JP2553648B2 - Reinforcing cage for cast-in-place concrete pile and construction method using it - Google Patents

Description

TECHNICAL FIELD The present invention relates to a reinforcing bar cage for cast-in-place concrete piles and a construction method using the same.

“Prior Art” Cast-in-place concrete piles are constructed by excavating the ground in a circular or rectangular cross-section to the support layer, constructing a rebar cage, and placing underwater concrete. At this time, the vertical ground bearing capacity generally decreases due to a part of the sediment of the excavated soil on the excavated tip ground and the accumulation of slime by a stable liquid such as bentonite liquid, and the looseness of the tip ground caused by excavation, It also causes uneven settlement of the structure.

That is, if the pile is constructed on the above-mentioned deposit or the ground in a loosened state, the tip supporting force thereof is small and the settlement is large and unstable.

There is a means for injecting and solidifying the grout material to the accumulated slime and the loose ground portion, which are sources of such inconvenience, to improve it.

However, with mere injection, slime is generally fine sand,
Since it is a mixture of silt and clay, the permeability of the grout material is low, and therefore, the range in which the grout material penetrates into the pores of the soil particles and solidifies is extremely narrow, so that a sufficient effect cannot be obtained.

On the other hand, the recent increase in the height of buildings has a tendency to greatly increase the load bearing load of a single pile, where the spacing between piles is restricted by legal regulations.

Therefore, various means have been proposed to improve the tip of the pile by injecting and cementing cement milk into the tip of the pile under high pressure.

Figures 2a-g show one of them. That is, after the excavation of the excavation hole 1, the slime treatment of depositing on the bottom of the hole is performed by the bucket 2 (Fig. A).

Then, the rebar cage 3 with the pressure cell 5 and the gravel chamber 4 attached to the lower end is inserted into the hole 1 (FIG. B).

The structure of the lower end of the above-mentioned reinforcing bar cage 3 is shown in detail in FIGS.

That is, the pressure cell 5 is mounted in such a manner as to cover the lower end surface of the rebar cage 3, and is a flat box body composed of a pair of upper and lower steel plates 7 and 8 with a spacer 6 interposed therebetween. A grout pipe 9 is connected to the steel plate 7. The steel plate 8 has through-holes 10, ... Which are even over the entire surface, and an elastically deformable film 11 of rubber or neoprene sheet is closely attached to the lower surface of the plate.

The membrane 11 has a through hole 1 that is displaced from the through holes 10 ,.
2, ... are evenly drilled over the entire surface.

Then, though the through holes 10 → 12 can be distributed, the through holes 12 → 10
Is blocked and constitutes a check valve. The gravel (gravel) chamber 4 formed below the overhead pressure cell 5 is a basket made of reinforcing steel bone and mesh, and is filled with gravel of the same size.

 In the figure, 13 is a hook for hanging.

Insert the tremie pipe 14 and insert concrete 15 into the borehole 1.
(Fig. F).

After the concrete 15 is hardened, cement milk is pressure-injected into the pile tip (the gravel chamber 4) through the grout pipe 9 and the pressure cell 5 to invade the gravel chamber 4, the hole bottom in contact with the gravel chamber 4, and the supporting ground area 16. It is allowed to pass through and cured with pressure applied (Fig. G).

That is, the injected cement milk enters the gravel chamber through the pressure cell, fills the voids in the chamber, and then applies pressure to the hole bottom to compact the hole bottom. When the cement milk inlet is closed while pressure is applied, the cement milk hardens as it is, and the ground that is well tightened at the tip of the pile and a mixed layer of hardened bulky gravel chamber and cement milk are created. It is an ideal pile with high bearing capacity and good performance.
Depending on the press-fitting of cement milk in this case, it penetrates into the supporting ground area 16 and brings about an improvement,
This is an added value, and the maximum purpose is to compact the supporting ground area 16 and residual slime by the pressure applied to the cement milk to enhance the tip supporting force, and the injection pressure can be up to 80 kg / cm ² ~ 120kg / cm ² is assumed.

However, when such a high pressure is applied, tensile cracks occur in the horizontal direction in the horizontal stratified ground. That is, as shown in FIG. 3, the pressure of the cement milk injected into the gravel chamber 4 acts on the surroundings, but as shown by the arrow in the figure, the pressure cell 5 is lifted above the weakest backup force. This causes tensile cracks 18 to occur, especially at the level of the pressure cell 5. Also, tensile cracks 18 are generated in the horizontal direction at other levels. This is called the hydraulic fracturing phenomenon (hydraulic fracturing), and once this occurs, even if cement milk is injected, escape occurs and the pressure does not rise. Also, once a tensile crack 18 occurs, the crack 18
As the cement milk spills out along the line, it becomes extremely difficult to control the injection amount.

For such a situation, conventionally, a method of performing injection in multiple stages, which is expected to have a filling effect of cement milk on the crack 18, has been adopted.

"Problems to be solved by the invention" However, in the above cement milk outflow prevention means, it is difficult to control the leaving time from one injection to the next and the injection amount, and the construction time is wide. The problem is to increase.

Incidentally, a means for applying a compaction pressure to the tip of the pile by attaching a non-water-permeable bag such as a rubber bag in order to apply a high pressure for compaction without running away of the liquid or paste is disclosed in JP-B-54-
Although disclosed in Japanese Patent No. 29805 and Japanese Patent Laid-Open No. 61-179918, a gravel chamber in which a pressure cell for planting a grout pipe is interposed is attached to the lower end of the target of the present invention. Gravel chamber 4 when applied to a rebar cage
There is a serious problem that the remaining mud water cannot be discharged.

The present invention has been made in view of the above circumstances, in a rebar cage with a gravel chamber having a pressure cell for grouting pipes installed at the lower end, even if a hydraulic charring phenomenon occurs, even if the injected cement milk is The purpose is to prevent runaway and prevent muddy water from remaining in the gravel chamber during cement milk injection.

[Means for Solving the Problems] In order to achieve the above-mentioned object, in the present invention, the circumference of the gravel chamber of a reinforced cage having a gravel chamber with a pressure cell for grouting pipes installed at the lower end is attached. Permeability coefficient of 1.0 × 10 ^-1 to 10 on the side, inner circumference, and bottom
It is surrounded by a wrapping body made of a highly stretchable woven fabric that uses high-strength synthetic fibers of about 10 ^-1 cm / sec.

[Operation] When high-pressure injection of cement milk is carried out in the rebar cage configured as described above, due to the permeability coefficient of the package, the residual mud water escapes in the gravel chamber, but the cement milk almost escapes. Without stopping inside the package.

[Example] An example will be described with reference to the drawings.
In, the wrapping body 17 is a bottomless or bottomed container body,
It hardly allows cement milk to pass through, but allows mud to pass through.It consists of a highly stretchable woven fabric made of high-strength synthetic fiber with a permeability coefficient of 1.0 × 10 ^-1 to 10 × 10 ^-1 cm / sec. The tensile strength may be about 200 to 400 kg / cm.

For example, “geotextile” is adopted as the above-mentioned woven fabric. The term "geotextile" means, for example, (1) a knitted fabric including monofilament, multifilament, various yarns, (2) woven fabric including monofilament, strip film, multifilament, spun fabric yarn, and (3) ) A non-woven fabric made of various fibers, (4) a composite made of a combination of the above (1) to (3), (5) a mat made of coarse or hard filament, etc. (6) fusion-bonded extruded plastic strands The thus formed net includes (7) a grit made of a perforated sheet of synthetic resin or the like.

The wrapping body 17 is mounted on the pressure cell 5 in such a manner as to surround the gravel chamber 4 via a mounting metal piece 19 provided on the pressure cell 5 as shown in FIG.

 In addition, in the figure, the case of the bottomless wrapping body 17 is shown.

According to such a rebar cage, even if the cement milk is pressed in, only the muddy water remaining in the gravel chamber 4 penetrates into the ground 16 through the wrapping body 17, and the cement milk hardly escapes.

Then, the cement milk is injected while preventing the tensile crack 18 and the outflow into the ground 16 due to the hydraulic fracturing phenomenon, so that it is possible to apply a high preload to the pile tip ground 16.

Moreover, since the approximate value of the injection amount per pile can be grasped in advance, construction management becomes easy.

In Fig. b, the seal on the bottom of the gravel chamber 4 is intentionally omitted, but this is because the ground is normally stratified horizontally, and the ground in this part is horizontal around the vertical load to be added. This is because it is more likely to omit the allowance because it is more likely that the additional force is generated, the compaction is caused, and the tensile crack is not easily generated.

However, when there is a possibility that hydraulic fracturing may occur in the lower part, such as when there is a crack in the bad ground, a wrapping body that is a bottomed whole surface should be adopted.

"Effects of the Invention" Since the present invention is configured as described above,
The following effects are achieved.

(1) The injection cement milk can be easily managed and a high preload can be applied, and the pile supporting capacity can be improved.

(2) High friction (textile) between the pile tip and the ground side
As a result of the inclusion of the wrapping body 17, the two are integrated, and the effect of reducing the occurrence of tensile cracks 18 due to the hydraulic fracturing phenomenon is obtained.

[Brief description of drawings]

1 (a) and 1 (b) are explanatory views of the main constituent members of the present invention, usage diagrams, and FIGS. 2 (a) to 2 (g) are cast-in-place concrete piles using a reinforced cage with a gravel chamber with a pressure cell at the lower end. FIG. 3 is a procedure diagram of the construction procedure of FIG. 1 ... Drilling hole, 2 ... Bucket, 3 ... Reinforcing cage, 4 ...
Gravel chamber, 5 ... pressure cell, 6 ...
Spacer, 7 ... Steel plate, 8 ... Steel plate, 9 ... Grout pipe, 10 ... Through hole, 11 ...
Membrane, 12 ... Through hole, 13 ... Hook, 14 ... Tremy tube, 15
…… Concrete, 16 …… Supporting ground area, 17 …… Package,
18 ... Tensile crack, 19 ... Mounting hardware.

Front Page Continuation (72) Inventor Kyosuke Sato 2-5-14 Minamisuna, Koto-ku, Tokyo Inside the Takenaka Corporation Technical Research Institute (72) Inventor Osamu Hase 2-5-14 Minamisuna, Koto-ku, Tokyo Stock Company Takenaka Corporation Technical Research Institute (56) Reference JP-A-53-21806 (JP, A) JP-A-48-15309 (JP, A) JP-A-62-280416 (JP, A)

Claims (2)

(57) [Claims] 1. A rebar cage having a gravel chamber having a pressure cell for grouting pipes installed at the lower end has a water permeability coefficient of 1.0 × 10 ⁻¹ to 10 × 10 on the peripheral side or the peripheral side and the bottom of the gravel chamber. ^-1 Reinforced basket of cast-in-place concrete pile, characterized by being surrounded by a wrapping made of highly stretchable woven fabric using high strength synthetic fiber of about ¹ cm / sec. 2. The rebar cage according to claim 1, wherein the concrete is cast by a tremie pipe, high-pressure injection of cement milk after hardening of the concrete and hardening of the cement milk under pressure are performed. Construction method for cast-in-place concrete piles.