JP6618114B2 - Construction method of mountain retaining wall by the retaining wall and parent pile sheet pile method - Google Patents

Description

  The present invention relates to a mountain retaining wall and a method for constructing a mountain retaining wall by a parent pile sheet pile method.

In the root cutting work to excavate the land to form the foundation of the building to form a space, the retaining wall is constructed so that the surrounding soil does not collapse into the excavated part.
At this time, when there is a groundwater level at a level higher than the bottom of the excavation part (root cutting bottom), it is general to construct a water blocking wall such as a soil cement column wall or a steel sheet pile.
On the other hand, there are the following methods for constructing a water blocking wall using the parent pile sheet pile method.
(1) A construction method (Patent Document 1) in which a gel-like water-stopping material is pressed into the back ground of the mountain retaining wall separately from the construction of the mountain retaining wall by the parent pile side sheet pile method.
(2) A method of injecting and filling a water-stopping material into the gap between the steel plate and ground of the retaining wall from the ground using a pressure pump or the like and solidifying it (Patent Document 2).

JP 2009-68203 A JP 04-143308 A

In the gazette of patent document 1, the chemical | medical solution injection | pouring construction using a heavy machine other than a mountain retaining construction is needed, and there exists a subject that a construction period and construction cost will increase.
In the construction method of Patent Document 2, there is a problem that construction work such as adjustment of the water stop material and pumping by a pump is large.
On the other hand, when aquifers exist in only a part of the height direction of the excavation surface, the flow of water can be sufficiently blocked by applying water shielding measures only to the location where these aquifers exist. There is also.

  The purpose of the present invention is a mountain retaining wall that can be constructed more easily and can sufficiently exhibit water shielding performance when the groundwater level at the site of the mountain retaining work is at a level higher than the root bottom, and a mountain retaining wall by the parent pile side sheet pile method It is to provide a construction method.

The first means is a retaining wall applied to the ground including an aquifer sandwiched between impermeable layers on both upper and lower sides,
A series of parent piles built in a row in the ground,
Comprising a wall formed between adjacent parent piles,
The parent pile has a front flange portion that appears on the excavation portion side formed on the surface side of the wall body and a web portion that is connected to the intermediate portion in the width direction of the front flange portion,
Each wall is
Between the front side flange portion thereof parent pile, and a plurality of transverse sheet pile construction has been so exposed to the drilling unit,
A backfill layer formed on the back surface and the ground in close contact with the back surface of the sheet pile,
Have
The backfill layer forms a flat groove portion having a flat groove bottom extending from one side of the inner surface of the web portion of the parent pile between the adjacent parent piles when viewed from above, and the pair of web portions. It is composed by throwing soil into the space surrounded by the inner surface of and the back of the sheet pile and the groove bottom,
Of the backfill layer, at least the part in contact with the aquifer is a water-impervious wall that blocks the flow of water within the region between the parent piles,
The water-impervious wall is formed by mixing a water-impervious material having swelling property into the backfill soil,
This impermeable wall covers substantially the entire excavated surface of the aquifer.

  This means is a mountain retaining wall 10 composed of a parent pile lateral sheet pile method applied to the ground including the aquifer 3 sandwiched between the impermeable layers 4 on both upper and lower sides. It is proposed that at least a portion of the layer 24 that is in contact with the aquifer 3 is formed on the impermeable wall 26 that covers the entire excavated surface of the aquifer 3 (see FIG. 1). The impermeable wall portion 26 is formed by mixing a impermeable material into the backfill soil.

“Water-impervious material” refers to a material that can be mixed with soil and exhibit water-impervious performance in a mixed state. As a preferred example, “an impermeable material that expands by absorbing water”, particularly bentonite, is preferable.
In this specification, “water-blocking” is a broader concept than “water-stopping” in which water is completely stopped like a conventional soil cement column wall, and a sufficiently low numerical value (for example, 2.0 × E-06m / s) is sufficient.

The second means has the first means,
The said water-impervious wall part has a core part which covers the range which touches an aquifer, and a wrap part which shields the end surface of the part adjacent to an aquifer layer among impermeable layers.

In this means, as shown in FIG. 1, in addition to the core portion 26 a that covers the area where the impermeable wall portion 26 is in contact with the aquifer 3, the portion of the impermeable layer that is adjacent to the aquifer layer. It has the lap | wrap part 26b which shields an end surface. By providing this wrap part 26b, the water leakage from the excavated surface of the aquifer 3 can be effectively suppressed.
The “wrap portion” has a length (wrap length) for wrapping with the impermeable layer to such an extent that the water shielding performance can be sufficiently exhibited. This wrap length is such that the permeability coefficient of the path from at least the end surface of the aquifer to the excavation portion bypassing the back surface of the wrap portion of the impermeable wall portion and the peripheral end surface of the impermeable wall portion penetrates the impermeable wall portion. It is desirable to set so as to be larger than the hydraulic conductivity of the route (see FIG. 6).

The third means has the first means or the second means,
The horizontal length of the horizontal sheet pile is shorter than the distance between the web portions of the adjacent parent piles and longer than the distance between the opposed end portions of the front side flanges of the adjacent parent piles,
Both ends of the horizontal sheet pile in the horizontal direction are locked in a state of being sandwiched between the backfill layer and the front flange,
A gap formed between the horizontal end of the horizontal sheet pile and the web was filled with a part of the backfill layer.

  In this means, as shown in FIG. 2 which is a cross-sectional view, the horizontal length of the horizontal sheet pile is shorter than the distance between the web portions of the adjacent parent piles, and is opposed to the front side flange of the adjacent parent piles. The gap G is formed so as to be longer than the distance between the ends, so that a gap G is formed between the horizontal end of the sheet pile and the web, and the gap G is filled with a part of the backfill layer. Provided. This further improves the water shielding performance.

The fourth means is a method of constructing a retaining wall on the ground including an aquifer sandwiched between impermeable layers on both upper and lower sides,
A first step of driving a plurality of parent piles into the ground along a boundary line of a certain ground portion;
A second step of excavating the ground part to form an excavation part;
A third step of cutting the surface side of the ground part between the parent pile parts exposed in the excavation part by a wall thickness equivalent to form a flat groove part with a flat groove bottom;
Near the excavation part inside the flat groove part, both ends are locked to adjacent parent piles and a horizontal sheet pile is fitted, and a backfill layer is placed in the gap between the back surface of the horizontal sheet pile and the groove bottom of the flat groove part. A fourth step of forming;
Consists of
The parent pile has a front flange portion that appears on the excavation portion side formed on the surface side of the wall body and a web portion that is connected to the intermediate portion in the width direction of the front flange portion,
And the said horizontal sheet pile is constructed between the front side flange parts of the adjacent parent pile,
The backfill layer forms a flat groove portion having a flat groove bottom extending from one side of the inner surface of the web portion of the parent pile between the adjacent parent piles when viewed from above, and the pair of web portions. It is composed by throwing soil into the space surrounded by the inner surface of and the back of the sheet pile and the groove bottom ,
In the step of forming the portion of the backfill layer that covers the aquifer, the portion was formed on the water-impervious wall by mixing a water-impervious material having swelling property into the soil.

  This means proposes the construction method of the retaining wall by the parent pile horizontal sheet pile method with improved water shielding performance. Specifically, when the backfill layer 24 is formed on the back side of the horizontal sheet pile 22, the water-impervious material is mixed into the backfill soil for the portion in contact with the aquifer 3 of the ground to constitute the water-impervious wall portion 26. Is. Since the worker confirms the aquifer during the backfilling operation and forms the impermeable wall portion 26, the impermeable wall portion 26 is formed more efficiently than in the case of separately injecting a chemical into the ground. can do. In addition, the construction period can be shortened compared to the prior art that requires work from the ground surface.

According to the invention relating to the first means, the backfill soil portion is a water-impervious wall portion in contact with the aquifer, and the water-impervious wall portion is formed by mixing a water-impervious material with the backfill soil, It can be easily formed without the need for special machines (such as large heavy machinery).
According to the invention relating to the second means, since the impermeable wall has the wrap portion that shields the end surface of the impermeable layer adjacent to the aquifer, the impermeable performance is further enhanced.
According to the invention relating to the third means, the gap formed between the horizontal end of the sheet pile and the web is filled with a part of the backfill layer, so that the water shielding performance is further improved. .
According to the fourth aspect of the invention, in the step of inserting the sheet piles and forming the backfill layer, a portion of the backfill layer that is in contact with the aquifer layer is water shielded by mixing the water shield material into the soil. Since it is formed on the wall, the position of the aquifer can be confirmed by visual observation, and the impermeable wall can be formed more reliably, and the construction period is shorter than the conventional technology that requires work from the ground surface. Can be shortened.

It is a longitudinal cross-sectional view of the mountain retaining wall which concerns on 1st Embodiment of this invention. It is a cross-sectional view of the retaining wall of FIG. It is a partial perspective view of the mountain retaining wall of FIG. It is explanatory drawing which shows the image of the swelling action of the water-impervious material (bentonite) used by this invention. It is a conceptual diagram of the model for demonstrating the wrap length of this invention. It is explanatory drawing of the wrap length of this invention. It is a figure which shows a part of process of constructing the retaining wall of FIG. 1, [1S] is a stage of forming a sheet pile and backfill soil to a level above the level (construction level) in contact with the aquifer. Plan view, [1P] is a longitudinal sectional view of the process at this stage, [2S] is a plan view of the process of excavating the inner side of the parent pile at the construction level, [2P] is a longitudinal sectional view of the process, [3S] is a plan view of the process of installing and backing the first and second horizontal sheet piles from the bottom in the construction level, [3P] is a longitudinal sectional view of the same process, [4S] is the construction level The top view of the process of installing the third sheet pile from the bottom, [4P] is a longitudinal sectional view of the same process. It is a figure which shows the remainder of the process of constructing the retaining wall of FIG. 1, [5S] is a top view of the process which backs in the 3rd horizontal sheet pile from the bottom, [5P] is a longitudinal cross-sectional view of the process [6S] is a plan view of the process of installing the fourth horizontal sheet pile from the bottom in the construction level, [6P] is a longitudinal sectional view of the same process, [7S] is backed by the fourth horizontal sheet pile from the bottom [7P] is a longitudinal cross-sectional view of the same process, [8S] is a plan view of the process of installing a horizontal sheet pile in the remaining part of the construction hierarchy above the fourth and back-filling , [8P] are longitudinal sectional views of the same process. It is explanatory drawing which shows the Example of this invention. It is an example of the data regarding the hydraulic conductivity of the backfilling material which can be used for implementation of this invention, (A) It is a test result of the hydraulic conductivity of the backfilling material, and (B) This is a document to be compared and explained.

  1 to 9 show a retaining wall and a method for constructing the retaining wall according to the first embodiment of the present invention.

In FIG. 1, which is a longitudinal sectional view, reference numeral 2 represents a ground, and this ground has an aquifer 3 sandwiched between a pair of upper and lower impermeable layers 4, 4.
Reference numeral 8 denotes an excavation part, and a retaining wall 10 is formed so as to surround the excavation part.

  The mountain retaining wall 10 includes a plurality of parent piles 12 and a wall body 20.

  The parent pile 12 is driven into the ground 2 preferably at regular intervals along the boundary line of the planned excavation location. In this embodiment, the main pile 12 is H-shaped steel in which a front flange portion 16 and a back flange portion 18 are attached to both ends of the web portion 14. Of course, the rear flange portion 18 may be omitted to form a T-shaped steel.

In addition, the flat groove part 6 formed by the operator excavating the soil part between the adjacent parent piles 12 is formed, leaving the lower part of each parent pile as a fixing part to the ground. The flat groove portion 6 has a groove bottom 6a is substantially flat et vertical plane.
The wall bodies 20 are respectively formed in the flat groove portions 6 between the adjacent parent piles 12. Each wall 20 includes a plurality of horizontal sheet piles 22 and a backfill layer 24 formed on the back surface of the horizontal sheet piles 22.

  Both lateral ends of the horizontal sheet pile 22 are in contact with and locked to the back surfaces of the front flange portions 16 of the parent piles 12 on both sides. A plurality of such horizontal sheet piles 22 are connected in the vertical direction, and the wall surface of the retaining wall 10 is formed. As shown in FIG. 2, the lateral width of the lateral sheet pile 22 is shorter than the distance between the facing surfaces of the web portions of adjacent parent piles, and the width between each end surface of the lateral sheet pile 22 and the web portion 14 is A gap G having Δg is formed.

As described above, the backfill layer 24 is formed in the space surrounded by the back surfaces of the plurality of horizontal sheet piles 22 extending in the vertical direction, the groove bottom 6a of the flat groove portion 6, and the inner surfaces of the pair of web portions . The backfill layer 24 is formed by an operator putting backfill material (mainly backfill soil) into the space and compacting.

In the present invention, at least a portion of the backfill layer 24 that is in contact with the aquifer 3 is formed in the impermeable wall portion 26. The water-impervious wall portion 26 is formed by mixing and stirring the backfill soil and the water-impervious material as a backfill material, and the worker puts the backfill material into the space and compacts it.
A part of the backfill material including the water shielding material is filled in the gap G shown in FIG. 2 and is closely attached to the end surface of the lateral sheet pile 22 and the back surface of the front flange portion 16 by the compacting operation, so that the water shielding performance is remarkably improved. To do.
As the water shielding material, for example, a material that expands by water absorption and exhibits water shielding performance, such as bentonite, may be used.
The backfill soil should be the soil that was originally there (in-situ soil).
By doing so, a material to be prepared for carrying out the present invention is only a water shielding material such as bentonite. And since the said material is cheap compared with a water glass type | system | group chemical | medical agent, since the place which uses the said material is limited to the location corresponding to the position of an aquifer, the construction cost of a retaining wall can be reduced effectively. .

The water-impervious wall portion 26 of the present invention has a function of shielding water in a region (flat groove portion 6) between adjacent parent piles 12.
Compared to the technique of providing a water stop separately on the back side of the retaining wall as in Patent Document 1, the water shielding wall 26 can be formed as part of the backfilling process of the parent pile sheet pile method. Work from the ground surface is not required other than driving piles, and the construction period can be shortened compared to the prior art.
Further, when performing the backfilling operation, the worker visually confirms the position of the aquifer 3 and forms the water-impervious wall portion 26 corresponding to the position of the aquifer, so that the operation is remarkably simplified. The Further, when the backfill material is introduced between the back surface of the lateral sheet pile 22 and the groove bottom 6a of the flat groove portion 6, for example, as shown in FIG. 9, the worker M fills the lateral sheet pile 22 with the backfill material B. Can be visually recognized. In particular, since it can be compacted after directly observing that the backfill material is firmly contained in the gap G, a water shielding effect can be sufficiently achieved with a simple configuration.

FIG. 4 is a conceptual diagram illustrating the action of the curable material.
In the figure, the first column shows a state where the blending ratio of bentonite is zero. The upper part of the row is in an unsaturated state (A-1), and pure mountain sand is drawn. The middle row in the row is in an unsaturated state immediately after passing water (A-2), and since the unsaturated portion is not passed, the apparent permeability coefficient is small. The lower part of the row is a saturated state in which sufficient time has passed since the passage of water (A-3), and when saturated, the water path increases and the hydraulic conductivity increases.
In the figure, the second column shows a state where the blending ratio of bentonite is 5 to 10%. The upper row in the same row is in an unsaturated state (B-1), and the bentonite mixing ratio is small. The middle row in the row is in an unsaturated state immediately after passing water (B-2), and since the unsaturated portion is not passed, the apparent permeability coefficient is small. The lower part of the row is in a saturated state after a sufficient amount of time has passed since passing water (B-3), and bentonite swells but does not block the water channel.
In the figure, the third column shows a state where the blending ratio of bentonite is 15 to 20%. The upper row in the same row is in an unsaturated state (C-1), and the mixing ratio of bentonite is large. The middle row in the row is in an unsaturated state immediately after water flow (C-2), and the bentonite unexpanded portion becomes a water channel and water is passed. The lower part of the row is in a saturated state after a sufficient amount of time has passed since passing water (C-3), and the water channel is blocked by the swelling of bentonite.
From the above, as a preferred embodiment of the present invention, the water content of the in situ soil is about 20%, and bentonite is mixed and stirred at a mass ratio of about 15% with respect to the dry mass of the in situ soil. Good. Of course, the above numerical values can be appropriately changed according to the water shielding performance required by the amount of water passing through the aquifer and various conditions at the site.

  Since the above-mentioned mixed agitation can use heavy machinery (for example, small backhoe) used for excavation, there is no need to prepare other heavy machinery (especially large heavy machinery), and soil bentonite (water-impervious wall) can be easily and inexpensively prepared. Part 26) can be formed.

  In the present embodiment, not only the range in which the impermeable wall portion 26 is in contact with the aquifer 3 in the ground 2 but also the portion of the upper and lower impermeable layers 4 adjacent to the aquifer 3 is overlapped. It is configured as follows. In the present specification, a portion of the impermeable wall portion 26 that covers the end surface of the aquifer 3 is referred to as a core portion 26a, and a portion that covers the end surface of the impermeable layer 4 is referred to as a wrap portion 26b. With such a configuration, groundwater passing through the aquifer 3 is prevented from bypassing the impermeable wall portion 26 and reaching the excavation portion 8. The length of the impermeable wall portion 26 extending beyond the end surface of the aquifer 3 to the impermeable layer side is referred to as a wrap length of the wrap portion 26b. Basically, the wrap length to the upper and lower impermeable layers is desirably determined by the interfacial permeability test described later, but otherwise 20 cm is the standard.

5 and 6 are explanatory diagrams for illustrating the above-described wrap length design method.
FIG. 5 shows a ground model in which the ground including an aquifer sandwiched between upper and lower impermeable layers is more abstracted. That is, the aquifer in the ground is represented as a single water path, and the flow rate is Q. A disk-shaped impermeable wall 26 is assumed to close the water channel. It is assumed that an annular backfill layer 24 extends around the impermeable wall portion 26.

  As shown in FIG. 6, the basic idea of the design method described above is more than the flow rate (Qv) when groundwater passing through the aquifer passes through the impermeable wall and the annular backfill layer in the orthogonal direction. In other words, the wrap length is determined so that the flow rate (Qh) when passing through the detour along the back surface of the water-impervious wall portion to the boundary line with the annular backfill layer portion becomes small. Then, since Qv is generally designed to be sufficiently small, it can be considered that Qh is also sufficiently small.

As shown in FIG. 5, the water channel passes through the impermeable wall (flow rate Qs), flows through the boundary between the impermeable wall and the backfill layer 24 (flow rate Qb), and the backfill layer. 24 is assumed to branch to a flow (flow rate Qc) that permeates 24. Then, each flow rate has the following relationship.
[Formula 1] Q = Qs + Qb + Qc
Next, each flow rate is expressed as follows by Darcy's law. However, the sum of the area of the impermeable wall and the backfill layer is A, the permeability coefficient within this area is k, the dynamic pressure gradient is i, the permeability coefficient of the impermeable wall is ks, and the annular backfill layer And kc, and the boundary flow coefficient between the impermeable wall and the backfill layer is α. For the sake of convenience, the diameter of the water-impervious wall is half the diameter of the annular backfill layer. Further, L is defined as the boundary length of Qb (the length of the detour passing from the end point of the water path to the back surface of the impermeable wall portion and the peripheral surface of the impermeable wall portion).
[Formula 2] Q = k · i · A
[Formula 3] Qs = ks · i · (1/4) A
[Formula 4] Qb = α · i · L
[Formula 5] Qc = kc · i · (3/4) A
And when substituting Formulas 2-5 into Formula 1,
[Formula 6] Qb = Q−Qs−Qc
= I · A [k− (3/4) × kc− (1/4) × ks]
Moreover, when the amount of water permeation on the boundary surface is expressed by the boundary length L and the boundary flow coefficient α, Qb = α × i × L
When α is calculated by substituting this into Formula 6, [Formula 6] α = (A / L) × [k− (3/4) × kc− (1/4) × ks] (m ² / s)

Consider the relationship between the flow rate Qh of the flow passing through the impermeable wall portion and the annular backfill layer portion shown in FIG. 6 and the flow rate Qv of the flow bypassing the impermeable wall portion. As mentioned above,
[Formula 7] Qv> Qh
In order to simplify the calculation, the latter is approximated to the boundary flow rate in the vertical direction, and each is expressed by an equation.
The pressure of the flow of the aquifer and Wp, the thickness of the water shield wall and t _1. Since the pressure drop while traveling the distance t ₁ is Wp, it is a dynamic pressure gradient (Wp / t ₁ ). From Darcy's law described above,
[Formula 8] Qh = k · (Wp / t ₁ ) · A
Next, assuming that the radius of the impermeable wall portion (corresponding to the lap length in this model) is t ₂ , the pressure drop while traveling the distance t ₂ is (Wp / t ₂ ), so that the boundary length is L,
[Formula 9] Qv = α · (Wp / t ₂ ) · L

From Expressions 7 to 9 k · (Wp / t ₁ ) · A> α · (Wp / t2) · L
Next, returning to the structure of an actual retaining wall as shown in FIG. 3, assuming that the lap length is t ₂ , the lateral length is L, and the unit width is A = L × t ₂ L = 1, [Formula 9] t ₂ > [(α / k) × t ₁ ] ^ 0.5
On the other hand, a necessary wrap length for t ₁ = 0.05 m is calculated by substituting the interfacial permeability test result. At the time of construction, the expected wrap length is set to a safety factor of about 10 times.

7-9 has shown the construction method of the retaining wall of this invention by the parent pile cross-sheet pile method.
In the construction method of the retaining wall by the general horizontal pile horizontal sheet pile method, it consists of the following steps.
(1) A step of driving a plurality of parent piles preferably at regular intervals along a boundary line of a certain ground portion that is a planned excavation location.
Specifically, a main pile may be built by drilling a hole in the boundary line with an earth auger machine.
(2) A step of excavating the ground portion to form the excavation portion 8.
When forming the excavation part 8, a relatively small heavy machine E is used. Even the excavation part 8 having a certain depth can be handled by a relatively small heavy machine E by excavating the planned excavation depth into a plurality of layers as shown in FIG.
(3) A step of cutting the surface side of the ground portion between adjacent parent piles exposed to the excavation part 8 by an amount corresponding to the wall thickness.
An operator can perform the operation of cutting the surface side of the ground portion. After the cutting, the flat groove portion 6 having the groove bottom 6a which is a substantially flat vertical surface is formed.
(4) A plurality of horizontal sheet piles 22 are installed between adjacent parent piles so as to be connected in the vertical direction, and a backfill layer is provided between the back surface of the horizontal sheet pile and the groove bottom of the flat groove portion. Forming.
When H-shaped steel is used as the parent pile, it is installed so that both end portions of the lateral sheet pile 22 are locked to the back surface of the front flange portion 16. In addition, the edge part of a horizontal sheet pile is fixed by being pinched | interposed between the back surface of the front side flange part 16, and a backfill.

  In this embodiment, regarding the first level of the excavation part 8, it is assumed that the retaining wall is formed by the normal pile pile sheet pile method as usual, and the aquifer appears on the ground that appears in the excavation part below the second level. The method for constructing the retaining wall according to the present invention will be described with reference to FIGS. However, even when the aquifer 3 appears in the first layer, it can be dealt with similarly.

[1S] and [1P] in FIG. 7 represent a state before a mountain retaining wall is constructed in the second layer, respectively, in a plan view and a side view.
[2S] and [2P] in FIG. 7 represent a state in which the inside of the main pile 12 is excavated by a heavy machine (not shown) and the second layer of the excavation unit 8 is excavated.
When an operator enters the excavation part 8 after excavating the inner side of the parent pile 12 and cuts the surface side of the ground portion between the adjacent parent piles 12 by a certain width, the above-described flat groove part 6 is formed.
The cut soil is stored in a predetermined place for later use as backfill soil.
In addition, when an operator enters the excavation part 8 excavated to the second level, the presence and position of the aquifer 3 can be visually confirmed by observing the surface of the ground newly appearing in the excavation part. This is because the aquifer 3 is damper than the impermeable layer 4 and usually has a different appearance. Even if it cannot be discriminated from the appearance, it can be easily noticed that it is an aquifer 3 because it is in direct contact with the soil during the cutting operation.
[3S] and [3P] in FIG. 7 represent a process of constructing a retaining wall below the aquifer 3 in this hierarchy.
Specifically, the horizontal sheet piles 22a and 22b are sequentially installed between the main piles 12 from the bottom of the excavation part 8 to the vicinity of the lower end of the aquifer 3, and the back side of the horizontal sheet pile 22 is filled with backfill soil. Compact. The height of the upper surface of the backfill soil is set lower than the lower end of the aquifer 3 by the wrap length. This is to secure a space for forming the wrap portion 26b of the water shielding wall portion 26.
[4S] and [4P] in FIG. 7 represent a stage in which a horizontal sheet pile 22c is installed at a position facing the lower half of the aquifer 3 and a backfill material is put on the back side of the horizontal sheet pile 22c.
The backfill material is manufactured by mixing the soil obtained by cutting the ground at the stage of [2P] in FIG. 7 and bentonite by mechanical stirring.
Since the heavy machinery used for excavation is used for mechanical stirring, no separate heavy machinery is required.
Depending on the quantity, it is also possible to use manual stirring instead of mechanical stirring.

[5S] and [5P] in FIG. 8 represent a stage in which the backfill layer 24 put on the back side of the lateral sheet pile 22c facing the lower half of the aquifer 3 is compacted.
[6S] and [6P] in FIG. 8 represent a stage in which a cross sheet pile 22d is installed at a position facing the upper half of the aquifer 3.
[7S] and [7P] in FIG. 8 represent a stage in which a backfilling material is charged on the back side of the lateral sheet pile 22d facing the upper half of the aquifer 3 and compacted to form a backfill layer.
[8S] and [8P] in FIG. 8 represent the stage of formation of the last lateral sheet pile 22e and the backfill layer in this hierarchy. In this stage, first, the backfill material is attached to the groove bottom 6a of the flat groove portion 6 with a certain thickness, and then the cross sheet pile 22e is installed. This is because if the order is reversed, it is difficult to fill the backfill material into the back side of the lateral sheet pile 22e.

FIG. 10 shows an example of a water permeability test.
FIG. 4A shows the result of a water permeability test of a backfilling material formed by mixing and stirring bentonite with the backfilling soil. The figure (B) is the data of the hydraulic conductivity of various soils shown in order to understand the magnitude of the hydraulic conductivity as the test result.
In the above test, the experiment was performed six times using a predetermined soil as a raw material and changing the water content ratio and the Bt (bentonite) ratio. When this raw material was used, a result of 2.0E-09 m / s was obtained when the water content ratio was 15% and the Bt content ratio was 15%. Such a permeability coefficient can be sufficiently used as the backfill material of the present invention.

  It should be noted that the embodiment of the present invention is only a preferred example, and the mode of the embodiment can be appropriately changed as long as it does not contradict the spirit of the present invention.

DESCRIPTION OF SYMBOLS 2 ... Ground 3 ... Aquifer 4 ... Impervious layer 6 ... Flat groove part 6a ... Groove bottom 8 ... Excavation part 10 ... Mountain retaining wall 12 ... Master pile 14 ... Web part 16 ... Front side flange part
18 ... Back side flange
DESCRIPTION OF SYMBOLS 20 ... Wall body 22,22a, 22b, 22c, 22d, 22e, 22f ... Lateral sheet pile 24 ... Back-filling layer 26 ... Water shielding wall part 26a ... Core part 26b ... Lap part E ... Heavy machine G ... Gap M ... Worker

Claims (4)

A retaining wall applied to the ground including an aquifer sandwiched between upper and lower impermeable layers,
A series of parent piles built in a row in the ground,
Comprising a wall formed between adjacent parent piles,
The parent pile has a front flange portion that appears on the excavation portion side formed on the surface side of the wall body and a web portion that is connected to the intermediate portion in the width direction of the front flange portion,
Each wall is
Between the front side flange portion thereof parent pile, and a plurality of transverse sheet pile construction has been so exposed to the drilling unit,
A backfill layer formed on the back surface and the ground in close contact with the back surface of the sheet pile,
Have
The backfill layer forms a flat groove portion having a flat groove bottom extending from one side of the inner surface of the web portion of the parent pile between the adjacent parent piles when viewed from above, and the pair of web portions. It is composed by throwing soil into the space surrounded by the inner surface of and the back of the sheet pile and the groove bottom,
Of the backfill layer, at least the part in contact with the aquifer is a water-impervious wall that blocks the flow of water within the region between the parent piles,
The water-impervious wall is formed by mixing a water-impervious material having swelling property into the backfill soil,
A mountain retaining wall, wherein the impermeable wall covers substantially the entire excavated surface of the aquifer.   The water-impervious wall portion includes a core portion that covers a range in contact with the aquifer and a wrap portion that shields an end surface of a portion of the impermeable layer adjacent to the aquifer. The mountain retaining wall according to 1. The horizontal length of the horizontal sheet pile is shorter than the distance between the web portions of the adjacent parent piles and longer than the distance between the opposed end portions of the front side flanges of the adjacent parent piles,
Both ends of the horizontal sheet pile in the horizontal direction are locked in a state of being sandwiched between the backfill layer and the front flange,
The mountain retaining wall according to claim 1 or 2, wherein a gap formed between a horizontal end portion of the horizontal sheet pile and the web is filled with a part of the backfill layer. A method of constructing a retaining wall on the ground including an aquifer sandwiched between impermeable layers on both upper and lower sides,
A first step of driving a plurality of parent piles into the ground along a boundary line of a certain ground portion;
A second step of excavating the ground part to form an excavation part;
A third step of cutting the surface side of the ground part between the parent pile parts exposed in the excavation part by a wall thickness equivalent to form a flat groove part with a flat groove bottom;
Near the excavation part inside the flat groove part, both ends are locked to adjacent parent piles and a horizontal sheet pile is fitted, and a backfill layer is placed in the gap between the back surface of the horizontal sheet pile and the groove bottom of the flat groove part. A fourth step of forming;
Consists of
The parent pile has a front flange portion that appears on the excavation portion side formed on the surface side of the wall body and a web portion that is connected to the intermediate portion in the width direction of the front flange portion,
And the said horizontal sheet pile is constructed between the front side flange parts of the adjacent parent pile,
The backfill layer forms a flat groove portion having a flat groove bottom extending from one side of the inner surface of the web portion of the parent pile between the adjacent parent piles when viewed from above, and the pair of web portions. It is composed by throwing soil into the space surrounded by the inner surface of and the back of the sheet pile and the groove bottom ,
In the step of forming the portion of the backfill layer that covers the aquifer, the portion is formed on the water-impervious wall by mixing the soil with a water-impervious material having swelling properties. The construction method of the retaining wall by the parent pile side sheet pile method.