JP2000129665A - Soil-improvement method for soft ground - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the improvement method for a soft ground and the construction method for a structure in the soft ground, in which no settlement, landslide, elevation and ground collapse is generated in a ground in the periphery of a ground to be improved, the vibrations and noises of construction works are lowered and accuracy and safety are obtained and cost can be reduced. SOLUTION: The soft ground S is excavated in critical height of approximately 1.5 m, a plurality of small-sized pontoons 2a are floated on the excavated soft ground S, these pontoons are connected by connecting members 2b and a hull 2c is formed, a travelling rail 2e is laid on the hull, a traversing base 2d is placed on the travelling rail, and a soft-ground improving machine 2f is installed onto the traversing base. The hull 2c is moved by a winch 2 m mounted at a remote place at that time, the soft-ground traversing machine 2f is traversed and beltlike soft-ground improvement is conducted, the hull 2c is moved forward and the beltlike soft-ground improvement is performed similarly and the ground is improved, and a structure is constructed after the curing of the ground.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground improvement technology for a soft ground area where buildings such as houses, roads, buildings, etc. are in close proximity, and a method for constructing a sewer, a waterway, a culvert, a tunnel, a building, and other basements in a soft ground. The present invention relates to a construction method of a ground structure.

[0002]

2. Description of the Related Art Conventional soft ground improvement technology is to remove mountain soil and sand on soft ground so that a heavy working machine or truck which can travel by a crawler weighing 10 to 100 tons can move on the soft ground. The scaffold is embanked to a thickness of about 1 to 2 m to withstand the load of heavy equipment. After that, the ground improvement work heavy equipment was moved on the scaffold embankment, and the ground improvement material was pressed into the ground and stirred to improve the ground. In this conventional working method, a large working heavy machine runs on the scaffolding embankment, so that a high contact pressure is applied to the scaffolding embankment. For example, with normal heavy equipment,
4-5N / cm ² , 12N for pile driver and soft ground improvement machine
/ Cm ² is applied. As a result, consolidation settlement due to scaffolding embankment, sliding destruction due to insufficient supporting capacity, and lateral flow have occurred, and a heavy machinery has fallen. In addition, the noise and vibration caused by the movement of the heavy equipment had a large effect on residents, dwelling houses, and buildings near the soft ground improvement area. In addition, the weight of the thick scaffolding embankment and the working heavy equipment acts so as to push the ground improvement material into which the soft ground below the soft ground and the soft ground through the surface layer of the soft ground which is slightly harder and the soft ground from the top downward. As a result, strong pressure was applied to the ground around the soft ground improvement area from the side, which had the adverse effect of causing collapse, landslides, subsidence, and uplift on the surrounding ground. Therefore, houses, buildings,
It caused slopes, collapses, and depressions on roads. Furthermore, 1
The ~ 2m scaffolding embankment can be lifted up by about 1-2m further by injecting and agitating the ground improvement material, and the improved area is greatly swelled. In addition, the excavated soil becomes an industrial waste due to the presence of a cement component, and the disposal of the excavated soil is troublesome and costly. As a conventional soft ground improvement work instead of this, digging is performed on the soft ground area boundary using a sheet pile etc., and deep excavation in the soft ground area,
Although there is a method of improving the ground, a large amount of excavated soil is discarded, and there has been an adverse effect such as a drastic settlement of the surrounding drainage due to rapid excavation of the ground and a decrease in strength due to release of stress. In addition, there is a problem that the cutting beams of the mountain retaining method hinder the movement of the ground excavator and the ground improvement machine, and the excavation and improvement work is troublesome.

[0003]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is to solve these conventional problems and to reduce the ground strength, settle, tilt, slip, sink, rise, etc. Excellent ground improvement method for soft ground, which can reduce the vibration and noise, reduce the amount of industrial waste disposal, and can surely improve the ground, and can safely and reduce the cost of construction. An object of the present invention is to provide a method for constructing a structure.

[0004]

Means for Solving the Problems The constitution of the present invention which has solved the above problems is: 1) A method for improving the ground of soft ground where houses and buildings are present in proximity to each other. Excavation shallow within the limit self-supporting height, and then a ground improvement machine that presses ground improvement material into the ground and stirs around the deck of the hull formed by connecting multiple small barges at intervals Floats the workboat installed on the excavated soft ground above the excavated soft ground, traverses the ground improvement machine of the workship on the hull, and changes the left and right position to improve the ground in the belt-like area that extends left and right. After that, the work boat was indexed with a winch, moved forward by the width of the belt-shaped area, stopped, and in the stopped state, the soft ground improvement machine was traversed in the same manner as described above to improve the ground area extending to the next left and right. And the escaping of this ground improvement machine and the work boat The soft ground is characterized by improving the entire improved area by repeating the forward movement of the body, improving the ground strength of the surrounding ground close to the improved area, and reducing vibration and noise. Ground improvement method 2) Soft ground improvement A ground improvement machine is traversed in a direction away from the place near the boundary on the side where the houses and buildings in the improved area are close to each other, and the underground barrier by early soft ground improvement near the boundary The method for improving the ground of soft ground described in 1) above, wherein the pressure is transmitted to the side of the area to reduce the influence on the outside of the area, and the ground pressure of the work boat is reduced to 0.
The soil improvement method for soft ground described in 1) or 2) above, wherein the excavation opening pressure is 5 N / cm ² or less. 4) A cement slurry is used as a soil improvement material, and the specific gravity of the cement slurry is set to the unit volume weight of the soft ground. Any one of the above items 1) to 3), wherein a uniform agitation and an upward sludge effect are enhanced to make the injected amount easily swell upward and a change in unit volume weight is suppressed even after the improvement, as a value equal to or less than this. 5) Soft ground improvement method for soft ground 5) 100 N / cm ^{2 in} soft ground
The method for improving the ground of soft ground according to any one of the above 1) to 4), wherein the ground is discharged at the following low pressure and forced stirring is performed. The method for improving the ground of soft ground according to any one of the above 1) to 5) for the purpose of effectively utilizing excavated soil 7) A part of the hardened ground improved by the method for improving soft ground according to any of the above 1) to 5) Method of constructing a sewer, culvert, and tunnel in the re-excavated space, and then backfilling and embedding the soft ground underground structure 8) Any of the soft ground described in 1) to 5) above A part of the hardened ground improved by the improved method is re-excavated, and a structure is constructed in the space based on the improved ground below the bottom of the re-excavated space and the improved ground part on the outer periphery of the side of the space is a retaining wall To build structures on soft ground.

[0005]

According to the present invention, the surface soil of the improved area of the soft ground is excavated by about 1 to 2 m within the limit independence height. Since the excavation is within the limit self-supporting height, the ground around the area collapses
It rarely causes slippage, subsidence, etc. Excavated excavated soil and excavated soil are small and do not contain a cement component, so that processing is easy. In addition, there is almost no need to perform hill work around the periphery, and even when hill work is performed, a simple hill work is sufficient and the work is simplified. In addition, a work boat of a hull in which a plurality of small barges are connected is floated on the excavated soft ground. Since the workboats are connected by small barges, the workboats can be moved to the construction site by disassembling them into trucks and transported by truck, and the workboats can be transported quickly. Also, since the weight of the work boat / ground improvement machine is supported by a plurality of small barges, the pressure is locally applied to the soft ground below, and the pressure is released from the gap between the small barges and the upper surface of the outer periphery of the hull, There is no pressure on the side of the soft ground, and the pressure on the ground around the improved area is weak, which can reduce the strength of the surrounding ground and reduce adverse effects such as collapse, collapse, inclination, and settlement. In addition, since the ground improvement machine on the work boat is traversing on the hull, the movement is quiet, and the work for improving the band-like area of the soft ground can be performed precisely. Since the work boat itself uses winch wires, it can be pulled quietly,
Low vibration. Moreover, even if the ground improvement material is press-fitted and agitated and agitated, the ground improvement area surface layer rises by 1 to 2 m,
Since it is about the excavated depth and close to the height (level) of the original soft ground, excavation work on the improved ground surface layer is unnecessary, and even if there is excavation work, almost only a small amount of excavation is sufficient, The amount of industrial waste can be reduced. If the surface level of the improved ground is lower than the surroundings, the excavated soil of the first soft ground can be returned and embedded. This ground surface can be used directly as a pile driving scaffold without buying embankment soil. After the improved soft ground has hardened, the land is leveled and re-excavated according to the buildings, buildings, sewers and culverts on the ground. In addition, if the soft ground improvement work is performed in a direction away from the area near the boundary of the improved area with the neighboring houses, the underground wall of the improved soft ground will be formed at the boundary first, and this will cause pressure outside the area. Cut off. If the soft ground improving material is a cement slurry of 1.5 or less which is equal to or less than the unit volume weight of the soft ground, the fluidity is improved, the stirring can be effectively performed, and the tendency of bulging upward ( Enhances the sludge effect).

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The critical depth of soft ground according to the present invention varies depending on the type and condition of the ground, but is about 1-2 m,
In addition, simple earth retaining will be performed as needed at the area border. The size of the small barge of the work boat of the present invention is preferably 10 m in length and 2.2 m in width, which facilitates land transportation.
The number of small boats connected to the hull and the gap between them will be determined appropriately according to the topography of the site area. Also, since the ground improvement work machine that presses in and agitates the ground improvement material is several tens of meters high, it is disassembled into multiple pieces that can be disassembled and transported by truck, and transported and stored.
It is good to be able to assemble on site. In addition, the ground improvement work machine is preferably provided with a traverse table that slightly extends from the stern of the hull so as to be able to run on rails, and the ground improvement work machine is installed at the stern end of the traverse table.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. 1 to 5 are process diagrams of the embodiment. FIG. 6 is an explanatory diagram showing an example in which a building is built on the improved ground. FIG.
It is explanatory drawing which shows the example which constructed the culvert by re-digging the improved ground. FIG. 8 is an explanatory diagram showing an example in which a building with an underground is constructed by re-digging the improved ground. FIG. 9 is a plan view showing a work boat without a deck used in the embodiment. FIG.
FIG. 2 is a front view showing a work boat used in the embodiment. FIG.
FIG. 1 is an explanatory diagram showing an arrangement state of a small barge of a work boat used in the embodiment. In the figure, S is the soft ground, A is the improved area of the soft ground, B is the boundary of the improved area, C is the surrounding ground of the improved area, D is the house constructed on the surrounding ground, T is the culvert, and M is the ground building. It is. In the figure, 1 is an excavation space of soft ground, 2 is a work boat, 2a to 2o are components of the work boat, and 2
a is a small barge with a size of 10 m and a width of 2.2 m, 2b is a connecting member of the small barge 2a, 2c is a hull of 16m in width and 10m in length connected to four small barges 2a, and 2d is on the hull. 2e is a traveling rail of the traverse, and 2f is a 15 m high sternable free ground improvement machine provided on the stern side of the traverse. The vertically moving stirring blades 2h of the soft ground improvement machine are injection pipes having the stirring blades attached to the lower end thereof, and the ground improvement material is fed into the pipe and ejected from the stirring blades 2g. 2i is a guide post having a height of about 15 m for vertically moving the injection pipe, 2j is a vertical feeder for vertically moving the injection pipe, and 2k is a pressure feed for feeding the ground improvement material into the injection pipe. The tube, 2l is a ground improvement material pump, 2m is a winch, 2n is a wire, 2o is a driver's seat, and 2p is a deck of the hull 2c.

[0008] The steps of the ground improvement method of this embodiment are as follows:
The ground surface excavation process, (2) work boat preparation process, (3) ground improvement main process, and (4) surface leveling ground surface construction process will be performed in this order. This will be described in the following order. (1) Ground surface excavation process (refer to FIG. 1) First, the ground surface layer in the improved area A of the soft ground S is lowered to a depth of about 1.5 m, which is the limit self-supporting height, by a relatively small excavation machine such as a bucket excavator. Excavation is performed using an earthmoving machine (see FIG. 1). This excavation of 1 to 2 m is a relatively easy and quick construction work that does not require embankment embankment and can be carried out without applying soil retaining to the boundary B of the improved area A. The amount of excavated soil is small. (2) Work boat preparation process (see FIGS. 2 and 9 to 11) Next, the work boat 2 is moved from the factory / storage location to the small barge 2a,
Connecting member 2b, traversing platform 2d, rail 2 disassembled into a plurality
e, 2g of stirring blades and 2h of injection pipe decomposed into a plurality
Guide post 2i, vertical feeder 2j, pressure feed tube 2
k and the pump 2l, etc., and transported by truck or ship to the soft ground at the site. First, float the small barge 2a on the excavated ground surface of the soft ground S at a required interval,
The space therebetween is connected by a connecting member 2b and integrated to form a hull 2c. Also, the rail 2e is laid between the small barges 2a in the horizontal direction (left-right direction), and the traversing platform 2d runs on the rail 2e. The soft ground improvement machine 2f that has been disassembled and sent is assembled and installed on the traversing platform 2d. 9 to 11
2 shows the assembled work boat 2. The work boat 2 is a winch 2 m installed in a place where there are relatively few people such as private houses, buildings, buildings, etc. outside the improved area A of the soft ground S.
To be able to move forward by being pulled by the wire 2n.
At this time, since the contact pressure of the work boat 2 is received by the large bottom area of the small barge 2a, the contact pressure is about 0.4 N / cm ² ,
This is about 1/10 that of a normal heavy machine and about 1/30 that of a crawler-type soft ground improvement machine. In addition, the upper portion of the soft ground other than the ground contact surface of the small barge 2a is opened and the load is applied with a low ground pressure. Further, the small boats 2a are connected at a required interval to secure a wide deck 2p, and the work boat 2d can float very stably since the ground contact surfaces are widely dispersed.

(3) Ground improvement main process (see FIGS. 3 and 4) The work boat 2 floats in the improved area A excavated by about 1.5 m, and is towed to the improvement work start position using a winch 2 m and a wire 2 n. First, the pedestal 2d is moved to the left and right ends of the boundary B on the side where the house / building near the improved area A is located. Next, the soft ground improvement machine 2f on the horizontal platform is operated. The pressure pump 21 is operated to feed a cement slurry having a specific gravity of 1.5 or less, which is smaller than the unit volume weight of the soft ground, at a low pressure of 40 to 50 N / cm ² as a ground improving material. The cement slurry is sent to the stirring blade 2g via the pressure feeding tube 2k and the injection pipe 2h. The injection pipe 2h and the stirring blade 2g are lowered along the guide pipe 2i by the vertical feeder 2j, inserted into the ground, and spouted from the inside of the stirring blade 2g in the soft ground, and the injection pipe 2h is rotated ( (Not shown), cement slurry is 40-50N
/ Cm ^{2 at} a low pressure and is agitated under the ground, becomes uniform by stirring, and because of its low specific gravity, the fluidity is improved, and due to the low specific gravity, the mud is drained upward and the whole soft ground is swollen upward. . After the injection, curing starts about 2 to 3 hours (see FIG. 4).
Since the first soft ground improvement is started from the boundary side near the house of the work boat, the improved soft ground hardened in the ground at the boundary near the house forms an underground shielding wall. The cement slurry is slightly traversed in a direction away from the ground, stopped, and the cement slurry is injected at a low pressure by the injection pipe 2h and the stirring blade 2g and stirred as described above to improve the soft ground and harden. The increase in pressure due to the improvement of the ground improvement ground inside the underground barrier at the boundary is interrupted by the underground wall of the hardened soft ground that was previously constructed, so that the ground around the boundary will not be adversely affected ( 3 and 4). The earth pressure due to the injection and agitation of the cement slurry causes the soft ground to bulge upwards to the open top. Ground pressure of the working ship 2 is very small due to the buoyancy of the small barge 2a, in about 0.4 N / cm ^2, and typically less than 1/10 of 4~5N / cm ² of heavy equipment, Matakui driving machine or crawler-type It is about 1/33, which is extremely small compared to 12 N / cm ² of the soft ground improvement machine. Furthermore, since the surface soil is excavated for 1 to 2 m, the downward pushing force by the upper soft ground is small and it is well opened upward, allowing the soft ground to rise,
It appears as swelling. The work boat 2 is stopped, the traversing platform 2d is traversed on the traveling rail 2e, and the soft ground improvement is performed along the stern. One injection pipe 2h and stirring blade 2g
A column-shaped improvement area is formed above and below, and a large number of improvements are made so as to slightly overlap each other to form a belt-like improvement area. Since the movement of the traversing table 2d can be performed accurately and easily, the accuracy of construction is high and the working speed is much higher than the movement by the crawler. In addition, since it is supported by the plurality of small barges 2a, the operation can be performed extremely stably and safely. After the ground improvement was carried out in a belt shape, using a winch 2m and a wire 2n,
The work boat 2 is advanced and stopped at an extremely low speed of about 1.0 m / min. At this position, the belt 2d is similarly traversed to form a belt-shaped improvement area, and then the work boat 2 is advanced. This is repeated to improve the ground on the entire soft ground.

(4) Surface leveling ground construction process (see FIG. 5) The upper surface of the improved area A is at the level of the soft ground before surface digging. After the improved soft ground is hardened by the cement slurry, the hardened ground to a predetermined height level is flattened, and if necessary, the surface excavated soil is backfilled to obtain a flat hardened ground. In addition, necessary water channel M is excavated and constructed. Emissions from hardened soft ground can be reduced. According to the present embodiment, the excavation process of the ground surface layer as shallow as about 1.5 m is an operation that can be performed easily and quickly, and since the surface excavation is within the limited self-supporting depth, the strength of the ground around the improved area is improved. To cause adverse effects such as collapse, slippage, and depression. Rather, the upper part of the soft ground is opened by removing the surface layer of the soft ground, and the pressure accompanying the improvement of the soft ground is made to open upward without acting on the side as much as possible. This greatly reduces the adverse effects on the ground around the improved area. Moreover, even if the soft ground swells upwards, the excavation depth is about 1.5 m and it does not bulge more than the original soft ground surface.Therefore, it is not necessary to scrape the swelled part and discard it. Industrial waste can be extremely reduced. If the amount of bulge is less than the amount of surface excavation,
The first excavated soil is used as backfill soil. Furthermore,
In this embodiment, the ground in the improved area is traversed with the ground improvement machine in a direction away from the close boundary, so that an underground wall is first formed at the house adjacent boundary in the improved area. Pressure can reduce the impact on houses outside the area.

A building such as a concrete building K or a house may be erected on the basis of the improved ground thus improved (see FIG. 6), or a part of the hardened and stabilized improved ground may be used. Re-digging to a predetermined depth to create an open space 1 and installing underground structures such as culvert T on the bottom of the space 1,
Thereafter, the first excavated surface excavated soil can be backfilled to bury underground structures such as culvert T underground (see FIG. 7). Or, based on a stable and hardened improved ground below the bottom of the space 1 for re-excavation of the improved ground,
A ground building M such as a building can also be constructed using the stable hardened improved ground on the outside of the side surface as a earth retaining material (see FIG. 8). In any of the cases of FIGS. 6 to 8, the portion of the improved ground below the building and the culvert serves as a foundation, and the improved ground around the remaining space 1 that is not re-excavated becomes the earth retaining portion. The structures became stable, and these underground structures on soft ground could be easily and firmly constructed in a stable state. In addition, the construction can be done with little effect on the surrounding ground and houses.

[0012]

As described above, according to the present invention, the surface excavation is first performed within the limit self-supporting depth to open the upper part of the soft ground, so that the pressure accompanying the improvement of the soft ground is released upward to reduce the pressure in the local area. The effect on the outer circumference is reduced. Also, even if the stirred soft ground swells upwards, it only fills this excavated depth, so the rise from the original ground level is small, and the rise from the ground surface of the improved ground containing cement is small. There is not much need to re-drill uphill, and industrial waste is low. Conversely, when the swollen portion is small, the amount of soil removed can be reduced by backfilling the soil from the first surface excavation. By using a work boat with a plurality of small barges connected, the ground pressure can be greatly reduced to about 1/10 to 1/30 of the working heavy equipment, and the work boat is stably floated because it is spaced apart. be able to. In addition, the upper part of the soft ground is opened so that the pressure of the soft ground improvement is released upward so as not to act on the side, thereby further reducing the adverse effect on the ground around the improved area. Since the improvement work is performed by moving the soil improvement machine on the work boat, the soft ground improvement work can be performed accurately and quickly. Further, since the towing of the work boat is performed by using a winch and a wire, the winch can be arranged at a position away from a house, a building or a condominium, and the influence of noise and vibration can be reduced. Since the work boat is constructed by connecting a plurality of small barges, it can be disassembled and transported by land, so that the work boat can be quickly and easily transported and stored. Also, by adjusting the number of small barges, the size can be adjusted to the size of the soft ground improvement area at the site. If the ground improvement machine is laid in a direction away from the boundary of the improvement area on the side close to the houses, etc., it will be an improvement work for the soft ground after forming the underground wall at the boundary first, and the underground wall formed Blocks the transmission of the pressure of the improved ground to the side, further reduces the adverse effect on the surrounding ground, and ensures that inclination, collapse, slippage, depression, etc. of the surrounding ground do not occur. In addition, safety is enhanced by the load distribution and low center of gravity effect by connecting the ships. If the soil improvement material is a cement slurry with a specific gravity smaller than the unit volume weight of the soft ground, and it is jetted at a low pressure, it will ensure uniform and efficient stirring, improve fluidity, and improve the upward sludge discharging effect. Enhance.

[Brief description of the drawings]

FIG. 1 is a process chart of an embodiment.

FIG. 2 is a process chart of an example.

FIG. 3 is a process drawing of an example.

FIG. 4 is a process drawing of an example.

FIG. 5 is a process drawing of an example.

FIG. 6 is an explanatory diagram showing an example in which a building is built on the improved ground.

FIG. 7 is an explanatory diagram showing an example of constructing a culvert by re-digging the improved ground.

FIG. 8 is an explanatory diagram showing an example in which a building with an underground is constructed by re-digging the improved ground.

FIG. 9 is a plan view showing a work boat without a deck used in the embodiment.

FIG. 10 is a front view showing a work boat used in the embodiment.

FIG. 11 is an explanatory view showing an arrangement state of a small barge of a work boat used in the embodiment.

[Explanation of symbols]

 A Improvement area B Boundary C Peripheral ground D House S Soft ground T Underdrain M Ground structure 1 Excavation space 2 Work boat 2a Small barge 2b Connecting member 2c Hull 2d Crossing platform 2e Rail 2f Soft ground improvement machine 2g Stirrer blade 2h Injection pipe 2i Guide post 2j Vertical feed device 2k Pumping tube 2l Ground improvement material pump 2m Winch 2n Wire 2o Operator's cab 2p Deck

Claims (8)

[Claims] Claims 1. A soil improvement method for soft ground in which houses and buildings are located close to each other, wherein a surface layer of the soft ground improvement area is first excavated shallowly within a limit self-supporting height, and then small barges are spaced apart. A work vessel equipped with a ground improvement machine that presses the ground improvement material into the ground and stirs it around the deck of the hull formed by connecting multiple units and floats on the excavated soft ground surface The ground improvement machine of the ship is traversed on the hull to change the left and right position, and the ground improvement machine is used to improve the ground in the belt-shaped area extending to the left and right. In the stopped state, the soft ground improvement machine is traversed in the same manner as described above to improve the ground in the next belt-like area extending left and right, and the traverse of the ground improvement machine and the forward movement of the entire work boat are repeated. To improve the ground of the entire improved area and improve the ground A ground improvement method for soft ground, characterized in that it does not affect the ground strength of a nearby ground in the vicinity of the area and can perform improvement work with less vibration and noise. 2. A ground improvement machine is traversed in a direction away from a place near a boundary on a side where a house or a building in a soft ground improvement area is close to the ground, and an underground barrier is provided near the boundary by early soft ground improvement. 2. The method for improving the ground of soft ground according to claim 1, wherein the pressure is transmitted to the side of the area to reduce the influence outside the area. 3. The method for improving the ground of soft ground according to claim 1, wherein the ground pressure of the work boat is adjusted to be less than or equal to 0.5 N / cm ² by the float of the small barge. 4. A cement slurry is used as a soil improvement material, and the specific gravity of the cement slurry is set to a value equal to or less than the unit volume weight of the soft ground, and the injection is carried out with uniform stirring and an upward drainage effect. Claims 1 to 1 wherein the change in the unit volume weight is suppressed even after the improvement by making the component easily swell upward.
3. The soil improvement method for soft ground according to any one of 3. 5. A soft ground improving material having a strength of 100 N in soft ground.
The liquid is discharged at a low pressure of not more than / cm ² and is forcibly stirred.
4. The soil improvement method for soft ground according to any one of 4. 6. The soil improvement of a soft ground according to claim 1, wherein the soil of the surface layer of the excavated improvement area is diverted to the hardened improvement area and to the surrounding area for effective use of the excavated residual soil. Construction method. 7. A part of the hardened ground improved by the method for improving soft ground according to claim 1 is re-excavated, and a sewer, a culvert, and a tunnel are constructed in the re-excavated space, and then buried. Construction method of underground structure of soft ground to be buried back. 8. A part of the hardened ground improved by the method for improving soft ground according to any one of claims 1 to 5, based on the improved ground below the bottom of the re-excavated space, and a side surface of the space. A method for constructing structures on soft ground using the improved ground on the outer periphery as a retaining wall to build structures in space.