JPS6216285B2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) The present invention relates to a construction method for cast-in-place concrete piles carried out in the field of pile foundation work, and more specifically to a construction method that improves the concrete placing process. .

(Conventional technology) Conventionally, cast-in-place concrete piles have been constructed by inserting reinforcing bars into holes dug in the ground, inserting tremie pipes, and simply pouring ordinary concrete underwater through the tremie pipes. .

Next, the cast-in-place pile construction method described in Japanese Patent Publication No. 47-42085 relates to so-called expanded-bottom piles, in which an initial filler such as mortar is put into the bottom of the hole in a bucket, and then the bottom is expanded. The slime and the like are then mixed into the initial filling material, and then a tremie tube is inserted, fresh concrete is supplied below the initial filling material, and the concrete placing process is performed.

Next, in the case of the concrete casting method described in Japanese Patent Publication No. 52-27922, excavation is carried out by injecting a ground stabilizing liquid and a shielding liquid with a higher specific gravity, and after excavation, the shielding liquid is poured under the stabilizing liquid. It accumulates in layers. After that, when concrete is placed through a tremie pipe, the shielding liquid, which has a specific gravity lower than that of fresh concrete, maintains its position between the concrete and the stabilizing liquid, and the concrete and the stabilizing liquid do not come into direct contact. It is a construction method.

(Problems to be Solved by the Invention) (1) In conventional cast-in-place concrete piles constructed using general construction methods, the concrete at the head of the pile usually deteriorates over a length range of 50 cm to 100 cm. It is normal for the structure to have a considerable lack of strength in this area. The reason for this is thought to be as follows.

The concrete that first comes out of the tremie pipe is washed by the water in the hole (hole wall stabilizing liquid), and the concrete is dispersed and separated.

The slime that has settled at the bottom of the hole is rolled into the concrete.

Sediment from the hole wall falls and mixes into the concrete.

As the concrete rises through the hole, it crosses the reinforcing bars and entrains impurities attached to the reinforcing bars into the concrete.

Breathing of concrete.

Conventionally, as a method to deal with the reality of concrete deterioration at the pile head mentioned above, for example, as shown by the dotted line in Figure 3, the pile is built longer (higher) in the defective part where the strength is insufficient, and the concrete hardens. Afterwards, the defective parts were scooped out and removed, that is, the good quality concrete parts were exposed, and then the superstructure was poured. Therefore, the concrete material scraped off as defective parts is completely wasted, and the cost of scraping the concrete is also a completely negative cost, resulting in problems such as extremely poor workability and economic efficiency.

(Part 2) In the case of the cast-in-place pile construction method described in the above-mentioned Japanese Patent Publication No. 47-42085, the initial filler (mortar) is only used to prevent slime from accumulating at the bottom end of the pile due to bottom-expanding excavation. It is. In other words, with regard to the initial filling, deterioration of the pile cap due to the causes mentioned in (Part 1) above is unavoidable, and the work of scooping out the pile cap is naturally necessary. There were exactly the same problems as the construction method.

(Part 3) In the case of the concrete pouring method described in the above-mentioned Japanese Patent Publication No. 52-27922, a shielding liquid is interposed between the poured concrete and the stabilizing liquid. The aim is to provide a shielding liquid to prevent the bentonite contained in the concrete from reacting with fresh concrete and causing gelation, thereby protecting the stabilizing liquid and increasing its recovery rate. Therefore, it is unavoidable that the concrete will be washed with a shielding liquid consisting of an aqueous inorganic salt solution, dispersed, separated, and deteriorated, so post-treatment of scraping and removing defective pile caps after construction is essential. It is.

Therefore, the purpose of this invention is to create cast-in-place concrete piles of high quality so that the concrete exhibits a certain level of strength over its entire length.Therefore, there is no need to scoop out the top of the pile, which wastes concrete material. The object of the present invention is to provide a construction method for cast-in-place concrete piles that does not produce any problems and is excellent in construction method and economic efficiency.

A further object of the invention is to provide a method for constructing cast-in-place concrete piles that is technically easy to implement in much the same manner as conventional cast-in-place concrete pile construction methods.

(Means for Solving the Problems) As a means for solving the above problems, the method for constructing cast-in-place concrete piles of the present invention, as shown in the embodiment in the drawings, includes the following steps when constructing cast-in-place concrete piles: In particular, in the concrete pouring process, (a) At the beginning of concrete pouring, the content ratio of cement and water is increased and an appropriate amount of polymer flocculant is added to create concrete that is non-separable in water and has high fluidity. 5 is passed through the tremie tube 4 whose lower end is held at a constant height from the hole bottom (usually about 50 cm from the hole bottom) in an amount that at least wraps around the lower end of the tremie tube 4 (for example, the tremie tube 4 is (b) Continuously pour ordinary concrete 7 through the same tremie pipe 4. The structure consists of a step of pouring concrete 5, which is inseparable from water and has high fluidity, which was previously poured, until the upper surface thereof rises to a predetermined pile head height position.

(Function) After pouring a predetermined amount of highly fluid concrete 5, the same tremie pipe 4 is used to continue pouring ordinary concrete 7, so that the subsequently poured concrete 7 is placed below the previous highly fluid concrete 5. As the concrete sinks in and increases in volume, the highly fluid concrete 5 is pushed up and concrete placement progresses.
Therefore, so to speak, pre-cast highly fluid concrete 5
The post-cast regular concrete 7 is placed using the post-cast concrete 7 as a floating lid.
There is no opportunity for the liquid to come into contact with the pore wall stabilizer 6.

Therefore, this post-cast concrete 7 will never be washed away by water in the hole and dispersed or separated. In addition, most of the slime at the bottom of the hole is blown upward by an air cleaning method or the like before pouring the pre-cast high fluidity concrete 5, so even if the slime settles, the high fluidity that rises The concrete 5 is simply placed on the upper surface of the concrete 5 and is pushed up, and there is no risk of it getting caught up in the post-cast concrete 7. Furthermore, impurities attached to the soil or reinforcing bars from which the hole walls have collapsed may be mixed into the pre-cast concrete 5, but are almost never mixed into the post-cast concrete 7.

Therefore, there is almost no cause for deterioration of the post-cast ordinary concrete 7.

On the other hand, the pre-cast high fluidity concrete 5 has properties that prevent the concrete from separating and dispersing even if washed by water in the pores due to its inseparability in water, and also has a strong bonding force between concrete particles. Even if slime that floats and settles in the water, sediment that has collapsed from the hole wall, or impurities that have adhered to the reinforcing steel are mixed in, it exerts a resistive action that eliminates them and is extremely unlikely to entrain them. Therefore, the highly fluid concrete 5 that was poured first over the entire length
There is very little deterioration of the concrete piles, and it is possible to construct high-quality concrete piles with uniform strength as a whole, and there is no need to scoop out the pile heads at all.

(Example) Next, the present invention will be described with reference to illustrated preferred examples.

First of all, FIG. 1 shows that as the first step in the construction method of cast-in-place concrete piles according to the present invention, reinforcing bars 3 are inserted into holes 2 of the required depth dug in the ground 1, tremie pipes 4 are inserted, and tremie pipes 4 are inserted. The process is shown in which concrete 5, which is non-separable in water and has high fluidity, is being poured through pipe 4. This concrete 5, which is non-separable in water and has high fluidity, is not very effective and is uneconomical if poured in a larger amount than necessary, so it is poured only in the minimum necessary amount. As a guideline, at least tremie tube 4
Pour enough to cover the bottom edge of the concrete. Incidentally, at the beginning of concrete pouring, the lower end of the tremie pipe 4 is normally maintained at a height of about 50 cm from the bottom of the hole, and the above-mentioned underwater inseparable concrete 5
is cast to a height of about 30 cm above the lower end of the tremie pipe 4. If the amount of underwater inseparable concrete 5 is poured in such a way that it wraps around the lower end of the tremie pipe 4, then when the ordinary concrete 7 is poured subsequently, the underwater inseparable concrete 5 will be placed in the hole. The contact between the wall stabilizing liquid 6 and the post-cast ordinary concrete 7 is completely broken, and the submersible inseparable concrete 5 acts as a so-called floating lid that rises inside the hole 2 as the amount of ordinary concrete 7 placed increases. The effects of the above are reliably achieved.

By the way, the above-mentioned underwater non-separability, which is important for high fluidity concrete 5, means: (a) The degree of separation and dispersion of concrete in water is extremely small, and therefore concrete cannot be easily washed away by water. The property of preventing being exposed.

(b) Even if it comes into contact with slime, earth and sand, and other impurities, the bonding force between the particles in concrete is strong and they will not become entangled;
A property that prevents the overall quality of concrete from deteriorating.

It refers to the performance that includes the following. Furthermore, high fluidity means that, contrary to the above-mentioned inseparability in water, the concrete itself that comes out of the tremie pipe 4 can stand on its own even if the gap between the lower end of the tremie pipe 4 and the bottom of the hole 2 is small. It has the property of spreading well to the outer periphery.

Fluidity is such that when the gap between the lower end of the tremie pipe 4 and the bottom of the hole 2 is increased, there is no risk that the entire concrete column that comes out of the tremie pipe 4 and stands on its own will collapse and pile up in a heap.

It refers to the performance that includes the following.

Specifically, the composition of concrete 5 that is non-separable in water and has high fluidity as described above is such that the amount of cement per 1 m ³ of concrete is
The material composition is 400-600Kg, water 200-300Kg, sand 800-1000Kg, and polymer flocculant 0.15Kg-0.3Kg. That is, it is a concrete with a composition in which the content ratio of cement and water is increased and an appropriate amount of a polymer flocculant is added, and this concrete satisfies the above-mentioned properties of inseparability in water and high fluidity.

An example of the composition is shown below.

Cement 520Kg/m ³ Water 270Kg/m ³ Gravel 892/m ³ Sand 595Kg/m ³ Polymer flocculant 0.3Kg/m ³ (Sunpoly N-500 manufactured by Sankyo Kasei Kogyo Co., Ltd.) Slump: 25cm Compressive strength at 4 weeks of age :285Kg/m ^3By the way, the strength of concrete is generally determined by the weight ratio of water and cement, so if the content ratio of both cement and water is increased at the same time, there will be no change in the strength of concrete. However, the fluidity of concrete is mainly determined by the unit amount of water, that is, the water content ratio.

Therefore, the water-cement ratio in the above composition example is
270/520=51.9%, which is close to the water-cement ratio in ordinary concrete (used in civil engineering and construction work). Incidentally, the strength of the concrete in this composition example was 285 Kg/cm ² , which is also the same as the strength of ordinary concrete 7.

However, the unit water amount (270Kg/m ³ ) in the concrete mix in the above composition example is a large value compared to the unit water amount (170-200Kg/m ³ ) of normal concrete 7, so the fluidity of the concrete is very different. In other words, the unit water volume is 170
In the case of normal concrete of ~200Kg/ ^m3 , the slump of concrete is about 15-20cm, but in the same composition as above, it is 25cm.

Water inseparability, which is a feature of the present invention, is added by adding a polymer flocculant. The polymer flocculant functions as a viscosity agent, giving concrete the property of not separating or dispersing even when it comes into contact with water. However, when a polymer flocculant is added to concrete, there is a problem in that the fluidity of the concrete decreases. purpose is not achieved.

That is, although concrete has inseparability in water, it does not spread smoothly to the bottom of the pile because of its fluidity. In order to overcome such problems, the concrete 5 used in the present invention must have a larger unit water content than normal concrete. As mentioned above, the strength of concrete is determined by the water-cement ratio, so in order not to reduce the strength of concrete, the amount of cement must also be increased. Based on the above-mentioned grounds, the water-separable and highly fluid concrete 5 must contain a polymer flocculant and have an increased content ratio of cement.

Next, polymer flocculants have the function of flocculating and precipitating particles contained in water, and are widely used in wastewater treatment and the like. A polymer flocculant is characterized by its high molecular weight, and generally the higher the molecular weight, the stronger the flocculating effect. Generally, when a water-soluble polymer compound is added to water, the viscosity coefficient of the solution increases as the molecular weight of the polymer compound increases. Due to these properties, polymer flocculants have the effect of significantly increasing the viscosity coefficient of water and, by extension, the viscosity coefficient of concrete, even with a very small amount added.

Polymer flocculants are classified into cationic, nonionic, and anionic based on their properties, and nonionic or anionic polymer flocculants are preferable for use in the present invention. When added to concrete, cationic polymer flocculants have the effect of significantly lowering the strength of concrete, which is not preferable.

Next, Figure 2 shows the second stage of construction of cast-in-place concrete piles, which have the above-mentioned underwater non-separability and
The process is shown in which, after a predetermined amount of highly fluid concrete 5 has been poured, concrete 7 having a normal material composition is being poured through the same tremie pipe 4. As the amount of the conventional concrete 7 increases, the water-inseparable concrete 5 placed earlier acts like a floating lid that completely separates the hole wall stabilizing liquid 6 from the subsequent ordinary concrete 7. This prevents the ordinary concrete 7 discharged from the tremie pipe 4 from being washed away by the hole wall stabilizing liquid 6, and also prevents slime, earth and sand impurities from being mixed in.

Next, Figure 3 shows the completed stage of construction of cast-in-place concrete piles. That is, normal concrete 7
is poured into the hole 2 until the upper surface of the underwater inseparable concrete 5 rises to a predetermined pile head height position, in the case of the illustrated example, to the ground level.

In the case of the illustrated example, for convenience of explanation, the boundary between the underwater inseparable concrete 5 and the normal concrete 7 is shown clearly divided, but in reality, such a boundary or division does not occur. , the two concretes 5 and 7 are intimately blended and integrated, and a high-quality cast-in-place concrete pile that is homogeneous over its entire length is completed.

(Effects of the Invention) As described above in detail in conjunction with the examples, the method for constructing cast-in-place concrete piles of the present invention is to form the head of the pile with concrete that is non-separable in water and has high fluidity. Formed by 5. Even when the concrete 5 is washed with the hole wall stabilizing liquid 6, it does not disperse or separate, and since the inclusion of slime and the like is avoided as much as possible, there is almost no deterioration in quality. Also,
In the subsequently poured ordinary concrete 7, the above water-inseparable and highly fluid concrete 5 acts as a floating lid to prevent contact between the concrete 7 and the hole wall stabilizing liquid 6, and It also prevents contamination by dirt, slime, etc.

Therefore, the finished cast-in-place concrete pile is of good quality, with the concrete 5 and 7 exhibiting a certain level of strength over its entire length. Therefore, unlike the conventional method, it is not necessary to remove the head of the pile over a certain length, and there is no cost for scooping, and there is no waste of concrete material due to scooping. In addition, it is not necessary to build long piles in anticipation of plowing. Therefore, the workability and economic efficiency are very good. In other words, although concrete 5, which is non-separable in water and has high fluidity, is slightly more expensive than ordinary concrete 7, since the amount used is small, the overall cost can be significantly reduced and the construction period can be shortened. It is.

Furthermore, the method for constructing cast-in-place concrete piles of the present invention requires only pouring a certain amount of water-inseparable and highly fluid concrete 5 before pouring ordinary concrete 7. No special technology is required, and it can be easily carried out using the same level of technology as conventional construction methods, using exactly the same method, and with the same construction efficiency.

[Brief explanation of the drawing]

1 to 3 are cross-sectional views showing the main steps in the method of constructing cast-in-place concrete piles according to the present invention.

Claims (1)

[Scope of Claims] 1. The concrete placing process for cast-in-place concrete piles consists of: (a) At the beginning of concrete placing, the content ratio of cement and water is increased and an appropriate amount of polymer flocculant is added. Separable and highly fluid concrete 5 is poured into the bottom of the hole through a tremie tube 4 whose lower end is held at a constant height from the hole bottom in an amount that at least wraps around the lower end of the tremie tube 4. (b) Continuously, the upper surface of the concrete 5, which is inseparable from water and has high fluidity, is raised to a predetermined pile cap height position, in which ordinary concrete 7 was first cast through the tremie pipe 4. A construction method for cast-in-place concrete piles, which is characterized by the following steps: