JPH1088564A - Jet grout method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the scale of equipment while securing cutting and stirring capability equal to or more that of a triple pipe system and, in addition, remarkably reduces a grout amount in an exhausted slime. SOLUTION: According to a jet grout method, an injection rod 5 of such a double tube structure that a drill bit 22 is provided on the tip, a double nozzle 20 is provided on a side wall, and a differential valve is provided in the inside is rotated and lowered to first drill a hole 51 by the drill bit 22 while low pressure water is supplied to the drill bit 22. When drilling is performed up to the upper limit of the planned establishment area, water supplied into the injection rod 5 is switched to superhigh pressure water, the differential valve is closed, and superhigh pressure water accompanied with air is jetted from the double nozzle 20 to cut and stir the ground 50. After the end of cutting and strirring to the lower limit of the planned establishment area, superhigh pressure water is switched to high pressure grout, and while grout with air is jetted from the double nozzle 20, the injection nozzle 5 is rotated and raised to establish an improved post.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ground improvement method, and more particularly, to a jet grouting method in which grout is injected under high pressure into a ground to form an improved pillar.

[0002]

2. Description of the Related Art The jet grout method is roughly divided into a double nozzle provided on a side wall of a tip portion of an injection rod while rotating, ascending or descending an injection rod formed of a double pipe into the ground. Hardening agent (grout) is injected at high pressure to cut the ground and at the same time to form a columnar improved body (for example, JP-B-56-44).
No. 206) and an injection rod consisting of a triple pipe is rotated and lowered into the ground, and precutting is performed by jetting ultra-high pressure water accompanied by air from a double nozzle provided on a tip side wall thereof, After precutting to a predetermined depth, the injection rod is rotated while continuously jetting air and ultra-high-pressure water from the double nozzle, and injecting high pressure grout from a nozzle provided on the tip side from the double nozzle, A triple-pipe method of raising and building improved columns (for example,
Japanese Patent Publication No. 58-27364).

According to the double-pipe jet grout method, since the air jet extends the grout range, there is an advantage that an improved body having a large diameter can be formed, but the ability to cut (break) the ground. Due to its small size, it is subject to restrictions on the target ground, such as soft clayey soils and loose sandy layers. On the other hand, according to the triple-pipe jet grout method, the cutting and stirring capacity increases with the use of ultra-high-pressure water with a large injection energy, so that large diameters can be applied to gravel, clay, hard sandy layers, etc. An improved body can be efficiently created, and its use is expanding in recent years.

[0004]

However, according to the above-mentioned triple-pipe jet grout method, ultra-high pressure water,
Since the compressed air and the high-pressure grout must be simultaneously injected, there is a problem that the equipment becomes large. Also,
Despite spraying from different nozzles, since water and grout are simultaneously sprayed from a position that is not so far away, the grout is diluted with water and easily guided and discharged, and the amount of slime discharge combined with the air lift effect by air injection In addition, there is a problem that the grout consumption per unit volume of the formation increases and the cost burden increases, and furthermore, the discharged slime contains a large amount of grout and the subsequent treatment becomes extremely troublesome.

Further, depending on the target ground, it is necessary to mount a drill bit at the tip of the injection rod and penetrate the injection rod to the planned improvement area while mechanically drilling.
Since the injection rod having the triple pipe structure is weaker in strength than the injection rod having the double pipe structure, it is difficult to adopt such a drilling method. A process is required, and there is a problem that a reduction in construction efficiency and an increase in cost burden cannot be avoided.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems. One of the problems is to reduce the size of equipment while ensuring a cutting and stirring capacity equal to or higher than that of a triple pipe method.
At the same time, the amount of grout in the discharged slime is significantly reduced to facilitate subsequent processing. Another object of the present invention is to enable efficient drilling up to a plan improvement area,
The object of the present invention is to eliminate the need for pre-drilling, thereby improving construction efficiency and reducing construction costs.

[0007]

In order to solve the above-mentioned problems, the invention according to claim 1 is directed to a rod body having first and second flow paths therein, and a first side wall and a second side wall formed on a side wall.
An injection rod is prepared by connecting an injection head provided with a double nozzle in which injection holes communicating with the respective flow paths are superimposed, and the injection head of this injection rod is penetrated to the upper limit of the planned improvement area, Ultra high pressure water in the first flow path,
The compressed air is supplied to each of the flow paths, and while the mixed fluid of water and air is jetted at a high pressure from the double nozzle, the injection rod is rotated and lowered to cut and agitate the ground. When reaching the lower limit, while switching the ultra high pressure water supplied to the first flow path to high pressure grout,
The injection rod is rotated and raised while adjusting the air to be supplied to the second flow path and injecting the mixed fluid of grout and air or only the grout from the double nozzle at a high pressure. Is characterized in that it is constructed.

In the jet grout method constructed as described above, a ground fluid can be highly efficiently cut and agitated (precutting) by injecting a mixed fluid of ultra high pressure water and compressed air having a large injection energy, and thereafter, By switching the ultrahigh pressure water to grout and injecting grout into the precut ground, grout can be efficiently injected into the ground, and of course, the induced discharge of grout can be suppressed. Further, the switching between the ultrahigh-pressure water and the grout can be dealt with by switching between the water source and the grout source for one high-pressure pump, so that the equipment can be reduced in size accordingly.

In the invention according to claim 1, the mixing of the air with the grout is adjusted according to the purpose, and when it is desired to increase the diameter of the improved body, the air is mixed to extend the range of the grout. When the purpose is to increase the strength, the air is stopped and only the grout is injected.

[0010] Here, depending on the target ground, it is necessary to penetrate the injection rod into the planned improvement area while mechanically drilling. In such a case, as in the invention described in claim 2, As an injection head, in addition to the double nozzle, a drill bit is provided at the tip, and a differential pressure valve that opens and closes a communication path connecting the first flow path in the rod body and the drill rod is provided inside. And first, the first
The low pressure water is supplied to the flow path of this, and while the low pressure water is jetted around the drill bit through the differential pressure valve, the injection rod is rotated into the ground and lowered to perform drilling, and the injection head is planned. When the upper limit of the improvement area is reached, the low pressure water supplied to the first flow path is switched to ultra high pressure water to close the differential pressure valve, and at the same time, compressed air is supplied to the second flow path in the rod main body. The same pre-cutting and grouting as in the first aspect of the present invention are performed continuously.

According to the second aspect of the present invention, since the ground can be cut while the drill bit is cooled with low-pressure water, drilling can be reliably performed even on hard ground while suppressing tool wear. Become. In addition, since the differential pressure valve is automatically closed simultaneously with the switching to the high-pressure water, the operation transition from drilling to pre-cutting can be performed continuously.

According to the second aspect of the present invention, a check valve is provided in the communication passage of the injection head to ensure smooth operation of the differential pressure valve, and the check valve is operated by the check valve. It is desirable to prevent the muddy water from flowing back into the water.

[0013]

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

In practicing the present invention, as shown in FIGS. 1 and 2, a rod body 3 having a double pipe structure having an outer pipe 1 and an inner pipe 2 and a rod body 3 described later connected to the tip of the rod body 3 will be described. An injection rod 5 including an injection head 4 is prepared.
Then, the injection rod 5 is supported by a rotation and elevating unit 8 attached to a leader 7 of a self-propelled construction machine 6 as shown in FIG. 3, and a double pipe swivel 9 is attached to the upper end of the rod body 3. Then, a high pressure pump 11 and an air compressor 12 in a construction plant 10 are connected to the double pipe swivel 9 by piping. In the present embodiment, the high-pressure pump 1
Reference numeral 1 denotes a first flow path a in the inner pipe 2 constituting the rod body 3.
(FIG. 2), while the air compressor 12 is connected to an annular second flow path b (FIG. 2) between the outer pipe 1 and the inner pipe 2.

As shown in FIG. 3, a water tank 13 and a grout mixer 15 connected to a cement silo 14 are installed in parallel in the construction plant 10. The grout mixer 15 has a function of mixing and agitating the cement taken in from the cement silo 14 and the water taken in from the water tank 13 to produce grout (cement milk). The admixture is supplied from 16. The water tank 13 and the grout mixer 15 are connected to the high-pressure pump 1.
1 is connected to the piping via a switching valve 17, and the operation of the switching valve 17 allows water or grout to be selectively supplied to the high-pressure pump 11. The high-pressure pump 11 has a function of obtaining low-pressure water of about ² to 5 MPa (about 20 to 50 kgf / cm ² ) to ultra-high-pressure water of about 35 to 45 MPa (about 350 to 450 kgf / cm ² ). ~
It has a function of obtaining a high-pressure grout of about 45 MPa, and any one of these low-pressure water, ultra-high-pressure water and high-pressure grout is selectively supplied to the first flow path a in the injection rod 5. Become. In addition, 18 is the construction plant 10
Generator as a power source for the vehicle.

As shown in FIG. 2, the injection head 4 has an upper head portion 21 having a plurality of double nozzles 20 on the side and a lower head portion 23 having a drill bit 22 at the tip. It is roughly constituted from. Upper head part 21
Has a double structure including an outer cylinder 24 and an inner cylinder 25, and an annular passage c is formed between the outer cylinder 24 and the inner cylinder 25. The lower portions of the outer cylinder 24 and the inner cylinder 25 are closely fitted to each other, and the bottom of the annular passage c is closed at the fitting portion. A first nozzle unit 26 that forms the double nozzle 20 is screwed and fixed to the outer tube 24, and a second nozzle unit 27 that also forms the double nozzle 20 is screwed to the inner tube 25. . The second nozzle unit 27 is extended across the annular passage c, and the leading end of the second nozzle unit 27 is inserted into the first nozzle unit 26. A gap of a predetermined size is ensured between the first nozzle unit 26 and the second nozzle unit 27. Therefore, the double nozzle 20 is provided at the center thereof with the injection hole communicating with the passage d in the inner cylinder 25. , Around which the injection holes communicating with the annular passage c are independently arranged.

The upper head portion 21 is connected to the rod body 3 by screwing the outer cylinder 24 to the outer tube 1 of the rod body 3, and in this connection state, the upper body of the inner cylinder 25 is attached to the upper end of the inner cylinder 25. The third inner cylinder 2 is fitted in a liquid-tight manner via a seal member 28. Therefore, the first flow path a in the rod body 3 passes through the passage d in the inner cylinder 25 to the injection hole on the core side of the double nozzle 20, and the second flow path b in the rod body 3 The nozzles communicate with the injection holes outside the double nozzle 20 via the annular passage c.

The upper head portion 21 is connected to the lower head portion 23 by screwing the outer cylinder 24 to the main body 29 of the lower head portion 23. In this connected state, the inner cylinder 25 is connected to the lower head portion 23. The main body 29 has a liquid-tight abutment with the upper end of the main body 29 via a seal member 30. The main body 29 of the lower head portion 23 has a tapered screw hole 31 at the lower end thereof for screwing the shank portion 22a of the drill bit 22 therein, and the screw hole 31 and the passage in the inner cylinder 25 are provided therein. and a communication hole (communication passage) 32 with a step for communicating with d. A differential pressure valve 33 is arranged on the upper side of the communication hole 32, that is, on the side connected to the upper head portion 21.

The differential pressure valve 33 is fitted and fixed to the main body 29 and has a bottomed cylindrical valve box 35 having a through hole 34 at the bottom. The valve box 35 extends on the axis of the valve box 35 and is screwed to the lower end. A valve rod 37 whose upper part is restricted from falling off from the valve box 35 by a nut 36, and a valve body which is integrally provided at the upper end of the valve rod 37 and which can be detached and seated on the edge (valve seat) of the valve box 35. 38
And a valve spring 39 which is disposed in the valve box 35 and normally biases the valve body 38 in a direction away from the valve seat.
The set load of the valve spring 39 is larger than the pressure (several MPa) of the low-pressure water supplied to the first flow path a in the rod body 3 and the pressure of the ultra-high-pressure water or the high-pressure grout supplied to the flow path a. (For example, several tens MPa). Therefore, when low-pressure water is supplied to the first flow path a in the rod body 3, the valve body 38 maintains a state of being separated from the valve seat of the valve box 35, and the low-pressure water is supplied to the valve box 35. 3
5 and through the through hole 34 at the bottom thereof, the inside of the communication passage 32 is sent to the drill bit 22 side. On the other hand, when ultra-high pressure water or high pressure grout is supplied to the first flow path a, the valve body 38 Is seated on the valve seat of the valve box 35 against the spring force of the valve spring 39 and closes the communication hole 32, so that the ultra-high pressure water or high pressure grout is sent to the double nozzle 20 side.

In the communication hole 32 in the lower head portion 23, a check valve 40 is arranged on the side of the drill bit 22. The check valve 40 includes a hemispherical valve body 42 that can be attached to and detached from a seat portion 41 provided in the middle of the communication hole 32, and a communication hole 3.
Stopper plate 43 attached to the opening end of the second drill bit 22 side
And a valve spring 44 for urging the valve body 42 in a direction of always seating on the seat portion 41. The set load of the valve spring 44 is set to be much smaller than that of the valve spring 39 of the differential pressure valve 33, and the valve body 42 is easily opened even with the above-described low-pressure water pressure. The drill bit 22 is provided with a water hole 22 b communicating with the communication hole 32.

At the time of construction, the injection rod 5 composed of the rod body 3 and the injection head 4 is supported by the rotation and lifting unit 8 of the construction machine 6 in the mode shown in FIG. Is connected to a high pressure pump 11 and an air compressor 12 in a construction plant 10 via a double pipe swivel 9. After completion of the preparation, the set pressure of the high-pressure pump 11 is adjusted to supply low-pressure water of several MPa to the first flow path a in the injection rod 5, and as shown in FIG. The injection rod 5 is rotated and lowered into the ground 50 by operating the rotation and elevating unit 8 while ejecting the water from the water hole 22 b of the drill bit 22 through the differential pressure valve 33 in the injection head 4. Thereby, the ground 50 is mechanically drilled by the drill bit 22 and the ground 5
A hole 51 having substantially the same diameter as the drill bit 22 is formed in the hole 0 (see FIG. 1).

The formation of the hole 51 by the above-described drilling is shown in FIG.
Upon reaching up plan improved range upper limit D _U as shown in, by adjusting the set pressure of the high pressure pump 11, switching the low-pressure water is supplied to the first flow path a ultra high pressure water, and at the same time air Compressed air is supplied from the compressor 12 to the second flow path b in the injection rod 5. By supplying the ultrahigh-pressure water to the first flow path a, the valve element 38 of the differential pressure valve 33 closes the communication hole 32, and as a result, the ultrahigh-pressure water with air (from the double nozzle 20 of the injection head 4). The mixed fluid) is injected, and the ground 50 is strongly cut and stirred by the mixed fluid having a large injection energy. In this way, a large-diameter cutting and stirring layer 52 is formed in the ground.
Is formed, and the cutting and stirring layer 52 gradually expands downward as the injection rod 5 rotates and descends. In addition, a part of the cutting slime generated at this time is
The waste water is discharged to the slime pit 53 (FIG. 1) on the ground, and further sent to a sludge pond by a sludge discharging means (not shown). Further, a part of the cut soil tends to flow back to the communication hole 32 in the injection head 4 through the water hole 22 b of the drill bit 22, but this backflow is prevented by the check valve 40.

When the formation of the cutting agitation layer 52 by the above-described cutting agitation reaches the lower limit D _{L of the} planned improvement area, as shown in FIG.
Is switched to the grout mixer 15 side, high-pressure grout is supplied to the first flow path a in the injection rod 5, and supply of compressed air to the second flow path b in the injection rod 5 is continued. The injection rod 5 is rotated and raised as shown in FIG. As a result, high-pressure grout (mixed fluid) accompanied by air is jetted from the double nozzle 20 of the injection head 4, and the grout is injected into the cutting and stirring layer 52 to form the grout injection layer 54. At this time, surplus slime in the cutting and stirring layer 52 on the grout injection layer 54 is released through the holes 51 by the pressure of the grout and the air lift effect.
At this stage, since the injection of water has been stopped, the induced discharge of grout is significantly suppressed, and the amount of grout in the excess slime is minimized.

The injection of the high-pressure grout with the air described above gradually expands upward as the injection rod 5 rotates and ascends. When a quick-hard grout is used, as shown in FIG. The grout injection layer 54 partially solidifies from the stage before 4 reaches the planned improvement area upper limit D _U , and the growth of the hard improved columns 55 starts. In this way, when finishing the injection of grout to plan improved range upper limit D _U, stopping the supply of grout and compressed air to the injection rod 5,
The rotation of the construction machine 6 and the elevating unit 8 are largely moved upward, and the injection rod 5 is pulled out from the ground 50 as shown in the figure, whereby the formation of one improved column 55 in the planned improvement area is completed. .

[0025]

As described above, according to the jet grouting method according to the first aspect, the cutting and stirring ability equal to or higher than that of the triple pipe method is achieved despite the use of the double pipe method. It is possible to secure large-diameter improved pillars with high efficiency.
Further, since the ultrahigh-pressure water and the high-pressure grout are switched and used, one high-pressure pump can be shared, and the size of the equipment can be reduced. Further, since the high-pressure grout is not injected together with the water, the induced discharge of the grout is suppressed, the amount of the grout in the discharged slime can be greatly reduced, and the subsequent treatment becomes easy. According to the jet grouting method according to claim 2, in addition to the above-described effects, since the drilling bit at the tip of the injection rod can be drilled with high efficiency up to the planned improvement area, the prior drilling becomes unnecessary, Improvement of construction efficiency and reduction of construction cost can be achieved. In addition, during this drilling, the cooling water is supplied to the drill bit through the differential pressure valve, so that the drill bit can be reliably drilled on the hard ground and the life of the drill bit is extended.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing an intermediate stage when a jet grout method according to the present invention is performed.

FIG. 2 is a sectional view showing a structure of an injection head constituting an injection rod used in the method of the present invention.

FIG. 3 is a schematic diagram showing an entire system for implementing the method of the present invention.

FIG. 4 is a schematic view showing a process of implementing the method of the present invention in the order of steps.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Outer pipe 2 Inner pipe 3 Rod main body 4 Injection head 5 Injection rod 6 Construction machine 9 Double pipe swivel 10 Construction plant 11 High pressure pump 12 Air compressor 17 Switching valve 20 Double nozzle 22 Drilling bit 32 Communication hole (communication passage) ) 33 Differential pressure valve 40 Check valve 51 Hole 52 Cutting stirrer layer 54 Grout injection layer 55 Improved column a First flow path b Second flow path

Claims (3)

[Claims] 1. An injection head comprising a rod body having first and second flow paths therein, and a double nozzle formed by superimposing injection holes communicating with the first and second flow paths on a side wall, respectively. Prepare an injection rod consisting of the following, and after injecting the injection head of this injection rod to the upper limit of the planned improvement area,
Ultra high pressure water is supplied to the first flow path, compressed air is supplied to the second flow path, and the injection rod is rotated while the mixed fluid of water and air is injected at a high pressure from the double nozzle,
When the injection head reaches the lower limit of the planned improvement area, the ultrahigh-pressure water supplied to the first flow path is switched to high-pressure grout, and the air supplied to the second flow path is reduced. Jet grout, wherein the injection rod is rotated and raised to form an improved column in the planned improvement area while the mixed nozzle of grout and air or only the grout is injected under high pressure from the double nozzle. Construction method. 2. A double nozzle in which injection holes communicating with the first and second flow paths are superposed on a side wall of a rod body having first and second flow paths therein, and a tip thereof is provided. An injection rod is prepared by connecting an injection head provided with a drilling bit and internally provided with a differential pressure valve for opening and closing a communication path connecting the first flow path and the drilling bit. The low pressure water is supplied to the first flow path, and while the low pressure water is jetted around the drill bit through the differential pressure valve, the injection rod is rotated into the ground and lowered to perform drilling. When the head reaches the upper limit of the planned improvement area, the low pressure water supplied to the first flow path is switched to the ultra high pressure water to close the differential pressure valve, and at the same time, the compressed air is supplied to the second flow path, High pressure jet of mixed fluid of water and air from double nozzle When the ground is cut and agitated and the injection head reaches the lower limit of the planned improvement area, the ultra high pressure water supplied to the first flow path is switched to high pressure grout, and the air supplied to the second flow path is adjusted. A jet grouting method, wherein the injection rod is rotated and raised to form an improved column in a planned improvement area while a mixed fluid of grout and air or only grout is injected at a high pressure from the double nozzle. 3. The jet according to claim 2, wherein a check valve is provided in the communication passage of the injection head, and the check valve prevents backflow of muddy water to the differential pressure valve side. Grouting method.