JPH0751782B2 - Construction method of the root fixing part for fixing the pile - Google Patents

Description

[Detailed Description of the Invention] [Field of use for work] The present invention makes the anchoring of the lower end of the pile to the root consolidation part highly reliable, improves the efficiency of pile laying construction, and improves the economy of pile laying construction. The present invention relates to a method of constructing a root-fixing part for anchoring piles, which greatly contributes to improving the property.

[Conventional technology]

As one of the construction methods for constructing a pile foundation in the ground, pre-boring is performed while injecting drilling fluid to form a pile sinking hole reaching the supporting ground, and the pile is sunk in the pile sinking hole, and the lower end portion of the pile is formed. There is a construction method to fix the soil to the root consolidation section provided on the support ground, and this construction method has been widely spread as a low vibration / low noise construction method.

In order to build a root consolidation part in the method, conventionally, root compaction cement milk is ejected from the tip end head of the excavating rod, and the sand or gravel or Dotan layer of the supporting ground and the root consolidation cement milk are mixed and stirred. A mortar-shaped or concrete-shaped root consolidation part was built, or the pile sunk holes in the supporting ground were replaced with cement milk or concrete to build the root consolidation part.

[Problems to be Solved by the Invention]

However, the above-mentioned conventional method of constructing a rooted portion has the following problems, and there is an urgent need to solve them.

There is a problem that it is difficult to build a highly reliable root consolidation part, such as the hole wall of the pile sunk hole in the supporting ground partially collapses or the cement component sequentially flows out and diffuses from the outer periphery of the root consolidation part. It was

As described above, the irregular shape of the root consolidation part due to the collapse of the hole wall in the supporting ground and the uneven state of the strength of the root consolidation part due to the outflow / diffusion of the cement component of the root consolidation part are invisible, Since it was difficult to accurately detect or predict the situation, there was a tendency to inject more cement milk than necessary, and there was a problem in terms of economy.

When the root consolidation portion in which unstable foreign matter is mixed is built by the collapse of the hole wall in the support ground, there is a problem that a high stop phenomenon that the pile cannot be inserted to a predetermined position of the root consolidation portion is caused.

Recently, since the length of buried piles tends to be long, it is necessary to connect ready-made piles of a certain length in sequence and to sunk them in the pile pit. To do so, it took a relatively long time to prepare, such as lifting the pile to be buried and welding the joints between the piles before the next pile was sunk. It was usual that a considerably long time (for example, about 3 to 4 hours) had elapsed after the rooted part was built by the time it started. However, since the hardening of the built up root begins to take place within 1-2 hours after the cement milk is injected, the hardening of the root uptake is considerably advanced by the time the final pile laying work begins. However, there was a problem that the specified rooting length for the root consolidation part could not be obtained and therefore the pile could not be firmly fixed to the supporting ground.

[Means for Solving the Problems]

In order to solve the above problems, the present invention employs the following means.

That is, the method for constructing a pile anchoring portion according to the present invention (hereinafter referred to as a "construction method") is to form a pile pit 2 reaching the support ground 1 by performing pre-boring while injecting a drilling liquid and to form a mortar. Alternatively, it was obtained by refining holmite-based minerals (sepiolite minerals, attapulgite minerals, etc.) into the pile hole 2 excavated in the supporting ground 1 when constructing the concrete-like rooting part 3 in the supporting ground 1. It is characterized by injecting root-hardening cement milk obtained by debunching and dispersing mineral fibers into cement milk with a grout pump.

Cement milk is adjusted to a water-cement ratio of 50 to 80% by weight (the lower limit of 50% by weight is set in consideration of the economy of addition and the ease of injection work by a grout pump, and the upper limit of 80% by weight). (% By weight is set from the viewpoint of strength) and the addition rate of mineral fiber is 0.
Adjusted within the range of 1 to 10% by weight (the lower limit of 0.1% by weight is set so that the various effects due to the addition are effectively exerted, and the upper limit of 10% by weight is the economic efficiency of the addition and the injection work by the grout pump. It is better to set it in consideration of ease.

Further, the pile sinking hole 2a in the support ground 1 is formed to have the same diameter over the entire length, or the lower end portion thereof is an enlarged hole 2a.
When the lower end portion is the enlarged hole 2a, at least the pile sinking hole in the support ground 1 is an enlarged hole and has a hole diameter having a cross-sectional area of 1.1 to 4 times the cross-sectional area of the pile to be sunk. .

[Action]

(1) Root-hardening cement milk has excellent suspending properties because it is composed of holmite-based mineral fibers which are disentangled and dispersed, and the sedimentation of cement with high specific gravity in cement milk is suppressed as much as possible. It is in. For this reason, the root-cemented cement milk has a high fluidity and can be smoothly pumped by the grout pump.

(2) Root-hardening cement milk has a large viscosity because the demineralized mineral fibers are dispersed in the cement milk and the fibers are intertwined with each other.

Therefore, the hole wall 4 in the supporting ground 1 is surely protected by the cement cement (the viscosity of the cement cement and the synergistic effect of the adhesion of the holmite-based mineral fiber to the hole wall 4 ensure the protection. In this state, the collapse of the hole wall will be prevented.

Settling of cement milk and settling of sand or gravel in the mortar-like or concrete-like root-setting part 3 is suppressed. That is, the breathing rate is significantly reduced.
As a result, the pile to be sunk can be correctly inserted to the required position of the root consolidation part.

Since the dispersion of cement milk in the mortar or concrete in the root consolidation part 3 is prevented as much as possible and the breathing phenomenon hardly occurs as described above, in addition, the compression strength of the hardened root consolidation part is improved, This will ensure the strength stability of the root consolidation part.

(3) Since the root-hardening cement milk is formed by dispersing the holmite-based mineral fibers, the mortar or concrete in the root-hardening part 3 exhibits remarkable thixotropy for a long time, and the mineral in the dispersed state. The high quality fiber has an excellent lubricating effect. As a result, even after a long time has passed since the root consolidation portion was built, it is very easy to lay the pile by its own weight or to lay the pile while rotating it around the axis.

What has been described above is the viscosity graph shown in FIG. 5, the measurement results of the breathing rate shown in Table 2, the dispersion state of the root cement cement milk shown in FIG. 9, and the thixotropic test results shown in Tables 5-6. This is supported by the strength test results shown in Table 8.

(1) Viscosity of cement-hardened cement milk Generally, the viscosity of cement-milk that can be retained in the hole wall by preventing the collapse of the hole wall of the pile sunk hole with the cement-hardened cement milk is measured by a Marsh Funnel viscometer.
It is said that more than 45 seconds is ideal.

Fig. 5 shows the "flow-down time" by the Marsh Funnel viscometer against the "addition ratio of the holmite-based mineral fiber to the cement weight" (water-cement ratio 60% by weight), the addition of the holmite-based mineral fiber. It can be seen that even if the rate is slightly increased, the downflow time changes greatly in the increasing direction.

As is clear from Fig. 5, it is possible to increase the viscosity of cement milk by adding holmite-based mineral fibers, but the addition rate is about 45 seconds, which is the ideal flow time. Addition rate to achieve time 0.
It is preferable to set it to 3% or more. The Marsh Funnel viscometer was unable to measure when the addition rate of the holmite-based mineral fiber was 1.5% or more due to the increased viscosity of the cement milk, but even in the cement milk in such a state. I could infuse with a grout pump without any problems.

(2) Breathing rate The mortar adjusted by the respective mixing ratios of No. 1, No. 2, No. 3, and No. 4 shown in Table 1 was used as the breathing ratio of "injection mortar of prepact concrete". And expansion rate test method ", put it in a polyethylene bag with a diameter of 5 cm and a length of 50 cm or more, and measure the breathing rate after 3 hours and 20 hours. For each of compound Nos. 1 to 4, The results shown in Table 2 were obtained.

As is clear from these results, the addition of holmite-based mineral fiber significantly reduced the breathing rate after 3 hours and 20 hours, and the addition rate (the ratio of holmite-based mineral fiber to cement weight) It is recognized that the breathing rate tends to decrease as the addition rate) increases.

(3) Dispersion state of root-solidified cement milk Since the phenomenon of cement-milk dispersion in the root-solidified part cannot be visually observed, the phenomenon of root-solidified cement milk dispersion was experimentally understood using the experimental equipment described below. did.

This experimental device has an outer diameter of 7.5 cm, an inner diameter of 6.7 cm, and a length of 15
7th, which is obtained by covering a cut surface of a half-split piece 6 shown in FIG. 6 formed by splitting a synthetic resin circular tube of cm into a resin sheet 7.
Two pieces of the half-divided tube 8 shown in the figure are used. The half-divided tube 8 is made so that the lower end 9 of the half-divided tube exists at a position approximately 15 cm from the bottom of the glass water tank 10 as shown in FIG. The sheet (OHP paper, etc.) is arranged at a required interval in the glass water tank so that the coated surface is in contact with the inner surface of the side glass 11 of the glass water tank, and the diameter is set around the fixed half-split tube 8. Is 2.3 to 9.6 mm
The sea gravel is spread to a depth of about 20 cm, so that the half pipe 8 is fixed. The sea gravel is spread to form the layer 12 in this manner so that the layer 12 can be approximated to what is often found as an actual supporting ground.

Using the above-mentioned device, the root-setting cement milk of the combination No. 1 and the root-setting cement milk of the combination No. 2 shown in Table 3 were injected from the upper end opening of each half-split tube 8, and after 30 minutes, The state of dispersion of the root-hardening cement milk was observed. The shaded area A given in the layer 12 in FIG. 9 shows the dispersion state of the root-solidifying cement milk after 30 minutes from the injection, and the state a indicated by the one-dot chain line in the figure shows the state immediately after the injection. Show. The dispersed state was observed 120 minutes after the injection, but the state was the same as that after 30 minutes, so the illustration is omitted.

Formulation No. 1 root cement cement milk does not contain holmite-based mineral fibers, so the dispersion of root cement cement is very large, and root cement cement milk exists around the lower end of the half tube 8. An injection amount of 950 cc was required to reach the state of being activated (state on the left side in FIG. 9). On the other hand, in the root cement cement milk of the compound No. 2 to which the holmite type mineral fiber was added, the dispersion is considerably smaller than the case of the compound No. 1, and the injection amount of 350 cc around the lower end part of the half-split pipe. It became covered with root-hardening cement milk (the state on the right side in Fig. 9). The injection was continued until the lower end portion of the half-split pipe was covered with the cement cement milk, in order to approximate the actual state of the root consolidation part.

From the above results, it is considered that the root cement cement milk of the compound No. 1 has a very large dispersion of the root cement cement and it is difficult to construct a strong root cement portion, whereas the holmite mineral fiber is used. It is considered that the dispersion is small and there is no worry when using the root cement cement milk of the compounding No. 2 containing.

(4) Thixotropy Put mortar containing holmite-based mineral fibers adjusted to No. 1 and No. 2 in Table 4 into a container and use PC steel wire (diameter 9 m
m, length 46.7cm, weight 232g), after adjusting the blending amount, 30
The measurement was performed after 1 minute, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, and 7 hours.

This measurement was first performed when the PC steel wire was gently submerged. If the lower end of the PC steel wire does not reach the bottom of the container due to penetration by self-precipitation, after self-precipitation, after gripping the PC steel wire with the thumb and forefinger and repeating forward and backward half rotations 15 times,
The amount of penetration in this state was measured. If fixing does not occur even after repeating this forward / reverse half rotation, forward / reverse 4
The final amount of penetration was measured by rotating twice. The results are shown in Table 5 (results in case of compound No. 1) and Table 6 (composition N).
The result in case of o.2.)

From the above results, it is confirmed that in the case of the mortar to which the holmite-based mineral fiber is added, remarkable thixotropy of the holmite-based mineral fiber is exhibited.

(5) Strength test Table 8 shows the results of a strength test performed on the root-hardening cement milk adjusted to have the composition shown in Table 7. In this strength test, a polyethylene bag filled with cement milk prepared as described above was cured by hanging it for 7 days, then cut into a cylindrical shape with a diameter of about 5 cm and a length of 10 cm. A compressive strength test conducted on a test piece that has been aged in water at 20 ° C ± 3 ° C until the 28th day of the Ordinance.

From the above results, it is recognized that the compressive strength is significantly improved by adding the holmite mineral fiber,
It is also recognized that the compressive strength increases as the addition rate of the holmite-based mineral fiber increases.

〔Example〕

 Embodiments of the present invention will be described below with reference to the drawings.

In the construction method according to the present invention, first, as shown in FIG. 1, pre-boring is performed while injecting a drilling fluid to form a pile pit 2 reaching the support ground 1. In addition, the hole diameter of the pile sinking hole is, for example, larger than the pile diameter by about 5 to 10 cm, and the depth L of the pile sinking hole 2a in the supporting ground is set to, for example, about 2 to 5 times the diameter of the pile sinking hole.

Next, as shown in FIG. 2, grouting pump is used to inject root-hardening cement milk into the pile digging hole 2a excavated in the supporting ground, and the injected root-hardening cement milk and the inside of the pile digging hole 2a in the supporting ground are filled. By sufficiently mixing and stirring sand or gravel, a mortar-like or concrete-like root consolidation part 3 is built on the support ground. Root-hardening cement milk has 8 mesh under mineral fiber obtained by refining and processing Chinese sepiolite minerals to cement milk with a water-cement ratio of 50-80% by weight.
It is obtained by debundling and dispersing in an amount of 0% by weight. In addition, this mineral fiber is not a granular material that cannot be unbunched,
To the last, it is indispensable to present a fibrous shape that can be unbundled.

During the injection with the grout pump, the cement-solidified cement milk has a high fluidity as described in the section [Operation], so that the cement-solidified cement milk can be smoothly fed under pressure.

In addition, when the ready-made concrete pile 5 is set in the pile settling hole 2 of the support ground 1 by its own weight, or when the pile is set by gently rotating the pile about its axis, as described in [Operation]. The piled holes in the supporting ground are held in an almost circular shape, and the thixotropy of the root consolidation portion due to the dispersion of the fibers of the sepiolite acts, and the formite-based mineral fibers in the dispersed state have an excellent lubricating effect. Even if many piles are successively connected and sunk by demonstrating the effect, etc., the bottom end of the pile will have the required depth (intermediate position depth of the root consolidation part or the depth reaching the bottom of the pile digging hole). Up to), it can be smoothly sunk by gravity or can be sunk while rotating without requiring a large torque. Further, since the required amount of mineral fibers is added to the root cement cement milk, the lower end portion 5a of the pile is firmly fixed to the root root by hardening the root root which is mortar or concrete. The fixed state will be maintained.

FIG. 4 shows the pile grounding holes 2a in the support ground 1 in order to increase the ground bearing capacity of the root consolidation portion 3 according to the situation of the support ground 1.
Is formed to have a larger diameter than the pile sunk hole 2b above the supporting ground and to have a hole diameter having a cross-sectional area of about 2 to 3 times the cross-sectional area of the pile 5 to be sunk. In the same manner as described above, root cement cement milk is poured and mixed and stirred to construct a root fixing section 3 having a mortar shape or a concrete shape. Then, the lower end portion 5a of the concrete pile 5 is firmly fixed to the built up root portion in the same manner as described above.

At the actual pile construction site, the results of comparison of the pile laying construction speed were compared between the case of using the ordinary root cement cement milk and the case of using the root cement cement milk prepared by adding holmite mineral to it. Shown in.

Construction Example 1 Construction location: Inside the Wada-Higashichi, Fukui City Pile used: PHC pile outer diameter 50 cm, length 15 m Number of pile constructions per day when using root cement cement milk adjusted to formulation No. 1 in Table 9 Was 4, and the number of constructions per day was 6 when the root-hardening cement milk adjusted to No. 2 was used. In addition
No. 1 and No. 2 show the case of one pile.

The soil in the consolidation section at the construction site is a gravel layer that is stronger than the depth of 13.3 m and is a supporting foundation with an N value of 50 or more from the depth of 14.0 m, but the consolidation cement containing the holmite-based mineral fiber is added. By using the milk, it was possible to efficiently perform the pile digging construction and to fix the pile in the predetermined position as designed.

Construction example 2 Construction site: Itagaki, Fukui City Pile used: PHC pile Outside diameter 45 cm, length 23 m (plurality of multiple piles connected to form one pile) Root adjusted to compound No. 1 in Table 10 The number of piles constructed using hardened cement milk per day is 4, and the compounding number is 2.
The number of piles constructed per day was 5 when the soil-hardened cement milk adjusted to 1. was used. Formula No. 1, N
o.2 shows the composition per pile.

The root consolidation ground is a gravel layer from a depth of 20.3 m and a depth of 21.
Although it is a strong support ground with an N value of 50 or more from 0 m, by using root cement cement milk containing holmite-based mineral fiber added, it is possible to efficiently carry out pile laying work and it is designed as designed. It was possible to fix the pile at the position.

(Effect of the invention) The present invention forms a pile sunk hole reaching the supporting ground by performing pre-boring while injecting the drilling fluid, and at the time of constructing a mortar-like or concrete-like root consolidation portion on the supporting ground, In the pile digging hole excavated in the support ground,
Root compaction, which is obtained by debundling and dispersing mineral fibers obtained by refining holmite-based minerals in cement milk, is to inject cement milk with a grout pump. Not only can it be made highly reliable, but it will also contribute significantly to the efficiency of pile laying construction and the economic efficiency of pile laying construction. This will be described more specifically as follows.

Since the root-hardening cement milk has a high fluidity due to the unbundling and dispersion of the holmite-based mineral fibers, the pressure feeding by the grout pump can be carried out more smoothly than in the case of ordinary cement milk.

The root cement cement milk has a high viscosity and the adhesion of the mineral fiber to the hole wall ensures that the hole wall in the supporting ground is protected by the root cement cement milk (by adding the holmite type mineral fiber). The large viscosity of the root-cemented cement milk and the synergistic effect of the adhesion of the holmite-based mineral fibers to the pore wall ensure a protected state), and the collapse of the pore wall is prevented. Furthermore, the compressive strength of the root-hardening part due to the holmite-based mineral fiber is improved.

Therefore, unlike the conventional case, there is no possibility that the pile settling is hindered by the unstable foreign matter mixed due to the collapse of the hole wall and the pile cannot be inserted to the required position of the root consolidation portion. In addition, each part is constructed to have a substantially uniform strength-stabilizing part, so that the fixing of the lower end of the pile to the root-fixing part can be made even stronger than in the conventional case and the fixing state can be improved. Since it can be sustained, it is possible to build a reliable pile foundation.

Since the root-hardening cement milk has holmite-based mineral fibers dispersed therein, it exhibits remarkable thixotropy over a long period of time, and the mineral fibers in the dispersed state exhibit an excellent lubricating action. Therefore, even after a long time (for example, about 3 to 8 hours) has passed since the root consolidation portion was built, it is possible to easily perform the pile digging by its own weight or the pile digging while rotating around the shaft center. As a result, there is no possibility of causing a high stop phenomenon due to the hardening of the root consolidation part.

From the above, when the construction method according to the present invention is used,
It is possible to meet the demand for lengthening of buried piles in recent years.

By injecting the cement milk as designed, it is difficult to cause the irregular shape of the root consolidation part due to the collapse of the hole wall in the support ground and the uneven state of the root consolidation part due to the outflow / diffusion of cement in the root consolidation part. The desired root consolidation can be built. Therefore, there is no economic disadvantage associated with injecting more cement milk than necessary. Further, as mentioned above, since the root-hardening portion exhibits remarkable thixotropy over a long period of time, the difficult piles can be efficiently deposited.

From this, the present invention greatly contributes to improving the economical efficiency of pile digging construction.

[Brief description of drawings]

1 to 4 are explanatory views for explaining the construction method according to the present invention, and FIG.
Figure is a graph showing viscosity change of root cement cement milk to which holmite mineral fiber is added, Figure 6 is a perspective view showing a half-split piece, Figure 7 is a perspective view showing a half-split tube, and Figure 8 is FIG. 9 is a perspective view showing an apparatus for a root cement cement milk dispersion experiment.
The figure is an explanatory view of a dispersed state of root cement cement milk. 1 ... Supporting ground, 2 ... Pile sinking hole, 2a ... Pile sinking hole in supporting ground, 3 ... Root consolidation part.

Claims (3)

[Claims] 1. When pre-boring is performed while pouring a drilling fluid to form a pile sunk hole 2 reaching a support ground 1 and a mortar-like or concrete-like root consolidation portion 3 is built on the support ground 1, It is characterized by injecting a root cement cement milk obtained by refining and dispersing mineral fibers obtained by refining and processing holmite-based minerals into cement milk into a pile pit 2 drilled in a supporting ground 1 with a grout pump. The construction method of the root fixing part for anchoring the pile. 2. The cement milk is adjusted to a water cement ratio of 50 to 80% by weight, and the holmite-based mineral fiber is adjusted to a cement ratio of 0.1 to 10% by weight (1). The method of constructing the consolidation section for fixing the piles described. 3. The lower end portion of the pile sunk hole 2 is an enlarged hole 2a, and at least the pile sunk hole in the support ground 1 is an enlarged hole, and the enlarged hole has a cross-sectional area of the pile to be sunk.
The method for constructing a root consolidation part according to claim 1, wherein the pore size has a cross-sectional area of 1.1 to 4 times.