JPH011823A - Root hardening method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for cementing concrete piles, and is used in the industrial field of foundation pile installation.

(Prior Art) Conventionally, when piles are buried underground, a construction method is known in which a foot protection is constructed at the bottom of the pile hole in order to ensure the connection between the lower end of the pile and the supporting ground.

In this method, a part (expanded bottom part) with a diameter larger than the diameter of the pile hole is formed at the bottom of the pile hole, cement milk is poured into this part or concrete is poured, and the part is integrated with the lower end of the pile. hardened (for example, JP-A-61-10625).

(Problems to be Solved by the Invention) In the conventional foot protection method described above, when the piles and the supporting ground are connected using cement milk, there is a problem in that there is a difference in strength between the upper and lower parts of the foot protection part. In addition, when injected into a hole, it may be diluted by water in the supporting ground, causing variations in strength and tending to reduce the overall strength. Furthermore, pouring concrete not only requires a concrete pump, but also suffers from a decrease in strength due to water dilution.

In addition, when a load is applied to the pile, the foot protection part that is located between the ground and the pile and connects them tends to penetrate into the hollow part of the pile. Measures such as installing closed iron plates were also necessary.

On the other hand, the most common supporting layer is overwhelmingly the sand and gravel layer, and when cement milk (root hardening solution) is injected into this layer, the milk tends to permeate through the gaps and escape. In particular, construction was often impossible in the sandy layer.

(Means for Solving the Problems) Therefore, in this invention, mortar is injected instead of the cement milk, thereby solving the problems in terms of strength and construction.

That is, the root hardening method of this invention reduces the viscosity to (3Q sec~
It is characterized by injecting mortar adjusted to 9 Q sec into the bottom of the pile hole using a cement milk pump and hardening it.

In this case, if the viscosity of the mortar is less than 6Qsec,
This is undesirable because the suspension becomes high and mixes with the muddy water in the pile hole, resulting in a decrease in strength and a loss of reliability in construction.

Furthermore, if the clay exceeds 9 Qsec, it becomes impossible to pump the clay using a conventional cement milk pump, it becomes necessary to significantly change the injection equipment, and there is a possibility that the workability in the case of a deep pile hole will be significantly deteriorated.

The pile tip bearing capacity Ra is determined by Ra-old・α・n−AI) [α: pile tip bearing capacity coefficient, Agony: pile tip N value, Ap: anti-closure cross-sectional area (e)], and α = 25 (in the case of expanded foot protection), F1 = 60, the required strength of the foot protection material for a 600φ pile is 150 K'l/crA or more, and usually about 200 Kg/ci is set for 1q. .

In this invention, the target is 250 to 300 Ky/CIi,
and a viscosity of 60 to 90 sec [To adjust the rutal, use #medium-medium; fine sand and adjust the sand/cement ratio to 100 to 100.
150 (wt%), water/cement ratio 53-58 (wt%), superplasticizer/cement ratio 0°4-0.7 (wt%)
) can be adjusted as The fine sand mentioned above is JASS (Japanese＾rchitec
tural 5standard 5specificat
ion (Japanese Building Construction Standard Specifications) 5, and has a coarse grain ratio of 2.2 (i major dimension 1.2 m+).

(Action of the invention) According to the foot hardening method of this invention, the viscosity of mortar is 60
sec to 9QSeC, injection into the bottom of the pile hole can be easily performed using a cement milk pump. Furthermore, since mortar has a higher specific gravity than cement milk, the filling effect can be increased.

In addition, since it has a relatively high viscosity, the dispersibility of cement particles is improved, and the compressive strength of the hardened mortar reduces the difference in strength between the upper and lower parts, and is even higher than that obtained with conventional cement milk. It is possible to obtain equivalent or higher values. In addition, since mortar has low suspensibility, it is not diluted by water in the supporting ground, so there is no variation in strength when hardened, and stable strength can be obtained. Furthermore, since there is no risk of mortar escaping through the gaps between the sand stones on the supporting ground of the sand stones, highly reliable construction can be achieved.

In addition, since ordinary mortar cannot be pumped without using a special concrete pump, even in the foot protection method,
Although it requires a huge amount of equipment, leading to a significant increase in costs and complexity of construction, the method of this invention increases fluidity and
They were able to inject it without any problems using a cement milk pump.

In addition, when adjusting the commonly used mortar, a concrete mixer or mortar mixer is required for mixing, which increases the size of the equipment, but in this invention, the fluidity is increased and the equipment for cement milk is improved. can be used.

In addition, when aggregates such as sand are included in the mixture, it is necessary to control the mixture, but in this regard, by adjusting the sand and water in a predetermined ratio in advance and mixing this with cement. , it is possible to facilitate on-site formulation management.

(Example) Examples of the present invention will be described below.

First, a pile hole 1 as shown in Fig. 1 is excavated, and a large diameter part 2 with a diameter larger than the diameter of the pile hole 1 (about 1°5 times, but the same diameter is also acceptable) is placed at the bottom of the pile hole 1. was formed to a predetermined depth (for example, about twice the diameter).

Next, mortar is prepared according to the composition shown in Table 1, and this mortar is injected into the large diameter portion 2 using a cement 1 to milk pump (FIG. 2). Next, a ready-made concrete pile 3 is sunk into the pile hole 1 with the lower end open, and the pile 3
Insert the lower end of the into the mortar (up to the middle of the mortar)
! jru. When the mortar injected in this manner hardens, the installation work of the foundation pile with the foot protection 4 formed is completed.

In the above embodiment, the lower end of the pile 3 was inserted almost halfway into the mortar, but the insertion depth was 1.5 of the diameter of the pile 3.
It may be more than double that and reach the bottom of the pile hole 1 in some cases.

Table 1 Sand: Fine, surface dry Fluidizer: High performance water reducer (Mighty/Kao Soap) Sand/
Cement ratio c/5=100, (wt%) water/
Cement ratio w/c = 55 (wt%) Superplasticizer/cement ratio H/c = 0.5 (wt%) Mortar could be injected without any problem using a cement milk pump.

When adjusting the mortar, the sand/cement ratio C/S is 100.
If the amount is less than 150 (wt%), the effects as a mortar will be lost, i.e. ■Improvement in the dispersibility of cement, ■Increase in specific gravity, improvement in strength, and ■Improvement in economical efficiency.If it exceeds 150 (wt%), the viscosity will decrease. It was difficult to pump the cement with a milk pump.

On the other hand, the water-cement ratio W/C has a fourth relationship with the compressive strength.
There is a relationship as shown in the figure, and the desired compressive strength (250~
300 Kg/ca was obtained, and 53 to 581 ω% was recognized as appropriate in order to reduce the dispersion in the compressive strength between the upper and lower parts. In addition, the strength in Figure 4 is 50aR in diameter and 3 in height.
An oCIR specimen was prepared, and the compressive strength of the upper part was determined as the 200 m height part, and the lower part was determined as the compressive strength of the 100 m height part.

In addition, there is a relationship between the fluidizer/cement ratio H/c and the viscosity of mortar as shown in Figure 5. If the amount added is large, aggregate separation will occur, and if the amount added is small, the viscosity will not be improved. Therefore, it is considered that H/c of 0°4 to 0.7 (wt%) is appropriate. Note that CellFlow in the figure is a fluidizing agent manufactured by Daiichi Kogyo Seiyaku Co., Ltd.

(Effect of the invention) As explained above, according to this invention, the viscosity is
Mortar adjusted to 90 seconds is injected into the pile hole and hardened to form the footing, so a cement milk pump can be used to pump the mortar, and with the same equipment and work as before, the compressive strength is high and there is no variation. This has the effect of reliably forming root hardening with little water.

[Brief explanation of the drawing]

Figures 1 to 3 are cross-sectional views of pile holes in embodiments of the present invention, Figure 4 is a graph showing the relationship between water/cement ratio and compressive strength, and Figure 5 is a graph showing the relationship between fluidizer/cement ratio and viscosity. It is a graph showing a relationship.

Claims (1)

[Claims] 1. After excavating the bottom of the pile hole to a shape and size suitable for foot protection, mortar whose viscosity is adjusted to 60 seconds to 90 seconds is injected into the bottom of the pile hole with a cement milk pump and hardened. Featured foot hardening method 2 Mortar uses fine sand, with a sand/cement ratio of 100 to 150 (wt%) and a water/cement ratio of 53 to 5.
8 (wt%), superplasticizer/cement ratio 0.4 to 0.7
The foot hardening method according to claim 1, which is adjusted as (wt%)