JPS61290120A - Construction work of underground continuous wall or in-situ pile - Google Patents

Abstract

PURPOSE:To form a reinforced layer in part of usual concrete layer by a method in which a tremie tube is led to a given depth in a pit, correspondingly to the tip position of the tremie tube, and concrete containing an admixture for underwater concrete is placed through the tremie tube. CONSTITUTION:A tremie tube 2 is inserted into a pit 1 and set in such a way that the tip of the tube 2 is positioned 20-30cm above from the bottom of the pit 1. Concrete 4 to which is added segregation-reducing agent (or plasticizer) composed primarily of water-soluble cellulose-ether, e.g., alkyl cellulose, etc., is placed through the tube 2. After the tip of the concrete 4 reaches 2.5-3m above from the bottom of the pit 1, the tube 2 is pulled up until the tip of the tube 2 is pulled up 0.5-1 m below the upper end of the concrete 4, and concrete 5 without the segregation-reducing agent is placed. Further, drawing up the tube 2, the concrete 5 is placed to replace mud water 3.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Life) The present invention relates to a construction method for an underground continuous wall or cast-in-place pile.

(Conventional technology) In the 4-4 construction method for underground Ml and cast-in-place piles, a tremie pipe is inserted into an excavated vertical hole, concrete is poured while the tremie pipe is pulled up, and the concrete is poured into the vertical hole. A commonly used construction method is to replace the muddy water that fills the ground with walls and piles underground.

In this type of construction method, the concrete is placed in muddy water, so there is a drawback that the concrete tends to separate.Especially, the concrete placed in the initial stage is supplied to the bottom from a certain height from the bottom of the hole. Therefore, it was easy to separate.

Therefore, the concrete at the bottom of the hole becomes uneven and weak in strength, and a mixture of separated concrete and slime accumulates at the bottom of the hole, reducing the supporting capacity of the structure against vertical loads and reducing the amount of settlement. This could lead to an increase.

In addition, underground walls and cast-in-place piles are now being installed at greater depths.
They tend to be longer. For this reason, prestressing has been introduced with the aim of increasing the bearing capacity and reducing the amount of displacement when a load is applied, improving safety, and reducing construction costs. It is considered to improve the strength and deformation performance against.

However, as mentioned above, since concrete is easy to separate due to muddy water, the concrete may not wrap around the anchoring part of the prestressing steel material sufficiently, and if separated concrete is interposed in the anchoring part, Due to the introduction of prestress, there are problems such as excessive leap deformation in the concrete at this anchorage part, and the effect of introducing press 1-less cannot be fully realized, so it is recommended to introduce prestress into this type of construction method. has not actually been adopted.

(Problems to be Solved by the Invention) Conventional methods for solving the above-mentioned drawbacks of the prior art include improving the tremie pipe itself and improving the mix of concrete.

The former is a method such as a plunger type or bottom opening type, in which the initial concrete supplied from the tip of the tremie tube is poured so as to prevent it from separating with muddy water as much as possible. However, even if these methods are used, it is impossible to sufficiently suppress separation because the poured concrete is always in contact with muddy water.

As one of the latter methods, there is a method of mixing a large amount of cement in the mix design of concrete to increase the fluidity of concrete and increase the strength after hardening. However, even with this method, it is difficult to significantly reduce the separation of concrete, and the heat of hydration increases due to the increase in cement density, which causes cracks to occur after hardening. It is not a strategy.

There is also a method of adding a high-performance water reducing agent or a fluidizing agent to concrete to prevent a decrease in the strength of concrete and improve its fluidity. However, this is not a fundamental solution to preventing concrete from separating underwater.

On the other hand, recently, when concrete is placed underwater in construction methods for offshore structures, an admixture for underwater concrete is sometimes added to the concrete. It is easy to imagine adding this underwater concrete admixture to concrete used in construction methods for underground walls and cast-in-place piles. However, since the cost of this underwater concrete admixture is extremely high, it is not actually applied.

This invention has been made in view of the above-mentioned current situation, and its purpose is to prevent concrete damage, especially at the bottom of a hole or at the anchorage of prestressed steel materials, when pouring concrete for an underground continuous wall or cast-in-place pile. The purpose is to partially form a uniform and strong layer in this area by preventing separation.

(Means for Solving the Problems) In order to achieve the above object, the present invention has a construction method in which a tremie pipe is inserted into an excavated vertical hole and concrete is poured while the tremie pipe is pulled up. Concrete added with an admixture for underwater concrete is poured through the tremie pipe at a predetermined depth in the vertical hole according to the position of the tip of the tremie pipe along with the concrete, forming a reinforcing layer in a part of the normal concrete layer. It is characterized by

(Embodiments) Hereinafter, preferred embodiments of the present invention will be described in detail using the drawings.

In addition, the admixture for underwater concrete used in the present invention in the following examples is intended to prevent material separation of concrete underwater and improve fluidity, and is suitable for casting concrete structures with high strength and strong adhesive strength underwater. It is an admixture developed for the purpose of
These include separation reducing agents whose main component is water-soluble cellulose ether such as hydroxyallylalkyl cellulose.

Concrete mixed with this type of separation-reducing agent has little separation in water, and is used for underwater construction of structures in oceans and rivers, and its effectiveness has been confirmed.

FIG. 1 shows a first embodiment of the invention. The purpose of this example is to improve the quality of concrete at the tip of an underground continuous wall or cast-in-place pile, and to increase the supporting capacity of the structure against vertical loads.

First, in (a), tremie tubes 1 to 2 were inserted into the vertical hole 1 that had been drilled in advance, and the tremie tube 2 was installed so that the tip of the tremie tube 2 was located 20 to 3 Qcm above the bottom of the hole. Concrete 4 containing a bond and a separation reducing agent is poured. By this pouring, the concrete 4 replaces the muddy water 3 filling the bottom of the hole. The tip of concrete 4 is 2.5 to 3. After confirming that the tip of the tremie pipe 2 is 0.5 to 1.5 mm above the upper end of the concrete 4, as shown in FIG. Then, concrete 5 with no segregation reducing agent added, that is, concrete 5 of a composition used in conventional pouring, is poured. This state is shown in <C>.

As a result, the concrete 4 at the bottom of the hole and the concrete 5 of the conventional mix have a concave distribution according to the shape discharged from the tremie pipe 2, and in this state, when the concrete 5 is poured while pulling the tremie pipe 2 upward. , all the muddy water 3 between the vertical holes 1 will be replaced with concrete 4.5. When the concrete 4 and 5 harden, there is little separation in the water from the bottom of the hole to a predetermined height position C.
Since it becomes a high-strength reinforcing layer, the resulting structure has a significantly increased supporting capacity against vertical loads.

FIG. 2 shows a second embodiment of the invention. In the drawings, the same parts as those in the embodiment described above are designated by the same reference numerals.

In this example, the fixing part of the prestressed steel material is
The purpose is to hold it firmly within the country.

First, in <a>, a prestressed steel material 10 is placed in the vertical hole 1 in an amount required by the design, and the anchoring part 12 with J3 at the tip thereof is located at a predetermined height above the bottom of the hole. There is. Contrary to the above embodiment, ordinary concrete 5 is poured through the tremie pipe 2, and this concrete 5 is 1.0 to 1.5 m below the lower part of the anchoring part 12.
After confirming that it has risen to the bottom using a measuring method or the like, raise the tremie pipe 2 so that the tip thereof is 1.0 to 1.5 m below the surface layer of the concrete 5. Next, as shown in (b), if the concrete 4 to which the separation reducing agent has been added is cast through the tremie pipe 2, the anchoring portion 12 will be placed in the concrete 4.
It will be buried within the layer.

This concrete 4 is 2°0 to 2° from the top of the anchoring part 12.
．． After confirming that the tremie pipe 2 is located above the surface layer of the concrete 4 using a measuring scale, etc.
．． 5-1. Raise it to below OIQ. Next, as shown in (C), the conventional concrete 5 is replaced and poured on top of the layer of concrete 4. Thereafter, the tremie pipe 2 is gradually pulled up and the concrete 5 is poured into the vertical hole.

As a result, 11a reinforced with the separation reducing agent is distributed in a concave shape, sandwiched between 5b+ of the lowest layer of concrete and Mhz of the upper layer of concrete, and the anchoring portion 12 is buried within the reinforcing layer a. That will happen.

Therefore, in J3 of this embodiment, the concrete wraps around the anchoring part of the prestressed structure reliably, and creep deformation in this part is reduced.

In the second actual fMFA as well, it is of course possible to pour the concrete 4 mixed with the separation reducing agent to the bottom of the hole below the press 1 to the fixing portion 12 of the steel material 10.

(Effects of the Invention) As explained in detail in the embodiments above, in the method of constructing underground continuous walls or cast-in-place piles according to the present invention, it is particularly important to apply this method to parts that require uniformity and high strength. By pouring concrete containing an admixture for underwater concrete, reinforcement layers can be formed at the necessary locations within the normal concrete layer, making it particularly suitable for constructing deep and long underground structures. Furthermore, since expensive admixtures for underwater concrete are not used throughout the system and are used only where necessary, the increase in costs can be kept to a necessary minimum. Further, in the present invention, since the anchoring portion of the steel material for introducing prestress can be reinforced, prestress can be introduced into this type of construction method.

[Brief explanation of drawings]

Figures 1 (a), (b), and (c) are cross-sectional explanatory diagrams showing the first embodiment of the construction method according to the present invention in the order of steps, and Figures 2 (a), (b), and (c) are FIG. 7 is an explanatory cross-sectional view showing a second embodiment of the invention in order of steps. 1... Tremy pipe 4... Concrete with admixture added for underwater concrete 5... Normal concrete 10...
・・Prestressed steel material 12 ・・・Fixing department Patent applicant Obayashi Corporation Representative Patent attorney - Shikiken Ken No. 1 (a) (b) (C)

Claims (4)

[Claims] (1) In a construction method in which a tremie pipe is inserted into an excavated vertical hole and concrete is poured while the tremie pipe is pulled up, the tremie pipe is inserted into the water at a predetermined depth within the vertical hole depending on the position of the tip of the tremie pipe. A construction method for underground continuous walls or cast-in-place piles, which is characterized by pouring concrete containing a concrete admixture to form a reinforcing layer in a part of the normal concrete layer. (2) Concrete to which the above-mentioned underwater concrete admixture has been added is poured into the bottom of the vertical hole, and then ordinary concrete is poured into the upper layer thereof. Construction method of underground continuous walls or cast-in-place piles. (3) The concrete according to claim 1, characterized in that concrete to which the above-mentioned admixture for underwater concrete is added is poured into the fixed part of the steel material for introducing prestress placed in the vertical hole. A method of constructing continuous walls or cast-in-place piles. (4) The method for constructing an underground continuous wall or cast-in-place pile according to any one of claims 1 to 3, wherein the admixture for underwater concrete is a water-soluble cellulose ether.