JP4300367B2 - Ground improvement method - Google Patents

Description

  The present invention belongs to the technical field of a ground improvement method using a static press-fit compaction method represented by a compaction grouting method.

  In static press compaction methods such as the static sand compaction pile method, the surrounding ground is compacted by continuously creating expanded sand piles. In this method, the compaction effect is small compared to the conventional vibration compacted sand pile, and a certain correction is performed. Further, when the ground fine particle content increases, there is a fear that a predetermined compaction effect cannot be obtained.

  Further, in the static press-fit compaction method represented by the compaction grouting method, generally press-fitting is performed while stepping up. The press-fitting in the step is continuously performed. However, when the pressure at the time of the press-fit exceeds the control reference value, the predetermined injection amount is not reached, and the improvement effect remains uneasy.

  In view of the above-described problems of the prior art, an object of the present invention is to improve the method for press-fitting an injection material and improve the ground improvement effect in the static press-fit compaction method.

  The object described above is achieved by the ground improvement method described in the following (1) to (5).

(1) A ground improvement method using a static press-fit compaction method, wherein the ground improvement material is pressed into the ground while repeatedly loading and unloading the ground improvement material. Improvement method.

(2) A method of improving the ground using a static press-fit compaction method,
Pumping the ground improvement material with an interval between the extrusion stroke of the ground improvement material by the pump and the next extrusion stroke,
During the extrusion stroke, the ground improvement material is loaded,
During the interval, the ground improvement material is unloaded from the ground improvement material.

(3) A method of improving the ground using a static press-fit compaction method,
After pushing out the ground improvement material by the pump, the suction is performed with the reverse stroke, and the ground improvement material is pumped.
During the extrusion stroke, the ground improvement material is loaded,
The ground improvement method, wherein unloading of the ground improvement material is performed during the suction.

(4) A method of improving the ground using a static press-fit compaction method in which a ground improvement material is press-fitted using a pump,
Extruding the ground improvement material with a pump and press-fitting it into the ground through an injection pipe;
After the extruding step, pulling up the injection tube to a minute length of less than 33 cm,
A ground improvement method characterized by continuously forming a consolidated body composed of the ground improvement material by repeating the above steps.

(5) A method of improving the ground using a static press-fit compaction method in which a ground improvement material is press-fitted using a pump,
Extruding the ground improvement material with a pump and press-fitting it into the ground via the first injection pipe;
Pumping the ground improvement material with a pump and press-fitting it into the ground through a second injection pipe adjacent to the first injection pipe,
A ground improvement method characterized by continuously forming a consolidated body made of the ground improvement material in the ground by repeating the above steps alternately.

  According to the present invention described above, in a static press-fit compaction method typified by a compaction grouting method, an injection material is press-fitted into the ground while loading and unloading are repeated. As a result, the compression efficiency of the ground is improved, the density of the ground is increased, the K value is increased, and the bulge is suppressed, and liquefaction countermeasures can be efficiently and effectively performed.

<Outline of compaction grouting method>
First, a CPG (compact grouting) method, which is a static press-fit compaction method, will be schematically described with reference to FIG. In the present invention, the “static press-fit compaction method” means a compaction method using static force (injection pressure by a pump) that does not give dynamic energy (striking and vibration). The CPG method is a typical example of a static press-fit compaction method.

  In the CPG method, using a boring machine, a rod-shaped injection tube 1 is drilled to a predetermined depth while being added, and the injection tube is allowed to face the hole. The injection tube 1 is provided so as to be movable up and down by an injection tube lift device 3. The injection material (a mortar-like ground improvement material composed of special aggregate, solidification material, and water) generated by the special injection plant 5 is forcibly pumped by the special injection pump 7 and fed to the pressure hose 9. It press-fits into the ground through the connected injection tube 1. The injection tube 1 is stepped up by 33 cm to 50 cm per step in the conventional case.

The injection material press-fitted into the ground is consolidated at a predetermined position without straying in the soil due to its low fluidity. Therefore, by repeating the above-described pumping of the low-fluidity material by the special injection pump and the step-up of the injection tube, a bulb-shaped solid body made of an injection material as shown in the figure is continuously formed. And by compressing the surrounding ground by increasing the volume of the consolidated body and increasing the density, the liquefied ground can be improved to the non-liquefied ground.
Hereinafter, the ground improvement method of the present invention based on the above-described CPG method will be described.

<First Embodiment>
Based on FIG. 2, 1st Embodiment of the ground improvement method which concerns on this invention is described.

  In FIG. 2, a first conduit 11 and a second conduit 12 are connected to the upper portion of the injection tube 1. The first pipe 11 is provided with a first valve 21, one end of which is connected to a special infusion pump via a pumping hose or the like. The second conduit 12 is provided with a second valve 22 and one end thereof is open.

  At the time of construction, the injection material is pumped by a special injection pump, and the injection material is pressed into the ground through the injection pipe 1. At that time, an interval (time interval) is provided between the extruding stroke of the injection material by the special infusion pump and the next extruding stroke. In FIG. 2, the extrusion stroke process is shown in FIGS. 2A and 2C, and the interval process is shown in FIGS. 2B and 2D.

  During the extrusion stroke shown in FIGS. 2A and 2C, the first valve 21 is opened and the second valve 22 is closed. As a result, loading on the injecting material is performed during the extrusion stroke. On the other hand, during the interval shown in FIGS. 2B and 2D, the first valve 21 is closed and the second valve 22 is opened. As a result, during the interval, the pressure is released via the second conduit 12 and unloading of the injected material is performed.

  Note that a suction device may be connected to the second pipe line 12 and forced suction may be performed only while the second valve 22 is opened. This method also allows unloading of the injected material during the interval. Further, the valve opening and closing operations may be performed manually or automatically by electronic control.

  When the above-described steps are repeated and a predetermined amount of the injection material is press-fitted, the injection tube 1 is stepped up by a predetermined length, and the injection material is press-fitted while repeating the extrusion stroke and the interval as described above.

  According to the above-described method, instead of continuously performing press-fitting within one step as in the prior art, an interval is provided between the extrusion strokes, and the injection material is intermittently pumped. As a result, it becomes possible to press-in the injection material while repeating loading and unloading, and as a result, the compression efficiency of the ground can be improved, the density of the ground can be increased, the K value can be increased, and the rise can be suppressed. Effective liquefaction measures can be taken. And the following points are mainly mentioned as a factor which achieves such an effect.

  That is, according to the experiments by the inventors, it has been clarified that when the injection material is press-fitted, the press-fitting pressure is reduced immediately after the press-fitting is stopped (FIG. 3). As the press-fitting pressure decreases, the horizontal stress in the surrounding ground also decreases (FIG. 4). Further, the decrease in the press-fitting pressure and the horizontal stress rapidly decreases immediately after the press-fitting is stopped.

  Therefore, rather than continuously press-fitting, press-fitting the injecting material while repeating intermittent press-fitting or loading and unloading, so that the desired amount of the injecting material does not exceed the control standard value. Can be pressed into the ground. Therefore, if press-fitting is repeated while loading and unloading, the ground compression efficiency can be improved, the density of the ground can be increased and the K value can be increased, and the ground uplift can be suppressed as compared with the case of continuous loading.

Second Embodiment
Next, a second embodiment of the ground improvement method will be described based on FIG.

  The special infusion pump 7 shown in FIG. 5 is a double-type piston pump including a switchable swing tube 30. The special injection pump 7 has a first piston 31 and a second piston 32, and is connected to an injection pipe through a pressure feed hose or the like. The first piston 31 and the second piston 32 that reciprocate are provided so as to extrude the injection material alternately.

  When pumping using the special injection pump 7 having the above-described configuration, for example, the injection material is filled in the cylinder on the second piston 32 side during the extrusion by the first piston 31 (FIG. 5A). . Then, when the extrusion by the first piston 31 is completed, the swing tube 30 is switched to the second piston 32 side (FIG. 5B). Through this series of operations, “one stroke” for extruding the injection material is completed.

  When the swing tube 30 is switched to the second piston 32 side, the injection material is filled into the cylinder on the first piston 31 side during the extrusion by the second piston 32 as described above (FIG. 5C). ). In this way, by repeating the switching and the extrusion stroke, the pressure is released each time the switching is performed, and the injection material is pumped in a pulsating manner.

  Then, once every few strokes, without switching the swing tube 30, the piston that has finished the pushing stroke is reversed, and suction is performed on the pumped injection material (FIG. 5D). This suction is performed by a drawing stroke (a stroke opposite to the pushing stroke). The reverse of the piston may be performed automatically or manually.

  According to the method described above, loading (pressurizing action) is performed on the injection material during the extrusion stroke, and unloading (negative pressure action) is performed on the injection material during the extraction stroke. Therefore, by repeating a series of operations including a plurality of extrusion strokes and subsequent drawing strokes, it is possible to press-fit the injection material while repeatedly loading and unloading the injection material. Therefore, the same effect as described in the first embodiment can be achieved.

  In the above-described embodiment, the case of using a double-type piston pump provided with the swing tube 30 is exemplified, but the type of pump used in the present invention is not particularly limited to this. That is, any type of pump can be used as long as it can operate in either the pushing direction (forward direction) or the suction direction (reverse direction) of the injection material. For example, a known squeeze pump can be mentioned.

<Third Embodiment>
Next, a third embodiment of the ground improvement method will be described based on FIG.
In FIG. 6, the upper stage shows a conventional method corresponding to the present invention, and the lower stage shows a ground improvement method according to the third embodiment.

  In FIG. 6, the injection tube 1 is connected to a special injection pump via a pressure feed hose or the like. The injection material pumped from the special injection pump is press-fitted into the ground via the injection pipe 1.

  At the time of construction, the injection material is first pushed out by a special injection pump and is pressed into the ground through the injection pipe 1. When the injection of a predetermined amount of the injection material is completed, the injection tube 1 is pulled up to a minute length of less than 33 cm (for example, about 10 cm). And the solidified body which consists of injection material is continuously produced | generated by repeating the press injection process and injection pipe pulling-up process which were mentioned above.

According to the method described above, the following effects are achieved.
That is, in the case of the conventional CPG method shown in the upper part of FIG. On the other hand, in the case of the present invention shown in the lower part of FIG. 6, the step-up length is shortened (for example, shortened to about 10 cm). As shown in FIG. 3, at the time of step-up, the press-fitting pressure is unloaded, and at this time, the stress applied to the ground is also reduced. Therefore, according to the present invention, the number of step-ups per injection tube increases and the number of press-fitting repetitions increases, resulting in an increase in compression efficiency.

<Fourth embodiment>
Next, based on FIG. 7, 4th Embodiment of the ground improvement method is described.

  In FIG. 7, in the ground to be improved, two injection pipes 1a and 1b are arranged adjacent to each other. The first injection pipe 1a and the second injection pipe 1b are each connected to a special injection pump via a pressure feed hose or the like.

  At the time of construction, the injection material is pushed out by a special injection pump and is pressed into the ground through the first injection pipe 1a (FIG. 7A). At this time, the horizontal stress generated with the press-fitting acts in the direction of the second injection tube 1b as indicated by an arrow R. When the press-fitting within one step is completed on the first injection pipe 1a side, the injection material is subsequently injected into the ground through the second injection pipe 1b (FIG. 7B). At this time, as indicated by an arrow L, the horizontal stress generated with the press-fitting acts in the direction of the first injection tube 1a.

  When the press-fitting in one step is completed on the second injection tube 1b side, the first injection tube 1a is then stepped up (FIG. 7C). Then, after stepping up by a predetermined length, the injection material is press-fitted into the ground through the first injection pipe 1a (FIG. 7D). When the press-fitting in one step is completed on the first injection pipe 1a side, the second injection pipe 1b is stepped up to inject the injection material. Then, by repeating these steps shown in the figure, a continuous consolidated body is created in parallel in the adjacent ground.

  According to the method described above, the injection material is alternately pumped from the special injection pump to the two adjacent injection pipes. Therefore, in the ground interposed in the intermediate region between the two injection pipes, loading by press-fitting on one side and loading by press-fitting on the other side are alternately received. Further, stress release by stepping up the injection tube on one side and stress release by stepping up the injection tube on the other side are alternately received. As a result, the compression efficiency of the ground can be improved as compared with the case of press-fitting with one injection tube.

It is a figure which shows the outline of the embodiment of a compaction grouting method. It is process drawing which shows the ground improvement method which concerns on 1st Embodiment. It is a figure which shows the time-dependent change of press-fit pressure. It is a figure which shows the time-dependent change of horizontal stress. It is process drawing which shows the ground improvement method which concerns on 2nd Embodiment. It is process drawing which shows the ground improvement method which concerns on 3rd Embodiment. It is process drawing which shows the ground improvement method which concerns on 4th Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Injection pipe 1a 1st injection pipe 1b 2nd injection pipe 3 Injection pipe lift apparatus 5 Special injection plant 7 Special injection pump 9 Pumping hose 11 1st pipe line 12 2nd pipe line 21 1st valve 22 1st 2 valve 30 swing tube 31 first piston 32 second piston

Claims (2)

This is a method to improve the ground by compressing the surrounding ground using a compaction grouting method using a low fluidity ground improvement material, and it works in both the direction of extrusion to the ground and the direction of suction from the ground. In the method of pumping the ground improvement material using a possible pump,
Between the extrusion stroke of the ground improvement material by the pump and the next extrusion stroke, so as to leave a time interval in which extrusion is not performed, the ground improvement material is pumped.
During the extrusion stroke, the ground improvement material is loaded,
During the time interval during which the extrusion is not performed, unloading of the ground improvement material is performed,
A ground improvement method comprising press-fitting the ground improvement material while repeatedly loading and unloading the ground improvement material.   The ground improvement method according to claim 1, wherein suction is performed on the ground improvement material that has been fed during a time interval in which the extrusion is not performed.

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