheet members are set to the lengths of about 1/3 or more of the lengths of the wall face panels 1 in a height direction thereof.

10. The backfill structure according to claim 7, wherein the lengths of the plurality of sheet members are set to the lengths of about 1/3 or more of the lengths of the wall face panels 1 in a height direction thereof.