Title:
Soil Improvement Apparatus And Soil Improvement Method
Kind Code:
A1


Abstract:
A soil improvement apparatus where an auger head is rotated even with small power and where an improvement material is extruded only in the horizontal direction. The soil improvement apparatus has soil compacting means that is constructed by inserting an auger in a tubular casing. The auger has a rotating shaft and a rotating tube that are coaxially arranged and rotate independently in the circumferential direction, an auger head attached to the lower end of the rotating shaft, and a screw provided on the outer periphery of the rotating tube. The auger head is constructed by arranging wedge-shaped auger blades, having recessed pressing sections, on the lower end of the rotating shaft projecting from the casing, and the auger blades are arranged in a radial pattern with the pressing sections facing the radial direction.



Inventors:
Okita, Kozo (Osaka, JP)
Application Number:
11/631442
Publication Date:
02/21/2008
Filing Date:
06/22/2005
Assignee:
OKITA-KO. CO., LTD. (Izumisano-shi, Osaka, JP)
Primary Class:
International Classes:
E02D3/12
View Patent Images:



Primary Examiner:
MAYO-PINNOCK, TARA LEIGH
Attorney, Agent or Firm:
The Webb, Law Firm P. C. (700 KOPPERS BUILDING, 436 SEVENTH AVENUE, PITTSBURGH, PA, 15219, US)
Claims:
1. A soil improvement apparatus comprising a soil consolidating means that includes a tubular casing and an auger that is inserted into the casing, said auger including a rotational shaft and a rotational tube that are disposed coaxially with each other and circumferentially rotated independently of each other, an auger head that is attached to a lower end of the rotational shaft, and a screw that extends around the outer circumference of rotational tube, wherein said auger head includes plural wedge-shaped auger blades that each have a pressing part inwardly recessed and are disposed radially around a lower end of the rotational shaft with the pressing parts oriented in a radial direction, said lower end of the rotational shaft extending outwards from the casing.

2. The soil improvement apparatus according to claim 1, wherein a plural number of the soil consolidating means are disposed adjacent to each other, with each of said soil consolidating means having said auger head provided therein.

3. The soil improvement apparatus according to claim 1, wherein the auger head is rotated at such a low speed as to allow an improvement material to be repeatedly kneaded, wherein said improvement material is to be extruded outwards.

4. The soil improvement apparatus according to claim 1, wherein the auger head is rotated by an electric motor that is controlled so that when the value of the electric current being variable depending on the magnitude of load applied reaches a given value, the electric motor is stopped.

5. The soil improvement apparatus according to claim 1, further comprising a pressure measuring means that is combined with the soil consolidating means, and that includes a pipe to be embedded in soil, said pipe having a leading end portion and a main body separable from each other, a pressure sensitive element that is accommodated within the pipe so as to be exposed to the outside when the pipe is separated and is deformed upon receiving a given pressure, and a measuring instrument that measures, on the basis of the resultant deformation of the pressure sensitive element, a pressure applied to the pressure sensitive element.

6. A soil improvement method comprising providing the soil improvement apparatus according to claim 1 and extruding an improvement material into soft soil by the pressing parts of the auger blades, wherein said improvement material is made up of soil drilled out and a fastening material in filament form mixed into the soil.

7. The soil improvement apparatus according to claim 2, wherein the auger head is rotated at such a low speed as to allow an improvement material to be repeatedly kneaded, wherein said improvement material is to be extruded outwards.

8. The soil improvement apparatus according to claim 2, wherein the auger head is rotated by an electric motor that is controlled so that when the value of the electric current being variable depending on the magnitude of load applied reaches a given value, the electric motor is stopped.

9. The soil improvement apparatus according to claim 3, wherein the auger head is rotated by an electric motor that is controlled so that when the value of the electric current being variable depending on the magnitude of load applied reaches a given value, the electric motor is stopped.

10. The soil improvement apparatus according to claim 2, further comprising a pressure measuring means that is combined with the soil consolidating means, and that includes a pipe to be embedded in soil, said pipe having a leading end portion and a main body separable from each other, a pressure sensitive element that is accommodated within the pipe so as to be exposed to the outside when the pipe is separated and is deformed upon receiving a given pressure, and a measuring instrument that measures, on the basis of the resultant deformation of the pressure sensitive element, a pressure applied to the pressure sensitive element.

11. The soil improvement apparatus according to claim 3, further comprising a pressure measuring means that is combined with the soil consolidating means, and that includes a pipe to be embedded in soil, said pipe having a leading end portion and a main body separable from each other, a pressure sensitive element that is accommodated within the pipe so as to be exposed to the outside when the pipe is separated and is deformed upon receiving a given pressure, and a measuring instrument that measures, on the basis of the resultant deformation of the pressure sensitive element, a pressure applied to the pressure sensitive element.

12. The soil improvement apparatus according to claim 4, further comprising a pressure measuring means that is combined with the soil consolidating means, and that includes a pipe to be embedded in soil, said pipe having a leading end portion and a main body separable from each other, a pressure sensitive element that is accommodated within the pipe so as to be exposed to the outside when the pipe is separated and is deformed upon receiving a given pressure, and a measuring instrument that measures, on the basis of the resultant deformation of the pressure sensitive element, a pressure applied to the pressure sensitive element.

13. The method of claim 6, wherein a plural number of the soil consolidating means are disposed adjacent to each other, with each of said soil consolidating means having said auger head provided therein.

14. The method of claim 6, wherein the auger head is rotated at such a low speed as to allow an improvement material to be repeatedly kneaded, wherein said improvement material is to be extruded outwards.

15. The method of claim 6, wherein the auger head is rotated by an electric motor that is controlled so that when the value of the electric current being variable depending on the magnitude of load applied reaches a given value, the electric motor is stopped.

16. The method of claim 6, wherein said soil improvement apparatus further comprises a pressure measuring means that is combined with the soil consolidating means, and that includes a pipe to be embedded in soil, said pipe having a leading end portion and a main body separable from each other, a pressure sensitive element that is accommodated within the pipe so as to be exposed to the outside when the pipe is separated and is deformed upon receiving a given pressure, and a measuring instrument that measures, on the basis of the resultant deformation of the pressure sensitive element, a pressure applied to the pressure sensitive element.

Description:

FIELD OF THE INVENTION

The present invention relates to a soil improvement apparatus for improving soft soil to have a consolidated soil condition, and more specifically to a soil improvement apparatus that has an auger for drilling into soil and extruding an improvement material into soft soil from a drilled hole.

BACKGROUND OF THE INVENTION

As a method of improving soft soil to have a consolidated soil condition, an auger drilling method is known. A soil consolidating apparatus using this auger drilling method is disclosed in Patent Reference 1, which will be described with reference to FIG. 6.

This soil consolidating apparatus has a tubular casing 101 that is held in a vertical position and a driving shaft 102 inserted therein. The driving shaft 102 has a screw (helical blade) 103 disposed on the outer circumference thereof from the lower end to the middle portion, or throughout the entire length. Mounted to a lower end of the driving shaft 102 is a consolidating cam 104 that projects outwards from the lower end of the casing 101 to drill into soft soil and extrude an improvement material S into the soft soil from a drilled hole. The improvement material S is made by mixing pit sand (and cement according to needs and circumstances) into soil drilled out.

Installed at an upper end of the casing 101 is a driving means 105 made up of a hydraulic motor or the like, which is to rotate the driving shaft 102 in both directions, namely a forward direction and a reverse direction. Connected to an upper portion of the casing 101 is a hopper 106 for introducing the improvement material S into the casing 101 therethrough.

For improving soft soil to have a consolidated soil condition by the soil consolidating apparatus having the above arrangement, the driving shaft 102 is first rotated in the forward direction, thereby allowing the consolidating cam 104 to drill into soil while transporting drilled soil out of the ground by the screw 103 and hence forming a drilled hole.

Then, the driving shaft 102 is rotated in the reverse direction and at the same time the improvement material S is introduced into the casing 101 through the hopper 106. This improvement material S is transported downwards within the casing 101 by the screw 103. At this moment, the drilled hole is held surrounded by the casing 101, so that the improvement material S is transported to the consolidating cam 104 without being subjected to the influences of the soft soil. Then, the improvement material S is extruded outwards from the drilled hole in a horizontal direction by the rotation of the consolidating cam 104. The soft soil S extending in the horizontal direction with the improvement material S extruded thereinto is thus improved to have a consolidated soil condition.

Soft soil is improved in the form of a layer having a width substantially equal to the length of the consolidating cam 104. Therefore, the driving shaft 102 and the casing 101 are moved upwards by a distance corresponding to the width of the consolidating cam 104 so as to extrude the improvement material S onto an improved soil having a consolidated soil condition, thereby forming consolidated soil in layers. Thus, this soil consolidating apparatus improves soil throughout the depth through which a drilled hole has been formed, by the driving shaft 102 and the casing 101 that are moved upwards at constant intervals.

Patent Document 1: Official Gazette of Japanese Patent No. 3259910 (FIG. 6)

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

The conventional soil consolidating apparatus has the casing 101, the driving shaft 102 and the like designed to change from the horizontal to the vertical position by a device such as a boom or leader.

However, the driving means 105 used in the soil consolidating apparatus disclosed in the Patent Document 1 is required to drive the heavy consolidating cam 104, and therefore even for the soil consolidating apparatus of the other type, a large sized driving means with a power of about 3×104 (W) per shaft is usually used. Because of this, when the casing 101, the driving shaft 102 and the like are to have their position changed, an upper end portion of the casing 101 with the driving means 105 installed thereon becomes unstable and the changing operation may not be safe.

The conventional soil improving apparatus may have auger blades each having a right triangle cross section that are disposed radially around a rotational shaft, in place of the consolidating cam 104 as disclosed in the Patent Document 1.

However, according to the auger blades having the right triangle cross section, the improvement material S introduced in a drilled hole is also extruded into soil below the auger blades so that this soil is also consolidated, and hence, regardless of the fact that soft soil has yet been extensively improved, the auger blades are forced upwards upon receiving a reaction force of the consolidated soil below the blades. For this reason, the soil improvement apparatus using the auger blades having a right triangle cross section can improve soft soil of only a narrow area, necessitates to drive the casing 101 and the driving shaft 102 into soil at many sites and hence it takes a long time to complete the operation.

Accordingly, it is an object of the present invention to provide a soil improvement apparatus that has an auger head rotatable even with a small power and enables an improvement material to be extruded only in the horizontal direction.

Means to Solve the Problems

According to the present invention, there is provided a soil improvement apparatus, which is characterized in that it includes a soil consolidating means that includes a tubular casing and an auger that is inserted into the casing, the auger including a rotational shaft and a rotational tube that are disposed coaxially with each other and circumferentially rotated independently of each other, an auger head that is attached to a lower end of the rotational shaft, and a screw that extends around the outer circumference of the rotational tube, wherein the auger head includes plural wedge-shaped auger blades that each have a pressing part inwardly recessed and are disposed radially around a lower end of the rotational shaft with the pressing parts oriented in a radial direction, the lower end of the rotational shaft extending outwards from the casing.

With this soil improvement apparatus, a drilled hole is formed by the rotation of the auger blades disposed radially around the lower end of the rotational shaft and an improvement material is introduced into the drilled hole. This improvement material is forced outwards by the pressing parts of the auger blades and extruded into soft soil only in a horizontal direction. The pressing parts of the auger blades each being inwardly recessed allow the improvement material to be pressed in such a direction as to be converged towards the center of each pressing part without being dispersed from the pressing parts, and thus allow the improvement material to be extruded only in the horizontal direction. Thus, the soft soil is improved to have a layered consolidated soil condition. In addition, these auger blades can be rotated with a small torque since it efficiently extrudes the improvement material into soft soil, and therefore a driving means for rotating the auger blades may be of the lightweight as compared with a conventional type.

The rotational shaft and the rotational tube that are disposed coaxially with each other are independently rotated so as to be respectively rotated in the opposite directions and the rotational shaft is rotated slightly faster than the rotational tube. This allows for smooth transportation of the improvement material by the screw.

In the soil improvement apparatus, it is preferable to provide plural number of the soil consolidating means disposed adjacent to each other, each having the auger head.

With this soil improvement apparatus, the improvement material is introduced into a drilled hole formed by each of the soil consolidating means, and extruded from the pressing parts of each auger head. Accordingly, the improvement material is extruded from two sides, and the two streams hit each other and repeatedly kneaded together in an area between the adjacent soil consolidating means, so that soft soil is transformed into a consolidated zone having a more highly consolidated soil condition. This consolidated zone forms into a shape simulating a circumferential wall or the like and is peripherally expanded.

In the soil improvement apparatus, the auger head is preferably rotated at such a low speed as to allow an improvement material, which is to be extruded, to be repeatedly kneaded together.

With this soil improvement apparatus, the rotation of the auger head at a low speed allows the improvement material to be slowly extruded and repeatedly kneaded, so that soft soil is improved to have a consolidated soil condition with a higher density.

In the soil improvement apparatus, the auger head is preferably rotated by an electric motor that is controlled so that when the value of the electric current being variable depending on the magnitude of load applied reaches a given value, it is stopped.

With the soil improvement apparatus, the electric motor is rotated with a small current when the improvement material is being extruded into soft soil that has not yet been consolidated, and is rotated with a large current when the soft soil has been improved to a consolidated soil. When the soft soil has been excessively consolidated, the auger blades cannot be rotated. Therefore, the electric motor is controlled so as to be stopped when the current being slightly smaller than this maximum limit current flows. It is also possible to employ an arrangement where the value of the current of the electric motor at the time when soft soil at a site away from the soil consolidating means has a predetermined consolidated soil condition is previously detected so that the electric motor is stopped when the current, which has this value, flows in the electric motor.

The soil improvement apparatus preferably further includes a pressure measuring means that is combined with the soil consolidating means, and that includes a pipe to be embedded in soil, the pipe having a leading end portion and a main body separable from each other, a pressure sensitive element that is accommodated within the pipe so as to be exposed to the outside when the pipe is separated and is deformed upon receiving a given pressure, and a measuring instrument that measures, on the basis of the resultant deformation of the pressure sensitive element, a pressure applied to the pressure sensitive element.

With this soil improvement apparatus, the pressure measuring means is embedded in soil at a site away from the soil consolidating means, so that it is possible to detect that soft soil at the site has reached a predetermined consolidated condition. Also, the pressure sensitive element accommodated within the pipe can be efficiently embedded in soil, and it is possible to accurately detect the consolidated condition of soft soil on the basis of the deformation of the pressure sensitive element resulting from the pressure by an improved soil.

A soil improvement method of the present invention, which uses the aforesaid soil improvement apparatus, is characterized in that it includes extruding an improvement material into soft soil by the pressing parts of the auger blades, wherein the improvement material is made up of soil drilled out and a fastening material in filament form mixed into the soil.

With this soil improvement method, the fastening material having a filament form acts as a binding material so that the improvement material is further hardened and hence soft soil can be improved to have a consolidated soil condition with a higher density.

ADVANTAGES OF THE INVENTION

According to the present invention, the plural wedge-shaped auger blades that each have the pressing part inwardly recessed are radially disposed on the lower end of the rotational shaft that extends outwards from the casing, and therefore an improvement material that has been introduced into a drilled hole is converged towards the center of each pressing part and extruded into soft soil. Therefore, the soft soil is improved to have a layered consolidated soil condition so that the auger blades are unlikely to receive a reaction force from the lower side and are unlikely to be forced upwards. As a result, the soil improvement apparatus can improve soft soil to a large extent to have a consolidated soil condition and hence enhance the workability.

Since the auger can be rotated at a small torque, it is possible to reduce the weight of the driving means for rotating the rotational shaft as compared with a conventional type. Accordingly, it is possible to prevent an upper end portion of the soil consolidating means from being unstabilized when it is shifted from the horizontal position to the vertical position, and hence improve the safety to avoid occurrence of an injury accident or the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross sectional front view of a soil improvement apparatus according to one embodiment of the present invention, illustrating a soil consolidating means.

FIG. 2(a) is a schematic cross sectional plan view illustrating one embodiment of the soil improvement apparatus of the present invention. FIG. 2(b) is a cross sectional view taken along a line X-X in FIG. 2(a). FIG. 2(c) is a cross sectional view taken along a line Y-Y in FIG. 2(a). FIG. 2(d) is a cross sectional view taken along a line Z-Z in FIG. 2(a).

FIG. 3 is a schematic cross sectional plan view illustrating one embodiment of the soil improvement apparatus of the present invention.

FIG. 4 is a schematic cross sectional view of the soil improvement apparatus taken along a line V-V in FIG. 3, according to one embodiment of the present invention.

FIG. 5 illustrate the soil improvement apparatus according to one embodiment of the present invention, in which FIG. 5(a) is a front view illustrating a pressure measuring means in an initial state, and FIG. 5(b) is a front view illustrating the pressure measuring means that is being measuring the pressure.

FIG. 6 is a partially cross sectional front view of the conventional soil consolidating apparatus.

DESCRIPTION OF THE REFERENCE CODES

    • A: Soil consolidating means
    • B: Pressure measuring means
    • 10: Casing
    • 20: Auger
    • 21: Rotational shaft
    • 22: Rotational tube
    • 23: Auger head
    • 24: Screw
    • 30: Auger blade
    • 40: Pipe
    • 41: Leading end portion
    • 42: Main body
    • 50: Pressure sensitive element

BEST MODE FOR CARRYING OUT THE INVENTION

The description will be made hereinafter for a soil improvement apparatus according to one embodiment of the present invention with reference to FIGS. 1 to 5. The soil improvement apparatus is arranged with a soil consolidating means A, a pressure measuring means B and the like centrally located.

The soil consolidating means A has, as illustrated in FIG. 1, a tubular casing 10 that is moved upwards and downwards in the vertical direction within soil, and an auger 20 that is inserted into the casing 10. The auger 20 is made up of a rotational shaft 21 and a rotational tube 22 that are disposed coaxially with each other, an auger head 23 that is attached to a lower end of the rotational shaft 21, and a screw 24 that extends around the outer circumference of the rotational shaft 21.

Attached to the lower end of the rotational shaft 21 is the auger head 23 that projects outwards from the lower end of the casing 10. The auger head 23 has, as illustrated in FIG. 2(a), plural auger blades 30, 30, 30 radially disposed at equal distance from each other. Although the three auger blades 30 are illustrated, any number of auger blades may be provided. The auger blades 30 each have a leading end that slightly projects outwards from the outer circumference of the casing 10, and in other words, the outer circumference of the casing 10 is positioned inwards from the leading ends of the auger blades 30.

The auger blades 30 each are formed by, for example, completely welding flat plates into a wedge shape to have a bottom part 31, a drilling part 32 and a pressing part 33. The inside surrounded by these parts 31, 32, 33 is hollow, aiming at reducing the weight. The bottom part 31 is oriented at a right angle to the rotational shaft 21, as illustrated in FIGS. 2(b)-2(d), and has a width gradually narrowed from the side of the rotational shaft 21 towards a leading end. The drilling part 32 is inclined from a first edge of the bottom part 31, and has the same height from the side of the rotational shaft 21 to the leading end. A sharp edge 34 formed by the bottom part 31 and the drilling part 32 drills into soft soil.

Further, the pressing part 33 has a portion between a second edge of the bottom part 31 and an upper edge of the drilling part 32, which portion is inwardly recessed, and is provided with a lower projection 33a and an upper projection 33b. This pressing part 33 is bent into a “<” shape (a “>” shape in Figures), as illustrated in FIGS. 2(b)-2(d). However, when the auger blades 30 are formed by extrusion molding or injection molding, the pressing parts 33 each may be formed into a circular arc shape, as well as the L-shape.

In either arrangement, an improvement material introduced into a drilled hole is converged into the deepest center portion of each pressing part 33 (a boundary portion of the lower projection 33a and the upper projection 33b) by the pressing parts 33 inwardly recessed, and is extruded only in the horizontal direction. That is, when each pressing part 33 is flat, the improvement material is spread over the width of the pressing part 33 and hence is extruded downwards as well, but when the pressing part 33 is inwardly recessed and is provided with the lower projection 33a and the upper projection 33b, the improvement material is pressed upwards by the lower projection 33a and pressed downwards by the upper projection 33b, producing a resulting force allowing the improved material to be extruded only in the horizontal direction.

As described in the Background of the Invention, an improvement material may be made by mixing pit sand (and cement according to needs and circumstances) into soil drilled out of the ground. In addition to this, it is preferable to use an improvement material made by mixing a fastening material in filament form into soil drilled out, with or without pit sand, cement or the like. As this fastening material, for example, carbonized and crystallized bamboo or jute, or PET cut into strips or the like is used.

Bamboo and jute are natural materials and therefore can melt into soil even if they are rotten. On the other hand, PET is not required to be rinsed unlike a conventional recycling, and can be reused at low cost, when it is used as a fastening material of the improvement material. In either case, the fastening material has a filament form with a length of about 50 mm to 150 mm and acts as a binding material.

The rotational shaft 21 with the thus arranged auger head 23 mounted thereto and the rotational tube 22 with the screw 24 provided thereto are circumferentially rotated independently of each other in the forward and the reverse direction by a driving means (not shown) installed at an upper end of the auger 20, and are preferably rotated at a speed ratio of such as 0.9:1, so that the rotational tube 22 is rotated slightly faster. It is possible to smoothly transport soil, an improvement material and the like without clogging by the rotation of the rotational shaft 21 and the rotational tube 22 in the opposite directions at the speed ratio as mentioned above.

The driving means having a weight lighter than a conventional one and a power of about 7.5×104(W) is used by the employment of the wedge-shaped auger blades 30, and the rotational shaft 21 and the rotational tube 22 that are rotated in the opposite directions. This driving means is decelerated to 1/20- 1/200 by a planet gear (not shown) so that the rotational shaft 21 and the rotational tube 22 are rotated at a slow speed such as about 25 rpm.

As the driving means of the type mentioned above, an electric motor that is driven by an engine generator (not shown) is employed. The electric motor is designed to have a small current flowing when it is rotated with a small torque and have a large current flowing when it is rotated with a large torque. Accordingly, in an initial stage when an improvement material starts to be extruded into soft soil with a small torque, the electric motor is rotated with a small current. Then, in a stage when the soft soil becomes consolidated and the improvement material is extruded with a large torque, the electric motor is rotated with a large current. When the improvement material is extruded into soft soil that has been consolidated beyond necessity, the auger blades 30 are not able to be rotated.

Therefore, a control unit is incorporated into this driving means so as to stop the electric motor when a given value of the current that flows when soft soil has been improved to have a given consolidated level is detected. This control unit includes an A-D converter for converting the current flowing in the electric motor to digital values, and a comparator such as a computer for comparing the digitized current value with a set current value for stopping the electric motor to determine whether the digitized electric value is smaller or larger than the set value.

As illustrated in FIG. 3, three soil consolidating means A are located adjacent to each other, in which the rotational shaft 21 and the rotational tube 22 of each soil consolidating means A is rotated by an exclusively used electric motor. When the value of the current flowing in any one of the electric motors reaches the set value for stopping, the residual electric motors are also stopped. Two posts 11, 11 are set up at sites near the two soil consolidating means A adjacent to each other, and are connected to each other by a girder 12 so that the auger blades 30 can achieve stabilized drilling operation.

The engine generator for driving the electric motors actuate hydraulic pumps (not shown) for actuating devices such as booms and leaders for positioning the soil consolidating means A in the vertical and horizontal positions, as well. Since the electric motors are not activated simultaneously with the hydraulic pumps, the single engine generator is switched to selectively actuate the electric motors and the hydraulic pumps.

The soil improvement apparatus is combined with a pressure measuring means B that is used at a site away from the soil consolidating means A. This pressure measuring means B includes a hollowed pipe 40, a pressure sensitive element 50 that is expanded and compressed simulating an air balloon, and a measuring instrument (not shown) that measures the compressed state of the pressure sensitive element 50.

The pipe 40 has a lower leading end portion 41 and an upper main body 42 that are separably connected to each other, and comb-shaped portions 41a, 42a that are provided at the connection portion at which they are engaged with each other. A supporting board 43 is mounted to an upper end of the leading end portion 41 to allow the pressure sensitive element 50 to be placed thereon, while a receiving plate 44 extends from a lower end of the main body 42 to block the pressure sensitive element 50. Filled within the pressure sensitive element 50 is fluid such as oil, water or air enabling the pressure sensitive element 50 to be compressed, and a pressure resistant hose 51, through which the fluid flows, is connected to the pressure sensitive element 50. The volume of the pressure sensitive element 50 that has been compressed is measured by the measuring instrument so as to be able to detect whether soft soil has been improved to have a consolidated soil condition.

The soil improvement apparatus of this embodiment is arranged in the manner mentioned above. Now, the description will be made for a soil improvement method.

First, the pipe 40 of the pressure measuring means B is embedded at a site with a given distance from the site at which the augers 20 are driven. As illustrated in FIG. 5(a), the pipe 40 has the leading end portion 41 connected to the main body 42, and is embedded into soil with the pressure sensitive element 50 mounted on the supporting board 43. The pressure sensitive element 50 is filled with fluid to be held in an expanded state. The pipe 40 is embedded to have the pressure sensitive element 50 located at the deepest position of soil to be improved. The pressure sensitive element 50 is unlikely to be damaged since it is accommodated in the pipe 40.

As illustrated in FIG. 5(b), only the main body 42 is moved upwards by a distance substantially equivalent to the diameter of the pressure sensitive element 50 away from the leading end portion 41 so that the pressure sensitive element 50 held in an expanded state is exposed inside the soil. The pressure sensitive element 50 is located close to the site at which the auger 20 is driven into soil, while the receiving plate 44 is located opposite to the site at which the auger 20 is driven into soil.

On the other hand, the soil consolidating means A is shifted from the horizontal position to the vertical position by driving the hydraulic pump by the engine generator. Since the driving means is reduced in size and weight as compared with the conventional one, the auger 20 can have its position shifted in a stabilized manner.

When the soil consolidating means A has been vertically positioned, the engine generator is shifted to drive the electric motor instead of the hydraulic pump, thereby rotating the rotational shaft 21 in the forward direction and rotating the rotational tube 22 in the reverse direction. Accordingly, the auger head 23 is rotated in the forward direction (F direction in FIG. 2(a)), and the sharp edges 34 of the auger blades 30 drill into soil so that a portion of soft soil is forced upwards through a space between the rotational tube 22 and the casing 10 and transported upwards by the screw 24 that is being rotated in the reverse direction. Thus, the soft soil is drilled and drilled holes are formed.

The casing 10 has an outer circumference located inwards of the leading ends of the auger blades 30, and therefore is inserted into a corresponding drilled hole. As such, the drilled hole is surrounded by the casing 10, so that the drilled hole is unlikely to be filled back with eroded soil.

When a hole has been drilled to a given depth, the electric motor rotates the rotational shaft 21 in the reverse direction and rotates the rotational tube 22 in the forward direction, while inserting an improvement material into the drilled hole. The improvement material is preferably mixed with a fastening material having a filament form, but may be used with pit sand or cement mixed into soil drilled out, according to the condition of soft soil. In either case, it is possible to smoothly transport the improvement material towards the auger head 23 without clogging within the casing 10 by rotating the rotational shaft 21 and the rotational tube 22 at a speed ratio of such as 0.9:1 so that the rotational tube 22 is rotated at a speed slightly higher than the rotational shaft 21.

Then, the improvement material is pressed by the pressing parts 33 of the auger blades 30 by the rotation of the auger head 23 in the reverse direction (R direction in FIG. 2(a)). The pressing parts 33 each are inwardly recessed and the lower projection 33a and the upper projection 33b together press the improvement material. When the pressing parts 33 each are flat, the improvement material is spread in the width direction of the pressing parts 33 (in the vertical direction) and thus is forced out to a lower side of the auger blades 30. However, the pressing parts 33 each having the inwardly recessed shape apply a force to the improvement material with the lower projection 33a and the upper projection 33b to allow the improvement material to be converged towards the center of each pressing part 33. Thus, with this force turning to be a resultant force, the improvement material is pressed out only in the horizontal direction, and soft soil is improved to have a layered consolidated soil condition (a portion shaded with dark gray), as illustrated in FIG. 4.

The soil improvement apparatus has three soil consolidating means A arranged adjacent to each other so that an improvement material is forced out of a portion between the adjacent ones, and more specifically forced out from two sides, as illustrated in FIG. 3, and the two streams hit each other and repeatedly kneaded together, thereby allowing sands or the like contained in the improvement material to tightly contact without clearances and thus achieving a rigid consolidation condition. Further, a large force is applied to the improvement material by the rotation of the auger blades 30 at a low speed, so that soft soil is improved to have a further consolidated soil condition.

Thus, soft soil around the soil consolidating means A is transformed into a consolidated zone W as illustrated in FIG. 3. This consolidated zone W is gradually developed to a large extent by the improvement material that is subsequently introduced into the drilled holes and forced outwards through the pressing parts 33 of the auger blades 30.

Since the improvement material is unlikely to be forced outwards to a portion below each auger head 23, the portion of soil below the auger head 23 does not turn into consolidated soil, and thus the auger head 23 is unlikely to receive a reaction force from the lower side. Accordingly, the consolidated zone W is developed to a large extent.

Then, the consolidated zone W reaches the pressure measuring means B having the pressure sensitive element 50 exposed to the outside. As illustrated in FIG. 5b), the pressure sensitive element 50 is held between a consolidated soil and the receiving plate 44. The pressure sensitive element 50 is prevented from being embedded in soft soil by the presence of the receiving plate 44 and therefore is compressed by the pressure of the consolidated soil. When the measuring instrument detects that the pressure sensitive element 50 has been compressed to a given pressure, it can be detected that soft soil has been improved within a certain area to have a consolidated soil condition. A signal output from the pressure measuring means B is transmitted to the driving means to stop the electric motors.

When the control unit detects that a portion around each auger head 23 is excessively consolidated and a given value of the current for stopping the electric motor flows within an electric motor before the pressure measuring means B detects a given pressure, the electric motor is stopped.

Thus, when soft soil located at the deepest portion of the drilled hole is transformed into the layered consolidated zone W, the auger 20 is moved upwards by a given distance, as illustrated in phantom lines in FIG. 4. Then, in the same manner as mentioned above, the rotational shaft 21 is rotated in the reverse direction and the rotational tube 22 is rotated in the forward direction, while the improvement material is introduced into the drilled hole. This improvement material is forced out onto the consolidated zone W, which has been transformed, and thus consolidated soil layers are accumulated. However, the electric motor is stopped not by additional detection of the compressed volume of the pressure sensitive element 50 by the pressure measuring means B, but is stopped when the current reaches the detected current.

Thus, when the consolidated zones W are accumulated in layers up to the surface of the ground, the operation at this site is finished and the same operation is repeated by moving the soil improvement apparatus to the next site. On the other hand, the pressure measuring means is operated so that the leading end portion 41 of the pipe 40 and the pressure sensitive element 50 are left in soil, the main body 42 of the pipe 40 is pulled out from the soil, and soil is placed back into the hole drilled by the pipe 40. The main body 42 of the pipe 40, the measuring instrument and the like pulled out are reused.

It is not necessary to limit the present invention to the aforesaid embodiments, while various modifications may be made within the technical scope as set forth in claims. For example, the present invention may be carried out without the combination with the pressure measuring device, or may be carried out with only a single soil consolidating means A or four or more soil consolidating means A.

Further, in the aforesaid embodiments, the description was made by taking for example the case where the electric motor is stopped upon detection of the fact by the pressure measuring means B that soft soil has been improved to have a consolidated condition, in the first soil improvement operation. It is possible to use the pressure measuring means B even in the first soil improvement operation, only for confirming the fact that soft soil has been improved to have a consolidated condition, by employing the arrangement where the electric motor is stopped when a given value of the current flows in the electric motor and the auger 20 is moved upwards by a given distance. In this case, the value of the current for stopping the motor is adjusted so as to improve soil to have a given consolidated condition in the next or subsequent operation unless the soil has been improved to have the given consolidated condition in the first soil improvement operation.