JPH0521530Y2 - - Google Patents

Description

[Detailed description of the invention] [Field of industrial application] The present invention relates to a ready-made concrete pile, and more specifically, to a ready-made concrete pile that can increase the bearing capacity of the lower end of the pile in the embedding method. .

[Conventional technology]

Conventionally, when a ready-made pile is buried in a hole excavated to a predetermined depth underground, various attempts have been made to improve the supporting force at the tip of the pile.

For example, in Japanese Patent Application Laid-Open No. 57-89020, bags are fixed to multiple locations on the outer circumferential surface of a ready-made pile, and cement milk or the like is press-fitted into the bags to inflate the bags, thereby increasing the circumferential surface of the pile. In order to increase the frictional force and pressurize cement milk etc. into the bags fixed to the bottom of the pile to improve the supporting force of the tip of the pile, bags are placed at multiple locations on the outer circumference of the pile and at the bottom of the pile. Ready-made piles with fixed bodies have been proposed.

In addition, Japanese Patent Application Laid-Open No. 57-24718 discloses a method for applying a so-called drain construction method in which water is drained from the surrounding ground by expanding the bags. A metal or plastic tube is shown with the entire surface fixed.

In light of this conventional construction method, which has been commonly used for burying ready-made piles, in which an enlarged section is provided at the bottom of the excavated hole and a hardened material such as cement milk is created there to increase the supporting capacity of the tip, the outer periphery of the pile is An attempt has been proposed to cover the bottom of the pile with a bag made of water-permeable cloth to prevent excavated soil from entering, and to expand and form a stronger hardened material on the bottom of the pile. ing.

[The problem that the idea attempts to solve]

However, although the pile shown in Japanese Patent Application Laid-open No. 57-89020 uses a bag, the supporting capacity at the tip of the pile is not sufficiently demonstrated, and it is not actually used for pile construction. There was nothing wrong with that.

Similarly, even if the structure shown in JP-A No. 57-24718 is applied to burying ready-made piles in a hole excavated to a predetermined depth underground, the structure shown in JP-A No. 57-24718 may be applied to a case where a ready-made pile is buried in a hole excavated to a predetermined depth underground. Regardless, sufficient supporting capacity at the tip of the pile cannot be exerted in a stable state.

The inventor of the present invention has investigated and analyzed various reasons why the above-mentioned conventional technology does not provide sufficient support at the tip of the pile even though the bag body is attached. The cause of this problem is that when burying a pile in an excavation hole, the bag that was fixed to the pile in a loose state at the bottom of the pile was damaged, and the bag was damaged by press-fitting cement milk, etc. into the bag. The bag tends to tear when it expands. Even if the bag is not damaged, when the bag expands due to the press-fitting of cement milk, etc. into the bag, an uplifting force is generated on the stake, so a large reaction force is placed on the top of the stake to prevent the pile from uplifting. It is necessary to apply force, but if the reaction force is too large, the bag at the bottom will not be able to inflate. Therefore, it is necessary to weaken the reaction force a little and allow the pile to float a little during construction, but even in that case, the side bags will also expand downwards of the pile, so the lateral expansion is uncertain. Therefore, it is difficult to ensure a stable cross-sectional area of the hardened material inside the bag (i.e., to control the lateral diameter of the inflated bag to a desired value), and the bearing capacity of the pile tip increases with each construction. This has the disadvantage that the stable tip support required for piles cannot be ensured due to large variations in the bearing capacity.

In addition, the second cause is insufficient adhesion between the hardened material obtained by press-fitting into the bag and the pile, and the bearing capacity of the tip of the pile is less than the bearing capacity expected due to the ground, the material of the pile, etc. The present inventor discovered that the attachment portion between the pile and the hardened body breaks down before reaching this point, resulting in a lack of actually measured bearing capacity.

The purpose of the present invention is to provide a ready-made pile that can stably provide a large tip supporting force when buried in a hole excavated to a predetermined depth underground.

[Means to solve the problem]

In the present invention, only the outer peripheral side surface of the lower part of the pile is covered by a bag body whose upper and lower ends are fixed to the pile, and an uneven part is provided on the outer peripheral side surface of the lower end portion of the pile covered by the bag body. This is a ready-made concrete pile that is characterized by:

The pile body needs to have approximately the same physical properties as a hardened material such as cement milk, and in this invention, it is a concrete pile. In this way, when used as concrete piles, the physical properties are almost the same as those of the hardened foot protection material, so
When a load such as an upper load is applied to the pile, the stress transfer from the concrete pile to the hardened foot hardening material becomes smooth, and the particles of the hardened foot hardening material penetrate into the coarse surface of the concrete pile, creating a high adhesion force. I can demonstrate it.

The irregularities provided on the outer periphery of the pile in the present invention can increase the adhesion between the hardened material (so-called enlarged part) that is expanded from the periphery of the pile obtained by press-fitting cement milk, etc. into the bag, and the pile. If possible, it is sufficient,
There are no particular limitations on the shape, pitch, number, etc. The method of providing this unevenness on the outer circumferential surface of the pile is relatively easy, by providing multiple ring-shaped steel members in the formwork or providing multiple convex protrusions when manufacturing concrete piles. It is possible.

The bag of the present invention should not be attached so as to cover the entire outer periphery of the pile along with its bottom, but should be attached only so as to cover the outer periphery of the pile, with the upper and lower ends of the bag fixed to the pile as shown in Figure 1. By press-fitting a hardened material such as cement milk into the bag through an injection tube, the bag is expanded and expanded in the lateral direction.

If the bag is placed only on the outer circumferential surface of the pile, covering the irregularities formed on the outer circumference of the pile, and both ends of the bag are fixed to the pile using bands, etc., the bag will By covering the cured product, the cured product can be made homogeneous without being contaminated with soil or the like.

At this time, if the bag is attached to cover the tip of the pile, even if there are irregularities on the surrounding surface of the pile, the bag will be present at the bottom of the pile as described above, so when burying the pile or reacting to the pile. When a force is applied, the bag may break or become unable to inflate, or even if it is able to inflate, the lateral diameter varies depending on the construction, resulting in an unstable value.
It becomes impossible to obtain the stable and large bearing capacity required of piles.

(Example) The present invention will be described below with reference to an example shown in the drawings.

First, as shown in Figure 1, ring-shaped unevenness 2 with a depth of 1 cm and a width of 10 cm was provided at a pitch of 20 cm on the outer peripheral side of the lower part of a concrete pile, with a diameter of 350 mm and a length of 2 m.
created a pile.

When cement milk is poured into the lower end of the pile body 1, the outer diameter of the enlarged part is 580 mm and the length of the enlarged part is 1 m.
The upper and lower ends of the bag body 4, which can be used as a cured body, were fastened together with a band using an adhesive to form a fixed part 5.

For comparison, a prefabricated concrete pile was created as a comparative example under similar conditions, except that a conventional pile with a smooth surface and no irregularities on the outer peripheral surface of the pile was used as the pile body.

After burying the piles of Examples and Comparative Examples in which the bag was attached only to the outer peripheral side of the lower part of the pile in a hole drilled to a predetermined depth underground, the pile was inserted into the bag using the injection pipe 3. Cement milk with a water-to-cement ratio of 67% was injected in an amount equivalent to enough for the bag to swell laterally, but no lifting of the stakes was observed, and the bag was able to reach the desired diameter due to the hardening of the cement milk. It was fully swollen.

On the other hand, two test specimens were prepared in which the piles according to the embodiment of the present invention and the piles according to the comparative example were each prepared, and cement milk was poured into the piles while standing vertically on the ground to form an enlarged part. Twenty-eight days after formation, the steel pipe 7 with an inner diameter of 600 cm shown in Fig. 2 was inserted into an artificial ground covered with sand 8, and the push-out shear failure between the hardened cement milk 6 and the pile was measured.

As a result, the shear strength (value obtained by dividing the shear failure load by the contact area) of the pile of the example of the present invention was 12.5 kg/
cm ² , whereas in the case of the comparative example it was 5 Kg/cm ² , which is 2.5 times higher in the example than in the comparative example.

If shear failure occurs between the hardened cement milk 6 and the pile, only a low value can be expected for the bearing capacity of the pile. The stronger the shear strength between the hardened body No. 6 and the pile, the higher the bearing capacity of the pile.

Furthermore, in order to confirm the effect of only the irregularities on the outer periphery of the lower part of the pile, we investigated the piles used in the above examples that do not have a bag body, and the conventional piles that have a smooth surface and do not have a bag body. An experiment was conducted to compare the supporting capacity.

First, as shown in Figure 3, the ground is
Excavation was expanded to 580 mm and depth of 1 m, and the cement milk used in the above example was injected into the expanded excavation hole 9. Immediately, the piles with the above-mentioned uneven portions and the conventional piles with smooth surfaces were drilled. It was inserted into the borehole. The amount of cement milk injected into the borehole was set so that it would not overflow onto the ground surface when the pile was inserted. Furthermore, the bottoms of the piles were closed so that the cement milk supported the piles only from the outer circumferential surface of the piles, and then the piles were inserted into the excavated holes.

After 28 days, these piles were dug out of the ground and subjected to a push-out shear test in the same manner as in the previous example in the state shown in FIG.

As a result, the shear strength of the former is 7.1Kg/cm ² and the latter is 4.5Kg/cm ² , and the shear strength of the former is 1.6 of the latter.
The shear strength itself was only twice as high, which was lower than the 2.5 times the value of the example and comparative example in which the bag was attached, and the shear strength itself was also low.

[Effect of idea]

By having the above structure, the pile of the present invention has the following features:
It has the following effects. The bag does not cover the entire outer periphery of the pile, including the bottom, but only the outer periphery of the sides, so when buried in a hole drilled to a specified depth underground, there is no harmful damage to the bag, and the cement inside the bag does not. Even when milk is press-fitted, the bag expands only in the lateral direction without causing the pile to lift up, and the bag expands stably to the desired diameter with enough cement milk in it to reach the desired diameter. An enlarged portion is formed.
An uneven portion is formed on the side surface of the pile body, and since the pile is a concrete pile and a bag body is attached, the shear strength between the hardened cement milk and the pile is increased. Due to the above-mentioned effects, a high supporting force unimaginable in the prior art can be stably obtained.

[Brief explanation of drawings]

Figure 1 is a partially cutaway front view of the bag body expanded with cement milk, Figure 2 is a cross-sectional view of the bag during a push-out shear test, and Figure 3 is a cross-sectional view of a pile in a comparative example. . 1...Pile body, 2...Irregularities, 3...Injection pipe, 4...
...Bag body, 5...Fixed part, 6...Cement milk,
7...Steel pipe, 8...Sand.

Claims (1)

[Scope of utility model registration request] Only the outer peripheral side surface of the lower part of the pile is covered by a bag body whose upper and lower ends are fixed to the pile, and an uneven part is provided on the outer peripheral side surface of the lower end portion of the pile covered by the bag body. Ready-made concrete piles.