JPS63315724A - Execution work of cast-in-place concrete pile with high yield strength - Google Patents

Abstract

PURPOSE:To obtain the high holding force by executing the works to make the required ground into the improved ground until a specific depth and placing concrete after excavating a pile hole within range of the improved ground. CONSTITUTION:The ground 1 is stirred until a specific depth, but, at the same time, the cement slurry is impregnated into the stirred ground and is stirred to form the improved ground 4. Then, after excavating a pile hole 2 within range of the improved ground, concrete 5 is placed into the pile hole 2 to form a concrete pile having about 1/2 diameter of that of the improved ground.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a construction method for cast-in-place concrete piles that are constructed on-site, and more particularly, the ground on which the piles are to be constructed is improved in advance to accommodate excavation. This article relates to a construction method for high-strength cast-in-place concrete piles that has been devised to eliminate the adverse effects of loosening and generate large pile bearing capacity.

Conventional technology (1) Regarding the construction method of cast-in-place concrete piles, so far there have been no slime removal methods, concrete placement techniques,
Numerous improvements and innovations have been made to the management of drilling mud, making great progress and making it highly reliable.

However, the technology for preventing the decline in pile bearing capacity due to the loosening of the ground due to drilling is still limited to preventing boiling caused by muddy water. By the way, when a pile hole 2 is excavated in the ground 1111 as shown in Fig. 4, the ground around it in the area indicated by the dotted line becomes loose. 3 in the figure is muddy water.

(2) As an improvement measure for the above-mentioned loosening of the ground, the pile tip treatment method described in Japanese Patent Publication No. 55-50132, Japanese Patent Publication No. 58-4885, and Japanese Patent Publication No. 60-58335 is to A ready-made tubular body with a shoe block attached to the tip is inserted into it, and the shoe block is first pushed into the tip j1 of the bottom of the excavation hole! It is noteworthy that the pile was compacted and solidified material was then placed on top of the shoe block to increase the pile supporting capacity.

Problem to be solved by the present invention (I) Regarding the bearing capacity performance of cast-in-place concrete piles, the properties of the ground that has loosened due to drilling are evaluated, and the strength that the ground originally had was lost. Underestimated due to condition.

For example, in the case of the Tokyo gravel layer, according to current standards, the apparent ultimate bearing capacity is estimated to be 750 tons/m2, but the true ultimate bearing capacity of this ground is 4000 tons.
It is estimated that the area will not be less than 7m2. This is because, depending on the loading test, the ultimate value is still not accurately recognized.

(IT) By the way, in conventional cast-in-place concrete piles, the rigidity of the ground at the tip of the pile is smaller than the rigidity of the friction force on the circumferential surface of the pile. For this reason, the reality is that it is not clear whether to expect the peripheral surface friction force, the pile tip support force, or how to evaluate both.

(III) Next, the main causes of the head difference between the design bearing capacity and the actual bearing capacity of current cast-in-place concrete piles,
The reasons include the following:

(1) Effects of slime.

(2) Loosening of the ground due to the unloading of the overburden weight associated with excavation.

(3) Differences in rigidity in the circumferential friction of the pile and the bearing capacity of the ground at the tip of the pile.

Generally speaking, conventional cast-in-place concrete piles make use of the naturally available ground conditions in poor conditions, which makes them unreasonable.

(IV) In this regard, the above-mentioned Special Publication No. 55-50132
The pile tip treatment method described in the publication is logical and effective in increasing the pile bearing capacity because the pile tip ground, which has been loosened by excavation, is compacted again by pushing in shoe blocks. It can be said.

However, even small cast-in-place concrete piles have a diameter of about 1000 mm. φ3000 for large ones
There are quite a few of them. However, it would be extremely difficult to manufacture a ready-made tubular body with such a large diameter, which is an unmet requirement of the pile tip treatment method, and even if it were possible to manufacture it, it would be impossible to use a shoe block with such a large diameter in the ground. There is a problem with the possibility of implementation, as there is still no means to push the material sufficiently to obtain the compaction effect.

Means for Solving the Problems As a means for solving the problems of the above-mentioned prior art, the method for constructing high strength cast-in-place concrete piles according to the present invention is implemented as shown in FIGS. 1 to 3 of the drawings. As shown in the example, the target ground 1 is constructed into improved ground 4 to a predetermined depth using a deep mixing method in which cement slurry made of cement-based material is injected into the soil, mixed with the soil, and solidified, and the area of the improved ground 4 is The process consisted of excavating a pile hole 2 (or a trench for a continuous underground wall) of a predetermined depth inside the pile and pouring concrete 5.

The improved ground 4 that has been constructed has good water-stopping properties, and its strength and rigidity are higher than those of the original ground. For example, the unconfined compressive strength q in clayey soil is 30-40 kgf/c
m2, sand, gravel 300 kgf/cI1
It will be more than 2.

It is easy to adjust the strength appropriately so that it does not interfere with later excavation of the pile hole, and of course, by improving the strength from the original plate, the problem of loosening due to excavation can be prevented.

Therefore, a cast-in-place concrete pile constructed by pouring concrete 5 into a pile hole 2 excavated within the improved ground 4 has a large rigidity of circumferential friction force and a large rigidity of the tip ground, so the permissible pile support is Power is current 250ton/m
It is possible to easily achieve more than twice that of 2.

Moreover, since pile hole 2 is excavated within the improved ground area, dry excavation is possible compared to conventional methods of underwater excavation and underwater concrete, making concrete placement easier and allowing for lower stress levels than before. 1/4 of F c to 1/4
3 F c can be advantageously achieved.

Example Next, the embodiment shown in the drawings will be explained.

First, Fig. 1 shows a stage in which cast-in-place concrete piles have been constructed on the improved ground 4 to a predetermined depth for the target site @l where cast-in-place concrete piles are to be constructed.

In the construction of the improved soil 4, a stirring element 8 is installed at the tip of a shaft 7 that is rotatably driven by a kneader 6 installed on the ground, and this stirs the soil i1 to a predetermined depth and forms a cement-based slurry made of cement-based material. By using the so-called deep mixing method (however, this is not limited to this method), in which soil is poured into stirred soil and thoroughly kneaded and hardened, so-called soil columns are gradually wrapped to form a single lumpy solid. be done.

The improved ground 4 is formed to have a diameter I)+1 that is approximately twice the diameter D of the pile hole 2 to be excavated (that is, the outer diameter of the cast-in-place concrete pile) as shown in FIG. In addition, the depth (H + h) of the improved land @ 4 is determined by adding an extra length of about 1.0 to 1.5 times the diameter of the pile hole 2 to the depth H of the pile hole 2, as shown in Figure 2. formed to the added depth. This is to prevent as much as possible the adverse effects of loosening of the ground gills due to excavation.

In addition, as a matter of course due to its nature as a support pile, the lower end (supporting layer part) of the improved ground 4 is treated with a method such as increasing the concentration of the cement slurry to be injected, for example.
It is assumed that the pile exhibits a high strength of 0 to 50 kg/c+s2, and the strength of the friction portion of the pile circumference above this is improved to be as low as, for example, 4 to 5 kg/7 cm2, thereby increasing the bearing capacity of the pile tip. It is said to be large and to facilitate later pile hole excavation.

Figure 2 shows the area (center area) of the improved ground 4 constructed as described above after it hardens and develops strength.
Figure 2 shows the stage in which pile hole 2 was excavated in the same manner as in the previous construction method for cast-in-place concrete piles.

The pile hole 2 can be excavated by dry excavation because the improved ground 4 is watertight.

FIG. 3 shows the stage at which concrete 5 is poured into the pile hole 2 excavated as described above to complete construction of the cast-in-place concrete 1 pile. Note that when dry excavation is performed as described above, concrete placement is easy because there is no need to use underwater concrete. Illustrations of reinforcing bar scraps, etc. are omitted.

In the case of this cast-in-place concrete pile, since it is constructed within the area of the improved ground 4, there is no problem of loosening of the ground due to excavation of the pile hole 2. In addition, the rigidity and strength of the improved ground 4 have been improved by several orders of magnitude compared to the original ground, so the allowable bearing capacity of the constructed cast-in-place concrete piles is more than twice that of conventional ones. It can be expected to provide support.

Different Embodiments (Part 1) The above embodiments relate to straight piles with uniform diameters, but the same applies to expanded-bottomed piles in which the diameter of the tip of the pile is enlarged.

(Part 2) It can be applied not only to cast-in-place concrete piles, but also to the construction of continuous underground walls. That is, it can be carried out by first constructing the improved soil 4 on the ground where the continuous underground wall is to be constructed, and after the improved soil develops strength, excavating a trench for the underground wall within the improved soil area.

As described in detail in conjunction with the examples above and beyond the effects of the present invention, the method for constructing high-strength cast-in-place concrete piles according to the present invention includes the construction of improved soil 4 as a pretreatment in addition to the conventional construction procedure. Since it is just an addition, it can be easily implemented using the same mature technology level as before.

Furthermore, there is no problem of loosening of the ground due to excavation, and the strength and rigidity of the improved ground 4 has been greatly improved compared to the original ground, so the pile tip and the friction area on the pile circumferential surface are Because of the increased strength and rigidity, the combined effect of both makes it possible to provide high-strength cast-in-place concrete piles that can be expected to have an allowable pile bearing capacity that is more than twice that of the current pile.

[Brief explanation of the drawing]

Figures 1 to 3 are cross-sectional views showing the important steps of the high-strength cast-in-place concrete pile construction method according to the present invention, and Figure 4 is a cross-sectional view at the stage where a pile hole is excavated using the conventional construction method. . 3111A Figure 4

Claims (1)

[Scope of Claims] [1] The target ground (1) is constructed on improved ground (4) to a predetermined depth, and pile holes (
A method for constructing high-strength cast-in-place concrete piles, characterized by excavating 2) and pouring concrete (5). [2] Improved ground (4) described in claim 1
The improved construction method uses a deep mixing method in which cement slurry made from cement-based materials is injected into the soil and mixed with the soil to harden it, forming an improved ground in the form of a lumpy solid, and increasing the strength of the support layer. A construction method for high-strength cast-in-place concrete piles that is characterized by: