JP5922960B2 - Method for constructing cast-in-place piles and manufacturing method for cast-in-place piles - Google Patents

Description

  The present invention relates to a method for constructing cast-in-place piles used in various structures including viaducts, and a method for manufacturing cast-in-place piles.

  Foundation piles are provided in the ground as foundations for various structures including viaducts. In this foundation pile, there is a cast-in-place pile that is formed by placing reinforcing bars in a vertical shaft excavated in the ground and placing concrete.

  In order to prevent uneven settlement in multiple cast-in-place piles, a bag body is sunk at the tip of the pile, and after placing concrete, the pile body is expanded by feeding a fluid such as cement milk into the bag body. There is a method of loading a preload on the tip portion ground to increase the support force of the pile tip portion ground and reducing the amount of pile settlement (for example, see Patent Document 1).

Japanese Patent No. 3688546

  However, in the construction method in which the bag body as described above is provided at the tip of the pile, cement milk may flow out due to the bag body being torn or the like, and may penetrate into the surrounding ground from the bag body. As a result, cement milk is used wastefully and causes an increase in cost, or the effect of increasing the supporting force of the pile tip ground due to the expansion of the bag body and reducing the amount of pile settlement may not be obtained.

On the other hand, the present inventors tried improvement such as increasing the strength of the bag body, but the problem was not completely solved and there was still room for improvement.
An object of the present invention made there is a method for constructing cast-in-place piles and a method for producing cast-in-place piles that can sufficiently increase the bearing capacity of pile tip ground and reduce the amount of pile settlement while suppressing costs. Is to provide.

The present invention employs the following means in order to solve the above problems.
That is, the cast-in-place pile construction method of the present invention includes a foundation pile with a bag body attached to the tip, a cement milk inflow pipe to the bag body, a cement milk outflow pipe from the bag body, and the bag body. A step of installing a discharge pipe for discharging a fluid from a space between the ground and a shaft formed in the ground, and injecting cement milk containing a particle size adjusting material having a particle size finer than the size of the ground into the bag body while expanding the bag body, and the fluid between the ground and the bag was closed and a step of discharging through the discharge pipe, the cement milk, characterized in that it comprises a segregation reducing agent .
When cement milk containing the particle size adjusting material is injected into the bag body, the particle size adjusting material contained in the cement milk leaked from the bag body remains in the surrounding ground even if the bag body is torn. Thereby, the permeability of cement milk to the surrounding ground can be suppressed.

  Here, cement milk containing a particle size adjusting material may be injected into the bag body from the beginning. However, after injecting a predetermined amount of cement milk not containing the particle size adjusting material into the bag body, the particle size adjustment is performed. Cement milk containing the material may be injected.

The present invention discharges fluid from a reinforcing bar with a bag at the tip, a cement milk inflow pipe to the bag, a cement milk outflow pipe from the bag, and a space between the bag and the ground. A drain pipe to be installed in a vertical shaft formed in the ground, a step of injecting concrete into the vertical shaft to form a foundation pile, and after the concrete is hardened, the bag from the cement milk inflow pipe Injecting cement milk for bags into the body to expand the bags and discharging the fluid from between the bags and the ground, the cement milk for bags is It can also be set as the manufacturing method of the cast-in-place pile characterized by including the particle size adjustment material of a particle size finer than this particle size, and a separation reducing agent .

  Also in this manufacturing method, in the step of injecting the cement milk for the bag body, a predetermined amount of cement milk not containing the particle size adjusting material is injected into the bag body, and then the cement milk containing the particle size adjusting material is injected. You can also

  According to the present invention, when cement milk containing a particle size adjusting material is poured into a bag body, even if the bag body is torn, the particle size adjusting material contained in the cement milk leaked from the bag body remains on the surrounding ground. Thereby, the permeability of cement milk to the surrounding ground can be suppressed. As a result, it is possible to sufficiently increase the bearing capacity of the pile tip portion ground and reduce the amount of pile settlement while suppressing costs.

It is sectional drawing which shows the foundation pile in this embodiment. It is a figure which shows the flow of the construction method of a cast-in-place pile. It is an elevation view which shows the plane sectional view of the rebar basket of a cast-in-place pile, and the composition of the tip part of a rebar basket. It is a figure which shows the structure for inject | pouring cement milk into the bag body of a cast-in-place pile.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a best mode for carrying out a cast-in-place pile construction method and a cast-in-place pile manufacturing method according to the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited only to these examples.
As shown in FIG. 1, the foundation pile 10 is a reinforced concrete structure made of cast-in-place concrete, and is formed in a vertical shaft 11 formed in the ground G.
FIG. 2 is a diagram illustrating a flow of the construction method of the foundation pile 10 as described above.
As shown in FIG. 2A, in order to construct the foundation pile 10 in the ground G, a vertical shaft 11 is excavated in the ground G.

Next, as shown in FIGS. 2 (b) and 2 (c), a cylindrical rebar cage 12 assembled in advance is built into the shaft 11.
Here, as shown in FIG. 3, the reinforcing bar 12 includes a plurality of main bars 12 a that extend in the vertical direction and are arranged at intervals in the circumferential direction of the reinforcing bar 12, and annular annular bars 12 b. A bottom frame 14 is provided at a lower end portion of the reinforcing bar 12 via a slide mechanism 13 including a cylinder that can be expanded and contracted in the vertical direction. As a result, the vertical height of the rebar cage 12 can be changed. When the depth of the vertical shaft 11 is shallower than the design value, the bottom frame 14 slides as it contacts the bottom of the vertical shaft 11. The mechanism 13 is configured to contract.

  A bag body 20 is set on the lower end side of the bottom frame 14 at the lower end portion of the reinforcing bar 12. The bag body 20 is formed of a material having water impermeability, pressure resistance, and flexibility. Examples of the material forming the bag body 20 include synthetic resin materials, for example, plastics such as thermoplastic resins and thermosetting resins, specifically, polyethylene, polyvinyl chloride, vinylidene chloride, polypropylene, polyamide, and the like. Can be mentioned. Also, as the bag material, rubber materials (including synthetic rubber and elastomer materials) can be used. Moreover, as a bag body material, the sheet-like member, film-like member, film-like member, etc. which consist of these materials are mentioned. In this case, the bag body 20 is formed into a bag shape by bonding the above-mentioned bag body material with an adhesive, or pressure bonding by pressure, welding by heating, heat pressure bonding by pressure and heating, and the like. In this case, sewing is not used.

The bag body 20 has an injection hose (cement milk inflow pipe) 21 for injecting cement milk into the bag body 20 and a discharge hose (cement milk) for discharging cement milk from the inside of the bag body 20. Inflow pipe) 22 is connected. The injection hose 21 and the discharge hose 22 are inserted into the space between the inner wall surface of the vertical shaft 11 and the reinforcing bar 12, and are led out from the upper portion of the vertical shaft 11 to the ground.
The injection hose 21 and the discharge hose 22 are connected to a pump for injecting and discharging cement milk. As shown in FIG. 4, the injection hose 21 and the discharge hose 22 are provided with valves 23 and 24 that can be opened and closed, and pressure sensors 25 and 26 that measure the internal pressure.

  Further, as shown in FIG. 3, the rebar basket 12 is provided with a slime discharge hose 30. The slime discharge hose 30 is arranged so that one end 30 a thereof is positioned in the vicinity of the outer peripheral surface 20 a below the bag body 20 and the other end 30 b is positioned above the reinforcing bar 12. Here, one end 30a and the other end 30b of the slime discharge hose 30 are open ends.

  As shown in FIG. 2 (d), in a state where the rebar cage 12 including the bag body 20, the injection hose 21, the discharge hose 22, and the slime discharge hose 30 is inserted and arranged in the vertical shaft 11, Concrete C is poured into the pit 11. Concrete C is made by mixing cement, aggregate, additives, and the like in a predetermined composition and kneaded in advance by a mixer into the shaft 11 through a pump and an injection hose. Then, the slurry (sludge etc.) leaked into the vertical shaft 11 when excavating the vertical shaft 11 is pushed out of the vertical shaft 11 from the upper portion of the vertical shaft 11.

  As shown in FIG. 2 (e), the concrete C is poured to a predetermined level above the shaft 11, and after it hardens and develops a predetermined strength, cement milk is poured into the bag body 20. For this purpose, as in the case of injecting concrete C into the shaft 11, cement, aggregate, additives, etc. are mixed in a predetermined composition and cement milk obtained by kneading in advance by a mixer is pumped by a pump (not shown). Inject into the injection hose 21. At this time, both the valve 23 of the injection hose 21 and the valve 24 of the discharge hose 22 are kept open. Then, the cement milk flows from the injection hose 21 into the bag body 20 and flows to the discharge hose 22.

When the injected cement milk overflows from the outlet of the discharge hose 22 and it is confirmed that the specific gravity of the overflowed cement milk is within a predetermined range, the valve 24 on the discharge hose 22 side is turned on. close up.
Thereafter, the cement milk is continuously supplied from the injection hose 21. As a result, the bag body 20 is inflated.

  When the bag body 20 is inflated, the slime S in the space sandwiched between the outer peripheral surface 20a of the bag body 20 and the bottom of the vertical shaft 11 is pressed, whereby the slime S is connected to one end of the slime discharge hose 30. It flows into 30a. The slime S that has flowed in is discharged from the other end 30 b of the slime discharge hose 30 to the outside of the vertical shaft 11.

  Moreover, the surrounding ground Gb at the bottom of the vertical shaft 11 is compacted by the expanded bag body 20.

If cement milk is continuously poured into the bag body 20 in this way, the pressure of the cement milk increases. The pressure value is detected by pressure sensors 25 and 26 and monitored. Then, when the detected pressure value of cement milk reaches a specified value, injection of cement milk is stopped.
The pressure value at which the cement milk injection is stopped is set to 1.0 MPa for the purpose of preventing settlement of the foundation pile 10, for example, and to 1.5 MPa for the purpose of improving the tip bearing capacity of the foundation pile 10. can do. That is, in the case of the embodiment, the average value of the pressure measured by the pressure sensor 25 on the injection side and the pressure sensor 26 on the discharge side is used as the pressure value of the cement milk. Although it is determined that the injection is completed when 1.0 Mpa or 1.5 Mpa can be maintained for 10 minutes, the specified value is not limited at all.

  Thereafter, the valve 23 of the injection hose 21 and the valve 24 of the discharge hose 22 are closed. Thereby, the construction of the foundation pile 10 in the ground G is completed.

Now, when cement milk is poured into the bag 20 as described above, in the present embodiment, the cement milk having the following properties is used.
That is, when cement milk starts to be poured into the injection hose 21 and overflows from the outlet of the discharge hose 22, if the bag body 20 is broken and the cement milk leaks out, the permeable cement that permeates the surrounding ground Gb. Use milk.
Then, after cement milk overflows from the outlet of the discharge hose 22 and then closes the valve 24, when the bag body 20 is broken and the cement milk leaks out, the non-permeable cement that does not easily penetrate into the surrounding ground Gb. Use milk.

Here, as the permeable cement milk, for example, a combination of cement, water, a separation reducing agent (auxiliary), and a water reducing agent is used.
On the other hand, the non-permeable cement milk uses, for example, cement, water, a separation reducing agent (auxiliary), a particle size adjusting material, and a water reducing agent in a predetermined composition, and the particle size adjusting material is a particle size of the surrounding ground Gb. It is possible to use a fine aggregate such as sand having a smaller particle diameter.
Table 1 shows blending examples of such permeable cement milk and non-permeable cement milk.

  As described above, after filling the permeable cement milk into the injection hose 21, the bag body 20, and the discharge hose 22, when the cement milk to be injected is switched to the non-permeable cement milk, the bag body 20 is broken and the cement milk is exposed to the outside. In the case of leakage, the particle size adjusting material contained in the non-permeable cement milk clogs the surrounding ground Gb. Thereby, permeation into the surrounding ground Gb of cement milk is suppressed. As a result, while suppressing the consumption of cement milk due to permeation into the surrounding ground Gb, the supporting force of the surrounding ground Gb at the tip of the foundation pile 10 can be increased and the settlement amount of the foundation pile 10 can be reduced at a low cost. be able to.

(Other embodiments)
The present invention is not limited to the above-described embodiments described with reference to the drawings, and various modifications are conceivable within the technical scope thereof.
For example, in the above embodiment, the osmotic cement milk is first injected and then the non-permeable cement milk is injected. However, the non-permeable cement milk may be injected from the beginning.

  When the injected cement milk overflows from the outlet of the discharge hose 22 and it is confirmed that the specific gravity of the overflowed cement milk is within a predetermined range, the valve 24 on the discharge hose 22 side is turned on. Although it was made to close, it does not confirm that it overflows from the exit of the discharge hose 22, but since a predetermined amount, for example, the volume of the bag body 20, is known, the amount of cement milk that can satisfy this amount Alternatively, the valve 24 may be closed at the time of injection.

  Furthermore, cement milk is poured into the bag body 20, and the pressure value is detected and monitored by the pressure sensors 25 and 26, so that the cement milk injection is stopped. The injection of cement milk may be stopped when a predetermined amount of cement milk is injected.

In addition, the properties of the osmotic cement milk and the non-permeable cement milk may be other than those exemplified above, and further, in order to suppress the penetration of the non-permeable cement milk into the surrounding ground Gb, other than those described above. Additives and the like may be added.
In addition to this, as long as it does not depart from the gist of the present invention, the configuration described in the above embodiment can be selected or changed to another configuration as appropriate.

DESCRIPTION OF SYMBOLS 10 Foundation pile 11 Vertical shaft 12 Reinforcement basket 12a Main reinforcement 12b Annular reinforcement 13 Slide mechanism 14 Bottom frame 20 Bag body 20a Outer peripheral surface 21 Injection hose (cement milk inflow pipe)
22 Discharge hose (cement milk outflow pipe)
23 Valve 24 Valve 25 Pressure sensor 30 Slime discharge hose (discharge pipe)
30a One end 30b The other end C Concrete G Ground Gb Surrounding ground S Slime

Claims (6)

A foundation pile with a bag body attached to the tip, a cement milk inflow pipe to the bag body, a cement milk outflow pipe from the bag body, and a discharge pipe for discharging fluid from the space between the bag body and the ground And installing in a vertical shaft formed in the ground,
A step of discharging the fluid between the bag body and the ground through a discharge pipe while inflating the bag body by injecting cement milk containing a particle size adjusting material having a particle size finer than that of the ground into the bag body. When,
I have a,
The method for constructing cast-in-place piles, wherein the cement milk contains a separation reducing agent .   2. The cast-in-place pile construction method according to claim 1, wherein cement milk containing no particle size adjusting material is injected into the bag body, and then cement milk containing the particle size adjusting material is injected.   3. The cast-in-place pile construction method according to claim 2, wherein the cement milk containing the particle size adjusting material is injected after the pressure of the cement milk not containing the particle size adjusting material reaches a predetermined value.   3. The cast-in-place pile construction method according to claim 2, wherein the cement milk containing the particle size adjusting material is injected after a predetermined amount of cement milk not containing the particle size adjusting material is injected.   A reinforcing bar with a bag at the tip, a cement milk inflow pipe to the bag and a cement milk outflow pipe from the bag, and a discharge pipe for discharging fluid from the space between the bag and the ground In a vertical shaft formed in the ground,
  A step of injecting concrete into the vertical shaft to form a foundation pile;
  After the concrete is hardened, injecting the cement milk for bag body into the bag body from the cement milk inflow pipe, inflating the bag body, and discharging the fluid from between the bag body and the ground; Have
  The method for manufacturing a cast-in-place pile, wherein the cement milk for bag includes a particle size adjusting material having a particle size smaller than that of the ground and a separation reducing agent.   In the step of injecting the cement milk for bag body, the particle size adjusting material is not included in the bag body.
6. The method for manufacturing cast-in-place piles according to claim 5, wherein the cement milk containing the particle size adjusting material is injected after injecting a certain amount of cement milk with a predetermined amount.

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