Construction method for Continuous Cut-off wall using Overlap casing

[Technical Field] The present invention relates to a construction method of a cast-in-place cut-off wall using overlap casings and filling hoses, which can prevent sliding-down of earth and sand or subsidence of the ground occurring by underground water during public works, such as excavation, coffering, road extension, and so on. In more detail, the present invention relates to a construction method of a cast-in-placecut-off wall using overlap casings and filling hoses including the processes of: vertically drilling round holes to a predetermined depth of the ground using a general excavator! mounting overlap casings in each of the drilled holes, each of the overlap casings having an arc face formed on the outer circumference thereof in a straight line, the overlap casings being continuously mounted in such a way that the arc face of one overlap casing is in close contact with the outer circumference of another adjacent overlap casing, so that the overlap casings are overlapped with each other! filling the continuously mounted overlap casings with a cut-off wall forming material, such as concrete, and inserting reinforcing rods and H-beams into the overlap casings located at predetermined intervals! pulling out the overlap casings after a lapse of a predetermined time period! and filling spaces of the removed overlap casings wil h t he cut - off wall forming material and

hardening the cut-off wall forming material to thereby form a cast-in-place cut-off wall or an underground wall (hereinafter, called "cast-in-place cut off wall") in such a way that a filling hose is grouted into a discontinuous point of the cast-in-place concrete wall to form a cut-off wall body (discontinuous point) of excellent performance.

[Background Art]

In general, when various public works, such as an excavation work for constructing a building or a structure, a coffering work carried out in a river or in the sea, an extension work for extending a road, and so on, are carried out, in order to prevent sliding-down of earth and san or subsidence of the ground, a guard wall must be constructed and an impervious function to prevent an inflow of underground water gushed from the ground into a construction work zone must be provided. As described above, the cut-off method and the earth-retaining method for constructing the guard wall are conventionally used in earth retaining methods of various kinds.

A sheet pile method of the conventional earth retaining methods is divided into a pile driving type (directly driving type) method for directly driving and forcedly inserting a sheet pile into the ground by a Vibro hammer using a crane and a hydraulic NPS (Normal Power Steering) method for forcedly inserting the sheet pile by a forcedly

pulling-out device, and is used to construct a steel sheet pile, which simultaneously serves as a cut-off wall and an earth retaining wall.

In the above method, the steel sheet pile can sufficiently serve as the earth retaining wall as a continuous wall type rigid body if it has excellent degree of strength and durability, and obtain an excellent cut-off effect since it has excellent water tightness at contact portions if the steel sheet pile is made of a watertight material.

However, the pile driving (directly driving) method has problems in that it causes a severe noise pollution and a violent vibration since the sheet piles must be directly driven whenever they are mounted. Furthermore, while the hydraulic NPS method can be carried out in a non-vibration and non-noise state, the hydraulic NPS method has several problems in that it is complicated in work preparation and construction progress, work efficiency is deteriorated due to a slow progress, and it requires a great deal of expenses since a reaction abutment, a power unit and a forced pile driver must be separately mounted for construction and the reaction abutment must be removed when the construction is finished. Moreover, the hydraulic NPS method has another problem in that it causes underground water pollution by water discharged through a water jet.

A conventional water jet and sheet pile method is carried out in the same way as the conventional sheet pile method. However, differently from, the conventional sheet pile method, in the conventional

water jet and sheet pile method, after a water jet pipe is mounted on an edge portion of the sheet pile, the sheet pile is mounted by the Vibro hammer in the pile driving (directly driving) manner, and in this instance, the sheet pile is mounted while a jet pump is operated during the pile driving. Accordingly, the water jet and sheet pile method is effective when the sheet pile is mounted in cohesive soil, fine gravel layer, and weathered rock layer, in which it is difficult to drive the sheet pile by a general pile driving.

However, the conventional water jet and sheet pile method has several problems in that it is complex to separately manufacture the water jet pipes and mount them to the edges of all sheet piles, and it requires much time and many expenses since the jet pump, an auxiliary crane and power generators are additionally mounted.

As a general open excavation method, a conventional H-pile earth retraining wall method is a construction method to carry out excavation after mounting H-piles in the pile driving (directly driving) manner or after drilling vertical holes by an excavator for excavation and inserting H-piles into the vertical holes.

In the H-pile earth retraining wall method, a lagging may serve as an earth retaining wall since it is constructed of a rigid body. However, the conventional 11— pile earth retaining wall method has several problems in that it cannot provide the cut-off effect proper to soil conditions, in thai i t may cause a great relaxa tion of the real" ground

since the top part and the head part are relatively greatly displaced, in that it is difficult to select and additionally carry out a cut-off grout method proper to the soil conditions, and in that it cannot provide an excellent cut-off effect since there is a possibility of a water leakage from connected portions.

Furthermore, a conventional LW (Labile Washer Glass) and H-pile earth retaining method is a method that an LW method is additionally performed to the H-pile earth retaining wall in order to enhance the cut-off effect of the H-pile earth retaining wall, and includes the steps of: mounting H-piles in the pile driving (directly driving) manner; mounting a lagging while performing excavation; drilling grouting holes in such a way as to be adjacent to the rear face of the H-piles and overlapped with the adjacent H-piles inserting a man jet tube in a state where a casing is mounted; and mounting a double packer, and then, grouting a seal agent, such as water glass.

The conventional LW and H-pile earth retaining wall method can provide an earth retaining wall function and a cut-off effect as a ferromagnetic body, and particularly, be easily applied to geological strata of a substantially large porosity, such as sandy gravel layer or boulder layer. However, the conventional LW and H-pile earth retaining method has several problems in that it causes a severe noise since all 11— piles are mounted in the directly driving (pile driving) manner, in that it requires much time and main expenses since the 11 — pi Io earth

retaining method and the LW method are carried out together, and in that the soil conditions must be inspected before the construction since an LW grouting effect is reduced in geological strata of a small porosity.

A conventional S. CW (Soil Cement Wall) and H-pile earth retaining wall method is a construction method to provide the cut-off effect to the H-pile earth retaining wall and an effect for preventing relaxation of the rear ground of the earth retaining wall. In the S. C. W method, a plain cast-in-place underground wall, into which reaction woods (H-piles) are not inserted, is formed. The plain cast-in-place underground wall is formed through the steps of: mounting H-piles in the pile driving (directly driving) manner in such a way as to be adjacent to each other as close as possible; drilling soil cement grouting holes on the rear face of the H-piles in such a way as to be overlapped with each other in a state where a lagging is mounted; and grouting and hardening soil cement, in which soil and cement are mixed with each other.

The S. CW and H-pile earth retaining wall method can provide excellent earth retaining wall and cut-off effects since the wall body including the H-piles and the lagging and the cast-in-place wall body continuously installed in the ground are formed doubly. However, the S. C. W and 11— pile earth retaining wall method has several problems in that it causes a severe noise when the H-piles are mounted since the 11— piles are mounted in the pile driving (directly driving) manner, in that i t requires many equipment expenses since it requires large-scale

equipments, such as a large-scale crane, a mixer, and a pump, and in that it requires a long construction time period and many construction expenses since construction efficiency is low.

The conventional S. CW method is a construction method for constructing a cast-in-place underground wall, the construction method including the steps of: drilling soil cement grouting holes in the ground to a planned depth; grouting soil cement into the grouting holes to form a wall body; and inserting H-piles with reaction woods to thereby improve the earth retaining wall. In the above construction method, the continuous wall body serves to provide a cut-off function and an earth retaining function, but the S. C. W method has a problem in that a construction time period is increased and equipment expenses are also increased since the large-scale equipments, such as the large-scale crane, the mixer and the pump, are required and the construction efficiency is reduced.

The conventional C. I. P (Cast-In-Placed-Pile) method is a construction method for installing reinforced concrete columns in a cast-in-place manner on the spot by pouring reinforced concrete, and includes the steps of: drilling column holes and mounting a casing into each of the holes mounting reinforcing rods inside the casing! filling the casing with mortar, in which cement, gravels, sands are mixed together and hardening the mortar into a column! removing the casing and

inserting H-piles into the columns spaced apart from each other at predetermined intervals.

The C. I. P method has several problems in that it requires a long installation period since it is necessary to repeatedly perform a series of processes of drilling the column holes, mounting a form in each of the holes, filling the column holes with mortar in a state where reinforcing rods are mounted, and removing the form after the mortar is hardened whenever the reinforced concrete columns are mounted, and in that a water leakage may occur since a space between the columns is not tightly sealed.

A conventional auxiliary grouting and C. I. P method is a construction method including the steps of: mounting reinforced concrete columns by the C. I. P method, and inserting H-piles into the reinforced concrete columns; and carrying out an auxiliary grouting for cut-off on the rear face between the reinforced concrete columns. Since the auxiliary grouting for cut-off is carried out additionally after the C. I. P method, which requires many installation expenses and much construction time period, is first carried out, the conventional auxiliary grouting and C. I. P method can ensure excellent earth retaining wall and cut-off functions, but has a problem in that it requires more installation expenses and time.

Excepting the sheet pile method and the water jet and sheet pile method, all of the construction methods ai e performed in combination of

methods of several kinds according to soil pressure and ground conditions when an earth retaining work is performed.

There is another conventional earth retaining work performed when soil pressure is high and the ground is in a great danger of subsidence.

In the conventional earth retaining work, an earth retaining wall is installed on a boundary line between the ground and an excavated part. In this instance, since soil pressure is high and the ground is in a great danger of subsidence, the earth retaining wall is installed through the steps of: mounting H-piles at predetermined intervals on the boundary line of the excavated part by a Vibro hammer in the pile driving (directly driving) manner grouting a seal material to both sides of the inside of the H-piles by the LW method; carrying out the C. I. P method while grouting the seal material; and carrying out a J. S. P (Jumbo Special Pile Pattern) method to the outside of the H-piles, namely, on the boundary line of the ground to thereby support the ground more soundly.

In addition, when soil pressure is low and the ground is in a little danger of subsidence, the C. I. P method is performed on the boundary line between the excavated part and the ground, and if reinforcement is needed, the LW method is performed on the rear face of the reinforced concrete column mounted by the C. I. P method and the seal material (water glass) is grouted.

As described above, excepting the sheet pile driving method, the above construction methods for performing the earth retaining work have several problems in that the construction methods require a great deal of time and expenses since various construction methods are performed together according to soil pressure and ground conditions, and in that they cause a severe noise when the earth retaining work is performed since the H-piles are mounted in a forcedly and directly driving (pile driving) manner.

In order to solve the above problems, Korean Patent No. 375,020, which was patented to the same inventor as the present invention, discloses a "cylindrical columns for constructing earth retaining wall and earth retaining method using the same". Referring to

FIGS. Ia to 3b, Korean Patent No. 375,020 will be described.

As a first process (1- 1), a drilling process (DRA drilling process) of drilling round holes in the ground to a predetermined depth using a general excavator 6 is carried out, and then, an outer casing 2 is (longitudinally) inserted into each of the drilled holes.

As shown in FIG. Ib, as a second process (outer casing penetrating process), an overlap casing 3 or an overlap square pipe 4 having an arc face 3- 1 formed on a side thereof is inserted (penetrated) into the outer casing 2, and then, as shown in FIG. Ic, the outer casing 2 is pulled out and removed through a third process (outer casing pulling out process) ( 1 -, ^' >).

As a fourth process, a process of repeatedly forming a cast-in-place concrete wall is carried out. That is, the first process (1- 1 ; drilling process), the second process (1 -2; outer casing penetrating process) and the third process (1-3; outer casing pulling out process) are carried out repeatedly, so that the overlap casings 3 or the overlap square pipes 4 are continuously mounted as shown in FIG. 2a or 3a.

As shown in FIG. 2b or 3a, after reinforcing bars 12, H-beams 13 or square beams/ round beams are longitudinally inserted into each of the overlap casings 3 or the overlap square pipes 4, which are mounted continuously in such a way as to be adjacent to each other, concrete 11 , cement stabilizer or mortar is grouted up to the top of each of the overlap casings 3 or the overlap square pipes 4, and then, the overlap casings 3 or the overlap square pipes 4, which were used for grouting the concrete 11 , cement stabilizer or mortar, are pulled out to be removed.

When the overlap casings 3 or the overlap square pipes 4 are pulled out to be removed, the concrete 11 , cement stabilizer or mortar, which fills each of the overlap casings 3 or the overlap square pipes 4, is packed (filled) from the lower portion as much as a volume of a space portion 5 formed by the outer casing 2, and accordingly, the initially packed concrete 11 , cement stabilizer or mortar lowers from the top to a predetermined height, so that as pace portion is formed on the upper portion. After that, the concrete 1 1 . cement stabilizer or mortar is

packed in the space portion formed on the upper portion of the geological stratum.

As described above, each of the overlap casings 3 or the overlap square pipes 4 is filled with the concrete 11, cement stabilizer or mortar, and then, pulled out. After the overlap casing 3 or the overlap square pipe 4 is pulled out, the process of filling a space of the removed overlap casing 3 or overlap square pipe 4with the concrete 11, cement stabilizer or mortar is repeatedly performed to make good a deficiency, whereby a cast-in-place cut-off wall 10 is formed as shown in FIG. 2d or 3b. However, in the cylindrical columns for constructing earth retaining and earth retaining method using the same, as shown in FIGS. 4b and 5b, when a new cast-in-place cut-off wall 10 is continuously mounted on the previously formed cast-in-place cut-off wall 10, since the previously formed cast-in-place cut-off wall 10 keeps a previously hardened state and the post formed cast-in-place cut-off wall 10 is not in the hardened state but in a dough state, a discontinuity occurs between the previously formed cast-in-place cut-off wall 10 and the post formed cast-in-place cut-off wall 10. As described above, when a gap is formed due to the discontinuity between the previously formed cast-in-place cut-off wall 10 and the post formed cast-in-place cut-off wall 10, the perfect cut-off effect is partially deteriorated.

[Disclosure ]

Accordingly, the present invention provides an improved construction method of a cast-in-place cut-off wall using overlap casings and filling hoses to solve the above-mentioned problems occurring in the prior arts. It is an object of the present invention to provide an improved construction method of a cast-in-placecut ^~ off wall using overlap casings and filling hoses includes the processes of: vertically drilling round holes to a predetermined depth of the ground using a general excavator; mounting overlap casings in each of the drilled holes, each of the overlap casings having an arc face formed on the outer circumference thereof in a straight line, the overlap casings being continuously mounted in such a way that the arc face of one overlap casing is in close contact with the outer circumference of another adjacent overlap casing, so that the overlap casings are overlapped with each other; filling the continuously mounted overlap casings with a cut-off wall forming material, such as concrete, and inserting reinforcing rods and H-beams into the overlap casings located at predetermined intervals! pulling out the overlap casings after a lapse of a predetermined time period! and filling spaces of the removed overlap casings with the cut-off wall forming material and hardening the cut-off wall forming material to thereby form a cast-in-place cut-off wall or an underground wall (hereinafter, called "cast-in-place cut off wall") in such a way that a filling hose is grouted into a discontinuous point of the ¹ cast -in-place concrete wall.

It is another object of the present invention to provide an improved construction method of a cast-in-place cut-off wall using overlap casings and filling hoses, which can greatly improve the cut-off effect at the discontinuous point since the cast-in-place cut-off wall is formed by inserting the filling hose into the discontinuous point of the cast-in-place concrete wall, and which can prevent the ground weakening and ground subsidence occurring by a leakage of underground water since the cut-off effect at the discontinuous point is greatly improved. To achieve the above objects, the present invention provides a construction method of a cast-in-place cut-off wall using overlap casings and filling hoses, which includes: a drilling process (1-1) of vertically drilling round holes in the ground to a predetermined depth using a general excavator (6), and inserting an outer casing (2) into each of the holes; an outer casing penetrating process (1-2) of penetrating an overlap casing (3) or an overlap square pipe (4) into the outer casing (2) inserted into each of the holes; an outer casing pulling out process (1-3) of pulling out the outer casing (2), in which the overlap casing (3) or the overlap square pipe (4) is penetrated; a cast-in-place concrete wall forming process (1-4) of repeatedly performing the drilling process (1 ^~ 1), the outer casing penetrating process (1-2) and the outer casing pulling out process (1-3) in such a way that an arc face (3- 1) of one overlap casing (3) or overlap square pipe ( I ) is in close contact with the

outer circumference of another overlap casing (3) or overlap square pipe (4), so that the overlap casings (3) or the overlap square pipes (4) are overlapped with each other and continuously mounted; inserting reinforcing rods (12) or H-beams (13) into the overlappedly and adjacently mounted overlap casings(3) or overlap square pipes (4), and filling the overlap casings (3) or overlap square pipes (4) with a cut-off wall forming material, such as concrete, mortar, and cement stabilizer! and pulling out the overlap casings (3) or overlap square pipes (4), each of which are filled with the cut-off wall forming material, and refilling a space of the removed overlap casing (3) or overlap square pipe (4) with the cut-off wall forming material and hardening the cut-off wall forming material to thereby continuously form a cast-in-place cut-off wall (10), the construction method comprising the processes of: penetrating a filling hose (20) and the overlap casing (3) or the overlap square pipe (4) into the outer casing (2) of a predetermined location when each of the outer casings (2) is inserted into each of the holes drilled by the excavator (6); grouting and filling the filling hose (20) with a filling material; pulling out each of the outer casings (2), in which the filling hose (20) and the overlap casing (3) or the overlap square pipe (4) are penetrated, inserting the reinforcing rods (12) or the H-beams (13) into the overlap casing (3) or the overlap square pipe (4), and filling the overlap casing

(3) or the overlap square pipe (4) with the cut-off wall forming material; and pulling out the overlap casing (3) or the overlap square pipe (4), to which the filling hose (20) is adjacent, refilling a space of the removed overlap casing (3) or overlap square pipe (4) with the cut-off wall forming material and hardening the cut-off wall forming material, so that the filling hose (20) is embedded between the cast-in-place cut-off walls (10).

In brief, the construction method of a cast-in-place cut-off wall using overlap casings and filling hoses according to the present invention includes the processes of: vertically drilling round holes to a predetermined depth of the ground using a general excavator mountingoverlap casings in each of the drilled holes, each of the overlap casings having an arc face formed on the outer circumference thereof in a straight line, the overlap casings being continuously mounted in such a way that the arc face of one overlap casing is in close contact with the outer circumference of another adjacent overlap casing, so that the overlap casings are overlapped with each other; filling the continuously mounted overlap casings with a cut-off wall forming material, such as concrete, and inserting reinforcing rods and H-beams into the overlap casings located at predetermined intervals; pulling out the overlap casings after a lapse of a predetermined time period; and filling spaces of the removed overlap casings w i th the cut- o ff wall forming material and

hardening the cut-off wall forming material to thereby form a cast-in-place cut-off wall or an underground wall (hereinafter, called "cast-in-place cut off wall") in such a way that a filling hose is grouted into a discontinuous point of the cast-in-place concrete wall. Accordingly, the construction method of a cast-in-place cut-off wall using overlap casings and filling hoses can greatly improve the cut-off effect at the discontinuous point since the cast-in-place cut-off wall is formed by inserting the filling hose into the discontinuous point of the cast-in-place concrete wall, and which can prevent the ground weakening and ground subsidence occurring by a leakage of underground water since the cut-off effect at the discontinuous point is greatly improved.

[Description of Drawings]

FIGS. Ia to Id are views showing a conventional construction progress of a cast-in-place cut-off wall using overlap casings.

FIGS. 2a to 2d are exemplary views showing an installation state of the cast-in-place cut-ff wall using the overlap casings continuously mounted by the construction progress.

FIGS. 3a and 3b are exemplary views showing another installation state of the cast-in-place cut-off wall using the overlap casings continuously mounted by the construction progress. FIGS. 4a and 4b are a construction progress view of a construction method of a cast-in-place cut-off wall using an overlap casing and a filling hose and a view showing an installation state of the cast-in-place cut-off wall according to a preferred embodiment of the present invention. FIGS. 5 a and 5b are a construction progress view of a construction method of a cast-in-place cut-off wall using an overlap casing and a filling hose and a view showing an installation state of the cast-in-place cut-off wall according to another preferred embodiment of the present invention. FIGS. 6, 7a and 7b are a view showing an inserted state of the filling hose and an exemplary view of the filling hose in the construction method of the cast-in-place cut-off wall according to the present invention.

<Explanation of essential reference numerals in drawings> 1 : construction progress of cast-in-place cut-off wall 2: outer casing 3: overlap casing

4: overlap square pipe 5: space portion 10: cast-in-place cut-off wall

20: filling hose

[Best Mode]

Reference will be now made in detail to the preferred embodiment of the present invention with reference to the attached drawings.

FIGS. 4a to 7b illustrate detailed examples of a construction method of a cast-in-place cut-off wall using an overlap casing and a filling hose according to the present invention, wherein FIGS. 4a and 4b are a construction progress view of the construction method of the cast-in-placecut-off wall using the overlap casing and the filling hose and a view showing an installation state of the cast-in-place cut-off wall according to a preferred embodiment of the present invention, FIGS. 5 a and 5b are a construction progress view of the construction method of the cast-in-place cut-off wall using the overlap casing and the filling hose and a view showing an installation state of the cast-in-place cut-off wall according to another preferred embodiment of the present invention, and MGS. 6, 7a and 7b are a view showing an inserted state of

the filling hose and an exemplary view of the filling hose in the construction method of the cast-in-place cut-off wall according to the present invention.

The cast-in-place cut-off wall 10 according to the present invention is constructed on the basis of the cast-in-place cut-off wall construction progress 1 shown in FIGS. Ia to Id as follows.

A drilling process (1- 1) of vertically drilling round holes in the ground to a predetermined depth using a general excavator 6 is performed. An outer casing penetrating process (1-2) of penetrating an overlap casing 3 or an overlap square pipe 4 into an outer casing 2 inserted into each of the holes is performed.

An outer casing pulling out process (1-3) of pulling out the outer casing 2, into which the overlap casing 3 or the overlap square pipe 4 is penetrated, is performed.

A cast-in-place concrete wall forming process (1-4) is performed. In the cast-in-place concrete wall forming process ( 1 -4), the drilling process (1- 1), the outer casing penetrating process (1 -2) and the outer casing pulling out process (1-3) are repeatedly performed in such a way that an arc face (3- 1X4- 1) of one overlap casing 3 or overlap square pipe 4 is in close contact with the outer circumference of another overlap casing 3 or overlap square pipe 4 , so

that the overlap casings 3 or the overlap square pipes 4 are overlapped with each other and continuously mounted.

Reinforcing rods 12 or H-beams 13 are inserted into the overlappedly and adjacently mounted overlap casings 3 or overlap square pipes 4, and then, the overlap casings 3 or overlap square pipes 4 are filled with a cut-off wall forming material, such as concrete, mortar, and cement stabilizer (cut-off wall forming material filling process).

After the overlap casings 3 or overlap square pipes 4, which are filled with the cut-off wall forming material, are pulled out, space portions of the removed overlap casings 3 or overlap square pipes 4 are filled with the cut-off wall forming material, and then, the cut-off wall forming material is' hardened to thereby continuously form the cast-in-place cut-off wall 10 as shown in FIG. 2d or 3b.

A detailed description of the method for continuously forming the cast-in-place cut-off wall 10 will be omitted since it is the same as the conventional methods.

As described above, in order to continuously form the cast-in-place cut-off wall 10, when each of the outer casings 2 is inserted into each of the holes drilled in the ground by the excavator 6, the overlap casing 3 or the overlap square pipe 4 and a filling hose 20 are inserted into a predetermined position of each outer casing 2. Alternatively, as shown in FlG. 4a or 5a, when a new cast-in-place rut-off wall 10 is continuousl y mount ed on the previously mounted

cast-in-place cut-off wall 10, the general filling hose 20 and the overlap casing 3 or the overlap square pipe 4 are inserted into the outer casing 2 adjacently connected (discontinuous point) to an end portion of the previously mounted cast-in-place cut-off wall 10 as shown in FIG. 7a or 7b.

The filling hose 20 shown in FIG. 7a or 7b is a general hose, and may be a double pipe as shown in FIG. 7a or a hose having a plurality of holes (circulation holes) formed on the outer periphery thereof at uniform intervals so that the inside communicates with the outside as shown in FIG. 7b.

A detailed description of the filling hose 20 will be omitted since it is commonly used in markets.

The outer casing 2, into which the filling hose 20 and the overlap casing 3 or the overlap square pipe 4 are inserted, is pulled out, and then, the filling hose 20 is filled with a filling material, such as micro cement or cement mortar.

When the filling hose 20 is filled with the filling material, a state where the previously mounted cast-in-place cut-off wall 10 and the post mounted overlap casing 3 or overlap square pipe 4 are in close contact with each other can be kept while the filling hose (20) is expanded.

Particularly, in case of the filling hose 20 having the holes formed on the outer periphery thereof at uniform intervals, the filling mat erial, which fills the filling hose 20, is discharged through the holes

(circulation holes) and fills a space between the previously mounted cast-in-place cut-off wall 10 and the post mounted overlap casing 3 or overlap square pipe 4 to thereby keep the close contact state between the previously mounted cast-in-place cut-off wall 10 and the post mounted overlap casing 3 or overlap square pipe 4.

The reinforcing rods 12 or the H-beams 13 are inserted into a remaining portion of the overlap casing 3 or the overlap square pipe 4, and then, the cut-off wall forming material, such as concrete or cement stabilizer, is packed in the overlap casing 3 or the overlap square pipe 4. Each of the overlap casings 3 or the overlap square pipes 4, which is in close contact with the filling hose 20 and filled with the cut-off wall forming material, is pulled out.

When the overlap casing 3 or the overlap square pipe 4 is pulled out, a space is formed at the upper portion of the hole while the cut-off wall forming material packed in the overlap casing 3 or the overlap square pipe 4 is introduced into the space of the removed overlap casing 3 or overlap square pipe 4. The upper space of the hole is refilled with the cut-off wall forming material, and then, the state is let alone for a long time so that the cut-off wall forming material is hardened, whereby the cast-in-place cut-off wall 10 is formed.

As shown in FIG. 4b or 5b, the filling hose 20, which is filled with a filling material, is integrally embedded at the center of the formed

cast-in-place cut-off wall 10 or at the discontinuous point between the cast-in-place cut-off walls 10 to thereby keep a watertight state.

As described above, the sealing (watertight) state can be kept by the filling hose 20, which is integrally embedded at the center of the formed cast-in-place cut-off wall 10 or at the discontinuous point between the cast-in-place cut-off walls 10, and hence, the cast-in-place cut-off wall 10 according to the present invention can greatly improve the cut-off effect at the discontinuous point and prevent the ground weakening and ground subsidence occurring by a leakage of underground water since the cut-off effect at the discontinuous point is improved greatly.

While the present invention has been described with reference to the particular illustrative embodiments, it is not to be restricted by the embodiments but only by the appended claims. It is to be appreciated that those skilled in the art can change or modify the embodiments without departing from the scope and spirit of the present invention.